Calibration system for an esophageal catheter with a balloon probe for determining intraesophageal pressure - Patent Application 20070122997

Abstract

A calibration system (60) for automatically setting a desired operational filling for an esophageal catheter (48) with a balloon probe (46) insertable into an esophagus (34) for determining an esophageal pressure (Peso), the calibration system (60) comprises a device for filling the balloon probe with a measurement fluid after placing the balloon probe in the esophagus, a pressure sensor for detecting the esophageal pressure in the balloon probe, and a calibration controller (60) designed to vary the amount of measurement fluid in the balloon probe stepwise, the calibration controller recording the esophageal pressure detected by the pressure sensor for each amount of measurement fluid in the balloon probe set stepwise as measurement points and correlating the esophageal pressure with each set amount of measurement fluid in the balloon probe. The calibration controller monotonically varies the amount of measurement fluid in at least two steps from a start value to an end value to approach each measurement point.

Description

[Technical Field]

[0001] The present invention relates to a calibration system for an esophageal catheter equipped with a balloon probe for determining intraesophageal pressure. [Background technology]

[0002] Esophageal catheters equipped with a balloon probe for determining esophageal pressure (hereinafter also simply referred to as balloon catheters) are used to determine transpulmonary pressure, particularly in mechanical ventilation devices. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 037175 [Non-patent literature]

[0004] [Non-Patent Document 1] Mojoli et al.Crit.Care(2016)20:98 [Non-patent document 2] Hotz et al.Respir.Care(2018)63(2):177-186 [Non-patent document 3] Benditt J. Resp.Care 2005,50:pp.68-77 [Non-patent document 4] Lotti IA et al. Intensive Care Med. 1995,21:406-413 Summary of the Invention [Problem to be solved by the invention]

[0005] Today's common mechanical ventilation method involves delivering breathing gas to patients at positive pressure. Therefore, during ventilation, airway or alveolar pressure is greater than the pressure in the pleural cavity or interstitial space surrounding the alveoli, at least during inspiration. During expiration, however, the ventilator does not pressurize the airways, allowing the lung tissue to relax and reduce airway or alveolar pressure. Under certain circumstances, this type of positive pressure ventilation can create very unfavorable airway or alveolar pressure conditions at the end of expiration, leading to partial alveolar collapse. During the subsequent respiratory cycle, the initially collapsed portion of the lung volume is re-expanded, significantly compromising the lung's functional residual capacity, resulting in a decrease in oxygen saturation and potentially permanent lung tissue damage.

[0006] To prevent alveolar collapse at the end of expiration, positive end-expiratory pressure, commonly referred to as PEEP, is used during positive pressure mechanical ventilation, which often results in improved oxygen saturation.

[0007] When ventilation is performed with PEEP, a certain positive airway pressure, i.e., PEEP, is applied by the ventilator permanently, i.e., during both inspiration and expiration, and therefore continues to exist after expiration.

[0008] Ideally, PEEP is set so that intra-alveolar pressure does not fall below the pleural space pressure during expiration, or at least so high that the pressure in the pleural space does not cause the alveolar tissue to collapse. In other words, PEEP prevents the transpulmonary pressure, which is the pressure difference between the intra-alveolar pressure and the pleural space pressure, from falling below zero or below a negative threshold at which some alveoli begin to collapse.

[0009] On the other hand, too high a PEEP value can have adverse effects, especially during inspiration. Extremely high airway pressure during inspiration can stretch lung tissue excessively. Numerous studies have also shown that high PEEP can impair venous return to the heart, with consequent adverse effects on the cardiovascular system.

[0010] PEEP should be set to the effective transpulmonary pressure. However, it is not easy to determine the transpulmonary pressure of a patient during ventilation. Therefore, a balloon probe is inserted into the esophagus of a ventilated patient using an esophageal catheter, and the pressure inside the balloon probe is measured. By properly positioning and configuring the balloon, the pressure inside the balloon can be used to determine the approximate pressure inside the pleural space.

[0011] WO 2014 / 037175 (Patent Document 1) discloses a technique for automatically setting pressures, particularly positive end-expiratory pressure (PEEP) and maximum airway pressure, specified by a ventilation device based on the transpulmonary pressure, i.e., the pressure detected by a measuring device, which is considered to be an index between the alveolar pressure and the pressure in the pleural space. Once the transpulmonary pressure is determined, the pressure in a balloon catheter inserted in the esophagus is measured as a measure of the pressure in the pleural space.

[0012] In practice, the relationship between the pressure measured in the balloon catheter inserted into the esophagus and the pressure in the pleural space can change during ventilation for a variety of reasons that are generally not well characterized.

[0013] Mojoli et al. Crit. Care (2016) 20:98 (Non-Patent Document 1) describes a procedure for calibrating a balloon catheter designed for measuring esophageal pressure. The purpose of calibration is to optimally fill the balloon catheter with air so that it responds as sensitively as possible to changes in the pressure in the pleural space acting on the esophagus and accurately reflects the pressure in the pleural space. Calibration is performed in vivo with the balloon catheter inserted into the esophagus. The amount of fluid (air) filled into the balloon catheter is changed, and the pressure at the end of inspiration and the end of expiration are continuously measured, and the difference between these measured pressures is determined. The optimal balloon filling volume is determined as the maximum pressure difference within the measurement range where both the pressure measured by the balloon catheter at the end of inspiration and the pressure measured by the balloon catheter at the end of expiration increase quasi-linearly with the amount of fluid filled into the balloon. To obtain reproducible results in this in vivo calibration, the balloon filling volume in this study was adjusted using the same procedure, as follows: Specifically, an empty balloon catheter in pressure equilibrium with the environment is first overfilled to a value equal to or greater than the measurement range, and then fluid is expelled from the balloon until the desired balloon filling volume is reached. Care must be taken to avoid instability by ensuring sufficient time for correction of fluid flow, pressure, and relaxation processes occurring in the catheter and esophageal tissue before recording a new measurement point. Thus, the measurement procedure described by Mojoli et al. is relatively complex and sensitive, resulting in a balloon catheter calibration time of approximately 15 minutes or more. Therefore, in practice, only the optimal filling volume of the balloon probe is determined and preset before the start of ventilation, and this optimal filling volume remains unchanged during ventilation.

[0014] Similarly, Hotz et al., Respir. Care (2018) 63(2):177-186, recommends calibrating the volume of fluid filled into the balloon catheter to maximize the sensitivity of the measured pressure to pressure changes in the pleural space and improve measurement accuracy. However, the in vivo calibration proposed here is similar to the calibration proposed by Mojoli et al., and in particular, it is time-consuming.

[0015] The present invention provides a calibration system that improves the accuracy of pressure measurements obtained using a balloon catheter inserted into the esophagus. In particular, the calibration system of the present invention allows the pressure in the pleural space to be more accurately reproduced by the balloon catheter, and allows measurements to respond more quickly to changes in environmental conditions during ventilation. This allows calibration of the balloon catheter during ventilation without interrupting ventilation. This can also be applied when ventilation is performed using a fully automatic ventilation mode, such as closed-loop ventilation, such as adaptive assisted ventilation (ASV ventilation) developed by the applicant. [Means for solving the problem]

[0016] The present invention proposes a calibration system, in particular for ventilation devices, for automatically setting a desired operational filling for an esophageal catheter with a balloon probe insertable into the esophagus for determining the esophageal pressure. The calibration system according to the invention comprises a device for filling the balloon probe with a measurement fluid after placing the balloon probe in the esophagus, a pressure sensor for detecting the esophageal pressure in the balloon probe, and a calibration controller designed to gradually change the amount of measurement fluid in the balloon probe, the calibration controller recording the esophageal pressure detected by the pressure sensor for each amount of measurement fluid in the balloon probe that is gradually set as measurement points, and correlating the esophageal pressure with each set amount of measurement fluid in the balloon probe.

[0017] The calibration controller is designed to monotonically vary the amount of measurement fluid in at least two steps to approach each measurement point from a start value until an end value is reached.

[0018] The measuring fluid is in particular air.

