Medical tube for breathing circuit

Abstract

To provide a medical tube used for a breathing circuit suited for supplying a patient with humidification gas and / or removing gas from the patient.SOLUTION: An intake rim may include: a hollow body which is wound spirally and at least partially forms a first elongated pipe having an axis in a longitudinal direction; a first lumen extending along the axis in the longitudinal direction; and a first elongated member including a hollow wall surrounding the lumen. The intake rim is wound spirally and may include a second elongated member combined among windings adjacent to the first elongated member. The second elongated member forms at least a part of the lumen of the first elongated pipe. A breathing circuit may include an exhalation rim for transporting exhalation gases from a patient. The exhalation rim may include an inlet and an outlet. The exhalation rim may include a third elongated member including a second pipe surrounding a second lumen.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] Incorporation by Reference This application claims priority from U.S. Provisional Patent Application No. 62 / 365,285, filed July 21, 2016, the entire contents of which are incorporated herein by reference in their entirety. Additionally, the following disclosure references various features of U.S. Patent Application Publication No. 13 / 517,925, published as U.S. Patent Application Publication No. 2013 / 0098360 A1, U.S. Patent Application Publication No. 14 / 123,485, published as U.S. Patent Application Publication No. 2014 / 0202462 A1, and U.S. Patent Application Publication No. 14 / 649,801, published as U.S. Patent Application Publication No. 2015 / 0306333 A1. The entire disclosures of these applications and publications are hereby incorporated by reference for all purposes as if fully set forth herein.

[0002] The present disclosure relates generally to tubing suitable for medical use, particularly for use in breathing circuits suitable for supplying humidified gas to a patient and / or removing gas from a patient, such as in a respiratory humidification system. [Background technology]

[0003] In a breathing circuit, various components transport warm and / or humidified gases to and from a patient. Respiratory humidification helps reduce the chance of infection and / or tissue damage. Summary of the Invention [Problem to be solved by the invention]

[0004] Certain features, aspects, and advantages of the present disclosure recognize a need for an improvement that can increase vapor removal from exhaled gases in the expiratory tubing while increasing the amount of vapor in the humidified gas delivered to a patient through the inspiratory tubing without increasing the overall resistance to flow within the tubing. Certain features, aspects, and advantages of the present disclosure recognize a need for an improvement that reduces the compressible volume of a breathing circuit, or at least reduces the compressible volume of the rim of the breathing circuit. As described herein, there can be a trade-off between the compressible volume and resistance to flow between the inspiratory tubing and the expiratory tubing. There can be a reduction in the compressible volume and / or resistance to flow within the inspiratory tubing, and an increase in the compressible volume and / or resistance to flow within the expiratory tubing. The reduction in compressible volume within the inspiratory tubing can be due, at least in part, to a reduction in the diameter of the inspiratory tubing. The reduction in tubing diameter can be made possible by reducing the resistance to flow, which can be due, at least in part, to having a smooth bore. The increased compressible volume in the expiratory tube can be due, at least in part, to an increased wall surface area, tube diameter, tube cross-sectional area, or expiratory tube wall length. The increased resistance to flow in the expiratory tube can be due, at least in part, to corrugations. The increased compressible volume and increased resistance to flow in the expiratory tube can improve its permeability by various factors described herein. This tradeoff between the inspiratory and expiratory tubes can maintain the same overall compressible volume and / or resistance to flow throughout the breathing circuit. [Means for solving the problem]

[0005] The smaller the compressible volume of the breathing circuit, the lower the pneumatic compliance of the breathing circuit for a given compliance, and the lower the pneumatic compliance of the breathing circuit relative to the patient's lung compliance, the lower the chance of error in the delivered tidal volume.

[0006] The breathing circuit can include an inspiratory rim for delivering inhaled gas to the patient. The inspiratory rim can include a first elongate member including a hollow body spirally wound to at least partially form a first elongate tube having a longitudinal axis, a first lumen extending along the longitudinal axis, and a hollow wall surrounding the lumen. The inspiratory rim can include a second elongate member spirally wound and coupled between adjacent windings of the first elongate member, the second elongate member forming at least a portion of the lumen of the first elongate tube. The breathing circuit can include an expiratory rim for delivering exhaled gas from the patient. The expiratory rim can include an inlet and an outlet. The expiratory rim can include a third elongate member including a second tube surrounding the second lumen. The second lumen can be configured to accommodate a bulk flow of exhaled gas, and the second tube can be permeable to water vapor and substantially impermeable to liquid water and the bulk flow of exhaled gas.

[0007] The wall of the expiratory tube can comprise a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of expiratory gas. The foamed polymer can comprise a solid thermoplastic elastomer material having cell voids dispersed throughout. The first lumen of the inhalation rim can have a smooth bore. The second elongate member of the inhalation rim can surround at least one heating element. The first elongate member of the inhalation rim can define, in longitudinal cross section, a plurality of bubbles, the plurality of bubbles having flat surfaces in the lumen. The second elongate member of the inhalation rim can surround at least one heating element, with the at least one inhalation heating element being between one of the plurality of bubbles and the inhalation central bore. The third elongate member of the expiratory rim can be corrugated. The first elongate tube can surround a heating element within its lumen. The third elongate member of the expiratory rim can surround a heating element within the second lumen. The third elongate member of the expiratory rim can include a heating element attached to an inner wall of the second tube. The third elongate member of the expiratory rim can include a heating element embedded within a wall of the second tube. The second tube can have an inner surface adjacent to the second lumen, and the expiratory rim further includes a plurality of reinforcing ribs disposed circumferentially around the inner surface and generally aligned longitudinally between the inlet and outlet.

[0008] The device may include a breathing circuit. The breathing circuit may include an inspiratory tube configured to receive an inspiratory gas flow from a gas source, the inspiratory tube including an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore. The inner wall of the inspiratory tube may be smooth. The breathing circuit may include an expiratory tube configured to receive an expiratory gas flow from a patient. The expiratory tube may include an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore. The inner wall of the expiratory tube may be corrugated. The wall of the expiratory tube may be permeable to water vapor and substantially impermeable to liquid flowing therethrough and the bulk flow of expiratory gas.

[0009] The wall of the expiratory tube may comprise a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of expiratory gas. The inspiratory tube may enclose a heating element within its central bore. The inspiratory tube may comprise a heating element attached to its inner wall. The inspiratory tube may comprise a heating element embedded within its wall. The expiratory tube may comprise a heating element within its central bore. The expiratory tube may comprise a heating element attached to its inner wall. The expiratory tube may comprise a heating element embedded within its inner wall. The inspiratory tube may comprise, in longitudinal cross section, a plurality of bubbles having flat surfaces at the lumen. The inspiratory tube may comprise at least one heating element, the at least one inspiratory heating element being between a bubble of the plurality of bubbles and the inspiratory central bore. The expiratory tube may comprise a plurality of reinforcing ribs arranged circumferentially around the inner surface and generally aligned longitudinally between the inlet and the outlet. The breathing circuit may comprise a humidifier configured to humidify the inspiratory gas flow to the patient. The humidifier can include a humidification chamber configured to store a volume of liquid and configured to be in fluid communication with the inhaled gas flow, and can include a heater configured to heat the volume of liquid in the humidification chamber to produce vapor such that the inhaled gas flow is humidified by the vapor.

[0010] The ventilator may include a humidifier configured to humidify an inhaled gas flow to a patient. The ventilator may include an inhalation tube configured to receive the inhaled gas flow from the humidifier. The inhalation tube may include an inhalation inlet, an inhalation outlet, and a wall surrounding an inhalation central bore. The inner wall of the inhalation tube may be smooth. The ventilator may include an expiratory tube configured to receive an expiratory gas flow from the patient. The expiratory tube may include an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore. The expiratory central bore may be corrugated. The wall of the expiratory tube may be permeable to water vapor and substantially impermeable to liquid flowing therethrough and the bulk flow of expiratory gas.

