Medical ablation system

Abstract

In some examples, a medical system includes processing circuitry configured to determine a periodicity of a flow rate delivered by a medical system to a balloon for a medical ablation. The balloon is configured to expand facilitate a heat transfer between a vessel wall and the fluid flowing through the balloon. The medical system is configured to vary a flow rate of the fluid delivered to the balloon between an upper flow rate and a lower flow rate over the periodicity. The upper flow rate, the lower flow rate, and the periodicity maintains tissues at a tissue depth within a narrow temperature range around a target temperature as the medical system delivers the fluid at the upper flow rate, the lower flow rate, and the periodicity.

Description

MEDICAL ABLATION SYSTEM

[0001] This application claims the benefit of U.S. Provisional Patent application Serial No. 63 / 606,769, filed December 6, 2023, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present technology is related to medical devices and systems, such as medical devices and systems for ablation and / or neuromodulation.BACKGROUND

[0003] Catheters have been proposed for use with various medical procedures. For example, a catheter can be configured to deliver neuromodulation therapy to a target tissue site to modify the activity of nerves at or near the target tissue site. The nerves can be, for example, sympathetic nerves. The sympathetic nervous system (SNS) is a primarily involuntary bodily control system typically associated with stress responses. Chronic overactivation of the SNS is a maladaptive response that can drive the progression of many disease states. For example, excessive activation of the renal SNS has been identified experimentally and in humans as a likely contributor to the complex pathophysiology of arrhythmias, hypertension, states of volume overload (e.g., heart failure), and progressive renal disease.SUMMARY

[0004] The present disclosure describes devices, systems, and techniques for medical ablation and / or neuromodulation. The medical system is configured to deliver a fluid to a balloon positioned within a blood vessel to deliver a therapy to a patient. The therapy can include, for example, neuromodulation therapy, such as renal denervation, hepatic denervation, or denervation of other nerves or combination of nerves. The system includes an elongate body (e.g., a catheter body) configured to deliver a fluid to the balloon. The balloon is configured to expand (e.g., under the influence of the fluid) within the blood vessel to contact a vessel wall of the blood vessel. The balloon is configured to facilitate a heat transfer between the vessel wall and the fluid flowing through the balloon to modify a temperature at or near a target tissue site. For example, the balloon may facilitate a heat transfer from the vessel wall to the fluid to cool the target tissue site, which can cause cryoablation of nerves atthe target tissue site. As another example, the balloon may facilitate a heat transfer from the fluid to the vessel wall to heat the target tissue site, which can cause thermal ablation of nerves at the target tissue site.

[0005] The medical system is configured to vary a flow rate of the fluid delivered to the balloon during the therapy. The varying flow rate maintains a target temperature of tissue at a particular tissue depth (e.g., of the target tissue site) within a relatively narrow temperature range around a target temperature as compared to a temperature range experienced by the balloon as the balloon receives the fluid. The narrowed temperature range may allow for reduced therapy times and / or reduced inflammation of tissue proximate the target tissue site during the therapy delivery. For example, during a cryotherapy, the medical system may enable reduced procedure times and / or reduced inflammation as compared to systems in which a fluid is circulated through a balloon to hold tissue at / or below a reduced temperature for some period of time, followed by a warming period during which the balloon allows the tissue to substantially return to higher temperature (e.g., a typical body temperature in the absence of cryotherapy or heat therapy), and subsequently followed by the balloon acting to return the tissue to the reduced temperature. The medical system disclosed is configured to vary a flow rate of the fluid delivered to the balloon in a manner which substantially holds the temperature of the tissue at the target tissue site within a relatively narrowed temperature range around the target temperature (e.g., to mitigate warming) to reduce procedure times and / or inflammation while accomplishing denervation.

[0006] In some examples, the medical system includes processing circuitry configured to determine a target temperature indicative of a desired temperature of a target tissue site as the medical system delivers a fluid to a balloon. The processing circuitry is configured to determine a periodicity of a flow rate of the fluid (e.g., delivered to an inlet of a catheter body or to a balloon) to maintain a tissue temperature at a tissue depth within a temperature range around a target temperature. The periodicity is indicative of a time period over which the flow rate varies from an upper flow rate to a lower flow rate and returns to the upper flow rate.

[0007] In some examples, the medical system includes a catheter body mechanically supporting the balloon. The medical system may be configured to deliver the fluid to the catheter body. The catheter body may be configured to deliver the fluid to a balloon interior of the balloon.

[0008] In examples, a medical system comprises: a medical device configured to deliver a fluid to a balloon, wherein the balloon is configured to expand within a vessel of a patient;and processing circuitry configured to: determine a target temperature indicative of a desired temperature of a target tissue site of the patient, the target tissue site being at a tissue depth, and determine, using a representative temperature of the balloon and the tissue depth, a periodicity of a flow rate of the fluid to maintain a temperature of the target tissue site within a temperature range when the medical device provides the fluid to the balloon, wherein the target temperature is within the temperature range, wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity.

[0009] In some examples, a medical system comprises: a catheter body configured to be positioned within a vessel of a patient, wherein the catheter body defines an inlet lumen configured to receive a fluid; a balloon supported by the elongate body, wherein an interior volume of the balloon is in fluidic communication with the inlet lumen, and wherein the balloon is configured to expand within the vessel; a flow actuator configured to position to control a flow rate of the fluid received by the inlet lumen; and processing circuitry configured to: determine a target temperature indicative of a desired temperature of a target tissue site of the patient, the target tissue site being at a tissue depth, and determine, using a representative temperature of the balloon and the tissue depth, a periodicity of a flow rate of the fluid to maintain a temperature of the target tissue site within a temperature range when the medical device provides the fluid to the balloon, wherein the target temperature is within the temperature range, wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity; and cause the flow actuator to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0010] In some examples, a method comprises: determining, by processing circuitry and based on a representative temperature of a balloon and a tissue depth, a periodicity of a flow rate of a fluid to maintain a target temperature of a target tissue site of a patient within a temperature range when a medical device provides the fluid to the balloon, wherein the target tissue site is at the tissue depth, wherein the target temperature is within the temperature range, and wherein the periodicity is indicative of a time period over which the flow rate ofthe fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, wherein the balloon is configured to expand within a vessel of the patient, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity.

[0011] In some examples, a medical system includes processing circuitry configured to determine a periodicity of a flow rate delivered by a medical system to a balloon for a medical ablation. The balloon is configured to expand facilitate a heat transfer between a vessel wall and the fluid flowing through the balloon. The medical system is configured to vary a flow rate of the fluid delivered to the balloon between an upper flow rate and a lower flow rate over the periodicity. The upper flow rate, the lower flow rate, and the periodicity maintains tissues at a tissue depth within a narrow temperature range around a target temperature as the medical system delivers the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0012] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic illustration of an example medical system including a catheter system.

[0014] FIG. 2 is a schematic illustration of the medical system of FIG. 1 within a blood vessel of a patient.

[0015] FIG. 3 is a schematic illustration of the medical system of FIG. 1 accessing a renal artery of a patient.

[0016] FIG. 4 is a schematic illustration of the medical system of FIG. 1 in a delivery configuration.

[0017] FIG. 5 is a schematic illustration of the medical system of FIG. 1 in an expanded configuration.

[0018] FIG. 6 is an example illustration depicting a flow rate waveform delivered by a medical system which includes a balloon.

[0019] FIG. 7 is an example illustration depicting an example flow rate through the balloon caused by the flow rate waveform of FIG. 6.

[0020] FIG. 8 is an example illustration depicting a balloon temperature range, a temperature range at a first tissue depth, and a temperature range at a second tissue depth caused by at least one of the flow rate waveform of FIG. 6 or the flow rate through the balloon of FIG. 7.

[0021] FIG. 9 is an example illustration of a flow rate waveform having a first periodicity and a second periodicity.

[0022] FIG. 10 is an example illustration of a sensed rate of change of a parameter and an expected rate of change of the parameter for the first periodicity and a second periodicity.

[0023] FIG. 11 is an example illustration depicting a flow rate waveform having a third periodicity and a fourth periodicity.

[0024] FIG. 12 is an example illustration of a sensed rate of change of a parameter and an expected rate of change of the parameter third periodicity and the fourth periodicity.

[0025] FIG. 13 is a flow diagram illustrating an example technique for determining a periodicity of a flow rate of a fluid delivered to a balloon for a medical procedure.DETAILED DESCRIPTION

[0026] The present disclosure describes example medical devices and medical systems configured to deliver a fluid to a balloon positioned within a blood vessel to deliver a therapy to a patient. The therapy can include, for example, neuromodulation therapy, such as renal denervation, hepatic denervation, or denervation of other tissue sites or combination of tissue sites. The balloon is configured to expand (e.g., under the influence of the fluid) within the blood vessel to contact a vessel wall of the blood vessel to modify a temperature at or near a target tissue site. For example, the balloon may facilitate a heat transfer from the vessel wall to the balloon to cool the target tissue site. As another example, the balloon may facilitate a heat transfer from the balloon to the vessel wall to heat the target tissue site.

[0027] The medical system is configured to maintain a tissue temperature of tissue at a target tissue site within a relatively narrow temperature range as the balloon facilitates the heat transfer. The temperature range includes a target temperature of the tissue at the target tissue site. The target temperature can be, for example, a temperature that is sufficient to cause the desired tissue ablation and / or neuromodulation (e.g., an attenuation of neural activity of nerves at the target tissue site). In examples, the target tissue site is located at a tissue depth within the vessel wall, such that the target tissue site is displaced from the exterior surface of the balloon contacting an inner surface of the vessel wall. The medicalsystem is configured to conduct a plurality of (e.g., a series of) flow rate cycles to cause the balloon to transfer heat from or to tissue at the target tissue site in a periodic manner, which can also be referred to as substantially cyclic manner in some examples. A periodicity (e.g., cycling) of the heat transfer maintains a tissue temperature at the target tissue site within a relatively narrow temperature range (e.g., around the target temperature) to provide more precise and / or consistent control of tissue temperature at the target tissue site that is displaced relative to the interface between the balloon and the vessel wall.

[0028] For example, the medical system may deliver fluid to the balloon using a flow cycle whereby delivery of a upper flow rate of fluid to the balloon is followed by delivery of a lower flow rate of fluid to the balloon. Delivery of the fluid at the upper flow rate followed by the lower flow rate may cause the balloon to enable a higher amount of heat transfer with the tissue followed by a lower amount of heat transfer. The higher amount of heat transfer may substantially drive the tissue at the target tissue site to or toward a first tissue temperature (e.g., a lower tissue temperature during a cryotherapy or a higher temperature during thermal ablation). The subsequent lower amount of heat transfer may allow the tissue temperature at the target tissue site to trend toward and / or reach a second tissue temperature (e.g., a higher tissue temperature during the cryotherapy or a lower temperature during thermal ablation). The medical system is configured to conduct subsequent flow rate cycles to substantially maintain the tissue temperature at the target tissue site in a temperature range substantially bounded by the first tissue temperature and the second tissue temperature, such that the tissue temperature at the target tissue site is maintained in a relatively narrow temperature range which includes the target temperature.

[0029] The medical system is configured to maintain the tissue temperature at the target tissue site in a manner which accounts for temperature profiles which may develop across intervening tissue of a vessel wall situated between the balloon and the target tissue site. The medical system is configured to account for the temperature profiles using thermal characteristics of the intervening tissue and a representative balloon temperature (e.g., either actually sensed or expected or predicted) when the medical system delivers the fluid to the balloon. For example, the target tissue site may be located substantially at a tissue depth within the vessel wall, such that the target tissue site is displaced from the exterior surface of the balloon contacting the vessel wall. As examples, the target tissue site may be a tissue depth of from about 0.5 millimeters (mm) to about 7 mm from the inner surface of the vessel wall, or some other tissue depth. The tissue depth may cause the tissue temperature at thetarget tissue site to depart from the representative balloon temperature due to, for example, a temperature profile developed across the intervening tissue as the balloon causes heat transfer from or to the vessel wall. The temperature profile may result from thermal characteristics of and / or thermal impacts on the intervening tissue, such as conduction heat transfer characteristics of the intervening tissue, convection heat transfer characteristics of the intervening tissue, patient body temperatures proximate the target tissue site, thermal energy generations of the patient (e.g., due to patient metabolism), blood flow characteristics, and / or other characteristics and / or thermal impacts. The medical system is configured to account for this temperature profile to maintain the tissue temperature at the target tissue site within the relatively narrow temperature range as the medical system delivers the fluid to the balloon.

[0030] The medical system may be configured to maintain the tissue temperature at the target tissue site within a temperature range narrower (e.g., less than) than a balloon temperature range experienced by the balloon as the medical system delivers the flow cycles. In some examples, the temperature range of the desired tissue temperature is less than or equal to about 50% of the balloon temperature range. In some examples, the temperature range of the desired tissue temperature is less than or equal to about 25% of the balloon temperature range. In some examples, the temperature range is a range of less than or equal to about 10 degrees Celsius (“deg C”) when the balloon temperature range is greater than about 35 deg C. As used herein, “about” can refer to the exact value or a particular range of the recited value (e.g., within 1% to 10%, which may vary based on manufacturing tolerances or other tolerances).

[0031] In examples, the medical system is configured to utilize the natural tendency of a body of the patient to thermoregulate the temperature of tissues at the target tissue site. For example, the medical system may be configured to maintain the tissue temperature at the target tissue site in a temperature range substantially bounded by a first tissue temperature and a second tissue temperature. When the medical system causes the higher amount of heat transfer (e.g., when the medical system delivers fluid at the upper flow rate), the higher heat transfer may be sufficient to substantially overcome the thermoregulation tendency of the patient and drive tissue temperature at the target tissue site (which again is at some tissue depth and not at the balloon / vessel wall interface) to or toward the first tissue temperature. When the medical system transitions from the higher amount of heat transfer to the lower amount of heat transfer (e.g., when the fluid delivered transitions from the upper flow rate to the lower flow rate), the lower heat transfer may be such that the thermoregulation tendencyof the patient causes the tissue temperature to trend in a direction from the first tissue temperature to the second tissue temperature. The medical system may be configured to adjust a periodicity of the cycling heat transfer such that the cycling heat transfer more closely matches and / or mimics an inherent capacity of the patient to transition the tissue temperature between the first tissue temperature and the second tissue temperature.

[0032] For example, in a cryoablation, the first tissue temperature may be less than a body temperature and the second tissue temperature may be a temperature between the first tissue temperature and the body temperature, such that the thermoregulation tendency of the patient tends to cause the tissue temperature at the target tissue site to increase from the first tissue temperature to the second tissue temperature. The medical system may control the flow rate of the cryofluid to cause the higher amount of heat transfer to substantially overcome the thermoregulation tendency of the patient and decrease tissue temperature at the target tissue site to or toward the first tissue temperature. The medical system may subsequently reduce the flow rate of the cryofluid to achieve a lower amount of heat transfer such that the thermoregulation tendency of the patient drives the tissue temperature from the first tissue temperature to the second tissue temperature in order to maintain the tissue temperature in the temperature range. The medical system may be configured to substantially adjust the periodicity of the cycling heat transfer to more closely match and / or mimics the thermoregulation of the patient as the tissue temperature transitions between the first tissue temperature and the second tissue temperature.

[0033] In a heat-based thermal ablation, the first tissue temperature may be greater than a body temperature and the second tissue temperature may be a temperature between the first tissue temperature and the body temperature, such that the thermoregulation tendency of the patient tends to cause the tissue temperature at the target tissue site to decrease from the first tissue temperature to the second tissue temperature. The medical system may control the flow rate of fluid to cause the higher amount of heat transfer to substantially overcome the thermoregulation tendency of the patient and increase tissue temperature at the target tissue site to or toward the first tissue temperature. The medical system may subsequently reduce the flow rate of the thermal ablation fluid to cause a lower amount of heat transfer such that the thermoregulation tendency of the patient drives the tissue temperature from the first tissue temperature to the second tissue temperature in order to maintain the tissue temperature in the temperature range.

[0034] Maintaining the tissue temperature at the target tissue site within the temperature range may allow for reduced medical procedure times and / or reduced inflammation of surrounding tissues during the therapy delivery. For example, during a cryotherapy or heatbased thermal ablation, the cyclic heat transfer may be conducted such that the higher heat transfer of the cycle limits the tissues at the target depth from experiencing a tissue temperature lower or higher than what might be required for sufficient efficacy of the therapy, limiting impacts on tissue proximate the target tissue site (e.g., between the inner surface of the vessel wall and the target tissue site) during the therapy delivery. The cyclic heat transfer limit impacts on tissues deeper than the target site (e.g., beyond the tissue target site relative to the vessel wall). The lower amount of heat transfer portion of the cycle may be conducted in a manner which limits a temperature rise or a temperature decrease of the tissues, allowing for more consistent time at the desired temperature for the therapy and reduction of overall medical procedure times.

[0035] In some ablation systems, fluid delivery to a balloon is controlled in a manner that can cause a transfer of heat with tissue during relatively long and discrete periods, potentially subjecting both tissue at a target tissue site and tissue proximate to and / or deeper than the target tissue site to undesirable temperature excursions. For example, the ablation system may cause the balloon to maintain a relatively constant balloon temperature for some freeze period (e.g., a freeze period on the order of minutes) to establish and hold tissue temperatures at / or below a reduced temperature. Fluid may be circulated and / or retained in the balloon during the freeze period to maintain the low temperature of the balloon. The freeze period may be followed by a warming period (e.g., a warming period one the order of minutes) during which the balloon allows the tissues warm to a higher temperature (e.g., to substantially return to a typical body temperature or another higher temperature). Following the warming period, the ablation system may be required to deliver additional freeze and warming periods. The relatively lengthy freeze period may result in significant heat transfers with other tissues and / or anatomical structures adjacent to the target tissues at the target site, resulting in the other tissues and / or anatomical structures experiencing potentially undesirable temperature excursions.

[0036] The medical system disclosed herein is configured to deliver fluid to a balloon expanded within a vessel in a cycling, periodic manner to substantially control heat transfer between the balloon, the target tissue, and other tissues and / or anatomical structures adjacent to the target tissue. The cyclic delivery of the fluid may provide more precise and / orconsistent control of tissue temperature at a target tissue site and / or limit temperature excursions experienced by other tissue and / or anatomical structures during delivery of a therapy.

[0037] In examples, the medical system includes an elongate body configured to be positioned within a blood vessel of a patient, at least one balloon carried by the elongate body, and control circuitry configured to control therapy delivery via the elongate body and the balloon. The medical system is configured to deliver a fluid to the balloon to expand (also referred to herein as inflate) the balloon within a blood vessel such that, for example, an exterior surface of the balloon contacts a vessel wall of the blood vessel. The medical system is configured to substantially circulate the fluid through an interior volume of the balloon to modify a temperature at or near the target tissue site. For example, the medical system may circulate a cryogenic fluid through the balloon to deliver a cryoablation to the target site. As another example, the medical system may circulate a heated thermal fluid through the balloon to deliver a thermal ablation to the target site.

[0038] The medical system, as well as devices of the systems and methods of using the systems, can be used for any suitable medical procedure, such as neuromodulation (e.g., denervation), that include delivering a therapy (e.g., cryoablation or heat-based thermal ablation) to a target tissue site via the balloon. The elongate body may be configured to be positioned (e.g., by a clinician) within a blood vessel or other anatomical lumen of a patient.

[0039] The temperature modification at or near the target tissue site can be used to provide a therapeutic outcome (e.g., cryotherapy or heat-based therapy) or can be used to help protect the vessel wall or other anatomical lumen wall. For example, to help achieve a therapeutic outcome, the medical system can be further configured to cool the fluid to, for example, freeze tissues at a target tissue site. As another example, the medical system can be configured to heat the fluid, to, for example, create a lesion at the target tissue site. While blood vessels are primarily referred to throughout the disclosure, the devices, systems, and techniques described herein are also applicable to other target tissue sites. In addition, while a single balloon catheter is primarily referred to throughout the disclosure, medical systems described herein can include more than one balloon, such as two, three, four or more balloons.