[0019] In particular, the calibration system may further include a device (fluid discharge device) for discharging the measurement fluid from the balloon probe after the balloon probe is positioned in the esophagus. One or more valves may be provided in both the device for filling the balloon probe with the measurement fluid after the balloon probe is positioned in the esophagus and the device for discharging the measurement fluid from the balloon probe after the balloon probe is positioned in the esophagus, and the valves are arranged in a delivery line for the measurement fluid that is fluidly connected to the balloon probe. When the measurement fluid in the balloon probe is at positive pressure, the fluid discharge device can be realized simply by controlling a valve in a fluid line that is fluidly connected to the balloon probe.

[0020] The device for filling the balloon probe with a measurement fluid after positioning the balloon probe in the esophagus may include a pump device for pumping the measurement fluid into the balloon probe. In this case, the pump device may be configured to draw (eject) the measurement fluid from the balloon probe. Alternatively, the fluid ejection device may comprise the pump device.

[0021] In a further embodiment, the device for filling the balloon probe with the measurement fluid and the device for discharging the measurement fluid from the balloon probe may be provided with a flow sensor, in particular a mass flow sensor designed to determine the amount of measurement fluid introduced into or discharged from the balloon probe. For example, the amount of measurement fluid introduced into or discharged from the balloon probe can be determined by integrating the flow rate measured by the flow sensor over a period between a start and end time. When the flow rate of the measurement fluid is determined based on a differential pressure, the flow sensor may be used to detect the intraesophageal pressure within the balloon probe. A separate pressure sensor may also be provided.

[0022] The calibration controller may be implemented as an independent component "in hardware." Alternatively, the calibration controller may be realized as a computer program product, i.e., by a corresponding software program running on a processor, in particular a microprocessor or microcontroller. In this case, the software may be stored on a suitable local storage medium or a storage medium that can be accessed over a network. The software includes instructions coded as a computer program that, when loaded into the processor's RAM memory and translated into machine language, cause the processor to carry out the procedures described in more detail herein. Of course, a mixture of hardware and software implementations is also conceivable. A microprocessor or microcomputer may be associated with, and in particular be part of, the control of the calibration system.

[0023] The term "monotonic" as used herein means that the amount of measurement fluid in the balloon probe always changes in the same direction during a measurement cycle. This means that the amount of measurement fluid either continues to decrease or continues to increase during the measurement cycle between the start and end values for reaching each measurement point. In this context, a measurement cycle is defined by approaching measurement points between the start and end values. The start and end values of a measurement cycle can be defined by a predetermined amount of measurement fluid being introduced into or discharged from the balloon probe. Alternatively, the start and end values can be defined by a predetermined value of the pressure detected in the balloon probe. It has been found to be simpler and faster, at least, to always discharge or introduce a predetermined amount of measurement fluid into or from the balloon probe when approaching successive measurement points between the start and end values (which may not be included).

[0024] According to the present invention, the calibration can be significantly accelerated by monotonically passing through the measurement range between the start and end values in a measurement cycle. This is because successive measurement points can be approached directly one after the other within a measurement cycle, from the start value to at least the end value. In particular, the calibration procedure does not require intermediate steps for emptying the balloon probe or for setting reproducible initial conditions for each measurement point. Furthermore, there is no need to wait for pressure equalization or pressure relaxation. It has been found that omitting the step of setting the same initial conditions for each measurement point does not have a significant negative effect on the calibration, resulting in an unacceptable calibration. In particular, any hysteresis effects do not interfere with the calibration, since all measurement points within a measurement cycle are affected in approximately the same way.

[0025] Particular embodiments of the calibration system according to the invention may comprise one or more of any of the features described below. If a feature is exclusively relevant to an embodiment, this is explicitly indicated below. Thus, the features described below can be combined in any way with each of the features described above or below, unless expressly excluded.

[0026] As mentioned above, the calibration system may further comprise a fluid ejection device designed to eject the measurement fluid from the balloon probe. The calibration controller controls the fluid ejection device to monotonically decrease the amount of measurement fluid in the balloon probe in at least two steps from a start value to an end value to approach each measurement point. This control can be performed, for example, by temporarily opening a valve in a delivery line in fluid communication with the balloon probe. Alternatively, a corresponding pump device may be actively actuated.

[0027] The calibration controller may be configured to introduce an amount of measurement fluid into the balloon probe (46) between a start value and an end value that is greater than the upper limit of the measurement range associated with the measurement cycle during at least a first measurement cycle for filling the balloon probe with measurement fluid. In this case, the start value defining the start of the measurement cycle is approached only after a first amount of measurement fluid has been discharged from the balloon probe. The calibration controller may control the arrangement for initially filling the balloon probe with an amount of measurement fluid greater than the amount of measurement fluid corresponding to the start value. Thereafter, the calibration controller may control the fluid discharge device to discharge the measurement fluid from the balloon probe until the amount of measurement fluid in the balloon probe reaches the amount corresponding to the start value.

[0028] These measures allow the balloon probe to be overstretched to some extent before the start of the next measurement cycle. This allows the measurement cycle to cover the entire usable measurement range, and the pressure measured by the balloon probe varies approximately linearly with the amount of measurement fluid in the balloon probe. In the procedure according to the present invention, which involves overstretching the balloon probe before it approaches the starting value, the pressure measured by the balloon probe decreases approximately linearly with the amount of measurement fluid in the balloon probe, at least in the middle of the measurement cycle. The linear decrease defines a range between the upper and lower limit filling amounts of measurement fluid in the balloon probe, which can be used as the measurement range of the esophageal catheter.

[0029] Because measurements are performed in vivo, i.e., using a balloon probe placed in the patient's esophagus, the slope of the esophageal pressure / measurement fluid volume curve in the linear portion used as the measurement range is determined by the distensibility of the esophagus, and less by the distensibility of the balloon probe. In the linear portion, as the amount of measurement fluid decreases, the esophageal stretch decreases and the cross-sectional area of the esophagus decreases, but the distensibility remains almost unchanged.

[0030] In the range above the linear portion of the measurement range, the esophageal distensibility reaches a maximum, at least if the diameter of the balloon probe is large enough. At this point, the balloon probe will hardly expand any further, even if the amount of fluid filled in it increases further. Therefore, the pressure in the esophageal balloon increases more rapidly with an increase in the amount of measurement fluid than in the linear portion of the measurement range. As a general rule, the starting value of the measurement fluid is selected so that, at least in the first measurement cycle, the starting value of the measurement fluid for the esophageal pressure is in the range above the linear portion of the measurement range.

[0031] In a further embodiment, the calibration controller may be designed to perform at least two measurement cycles in succession, where the measurement ranges of the at least two successive measurement cycles may be different, in particular the measurement range of the subsequent measurement cycle may be determined by the preceding measurement cycle.

[0032] For example, a first measurement range between a first start value and a first end value may be traversed in a preceding measurement cycle to find a linear range where esophageal distensibility remains approximately constant, and a subsequent measurement cycle may then provide finer gradation of measurement points between a second start value and a second end value.

[0033] Furthermore, the calibration controller may be designed to set different distances between successive measurement points in a preceding measurement cycle than in a subsequent measurement cycle, in this context the expression "distance between measurement points" is used to refer to the difference between the volumes of relevant measurement fluid in the balloon probe.

[0034] For example, by setting a relatively large distance between successive measurement points in a previous measurement cycle, it is possible to identify a range in which the intraesophageal pressure detected by the esophageal catheter changes approximately linearly with the amount of measurement fluid in the balloon probe, and in the next measurement cycle, it is possible to find the optimal amount of measurement fluid to fill the esophageal catheter by passing through this linear range between the maximum and minimum amounts of measurement fluid in smaller steps.

[0035] Furthermore, the calibration controller may be configured to adaptively determine the step size or increment between successive measurement points within the measurement range during a measurement cycle, for example, using a gradient method such as the Newton algorithm to adaptively determine the increment.

[0036] When multiple measurement cycles are performed in succession, it is useful to initially "overstretch" the balloon probe to a certain degree before each measurement cycle, i.e., to initially introduce a larger amount of measurement fluid than corresponds to the starting value of each measurement cycle. In this case, the calibration controller may be designed to prevent the balloon probe from being completely emptied of measurement fluid between the preceding and succeeding measurement cycles. In particular, in such an embodiment, the cavity or volume enclosed by the balloon probe is not completely emptied even between successive measurement cycles. Rather, the exact amount of measurement fluid present in the balloon probe before the start of a measurement cycle is not important; starting from any starting value, a larger amount than required for the starting value may be introduced. Furthermore, the exact amount by which the balloon probe is overstretched is often not important at all. This is because the desired starting value for each measurement cycle can be determined from the detected esophageal pressure when withdrawing measurement fluid from the balloon probe to reach the starting value for the subsequent measurement cycle.