[0011] The inhalation tube may include at least one heating element within its central bore. The inhalation tube may include at least one heating element attached to its inner wall. The inhalation tube may include at least one heating element enclosed within its wall. The expiratory tube may include at least one heating element within the expiratory central bore. The expiratory tube may include at least one heating element attached to its inner wall. The expiratory tube may include at least one heating element embedded within its inner wall. The inhalation tube may include, in longitudinal cross section, a spirally wound member forming a plurality of bubbles, the plurality of bubbles having flat surfaces at the inhalation central bore. The inhalation tube may surround the at least one heating element, and the at least one inhalation heating element may be between a bubble of the plurality of bubbles and the inhalation central bore. The wall of the expiratory tube may include a foamed polymer.

[0012] The ventilator may include a humidifier configured to humidify an inhaled gas flow to a patient. The humidifier may include a humidification chamber configured to store a volume of liquid and configured to be in fluid communication with the inhaled gas flow. The humidifier may include a heater configured to heat a volume of liquid in the humidification chamber to generate steam such that the inhaled gas flow is humidified by the steam. The ventilator may include an inhalation tube configured to receive the humidified inhaled gas flow from the humidifier. The inhalation tube may include a wall surrounding an inhalation central bore. The inhalation central bore of the inhalation tube may be smooth. The inhalation tube may include a spirally wound first elongate member forming a plurality of bubbles in a longitudinal cross section, the bubbles having flat surfaces at the inhalation central bore. The bubbles may be configured to insulate the inhalation central bore. The inspiratory tube can include a spirally wound second elongate member coupled between adjacent turns of the first elongate member, the second elongate member forming at least a portion of the lumen of the first elongate tube and including at least one inspiratory heating element embedded within the second elongate member. The ventilator can include an expiratory tube configured to receive an expiratory gas flow from the patient. The expiratory tube can include a conduit surrounding an expiratory central bore. The expiratory central bore can be corrugated. The conduit can be permeable to water vapor and substantially impermeable to the flow of liquid therethrough. The expiratory tube can include at least one expiratory heating element within the expiratory central bore. The ventilator can include a control system configured to deliver power to the humidifier heater, the at least one inspiratory heating element, and the at least one expiratory heating element.

[0013] The wall of the expiratory tube may comprise a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of expiratory gas. The foamed polymer may comprise a solid thermoplastic elastomer material having cell voids dispersed throughout. At least one inspiratory heating element may be between a bubble of the plurality of bubbles and the inspiratory central bore. The ventilator may include a patient interface assembly between the inspiratory tube and the expiratory tube. Power delivered by the control system may be calculated to provide increased humidification by the humidifier and controlled condensation management by the at least one expiratory heating element and the at least one inspiratory heating element. The ventilator may include a ventilator configured to provide an inspiratory gas flow and receive an expiratory gas flow. The ventilator may be configured to supply a pulsed inspiratory gas flow to the humidifier. The ventilator may be configured to supply a constant inspiratory gas flow to the humidifier. The ventilator may be configured to provide a bias flow of gas.

[0014] The ventilator may include a humidifier configured to humidify an inhaled gas flow to a patient. The ventilator may include an inhalation tube configured to receive an inhaled gas flow from a gas source. The inhalation tube may include an inhalation inlet, an inhalation outlet, and a wall surrounding an inhalation central bore. The inner wall of the inhalation tube may be smooth. The ventilator may include an expiratory tube configured to receive an expiratory gas flow from a patient. The expiratory tube may include an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore. The inner wall of the expiratory tube may be corrugated. The wall of the expiratory tube may be permeable to water vapor and substantially impermeable to liquid flowing therethrough and the bulk flow of expiratory gas.

[0015] The wall of the expiratory tube may comprise a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of expiratory gases. The inhalation tube may comprise at least one heating element within its central bore. The inhalation tube may comprise at least one heating element attached to its inner wall. The inhalation tube may comprise at least one heating element enclosed within its wall. The first elongated member of the inhalation rim may define, in longitudinal cross section, a plurality of bubbles, the plurality of bubbles having flat surfaces at the lumen. The inhalation tube may surround the at least one heating element, and the at least one inhalation heating element may be between a bubble of the plurality of bubbles and the inhalation central bore. The expiratory tube may comprise at least one heating element within the expiratory central bore. The expiratory tube may comprise at least one heating element attached to its inner wall. The expiratory tube may comprise at least one heating element embedded within its inner wall. The exhalation tube may include a plurality of reinforcing ribs disposed circumferentially around the inner wall and generally aligned longitudinally between the inlet and the outlet. The respirator may include a heater of the humidifier and a control system configured to deliver power to the at least one heating element.

[0016] The breathing circuit may include a combination of a smooth-bore inspiratory tube and a corrugated, vapor-permeable expiratory tube to increase vapor in the humidified gas delivered to the patient through the inspiratory limb of the circuit and increase vapor removal from the exhaled gas in the expiratory limb of the circuit without increasing the overall resistance to flow in the tubing, thus avoiding increased pressure drop within the breathing circuit. A smooth-bore inspiratory tube may offer an opportunity for a trade-off. A smooth bore may reduce resistance to flow, thereby allowing for a reduction in the diameter or cross-sectional area of ​​the inspiratory tube while maintaining an acceptable resistance to flow. This reduction in the diameter or cross-sectional area of ​​the inspiratory tube reduces the compressible volume of the inspiratory tube. A smaller diameter inspiratory tube may reduce the compressible volume of at least a portion of the breathing circuit, which reduces the likelihood of error in the delivered tidal volume. Ventilators are typically intended to deliver a set volume of gas (the “tidal volume”) to a patient with each breath. Reducing the error in the delivered tidal volume ensures that the patient receives the correct volume of gas.

[0017] The use of a combination of a smooth-bore inspiratory tube and a corrugated expiratory tube has an unexpected synergistic effect that improves the performance of the breathing circuit and its components beyond expectations. Using a smooth-bore inspiratory tube with a smaller inner diameter than a comparable corrugated tube can reduce the compressible volume of the tube. This reduction in compressible volume can ensure that an appropriate volume of gas is delivered to the patient. As described herein, an inspiratory tube with a smaller inner diameter can reduce the overall compressible volume and pneumatic compliance of the breathing circuit. As described herein, an inspiratory tube with a smaller inner diameter can have a reduced compressible volume, which can be traded off for an increased compressible volume of the expiratory tube.

[0018] For practical reasons, the compressible volume, and therefore compliance, of breathing circuit tubing is typically much greater than that of the patient's lungs. Factors that influence the compressible volume of breathing circuit tubing include minimizing the tubing's resistance to gas flow and ensuring that the tubing is long enough to manage the patient within the bed space. This is exacerbated by some pulmonary disease states in which the patient's lungs become very stiff and less compliant. Additionally, a small compressible volume due to reduced length (e.g., shortened tubing) directly conflicts with both the usability and breathability of the expiratory limb. In practice, longer tubing is generally better, for example, allowing for greater freedom of patient movement and positioning. In practice, a larger surface area of ​​the expiratory limb is generally better, increasing its breathability.