[0040] The medical system is configured to cause a heat transfer between the balloon (e.g., a body of the balloon) and the tissue at the target tissue site as the fluid circulates and / or is retained within the interior volume of the balloon. The medical system is configured to cycle a rate of the heat transfer (e.g., by cycling the representative balloon temperature) tomaintain the tissue temperature at the target tissue site within the temperature range. The substantially cycling rate of heat transfer may cause the temperature profile developed between the balloon (e.g., a balloon body) and the target tissue site to produce a tissue temperature at the target tissue site which remains within a relatively narrow temperature range (e.g., as compared to a range of temperatures experienced by the balloon as the fluid circulates and / or is retained within the interior volume).

[0041] The medical system is configured to cycle the rate of heat transfer by varying a flow of the fluid delivered to the balloon in a periodic manner. In examples, the medical system is configured to deliver the fluid to the balloon at an upper flow rate (e.g., to cause a higher rate of heat transfer) and a lower flow rate (e.g., to cause a lower rate of heat transfer). The medical system may deliver the fluid in a substantially cyclic manner described by the upper flow rate, the lower flow rate, and a periodicity over which the flow rate varies from the upper flow rate to the lower flow rate and subsequently returns to the upper flow rate. The medical system is configured to control the periodicity of the flow rate of the fluid such that that the temperature profiles developed across intervening tissue between the balloon and the target tissue site as the fluid is delivered at the upper flow rate, the lower flow rate, and the periodicity substantially result in maintaining the tissue temperature at the target tissue site within the temperature range.

[0042] The medical system is configured to control the periodicity of the flow rate of the fluid to achieve a plurality of sequential flow rate cycles, with each flow rate cycle including fluid flow at the upper flow rate, the lower flow rate, and the periodicity. For example, the medical system may be configured to deliver a first flow rate cycle wherein the flow rate varies from the upper flow to the lower flow and returns to the upper flow rate over the periodicity, followed by a second flow rate cycle wherein the flow rate varies from the upper flow to the lower flow and returns to the upper flow rate over the periodicity, followed by a third flow rate cycle wherein the flow rate varies from the upper flow to the lower flow and returns to the upper flow rate over the periodicity, and so on. The medical system may control the flow rate such that the first flow rate cycle, the second flow rate cycle, and the third flow rate cycle define a flow rate waveform having a frequency substantially equal to the reciprocal of the periodicity (e.g., the first flow rate cycle may chronologically complete as the second flow rate cycle chronologically begins, and the second flow rate cycle may chronologically complete as the third flow rate cycle chronologically begins, and so on). The flow rate waveform delivered by the medical system substantially maintains the tissuetemperature at the tissue depth within a relatively narrow temperature range as the medical system control the flow rate of the fluid delivered to the balloon.

[0043] The processing circuitry is configured to determine at least the periodicity of the flow rate to maintain the tissue temperature at the target tissue site within a desired temperature range. In examples, the processing circuitry is configured to determine the periodicity prior to a delivery of therapy to the patient (e.g., prior to the medical system delivering the fluid). For example, the processing circuitry may determine a periodicity sufficient to maintain the tissue temperature within the temperature range based on, for example, a balloon temperature and / or heat transfer rate with a vessel wall expected to result when the balloon is expanded in a vessel and receives the fluid at a given flow rate (e.g., the upper flow, the lower flow rate, and / or a flow rate between the upper flow rate and the lower flow rate). The medical system is configured to deliver the fluid to the balloon at the thus determined periodicity, such that the medical system substantially maintains the tissue temperature at the target tissue site within the temperature range. In some examples, the processing circuitry is configured to determine the upper flow rate and / or the lower flow rate based on the balloon temperature and / or the heat transfer rate. In some examples, instead of or in addition to the processing circuitry making a prior determination, the processing circuitry is configured to determine the periodicity during delivery of therapy to the patient (e.g., as the tissue temperature approaches the target temperature, or as the tissue temperature transitions from a first tissue temperature to a second tissue temperature).

[0044] In some examples, the processing circuitry is configured to adjust one or more of the upper flow rate, the lower flow rate, and / or the periodicity during the delivery of the therapy (e.g., while the balloon is expanded within the vessel and receiving the fluid). For example, the medical system may be configured to determine a parameter indicative of a temperature of the balloon (e.g., an actual measured temperature or a pressure of the fluid) as the balloon is expanded within the vessel and receiving the fluid. The processing circuitry may adjust one or more of the upper flow rate, the lower flow rate, and / or the periodicity based a measured parameter indicative of a temperature of the balloon, a change in the parameter (e.g., an increase or decrease), and / or a rate of change of the parameter. In some examples, the processing circuitry may be configured to adjust a duration of the upper flow rate and / or a duration of the lower flow rate which occurs over the periodicity.

[0045] In some examples, the processing circuitry is configured to determine at least the periodicity of the flow rate of the fluid by at least determining a representative balloontemperature and accounting for the temperature profile developed or expected to develop across intervening tissue between the balloon and the target tissue site when the balloon receives the fluid. The representative balloon temperature may be based on (e.g., dependent on), among other factors, a flow rate of the fluid delivered to the balloon. In examples, the representative balloon temperature is an expected balloon temperature (e.g., a temperature of a balloon body contacting the vessel wall) anticipated to occur when the balloon is expanded in the vessel and receives one or more flow rates of the fluid. The expected balloon temperature may be based on, for example, laboratory and / or bench testing, heat transfer characteristics of the medical system, previous use of similar medical systems, characteristics of the patient, and / or other characteristics. In some examples, the representative balloon temperature is a sensed balloon temperature provided by a sensor (e.g., a temperature or pressure sensor) and communicated to the processing circuitry such that, for example, the representative balloon temperature is indicative of a measured temperature when the balloon is expanded within the vessel.

[0046] In some examples, the processing circuitry is configured to determine (e.g., receive as an input) a target temperature of the target tissue site. For example, a user may input the target temperature or the processing circuitry can determine the target temperature based on stored information or information received from another device. The control system is configured to determine a periodicity of a flow rate of the fluid delivered to the balloon (e.g., a flow rate waveform) which causes or is expected to cause the tissue temperature at the target tissue site to remain within a temperature range that includes the target temperature. As an example, the processing circuitry can be configured to determine a periodicity of the flow rate of the fluid which causes the tissue temperature at the target tissue site to remain within a temperature range of less than about 10 deg C, less than about 5 deg C, or within another temperature range. As used herein, when a temperature is within a temperature range, the temperature is within a range inclusively bounded by a first temperature and a second temperature, such that the first temperature and the second temperature are included within the temperature range.

[0047] In examples, the processing circuitry is configured to determine at least one or the upper flow rate, the lower flow rate, and / or the periodicity based on a balloon temperature range which corresponds to a temperature range desired at the target tissue site. For example, the temperature range desired at the target tissue site may be a range bounded by a first tissue temperature and a second tissue temperature. The temperature range desired at the targettissue site can be, for example, a range of temperatures at which the target tissue, such as nerve tissue, is modulated, such as ablated. The processing circuitry may be configured to determine a balloon temperature range bounded by a first balloon temperature and a second balloon temperature. The processing circuitry may be configured to determine (e.g., using representative heat transfer characteristics of intervening tissue, intervening between the balloon at the target tissue site) that the first balloon temperature is expected to cause tissues at the target tissue site to achieve a temperature substantially equal to or in proximity to the first tissue temperature. The processing circuitry may be configured to determine (e.g., using representative heat transfer characteristics of intervening tissue) that the second balloon temperature is expected to cause tissues at the target tissue site to achieve a temperature substantially equal to or in proximity to the second tissue temperature. The processing circuitry may be configured to determine at least one of the upper flow rate, the lower flow rate, and / or the periodicity by at least determining a flow rate cycle (e.g., a fluid delivery cycle) which causes the representative balloon temperature (e.g., either an expected balloon temperature or a sensed balloon temperature) to vary cyclically between the first balloon temperature and the second balloon temperature over the balloon temperature range.

[0048] In some examples, the upper flow rate and the lower flow rate are inputs provided to the processing circuitry rather than determined by the processing circuitry. For example, the medical system may be configured to provide the fluid (e.g., from a fluid reservoir) at the upper flow rate when a flow actuator (e.g., a valve or a pump) is placed in a first configuration (e.g., a first valve position or a first pump speed). The medical system may be configured to provide the fluid at the lower flow rate when the flow actuator is placed in a second configuration (e.g., a second valve position or a second pump speed). Hence, the upper flow rate and the lower flow may substantially be determined by other components of the medical system. The processing circuitry may be configured to determine the periodicity over which the fluid delivered to the balloon should vary from the known upper flow rate to the known lower flow rate and return to the known upper flow rate in order to cause representative balloon temperature to vary cyclically between the first balloon temperature and the second balloon temperature over the balloon temperature range.

[0049] In some examples, for example when the representative balloon temperature is an expected balloon temperature, the processing circuitry is configured to determine the periodicity by at least determining (e.g., through simulation or other modeling) a first time period required for the representative balloon temperature to transition from the first balloontemperature to the second balloon temperature when the fluid delivered to the balloon transitions from the upper flow rate to the lower flow rate. The processing circuitry may be configured to determine (e.g., through simulation or other modeling) a second time period required for the representative balloon temperature to transition from the second balloon temperature to the first balloon temperature when the fluid delivered to the balloon transitions from the lower flow rate to the upper flow rate. The processing circuitry may be configured to determine the periodicity based on the first time period and the second time period. The processing circuitry may utilize the determined periodicity to substantially maintain the tissue temperature in the temperature range substantially bounded by the first tissue temperature and the second tissue temperature.

[0050] In some examples, for example when the representative balloon temperature is a sensed balloon temperature, either sensed by a temperature sensor or determined based on fluid pressure, the processing circuitry is configured to determine the periodicity by at least causing the medical system to deliver the fluid at the upper flow rate until the sensed balloon temperature indicates the first balloon temperature. The processing circuitry may subsequently cause the medical system to deliver the fluid at the lower flow rate until the sensed balloon temperature indicates a temperature at or in proximity to the second balloon temperature. The processing circuitry may cause the medical system to deliver the fluid at the upper flow rate when the sensed balloon temperature indicates the second balloon temperature. The processing circuitry may determine the periodicity by at least determining an elapsed time over which the medical system caused the fluid flow to transition from the upper flow rate to the lower flow rate and return to the upper flow rate in order to cause the sensed balloon temperature to cycle from the first balloon temperature to the second balloon temperature and return to the first balloon temperature. The processing circuitry may utilize the determined periodicity to substantially maintain the tissue temperature in the temperature range substantially bounded by the first tissue temperature and the second tissue temperature.

[0051] In some examples, the processing circuitry is configured to determine the periodicity based on, for example, previous ablation procedures, computer modeling and / or measurement of fluid flow through the catheter system and / or balloon, modeling and / or measurement of heat transfer characteristics of a balloon experiencing a given fluid flow, and / or other data indicative of a heat transfer between an expanded balloon and a vessel wall. In examples, the processing circuitry may determine the periodicity using a memory storing a plurality of periodicities. A periodicity in the plurality of periodicities may be associated withother data, such as an upper flow rate, a lower flow rate, a vessel size (e.g., vessel diameter), an ablation level, and / or other data. In examples, the processing circuitry is configured to determine (e.g., receive as an input or a measured quantity) an upper flow rate, a lower flow rate, a vessel size (e.g., vessel diameter), an ablation level, and / or other data and select a periodicity from among the plurality of periodicities based on an association with the upper flow rate, the lower flow rate, the vessel size, the ablation level, and / or the other data. In some examples, the processing circuitry may be configured to determine the periodicity using an input provided from a control console.

[0052] The medical system is configured to deliver the fluid at an upper flow rate, a lower flow rate, and a periodicity which causes the balloon to remain expanded within the vessel of the patient as the delivered flow rate varies (e.g., causes a body of the balloon to remain in contact with a vessel wall as the delivered flow rate varies). For example, during a flow rate cycle, the medical system may be configured to decrease the flow rate from the upper flow rate to the lower flow rate and subsequently return the flow to the upper flow rate over a relatively short periodicity such the balloon remains expanded within the vessel during the flow rate cycle. Hence, the medical system may be configured to deliver the fluid over the first flow rate cycle, the second flow rate cycle, the third flow rate cycle, and succeeding cycles using a periodicity sufficient to cause the balloon to remain expanded within the vessel as the medical system delivers the fluid over the first flow rate cycle, the second flow rate cycle, the third flow rate cycle, and the succeeding cycles. In some examples, the periodicity is less than or equal to about 30 seconds.

[0053] In examples, the processing circuitry is configured to consider a response of the patient (e.g., a thermoregulation) during delivery of the therapy and adjust one or more of the upper flow rate, the lower flow rate, and / or the periodicity based on the response. In this way, the upper flow rate, the lower flow rate, and / or the periodicity may be patient-specific. For example, the processing circuitry may be configured to receive a sensed balloon temperature and determine a rate of change of the sensed balloon temperature during delivery of the fluid (e.g., a rate of change as the sensed balloon temperature changes from the first balloon temperature to the second balloon temperature). The processing circuitry may treat the rate of change of the sensed balloon temperature as a proxy for a rate of change of the tissue temperature at the target tissue site of the patient. The processing circuitry may adjust the periodicity of the delivered fluid such that the rate of change of the sensed balloon temperature more closely matches and / or mimics an inherent capacity of the patient totransition the tissue temperature between the first tissue temperature and the second tissue temperature which substantially bound the desired temperature range at the target tissue site. For example, if the rate of change of the sensed balloon temperature from the first balloon temperature to the second balloon temperature (e.g., because of the thermoregulation tendency of the patient) is greater than a rate of change expected when the medical system delivers the fluid at the upper flow rate, the lower flow rate, and the periodicity, the processing system may be configured to determine a shorter periodicity to more closely match and / or mimic the thermoregulation tendency of the patient.

[0054] In some examples, the processing circuitry is configured to determine a rate of change of the sensed balloon temperature and issue a communication and / or notification if the rate of change is greater than or equal to a threshold. The processing circuitry may issue a communication (e.g., an notification) as an indication that the upper flow rate, the lower flow rate, the periodicity, a positioning of the balloon in the vessel, or some other aspect of the medical system is causing a potentially undesired and / or unexpected heat transfer with tissue and / or anatomical structures which may be proximity to the target tissue site. In response, a clinician may adjust one or more parameters of the therapy delivery or a position of the balloon within the patient. In some examples, the processing circuitry automatically stops delivery of fluid to the balloon in response determining the rate of change of the sensed balloon temperature and issue a communication and / or notification if the rate of change is greater than or equal to the threshold.

[0055] In examples, the medical system is configured to deliver a fluid which undergoes a phase change from a liquid phase to a gas phase. For example, the medical system may be configured to deliver the fluid at the upper flow rate, the lower flow rate, and the periodicity when the fluid is in the liquid phase. The medical system may be configured to allow the fluid to subsequently change phase from the liquid phase to the gaseous phase before the fluid flows through the interior volume of the balloon. For example, the medical system may include a distributor (e.g., distributor 114 shown in FIGS. 1, 4, and 5) configured to cause and / or allow the fluid to change from the liquid phase to the gas phase. The compressibility of the gas phase may result in the balloon experiencing flow through the interior volume at flow rates different than the flow rates of the liquid phase delivered by the medical system over the periodicity. Hence, as the medical system delivers the fluid in the liquid phase at the upper flow rate and the lower flow rate, the balloon may experience a flow of the gas phase throughthe interior volume at rates (e.g., mass flow rates) different from the upper flow rate and the lower flow rate.

[0056] For example, when the medical system decreases the liquid phase delivery from the upper flow rate to the lower flow rate, this may cause an expansion of the gas phase within the interior volume (e.g., due to a decreased pressure in the interior volume). This expansion may cause the flow rate of the gas phase through the interior volume to decrease at a rate less than a rate of decrease of the liquid phase as the liquid phase decreases from the upper flow rate to the lower flow rate. When the medical system increases the liquid phase delivery from the lower flow rate to the upper flow rate, this may cause a compression of the gas phase within the interior volume (e.g., due to an increased pressure in the interior volume). This compression may cause the flow rate of the gas phase through the interior volume to increase at a rate less than a rate of increase of the liquid phase as the liquid phase increases from the lower flow rate to the upper flow rate. The processing circuitry may be configured to determine one or more of the upper flow rate, the lower flow rate, and / or the periodicity to account for the differing flow rates of the gas phase through the balloon as compared to the liquid phase delivered by the medical system.

[0057] In examples, the medical system includes a flow actuator configured to cause the delivery of the fluid at the upper flow rate, the lower flow rate, and the periodicity. The processing circuitry can directly or indirectly control the flow actuator. The flow actuator may be, for example, a valve, a pump, or another component configured to control a flow rate. In examples, the flow actuator is configured to cause the flow rate to vary between the upper flow rate and the lower flow rate at a substantially linear rate such that, for example, the flow rate waveform delivered by the system is substantially a sawtooth-type wave. In some examples, the flow actuator is configured to cause the flow rate to vary between the upper flow rate and the lower flow rate at a substantially nonlinear rate such that, for example, the flow rate waveform delivered by the system is substantially a sinewave-type wave or other relatively curved wave. The medical system is configured such that, as the medical system delivers the fluid (e.g., in a liquid phase) at the upper flow rate, the lower flow rate, and the periodicity (e.g., in a manner defining the flow rate waveform), the balloon experiences a flow rate (e.g., a gaseous flow rate) through the interior volume that causes the balloon to alternate between the higher heat transfer with the vessel wall and the lower heat transfer with the vessel wall, such that balloon enables maintaining the target tissue site within a temperature range that includes the target temperature.

[0058] In some examples, the medical system is configured such that the lower flow rate is substantially zero (e.g., zero or nearly zero to the extent permitted by manufacturing tolerances). The medical system may be configured to deliver the fluid from the upper flow rate to the lower flow rate of substantially zero. The medical system may be configured to deliver the fluid from the upper flow rate to the flow rate of substantially zero at a periodicity causing the balloon to remain expanded within the vessel as the medical system deliver the fluid from the upper flow rate to the flow rate of substantially zero.

[0059] In some examples, the elongate body is configured to provide a flow path for the fluid (e.g., nitrous oxide, nitrous oxide, nitrogen, argon, or helium) through the interior volume of the balloon to cause a heat transfer (e.g., via the balloon) between the fluid and the vessel wall of the blood vessel. The elongate body may define an inlet lumen configured to receive a supply of the fluid (e.g., a liquid) from a fluid delivery system, such as a fluid reservoir and / or fluid pump. The elongate body may be configured to provide the fluid to the interior volume of the balloon via the inlet lumen. In examples, the elongate body defines an outlet lumen configured to receive a discharge of the fluid (e.g., as a gas) from the balloon interior, such that the elongate body provides the fluid flow through the balloon interior.

[0060] In some examples, the system includes a cryoablation system and the fluid is a refrigerant that changes phase from a liquid to a gaseous physical state to enable the balloon to expand and assist a heat transfer from the vessel wall to the fluid. In some examples, the elongate body includes and / or supports (e.g., mechanically supports) a distributor positioned within the flow path configured to cause the fluid to expand from a liquid to a gas as the fluid flows through the distributor. In some examples, the system includes a cryoablation system and the fluid is a refrigerant that does not change phase and remains a liquid in the balloon interior and throughout the medical procedure.

[0061] The medical system described herein can be used to provide any suitable type of therapy, such as neuromodulation therapy or other ablation therapy. Neuromodulation therapy can include, for example, denervation therapy. Neuromodulation (e.g., renal neuromodulation) is the partial or complete incapacitation or other effective disruption of nerves (e.g., nerves terminating in the kidneys or in structures closely associated with the kidneys). Neuromodulation can include inhibiting, reducing, and / or blocking neural communication along neural fibers (e.g., efferent and / or afferent neural fibers). Such incapacitation can be long-term (e.g., permanent or for periods of months, years, or decades) or short-term (e.g., for periods of minutes, hours, days, or weeks). Neuromodulation may beexpected to contribute to the systemic reduction of sympathetic tone or drive and / or to benefit at least some specific organs and / or other bodily structures innervated by sympathetic nerves. Accordingly, neuromodulation may be expected to be useful in treating clinical conditions associated with systemic sympathetic overactivity or hyperactivity, particularly conditions associated with central sympathetic overstimulation.