[0037] However, to improve accuracy, the balloon probe may be set to a predetermined "zero state" by evacuating or otherwise discharging the measurement fluid from the balloon probe until a predetermined negative pressure (e.g., -20 hPa relative to ambient pressure) is reached before the start of a measurement cycle, or at least before the start of the first measurement cycle if multiple consecutive measurement cycles are performed. In this way, the calibration procedure can be reliably started from a predetermined initial state of the balloon probe (e.g., a completely collapsed state of the balloon probe). From this zero state, measurement fluid is introduced or pumped into the balloon probe until the balloon probe is overfilled to a predetermined pressure that exceeds the starting value of the first measurement cycle. From this state, the calibration procedure can be performed by monotonically successively approaching multiple measurement points between the starting and ending values.

[0038] The calibration controller may be designed to ascertain the measured esophageal pressure at the end of inspiration and the measured esophageal pressure at the end of expiration for each measurement point, i.e., for each set amount of measurement fluid in the balloon probe, between the start and end values of the measurement cycle (which preferably includes a start and end value), and then determine the difference between the esophageal pressure at the end of inspiration and the esophageal pressure at the end of expiration.

[0039] In this regard, the calibration controller may be designed to determine the maximum difference between the esophageal pressure at the end of inspiration and the esophageal pressure at the end of expiration (maximum pressure) for a range between (preferably including) a start value of the measurement fluid volume in the balloon probe and an end value of the measurement fluid volume in the balloon probe. The measurement fluid volume in the balloon probe corresponding to the maximum pressure corresponds to the optimal filling volume of the balloon probe, i.e., the measurement fluid volume in the balloon probe at which ventilation occurs.

[0040] Furthermore, the calibration controller may be designed to verify the esophageal pressure measurement at the end of inspiration and the esophageal pressure measurement at the end of expiration for each measurement point between the start and end values during ventilation.

[0041] Therefore, it is not necessary to interrupt the ventilation or breathing cycle to obtain esophageal pressure measurements. In particular, there is no need to establish a dead time during which the flow of ventilation or breathing gas is stopped and the airway is occluded in order to confirm these measurements. Therefore, the patient can continue to be ventilated while the esophageal catheter is being calibrated or recalibrated. This is a major advantage for the patient, as it not only avoids interruptions or interference with ventilation, but also allows the esophageal catheter calibration to be performed as close to life as possible.

[0042] Furthermore, the calibration controller may be configured to compare the difference between the esophageal pressure at the end of inspiration and the esophageal pressure at the end of expiration determined for each measurement point, and then, when the determined differences over a number of consecutive measurement points are each within a predetermined variation range centered on a maximum value, determine the optimal amount of measurement fluid in the balloon probe as an amount having a predetermined distance from the upper and / or lower ends of the number of consecutive measurement points.

[0043] For example, it may be determined that the volume of measurement fluid corresponding to the optimal filling volume of the balloon probe is closer to the lower end of the range of approximately equal pressure differences near the maximum than to the upper end of the range of approximately equal pressure differences. In this case, for example, the volume of measurement fluid in the balloon probe corresponding to the optimal filling volume of the balloon probe (the "optimal filling volume") may be greater than the volume of measurement fluid corresponding to the lower end of the range of approximately equal pressure differences by one-third of the distance between the volume of measurement fluid in the balloon probe corresponding to the upper end of the range of approximately equal pressure differences and the volume of measurement fluid in the balloon probe corresponding to the lower end of the range of approximately equal pressure differences.

[0044] In particular, the calibration controller may be designed to ascertain multiple measurements, particularly multiple pairs of measurements, of the esophageal pressure at end-inspiration and end-expiration for each measurement point between (and possibly including) a start value and an end value. This is typically done over successive ventilation cycles. The calibration controller may then be configured to determine a mean value and statistical variance or scatter for each measurement point based on the multiple measurements or pairs of measurements or a parameter derived therefrom, particularly the difference (pressure difference) between the esophageal pressure at end-inspiration and the esophageal pressure at end-expiration, and to determine the number of measurements per measurement point such that the resulting mean value is considered statistically significant.

[0045] As a general rule, the greater the statistical variability of the obtained measurements, the more respiratory cycles should be used as the basis for determining the pressure difference measurements associated with each measurement point. For example, cardiogenic vibrations or movements may play a role here. Such effects can be better distinguished by increasing the number of respiratory cycles per measurement. In particular, the average can be the arithmetic mean. However, averages such as the geometric mean are also conceivable.

[0046] Statistical dispersion can be expressed in particular by Gaussian standard deviation. In this case, it is conceivable to define a 2 sigma level as statistically significant, i.e., a Gaussian standard deviation of 95% or more is considered significant. In another variant, the determination of dispersion can proceed adaptively, for example, by using the change in the mean value after each new measurement as a measure of the significance of each measurement point. The smaller the change in the mean value after each measurement, the higher the significance. Measurements are repeated for each measurement point until the change in the mean value after the last measurement is smaller than a predetermined threshold. Then, the next measurement point can be started, e.g., by withdrawing a predetermined amount of measurement fluid from the balloon probe.

[0047] In a further embodiment, the calibration controller may be configured to monitor, for each measurement point between the start and end values, whether the esophageal pressure measurement (when multiple pressure differentials are measured at each measurement point) is affected by external conditions, and to discard each measurement if such an external condition is detected. An example of such an external condition is a patient's swallowing effort. Instead of discarding or halting the entire calibration, only the measurement affected by the external condition may be discarded. In particular, new measurements at each measurement point are immediately confirmed thereafter. The calibration procedure can then continue normally. In this way, artifactual measurements can be eliminated "in real time" without stopping or interrupting the calibration procedure for long periods of time. For example, if the patient makes a swallowing effort during one or more measurements, this may cause the patient to make a new swallowing effort, which would significantly increase the time required to restart the entire calibration procedure after detecting an external condition. This represents a significant improvement over known methods, which require operator judgment, are not automated, or must perform automatic calibration without considering external conditions. A calibration is discarded entirely only if analysis of the data reveals that at least one or several of the measurements used in the calibration in question may be subject to external influences such as swallowing effort. Therefore, it is not possible to know with certainty in advance before starting a calibration whether the calibration will be valid or whether it must be discarded.

[0048] Abnormal external conditions, such as a patient's efforts to swallow, can be detected by monitoring the esophageal pressure over time, particularly at the machine-specified end-of-inspiration and end-of-exhalation times, as changes in the pressure signal occur.

[0049] The calibration controller may be designed to suspend calibration if such a disturbance occurs, and resume calibration only when the detected esophageal and airway pressures indicate that no further disturbances will occur.

[0050] The calibration controller may further be designed to calculate a quality index based on the data acquired during the calibration procedure. The quality index represents a weighted summary of the influence of various factors. In such an embodiment, the quality index can be used to determine whether to modify ventilation parameters based on esophageal pressure data. Criteria related to the quality index may include the statistical dispersion of the measurement data or the uneven course of the esophageal pressure / measurement fluid volume curve. The dispersion of the measurement values, expressed as a Gaussian standard deviation, may be used as a measure of the quality index. Furthermore, specific rules may be defined for inclusion in the quality index. An example of such a rule is to lower the quality index if swallowing by the patient is detected during the calibration procedure. The quality index may be lowered if the maximum difference between the esophageal pressure at the end of inspiration and the esophageal pressure at the end of expiration at the measurement point is outside, and especially above, the range of the curve representing the relationship between esophageal pressure and the volume of measurement fluid in the balloon probe. The quality index may also be lowered if the baseline pressure, i.e., the esophageal pressure at the end of expiration, does not change or shows a stable change over consecutive measurements, but instead changes suddenly. The quality index is also reduced if the intraesophageal pressure detected at a high fluid volume in the balloon probe is less than the value corresponding to a lower fluid volume in the balloon probe.