[0019] To maintain a sufficiently small compressible volume, tradeoffs can be made among breathing circuit components. The diameter or cross-sectional area of ​​the inspiratory tubing can be reduced. However, reducing the inner diameter of the inspiratory tubing also increases the resistance to flow (RTF) within the inspiratory tubing. It has been found that smoothing the inner bore of the inspiratory tubing can compensate for this increased RTF, since a smooth bore reduces RTF compared to tubing with a corrugated or other type of non-smooth bore. The use of a smooth bore has the added benefit of reducing vapor and condensate trapping. It has also been found that if the RTF reduction from using a smooth bore outweighs the RTF increase from reducing the inner diameter of the tubing, there is a net decrease in RTF within the breathing circuit, or at least a net decrease in RTF within the inspiratory tubing. A smooth inspiratory tubing bore reduces RTF, thereby allowing for a smaller inspiratory tubing diameter that would normally increase RTF, balancing the smoothness of the bore with a smaller diameter. As described herein, a reduction in diameter or cross-sectional area can reduce the compressible volume. This reduction in the compressible volume of the inspiratory tract can offset an increase in the compressible volume of the expiratory tract, for example, due to an increase in the diameter or cross-sectional area of ​​the expiratory tract. Increasing the diameter or cross-sectional area of ​​the expiratory tract provides a larger surface area, thereby increasing the vapor permeability of the expiratory tract.

[0020] Specific features, aspects, and advantages of inventive implementations related to the compressible volume of breathing circuit components feature one or more combinations of the following: reduced inner diameter of the inspiratory tube, smooth bore of the inspiratory tube, reduced compressible volume of the smooth bore of the inspiratory tube, increased compressible volume of the expiratory tube, increased diameter of the expiratory tube, increased surface area of ​​the expiratory tube, and / or increased vapor permeability of the expiratory tube. Specific features, aspects, and advantages of the present disclosure reflect the inventive realization that this net reduction in RTF due to a smooth bore inspiratory tube allows for modifications to other components of the circuit without changing the overall compressible volume, overall RTF, and / or overall pressure drop for the entire circuit. The use of a smooth bore inspiratory tube allows for the use of a longer corrugated expiratory tube that would otherwise increase RTF within the circuit. Increasing the length of the expiratory tube improves the tube's ability to remove vapor from exhaled gases, at least in part due to increased residence time. Increasing the expiratory tube diameter can improve the tube's ability to remove vapor from exhaled gases because it increases the wall surface area through which vapor can permeate. If the RTF of the overall circuit is reduced by using a smooth-bore inspiratory tube, increasing the RTF by lengthening the expiratory tube may not result in a net increase in RTF, a net increase in compressible volume, and / or a corresponding pressure drop across the entire circuit. For example, based on the design, increasing the length of the inspiratory tube and reducing the diameter of the smooth-bore inspiratory tube may be net-neutral with respect to RTF.

[0021] The use of a smooth-bore inspiratory tube instead of a corrugated or similarly non-smooth-walled tube in the breathing circuit can be combined with the use of a wider (larger cross-sectional area or diameter) expiratory tube in the breathing circuit, which results in reduced RTF. There may be no trade-off in RTF, in which case it is reduced in either tube. A smooth bore reduces RTF compared to a tube with a corrugated or other type of non-smooth bore. However, the reduction in RTF in the inspiratory tube can be offset by a smaller diameter or cross-sectional area, which increases RTF. An expiratory tube with a larger cross-sectional area or diameter also reduces RTF. Alternatively, a trade-off can be made in compressible volume by changing the diameter or cross-sectional area of ​​the inspiratory and expiratory tubes, which decreases in the inspiratory tube but increases in the expiratory tube. A smaller diameter inspiratory tube has a smaller compressible volume. A larger diameter expiratory tube has a larger compressible volume.

[0022] The breathing circuit may include an inspiratory rim for delivering inspiratory gas to the patient. The inspiratory rim may include a first elongate member including a hollow body spirally wound to at least partially form a first elongate tube having a longitudinal axis, a first lumen extending along the longitudinal axis, and a hollow wall surrounding the lumen. The inspiratory rim may further include a second elongate member spirally wound and coupled between adjacent turns of the first elongate member, the second elongate member forming at least a portion of the inner wall of the lumen of the first elongate tube. The breathing circuit may further include an expiratory rim for transporting exhaled gas from the patient. The expiratory rim includes an inlet, an outlet, and a third elongate member including a second tube surrounding the second lumen. The second lumen is configured to accommodate a bulk flow of exhaled gas, and the second tube is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of exhaled gas.

[0023] The breathing circuit described above can also have one, some, or all of the following characteristics, as well as any one or more of the characteristics described in this disclosure: The wall of the expiratory tube can include a foamed polymer that is permeable to water vapor and substantially impermeable to the bulk flow of liquid water and expiratory gases. For purposes of this disclosure, any material described as "permeable to water vapor and substantially impermeable to the bulk flow of liquid water and gases" (or in substantially similar language) is defined herein as a material that allows water vapor molecules to pass therethrough by diffusion, facilitated diffusion, passive transport, active transport, or other similar mechanisms for selectively transporting water vapor molecules, but does not have a leak path that allows the bulk flow of liquid water or gas to pass through the leak path from one major exterior surface of the material to another major exterior surface of the material.

[0024] The foamed polymer may comprise a solid thermoplastic elastomer material having cell voids dispersed therethrough. The first lumen of the inhalation rim may have a smooth bore. The second elongate member of the inhalation rim may surround at least one heating element. The first elongate member of the inhalation rim may define a plurality of bubbles in longitudinal cross section, the plurality of bubbles having flat surfaces in the lumen. The second elongate member of the inhalation rim may further include at least one heating element, the at least one inhalation heating element being positioned between a bubble of the plurality of bubbles and the inhalation central bore. The third elongate member of the expiratory rim may be corrugated. The first elongate member may surround a heating element within its lumen. The third elongate member of the expiratory rim may surround a heating element within the second lumen. The third elongate member of the expiratory rim may include a heating element attached to the interior wall of the second tube. The third elongate member of the expiratory rim can include a heating element embedded in the wall of the second tube. The second tube can have an inner surface adjacent to the second lumen, and the expiratory rim can further include a plurality of reinforcing ribs circumferentially disposed around the inner surface and aligned generally longitudinally between the inlet and outlet. The foamed polymer is preferably selected or manufactured so that the solid thermoplastic elastomer material selectively transports water vapor molecules, but the cell voids dispersed throughout do not create leak paths that allow the bulk flow of liquid water or gas to pass therethrough.

[0025] The device may include a breathing circuit. The breathing circuit may further include an inspiratory tube configured to receive an inspiratory gas flow from a gas source. The inspiratory tube includes an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore, and the inner wall of the inspiratory tube is smooth. The breathing circuit may further include an expiratory tube configured to receive an expiratory gas flow from the patient. The expiratory tube includes an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore. The inner wall of the expiratory tube is corrugated, and the wall of the expiratory tube is permeable to water vapor and substantially impermeable to liquids and gases flowing therethrough.

[0026] The above device may also have one, some, or all of the following characteristics, as well as any one or more characteristics described in this disclosure: The wall of the expiratory tube may comprise a foamed polymer that is permeable to water vapor and substantially impermeable to the bulk flow of liquid water and expiratory gases. The inhalation tube may enclose a heating element within its central bore. The inhalation tube may include a heating element attached to its wall. The inhalation tube may include a heating element embedded in its wall. The expiratory tube may include a heating element within its central bore. The expiratory tube may include a heating element attached to its inner wall. The expiratory tube may include a heating element embedded in its inner wall. The inhalation tube may include, in longitudinal cross section, a plurality of bubbles having flat surfaces at the lumen. The inhalation tube may include at least one heating element, and the at least one inhalation heating element may be positioned between a bubble of the plurality of bubbles and the inhalation central bore.

[0027] Additionally, the expiratory tube may include a plurality of reinforcing ribs disposed circumferentially around the inner surface and generally aligned longitudinally between the inlet and the outlet. The breathing circuit may further include a humidifier configured to humidify the inspiratory gas flow delivered to the patient. The humidifier may include a humidification chamber configured to store a volume of liquid and configured to be in fluid communication with the inspiratory gas flow, and a heater configured to heat the volume of liquid in the humidification chamber to produce vapor such that the inspiratory gas flow is humidified by the vapor.