[0062] Conditions such as arrhythmias, hypertension, states of volume overload (e.g., heart failure), and progressive renal disease due to excessive activation of the sympathetic nervous system (SNS), may be mitigated by modulating the activity of overactive nerves (neuromodulating), for example, by denervating or reducing the activity of the overactive nerves. For example, renal neuromodulation may be expected to efficaciously treat hypertension, heart failure, acute myocardial infarction, metabolic syndrome, insulin resistance, diabetes, left ventricular hypertrophy, chronic and end stage renal disease, inappropriate fluid retention in heart failure, cardio-renal syndrome, polycystic kidney disease, polycystic ovary syndrome, osteoporosis, erectile dysfunction, other sexual dysfunction, and sudden death, among other conditions. In examples described herein, the neuromodulation is thermally-induced (by cryoablation or heating tissue) alone or in addition to being electrically induced, chemically-induced, or induced in another suitable manner or combination of manners at one or more suitable target sites during a treatment procedure.

[0063] Some sympathetic nerves, such as sympathetic nerves (renal nerves) of the kidneys, are positioned proximate to blood vessels, such that these overactive nerves may be chemically, thermally, or electrically denervated by ablating sympathetic nerve tissue in or near the blood vessels (e.g., renal blood vessels).

[0064] In neuromodulation, one or more therapeutic elements (e.g., a balloon as described herein) may be introduced near one or more target nerves. In renal neuromodulation, for example, the one or more therapeutic elements may be introduced near renal nerves located between an aorta and a kidney of a patient. For example, the one or more therapeutic elements can be positioned within or otherwise proximate to a renal lumen (e.g., a renal artery, a renal vein, a ureter, a renal pelvis, a major renal calyx, a minor renal calyx, or another suitable structure), and the treated tissue can include tissue at least proximate to a wall of the renal lumen. For example, with regard to a renal artery, a treatment procedure can include modulating nerves in the renal plexus, which lay intimately within or adjacent to the adventitia of the renal artery. In some examples, the one or more therapeutic elements may be carried by or attached to a catheter, and the catheter may be introduced intravascularly, e.g.,into a renal artery via a brachial artery, femoral artery, or radial artery approach. In other examples, the one or more therapeutic elements may be introduced extravascularly, e.g., using a laparoscopic technique.

[0065] Although the present technology is herein described in many instances with reference to renal nerves and vessels, the present technology also has application to ablation and / or neuromodulation at other anatomical sites (e.g., spinal neuromodulation, cardiac neuromodulation, brain neuromodulation, sacral neuromodulation, urinary neuromodulation, hepatic neuromodulation, and / or neuromodulation techniques directed to other portions of a body) and their associated nerves and that such devices and systems can be configured (e.g., have suitable shape and dimensions) for such sites. For example, a catheter may be configured to deliver neuromodulation therapy (e.g., thermal energy) to a particular anatomical lumen or a particular tissue (e.g., a renal artery, external iliac artery, internal iliac artery, internal pudendal artery, celiac artery, mesenteric artery, superior mesenteric artery, inferior mesenteric artery, hepatic artery, splenic artery, gastric artery, left gastric artery, pancreatic artery, uterine artery, ovarian artery, testicular artery, and / or their associated arterial branches, accessories, veins, and / or other hollow anatomical structures or combinations thereof).

[0066] As used herein, the terms “distal” and proximal” define a position or direction with respect to the treating clinician or clinician's control device (e.g., a handle assembly). “Distal” or “distally” can refer to a position distant from or in a direction away from the clinician or clinician's control device. “Proximal” and “proximally” can refer to a position near or in a direction toward the clinician or clinician's control device.

[0067] FIG. 1 is a partially schematic perspective view illustrating a medical system 100 configured in accordance with examples of the present disclosure. FIG. 2 is a schematic illustration of a portion of medical system 100 within a blood vessel 102 of a patient 106 (FIG. 3), the blood vessel 102 having a vessel wall 104. FIG. 3 illustrates medical system 100 being navigated through vasculature of patient 106 to a target treatment site within blood vessel 102. In the examples of FIGS. 2 and 3, blood vessel 102 is a renal artery and vessel wall 104 is a renal artery wall. However, in other examples, medical system 100 is be configured to deliver treatments to other blood vessels, anatomical lumens, and / or other tissues, such as an external iliac artery, internal iliac artery, internal pudendal artery, celiac artery, mesenteric artery, superior mesenteric artery, inferior mesenteric artery, hepatic artery, splenic artery, gastric artery, left gastric artery, pancreatic artery, uterine artery, ovarianartery, testicular artery, and / or their associated arterial branches, accessories, veins, and / or other hollow anatomical structures of a patient or combinations thereof.

[0068] Medical system 100 includes a catheter system 108 defining an elongate body 110 configured to be positioned (e.g., by a clinician) within blood vessel 102 of patient 106. Catheter system 108 includes one or more expandable elements such as balloon 112 configured to expand (e.g., by inflation) when elongate body 110 is positioned within blood vessel 102. Balloon 112 may be configured to expand to, for example, establish contact with vessel wall 104, assist in occluding blood vessel 102 during a procedure, assist in maintaining elongate body 110 within blood vessel 102, assist in displacing and / or maintaining a displacement between elongate body 110 and vessel wall 104, and / or for other reasons. Elongate body 110 defines a longitudinal axis L. Balloon 112 may be configured to expand radially outwards relative to longitudinal axis L (e.g., substantially perpendicular to longitudinal axis L) when balloon 112 is inflated within blood vessel 102 of patient 106. In some examples, catheter system 108 includes a distributor 114 configured to issue a fluid into an interior volume 116 defined by balloon 112 to deliver a therapy to tissue to, for example, conduct a neuromodulation or another procedure on vessel wall 104 and / or other tissues associated with blood vessel 102. While the therapy is primarily referred to as ablation (e.g., thermal ablation, such as cryoablation or heat-based ablation), the therapy can be in the form of any suitable modality in other examples.

[0069] Medical system 100 is configured to deliver a fluid to interior volume 116 of balloon 112 to inflate balloon 112 within blood vessel 102. Balloon 112 is configured such that the inflation causes an exterior surface (e.g., balloon exterior surface 168 (FIGS. 4 and 5) of balloon 112 to contact vessel wall 104. In examples, balloon 112 is a compliant balloon configured to substantially conform to vessel wall 104 when balloon 112 inflates to establish contact with vessel wall 104. In examples, balloon 112 and / or medical system 100 may be configured such that an expansion of balloon 112 during the inflation is substantially constrained by vessel wall 104. For example, blood vessel 102 (e.g., in the absence of medical system 100) may define a dimension such as a vessel diameter DV. Balloon 112 and / or medical system 100 may be configured such that, when balloon 112 inflates and contacts vessel wall 104, balloon 112 establishes a dimension such as balloon diameter DB which is substantially limited by vessel diameter DV.

[0070] Balloon 112 and / or medical system 100 may be configured such that the expansion of balloon 112 remains constrained by vessel wall 104 over a range of pressures of the fluidwithin interior volume 116, such that balloon 112 substantially retains a balloon diameter DB which is generally the same as vessel diameter DV as a pressure of the fluid within interior volume 116 varies. For example, balloon 112 may be configured to expand substantially in a distal direction D or a proximal direction P when a pressure increases within interior volume 116 and balloon 112 is constrained from radial expansion by vessel wall 104. In some examples, medical system 100 is configured to provide a relatively low pressure fluid (e.g., a relatively low pressure gas) to interior volume 116 to cause the expansion of balloon 112. For example the fluid may be a gas having a pressure of from about 1 atmospheres to about 5 atmospheres. Hence, in examples, balloon 112 is configured such that an inflated dimension of balloon 112 (e.g., balloon diameter DB) generally conforms to a dimension of blood vessel 102 (e.g., vessel diameter DV) when balloon 112 is inflated within blood vessel 102.

[0071] Medical system 100 is configured to circulate the fluid through interior volume 116 to modify a temperature at or near a target tissue site. For example, balloon 112 may be configured to cause a heat transfer between the fluid within interior volume 116 and vessel wall 104, such as a heat transfer through a body of balloon 112 (e.g., balloon body 166 (FIGS. 4 and 5)). In examples, medical system 100 is configured to provide a cryogenic fluid to balloon 112 to facilitate a cryoablation at the target tissue site. In some examples, medical system 100 is configured to provide a heated thermal fluid through balloon 112 to facilitate a heat-based thermal ablation to the target tissue site. The temperature modification can be used to provide a therapeutic outcome (e.g., neuromodulation or other lesion generation).

[0072] In some examples, balloon 112 is configured to help position catheter system 108 within blood vessel 102 during a procedure. For example, catheter system 108 may be configured such that inflation of balloon 112 helps retain elongate body 110 in a position (e.g., approximately centered in blood vessel 102) relative to vessel wall 104, helps maintain a displacement between elongate body 110 and vessel wall 104, and / or assists in other ways. In some examples, elongate body 110 supports (e.g., mechanically supports) balloon 112. In some examples, system 100 also includes a distributor 114 and elongate body 110 supports (e.g., mechanically supports) distributor 114. For example, elongate body 110 may support distributor 114 within interior volume 116 of balloon 112.

[0073] Medical system 100 is configured to provide a flow path for a fluid through interior volume 116 to cause the heat transfer (e.g., via balloon 112) between the fluid and vessel wall 104. For example, catheter system 108 may be configured such that the fluid may flow into a fluid inlet 118 (e.g., flow Fl), through an inlet lumen defined by elongate body110, through interior volume 116, then through an outlet lumen defined by elongate body 110, and subsequently discharge through a fluid outlet 120 (e.g., flow F2). Medical system 100 includes a flow actuator 122 (e.g., a valve or a pump) configured to control a flow rate of the fluid flowing through the flow path. At least some portion of flow actuator 122 is fluidically coupled to the flow path defined by medical system 100.

[0074] In the example shown in FIG. 1, medical system 100 includes a fluid delivery system 124 configured to provide the fluid to catheter system 108. Fluid delivery system 124 may include, for example, at least one of a fluid container defining a reservoir configured to hold a volume of the fluid or a pump configured to move the fluid. In some examples, medical system 100 includes an inlet conduit 126 defining an inlet flow path fluidically coupled to fluid delivery system 124 and fluid inlet 118. Medical system 100 may include an outlet conduit 128 defining an outlet flow path fluidically coupled to fluid outlet 120. Hence, in examples, two or more of fluid delivery system 124, inlet conduit 126, the inlet lumen of elongate body 110 (e.g., inlet lumen 170 (FIG. 4, FIG. 5)), interior volume 116, the outlet lumen of elongate body 110 (e.g., outlet lumen 172 (FIG. 4, FIG. 5)), and / or outlet conduit 128 define a flow path for the fluid flow through catheter system 108.

[0075] A state of flow actuator 122 controls a flow rate of the fluid within any of inlet conduit 126, the inlet lumen of elongate body 110, interior volume 116, the outlet lumen of elongate body 110, and / or outlet conduit 128. In examples, flow actuator 122 is configured such that altering a flow rate in any one of inlet conduit 126, the inlet lumen of elongate body 110, interior volume 116, the outlet lumen of elongate body 110, and / or outlet conduit 128 alters an amount of the flow of fluid through at least one other of inlet conduit 126, the inlet lumen of elongate body 110, interior volume 116, the outlet lumen of elongate body 110, and / or outlet conduit 128. In some examples, flow actuator 122 is configured such that altering the flow rate alters an amount of the flow of fluid through each of inlet conduit 126, the inlet lumen of elongate body 110, interior volume 116, the outlet lumen of elongate body 110, and outlet conduit 128.

[0076] In some examples, medical system 100 includes a regulating valve 130 in fluidic communication with at least one of the outlet flow path of outlet conduit 128 or the outlet lumen of elongate body 110. Regulating valve 130 may be configured to, for example, control a pressure of the fluid within some portion of the flow path defined by medical system 100, such as a pressure (e.g., a back pressure) in one or more of the outlet flow path of outlet conduit 128, the outlet lumen of elongate body 110, and / or interior volume 116. In someexamples, medical system 100 may include an evacuating pump (e.g., a vacuum pump) (not shown) in fluidic communication with at least one of the outlet flow path of fluid outlet 120 or the outlet lumen of elongate body 110 to, for example, control a pressure of the fluid within some portion of the flow path and / or evacuate the fluid from catheter system 108. In some examples, fluid delivery system 124 includes one or more additional components, such as a conditioning assembly (e.g., a cooling assembly) (not shown) configured to control a temperature of the fluid and / or a pressure of the fluid within fluid delivery system 124 and / or another portion of medical system 100. In some examples, medical system 100 (e.g., processing circuitry 132) is configured to control a pressure within interior volume 116 using, for example, regulating valve 130, the evacuating pump, and / or other components of medical system 100.

[0077] In some examples, such as in some cryoablation examples, medical system 100 is configured to expand the fluid from a liquid to gas to assist balloon 112 in facilitating a heat transfer from vessel wall 104 to the fluid within interior volume 116 of balloon 112. In examples, distributor 114 is configured to cause the fluid to expand from a liquid to a gas as the fluid flows through distributor 114. Distributor 114 may be positioned within (e.g., fluidically coupled to) the flow path defined by medical system 100. For example, distributor 114 may be positioned within interior volume 116, as shown in FIG. 1. Elongate body 110 may support distributor 114 such that distributor 114 receives the fluid as a liquid (e.g., from the inlet lumen of elongate body 110) and issues the fluid as a gas into interior volume 116. In examples, medical system 100 is configured to provide the fluid as a liquid via fluid delivery system 124 and inlet conduit 126 and discharge the fluid as a gas via outlet conduit 128 and, in some examples, regulating valve 130. In some examples, flow actuator 122 is configured to control the flow of the fluid as a liquid to control the flow rate of the fluid through medical system 100 (e.g., as a liquid issuing from fluid delivery system 124 of flowing through inlet conduit 126). However, flow actuator 122 may be configured to control the flow of the fluid as a liquid, a gas, and / or a mixture of a fluid and a gas to control the flow rate of the fluid through medical system 100. In other examples in which medical system 100 is configured for cryoablation, balloon 112 is inflated via the cryogenic fluid in liquid form.

[0078] Medical system 100 (e.g., flow actuator 122) is configured to deliver the fluid to balloon 112 (e.g., via distributor 114) at an upper flow rate, a lower flow rate, and a periodicity over which the fluid varies from the upper flow rate to the lower flow rate and returns to the upper flow rate. The medical system is configured such that that a temperatureprofile developed across intervening tissue between balloon 112 and the target tissue site (e.g., target tissue site 159, FIGS. 3-5) results in maintaining the tissue temperature at the target tissue site within a desired temperature range as the fluid is delivered at the upper flow rate, the lower flow rate, and the periodicity.

[0079] Medical system 132 includes processing circuitry 132 configured to control the delivery of fluid to balloon 112 at the upper flow rate, the lower flow rate, and the periodicity to help maintain the tissue temperature at the target tissue site at some depth greater than zero from the interface between balloon 112 and vessel wall 104. In addition, in some examples, processing circuitry 132 is configured to determine at least the periodicity of the flow rate delivered by flow actuator 122 to balloon interior 116. In some examples, processing circuitry 132 is configured to determine the periodicity prior to a delivery of therapy to patient 106. In some examples, processing circuitry 132 is configured to determine the periodicity during delivery of therapy to patient 106 (e.g., as the tissue temperature approaches the target temperature, or as the tissue temperature transitions from a first tissue temperature to a second tissue temperature). In examples, processing circuitry 132 is configured to adjust at least the periodicity during the delivery of the therapy to patient 106 (e.g., as the balloon is expanded within the vessel and receiving the fluid).

[0080] In some examples, medical system 100 includes a temperature sensor 133 configured to sense a parameter (e.g., a temperature and / or a pressure) indicative of a balloon temperature of balloon 112 (e.g., as balloon 112 is expanded within blood vessel 102 and receiving the fluid via flow actuator 122). The temperature can be, for example, a temperature in interior volume 116 of balloon 112. Processing circuitry 132 may be configured to adjust at least the periodicity based on the parameter sensed by temperature sensor 133. In examples, processing circuitry 132 is configured to adjust a duration of the upper flow rate and / or a duration of the lower flow rate which occurs over the periodicity (e.g., based on the parameter sensed by temperature sensor 133), e.g., based on the parameter sensed by temperature sensor 133.

[0081] In some examples, processing circuitry 132 is configured to determine at least the periodicity by at least determining a representative balloon temperature and accounting for a temperature profile developed or expected to develop across intervening tissue of vessel wall 104 between balloon 112 and the target tissue site when balloon 112 receives the fluid. In some examples, the representative balloon temperature is an expected balloon temperature anticipated to occur when balloon 112 is expanded in blood vessel 102 and receiving one ormore flow rates of the fluid (e.g., the upper flow rate, the lower flow rate, or a flow rate between the upper flow rate and the lower flow rate). In some examples, the representative balloon temperature is a sensed balloon temperature provided by sensor 133 and communicated to processing circuitry 132.

[0082] In some examples, processing circuitry 132 is configured to determine the upper flow rate and / or the lower flow rate. In some examples, the upper flow rate and the lower flow rate are inputs provided to processing circuitry 132, which can control the fluid flow rates to interior volume 116 of balloon based on the received lower and upper flow rates. For example, processing circuitry 132 can be configured to cause flow actuator 122 to alternate between a first configuration (e.g., a first position or a first pump speed) and a second configuration (e.g., a second position or a second pump speed). Medical system 100 may be configured to deliver the fluid at the first flow rate (e.g., to inlet conduit 126) when flow actuator 122 is in the first configuration and / or deliver the fluid at the second flow rate (e.g., to inlet conduit 126) when flow actuator 122 is in the second configuration. Processing circuitry 132 may be configured to determine the periodicity over which the fluid delivered to the balloon (e.g., via inlet conduit 126) should vary from the known upper flow rate to the known lower flow rate and return to the known upper flow rate in order to cause the representative balloon temperature of balloon 112 to vary cyclically between a first balloon temperature and a second balloon temperature over a balloon temperature range.

[0083] In some examples, processing circuitry 132 is configured to receive the upper flow rate and / or the lower flow rate from a sensor 136 configured to generate a signal indicative of a flow parameter (e.g., a pressure, a fluid flow rate, or other flow parameter) of a fluid within the flow path defined by medical system 100. Sensor 136 may be configured such that the signal is indicative of (e.g., proportional to) a flow rate of fluid flowing through interior volume 116 of balloon 112. In some examples, processing circuitry 132 is configured to receive the upper flow rate and / or the lower flow rate via a device 134. Device 134 may be, for example, a user input device configured to receive the upper flow rate and / or the lower flow rate from a user (e.g., a clinician), circuitry configured to receive input from a sensor, and / or other systems and / or devices. In examples, device 134 may be configured to receive a tissue depth of a target tissue site and / or a size (e.g., a diameter) of blood vessel 102. Processing circuitry 132 may be configured to determine one or more of the upper flow rate, the lower flow rate, and / or the periodicity using a tissue depth of a target tissue site and / or a size (e.g., a diameter) of blood vessel 102 received from device 134.

[0084] In some examples, device 134 has a suitable configuration sufficient to receive an input from a user. For example, device 134 can include a button or keypad, a touch screen, a speaker configured to receive voice commands from a user, and / or a display, such as a liquid crystal (LCD), light-emitting diode (LED), or organic light-emitting diode (OLED). In some examples, device 134 may include or be configured to be used in combination with a mobile phone, smartphone, tablet computer, personal computer, desktop computer, personal digital assistant, router, modem, remote server or cloud computing device, and / or related device. In some examples, device 134 is configured to display information, such as one or more upper flow rates, lower flow rates, periodicities, temperature ranges of a target tissue site, tissue depths of a target tissue site, representative balloon temperatures, a vessel sizes, setpoints, flow rates, and / or flow parameters.

[0085] In some examples, processing circuitry 132 is configured to determine at least the periodicity using stored data, such as, but not limited to, data obtained from, for example, previous ablation procedures, modeling and / or measurement of fluid flow through catheter system 108 and / or balloon 112, modeling and / or measurement of heat transfer characteristics of balloon 112 experiencing a given fluid flow, and / or other data indicative of a heat transfer between an expanded balloon such as balloon 112 and a vessel wall such as vessel wall 104. Although not shown in FIG. 1, medical system 100 can include a memory that stores a plurality of temperature ranges and / or tissue depths, and corresponding periodicities.