[0051] Additionally, the calibration controller may be designed to prevent the esophageal pressure from exceeding a predetermined maximum pressure. For example, the maximum esophageal pressure may not exceed twice the maximum airway pressure during ventilation. When this pressure is reached, the controller may stop introducing fluid into the balloon probe or expel fluid from the balloon probe. This prevents excessive stretching of the esophageal tissue. This also avoids the risk of damaging the balloon probe due to excessive stretching.

[0052] Finally, the calibration controller may be configured to control the discharge device to further gradually decrease the amount of measurement fluid in the balloon probe as each measurement point is approached, starting from a start value until an end value is reached, when a predetermined minimum value of the end-tidal esophageal pressure, for example 5 hPa, is reached or falls below it.

[0053] The invention further relates to a method, particularly for a ventilator, for automatically calibrating a desired operational fill for an esophageal catheter with a balloon probe insertable into the esophagus for determining intraesophageal pressure.

[0054] This method is a step of filling the balloon probe with a measurement fluid after placing the balloon probe in the esophagus; detecting intraesophageal pressure within the balloon probe; a step of gradually changing the amount of measurement fluid in the balloon probe, detecting the intraesophageal pressure for each amount of measurement fluid in the balloon probe set in stages as measurement points, and associating the detected intraesophageal pressure with each set amount of measurement fluid in the balloon probe; Includes:

[0055] In the method according to the present invention, the amount of the measurement fluid is monotonically changed in at least two steps from the start value to the end value in order to approach each measurement point.

[0056] In a further embodiment, the method according to the invention may further comprise at least one, in particular several, method steps implicitly mentioned above with regard to the formation of a calibration system, to avoid repetition, explicit reference is made to the detailed description of these method steps with regard to the functional features of the calibration system, in particular the functional features of the calibration controller.

[0057] Furthermore, the present invention relates to a computer program product comprising program instructions, which when executed on a data processing system, in particular a microprocessor or microcontroller for controlling an esophageal catheter with a balloon probe, performs the method or calibration system according to the invention. [Brief explanation of the drawings]

[0058] [Figure 1] FIG. 1 is a highly schematic illustration of the essential components of a ventilator, along with the intubated trachea and chest of a patient undergoing ventilation. [Figure 2] This figure shows the time course of the airway inlet pressure Paw (top), esophageal pressure Peso (middle), and the difference between the two pressures Paw-Peso over several consecutive respiratory cycles during mechanical ventilation including an occlusion maneuver. [Figure 3] FIG. 1 is a flowchart illustrating a series of in vivo calibration procedures for an esophageal catheter according to an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating the amount of measurement fluid set in the balloon probe of the esophageal catheter and the pressure detected in the balloon probe of the esophageal catheter during a calibration procedure according to an embodiment of the present invention. [Figure 5] (a) is a partial image showing the pressures detected in the balloon probe at the end of inspiration and at the end of expiration for each set amount of measurement fluid in the balloon probe during the measurement cycle; (b) is a partial image showing the resulting pressure differences between the pressure in the balloon probe at the end of inspiration and the pressure in the balloon probe at the end of expiration. DETAILED DESCRIPTION OF THE INVENTION

[0059] Further embodiments of the invention are described in detail below with reference to the drawings.

[0060] FIG. 1 shows, in a highly schematic and block diagram format, the essential components of a ventilator 10. The ventilator 10 shown in FIG. 1 is intubated into the trachea 12 of a patient undergoing mechanical ventilation. In addition to the trachea 12, FIG. 1 also highly diagrammatically illustrates the patient's lung lobes 28 and 30, heart 32, esophagus 34, and thorax 42. The ventilator 10 typically includes a tube 14 inserted a short distance into the trachea 12 through the patient's open mouth (not shown) to deliver respiratory gas to the airway. Exhaled air is similarly discharged through the tube 14, which branches upstream into a first end 16 and a second end 22. The first end 16 is connected to an airway inlet port of the ventilator 10 via an airway inlet valve 18 to apply an inspiratory pressure PInsp. When the airway inlet valve 18 is in its open position, an inspiratory pressure PInsp is applied to the airway. The second end 22 is connected to an airway outlet port of the ventilator 10 via an airway outlet valve 24 to apply an expiratory pressure PExp to the airway. When the airway outlet valve 24 is in the open position, an expiratory pressure PExp is applied to the airway.

[0061] The ventilator 10 generates inspiratory pressures PInsp and expiratory pressures PExp according to a predetermined time pattern. During inspiration, inhaled breathing gas flows toward the patient's lungs 28, 30, as shown by arrow 20 in FIG. 1, and during exhalation, expiratory breathing gas flows back from the patient's lungs 28, 30, as shown by arrow 26. Typically, during inspiration, the airway inlet valve 18 remains open, applying an inspiratory pressure PInsp, which is generally stronger than the expiratory pressure PExp, to the airway inlet. During exhalation, the airway inlet valve 18 closes, while the airway outlet valve 24 opens, applying an expiratory pressure PExp to the airway inlet.

[0062] In the present invention, any known ventilation mode can be used, such as a pressure-controlled ventilation mode, a volume-controlled ventilation mode, or a combined pressure- and volume-controlled ventilation mode. In addition to a purely mechanically controlled ventilation mode in which the ventilator 10 determines the time-dependent changes in the inspiratory pressure PInsp and, in some cases, the expiratory pressure PExp, a ventilation mode in which the mechanical ventilation is supported by the patient's spontaneous breathing, or in which the mechanical ventilation plays a role in supporting the patient's spontaneous breathing, is also contemplated. In such a ventilation mode, the time-dependent changes in the inspiratory pressure PInsp or the expiratory pressure PExp, and in particular the position of the inlet valve 18 or the outlet valve 24, are not determined solely by the ventilator 10, but the influence of the patient's spontaneous breathing is also taken into account.

[0063] The proposed calibration of an esophageal catheter equipped with a balloon probe, which is inserted into the esophagus and adapted to detect esophageal pressure for use in estimating transpulmonary pressure, is particularly suited to fully automatic ventilation modes, where ventilation is performed by a closed control loop, such as that used in adaptive assisted ventilation (ASV) developed by the applicant. Such ventilation modes are characterized by the fact that manual intervention by the operator is minimal, and the ventilator automatically sets or adjusts key ventilation parameters, such as positive end-expiratory pressure (PEEP) or maximum airway pressure (Paw_max), within predetermined ranges using an appropriate closed control loop.

[0064] The breathing gas may include ambient air, but typically contains a certain percentage of pure oxygen (hereafter referred to as FiO2) above the oxygen content of ambient air, and is typically humidified.

[0065] The flow of respiratory gas at the airway inlet is determined using an airway inlet flow sensor 36. The airway inlet flow sensor 36 is based on detecting the pressure difference dP between an input volume 38 and an output volume 40 in communication with the input volume 38, and determines the mass flow rate of respiratory gas at the airway inlet. At the same time, the value of the airway inlet pressure Paw can be derived quite easily from the pressure signal of the output volume 40.

[0066] In Figure 1, the pressure within the alveoli of the lungs 28 and 30 is designated Palv. This pressure depends on the airway inlet pressure Paw, the flow of respiratory gas V into and out of the lungs, and the airway resistance R. When the pressure between the airway inlet and the alveoli is equal, the alveolar pressure Palv is equal to the airway inlet pressure. In this state of pressure equilibrium, the flow of respiratory gas V ceases. For example, pressure equilibrium can be achieved by briefly closing the airway, i.e., by simultaneously closing the airway inlet valve 18 and the airway outlet valve 24. In this case, the closing maneuver must be continued long enough to stop the flow of gas V within the airways, typically for 1 to 5 seconds. In this state, the alveolar pressure Palv can then be determined by determining the airway inlet pressure Paw.

[0067] Respiratory gas flow is determined by the pressure difference between the alveolar pressure Palv and the airway entrance pressure Paw during both physiological and mechanical ventilation.

[0068] During purely physiological breathing, chest expansion (designated 42 in FIG. 1 ) and the resulting decrease in pressure Ppl within the pleural space or gap 44 between the chest 42 and the lungs 28, 30 creates a negative pressure difference between the alveolar pressure Palv and the airway entrance pressure Paw for inspiration, i.e., negative pressure. Exhalation occurs passively through chest relaxation and the resetting of lung tissue elasticity. Therefore, during physiological breathing, the pressure Ppl within the pleural space is always lower than the alveolar pressure Palv. Therefore, the transpulmonary pressure Ptp, defined as the difference between the alveolar pressure Palv and the pleural space pressure Ppl, is generally positive and zero when the pressures are perfectly equal.