[0028] The respiratory apparatus may include a humidifier, an inspiratory tube, and an expiratory tube. The humidifier is configured to humidify an inspiratory gas flow to a patient. The inspiratory tube is configured to receive the inspiratory gas flow from the humidifier. The inspiratory tube includes an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore, the inner wall of the inspiratory tube being smooth. The expiratory tube is configured to receive an expiratory gas flow from the patient. The expiratory tube includes an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore, the expiratory central bore being corrugated, the wall of the expiratory tube being permeable to water vapor and substantially impermeable to the bulk flow of liquid and expiratory gas flowing therethrough.

[0029] The respirator described above may also have one, some, or all of the following characteristics, as well as any one or more characteristics described in this disclosure: The inspiratory tube may include at least one heating element within its central bore. The inspiratory tube may include at least one heating element attached to its inner wall. The inspiratory tube may include at least one heating element enclosed within its wall. The expiratory tube may include at least one heating element within the expiratory central bore. The expiratory tube may include at least one heating element attached to its inner wall. The expiratory tube may include at least one heating element embedded within its inner wall. The expiratory tube may include, in longitudinal cross section, a spirally wound member forming a plurality of bubbles, the plurality of bubbles having flat surfaces at the inspiratory central bore. The inspiratory tube may surround the at least one heating element, and the at least one inspiratory heating element may be positioned between a bubble of the plurality of bubbles and the inspiratory central bore. The wall of the expiratory tube may include a foamed polymer.

[0030] The respiratory apparatus may include a humidifier, an inspiratory tube, an expiratory tube, and a control system. The humidifier is configured to humidify an inspiratory gas flow delivered to a patient. The humidifier includes a humidification chamber and a heater. The humidification chamber is configured to store a volume of liquid and is configured to be in fluid communication with the inspiratory gas flow. The heater is configured to heat the volume of liquid in the humidification chamber to generate vapor so that the inspiratory gas flow is humidified by the vapor. The inspiratory tube is configured to receive the humidified inspiratory gas flow from the humidifier. The inspiratory tube includes a wall surrounding an inspiratory central bore, and the inspiratory tube central bore is smooth. The inspiratory tube further includes a spirally wound first elongated member forming a plurality of bubbles in a longitudinal cross section, the bubbles having a flat surface at the inspiratory central bore. The bubbles are configured to insulate the inspiratory central bore. The inspiratory tube further includes a spirally wound second elongate member coupled between adjacent turns of the first elongate member. The second elongate member forms at least a portion of the lumen of the first elongate tube and includes at least one inspiratory heating element embedded within the second elongate member. The expiratory tube is configured to receive an expiratory gas flow from the patient. The expiratory tube includes a conduit surrounding an expiratory central bore, the expiratory central bore being corrugated, the conduit being permeable to water vapor and substantially impermeable to the flow of liquid therethrough. The expiratory tube further includes at least one expiratory heating element within the expiratory central bore. The control system may be configured to deliver power to a heater of the humidifier. The control system may be configured to deliver power to the at least one inspiratory heating element. The control system may be configured to deliver power to the at least one expiratory heating element. The control system may be configured to deliver power to the humidifier heater and the at least one inspiratory heating element. The control system may be configured to deliver power to the heater of the humidifier and to the at least one exhalation heating element. The control system may be configured to deliver power to the at least one inhalation heating element and to the at least one exhalation heating element. The control system is configured to deliver power to two or more of the following: the heater of the humidifier, the at least one inhalation heating element, and the at least one exhalation heating element.The control system is configured to deliver power to the heater of the humidifier, the at least one inspiratory heating element, and the at least one expiratory heating element.

[0031] The above-described ventilator may also have one, some, or all of the following characteristics, as well as any one or more characteristics described in this disclosure: The wall of the expiratory tube may comprise a foamed polymer that is permeable to water vapor and substantially impermeable to the bulk flow of liquid water and expiratory gases. The foamed polymer may comprise a solid thermoplastic elastomer material having cell voids dispersed throughout. At least one inspiratory heating element may be between a bubble of the plurality of bubbles and the inspiratory central bore. The ventilator may further include a patient interface assembly between the inspiratory tube and the expiratory tube. The power delivered by the control system may be calculated to provide increased humidification by the humidifier. The power delivered by the control system may be calculated to provide controlled condensation management by the at least one expiratory heating element. The power delivered by the control system may be calculated to provide controlled condensation management by the at least one inspiratory heating element. The power delivered by the control system can be calculated to provide increased humidification by the humidifier and controlled condensation management by the at least one expiratory gas heating element and the at least one inspiratory gas heating element. The respirator can further include a ventilator configured to supply the inspiratory gas flow and to receive the expiratory gas flow. The ventilator can be configured to supply a pulsed inspiratory gas flow to the humidifier. The ventilator can be configured to supply a constant inspiratory gas flow to the humidifier. The ventilator can be configured to supply a bias flow of gas.

[0032] The respiratory apparatus may include a humidifier, an inspiratory tube, and an expiratory tube. The humidifier is configured to humidify the inspiratory gas flow to the patient. The inspiratory tube is configured to receive the inspiratory gas flow from a gas source. The inspiratory tube includes an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore, and the inner wall of the inspiratory tube is smooth. The expiratory tube is configured to receive the expiratory gas flow from the patient. The expiratory tube includes an expiratory inlet, an expiratory outlet, and a wall surrounding an expiratory central bore. The inner wall of the expiratory tube is corrugated, and the wall of the expiratory tube is permeable to water vapor and substantially impermeable to liquids and gases flowing therethrough. The wall of the expiratory tube may include a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and the bulk flow of expiratory gas. The inspiratory tube may include at least one heating element within its central bore. The ventilator may also have one, some, or all of the following characteristics, as well as any one or more characteristics described in this disclosure: The inhalation tube may include at least one heating element attached to its inner wall. The inhalation tube may include at least one heating element enclosed within its wall. The first elongated member of the inhalation rim may define, in longitudinal cross section, a plurality of bubbles, the plurality of bubbles having flat surfaces at the lumen. The inhalation tube may surround the at least one heating element, and the at least one inhalation heating element may be between a bubble of the plurality of bubbles and the inhalation central bore. The inhalation tube may include at least one heating element within the inhalation central bore. The expiratory tube may include at least one heating element attached to its inner wall. The expiratory tube may include at least one heating element embedded within its inner wall. The expiratory tube may include a plurality of reinforcing ribs arranged circumferentially around the inner surface and generally aligned longitudinally between the inlet and the outlet. The ventilator may further include a control system configured to deliver power to the heater and at least one humidification element of the humidifier.