[0086] Temperature sensor 133 is configured to generate a signal indicative of a temperature (e.g., a temperature and / or a pressure) of balloon 112. For example, temperature sensor 133 may be configured such that the signal is indicative of (e.g., proportional to) a temperature of a fluid flowing through interior volume 116 of balloon 112, a temperature of a body of balloon 112 configured to contact vessel wall 104, or another temperature of medical system 100 indicative of a temperature of balloon 112. Temperature sensor 133 may be configured to sense the signal indicative of the temperature at any location of medical system 100, including inlet conduit 126, an inlet lumen defined by elongate body 110, interior volume 116, an outlet lumen defined by elongate body 110, outlet conduit 128, and / or another portion of medical system 100. Temperature sensor 133 may be configured to sense the signal indicative of the temperature at a location where the fluid is expected to be a gas liquid, a gas, or a mixture of a liquid and a gas.

[0087] Sensor 136 configured to generate a signal indicative of a flow parameter (e.g., a pressure, a fluid flow rate, or other flow parameter) of a fluid within the flow path defined bymedical system 100. Sensor 136 may be configured such that the signal is indicative of (e.g., proportional to) a flow rate of fluid flowing through interior volume 116 of balloon 112. Sensor 136 may be configured to sense the flow parameter at any location within the flow path defined by medical system 100, including inlet conduit 126, an inlet lumen defined by elongate body 110, interior volume 116, an outlet lumen defined by elongate body 110, outlet conduit 128, and / or another portion of the flow path. Sensor 136 may be configured to sense the flow parameter at a location where the fluid is expected to be a liquid, a gas, or a mixture of a liquid and a gas. In examples, sensor 136 is configured to sense the flow parameter when the fluid is a liquid flowing through inlet conduit 126.

[0088] In some examples, processing circuitry 132 is configured to control flow actuator 122 to cause medical system 100 to deliver the flow at the upper flow rate, the lower flow rate, and the periodicity. For example, processing circuitry 132 may be configured to control a configuration of a movable element of flow actuator 122 (e.g., a position of a valve, a speed of a pump) to control the flow rate. Hence, processing circuitry 132 may be configured to control the flow rate through balloon 112 based on at least the periodicity determined by processing circuitry 132 to, for example, substantially maintain a tissue temperature at a target tissue site within a temperature range (e.g., a temperature range less than a balloon temperature range experienced by balloon 112).

[0089] Elongate body 110 defines a distal portion 110A (“distal body portion 110A”) and a proximal portion HOB (“proximal body portion HOB”). Balloon 112 and / or distributor 114 are positioned on distal body portion 110A in the example shown in FIG. 1. In examples, catheter system 108 is configured to assume a relatively low profile delivery configuration in which at least one of distal body portion 110A and / or balloon 112 defines a dimension DS (e.g., a diameter), which can be measured in a direction perpendicular to longitudinal axis L. The dimension DS may define a displacement sufficient to allow the passage of at least distal body portion 110A and balloon 112 through vasculature of patient 106 to reach a target treatment site within patient 106. In some examples, distal body portion 110A is configured to locate balloon 112 and / or distributor 114 at an intraluminal (e.g., intravascular) location. In examples, catheter system 108 is configured such that, in the delivery configuration, the dimension DS measures 2, 3, 4, 5, 6, or 7 French or another suitable size. Balloon 112 is configured to expand from the delivery configuration to an expanded configuration (FIG. 2) to, for example, facilitate a heat transfer between vessel wall 104 and a fluid flowing through the flow path defined by medical system 100. Balloon 112 may be configured to establishinterior volume 116 in the expanded configuration such that balloon 112 may establish contact with vessel wall 104 for a plurality (e.g., a range) of vessel diameters that might be expected for a vessel such as vessel 102.

[0090] In some examples, medical system 100 (e.g., proximal body portion HOB) includes a handle portion 146, which is configured to remain outside vasculature of a patient when distal body portion 110A is within vasculature of the patient. Handle portion 146 may be configured to allow a clinician to navigate at least distal body portion 110A through the vasculature, allow inflation and / or deflation of balloon 112, allow and / or control a flow of fluid through balloon 112, and / or enable other functions of medical system 100 which may assist in the delivery of a treatment (e.g., a neuromodulation) to patient 106. At least some portion of catheter system 108 (e.g., distal body portion 110A) may be substantially flexible, such that catheter system 108 may flex and / or bend enroute to positioning distributor 114 substantially at a target location within a blood vessel of a patient. Hence, although illustrated as substantially linear in FIG. 1, catheter system 108 (or portions thereof) may be configured to assume linear, curved, and / or curvilinear shapes. Correspondingly, longitudinal axis L (and / or portions thereof) defined by catheter system 108 may be linear, curved, and / or curvilinear.

[0091] In examples, medical system 100 includes a console 148 including a console housing 150. Console 148 includes fluid delivery system 124, flow actuator 122, some portion of inlet conduit 126, some portion of outlet conduit 128, regulating valve 130, at least some portion of processing circuitry 132, device 134, and / or other components of medical system 100. In some examples, console 148 includes fluid delivery system 124, flow actuator 122, inlet conduit 126, outlet conduit 128, regulating valve 130, processing circuitry 132, and / or device 134 at least partially within (e.g., at least partially surrounded by) console housing 150.

[0092] In examples, fluid delivery system 124 includes a supply container 152 configured to hold the fluid supplied to catheter system 108. The supply container 152 can be a single-use cartridge or a larger container that contains a sufficient volume of fluid to perform multiple procedures. In examples, supply container 152 may be a refillable container (e.g., a refillable cylinder). Fluid delivery system 124 and / or supply container 152 may be configured to retain the fluid at a desired pressure and / or a desired temperature. For example, in one example, fluid delivery system 124 may be configured to hold nitrous oxide within supply container 152. Fluid delivery system 124 may be configured to hold the nitrous oxide at a pressure of 750 psi or greater (5.17 MPa or greater) to maintain the nitrous oxide in a substantially liquidstate at ambient temperatures. In other embodiments, the fluid may include carbon dioxide, a hydrofluorocarbon (“HFC”), and / or other suitable compressed or condensed refrigerant.

[0093] In examples, processing circuitry 132 is configured to receive the signal from temperature sensor 133 via a communication link 135. Processing circuitry 132 may be configured to receive the signal from sensor 136 via a communication link 138. Processing circuitry 132 may be configured to issue and / or receive signals to and / or from flow actuator 122 via a communication link 140. Processing circuitry 132 may be configured to receive a signal indicative of an indicated size of a vessel from device 134 via communication link 142. In some examples, processing circuitry 132 may be configured to issue and / or receive signals to and / or from regulating valve 130 via a communication link 144. Communication link 135, 138, 140, 142, 144 may be hard-line and / or wireless communications links. In some examples, communication link 135, 138, 140, 142, 144 may comprise some portion of processing circuitry 132. In some examples, communication link 135, 138, 140, 142, 144 may comprise a wired connection, a wireless Internet connection, a direct wireless connection such as wireless LAN, Bluetooth™, Wi-Fi™, and / or an infrared connection.

[0094] Processing circuitry 132, as well as other processors, processing circuitry, controllers, control circuitry, and the like, described herein, may include any combination of integrated circuitry, discrete logic circuity, analog circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs). In some examples, processing circuitry 132 includes multiple components, such as any combination of one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry, and / or analog circuitry.

[0095] Although not shown in FIG. 1, medical system 100 can also include a memory configured to store program instructions, such as software, which may include one or more program modules, which are executable by processing circuitry 132. When executed by processing circuitry 132, such program instructions may cause processing circuitry 132 to provide the functionality ascribed to processing circuitry 132 herein. The program instructions may be embodied in software and / or firmware. The memory can include any volatile, nonvolatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), ferroelectric RAM (FRAM), flash memory, or any other digital media.

[0096] FIG. 2 is a schematic illustration of a portion of medical system 100 (e.g., distal body portion 110A, balloon 112, and distributor 114) within blood vessel 102 defined by vessel wall 104 of patient 106. Catheter system 108 is configured to enable inflation of balloon 112 to cause catheter system 108 to transition from the delivery configuration (FIG. 1) to an expanded configuration when distal body portion 110A is positioned within blood vessel 102. In examples, catheter system 108 is configured to expand balloon 112 such that balloon 112 defines a dimension DB in an expanded configuration. The dimension DB defined in the expanded configuration may be greater than the dimension DS defined in the delivery configuration (FIG. 1). In examples, balloon 112 is configured to define the dimension DS, the dimension DB, and / or another dimension (e.g., a dimension substantially perpendicular to longitudinal axis L) based on a pressure PI of the fluid within interior volume 116.

[0097] In examples, medical system 100 (e.g., catheter system 108) is configured such that balloon 112 can expand to contact vessel wall 104. For example, balloon 112 may expand such that an exterior surface 168 of balloon 112 (“balloon exterior surface 168”) contacts vessel wall 104. Distal body portion 110A may support balloon 112 such that, when balloon 112 defines the dimension DB, catheter system 108 defines a displacement DP substantially between balloon exterior surface 168 and longitudinal axis L, distributor 114, and / or a therapeutic element of medical system 100. In examples, catheter system 108 is configured to substantially center (e.g., center or nearly center to the extent permitted by vessel symmetry) longitudinal axis L, distributor 114 and / or another element of medical system 100 within blood vessel 102 when balloon 112 expands to contact vessel wall 104.

[0098] Balloon 112 facilitates heat transfer between a fluid within interior volume 116 and vessel wall 104 to induce one or more desired effects (e.g., neuromodulation and / or ablation effects) on localized regions of blood vessel 102 and regions proximate blood vessel 102. For example, when blood vessel 102 defines a renal artery associated with a kidney 156, delivery of fluid through balloon 112 may induce one or more desired neuromodulating effects to a portion of Renal Plexus (RP) 158 lying within or adjacent to the adventitia of the renal artery, e.g., at a target tissue site 159 that is some depth from the interface between balloon 112 and vessel wall 104. The depth can be measured in a direction transverse (e.g., orthogonal) to a longitudinal axis of vessel 102. The heat transfer, whether cooling or heating of tissue, can create a lesion within tissue in or proximate to vessel wall 104.

[0099] FIG. 3 illustrates a portion of medical system 100 positioned within vasculature of a patient 106 to place balloon 112 and / or distributor 114 within blood vessel 102. FIG. 3 is described with primary reference to a renal artery, however similar devices, systems, and techniques may be adapted for accessing other anatomical lumens or tissues within patient 106.

[0100] Catheter system 108 (e.g., elongate body 110) may provide access to the renal plexus (RP) through an intravascular path (P), such as a percutaneous access site in the femoral (illustrated), brachial, radial, or axillary artery to a target treatment site within blood vessel 102. By manipulating proximal body portion 110B of elongate body 110 from outside the intravascular path (P), a clinician may advance at least distal body portion 110A through the sometimes-tortuous intravascular path (P) and remotely manipulate distal body portion 110A. In examples, distal body portion 110A may be remotely manipulated by a clinician using handle portion 146.

[0101] In the example illustrated in FIG. 3, balloon 112 is delivered intravascularly to the treatment site using a guidewire 160 in an OTW technique. Catheter system 108 (e.g., elongate body 110) may define a passageway for receiving guidewire 160 for delivery of elongate body 110 (e.g., distal body portion 110A) using either an OTW or a RX technique. At the treatment site, guidewire 160 can be at least partially withdrawn or removed, and balloon 112 may be expanded from the delivery configuration (FIG. 1) to an expanded configuration (FIG. 2). Balloon 112 may substantially position balloon 112 relative to blood vessel 102 for delivering energy to blood vessel 102 and / or other anatomical lumens or tissues within patient 106. In other examples, balloon 112 and / or distributor 114 may be delivered to the treatment site within a different guide device, such as guide sheath (not shown in FIG. 3), with or without using guidewire 160. In examples in which medical system 100 includes a guide sheath, when balloon 112 and / or distributor 114 are at the target treatment site, the guide sheath may be at least partially withdrawn or retracted and balloon 112 may be transformed into an expanded configuration. In still other examples, elongate body 110 may be steerable itself such that balloon 112 and / or distributor 114 may be delivered to the treatment site without the aid of guidewire 160 and / or a guide sheath.

[0102] FIG. 4 is a schematic illustration of medical system 100 with catheter system 108 in a relatively low profile delivery configuration within blood vessel 102, with catheter system 108 defining a dimension DS. FIG. 5 is a schematic illustration of medical system 100 within catheter system 108 in an expanded configuration within blood vessel 102, withcatheter system 108 defining a dimension DB. Dimension DB is greater than dimension DS. In examples, as shown in FIG. 5, catheter system 108 is configured to cause balloon 112 to contact vessel wall 104 in the expanded configuration. Dimension DS and / or the dimension DB may be a cross-sectional dimension of catheter system 108 (e.g., balloon 112), the crosssection being taken perpendicular to longitudinal axis L of elongate body 110. In examples, dimension DS and dimension DB define a displacement in a direction substantially perpendicular to longitudinal axis L. In examples, longitudinal axis L extends through catheter system 108 through a distal end 162 of elongate body 110 (“body distal end 162”). Longitudinal axis L may extend through at least some portion of distal body portion 110A and / or proximal body portion HOB. Distal end 162 may be substantially distal or substantially proximal to balloon 112 when balloon 112 is in either of the delivery configuration or expanded condition.

[0103] Medical system 100 (e.g., processing circuitry 132) is configured to deliver fluid to balloon 112 using a flow rate cycle whereby delivery of an upper flow rate is followed by delivery of a lower flow rate over a periodicity in which the fluid transitions from the upper flow rate to the lower flow rate and returns too the upper flow rate. For example, medical system 100 may deliver the fluid from fluid delivery system 124 via flow actuator 122 to inlet conduit 126. Medical system 100 (e.g., processing circuitry 132) is configured to conduct subsequent flow rate cycles to substantially maintain tissue temperature at a target tissue site 159 in a particular temperature range substantially bounded by the first tissue temperature and the second tissue temperature.

[0104] Target tissue site 159 is substantially at a tissue depth TD within vessel wall 104, such that the target tissue site is displaced from balloon exterior surface 168 when balloon exterior surface 168 contacts the vessel wall 104 (as depicted at FIG. 5). Tissue depth TD may cause the tissue temperature at target tissue site 159 to depart from a representative balloon temperature indicative of a temperature of balloon 112 (e.g., indicative of a temperature of balloon exterior surface 168) due to a temperature profile developed across tissue depth TD as balloon 112 causes heat transfer from or to vessel wall 104. Medical system 100 (e.g., processing circuitry 132) is configured to account for this temperature profile to maintain the tissue temperature at target tissue site 159 within the temperature range substantially bounded by the first tissue temperature and the second tissue temperature as medical system 100 delivers the fluid at the upper flow rate, the lower rate, and the periodicity. Tissue depth TD may be a displacement within vessel wall 104 and between target tissue site 159 and aninterface between balloon 112 and vessel wall 104 (e.g., between target tissue site 159 and balloon exterior surface 168). In examples, tissue depth TD is determined and / or measure in a direction transverse (e.g., orthogonal) to longitudinal axis L and / or a longitudinal axis of vessel 102.

[0105] Medical system 100 is configured to vary a rate of heat transfer between balloon 112 and vessel wall 104 as medical system 100 delivers the fluid at the upper flow rate, the lower rate, and the periodicity. In examples, the medical system 100 is configured to cycle the rate of heat transfer as medical system 100 delivers the fluid at the upper flow rate, the lower rate, and the periodicity. The cycling rate of heat transfer between balloon 112 and vessel wall 104 may help maintain tissue temperature at target tissue site 159 within the temperature range. Medical system 100 is configured such that that the temperature profiles developed over tissue depth TD as the fluid is delivered at the upper flow rate, the lower flow rate, and the periodicity substantially result in maintaining the tissue temperature at target tissue site 159 within the desired temperature range.

[0106] Processing circuitry 132 is configured to determine a target temperature of target tissue site 159. In examples, processing circuitry 132 is configured to receive the target temperature from device 134 (FIG. 1). In examples, processing circuitry 132 is configured to determine tissue depth TD (e.g., from device 134). Processing circuitry 132 is configured to determine at least the periodicity sufficient to maintain tissue temperature at target tissue site 159 within the temperature range when medical system 100 cycles the flow rate of the fluid between the upper flow rate and the lower flow rate. Processing circuitry 132 may determine the periodicity by determining a representative balloon temperature of balloon 112 and accounting for the temperature profile developed or expected to develop across tissue depth TD between balloon exterior surface 168 and target tissue site 159 when balloon 112 receives the fluid.

[0107] In examples, processing circuitry 132 determines the representative balloon temperature by determining an expected balloon temperature anticipated to occur when balloon 112 is expanded in blood vessel 102 and balloon interior 116 receives one or more flow rates of the fluid. The expected balloon temperature may be based on, for example, bench testing (e.g., in a laboratory), computer modeling, heat transfer characteristics of the medical system 100, previous use of similar medical systems, characteristics of the patient, and / or other characteristics. In some examples, the representative balloon temperature is asensed balloon temperature provided by temperature sensor 133 and communicated to processing circuitry 132.

[0108] Balloon 112 is configured such that a fluid in balloon interior 116 (e.g., the fluid supplied by fluid delivery system 124) establishes an inflation pressure PI within balloon interior 116. In examples, interior volume 116 is bound at least in part by an interior surface 164 (“balloon interior surface 164”) defined by a body 166 of balloon 112 (“balloon body 166”). Balloon body 166 also defines balloon exterior surface 168 substantially opposite balloon interior surface 164. Balloon body 166 is configured to cause a heat transfer between the fluid within interior volume 116 and vessel wall 104 when balloon exterior surface 168 contacts vessel wall 104. In examples, the heat transfer between the fluid within interior volume 116 and vessel wall 104 occurs via balloon interior surface 164, balloon body 166, and balloon exterior surface 168.

[0109] Balloon 112 is configured to inflate from the delivery configuration of FIG. 4 to the expanded configuration of FIG. 5 in response to an increase in the inflation pressure PI within balloon interior 116. In some examples, balloon 112 is configured to establish balloon diameter DB based on vessel diameter DV in the expanded configuration. In examples, balloon 112 is configured such that, in the expanded configuration of FIG. 5, balloon diameter DB is within a percentage range of vessel diameter DV. For example, balloon diameter DB may be at least 70 percent and less than 130 percent of vessel diameter DV, such as at least 80 percent and less than 120 percent of vessel diameter DV, at least 90 percent and less than 110 percent of vessel diameter DV in some examples, and / or substantially equal to vessel diameter DV. As used herein, vessel diameter DV may be equivalent to and / or representative of an indicated size of a blood vessel. In examples, medical system 100 (e.g., processing circuitry 132) is configured to receive an input (e.g., via console 148 and / or another system) indicative of the indicated size (e.g., a diameter) of blood vessel 102 in which a procedure is to be performed. For example, the indicated size may be obtained using a system configured to image vessel 102 and / or based on clinician input.

[0110] Medical system 100 is configured to circulate the fluid through interior volume 116 to modify a temperature of tissue at target tissue site 159. For example, balloon 112 may be configured to cause a heat transfer between the fluid within interior volume 116 and vessel wall 104, such as a heat transfer through balloon body 166. In examples, medical system 100 is configured to provide a cryogenic fluid to balloon 112 to deliver a cryoablation to the target site. In some examples, medical system 100 is configured to provide a heated thermal fluidthrough balloon 112 to deliver a heat-based thermal ablation to the target site. The temperature modification can be used to provide a therapeutic outcome (e.g., neuromodulation or other lesion generation) or can be used to help protect the vessel wall or other anatomical lumen wall. For example, the temperature modification can be used to cool the tissue prior to, during, or after delivery of other neuromodulation therapy, such as radiofrequency (RF) or ultrasound therapy that causes the tissue to heat up. As another example, the temperature modification can be used to heat the tissue between cycles of cryoablation, e.g., to help generate a lesion deeper into a wall of vessel 102 and maintain the integrity of the tissue at the direct interface between balloon 112 and vessel wall 104.[OHl] In examples, elongate body 110 is configured to circulate the fluid through interior volume 116 of balloon 112. For example, elongate body 110 may define an inlet lumen 170 configured to provide a flow of the fluid to interior volume 116 (e.g., via distributor 114). Inlet lumen 170 is fluidically coupled to balloon interior 116 and / or distributor 114. In examples, inlet lumen 170 is configured to provide a flow path for the fluid from fluid inlet 118 to interior volume 116 (e.g., via distributor 114). Inlet lumen 170 may be fluidically coupled to fluid inlet 118, inlet conduit 126, and / or flow actuator 122. Elongate body 110 may define an outlet lumen 172 fluidically coupled to balloon interior 116. In examples, outlet lumen 172 is configured to provide a flow path for the fluid from interior volume 116 to fluid outlet 120. In some examples, outlet lumen 172 is fluidically coupled to fluid outlet 120, outlet conduit 128, and / or regulating valve 130. Hence, elongate body 110 may be configured to circulate the fluid within balloon interior by providing the fluid to balloon interior 116 via inlet lumen 170 and / or another inlet lumen and discharging the fluid from balloon interior 116 via outlet lumen 172 and / or another outlet lumen. In some examples, elongate body 110 is configured to deliver the fluid (e.g., via inlet lumen 170) as a liquid and / or a liquid-gas mixture and discharge the fluid (e.g., via outlet lumen 172) substantially as a gas.