[0069] During mechanical ventilation, respiratory gas is delivered to the lungs at positive pressure. Therefore, in mechanical ventilation, the airway inlet pressure (Paw = PInsp) is greater than the alveolar pressure (Palv), which is greater than the pressure in the pleural space (Ppl) during inspiration. From these pressure relationships, the transpulmonary pressure (Ppl) in mechanical ventilation is positive during inspiration. During expiration, the airway inlet is subjected to an airway pressure (PExp) lower than the alveolar pressure (Palv), causing respiratory gas to flow out of the alveoli. If the airway pressure (PExp) is very low, at the end of expiration when there is little gas remaining in the lungs, the pressure in the pleural space (Ppl) may exceed the alveolar pressure (Palv), causing partial alveolar collapse. In this case, the transpulmonary pressure (Ptp) is negative.

[0070] Alveolar collapse can be prevented during expiration by applying additional positive airway pressure to the airway inlet, i.e., permanent positive airway pressure applied to the airway inlet during both inspiration and expiration. This positive airway pressure is called positive end-expiratory pressure, or PEEP.

[0071] Thus, the transpulmonary pressure Ptp is a relevant parameter for setting PEEP. However, it cannot be directly sensed, and as mentioned above, it cannot be determined from pressures sensed periodically during mechanical ventilation.

[0072] 1 shows a schematic diagram of an additional balloon probe 46 for measuring the pressure in the esophagus 34, indicated by the esophageal pressure Peso. The balloon probe 46 is in the form of a balloon and is attached to a catheter 48 inserted into the esophagus 34. The balloon probe 46 inscribes the wall of the esophagus 34 and provides the pressure exerted on the esophagus 34 at the location of the balloon probe 46. This pressure is a good approximation of the pressure Ppl in the pleural space when the patient is in the appropriate position. For details of the balloon probe 46 for detecting the esophageal pressure Peso and how to use this probe, see, for example, Benditt J. Resp. Care 2005, 50: pp. 68-77 (Non-Patent Document 3).

[0073] Determining the transpulmonary pressure Ptp requires information about the alveolar pressure Palv in addition to the pressure in the pleural space Ppl. To simply determine the alveolar pressure at a given time t, a flow sensor 36 may be used to detect the respiratory gas flow V(t). The alveolar pressure at time t can be estimated using the relationship Palv(t) = Paw(t) - R * V(t), where R represents airway resistance. For a given patient, airway resistance is an essentially unchanging or relatively slowly changing variable and can be determined according to methods known in the art. See, for example, Lotti IA et al., Intensive Care Med. 1995, 21:406-413. Since the transpulmonary pressure Ptp_ee at the end of expiration is most important for determining the appropriate PEEP, in connection with the automatic setting of PEEP, the determination of the alveolar pressure Palv is preferably performed at the end of expiration according to the following formula:

[0074] Ptp_ee=Palv_ee-Peso_ee=Paw_ee-R*V_ee-Peso_ee.

[0075] PEEP is set or adjusted so that Ptp_ee always remains positive, or at least does not fall significantly below zero.

[0076] The above-described method for determining alveolar pressure Palv is quite easy to implement in the automated ventilator 10, however, it only roughly estimates the appropriate PEEP, which is primarily due to airway resistance R, which is difficult to estimate accurately and, in practice, shows a certain trend over the course of treatment.

[0077] An alternative method for determining the alveolar pressure Palv is based on a short-term occlusion maneuver, in which both the airway inlet valve 18 and the airway outlet valve 24 are kept closed simultaneously. In the occlusion state, the prevailing pressure in the airways is equalized. By performing such an occlusion maneuver at the end of expiration, the pressure in the airways after a sufficient occlusion period is approximately equal to the alveolar pressure Palv at the end of expiration. This pressure can be detected very easily using a pressure probe placed at the airway inlet to measure the airway pressure Paw. Reference numeral 50 in Figure 2 indicates an occlusion state.

[0078] Figure 2 shows the time course of the airway pressure Paw (top), the esophageal pressure Peso (middle) measured by the balloon probe 46, and the difference between the two pressures Paw-Peso during successive respiratory cycles when an occlusion maneuver is performed. Figure 2 clearly shows the respiratory cycle, consisting of inspiration (increasing airway pressure Paw) and expiration (decreasing airway pressure Paw). The esophageal pressure Peso follows the airway pressure Paw, but in a damped form. The difference Paw-Peso shown in the lower curve corresponds fairly well to the transpulmonary pressure Ptp when respiratory gas is slowly delivered and pressures are constantly balanced. However, because the respiratory gas flow varies, this condition does not actually occur, except at the points indicated by reference numerals 50 and 52. At the locations indicated by reference numerals 50 and 52, short occlusions are performed at the end of expiration (reference numeral 50, between approximately 8 and 12 seconds) and at the end of inspiration (reference numeral 52, between approximately 18.5 and 24.5 seconds), respectively. In both cases, the occlusions last approximately 4 seconds, which corresponds roughly to the duration of one respiratory cycle shown. Generally, the occlusion should be maintained until pressure equalizes within the airway and gas flow ceases.

[0079] At the end of the time period designated by reference numeral 50 (between approximately 11 and 12 seconds, e.g., during the last approximately 200 milliseconds of the occlusion), the pressure Paw-Peso shown by the third line in FIG. 2 corresponds closely to the transpulmonary pressure Ptp_ee at the end of expiration. Ptp_ee can be determined, for example, by averaging Paw-Peso over the aforementioned period. At the end of the time period designated by reference numeral 52 (between approximately 21.5 and 22.5 seconds, e.g., during the last approximately 200 milliseconds of the occlusion), the pressure Paw-Peso shown by the third line in FIG. 2 corresponds closely to the transpulmonary pressure Ptp_ei at the end of inspiration. Ptp_ei can be determined, for example, by averaging Paw-Peso over the aforementioned period.

[0080] Determining transpulmonary pressure Ptp using the above-described occlusion maneuver is more accurate than the above-described method using airway resistance R. However, it requires an occlusion maneuver at the end of expiration or end of inspiration. Therefore, by its very nature, this method interrupts the respiratory cycle, and the duration of the occlusion has a more significant effect than the duration of the respiratory cycle. For this reason, it is advisable to proceed using the airway resistance method by checking fairly frequently, for example, every breath or every n breaths (n>1), whether the PEEP and / or peak airway pressure settings remain within specifications and whether the resulting transpulmonary pressure Ptp_ee value is within a certain specification for the normalized transpulmonary pressure Ptp_ee_ideal. If this check reveals that they are not within specifications and new (higher or lower) values for PEEP or peak airway pressure are required, an occlusion maneuver is performed in the next respiratory cycle at the end of expiration, and a new value for PEEP is determined based on the occlusion, as described above. Alternatively, the occlusion maneuver may be repeated every n respiratory cycles as described above, where n>1, for example n=10, 50, or 100.

[0081] As mentioned above, a prerequisite for determining transpulmonary pressure Ptp using an esophageal catheter 48 equipped with a balloon probe 46 is a certain relationship between the transpulmonary pressure Ptp detected within the balloon probe 46 and the esophageal pressure Peso. Ideally, the pressure Peso detected within the balloon probe 46 should closely match the pressure within the pleural space Ppl, so that transpulmonary pressure Ptp results from the difference between the airway pressure Paw and the esophageal pressure Peso. However, in reality, with the balloon probe 46 inserted into the esophagus 34, the relationship between the pressure Peso measured within the catheter 48 and the pressure within the pleural space Ppl during ventilation periodically changes. Such changes usually cannot be clearly attributed to a specific cause or event and often occur insidiously.

[0082] For this reason, it is desirable to calibrate such esophageal catheters 48. However, techniques proposed in the prior art for calibrating esophageal catheters in vivo have proven to be very sensitive and time-consuming, making these techniques unsuitable for use during patient ventilation, particularly for continuous monitoring in order to properly calibrate the esophageal catheter during ventilation.