[0033] Certain features, aspects, and advantages of the present disclosure will now be described with reference to the drawings. The drawings and their associated description are provided to illustrate certain features, aspects, and advantages of the present disclosure and do not limit the scope of the disclosure. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic diagram of a breathing circuit incorporating one or more medical tubing. [Figure 1A] FIG. 1 is a schematic diagram of a breathing circuit incorporating one or more medical tubing. [Figure 1B] Three graphs are shown demonstrating the effect of breathing circuit compliance on tidal volume error. [Figure 2A] FIG. 1 is a side view of a portion of a composite pipe. [Figure 2B] 2B is a longitudinal cross-sectional view of the composite pipe of FIG. 2A. [Figure 3A] FIG. 1 is a side view of a section of a tube incorporating a vapor-permeable foamed polymer material. [Figure 3B] FIG. 3B is a cross-sectional view of the tube of FIG. 3A. [Figure 4A] FIG. 1 is a front perspective view of a section of a pipe incorporating integral reinforcing ribs, the pipe being partially corrugated. [Figure 4B] 4B is a front perspective view of a portion of the tube of FIG. 4A, the tube being generally corrugated. [Figure 5A] FIG. 1 is a front perspective view of a section of a tube incorporating ribs. [Figure 5B] FIG. 5B is a front perspective view of the tube of FIG. 5A. [Figure 6] FIG. 1 is a schematic diagram of a portion of an expiratory tube. [Figure 7] FIG. 1 is a schematic diagram of a portion of an expiratory tube. [Figure 8] 1 is a schematic diagram of a breathing circuit including a humidifier, an inspiratory tube, and an expiratory tube. DETAILED DESCRIPTION OF THE INVENTION

[0035] A breathing circuit including one or more medical tubes To understand the present disclosure in more detail, reference is first made to FIG. 1 , which illustrates a breathing circuit 100. Such a breathing circuit 100 may be a breathing humidification circuit. The breathing circuit 100 includes one or more medical tubes. The breathing circuit 100 may include an inspiratory tube 103 and an expiratory tube 117.

[0036] As used herein, medical tubing is a broad term and shall be given its ordinary and accustomed meaning to those skilled in the art (i.e., it is not limited to a dedicated or specialized meaning), and includes, but is not limited to, cylindrical and non-cylindrical elongated shapes that define a lumen or include a passageway, such as hollow elongated bodies configured for use in medical procedures and otherwise conforming to applicable standards for such use. Inspiratory tubing is medical tubing configured to deliver respiratory gases to a patient. Expiratory tubing is medical tubing configured to remove exhaled gases from a patient.

[0037] Gases can be transported in circuit 100 of Figure 1. Ambient gas flows from gas source 105 to humidifier 107. Humidifier 107 can humidify the gas. Gas source 105 can be a ventilator, blower or fan, a tank containing compressed gas, a wall supply within a medical facility, or any other suitable source of breathing gas.

[0038] The humidifier 107 is connected to the inlet 109 (the end for receiving humidified gas) of the inspiratory tube 103 via port 111, thereby supplying humidified gas to the inspiratory tube 103. Gas flows through the inspiratory tube 103 to the outlet 113 (the end that discharges humidified gas) of the inspiratory tube 103 and to the patient 101 through a patient interface 115 connected to the outlet 113. An expiratory tube 117 is connected to the patient interface 115. The expiratory tube 117 returns exhaled humidified gas from the patient interface 115 to the gas source 105 or to the ambient atmosphere. As used herein, patient interface has a broad meaning and is given its ordinary and accustomed meaning to those skilled in the art, and also includes, but is not limited to, any one or more of a full face mask, a nasal mask, an oral mask, an oral-nasal mask, a nasal pillows mask, a nasal cannula, nasal prongs, a laryngeal mask, or any other suitable coupling between a medical circuit and a patient's airway.

[0039] Gas may enter gas source 105 through vent 119. A blower or fan 121 may draw air or other gas through vent 119, causing the gas to flow into gas source 105. Blower or fan 121 may be a variable speed blower or fan. An electronic controller 123 may control the speed of the blower or fan. In particular, the function of electronic controller 123 may be controlled by an electronic master controller 125. The function may be controlled in response to inputs from master controller 125 and user setting of pressure or blower or fan speed to predetermined required values ​​(preset values) via dials or other suitable input devices 127.

[0040] The humidifier 107 includes a humidification chamber 129. The humidification chamber 129 may be configured to contain a volume of water 130 or other suitable humidification liquid. The humidification chamber 129 is removable from the humidifier 107. This makes it easier to sterilize the humidification chamber 129 or to dispose of it after use. The humidification chamber 129 portion of the humidifier 107 may be of one piece, or may be formed from multiple components that are joined together to define the humidification chamber 129. The body of the humidification chamber 129 may be formed from a non-conductive glass or plastic material. The humidification chamber 129 may also include conductive components. For example, the humidification chamber 129 may include a highly thermally conductive base (e.g., an aluminum base) configured to contact or be associated with a heater plate 131 on the humidifier 107 when the humidification chamber 129 is attached to the humidifier 107.

[0041] The humidifier 107 may include electronic control functionality. The humidifier 107 may include an electronic, analog, or digital master controller 125. The master controller 125 may be a microprocessor-based controller that executes computer software commands stored in associated memory. In response to user-set humidity or temperature values ​​and other inputs via a user input device 133, the master controller 125 determines when (or to what level) to energize the heater plate 131 to heat the volume of water 130 in the humidification chamber 129.

[0042] The temperature probe 135 can be connected to the inlet conduit 103 near the patient interface 115, or the temperature probe 135 can be connected to the patient interface 115. The temperature probe 135 can be incorporated within the inlet conduit 103. The temperature probe 135 detects the temperature near or at the patient interface 115. A signal reflective of the temperature can be provided by the temperature probe 135 to an electronic, analog, or digital master controller 125. A heating element (not shown) can be used to regulate the temperature of the patient interface 115 and / or inlet conduit 103 to raise the temperature of the inlet conduit 103 and / or patient interface 115 above a saturation temperature, thereby reducing the chance of unwanted condensation.

[0043] 1, exhaled humidified gases are returned from the patient interface 115 to the gas source 105 via an expiratory tube 117. The expiratory tube 117 may comprise a vapor permeable material, which will be described in more detail below. The vapor permeable expiratory tube may be corrugated.

[0044] The expiratory tube 117 may have a temperature probe and / or heating element, as described above with respect to the inhalation tube 103, to reduce the chance of condensation reaching the gas source 105. The expiratory tube 117 does not need to return the exhaled gases to the gas source 105. The exhaled humidified gases may flow directly to the ambient environment or to other ancillary equipment, such as an air scrubber / filter (not shown).

[0045] In FIG. 1 , the intake tube 103 encompasses or includes a conduit having a smooth bore. The term smooth bore is given its ordinary and customary meaning to those skilled in the art and includes, but is not limited to, a non-corrugated bore, lumen, or passageway. The term "smooth bore" may be used to describe a tube whose interior surface does not contain significant internal corrugations, annular ribs, protrusions, or holes that would significantly affect gas flow within the tube. The term "smooth bore" may also be used to describe a tube that does not have repetitive interior surface features that would disrupt the generally laminar flow through the passageway or lumen defined by the smooth bore. The term corrugated is given its ordinary and customary meaning to those skilled in the art and includes, but is not limited to, having a ridged or grooved surface. Advantageously, a smooth bore results in a conduit having a lower RTF than a comparably sized conduit with a corrugated bore. A smooth bore provides lower resistance to flow, thereby allowing the bore (i.e., diameter or cross-sectional area) to be reduced, resulting in a smaller compressible volume compared to a corrugated tube with equivalent resistance to flow. The intake conduit may be a composite conduit. A composite conduit may be generally defined as a conduit including two or more individual sections, or more specifically, two or more components, that define an interconnected conduit. A composite conduit may be helically wound. A composite conduit may be helically wound in a manner such that two or more components are helically twisted together or connected side-by-side to form a helix.

[0046] The expiratory tube 117 includes or comprises a conduit, at least a portion of which is vapor permeable. Vapor permeability facilitates moisture removal. At least the vapor permeable portion of the expiratory tube 117 can be corrugated. The corrugations can be on the inside of the tube. The corrugations increase the inner surface area of ​​the tube. The amount of vapor that can diffuse through a vapor permeable material is a function of the surface area of ​​the material that is in direct contact with the vapor. The corrugations also increase the turbulence of the gas within the expiratory tube. Increased turbulence means that the gas is better mixed, which causes water vapor to migrate to the outer wall of the expiratory tube 117. Increased turbulence can increase localized retention within the corrugations within the expiratory tube, which, when combined with the vapor permeability attribute, further improves moisture removal. The increased local residence time causes the temperature of the gases swirling within each corrugated "pocket" to be lower than that of a comparable sized smooth-bore tube, thereby increasing the relative humidity of these gases compared to that of a comparable sized smooth-bore tube. The increased relative humidity causes a higher vapor pressure gradient across the walls of the expiratory tube 117 compared to that of a comparable sized smooth-bore tube, which therefore increases the diffusion of vapor through the walls of the corrugated expiratory tube compared to that of a comparable sized smooth-bore tube.