[0112] Balloon 112 is configured to transfer heat with vessel wall 104 when medical system 100 (e.g., elongate body 110) circulates the fluid through balloon interior 116 and a portion of balloon 112 (e.g., balloon exterior surface 168) is in thermal communication with vessel wall 104. Medical system 100 is configured such that an amount of heat transferred (e.g., transferred to or from vessel wall 104) is dependent on a balloon temperature of balloon 112 when balloon interior 116 receives the fluid. Medical system 100 is configured such that the balloon temperature is dependent on a flow rate and / or temperature of the fluid within balloon interior 116 (e.g., when balloon exterior surface 168 is in thermal communicationwith vessel wall 104). Thus, medical system 100 may vary the amount of heat transfer between balloon 112 and vessel wall 104 by varying a flow rate of the fluid delivered to balloon 112 to cause a variation in the balloon temperature of balloon 112. In examples, the balloon temperature is indicative of a temperature of balloon exterior surface 168, which is in contact with vessel 104.

[0113] The variation in balloon temperature of balloon 112 (e.g., to vary the amount of heat transferred) causes a variation in a tissue temperature at target tissue site 159. Medical system 100 is configured to cause a variation in the balloon temperature (e.g., by varying the flow rate of the fluid delivered to balloon 112) in order to cause the tissue temperature at target tissue site 159 to vary. Medical system 100 is configured to vary the flow rate of the fluid delivered to balloon 112 to maintain the tissue temperature at target tissue site 159 within a temperature range, which may also be referred to as a desired temperature range in some examples. The temperature range includes a target temperature, which is indicative of a desired temperature at target tissue site 159 that is expected to provide therapy (e.g., neuromodulation or other types of ablation) to patient 106. Medical system 100 is configured to vary the flow rate of the fluid delivered to balloon 112 such that the temperature range bounding the temperature at target tissue site 159 is relatively narrow as compared to a balloon temperature range experienced by balloon 112 as medical system 100 delivers the fluid to balloon interior 116.

[0114] Medical system 100 is configured to vary the flow rate of the fluid delivered to balloon 112 by delivering the fluid (e.g., via flow actuator 122) at an upper flow rate, a lower flow rate less than the upper flow rate, and over a periodicity. The periodicity is an elapsed time over which the flow rate varies from the upper flow rate to the lower flow rate and subsequently returns to the upper flow rate. Medical system 100 may deliver the flow rate at the upper flow rate, the lower flow rate, and the periodicity to cause the balloon temperature of balloon 112 to cycle within a balloon temperature range that causes the tissue temperature at target tissue site 159 to remain within the temperature range.

[0115] Processing circuitry 132 is configured to determine at least the periodicity of the flow rate delivered by medical system 100 (e.g., via flow actuator 122) to maintain a tissue temperature of target tissue site 159 within the temperature range that includes the target temperature. Processing circuitry 132 is configured to determine (e.g., receive as an input from device 134 or another device) the target temperature. In examples, processing circuitry132 is configured to determine (e.g., receive as an input from device 134 or another device) the tissue depth TD of target tissue site 159.

[0116] In examples, the temperature range is bounded by a first tissue temperature and a second tissue temperature. Processing circuitry 132 may be configured to determine the first tissue temperature, the second tissue temperature, and / or the temperature range defined by the first tissue temperature and the second tissue temperature. In some examples, processing circuitry 132 is configured to determine these values by at least receiving the first tissue temperature, the second tissue temperature, and / or the temperature range as an input from device 134 or another device and determine the periodicity based at least in part on the inputted first tissue temperature, the second tissue temperature, and / or the temperature range. In some examples, processing circuitry 132 is configured to determine the first tissue temperature, the second tissue temperature, and / or the temperature range based on the periodicity determined by processing circuitry 132. In some examples, processing circuitry 132 is configured to provide the first tissue temperature, the second tissue temperature, and / or the temperature range as an output (e.g., an output viewable by a user) using device 134 or another device.

[0117] Processing circuitry 132 is configured to determine the periodicity using a representative balloon temperature. The representative balloon temperature is indicative of a temperature of balloon 112 anticipated to occur or occurring as medical system 100 delivers the fluid to balloon 112. In some examples, the representative balloon temperature is an expected balloon temperature (e.g., a temperature of balloon body 166 and / or balloon exterior surface 168) anticipated to occur when balloon 112 is expanded in vessel 102 and receives the fluid within balloon interior 116. In some examples, the representative balloon temperature is a sensed balloon temperature provided by temperature sensor 133 and communicated to processing circuitry 132. Processing circuitry 132 is configured to determine the periodicity such that delivering the fluid at the upper flow rate, the lower flow rate, and the periodicity causes the balloon temperature of balloon 112 (as indicated by the representative balloon temperature) to cycle over a balloon temperature range which maintains the tissue temperature of target tissue site 159 within a temperature range. As noted above, the temperature range is bounded by a first tissue temperature and a second tissue temperature.

[0118] Processing circuitry 132 is configured to determine the periodicity using any suitable technique. In some examples, processing circuitry 132 is configured to determine the periodicity using a machine learning algorithm. In examples, the machine learning algorithmis trained to provide the periodicity based on, for example, previous ablation procedures performed on a cohort of patients, modeling and / or measurement of flow rates through medical system 100 (e.g., flow rate M, balloon flowrate MB, and / or other flowrates through other portions of medical system 100), modeling and / or measurement of heat transfer characteristics of balloon 112 experiencing a given flow rate, and / or other data indicative of a heat transfer between balloon 112 and target tissue site 159 when balloon 112 is positioned within vessel 102. In examples, the machine learning algorithm is configured to receive an input vector indicative of at least one or tissue depth TD and / or a target temperature (e.g., target temperature TGT) of target tissue site 159. The machine learning algorithm may be configured to provide an output vector indicative of the periodicity in response to receiving the input vector.

[0119] In some examples, processing circuity 132 is configured to determine a periodicity by at least assessing and / or determining a temperature difference which arises across tissue depth TD as medical system 100 provides the fluid at the upper flow rate, the lower flow rate, and the periodicity. Processing circuitry 132 may be configured to assess the temperature difference using the representative balloon temperature (e.g., as the representative balloon temperature cycles between the first balloon temperature and the second balloon temperature) and thermal characteristics of intervening tissue and / or objects present over tissue depth TD, such as conduction heat transfer characteristics of the intervening tissue and / or objects, convection heat transfer characteristics of the intervening tissue and / or other material, as well as blood flow, patient body temperatures proximate target tissue site 159, thermal energy generations of the patient (e.g., due to patient metabolism), blood flow characteristics, and / or other characteristics and / or thermal impacts. Processing circuitry 132 may be configured to determine the periodicity such that the cycling representative balloon temperature and corresponding temperature differences maintain the tissue temperature of target tissue site 159 within the temperature range.

[0120] In some examples, processing circuitry 132 is configured to assess and / or determine the temperature difference using a transfer correlation indicative of the heat transfer between balloon 112 and target tissue site 159. In some examples, the transfer correlation includes a mathematical expression (e.g., a mathematical expression relating at least the representative balloon temperature and the target temperature). In some examples, the transfer correlation is defined by a data structure (e.g., one or more tables) stored by a memory of system 100 or a memory of another device in communication with processing circuitry 132.The transfer correlation can be determined by processing circuitry 132 or other processing circuitry based on bench testing data, computer modeling, and / or machine learning algorithms.

[0121] In some examples, processing circuitry 132 is configured to determine at least one of the upper flow rate or the lower flow rate. In some examples, the upper flow rate and / or lower flow rate are inputs provided to processing circuitry 132. For example, the upper flow rate and lower flow rate may substantially be determined by other components of medical system 100, such as flow actuator 122. For example, medical system 100 may be configured such that flow actuator 122 provides a known upper flow rate in a first configuration (e.g., a first valve position or first pump speed) and a provides a known lower flow rate in a second configuration (e.g., a second valve position or second pump speed). Processing circuitry 132 may be configured to determine the periodicity over which medical system 100 should vary the flow rate of the fluid (e.g., by causing flow actuator 122 to shift between the first configuration and the second configuration) from the known upper flow rate to the known lower flow rate and return to the known upper flow rate in order to maintain the tissue temperature within the temperature range. In some examples, medical system 100 (e.g., flow actuator 122) is configured such that lower flow rate ML is substantially zero (e.g., zero or nearly zero to the extent permitted by manufacturing tolerances). For example, flow actuator 122 may include a valve configured to fluidically isolate fluid delivery system 124 and inlet conduit 126, fluid inlet 118, and / or inlet lumen 170 to cause a lower flow rate ML of substantially zero.

[0122] Hence, medical system 100 may be configured to deliver a fluid at an upper flow rate, a lower flow rate, and a periodicity to cause a balloon temperature of balloon 112 to cyclically vary between a first balloon temperature and a second balloon temperature. Medical system 100 may be configured such that the cyclic variation of the balloon temperature maintains a tissue temperature at target tissue site 159 within a temperature range that includes a target temperature. Processing circuity 132 is configured to determine at least the periodicity using at least the target temperature and a representative balloon temperature. In examples, processing circuitry 132 is configured to determine at least the periodicity by assessing and / or determining a temperature difference which arises across tissue depth TD as medical system 100 provides the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0123] As an example, FIG. 6 illustrates an example flow rate M of a fluid provided by medical system 100 (e.g., via flow actuator 122). In FIG. 6, flow rate M defines a flow rate waveform FW varying (e.g., cycling) between an upper flow rate MU and a lower flow rate ML over a time interval from a start time TS to a completion time TC. Upper flow rate MU is greater than lower flow rate ML. FIG. 7 illustrates a flow rate MB of the fluid through balloon interior 116 when the fluid is provided by medical system 100 at the example flow rate M of FIG. 6. In FIG. 7, flow rate MB varies (e.g., cycles) between an balloon upper flow rate MBU and a balloon lower flow rate MBL over the time interval between start time TS and completion time TC. FIG. 8 illustrates a balloon temperature TB and a tissue temperature TT at a tissue depth TD when balloon 112 experiences the flow rate MB of FIG. 7 through balloon interior 116.

[0124] In examples, flow rate M is a mass flow rate or volume flow rate of fluid provided to elongate body 110. For example, flow rate M may be a mass flow rate or volume flow rate provided to inlet conduit 126, fluid inlet 118, and / or inlet lumen 170 by fluid delivery system 124 (e.g., via flow actuator 122). Medical system 100 may be configured to deliver flow rate M when the fluid is in a liquid phase or a gaseous phase. In examples, for example when medical system 100 is configured to allow the fluid to change phase from a liquid phase to a gaseous phase, flow rate M is a mass flow rate or volume flow rate of the fluid in a liquid phase.

[0125] In examples, flow rate MB is a mass flow rate or volume flow rate provided to and / or flowing through balloon interior 116. For example, flow rate MB may be a mass flow rate or volume flow rate discharging through distributor 114, outlet lumen 172, fluid outlet 120, and / or regulating valve 130. Medical system 100 may be configured to enable flow rate MB when the fluid is in a liquid phase or a gaseous phase. In examples, for example when medical system 100 is configured to allow the fluid to change phase from a liquid phase to a gaseous phase, flow rate MB is a mass flow rate or volume flow rate of the fluid in a gaseous phase.

[0126] Medical system 100 is configured such that delivering fluid (e.g., to elongate body 110 in fluid communication with balloon 112) at flow rate M causes balloon flow rate MB. For example, flow rate M delivered (e.g., via flow actuator 122) to one or more of inlet conduit 126, fluid inlet 118, inlet lumen 170, and / or distributor 114 may cause balloon flow rate MB within one or more of balloon interior 116, outlet lumen 172, fluid outlet 120, outlet conduit 128, and / or regulating valve 130. The cycling of flow rate M between upper flow rateMU and lower flow rate ML may cause balloon flow rate MBU to cycle between balloon upper flow rate MBU and balloon lower flow rate MBL. In examples, processing circuitry 132 is configured to cause flow rate M to cycle from upper flow rate MU to lower flow rate ML and return flow rate M to upper flow rate MU over a periodicity P to cause balloon flow rate MBU to cycle between balloon upper flow rate MBU and balloon lower flow rate MBL.

[0127] Balloon temperature TB (FIG. 8) is dependent on flow rate MB through balloon interior 116. Balloon temperature TB may be, for example, a temperature of balloon outer surface 168 (e.g., when balloon outer surface is in contact with vessel wall 104), a temperature of the fluid within balloon interior 116, or another temperature indicative of a temperature of balloon 112. Medical system 100 is configured to cause balloon temperature TB to vary (e.g., cycle) between a balloon first temperature TB1 and a balloon second temperature TB2 as balloon flow rate MB cycles between balloon upper flow rate MBU and a balloon lower flow rate MBL. Balloon first temperature TB1 and a balloon second temperature TB2 define a balloon temperature range BTR. Hence, in some examples, processing circuitry 132 of medical system 100 is configured to cause balloon temperature TB to vary over balloon temperature range BTR by controlling the flow rate M. For example, processing circuitry 132 may be configured to cause balloon 112 to achieve or trend toward first balloon temperature TB1 when medical system 100 provides the fluid at upper flow rate M (e.g., provides the fluid to one or more of inlet conduit 126, fluid inlet 118, inlet lumen 170, and / or distributor 114). Processing circuitry 132 may be configured to cause balloon 112 to achieve or trend toward second balloon temperature TB2 when medical system 100 provides the fluid at lower flow rate ML (e.g., provides the fluid to one or more of inlet conduit 126, fluid inlet 118, inlet lumen 170, and / or distributor 114).

[0128] In examples, for example when medical system 100 is configured to provide the fluid to facilitate a cryoablation, first balloon temperature TB1 is less than second balloon temperature TB2. In some examples, for example when medical system 100 is configured to provide the fluid to facilitate a heat-based thermal ablation, first balloon temperature TB1 is greater than second balloon temperature TB2.

[0129] Medical system 100 is configured to maintain tissue temperature TT at target tissue site 159 within a temperature range TR as flow rate M causes balloon temperature TB to vary over balloon temperature range BTR. Temperature range TR includes target temperature TGT of target tissue site 159. Hence, medical system 100 may be configured to maintain tissue temperature TT within temperature range TR by varying flow rate M betweenupper flow rate MU and lower flow rate ML, such that flow rate MBU varies between balloon upper flow rate MBU and balloon lower flow rate MBL, and such that balloon temperature TB varies between first balloon temperature TB1 and second balloon temperature TB2. Processing circuitry 132 is configured to determine a periodicity P of flow rate M which causes or is anticipated to cause the variation of balloon temperature TB that maintains tissue temperature TT within temperature range TR. In some examples, processing circuitry 132 is configured to determine periodicity P such that temperature range TR is less than or equal to about 25% of balloon temperature range BTR. In some examples, processing circuitry 132 is configured to determine periodicity P such that temperature range TR is a range of less than or equal to about 10 deg C when balloon temperature range BTR is greater than about 35 deg C.

[0130] In examples, temperature range TR is defined by a first tissue temperature TP1 and a second tissue temperature TP2. Processing circuitry 132 may be configured to cause tissue temperature TT to achieve or trend toward first tissue temperature TP1 when medical system 100 provides the fluid at upper flow rate MU and / or balloon 112 experiences upper balloon flow rate MBU and / or first balloon temperature TB1. Processing circuitry 132 may be configured to cause balloon 112 to achieve or trend toward second tissue temperature TP2 when medical system 100 provides the fluid at lower flow rate ML and / or balloon 112 experiences lower balloon flow rate MBL and / or second balloon temperature TB2. In examples, for example when medical system 100 is configured to provide the fluid to facilitate a cryoablation, first tissue temperature TP1 is less than second tissue temperature TP2. In some examples, for example when medical system 100 is configured to provide the fluid to facilitate a heat-based thermal ablation, first tissue temperature TP1 is greater than second tissue temperature TP2.

[0131] Processing circuitry 132 is configured to determine at least a periodicity P of flow rate M which maintains tissue temperature TT at target tissue site 159 within temperature range TR, with temperature range TR including target temperature TGT. Processing circuitry 132 is configured to determine (e.g., receive as an input or retrieve from memory) the target temperature TGT. Processing circuitry 132 is configured to determine the periodicity P based on at least the target temperature TGT. In examples, processing circuitry 132 is configured to determine (e.g., receive as an input) a tissue depth TD (FIG. 4-5) of target tissue site 159. Processing circuitry 132 may be configured to determine the periodicity P based on the tissue depth TD.

[0132] Periodicity P is indicative of a time period over which flow rate M varies from upper flow rate MU to lower flow rate ML and returns to upper flow MU. In examples, periodicity P is indicative of a time period over which flow rate M begins to define an initial decrease from upper flow rate MU to lower flow rate ML and, following elapse of the periodicity P, begins to define a subsequent decrease from the upper flow rate MU to the lower flow ML. For example, processing circuitry 132 may be configured to cause flow rate M to define an initial decrease DI (FIG. 6) from upper flow rate MU to lower flow rate ML at a time Tl. Processing circuitry 132 may be configured to cause flow rate M to define a subsequent decrease D2 from upper flow rate MU to lower flow rate ML at a time T2. Periodicity P may be indicative of a time period elapsed between initial displacement DI at time Tl and subsequent displacement D2 at time T2.

[0133] Processing circuitry 132 is configured to control flow rate M (e.g., using flow actuator 122) over a plurality of sequential flow rate cycles, such as a first flow rate cycle Cl from time Tl to time T2, a second flow rate cycle C2 from time T2 to time T3, and / or a third flow rate cycle C3 from time T3 to time T4. Processing circuitry 132 may cause flow rate M to vary from upper flow rate MU to lower flow rate ML and return to upper flow rate MU over the periodicity P in each of first flow rate cycle Cl, second flow rate cycle C2, and third flow rate cycle C3. Processing circuitry 132 may control flow rate M first flow rate cycle Cl, second flow rate cycle C2, third flow rate cycle C3, and subsequent flow rate cycles to define at least an interval of flow rate waveform FW having a frequency substantially equal to the reciprocal of periodicity P. For example, first flow rate cycle Cl may chronologically complete as the second flow rate cycle C2 chronologically begins, and second flow rate cycle C2 may chronologically complete as third flow rate cycle C3 chronologically begins, and so on. Hence, a periodicity P determined by processing circuitry 132 may be indicative of a periodicity of a waveform such as flow rate waveform FW which includes a plurality of flow rate cycles such as first flow rate cycle Cl, second flow rate cycle C2, and third flow rate cycle C3.

[0134] In some examples, processing circuitry 132 is configured to determine the periodicity P based on a representative balloon temperature indicative of a temperature of balloon 112 anticipated to occur or occurring as medical system 100 provides flow rate M and balloon 112 experiences balloon flow rate MBU. In examples, the representative balloon temperature is an expected balloon temperature (e.g., a temperature of balloon body 166 and / or balloon exterior surface 168) anticipated to occur when balloon 112 is expanded invessel 102 and receives flow rate MB within balloon interior 116. In some examples, the representative balloon temperature is a sensed balloon temperature provided by temperature sensor 133 and communicated to processing circuitry 132. Temperature sensor 133 may provide the representative balloon temperature when balloon 112 expanded within vessel 102 and / or in contact with vessel wall 104 such that, for example, the representative balloon temperature is indicative of a measured temperature. In some examples, processing circuitry 132 is configured to determine the representative balloon temperature based on a sensed pressure in balloon interior 116. For example, balloon temperature and pressure may be proportional (e.g., linearly related in some examples) and / or otherwise correlated.