[0083] The present invention provides a calibration system 80 that improves the accuracy of pressure measurements made by a catheter 48 inserted into the esophagus 34. In particular, the calibration system 80 of the present invention more accurately reproduces the pressure Ppl within the pleural space via the esophageal catheter 48 and provides measurements that respond more quickly to changing environmental conditions during continuous ventilation. This allows the esophageal catheter 48 to be calibrated during ventilation without interrupting ventilation. Note that the present invention is also applicable when ventilation is performed using a fully automatic ventilation mode, for example, closed-loop ventilation such as adaptive assisted ventilation (ASV ventilation) developed by the applicant.

[0084] The calibration system 80 according to the present invention includes a calibration controller 60. The calibration controller 60 is designed to gradually change the amount of measurement fluid in the balloon probe 46, and records the esophageal pressure Peso detected by the pressure sensor for each of the amounts of measurement fluid in the balloon probe set as measurement points, thereby correlating the esophageal pressure with each set amount of measurement fluid in the balloon probe. For this purpose, the pressure signal Peso detected by the balloon probe 46 is also transmitted to the calibration controller 60.

[0085] Calibration system 80 includes a pump mechanism 62 configured to introduce and expel measurement fluid into and from balloon probe 46 when balloon probe 46 is positioned within esophagus 34. Pump mechanism 62 also includes a valve 64 disposed within a measurement fluid delivery line 66 that is in fluid communication with balloon probe 46. When the measurement fluid within balloon probe 46 is under positive pressure, measurement fluid can be drawn from balloon probe 46 simply by actuating valve 64 without the assistance of an actual pump.

[0086] The calibration system 80 further includes a flow sensor 68, particularly a mass flow sensor, configured to determine the amount of measurement fluid introduced into or discharged from the balloon probe 46. For example, the amount of measurement fluid introduced into or discharged from the balloon probe 46 can be determined by integrating the flow rate measured by the flow sensor 68 over a period of time between a start time and an end time, respectively. For example, the flow sensor 68 may determine the mass flow rate of the measurement fluid based on a differential pressure. In this case, the flow sensor 68 can also be used to detect the esophageal pressure Peso within the balloon probe 46.

[0087] The calibration controller 60 may be implemented as a separate component "in hardware." Alternatively, the calibration controller may be realized as a computer program product, i.e., by a corresponding software program running on a processor, in particular a microprocessor or microcontroller. In this case, the software may be stored on a suitable local storage medium or a storage medium accessible over a network. The software includes instructions coded as a computer program that, when loaded into the processor's RAM memory and translated into machine language, causes the processor to execute the procedures described in more detail herein. Of course, a mixture of hardware and software implementations is also possible. A microprocessor or microcomputer may be associated with, and in particular be part of, the control of the calibration system 80.

[0088] FIG. 3 is a flow chart illustrating a sequence of steps for in vivo calibration of an esophageal catheter 48 according to one embodiment of the present invention.

[0089] FIG. 4 shows a schematic diagram of the change over time in the amount of measurement fluid Vballoon placed in the balloon probe 46 of the esophageal catheter 48, as well as the pressure Peso detected within the balloon probe 46 of the esophageal catheter 48, during a calibration procedure according to one embodiment of the present invention.

[0090] The calibration controller 60 is designed to monotonically change the amount of measurement fluid Vballoon in the balloon probe 46 in at least two steps as it approaches each measurement point S1, S2, M1, M2...M7, E1, E2, E3, from a starting value S2 until it reaches an ending value E3.

[0091] The measuring fluid is in particular air.

[0092] The calibration procedure 100 shown in Figure 3 begins at step 102. First, at step 104, the measurement fluid is discharged from the balloon probe 46 until a predetermined initial pressure is generated within the balloon probe 46. The state established at step 104 is indicated by "N" in Figure 4.

[0093] Thereafter, in step 106, the measurement fluid is again pumped into the balloon probe 46 until the pressure inside the balloon probe 46 reaches a predetermined positive pressure that exceeds the measurement range expected in the measurement cycle. The state established in step 104 is indicated by "D1" in FIG. 4.

[0094] All other measurement points approached in subsequent steps 108-130 are designated in FIG. 4 as S1, S2, M1-M7, E1, E2, E3.

[0095] In the state set in step 106, the balloon probe 46 is clearly overstretched. This can be seen in Figure 4, where the value of the esophageal pressure Peso detected by the balloon probe 46 is significantly higher than the values at all other nearby measurement points S1, S2, M1-M7, E1, E2, and E3.

[0096] 4 and 5, the upper limit of the measurement range is indicated by O, and the lower limit of the measurement range is indicated by U. In the calibration procedure shown in FIGS. 4 and 5, the lower limit U of the measurement range is at measurement point M7, and the upper limit O of the measurement range is at measurement point M1. The amounts of measurement fluid Vballoon in the balloon probe 46 corresponding to these are selected as reference amounts for the upper limit O and the lower limit U, respectively. Therefore, O indicates the amount of measurement fluid in the balloon probe 46 at measurement point M1, which corresponds to the upper limit of the measurement range. Furthermore, U indicates the amount of measurement fluid in the balloon probe 46 at measurement point M7, which corresponds to the lower limit of the measurement range.

[0097] Following step 106, in step 108, a predetermined amount of measurement fluid is discharged from the balloon probe 46. This sets the amount of measurement fluid in the balloon probe 46 to a level at which a pressure Peso slightly exceeding the expected intraesophageal pressure within the measurement range is detected (see measurement points M1 to M7). This state is indicated by "S1" in FIGS. 4 and 5. Alternatively, the measurement fluid may be discharged from the balloon probe 46 until a predetermined value of Peso slightly exceeding the expected intraesophageal pressure within the measurement range is detected (see measurement points M1 to M7).

[0098] During the "S1" state, the esophageal pressure Peso is detected within the balloon probe 46 over multiple respiratory cycles. As is apparent from Figure 4, the esophageal pressure Peso reflects each respiratory cycle, but only to a very small extent, indicating the low sensitivity of the balloon probe 46.

[0099] Following step 108, in step 110, a predetermined amount of measurement fluid is expelled from balloon probe 46 until the state indicated as "S2" in Figures 4 and 5 is reached. In step 110, the same procedure described for step 108 is repeated for the "S2" state. Again, the sensitivity of balloon probe 46 is low, as it can only detect a small number of respiratory cycles.

[0100] After step 110 is completed, in step 112, a predetermined amount of measurement fluid is again expelled from the balloon probe 46 until the state indicated by "M1" in Figures 4 and 5 is reached. In step 112, the same procedure as described for step 108 is repeated for the "M1" state.

[0101] 4 and 5, the esophageal pressure Peso clearly reflects each respiratory cycle at measurement point M1 (and at subsequent measurement points M2 to M7). Here, the maximum value of the Peso curve corresponds to the esophageal pressure Peso_insp in the balloon probe 46 detected at the end of inspiration, and the minimum value of the Peso curve corresponds to the esophageal pressure Peso_exp in the balloon probe 46 detected at the end of expiration.

[0102] This procedure is then repeated several times as measurement points M2-M7, E1, and E2 are approached (see steps 114-130). At each of measurement points M2-M7, E1, and E2, the esophageal pressure Peso in the balloon probe 46 is detected over multiple respiratory cycles by the same method as described with reference to steps 108, 110, and 112. The maximum value of the Peso curve corresponds to the esophageal pressure Peso_insp in the balloon probe 46 detected at the end of inspiration, and the minimum value of the Peso curve corresponds to the esophageal pressure Peso_exp in the balloon probe 46 detected at the end of expiration.

[0103] In the flowchart of FIG. 3, steps 110 to 130 are not shown in detail.