[0047] The vapor-permeable corrugated conduit may be at least partially formed from a foamed polymer that is permeable to water vapor and substantially impermeable to the bulk flow of liquid water and gas. The expiratory tube 117 may include a wall that defines a space within the expiratory tube 117. At least a portion of the wall may be formed from a foam material configured to be permeable to water vapor and substantially impermeable to the bulk flow of liquid water and gas.

[0048] The vapor-permeable exhalation tube 117 can be formed from a non-foaming material. The non-foaming material can include a spirally wound vapor-permeable tape. The corrugation of the exhalation tube 117 can be achieved using a non-foaming material. The non-foaming material can include beads of different diameters arranged in an alternating pattern to form a corrugated interior surface.

[0049] The inlet tube 103 comprises a smooth-bore conduit. Smooth-bore conduits can be heated and insulated to minimize condensation and maximize moisture transport. Reducing condensation formation within the inlet tube allows for more vapor to be delivered to the patient in the humidified gas. Several factors affect condensation formation within the inlet tube 103, including the diameter of the inner bore, the degree of smoothness of the inner bore, the level of insulation of the tube, the presence of a heating element (such as a wire or element) associated with the tube 103, and the location of the heating element within the tube 103 (whether the heating element is within the inner bore of the tube 103 or within the wall of the tube 103). Specifically, reducing the diameter of the inner bore of the inlet tube 103 increases the velocity of the gas as it travels within the inlet tube 103. Increasing the smoothness of the bore reduces turbulence and creates a more parabolic wavefront across the inner wall of the lumen. Therefore, by reducing the diameter of the inner bore and making the inner bore smooth, the higher velocity gas near the center of the tube transfers less heat to the slower velocity gas near the wall of the tube. Smooth bore tubes do not provide pockets where vapor can become trapped or condensation can accumulate, as occurs in corrugated tubes. Gas-borne vapors are therefore more likely to exit the tube and be delivered to the patient.

[0050] Increasing the degree of tubing insulation reduces heat loss through the walls of the inspiratory tubing 103, thereby minimizing condensation formation and maximizing moisture delivery. Further increasing the insulation of the inspiratory tubing 103 reduces the extent to which the heating element must work to maintain the target temperature and humidity, and also makes the breathing circuit 100 more efficient, since the insulated tubing is better able to maintain the temperature and absolute humidity of the gases traveling through the tubing.

[0051] Adding a heating element to the inspiratory conduit 103 also maximizes humidification delivery and reduces condensation. Locating one or more heating elements within the wall of the inspiratory conduit 103 maximizes humidification and minimizes condensation formation, contributing to the efficiency of the inspiratory conduit 103, breathing circuit 100, or humidification system. When positioned within the wall of the inspiratory conduit 103, the heating element heats the wall and does not directly heat the gas. Heating the wall reduces the relative humidity of the gas near the wall (heating the gas increases its temperature, which reduces its relative humidity). Locating a heating element on the lumen side of the inner wall of the insulating "bubble" (defined below) of the inspiratory conduit 103 (described in more detail below) can further reduce outward heat loss through the wall of the inspiratory conduit 103, which therefore maximizes humidification while minimizing condensation formation. As used herein, the term "bubble" refers to the cross-sectional shape of a hollow body formed from an elongated wrapping or winding of a first elongate member 203, for example, as shown in FIG. 2B, in a transverse cross section through the wrapping or winding. As used herein, all references to a "bubble" refer to an elongated hollow body having a shape defined by a wall in cross section, with a hollow space therein. Such shapes can include an oval or "D" shape, with reference to FIG. 2B. Such shapes can include an "O" shape and other symmetrical and asymmetrical regular and irregular shapes.

[0052] The expiratory tube 117 can include a corrugated conduit to maximize vapor removal while minimizing condensation formation and increasing local residence time within the corrugations. The expiratory tube 117 can include a vapor-permeable conduit to maximize vapor removal. The expiratory tube 117 can include a heated conduit to maximize vapor removal while minimizing condensation formation. The expiratory tube 117 can include a corrugated, vapor-permeable, and / or heated conduit to maximize vapor removal while minimizing condensation formation and increasing local residence time within the corrugations. Reducing condensation formation in the expiratory tube 117 allows more vapor to diffuse through the walls of the expiratory tube 117. The presence of a heating element can keep the relative humidity of the gas below 100% (i.e., keep the gas temperature above the dew point saturation temperature). Positioning a heating element near or within the walls of the expiratory tube 117 heats the gas near the walls of the expiratory tube 117. Condensation formation is avoided or limited by maintaining the gas temperature near the walls of the expiratory tube 117 above the dew point. The inspiratory tube 103 and expiratory tube 117 are described in much greater detail elsewhere herein.

[0053] Referring again to FIG. 1 , a gas source 105 is typically intended to deliver a set volume of gas to a patient 101 per breath. This set volume can be referred to as the tidal volume. It is desirable for the patient 101 to receive the correct volume of gas to reduce the possibility of lung damage and increase the likelihood of adequate ventilation. When a gas source 105, such as a ventilator, produces a breath for a patient, the gas source 105 must fill both the patient's lungs and the breathing circuit 100, which may include filters, a supply tube from the ventilator to a humidifier, a humidification chamber, an inspiratory tube, an expiratory tube, and any other components shown or described with respect to FIG. 1 . Therefore, the gas source 105 must estimate or otherwise account for the gas used to fill the breathing circuit 100 and compensate for this, increasing the likelihood of accurately delivering the gas volume to the patient.

[0054] The gas source 105 can perform a pneumatic compliance test of the breathing circuit 100. In this test, the gas source 105 attempts to determine the volume required to create a specific pressure. Pneumatic compliance depends at least on the compressible volume. The smaller the compressible volume of the breathing circuit 100, the lower the pneumatic compliance of the breathing circuit 100 for a given compliance. The lower the pneumatic compliance of the breathing circuit relative to the patient's lung compliance, the lower the chance of an error in the delivered tidal volume. If the measurement of the pneumatic compliance of the breathing circuit is in error by a small amount and the pneumatic compliance of the breathing circuit is large compared to the patient's lung compliance, the percentage error in the tidal volume delivered to the patient can be very large. For example, if the measurement of the pneumatic compliance of the breathing circuit is in error by 5% and the pneumatic compliance of the breathing circuit is large compared to the patient's lung compliance, the percentage error in the tidal volume delivered to the patient can be much greater than 5%.

[0055] Figure 1B shows three graphs. The graph in Figure 1B shows the error in delivered tidal volume when a theoretical error of 10% is introduced in the gas source measurement of the pneumatic compliance of the breathing circuit. The three graphs are for three specifications of circuit compliance (e.g., neonatal, adult, and pediatric). For the neonatal circuit, the breathing circuit compliance (C bs ) is 0.9ml.cmH20 -1 For adult circuits, the compliance of the breathing circuit (C bs ) is 2.1ml.cmH20 -1 For pediatric circuits, the compliance of the breathing circuit (C bs ) is 1.3ml.cmH20 -1 Each graph shows the error in the delivered tidal volume for a patient with poor respiratory system compliance.