[0135] In examples, processing circuitry 132 is configured to determine the representative balloon temperature and assess a temperature difference TDIFF (FIG. 8) between balloon 112 and target tissue site 159. Processing circuitry 132 may assess temperature difference TDIFF based on a temperature profile developed or expected to develop across tissue depth TD between balloon 112 (e.g., balloon exterior surface 168) and target tissue site 159 as medical system 100 provides flow rate M. Processing circuitry 132 may be configured to assess temperature difference TDIFF (and, e.g., the temperature profile) using the representative balloon temperature and thermal characteristics of intervening tissue and / or material present over tissue depth TD, as well as other thermal influences, such as blood flow. For example, processing circuitry 132 may determine temperature difference TDIFF (and, e.g., a temperature profile) based at least in part on conduction heat transfer characteristics of intervening tissue and / or other material present over tissue depth TD, convection heat transfer characteristics of intervening tissue and / or material present over tissue depth TD, patient body temperatures proximate target tissue site 159, thermal energy generations of the patient (e.g., due to patient metabolism), blood flow characteristics, and / or other characteristics and / or thermal impacts. These parameters can be stored by a memory of system 100 or otherwise accessible to processing circuitry 132. Processing circuitry 132 may be configured to determine the periodicity P to maintain tissue temperature TT within temperature range TR using the representative balloon temperature and the temperature difference TDIFF.

[0136] For example, processing circuitry 132 may be configured to determine the periodicity P by assessing one or more potential periodicities. Processing circuitry 132 may be configured to determining a first time interval FT (FIG. 8) required for balloon temperature TB (e.g., either a representative balloon temperature or a sensed balloon temperature) to transition from first balloon temperature TB1 to second balloon temperature TB2 whenmedical system 100 delivers the fluid at upper flow rate MU, lower flow rate ML, and a potential periodicity. Processing circuitry 132 may be configured to determining a second time interval ST (FIG. 8) required for balloon temperature TB (e.g., either a representative balloon temperature or a sensed balloon temperature) to transition from second balloon temperature TB2 to first balloon temperature TB1 when medical system 100 delivers the fluid at upper flow rate MU, lower flow rate ML, and the potential periodicity. Processing circuitry 132 may be configured to determine a resulting temperature range for target tissue site 159 based on the temperature difference TDIFF which results when balloon temperature transitions from first balloon temperature TB1 to second balloon temperature TB2 over first time interval FT for the potential periodicity and transitions from second balloon temperature TB2 to first balloon temperature TB 1 over second time interval ST for the potential periodicity. Processing circuitry 132 may determine the periodicity P by determining a particular periodicity from the one or more potential periodicities which causes or is anticipated to cause tissue temperature TT to remain within temperature range TR as medical system 100 delivers the fluid at upper flow rate MU, lower flow rate ML, and the particular periodicity.

[0137] In examples, processing circuitry 132 is configured to determine the periodicity P using a transfer correlation indicative of the heat transfer between balloon 112 and target tissue site 159. The transfer correlation may be indicative of the thermal characteristics and / or thermal impacts of the intervening tissue and / or other material present over tissue depth TD. Processing circuitry 132 may be configured to assess temperature difference TDIFF and / or a temperature profile developed or expected to develop across tissue depth TD using the transfer correlation. In some examples, the transfer correlation includes a mathematical expression relating two or more of the representative balloon temperature, the target temperature, the tissue depth TD, the tissue temperature TT, and / or one or more thermal characteristics of and / or thermal impacts on intervening tissue over the tissue depth TD. In some examples, the transfer correlation is defined by a data structure (e.g., one or more tables) relating two or more of the representative balloon temperature, the target temperature, the tissue depth TD, the tissue temperature TT, and / or one or more thermal characteristics of and / or thermal impacts on intervening tissue over the tissue depth TD. The data structure may be stored by a memory of system 100 or a memory of another device in communication with processing circuitry 132.

[0138] In some examples, the transfer correlation is based on data obtained from, for example, previous ablation procedures, computer modeling and / or actual measurement of flow rates through medical system 100 (e.g., flowrate M, balloon flowrate MB, and / or other flowrates through other portions of medical system 100 ), computer modeling and / or actual measurement of heat transfer characteristics of balloon 112 experiencing a given flow rate, and / or other data indicative of a heat transfer between balloon 112 and target tissue site 159 when balloon 112 is positioned within vessel 102. The transfer correlation may define any curvature and / or slope over any interval of the transfer correlation, and may be a linear or a nonlinear function over one or more of the intervals. The transfer correlation may be defined in a space having any number of dimensions and defined by any number of variables and / or factors in addition to the representative balloon temperature, the target temperature, the tissue depth TD, the tissue temperature TT, and / or one or more thermal characteristics of and / or thermal impacts on intervening tissue over the tissue depth TD.

[0139] In some examples, processing circuitry 132 is configured to assess and / or determine a temperature difference such as TDIFF based on the representative balloon temperature. For example, processing circuitry 132 may be configured to assess and / or determine a given temperature difference using a specific representative balloon temperature and associate the given temperature difference with the specific representative balloon temperature. The specific representative balloon temperature may be indicative of (e.g., directly correspond to or be proportional to) a balloon temperature TB occurring or anticipated to occur when medical system 100 delivers flow rate M. Processing circuitry 132 may be configured to determine the periodicity P using a plurality of specific representative balloon temperatures and the given temperature difference associated with each representative balloon temperature. Hence, processing circuitry 132 may be configured to assesses and / or determine a temperature difference between balloon 112 and target tissue site 159 as balloon temperature TB cycles between balloon first temperature TB1 and second balloon temperature TB2.

[0140] For example, processing circuitry 132 may determine temperature difference TDIFF based on a first representative balloon temperature indicative of balloon temperature TB of point A of FIG. 8. Processing circuitry 132 may determine a second temperature difference based on a second representative balloon temperature indicative of balloon temperature TB of point B of FIG. 8. Processing circuitry 132 may determine a third temperature difference based on a third representative balloon temperature indicative ofballoon temperature TB of point C of FIG. 8. Processing circuitry 132 may associate temperature difference TDIFF and the first representative balloon temperature, associate the second temperature difference and the second representative balloon temperature, and associate the third temperature difference and the third representative balloon temperature. Processing circuitry 132 may be configured use the first representative balloon temperature and the associated temperature difference TDIFF, use the second representative balloon temperature and the associated second temperature difference, and / or use the third representative balloon temperature and the associated third temperature difference to determine a periodicity P which causes flow rate M to maintain tissue temperature TT within temperature range TR as balloon temperature TB cycles between balloon first temperature TB1 and second balloon temperature TB2. Processing circuitry 132 may be configured to associate any number of specific representative balloon temperatures with a given temperature difference.

[0141] Processing circuitry 132 may be configured such that a temperature difference such as TDIFF is dependent on the tissue depth TD. For example, for a first tissue depth, processing circuitry 132 may be configured to determine temperature difference TDIFF of FIG. 8. For a second tissue depth different from the first tissue depth, processing circuitry 132 may be configured determine a second temperature difference TDIFF2 of FIG. 8 (and, e.g., a second temperature profile associated with second temperature difference TDIFF2). Processing circuitry 132 may be configured to determine second temperature difference TDIFF2 using the representative balloon temperature and thermal characteristics of intervening tissue and / or material present over the second tissue depth.

[0142] In some examples, processing circuitry 132 is configured to determine at least one of the periodicity P, upper flow rate MU, and / or lower flow rate ML based on the balloon temperature range BTR occurring or expected to occur when medical system 100 provides fluid (e.g., provides fluid to balloon 116 via to elongate body 110) at flow rate M. For example, processing circuitry 132 may be configured to determine a balloon temperature range (e.g., balloon temperature range BTR) which corresponds to a temperature range (e.g., temperature range TR) desired at target tissue site 159. Processing circuitry 132 may be configured to determine and / or assess (e.g., using a transfer correlation) that first balloon temperature TB1 of balloon temperature range BTR is expected to cause a tissue temperature TT at target tissue site 159 substantially equal to or in proximity to the first tissue temperature TP1 of temperature range TR. Processing circuitry 132 may be configured to determineand / or assess (e.g., using a transfer correlation) that second balloon temperature TB2 of balloon temperature range BTR is expected to cause a tissue temperature TT substantially equal to or in proximity to the second tissue temperature TP2 of temperature range TR. Processing circuitry 132 may be configured to determine at least one of periodicity P, upper flow rate MU, and / or lower flow rate ML which causes balloon temperature TB to vary cyclically between first balloon temperature TB 1 and second balloon temperature TB2 in order to maintain tissue temperature TT within temperature range TR.

[0143] In some examples, upper flow rate MU and / or lower flow rate ML are inputs provided to processing circuitry 132 rather than determined by processing circuitry 132. For example, medical system 100 may be configured to provide the fluid at upper flow rate MU when flow actuator 122 (e.g., a valve or a pump) is placed in a first configuration (e.g., a first valve position or a first pump speed). Medical system 100 may be configured to provide the fluid at lower flow rate ML when flow actuator 122 is placed in a second configuration (e.g., a second valve position or a second pump speed). Hence, upper flow rate MU and lower flow rate ML may be determined by other components of medical system 100. Processing circuitry 132 may be configured to determine the periodicity P over which flow rate M should vary from the known upper flow rate MU to the known lower flow rate ML and return to the known upper flow rate MU in order to maintain tissue temperature TT within temperature range TR.

[0144] In some examples, for example when the representative balloon temperature is a sensed parameter (e.g., a temperature or a fluid pressure) provided by temperature sensor 133 to processing circuitry 132, processing circuitry 132 is configured to determine the periodicity by at least causing medical system 100 to deliver the fluid at upper flow rate MU until the sensed parameter indicates a temperature of or in proximity to first balloon temperature TB1. Processing circuitry 132 may subsequently cause medical system 100 to deliver the fluid at lower flow rate ML until the sensed parameter indicates a temperature of or in proximity to second balloon temperature TB2. Processing circuitry 132 may cause medical system 100 to deliver the fluid at upper flow rate MU when the sensed parameter indicates the temperature of or in proximity to second balloon temperature TB2. Processing circuitry 132 may determine periodicity P by at least determining an elapsed time over which medical system 100 caused flow rate M to transition from upper flow rate MU to lower flow rate ML and return to upper flow rate MU in order to cause the sensed parameter to cycle from first balloon temperature TB 1 to second balloon temperature TB2 and return to first balloontemperature TB1. Processing circuitry 132 may utilize the determined periodicity P to substantially maintain tissue temperature TT within temperature range TR.

[0145] In some examples, processing circuitry 132 is configured to determine an initial period TM indicative of a time period required to produce target temperature TGT at target tissue site 159. Processing circuitry 132 may be configured to substantially schedule flow rate waveform FW to commence subsequent to initial period TM. In examples, processing circuitry 132 is configured to cause medical system 100 to deliver the fluid (e.g., using flow actuator 122) at upper flow rate MU or another flow rate over initial period TM and deliver the fluid flow according to rate waveform FW following initial period TM. Processing circuitry 132 is configured to schedule flow rate waveform FW such that initial period TM substantially ends at start time TS and flow rate waveform FW substantially commences at start time TS. In this way, once the temperature at target tissue site 159 is within a temperature range that includes the target temperature, the temperature at target tissue site 159 can be maintained in the temperature range throughout the ablation procedure rather than, for example, falling below the temperature range after initial period TM.

[0146] In some examples, processing circuitry 132 may be configured to determine the initial period TM required based on upper flow rate MU or another flow rate of the fluid which might be provided by medical system 100. In examples, processing circuitry 132 is configured to determine initial period TM based on tissue depth TD and / or a representative temperature of balloon 112. In examples, processing circuitry 132 is configured to determine initial time period TM using the transfer correlation indicative of the heat transfer between balloon 112 and target tissue site 159 and / or another correlation relating tissue temperature TT and balloon temperature TB. In some examples, processing circuitry 132 determines the initial period TM based on a parameter indicative of balloon temperature TB (e.g., provided by temperature sensor 133). For example, processing circuitry 132 may determine initial period TM commences substantially at a time TO (e.g., when medical system 100 commences delivery of flow rate M). Processing circuitry 132 may determine initial period TM has concluded when the parameter indicative of balloon temperature TB achieves (e.g., is within at least 20% of) First balloon temperature TB1. Initial period TM may vary for different ablation procedures.

[0147] In examples, for example as depicted in FIG. 6, flow rate M defines flow rate waveform FW as a substantially sawtooth-type wave. When flow rate waveform FW is a substantially sawtooth-type wave, flow rate M may decrease from upper flow rate MU tolower flow rate ML and / or increase from lower flow rate ML to upper flow rate MU at a substantially steady rate (e.g., such that the increase or decrease of flow rate M is substantially linear). In some examples, medical system 100 may provide flow rate M such that the flow rate waveform FW is substantially a sinewave-type wave or other continuous-time waveform which includes intervals defining a curvature. For example, when flow rate waveform FW is substantially a sinewave-type wave or other continuous-time waveform defining one or more curvatures, flow rate M may decrease from upper flow rate MU to lower flow rate ML and / or increase from lower flow rate ML to upper flow rate MU at a varying rate (e.g., such that the increase or decrease of flow rate M defines a curvature). Also, although flow rate MB is depicted as defining a substantially curved and / or sinewave-type wave in FIG. 7 (e.g., such that the increase or decrease of flow rate MB between balloon upper flow rate MBU and balloon lower flow rate MBL defines a curvature), in examples, flow rate MB may define a substantially sawtooth-type wave (e.g., such that the increase or decrease of flow rate MB between balloon upper flow rate MBU and balloon lower flow rate MBL is substantially linear). In examples, the increase and / or decrease of flow rate M and / or is substantially linear and / or defines a continuous-time waveform with respect to a time axis TIME.

[0148] In some examples, medical system 100 is configured such that the flow rate M delivered (e.g., to elongate body 110) defines the flow rate waveform FW substantially as a sawtooth-type waveform, and the substantially sawtooth-type flow rate waveform FW causes the flow rate MB through interior volume 116 to define a substantially continuous-time waveform. As an example, when medical system 100 is configured to provide the fluid (e.g., to elongate body 110) in a liquid phase and circulate the fluid through balloon interior 116 in a gaseous phase, expansion and compression of the gaseous phase within balloon interior 116 may cause flow rate MB to define a substantially curved and / or sinewave-type (or other continuous-time) waveform when flow rate M defines a substantially sawtooth-type waveform. For example, when medical system 100 decreases flow rate M from upper flow rate MU to lower flow rate ML (with the fluid in the liquid phase), this may result in a decreased pressure in balloon interior 116, such that the gaseous phase within balloon interior 116 expands. The expansion may cause flow rate MB to decrease at a rate less than a rate of decrease of flow rate M. When medical system 100 increases flow rate M from lower flow rate ML to upper flow rate MU, this may result in an increased pressure in balloon interior 116, such that the gaseous phase within balloon interior 116 compresses. This compression may cause flow rate MB to increase at a rate less than a rate of increase of flow rate M.Hence, medical system 100 may be configured to deliver flow rate M (e.g., to elongate body 110) in a manner defining a substantially sawtooth-type waveform to cause flow rate MB to define a continuous-time waveform.

[0149] In some examples, medical system 100 (e.g., flow actuator 122) is configured such that lower flow rate ML is substantially zero (e.g., zero or nearly zero to the extent permitted by manufacturing tolerances). For example, flow actuator 122 may include a valve configured to fluidically isolate fluid delivery system 124 and inlet conduit 126, fluid inlet 118, and / or inlet lumen 170 to cause a lower flow rate ML of substantially zero. Medical system 100 may be configured such that balloon lower flow rate MBL of balloon flow rate MB is greater than the lower flow rate ML of flow rate M. For example, when lower flow rate ML is substantially zero, an expansion of the fluid (e.g., in the gaseous state) within balloon interior 116 may cause balloon lower flow rate MBL to exceed lower flow rate ML (e.g., to be greater than substantially zero). Hence, medical system 100 may be configured such that flow rate MB through balloon interior 116 continues as flow rate M decreases to a lower flow rate ML of substantially zero and subsequently increases from the lower flow rate ML to the upper flow rate MU.

[0150] In some examples, periodicity P is based at least in part in a minimum desired pressure of the fluid within inlet lumen 170. For example, when medical system 100 is configured to deliver the fluid (e.g., via flow actuator 122) in a liquid phase and cause balloon flow rate MU through balloon 112 with the fluid in the gaseous phase, periodicity P may be based at least in part on a minimum pressure within inlet lumen 170 that limits a phase change of the fluid from the liquid phase to the gaseous phase in inlet lumen 170. Periodicity P may be determined at least in part such that when medical system 100 delivers upper flow rate MU and lower flow rate ML over periodicity P, a pressure within inlet lumen 170 remains above the minimum desired pressure over periodicity P.

[0151] In some examples, processing circuitry 132 is configured to consider a response of the patient (e.g., a thermoregulation) to the delivery of the fluid to balloon 112 and adjust one or more of upper flow rate MU, lower flow rate ML, and / or periodicity P based on the patient response. In examples, processing circuitry 132 is configured to compare a sensed rate of change of balloon temperature TB with an expected rate of change and alter (e.g., in or decrease) the periodicity of flow rate M based on the comparison. In this way, upper flow rate MU, lower flow rate ML, and / or periodicity P may be patient-specific.

[0152] For example, processing circuitry 132 may be configured to receive a parameter indicative of balloon temperature TB (e.g., from temperature sensor 133). The parameter may be, for example, indicative of a sensed temperature of balloon body 166 and / or balloon exterior surface 168. In examples, the parameter is a measured temperature of some portion of balloon 112 (e.g., balloon body 166 and / or balloon exterior surface 168) or another portion of medical system 100. In some examples, the parameter is a measured temperature and / or a measured pressure of the fluid at some location within medical system 100 (e.g., within balloon interior 116, inlet lumen 170, outlet lumen 172, and / or outlet conduit 128, and / or another portion of medical system 100). Processing circuitry 132 may be configured to determine a rate of change of the parameter during delivery of flow rate M at periodicity P. Processing circuitry 132 may be configured to determine the sensed rate of change using the indicative parameter received from temperature sensor 133.

[0153] Processing circuitry 132 may be configured to determine an expected rate of change of the parameter when medical system 100 delivers flow rate M at the periodicity P .In examples, processing circuitry 132 is configured to determine the expected rate based on an expected balloon temperature when medical system 100 delivers the fluid at upper flow rate MU, lower flow rate ML, and over a periodicity. The expected balloon temperature may be an expected temperature of some portion of balloon 112, such as balloon outer surface 168, balloon body 166, a temperature within interior volume 116, or some other portion of balloon 112. The expected rate and / or expected balloon temperature may be based on, for example, previous ablation procedures, modeling and / or measurement of the rate of change when a balloon having a similar or the same configuration (e.g., material, size, and the like) experiences flow rate M at periodicity P, heat transfer and / or other thermal characteristics of a balloon, and / or other data indicative of a heat transfer between a balloon and a vessel wall when the balloon experiences flow rate M at periodicity P . In examples, processing circuitry 132 is configured to determine the expected rate and / or expected balloon temperature using a memory storing a plurality of expected rates of change. An expected rate of change may be associated with other data, such as upper flow rate MU, lower flow rate ML, a size of vessel 102, a tissue depth TD, a tissue target temperature, an ablation level, and / or other data. In examples, processing circuitry 132 is configured to determine (e.g., receive as an input or a measured quantity) an upper flow rate MU, a lower flow rate ML, a size of vessel 102, a tissue depth TD, a tissue target temperature, an ablation level, and / or other data select an expected rate of change based on the upper flow rate MU, the lower flow rate ML, the size ofvessel 102, the tissue depth TD, the tissue target temperature, the ablation level, and / or the other data.

[0154] In some examples, processing circuitry 132 is configured to compare the sensed rate of change to the expected rate of change and modify the periodicity P based on the comparison. In examples, processing circuitry 132 is configured to compare a sensed rate of change as balloon temperature TB transitions from balloon temperature TB 1 to balloon temperature TB2 and adjust periodicity P based on the comparison. In some examples, processing circuitry 132 is configured to compare a sensed rate of change as balloon temperature TB transitions between balloon temperature TB2 to balloon temperature TB 1 and adjust periodicity P based on the comparison.