[0104] 4, these steps correspond to specific amounts of the measurement fluid in the balloon probe 46 and are designated as measurement points S1, S2, M2 to M7, E1, and E2. The amount of the measurement fluid in the balloon probe 46 always changes monotonically, in particular, always decreases, during the transition from one measurement point to the next at measurement points S1, S2, M1 to M7, E1, and E2. In this case, the step width or increment, i.e., the amount by which the measurement fluid in the balloon probe 46 changes during the transition from one measurement point to the next, is always the same. However, the amount of change of the measurement fluid in the balloon probe 46 may be selected to be different in each step, as long as the change always occurs in the same direction (i.e., the amount always decreases or always increases). Because the correspondence between each measurement point in the balloon probe 46 and its associated amount of measurement fluid is unique, for the sake of simplicity, hereinafter, not only will each measurement point be designated as D1, S1, S2, M1-M7, E1, E2, etc., but also each associated amount of measurement fluid in the balloon probe 46 will be designated similarly. For example, M1 represents both the measurement point M1 and the associated amount of measurement fluid in the balloon probe 46. Furthermore, M1, which represents the amount of measurement fluid in the balloon probe 46, also represents the upper limit O of the measurement range. Similarly, for example, M7 represents both the measurement point M7 and the associated amount of measurement fluid in the balloon probe 46. Furthermore, M7, which represents the amount of measurement fluid in the balloon probe 46, also represents the lower limit U of the measurement range. The same applies to the other measurement points M2-M6.

[0105] In Figure 4, the detected esophageal pressure signal Peso clearly represents each respiratory cycle at measurement points M1 to M7. However, from measurement point E1 onward, the detected esophageal pressure signal Peso begins to become unstable. This is because the balloon probe 46 is not fully filled with the measurement fluid, and therefore falls into a range where it cannot adequately respond to pressure changes caused by each respiratory cycle. At measurement points E2 and E3, the balloon probe 46 is completely collapsed, and the esophageal pressure Peso is considered to barely reflect the respiratory cycle. The measurement cycle ends when measurement point E3 is reached. Measurement point E3 is different in that the esophageal pressure Peso is not detected and cannot be associated with it.

[0106] State M1 indicates the upper limit O of the measurement range that can be used for the measurement cycle. Therefore, the actual calibration is limited to this measurement range, defined by measurement points M1 to M7. As is clear from FIG. 4, the esophageal pressure Peso detected in the balloon probe for all measurement points M1 to M7 within the measurement range is substantially within the same range. This indicates that the balloon probe 46 and the esophageal wall form an essentially elastic system that expands or contracts depending on the amount of measurement fluid in the balloon probe 46. These ratios remain the same until the lower limit U of the measurement range, at measurement point M7, is reached. Between measurement points M1 and M7, and thus within the measurement range between upper limit O and lower limit U of the amount of measurement fluid in the balloon probe 46, there is an approximately linear relationship between each predetermined amount of measurement fluid from the balloon probe 46 and the detected esophageal pressure Peso. The slope of the line representing this linear relationship is approximately the same for the relationship between the esophageal pressure Peso_insp detected at the end of expiration and a given volume of measurement fluid in the balloon probe 46, and for the relationship between the esophageal pressure Peso_exp detected at the end of expiration and a given volume of measurement fluid in the balloon probe 46. In regions outside the measurement range (measurement points S1, S2, E1, E2), the relationship between the given volume of measurement fluid from the balloon probe 46 and the detected esophageal pressure Peso changes significantly. This relationship is no longer approximately linear in these regions, indicating that the detected esophageal pressure Peso fluctuates more significantly depending on whether the volume of measurement fluid in the balloon probe 46 is large or small. Furthermore, for a given volume of measurement fluid in the balloon probe 46, the difference between the esophageal pressure Peso_insp detected at the end of each expiration and the esophageal pressure Peso_exp detected at the end of each expiration rapidly decreases in regions (measurement points S1, S2, E1, E2) outside the actual measurement range (measurement points M1 to M7).

[0107] The significance of this calibration procedure is illustrated in Figure 5. Figure 5a shows a schematic representation of the esophageal pressure Peso_insp detected in the balloon probe 46 at the end of inspiration and the esophageal pressure Peso_exp detected in the balloon probe 46 at the end of expiration for each volume of measurement fluid Vballoon in the balloon probe 46, which are set as measurement points S1, S2, M1 to M7, E1, and E2 during a measurement cycle. Figure 5b shows the resulting differential pressure dP between the esophageal pressure Peso_insp in the balloon probe at the end of inspiration and the esophageal pressure Peso_exp in the balloon probe at the end of expiration for each measurement point S1, S2, M1 to M7, E1, and E2.

[0108] As is clear from FIG. 5, within the range of measurement points M1 to M7, the changes in the esophageal pressure Peso_insp detected by the balloon probe 46 at the end of inspiration and the esophageal pressure Peso_exp detected by the balloon probe 46 at the end of expiration are approximately linearly related to the changes in the volume of measurement fluid Vballoon in the balloon probe 46. The resulting slopes of the two curves Peso / Vballoon are very flat and essentially similar to the slopes for the esophageal pressure values Peso_insp at the end of inspiration and Peso_exp at the end of expiration. Therefore, the difference dP between the esophageal pressure Peso_insp detected by the balloon probe 46 at the end of expiration and the esophageal pressure Peso_exp detected by the balloon probe 46 at the end of expiration remains substantially constant within the measurement range defined by measurement points M1 to M7. However, this difference dP becomes very small outside the measurement ranges defined by measurement points S1, S2, E1, and E2. Therefore, optimal calibration of the esophageal catheter 48 is performed with an amount of measurement fluid within the measurement range defined by the measurement points M1 to M7, i.e., within the range of the amount of measurement fluid within the balloon probe 46 between the two vertical dotted lines O and U shown in FIG. 5a). Then, the calibration controller 60 selects, as a result of the calibration, an amount of measurement fluid within the balloon probe 46 that is within the measurement range of the measurement fluid defined by the measurement points M1 to M7. This amount is indicated by the vertical line K in FIG. 5b, and in FIG. 4, the point where the curve Vballoon extends horizontally is indicated by K, and is set as the amount of fluid within the balloon probe 46 after the calibration procedure is completed.

[0109] Figure 5b) shows how to select the optimal amount of measurement fluid in the balloon probe 46 within the measurement range defined by measurement points M1 to M7. Within the measurement range, the measurement point at which the difference dP between the esophageal pressure Peso_insp detected by the balloon probe 46 at the end of inspiration and the esophageal pressure Peso_exp detected by the balloon probe 46 at the end of expiration is maximized is first found. In the example shown in Figure 5b), this is measurement point M4. An allowable variation range around this maximum difference dPmax is then determined. The difference dP value within the variation range should not be significantly different from the maximum value dPmax. In the example shown in Figure 5b), the allowable variation range is 10% of the maximum difference dPmax at measurement point M4. This variation range is indicated by the dashed line r in Figure 5b). The differences dP determined for measurement points M3, M4, M5, M6, and M7 are within the variation range. All of these measurement points are adjacent to measurement point M4 and to each other. Therefore, the range of the amount of measurement fluid in the balloon probe 46 between measurement points M3 and M7 is considered to be equivalent in terms of filling the balloon probe 46 with the measurement fluid. This range is indicated by the vertical dashed lines a and b in FIG. 5b. The center of the range between lines a and b is selected as the optimal amount of measurement fluid in the balloon probe 46. In this way, the optimal amount of measurement fluid in the balloon probe 46 can be obtained as a result of calibration (see vertical line K in FIG. 5b). This amount K is set as the amount of fluid in the balloon probe 46 after the calibration procedure is completed (see the rightmost portion of the Vballoon curve in FIG. 4).

[0110] After the calibration procedure is completed, calibration system 80 again introduces an amount of measurement fluid into the balloon probe in step 132 that clearly exceeds the amount corresponding to measurement points M1-M7 of the measurement range. This step again overstretches balloon probe 46 (this state is indicated by "D2" in FIG. 4), and then, in step 134, expels a corresponding amount of measurement fluid from balloon probe 46, thereby establishing the calibration state indicated by "K" in FIG. 4 (a state in which balloon probe 46 is filled with the optimal amount of measurement fluid K), which was determined in the preceding calibration procedure.

[0111] Alternatively, the measurement cycle shown in Figures 3-5 may be followed by a further measurement cycle (or multiple further measurement cycles) before setting the calibration state K. In this case, the procedure returns from step 134 to step 108 and repeats the steps in the further measurement cycle similar to steps 110-130 of the first measurement cycle. This repetition is indicated in Figure 3 by line 138.