[0056] It was found that the error increased dramatically with decreasing patient weight. Patient weight correlates with the intended tidal volume. As the patient's weight decreases, the intended tidal volume decreases. Comparing the graphs in Figure 1B shows that for a given tidal volume, the error increases with higher breathing circuit compliance. It was found desirable to keep the overall compressible volume and compliance of the breathing circuit as low as possible relative to the lung characteristics of the patient to be treated.

[0057] For practical reasons, such as minimizing the resistance to gas flow in the tubing and allowing the tube to be long enough to manage the patient within the bed space, the compressible volume and therefore compliance of breathing circuit tubing is typically much greater than that of the patient's lungs. This difference is exacerbated by some pulmonary disease states in which the patient's lungs become very stiff and less compliant. The small compressible volume that can result from short tubing can be a disadvantage from a usability standpoint. Longer tubing and a breathable expiratory limb that benefits from a larger surface area can be a disadvantage from a compressible volume standpoint.

[0058] The relevance of the compressible volume is that maintaining a sufficiently small compressible volume allows for trade-offs between breathing circuit components. A smooth bore in the inspiratory tube 103 reduces resistance to flow, thereby allowing the diameter of the inspiratory tube 103 to be reduced, and therefore the compressible volume to be reduced. This reduction in the compressible volume of the respiratory tube 103 allows the compressible volume of the expiratory tube 117 to be increased by increasing its diameter. Increasing the diameter of the expiratory tube 117 provides a larger surface area for the expiratory tube 117, thereby increasing the vapor permeability of the tube 117.

[0059] It has been recognized that by incorporating an inspiratory tube 103 having a smaller diameter smooth bore conduit along with an expiratory tube 117 having a corrugated conduit, the expiratory tube 117 can be made larger in diameter and / or longer than would otherwise be possible while maintaining the compressible volume of the overall system. Additionally or alternatively, the combination of a smaller diameter smooth bore inspiratory tube 103 with a larger diameter corrugated expiratory tube 117 can maintain the overall pressure drop. Additionally or alternatively, the combination of a smaller diameter smooth bore inspiratory tube 103 with a larger diameter corrugated expiratory tube 117 can maintain the resistance to flow (RTF) of the breathing circuit 100 at a desired level. Increasing the length of the conduit typically undesirably increases the compressible volume of the conduit and therefore the compressible volume of the overall breathing circuit. Increasing the length of the conduit typically undesirably increases the RTF of the conduit and therefore the RTF of the overall breathing circuit. On the other hand, if the conduit is vapor permeable, increasing the length advantageously improves the ability of the conduit to remove vapors from the exhaled gases. It has been found that the combination of an inspiratory tube 103 having a smaller diameter smooth bore and an expiratory tube 117 having a larger diameter corrugated vapor permeable conduit increases the ability of the expiratory tube 117 to remove water vapor from the breathing circuit without increasing the compressible volume, pressure drop, and / or RTF of the overall system.

[0060] It has been further recognized that by incorporating an inspiratory tube 103 having a smooth bore conduit, along with an expiratory tube 117 having a corrugated conduit, the humidifier 107 can improve humidity performance and provide therapeutic benefit to the patient while approaching fully saturated gas without increasing the risk of liquid damage to the gas source 105 or condensate backflow to the patient.

[0061] An inlet tube 103 having a smooth-bore, spirally wound conduit can be paired with an expiratory tube 117 having a corrugated, vapor-permeable conduit. As previously mentioned, the smooth bore of the inlet tube 103 has a lower RTF than a comparably sized corrugated bore. It can also have a smaller inner diameter than the corrugated conduit. Typically, a smaller inner diameter reduces the compressible volume, undesirably increasing the RTF of the inlet tube. However, the characteristics of the smooth bore can be selected such that the reduced RTF associated with the smooth bore of the inlet tube 103 outweighs the increased RTF due to the smaller inner diameter of the inlet tube 103. This selection of a smaller diameter inlet tube 103 also reduces the compressible volume of the inlet tube 103. This selection allows the corrugated expiratory tube 117 paired with the smooth-bore inlet tube 103 to be longer and / or have a larger diameter or cross-sectional area without increasing the overall system pressure drop or compressible volume. Increasing the length of the expiratory tube 117 typically undesirably increases the tube's RTF and compressible volume. However, increasing the length also improves the vapor-permeable tube's ability to remove vapor from exhaled gases. In this configuration, pairing a smooth-bore inspiratory tube 103 with a corrugated expiratory tube 117 improves the performance of the expiratory tube 117. The system pressure drop of the breathing circuit that may exist from the ventilator outlet to the ventilator inlet can be affected by the pressure characteristics (RTF) of each element in the circuit. Referring again to FIG. 1 , assuming constant pressure characteristics of the supply tubing from the ventilator to the humidifier, humidification chamber, interface tubing, and interface body, the primary factors contributing to the system pressure drop are the resistance to flow and the dimensions (length and diameter) of the inspiratory tube 103 and expiratory tube 117. Any change in one of these factors should be advantageously balanced with the others to avoid increasing the system's pressure drop, RTF, and / or compressible volume. As described herein, the primary factors contributing to the compressible volume are the tube profile, compliance, and dimensions (length and diameter or cross-sectional area) of the inspiratory tube 103 and expiratory tube 117. A trade-off can be made between reducing the compressible volume of the inspiratory tube 103 and increasing the compressible volume of the expiratory tube 117, while preserving the compressible volume of the breathing circuit.As described herein, increasing the compressible volume of the expiratory tube 117 is beneficial for vapor permeability at the expiratory rim.

[0062] The smooth bore of the inhalation tube 103 reduces resistance to flow (compared to a corrugated inhalation tube), potentially reducing the overall system pressure drop. This allows any or all of the other three factors (resistance to flow of the corrugated expiratory tube 117 or the dimensions of the respective tubes) to be modified to increase system pressure drop. The inner diameter of the inhalation tube 103 can be smaller than that of a comparable corrugated inhalation tube, which desirably increases the velocity of gas flowing through the inhalation tube 103. However, a smaller diameter also increases resistance to flow to some extent. As long as the increase in RTF due to the smaller diameter is sufficiently smaller than the decrease in RTF resulting from the use of a smooth bore, the length of the corrugated expiratory tube 117 can be increased without increasing system pressure drop. Increasing the length of the expiratory tube 117 increases the surface area of ​​the expiratory tube 117 wall. The amount of vapor that can diffuse through a vapor-permeable material is a function of the material's surface area. Increasing the length of the expiratory tube 117 increases the surface area of ​​the walls of the expiratory tube 117 and also increases the residence time of gas in the expiratory tube 117. The amount of vapor that can diffuse through a permeable material is also related to the length of time that the vapor-carrying gas is in contact with the material.

[0063] The compressible volume of the breathing circuit (the cumulative volume of the entire gas flow path) can be balanced in a similar manner. For example, a change in the dimensions (cross-sectional area or diameter, length) of the inspiratory tube 103 can be offset by a change in the dimensions (cross-sectional area or diameter, length) of the corrugated expiratory tube 117. As described herein, decreasing the diameter of the inspiratory tube 103 can reduce the compressible volume. This reduction in compressible volume can increase the accuracy of the delivered tidal volume. As described herein, a decrease in the diameter of the inspiratory tube 103 can offset an increase in the diameter and / or length of the expiratory tube 117. As described herein, changing the dimensions of the expiratory tube 117 can enhance the function of the expiratory tube 117, for example, by increasing the vapor permeability of the expiratory tube 117. Because changing the tube diameter affects both the system pressure drop and the system compressible volume, advantageously, both equations should be balanced or selected simultaneously during the change. Reducing the diameter of the inhalation tube 103 can both increase resistance to flow and decrease compressible volume, resulting in a faster average gas velocity through the tube. Increasing the length of the corrugated exhalation tube 117 increases resistance to flow and also increases compressible volume. Table 1 summarizes the effect of various features on these two system metrics.