[0155] For example, FIG. 9 illustrates a flow rate waveform FW1 for a fluid delivered by medical system 100 (e.g., via flow actuator 122) over a time interval from TM-A to TM-B. FIG. 10 illustrates a sensed balloon temperature 174 (e.g., as indicated by temperature sensor 133) and an expected balloon temperature 176 (illustrated with dashed lines) as medical system 100 delivers flow rate waveform FW1. In the example associated with FIGS. 9 and 10, medical system 100 is configured such that delivery of the fluid at upper flow rate MU tends to drive balloon temperature TB toward first balloon temperature TB1 and such that delivery of the fluid at lower flow rate ML tends to drive balloon temperature TB toward second balloon temperature TB2.

[0156] Processing circuitry 132 may be configured to determine the expected rate of change of expected balloon temperature 176 over a time interval in which expected temperature 176 is expected to trend in a direction from balloon temperature TB1 toward balloon temperature TB2. For example, processing circuitry 132 may be configured to determine the expected rate of change of expected balloon temperature 176 based on a time interval TD over which expected temperature 176 predicts a change in balloon temperature TB from a balloon temperature TB-A to an expected balloon temperature TE-1. Processing circuitry 132 may determine the expected rate of change of expected balloon temperature 176 based on medical system 100 delivering the fluid at a first periodicity Pl. In examples, for example when medical system 100 is configured to provide the fluid to facilitate a cryoablation, balloon temperature TB-A is less than expected balloon temperature TE-1. In some examples, for example when medical system 100 is configured to provide the fluid to facilitate a heat-based thermal ablation, balloon temperature TB-A is greater than expected balloon temperature TE-1.

[0157] Processing circuitry 132 may be configured to determine the sensed rate of change of sensed balloon temperature 174 when sensed balloon temperature 174 indicates the trending of balloon temperature TB in a direction from balloon temperature TB1 toward balloon temperature TB2. For example, processing circuitry 132 may be configured to determine the sensed rate based on a change in sensed balloon temperature 174 from balloon temperature TB-A to a balloon temperature TB-B over the time interval TD. Processing circuitry 132 may determine the sensed rate of change of change of sensed balloon temperature 174 as medical system 100 delivers the fluid at the first periodicity Pl. In examples, for example when medical system 100 is configured to provide the fluid to facilitate a cryoablation, balloon temperature TB-A is less than sensed balloon temperature TB-B. In some examples, for example when medical system 100 is configured to provide the fluid to facilitate a heat-based thermal ablation, balloon temperature TB-A is greater than sensed balloon temperature TB-B.

[0158] Processing circuitry 132 may be configured to treat the sensed rate of change of sensed balloon temperature 174 as a proxy for the rate of change of a tissue temperature such as tissue temperature TT (FIG. 8) when, for example, balloon 112 (e.g., balloon body 166) is in contact with vessel wall 104. Hence, processing circuitry 132 may be configured to treat the sensed rate of change of sensed balloon temperature 174 as indicative of the inherent thermoregulation characteristics of the patient. Processing circuitry 132 may be configured to adjust the periodicity of flow rate waveform FW1 to cause the sensed rate of change of sensed balloon temperature 174 and the expected rate of change of expected balloon temperature 176 to more closely match to, for example, assist in maintaining tissue temperature TT within the temperature range.

[0159] As an example, when the sensed rate of change of sensed balloon temperature 174 is greater than the expected rate of change of expected balloon temperature 176 (e.g., as sensed balloon temperature 174 trends in a direction from first balloon temperature TB1 to second balloon temperature TB2), processing circuitry 132 may be configured to treat the greater sensed rate of change of sensed balloon temperature 174 as an indication that the thermoregulation characteristics of the patient may be driving tissue temperature TT from first tissue temperature TP1 to second tissue temperature TP2 at a rate greater than expected. Processing circuitry 132 may be configured to decrease a periodicity of flow rate waveform FW2 from the first periodicity Pl to a second periodicity P2 in response to determining thesensed rate of change of sensed balloon temperature 174 is greater than the expected rate of change of expected balloon temperature 176.

[0160] Processing circuitry 132 may be configured to determine second periodicity P2 by determining an updated expected balloon temperature 177 based on medical system 100 delivering the fluid at the second periodicity P2. Processing circuitry 132 may determine an updated expected rate of change based on updated expected balloon temperature 177. For example, The updated expected rate of change may be a rate at which updated expected balloon temperature 177 predicts (e.g., correlates with) a change in balloon temperature TB from balloon temperature TB-A to an expected balloon temperature TE-2 over time interval TD. Processing circuitry 132 may determine periodicity P2 such that updated expected balloon temperature 177 predicts and / or correlates with expected balloon temperature TE-2 being closer to and / or substantially matching balloon temperature TB-B as updated expected balloon temperature 177 increases over the time period TD. Hence, processing circuitry 132 may adjust the periodicity (e.g., from first periodicity Pl to second periodicity P2) to match and / or mimic an inherent capacity of the patient to transition the tissue temperature between first tissue temperature TP1 and second tissue temperature TP2 to assist in maintaining tissue temperature TT within temperature range TR.

[0161] In some examples, in addition to or instead of adjusting the periodicity (e.g., from first periodicity Pl to second periodicity P2), processing circuitry 132 is configured to alter a rate at which flow rate waveform FW 1 increases from lower flow rate ML to upper flow rate MU to cause expected balloon temperature TE-2 to be closer to and / or substantially match balloon temperature TB-B. For example, processing circuitry 132 may be configured to decrease a time interval over which flow rate waveform FW 1 increases from lower flow rate ML to upper flow rate MU from a first time interval TRI to a second time interval TR2 less first time interval TRI to cause expected balloon temperature TE-2 to be closer to and / or substantially match balloon temperature TB-B. In some examples, in addition to or instead of adjusting the periodicity or a rate at which flow rate waveform FW1 increases from lower flow rate ML to upper flow rate MU, processing circuitry 132 may be configured to adjust at least one of upper flow rate MU or lower flow ML. For example, processing circuitry 132 may be configured to increase upper flow rate ML and / or lower flow rate ML to cause expected balloon temperature TE-2 to be closer to and / or substantially match balloon temperature TB-B.

[0162] In some examples, in addition to or instead of adjusting the periodicity, and / or in addition to or instead of altering the rate at which a flow rate waveform increases from lower flow rate ML to upper flow rate MU, processing circuitry 132 may be configured to compare a monitored parameter to a threshold and alter one or more operations of medical system 100 based on the comparison. In examples, the monitored parameter is indicative of balloon temperature TB-B and / or a rate of change thereof. For example, in some examples, the monitored parameter may be a periodicity (e.g., periodicity Pl, periodicity P2), a sensed rate of change of sensed balloon temperature 174, and / or another parameter indicative of balloon temperature TB-B and / or a rate of change thereof. The threshold may be indicative of, for example, a value of the monitored parameter which may indicate a higher than expected thermal transfer is occurring in the patient during delivery of flow rate M. For example, the threshold might be indicative of a proximity of balloon 112 to an unexpected heat sink or heat source, such as veins and / or other anatomical structures in proximity to target tissue site 159. Hence, processing circuitry 132 may be configured to substantially treat the threshold as a proxy for a maximum or minimum thermal transfer anticipated to occur when medical system 100 delivers flow rate M, such that, for example, exceeding the threshold may be cause for further evaluation (e.g., by a clinician) and / or alterations to the operations of medical system 100.

[0163] For example, processing circuitry 132 may be configured to compare a periodicity (e.g., periodicity Pl, periodicity P2) with a periodicity threshold, and / or configured to compare a sensed rate of change of sensed balloon temperature 174 with a rate of change threshold, and / or configured to compare another parameter indicative of balloon temperature TB-B with a another threshold. Processing circuitry 132 may be configured to substantially treat the threshold as a proxy for a maximum or minimum thermal transfer anticipated to occur when medical system 100 delivers flow rate M, such that, for example, exceeding the threshold may be cause for further evaluation (e.g., by a clinician). Processing circuitry 132 may be configured to cause medical system 100 to take actions in response to the monitored parameter exceeding and / or equating with one or more of the thresholds. For example, processing circuitry 132 may issue an alarm or other indication based on the comparison of the monitored parameter and the threshold. Processing circuitry 132 may cause medical system 100 to alter flow rate M, upper flow rate UL, lower flow rate ML, and / or periodicity P based on the comparison of the monitored parameter and the threshold. In some examples, processing circuitry 132 may cause medical system 100 to take actions which substantiallycease and / or greatly reduce heat transfer between balloon 112 and vessel wall 104, such as ceasing delivery of the fluid to balloon interior 116 (e.g., using flow actuator 122).

[0164] FIG. 11 illustrates another example flow rate waveform FW2 for a fluid delivered by medical system 100 (e.g., via flow actuator 122) over a time interval from TM-C to TM-D. FIG. 12 illustrates a sensed balloon temperature 178 (e.g., as indicated by temperature sensor 133) and an expected balloon temperature 180 (illustrated with dashed lines) as medical system 100 delivers flow rate waveform FW2. Processing circuitry 132 may be configured to determine an expected rate of change of an expected balloon temperature 180 over a time interval in which expected temperature 180 is expected to trend in a direction from balloon temperature TB2 toward balloon temperature TB1. Processing circuitry 132 may be configured to determine a sensed rate of change of sensed balloon temperature 178 when sensed balloon temperature 178 indicates the trending of balloon temperature TB in a direction from balloon temperature TB2 toward balloon temperature TB1. Processing circuitry 132 may adjust a periodicity of flow rate waveform FW2 based on a comparison of the expected rate of change of expected balloon temperature 180 and the sensed rate of change of sensed balloon temperature 178.

[0165] For example, processing circuitry 132 may be configured to determine the expected rate of change of expected balloon temperature 180 based on a time interval TE over which expected temperature 180 predicts and / or correlates with a change in balloon temperature TB from a balloon temperature TB-C to an expected balloon temperature TE-3. Processing circuitry 132 may determine the expected rate based on medical system 100 delivering the fluid at a third periodicity P3. Processing circuitry 132 may be configured to determine the sensed rate of change of sensed balloon temperature 178 based on a change in sensed balloon temperature 178 from balloon temperature TB-C to a balloon temperature TB- D over the time interval TE. Processing circuitry 132 may be configured to adjust the periodicity of flow rate waveform FW2 to cause the sensed rate of change of sensed balloon temperature 178 and the expected rate of change of expected balloon temperature 180 to more closely match to, for example, assist in maintaining tissue temperature TT within temperature range TR.

[0166] In examples, when the sensed rate of change of sensed balloon temperature 178 is less than the expected rate of change of expected balloon temperature 180, processing circuitry 132 may be configured to substantially treat the lesser sensed rate of change of sensed balloon temperature 178 as an indication that the thermoregulation characteristics ofthe patient may be providing greater resistance to a change of tissue temperature TT from second tissue temperature TP2 to first tissue temperature TP1 than an anticipated resistance. Processing circuitry 132 may be configured to decrease a periodicity of flow rate waveform FW2 from third periodicity P3 to a fourth periodicity P4 to cause the sensed rate of change of sensed balloon temperature 178 and the expected rate of change of expected balloon temperature 180 to more closely match to, for example, assist in maintaining tissue temperature TT within temperature range TR.

[0167] For example, processing circuitry 132 may be configured to determine fourth periodicity P4 by determining an updated expected balloon temperature 181 based on the fourth periodicity P4. Processing circuitry 132 may determine an updated expected rate of change of updated expected balloon temperature 181 based on updated expected balloon temperature 181. The updated expected rate of change of updated expected balloon temperature 181 may be a rate at which updated expected balloon temperature 181 predicts a change in balloon temperature TB from balloon temperature TB-C to an expected balloon temperature TE-4 over time interval TE. Processing circuitry 132 may determine fourth periodicity P4 such that updated expected balloon temperature 180 predicts expected balloon temperature TE-4 to be closer to and / or substantially match balloon temperature TB-D as updated expected balloon temperature 181 increases over the time period TE. Processing circuitry 132 may adjust the periodicity from third periodicity P3 to fourth periodicity P4 to assist in maintaining tissue temperature TT within temperature range TR.

[0168] In examples, for example when medical system 100 is configured to provide the fluid to facilitate a cryoablation, balloon temperature TB-C is greater than sensed balloon temperature TB-D, expected balloon temperature TE-3, and / or expected balloon temperature TE-4. In some examples, for example when medical system 100 is configured to provide the fluid to facilitate a heat-based thermal ablation, balloon temperature TB-C is less than sensed balloon temperature TB-D, expected balloon temperature TE-3, and / or expected balloon temperature TE-4.

[0169] In some examples, in addition to or instead of adjusting the periodicity (e.g., from third periodicity P3 to fourth periodicity P4), processing circuitry 132 is configured to alter a rate at which flow rate waveform FW 1 increases from lower flow rate ML to upper flow rate MU (e.g., from first time interval TRI to second time interval TR2) to cause expected balloon temperature TE-4 to be closer to and / or substantially match balloon temperature TB-D. In some examples, in addition to or instead of adjusting the periodicity or a rate at which flowrate waveform FW 1 increases from lower flow rate ML to upper flow rate MU, processing circuitry 132 may be configured to adjust at least one of upper flow rate MU or lower flow ML. For example, processing circuitry 132 may be configured to increase upper flow rate ML and / or lower flow rate ML to cause expected balloon temperature TE-4 to be closer to and / or substantially match balloon temperature TB-D.

[0170] In some examples, processing circuitry 132 is configured to determine a sensed rate of change of a temperature of balloon 112 (e.g., sensed balloon temperature 174, 178) and issue a communication (e.g., a notification) if the sensed rate of change of the temperature is greater than or equal to a threshold. The threshold may be, for example, based on an expected rate of change of the temperature of balloon 112 (e.g., expected balloon temperature 176, 177, 180, 181). Processing circuitry 132 may issue the communication as an indication that upper flow rate MU, lower flow rate ML, periodicity P, Pl, P2, P3, P4, a positioning of balloon 112 in vessel 102, or some other aspect of medical system 100 is causing a potentially undesired and / or unexpected heat transfer with target tissue site 159 and / or anatomical structures which may be in proximity to target tissue site 159. In some examples, processing circuitry 132 automatically stops (e.g., cease) delivery of fluid (e.g., using flow actuator 122) to balloon interior 116 in response determining the sensed rate greater than or equal to the threshold. Processing circuitry 132 may be configured to issue the communication using device 134 and / or another device of medical system 100.

[0171] Referring to FIG. 6, in examples, processing circuitry 132 is configured to determine a first time period TU over which medical system 100 delivers the fluid at upper flow rate MU and / or a second time period TL at which medical system 100 delivers the fluid at lower flow rate ML. First time period TU and second time period TL are time intervals within periodicity P of flow rate waveform FW. In some examples, First time period TU and second time period TL define periodicity P. For example, first time period TU may comprise a first portion of a time period defined by periodicity P. Second time period TL may comprise a second portion of the time period defined by periodicity P. In some examples, first time period TU is substantially equal to second time period TL. In some examples, first time period TU is greater than second time period TL. In some examples, first time period TU is less than second time period TL. Medical system 100 may be configured to deliver (e.g., using flow actuator 122) the fluid at upper flow rate MU over first time period TU and / or deliver the fluid at lower flow rate LU over second time period TL.

[0172] In examples, processing circuitry 132 is configured to adjust at least one of first time period TU and / or second time period TL. For example, processing circuitry 132 may be configured to adjust at least one of first time period TU and / or second time period TL based on the parameter indicative of balloon temperature TB of balloon 112 (e.g., provided by temperature sensor 133) as medical system 100 provides the fluid at upper flow rate MU, lower flow rate ML, and periodicity P. Processing circuitry 132 may be configured to adjust at least one of first time period TU and / or second time period TL based on comparison of a sensed rate of change of a temperature of balloon 112 and an expected rate of change of an expected temperature of balloon 112 as medical system 100 provides the fluid at upper flow rate MU, lower flow rate ML, and periodicity P. In examples, processing circuitry 132 is configured to adjust at least one of first time period TU and / or second time period TL to more closely match a sensed temperature (e.g., TB-A, TB-B) and an expected temperature (e.g., TE-1, TE-2, TE-3, TE-4).

[0173] In some examples, processing circuitry 132 is configured to adjust periodicity P by at least adjusting at least one of first time period TU and / or second time period TL. For example, processing circuitry 132 may be configured to reduce periodicity P by reducing both first time period TU and second time period TL, reducing only one of first time period TU or second time period TL, and / or reducing first time period TU by an amount less than or greater than a reduction of second time period TL. Processing circuitry 132 may be configured to increase periodicity P by increasing both first time period TU and second time period TL, increasing only one of first time period TU or second time period TL, and / or increasing first time period TU by an amount less than or greater than an increase of second time period TL. In some examples, processing circuitry 132 may increase and / or decrease periodicity P by increasing first time period TU and decreasing second time period TL, and / or by decreasing first time period TU and increasing second time period TL. In some examples, processing circuitry 132 is configured to alter first time period TU and / or second time period TL in a manner which leaves periodicity P substantially unchanged.

[0174] An example technique for maintaining a temperature of a tissue target site within a temperature range is illustrated in FIG. 13. Although the technique is described mainly with reference to medical system 100 of FIGS. 1-5, the technique may be applied to other medical systems in other examples and by processing circuitry 132 alone or in combination with other control circuitry in other examples.

[0175] The technique includes determining, by processing circuitry 132, a target temperature TGT of a target tissue site 159 (1302). In examples, processing circuitry 132 determines the target temperature by at least receiving target temperature TGT from device 134 (e.g., a user input device) and / or based on information stored by a memory accessible to processing circuitry 132. In some examples, processing circuitry determines (e.g., receives from device 134 or another device or determines based on medical imaging) a tissue depth TD of target tissue site 159 and / or a size (e.g., a diameter) of a vessel wall 104 which includes and / or is proximate target tissue site 159. In examples, processing circuitry 132 determines (e.g., receives from device 134 or another device) a temperature range TR, a first tissue temperature TP1 bounding temperature range TR, and / or second tissue temperature TP2 bounding temperature range TR.

[0176] The technique includes determining, by processing circuitry 132, a periodicity P, Pl, P2, P3, P4 of a flow rate of a fluid provided to a balloon 112 to maintain a tissue temperature TT of target tissue site 159 within temperature range TR (1304). In examples, processing circuitry 132 determines periodicity P, Pl, P2, P3, P4 as an elapsed time over which a medical system 100 causes the fluid to decrease from an upper flow rate MU to a lower flow rate ML and return to the upper flow rate MU. In examples, processing circuitry 132 determines periodicity P, Pl, P2, P3, P4 using tissue depth TD and a representative balloon temperature of balloon 112.

[0177] Processing circuitry 132 can determine periodicity P, Pl, P2, P3, P4 using any suitable technique, such as based on a transfer correlation indicative of a temperature difference TDIFF between the representative balloon temperature of balloon 112 (e.g., balloon body 166) and target tissue site 159 when medical system 100 delivers the fluid. In some examples, the representative balloon temperature is an expected balloon temperature of balloon 112 anticipated to occur when medical system 100 delivers the fluid. In some examples, the representative balloon temperature is a sensed balloon temperature of balloon 112 determined by a temperature sensor 133.

[0178] In examples, medical system 100 delivers the fluid at the upper flow rate MU, the lower flow rate ML, and over the periodicity P, Pl, P2, P3, P4 using a flow actuator 122. Medical system 100 may cause a balloon flowrate MB to flow through a balloon interior 116 of balloon 112 when medical system 100 delivers the fluid. In examples, medical system 100 causes balloon flowrate MB to vary between an upper balloon flow rate MBU and a lower balloon flow rate MBL as medical system 100 delivers the fluid at the upper flow rate MU,the lower flow rate ML, and over the periodicity P, Pl, P2, P3, P4. Balloon 112 may cause and / or processing circuitry 132 may determine a balloon temperature range BTR over which the representative balloon temperature varies as medical system 100 delivers the fluid at the upper flow rate MU, the lower flow rate ML, and over the periodicity P, Pl, P2, P3, P4. In examples, tissue temperature TT of target tissue site 159 remains within temperature range TR as the representative balloon temperature varies over balloon temperature range BTR.