[0112] The calibration controller 60 monotonically changes the amount of measurement fluid in the balloon probe 46 in at least two steps to approximate each measurement point S1, S2, M1-M7, E1, and E2 from the start value S1 until the end value E3 is reached. This allows calibration to be completed in a short time, for example, within just a few minutes. This allows calibration to be repeated as needed during continuous ventilation. Therefore, even if the optimal filling of the balloon probe 46 changes during ventilation, the esophageal catheter 48 can always be accurately calibrated. This allows for long-term ventilation of patients in automatic ventilation mode.

Claims

1. A calibration system (60), particularly for a ventilation device (10), for automatically setting a desired operational fill for an esophageal catheter (48) with a balloon probe (46) insertable into the esophagus (34) for determining esophageal pressure (Peso), comprising: The calibration system (60) a device for filling the balloon probe (46) with a measurement fluid after placing the balloon probe (46) in the esophagus (34); a pressure sensor for detecting the intraesophageal pressure (Peso) within the balloon probe (46); a calibration controller (60) designed to gradually change the amount of the measurement fluid in the balloon probe (46), and recording the esophageal pressure (Peso) detected by the pressure sensor for each of the amounts of the measurement fluid in the balloon probe (46) set in stages as measurement points (S1, S2, M1 to M7, E1, E2), and correlating the esophageal pressure with each set amount of the measurement fluid in the balloon probe (46); Equipped with The calibration controller (60) The amount of the measurement fluid is designed to be monotonically changed in at least two stages from a start value to an end value in order to approach each of the measurement points (S1, S2, M1 to M7, E1, E2). A calibration system (60) characterized by:

2. a fluid discharge device configured to discharge the measurement fluid from the balloon probe (46); the calibration controller (60) controls the fluid discharge device to monotonically decrease the amount of the measurement fluid in the balloon probe (46) in at least two stages from the start value to the end value in order to approach each of the measurement points (S1, S2, M1 to M7, E1, E2); The calibration system (80) of claim 1, characterized in that:

3. the calibration controller (60) controls a configuration for filling the balloon probe (46) with an amount of measurement fluid greater than an upper limit of a measurement range between the start value and the end value during at least a first measurement cycle for filling the balloon probe (46) with measurement fluid; The calibration system (80) of claim 2, characterized in that:

4. the calibration controller (60) is designed to perform at least two measurement cycles in succession; A calibration system (80) according to any one of claims 1 to 3, characterized in that

5. the measurement ranges of the at least two consecutive measurement cycles are different from each other; In particular, the preceding measurement cycle determines the measurement range of the subsequent measurement cycle; The calibration system (80) of claim 4, characterized in that:

6. the calibration controller (60) is designed to set different distances between successive measurement points for the preceding measurement cycle and the following measurement cycle; A calibration system (80) according to claim 4 or 5, characterized in that

7. the calibration controller (60) is configured to determine the increment between successive measurement points within a measurement range in a measurement cycle using a gradient method; A calibration system (80) according to any one of claims 1 to 6, characterized in that

8. the calibration controller (60) is designed so that the measurement fluid is not completely expelled from the balloon probe (46) between the preceding and subsequent measurement cycles; A calibration system (80) according to any one of claims 4 to 7, characterized in that

9. the calibration controller (60) is designed to ascertain, between the start value and the end value, for each of the measurement points (S1, S2, M1-M7, E1, E2), i.e. for each set volume of measurement fluid in the balloon probe (46), a respective measured value of the esophageal pressure at the end of inspiration (Peso_insp) and a measured value of the esophageal pressure at the end of expiration (Peso_exp), and then determine the difference between the esophageal pressure at the end of inspiration (Peso_insp) and the esophageal pressure at the end of expiration (Peso_exp); A calibration system (80) according to any one of claims 1 to 8, characterized in that

10. the calibration controller (60) is configured to determine a maximum value of the difference between the esophageal pressure at the end of inspiration (Peso_insp) and the esophageal pressure at the end of expiration (Peso_exp) within a range between the start value of the amount of measurement fluid in the balloon probe (46) and the end value of the amount of measurement fluid in the balloon probe (46); The calibration system (80) of claim 9, characterized in that:

11. the calibration controller (60) is designed to ascertain, for each measurement point between the start and end values during ventilation, a measurement of the esophageal pressure (Peso_insp) at the end of inspiration and a measurement of the esophageal pressure (Peso_exp) at the end of expiration; A calibration system (80) according to claim 9 or 10, characterized in that

12. the calibration controller (60) is configured to compare the difference between the esophageal pressure at the end of inspiration (Peso_insp) and the esophageal pressure at the end of expiration (Peso_exp) determined for each of the measurement points (S1, S2, M1 to M7, E1, E2), and then, when the determined difference is within a predetermined variation range centered on a maximum value over a plurality of consecutive measurement points, determine the optimal amount of measurement fluid in the balloon probe (46) as an amount having a predetermined distance from the upper and / or lower ends of the plurality of consecutive measurement points; The calibration system (80) of claim 11, characterized in that:

13. the calibration controller (60) is designed to ascertain a plurality of measurements, in particular a plurality of pairs of measurements, of the esophageal pressure at the end of inspiration (Peso_insp) and the esophageal pressure at the end of expiration (Peso_exp) for each measurement point (S1, S2, M1-M7, E1, E2) between the start value and the end value, the calibration controller (60) determines for each of the measurement points (S1, S2, M1-M7, E2) a mean value and a statistical variance based on the plurality of measurements or the plurality of pairs of measurements or parameters derived therefrom, in particular the difference between the esophageal pressure at the end of inspiration (Peso_insp) and the esophageal pressure at the end of expiration (Peso_exp), and determines the number of measurements for each of the measurement points (S1, S2, M1-M7, E1, E2) so that the obtained mean value is considered statistically significant; A calibration system (80) according to any one of claims 1 to 12, characterized in that

14. the calibration controller (60) is configured to monitor, for each of the measurement points (S1, S2, M1-M7, E1, E2) between the start value and the end value, whether the measurement of the esophageal pressure (Peso) is affected by external conditions, and to discard each of the measurements if such external conditions are detected; A calibration system (80) according to any one of claims 1 to 13, characterized in that

15. The calibration controller (60) is designed to calculate a quality index based on the data ascertained during the calibration procedure; The quality index is An index that indicates the weighting of the influence of factors and determines whether to change ventilation parameters based on esophageal pressure data. The factors are: Including the scattering of measurements expressed as Gaussian standard deviation and / or the uneven course of the esophageal pressure / measured fluid volume curve A calibration system (80) according to any one of the preceding claims.

16. the calibration controller (60) is configured to prevent the esophageal pressure (Peso) from exceeding a predetermined maximum pressure; A calibration system (80) according to any one of claims 1 to 15, characterized in that

17. the calibration controller (60) controls the fluid discharge device to further gradually decrease the amount of the measurement fluid in the balloon probe (46) starting from the start value until the end value is reached when the end-tidal esophageal pressure (Peso) reaches or falls below a predetermined minimum value, for example, 5 hPa, as the measurement points (S1, S2, M1 to M7, E1, E2) are approached; A calibration system (80) according to any one of claims 2 to 16, characterized in that

18. A method for automatically calibrating a desired operational fill for an esophageal catheter (48) having a balloon probe (46) insertable into an esophagus (34) for determining esophageal pressure (Peso), the method comprising: The method comprises: the calibration system (80) positions the balloon probe (46) in the esophagus (34) and then fills the balloon probe (46) with a measurement fluid; the calibration system (80) detecting the esophageal pressure (Peso) within the balloon probe (46); a step in which the calibration system (80) gradually changes the amount of the measurement fluid in the balloon probe (46), detecting the esophageal pressure (Peso) for each amount of the measurement fluid in the balloon probe (46) set in stages as measurement points (S1, S2, M1 to M7, E1, E2), and associating the detected amount with each set amount of the measurement fluid in the balloon probe (46); Including, the calibration system (80) monotonically varies the amount of the measurement fluid in at least two steps from a start value to an end value in order to approach each of the measurement points (S1, S2, M1 to M7, E1, E2); A method characterized by:

19. further comprising at least one additional method step as defined in claims 1 to 17 for the formation of the calibration system (80), 20. The method of claim 18, wherein:

20. 20. A computer program product comprising program instructions for implementing the method according to claim 18 or 19 when executed on a data processing system, in particular a microprocessor or microcontroller for controlling an esophageal catheter (48) with a balloon probe (46).

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