[0179] In examples, processing circuitry 132 determines periodicity P, Pl, P2, P3, P4 by at least assessing one or more potential periodicities. Processing circuitry 132 may be configured to determine a resulting temperature range for target tissue site 159 based on a temperature difference TDIFF which results when a potential periodicity causes balloon temperature TB to vary between first balloon temperature TB1 and second balloon temperature TB2. Processing circuitry 132 may determine periodicity P, Pl, P2, P3, P4 by determining a particular periodicity from the one or more potential periodicities which causes or is anticipated to cause tissue temperature TT to remain within temperature range TR as medical system 100 delivers the fluid at upper flow rate MU, lower flow rate ML, and the particular periodicity.

[0180] In some examples, processing circuitry 132 determines periodicity P. Pl, P2, P3, P4 by at least causing medical system 100 to deliver the fluid at upper flow rate MU until balloon temperature TB achieves a temperature proximate first balloon temperature TB 1. Processing circuitry 132 may subsequently cause medical system 100 to deliver the fluid at lower flow rate ML to cause balloon temperature TB to transition to a temperature proximate second balloon temperature TB2. Processing circuitry 132 may subsequently cause medical system 100 to deliver the fluid at upper flow rate MU when balloon temperature TB achieves the temperature proximate second balloon temperature TB2. Processing circuitry 132 may determine periodicity P, Pl, P2, P3, P4 by determining an elapsed time over which medical system 100 caused the fluid flow to transition from upper flow rate MU to lower flow rate ML and return to upper flow rate MU in order to cause balloon temperature BT to cycle from first balloon temperature TB 1 to second balloon temperature TB2 and return to first balloon temperature TB 1.

[0181] In some examples, processing circuitry 132 determines periodicity P, Pl, P2, P3, P4 based on, for example, previous ablation procedures, computer modeling and / or measurement of fluid flow through the catheter system and / or balloon, modeling and / or measurement of heat transfer characteristics of a balloon experiencing a given fluid flow,and / or other data indicative of a heat transfer between an expanded balloon and a vessel wall. In some examples, processing circuitry 132 determines periodicity P, Pl, P2, P3, P4 using an input provided from device 134.

[0182] In examples, processing circuitry 132 adjusts one or more of upper flow rate MU, lower flow rate ML, and / or periodicity P, Pl, P2, P3, P4 based on a sensed balloon temperature received from temperature sensor 133. In some examples, processing circuitry 132 determines a rate of change of the sensed balloon temperature and issues a communication if the rate of change is greater than or equal to a threshold.

[0183] In some examples, processing circuitry 132 causes medical system 100 to deliver the fluid at upper flow rate MU, lower flow rate ML, and periodicity P, Pl, P2, P3, P4. Processing circuitry 132 may cause medical system 100 to deliver the fluid using flow actuator 122. In examples, medical system 100 delivers the fluid via flow actuator 122 to an elongate body 110 supporting balloon 112. In examples, medical system 100 delivers the fluid (e.g., via flow actuator 122) to one or more of inlet conduit 126, fluid inlet 118, inlet lumen 172, and / or distributor 114. In some examples, medical system 100 delivers the fluid via flow actuator 122 in a liquid phase and the fluid flows through interior volume 116 in a gaseous phase.

[0184] In one or more examples, the functions described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, as one or more instructions or code, a computer- readable medium and executed by a hardware-based processing unit (e.g., processing circuitry). The computer-readable medium may be an article of manufacture including a non- transitory computer-readable storage medium encoded with instructions. Instructions embedded or encoded in an article of manufacture including a non-transitory computer- readable storage medium encoded, may cause one or more programmable processors, or other processors, to implement one or more of the techniques described herein, such as when instructions included or encoded in the non-transitory computer-readable storage medium are executed by the one or more processors. Example non-transitory computer-readable storage media may include RAM, ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), electronically erasable programmable ROM (EEPROM), flash memory, a hard disk, a compact disc ROM (CD-ROM), a floppy disk, a cassette, magnetic media, optical media, or any other computer readable storage devices or tangible computer readable media.

[0185] In some examples, a computer-readable storage medium comprises non-transitory medium. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in RAM or cache).

[0186] The functionality described herein, e.g., with respect to processing circuitry 132, may be provided within dedicated hardware and / or software modules. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0187] Various examples of the disclosure have been described. Any combination of the described systems, operations, or functions is contemplated. These and other examples are within the scope of the following claims.

[0188] Example 1. A medical system comprising: a medical device configured to deliver a fluid to a balloon, wherein the balloon is configured to expand within a vessel of a patient; and processing circuitry configured to: determine a target temperature indicative of a desired temperature of a target tissue site of the patient, the target tissue site being at a tissue depth, and determine, using a representative temperature of the balloon and the tissue depth, a periodicity of a flow rate of the fluid to maintain a temperature of the target tissue site within a temperature range when the medical device provides the fluid to the balloon, wherein the target temperature is within the temperature range, wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity.

[0189] Example 2. The medical system of Example 1, wherein the processing circuitry is configured to control the medical device to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0190] Example 3. The medical system of Example 1 or Example 2, wherein the processing circuitry is configured to: determine an indicated size representative of a size ofthe vessel, and determine the representative temperature of the balloon based on the indicated size and the fluid provided by the medical device.

[0191] Example 4. The medical system of any of Examples 1-3, wherein the processing circuitry is configured to determine the periodicity to keep the representative temperature of the balloon within a range, and wherein the temperature range at the tissue depth is less than the range of the representative temperature.

[0192] Example 5. The medical system of any of Examples 1-4, wherein the temperature range includes a first temperature and a second temperature less than the first temperature, wherein the representative temperature of the balloon is in a balloon temperature range including a first representative balloon temperature and a second representative balloon temperature less than the first representative balloon temperature, and wherein the processing circuitry is configured to determine the periodicity to keep the second temperature between the first representative balloon temperature and the first temperature.

[0193] Example 6. The medical system of any of Examples 1-5, wherein the processing circuitry is configured to determine a sensed temperature of the balloon when the balloon is expanded within the vessel.

[0194] Example 7. The medical system of Example 6, wherein the processing circuitry is configured to determine the sensed temperature using a parameter indicative of a temperature of the balloon, wherein the parameter is at least one of a temperature of the balloon or a pressure of the balloon.

[0195] Example 8. The medical system of Example 6 or Example 7, wherein the processing circuitry is configured to adjust the periodicity based on the sensed temperature.

[0196] Example 9. The medical system of any of Examples 6-8, wherein the processing circuitry is configured to adjust at least one of the upper flow rate or the lower flow rate based on the sensed temperature.

[0197] Example 10. The medical system of any of Examples 6-9, wherein the processing circuitry is configured to determine an elapsed time as the sensed temperature of the balloon increases from a lower temperature to an upper temperature higher than the lower temperature as the medical device provides the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0198] Example 11. The medical system of Example 10, wherein the processing circuitry is configured to adjust the periodicity based on the elapsed time.

[0199] Example 12. The medical system of Example 10 or Example 11, wherein the processing circuitry is configured to compare the elapsed time to a threshold value and at least one of: provide, based on the comparison, a notification, or issue, based on the comparison, a ommunication to cause the medical device to cease providing the fluid to the balloon.

[0200] Example 13. The medical system of any of Examples 1-12, wherein the processing circuitry is configured to determine, using at least one of the representative temperature of the balloon, the tissue depth, or the target temperature, at least one of the upper flow rate or the lower flow rate.

[0201] Example 14. The medical system of any of Examples 1-13, wherein the lower flow rate is substantially zero.

[0202] Example 15. The medical system of any of Examples 1-14, wherein the processing circuitry is configured to determine the periodicity using a transfer correlation indicative of a heat transfer between the balloon and the target tissue site when the balloon is inflated within the vessel and the medical device provides the fluid to the balloon.

[0203] Example 16. The medical system of any of Examples 1-15, wherein the processing circuitry is configured to: determine, using the tissue depth and at least one of the representative temperature or a sensed temperature of the balloon, an initial period indicative of a time period required to produce the target temperature when the balloon is expanded within the vessel and the medical device provides the fluid; and schedule the periodicity to commence following the initial period.

[0204] Example 17. The medical system of any of Examples 1-16, wherein the processing circuitry is configured to: determine a first time period over which the medical device provides the fluid at the upper flow rate, and determine a second time period over which the medical device provides the fluid to the balloon at the lower flow rate, wherein the first time period comprises a first portion of the time period indicated by the periodicity and the second time period comprises a second portion of the time period indicated by the periodicity.

[0205] Example 18. The medical system of Example 17, wherein a duration of the first time period is different from a duration of the second time period.

[0206] Example 19. The medical system of Example 17 or Example 18, wherein the processing circuitry is configured to adjust the first time period or the second time period based on a sensed temperature of the balloon.

[0207] Example 20. The medical system of any of Examples 1-19, further comprising a sensor configured to sense at least one of a temperature of the balloon or a pressure of the balloon, wherein the processing circuitry is configured to determine a sensed temperature of the balloon based on input from the sensor.

[0208] Example 21. The medical system of Example 20, wherein the sensor is configured to sense the temperature of the balloon by at least sensing a temperature of a body of the balloon contacting a wall of the vessel when the balloon is expanded within the vessel.

[0209] Example 22. The medical system of any of claims 1-21, further comprising: a catheter body configured to be positioned within the vessel of the patient, wherein the catheter body defines an inlet lumen configured to receive the fluid from the medical device, wherein the medical device is configured to control the flow rate of the fluid received by the inlet lumen; and the balloon, wherein an interior volume of the balloon is in fluidic communication with the inlet lumen.

[0210] Example 23. The medical system of Example 22, wherein the periodicity is based on a minimum desired pressure of a liquid comprising the fluid within the inlet lumen, and wherein the minimum desired pressure is a pressure intended to limit a phase change of the liquid in the inlet lumen.

[0211] Example 24. The medical system of Example 22 or Example 23, wherein the catheter body defines an outlet lumen, and wherein the medical system defines a flow path through the inlet lumen, through the interior volume, and through the outlet lumen.

[0212] Example 25. The medical system of any of Examples 1-24, wherein the medical device includes at least one of a fluid container defining a reservoir configured to hold a volume of the fluid or a pump configured to move the fluid.

[0213] Example 26. The medical system of Example 25, wherein the medical device comprises a housing in which at least some portion of the processing circuitry is positioned.

[0214] Example 27. The medical system of any of Examples 1-26, wherein the processing circuitry is configured to determine the periodicity using a machine learning algorithm, wherein the machine learning algorithm is configured to receive an input vector indicative of the tissue depth and indicative of the target temperature and provide an output vector in response to the input vector, wherein the output vector is indicative of the periodicity.

[0215] Example 28. The medical system of Example 27, wherein, prior to determining the periodicity, the machine learning algorithm was trained using one or more training data sets including a training input vector and a training output vector, wherein the training input vector is representative of a depth within the tissue and representative of a temperature of the tissue at the depth, and wherein the training output vector is representative of a periodicity of a fluid flow rate.

[0216] Example 29. The medical system of Example 28, wherein at least one of the one or more training data sets is indicative of one or more physiological characteristics of a cohort of patients.

[0217] Example 30. The medical system of any of Examples 1-29, wherein the periodicity is less than or equal to about 30 seconds.

[0218] Example 31. The medical system of any of Examples 1-30, wherein the medical device comprises a flow actuator configured to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0219] Example 32. The medical system of Example 31, wherein the processing circuitry is configured to control the flow actuator to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0220] Example 33. A medical system comprising: a catheter body configured to be positioned within a vessel of a patient, wherein the catheter body defines an inlet lumen configured to receive a fluid; a balloon supported by the elongate body, wherein an interior volume of the balloon is in fluidic communication with the inlet lumen, and wherein the balloon is configured to expand within the vessel; a flow actuator configured to position to control a flow rate of the fluid received by the inlet lumen; and processing circuitry configured to: determine a target temperature indicative of a desired temperature of a target tissue site of the patient, the target tissue site being at a tissue depth, and determine, using a representative temperature of the balloon and the tissue depth, a periodicity of a flow rate of the fluid to maintain a temperature of the target tissue site within a temperature range when the medical device provides the fluid to the balloon, wherein the target temperature is within the temperature range, wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity; and cause the flow actuator to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

[0221] Example 34. The medical system of Example 33, further comprising a sensor configured to sense at least one of a temperature of the balloon or a pressure of the balloon, wherein the processing circuitry is configured to: determine a sensed temperature of the balloon based on input from the sensor; and adjust the periodicity based on the sensed temperature.

[0222] Example 35. The medical system of Example 34, wherein the processing circuitry is configured to: determine, using the sensed temperature, an elapsed time as the sensed temperature of the balloon increases from a lower temperature to an upper temperature higher than the lower temperature as the fluid flows at the upper flow rate, the lower flow rate, and the periodicity; and adjust the periodicity based on the elapsed time.

[0223] Example 36. A method, comprising: determining, by processing circuitry and based on a representative temperature of a balloon and a tissue depth, a periodicity of a flow rate of a fluid to maintain a target temperature of a target tissue site of a patient within a temperature range when a medical device provides the fluid to the balloon, wherein the target tissue site is at the tissue depth, wherein the target temperature is within the temperature range, and wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, wherein the balloon is configured to expand within a vessel of the patient, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity.

[0224] Example 37. The method of Example 36, further comprising causing, by the processing circuitry, a flow actuator to provide the fluid to a catheter body at the upper flow rate, the lower flow rate, and the periodicity, wherein the catheter body mechanically supports the balloon.

[0225] Example 38. The method of Example 36 or Example 37, further comprising determining, by the processing circuitry, at least one of the periodicity such that the representative temperature is within a balloon temperature range, wherein the temperature range at the tissue depth is less than 25% of the balloon temperature range.

[0226] Example 39. The method of any of Examples 36-38, further comprising determining, by the processing circuitry, at least one of the periodicity such that the time period is less than or equal to about 30 seconds.

[0227] Example 40. The method of any of Examples 36-39, further comprising: determining, by the processing circuitry, a sensed temperature of the balloon when the balloon is inflated within the vessel; and adjusting, by the processing circuitry, the periodicity based on the sensed temperature.

[0228] Example 41. The method of Example 40, further comprising: determining, using the processing circuitry, an elapsed time as the sensed temperature increases from a lower temperature to an upper temperature higher than the lower temperature as the medical device provides the fluid at the upper flow rate, the lower flow rate, and the periodicity; and adjusting, by the processing circuitry, the periodicity based on the elapsed time.

[0229] Example 42. The method of any of Example s 36-41, wherein the lower flow rate is substantially zero.

[0230] Example 43. The method of any of Examples 36-42, further comprising determining, by the processing circuitry, the periodicity using a transfer correlation indicative of a heat transfer between the balloon and the target tissue site when the balloon is inflated within the vessel.

[0231] Example 44. The method of any of Examples 36-43, further comprising: determining, using the processing circuitry, an initial period indicative of a time period required to produce the target temperature when the balloon is expanded within the vessel and the medical device provides the fluid; an initial period indicative of a time period required to produce the target temperature when the balloon is expanded within the vessel and medical device provides the fluid; and scheduling, by the processing circuitry, the periodicity to commence following the initial period.

[0232] Example 45. The method of any of Examples 36-44, further comprising determining, using the processing circuitry, the periodicity using a machine learning algorithm, wherein the machine learning algorithm is configured to receive an input vector indicative of the tissue depth and indicative of the target temperature and provide an output vector in response to the input vector, wherein the output vector is indicative of the periodicity.

Claims

CLAIMS1. A medical system comprising: a medical device configured to deliver a fluid to a balloon, wherein the balloon is configured to expand within a vessel of a patient; and processing circuitry configured to: determine a target temperature indicative of a desired temperature of a target tissue site of the patient, the target tissue site being at a tissue depth, and determine, using a representative temperature of the balloon and the tissue depth, a periodicity of a flow rate of the fluid to maintain a temperature of the target tissue site within a temperature range when the medical device provides the fluid to the balloon, wherein the target temperature is within the temperature range, wherein the periodicity is indicative of a time period over which the flow rate of the fluid varies from an upper flow rate to a lower flow rate and returns to the upper flow rate, and wherein the balloon is configured to remain expanded when the medical device provides the fluid to the balloon at the upper flow rate, the lower flow rate, and the periodicity.

2. The medical system of claim 1, wherein the processing circuitry is configured to control the medical device to provide the fluid at the upper flow rate, the lower flow rate, and the periodicity.

3. The medical system of claim 1 or claim 2, wherein the processing circuitry is configured to: determine an indicated size representative of a size of the vessel, and determine the representative temperature of the balloon based on the indicated size and the fluid provided by the medical device.

4. The medical system of any of claims 1-3, wherein the processing circuitry is configured to determine the periodicity to keep the representative temperature of the balloon within a range, and wherein the temperature range at the tissue depth is less than the range of the representative temperature.

5. The medical system of any of claims 1-4, wherein the temperature range includes a first temperature and a second temperature less than the first temperature, wherein the representative temperature of the balloon is in a balloon temperature range including a first representative balloon temperature and a second representative balloon temperature less than the first representative balloon temperature, and wherein the processing circuitry is configured to determine the periodicity to keep the second temperature between the first representative balloon temperature and the first temperature.

6. The medical system of any of claims 1-5, wherein the processing circuitry is configured to determine a sensed temperature of the balloon when the balloon is expanded within the vessel and adjust at least one of the periodicity, the upper flow rate, or the lower flow rate based on the sensed temperature.

7. The medical system of claim 6, wherein the processing circuitry is configured to determine the sensed temperature using a parameter indicative of a temperature of the balloon, wherein the parameter is at least one of a temperature of the balloon or a pressure of the balloon.

8. The medical system of any of claims 1-7, wherein the processing circuitry is configured to: determine a sensed temperature of the balloon when the balloon is expanded within the vessel, and determine, using at least one of the representative temperature of the balloon, the tissue depth, or the target temperature, at least one of the upper flow rate or the lower flow rate.

9. The medical system of any of claims 1-8, wherein the processing circuitry is configured to:determine a sensed temperature of the balloon when the balloon is expanded within the vessel, determine an elapsed time as the sensed temperature of the balloon increases from a lower temperature to an upper temperature higher than the lower temperature as the medical device provides the fluid at the upper flow rate, the lower flow rate, and the periodicity, and adjust the periodicity based on the elapsed time.

10. The medical system of any of claims 1-9, wherein the processing circuitry is configured to determine the periodicity using a transfer correlation indicative of a heat transfer between the balloon and the target tissue site when the balloon is inflated within the vessel and the medical device provides the fluid to the balloon.

11. The medical system of any of claims 1-10, wherein the processing circuitry is configured to: determine, using the tissue depth and at least one of the representative temperature or a sensed temperature of the balloon, an initial period indicative of a time period required to produce the target temperature when the balloon is expanded within the vessel and the medical device provides the fluid; and schedule the periodicity to commence following the initial period.

12. The medical system of any of claims 1-11, wherein the processing circuitry is configured to: determine a first time period over which the medical device provides the fluid at the upper flow rate, and determine a second time period over which the medical device provides the fluid to the balloon at the lower flow rate, wherein the first time period comprises a first portion of the time period indicated by the periodicity and the second time period comprises a second portion of the time period indicated by the periodicity.

13. The medical system of any of claims 1-12, further comprising a sensor configured to sense at least one of a temperature of the balloon or a pressure of the balloon, wherein theprocessing circuitry is configured to determine a sensed temperature of the balloon based on input from the sensor.

14. The medical system of any of claims 1-13, further comprising: a catheter body configured to be positioned within the vessel of the patient, wherein the catheter body defines an inlet lumen configured to receive the fluid from the medical device, wherein the medical device is configured to control the flow rate of the fluid received by the inlet lumen; and the balloon, wherein an interior volume of the balloon is in fluidic communication with the inlet lumen.

15. The medical system of any of claims 1-14, wherein the processing circuitry is configured to determine the periodicity using a machine learning algorithm, wherein the machine learning algorithm is configured to receive an input vector indicative of the tissue depth and indicative of the target temperature and provide an output vector in response to the input vector, wherein the output vector is indicative of the periodicity.

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