[0064] [Table 1]

[0065] Pairing a corrugated expiratory tube 117 with a smooth-bore inspiratory tube 103 can improve the performance of the inspiratory tube 103. Pairing a larger-diameter expiratory tube 117 with a smaller-diameter inspiratory tube 103 is net-neutral with respect to compressible volume but can increase the function of the breathing circuit (e.g., increased vapor diffusion in the expiratory tube 117). In this configuration, the smooth-bore inspiratory tube 103 minimizes condensation and therefore maximizes moisture delivery. The overall compressible volume can be reduced by changing the dimensions, e.g., the diameter and length, of the inspiratory tube 103 and expiratory tube 117. In some configurations, the inspiratory tube 103 is insulated, which helps make the humidifier 107 and / or heating elements, such as the heater plate 131, more efficient at generating moisture delivered to the patient 101. The heater plate 131 does not need to operate as hard because it does not have to generate a high target temperature at the humidification chamber port 111, and because the heated and insulated intake tube 103 better maintains the absolute humidity of the gas flowing from the humidification chamber port 111 through the intake tube 103.

[0066] Locating the heater wire within the wall of the intake tube 103 also increases the efficiency of the intake tube 103 in maintaining the relative humidity of the gas. The heater wire can heat the wall of the intake tube 103 and not the gas flowing through the lumen of the intake tube 103, thereby reducing the relative humidity of the gas near the wall of the intake tube 103. If the intake tube 103 includes a composite conduit having a spirally wound hollow body, or "bubble" tube (described in more detail below), the heater wire is below the insulating bubble (on the lumen side of the inner wall), thereby reducing heat loss outward through the wall of the intake tube 103.

[0067] The smooth bore intake tube 103 promotes laminar gas flow, which creates a more parabolic wavefront across the lumen of the intake tube 103, with gas closer to the center of the lumen having a higher velocity relative to gas closer to the walls of the intake tube 103. In this configuration, the higher velocity gas has less time to transfer heat to the adjacent lower velocity gas traveling from the inlet 109 to the outlet 113. This arrangement, along with the inward direction of the heat generated by the heater wire, helps to further increase the heat retained by the gas flow.

[0068] The smooth bore intake tube 103 also does not provide pockets where vapor can be trapped or condensation can accumulate, as corrugated tubes do. Gas-borne vapor therefore remains in the vapor phase and is more likely to exit the intake tube 103 and be delivered to the patient 101.

[0069] The corrugated expiratory tube 117 maximizes vapor removal and minimizes condensation. The expiratory tube 117 can be vapor permeable, which promotes vapor diffusion through the walls of the expiratory tube 117 and into the external atmosphere. In some configurations, the expiratory tube 117 is vapor permeable and heated, and controlled heating along the tube promotes vapor diffusion through the walls of the expiratory tube 117 and into the external atmosphere. Vapor transported to the external atmosphere is not delivered to the gas source 105. The corrugated expiratory tube 117 creates turbulence in the gas flow adjacent to the walls of the expiratory tube 117, which increases the residence time of gas adjacent to the walls of the corrugations. Increasing residence time increases the opportunity for vapor diffusion through the walls of the expiratory tube 117. Increasing residence time also reduces the temperature of gases swirling within each corrugation "pocket," thereby increasing the relative humidity of these gases. Higher relative humidity increases the vapor pressure gradient across the wall of the expiratory tube 117, which therefore increases the diffusion of vapor through the wall.

[0070] As described below, the expiratory tube 117 can include a heater wire wound near the center of the lumen of the expiratory tube 117. When positioned in this manner, the heater wire increases turbulence in the gas flow while minimizing condensation formation. Increased turbulence means better mixing of the gas, which causes water vapor to migrate to the outer wall of the expiratory tube 117. The corrugated expiratory tube 117 also provides corrugation "pockets," which have the advantage of collecting any liquid that condenses from the vapor. Liquid that accumulates in the corrugations is liquid that is not delivered to the gas source 105. In some configurations, the heater wire can be positioned within the wall of the expiratory tube 117. The presence of the heater wire within the expiratory tube 117 also reduces condensation formation within the expiratory tube.

[0071] The combination of a smooth bore inspiratory tube 103 and a corrugated expiratory tube 117 allows the humidifier 107 to enhance humidity performance. In both invasive and non-invasive ventilation, there is a contribution from the patient and bias flow. In both, the expiratory tube 117 can function to reduce the amount of humidity returned to the gas source 105. The function of the expiratory tube 117 can be to significantly reduce the amount of humidity returned to the gas source 105.

[0072] The function of the expiratory tube allows the humidifier 107 and inspiratory tube 103 to deliver more moisture to the patient 101. If the expiratory tube 117 is unable to sufficiently reduce the amount of moisture returned to the gas source 105, the ability of the humidifier 107 and inspiratory tube 103 to deliver more moisture to the patient 101 must be reduced or reversed because some of the excess moisture will be carried through the expiratory tube 117 to the gas source 105.

[0073] 1A shows a breathing circuit 100, which may be similar to FIG. 1 described herein. Such a breathing circuit 100 may be a respiratory humidification circuit. The breathing circuit 100 includes one or more medical tubes. The breathing circuit 100 may include an inspiratory tube 103 and an expiratory tube 117.

[0074] Gases can be transported in circuit 100 of Figure 1A. Ambient gas flows from a gas source 105 to a humidifier 107. The humidifier 107 can humidify the gas. The gas source 105 can be a ventilator, a blower or fan, a tank containing compressed gas, a wall supply in a medical facility, or any other suitable source of breathing gas.

[0075] The humidifier 107 is connected to the inlet 109 (end for receiving humidified gas) of the inhalation tube 103 via port 111, thereby supplying humidified gas to the inhalation tube 103. Gas flows through the inhalation tube 103 to the outlet of the inhalation tube 103 (end for discharging humidified gas) and then to the patient 101 through a patient interface 115 connected to the outlet 113. An expiratory tube 117 is connected to the patient interface 115. The expiratory tube 117 returns exhaled humidified gas from the patient interface 115 to the gas source 105 or to the ambient atmosphere.

[0076] Gas may enter gas source 105 through vent 119. A fan 121 blower may draw air or other gas through vent 119, causing the gas to flow into gas source 105. Blower or fan 121 may be a variable speed blower or fan. An electronic controller 123 may control the speed of the blower or fan. In particular, the function of electronic controller 123 may be controlled by an electronic master controller 125. The function may be controlled in response to inputs from master controller 125 and user setting of pressure or blower or fan speed to predetermined required values ​​(preset values) via dials or other suitable input devices 127.

[0077] The humidifier 107 includes a humidification chamber 129. The humidification chamber 129 may be configured to contain a volume of water 130 or other suitable humidification liquid. The humidification chamber 129 is removable from the humidifier 107. This allows the humidification chamber 129 to be more easily sterilized or disposed of after use. The humidification chamber 129 portion of the humidifier 107 may be of one piece or may be formed from multiple components that are joined together to define the humidification chamber. The body of the humidification chamber 129 may be formed from a non-conductive glass or plastic material. The humidification chamber 129 may also include conductive components. For example, the humidification chamber 129 may include a highly thermally conductive base (e.g., an aluminum base) configured to contact or be associated with a heater plate 131 on the humidifier 107 when the humidification chamber 129 is attached to the humidifier 107.

[0078] The humidifier 107 may include electronic control functionality. The humidifier 107 may include an electronic, analog, or digital master controller 125. The master controller 125 may be a microprocessor-based controller that executes computer software commands stored in associated memory. In response to user-set humidity or temperature values ​​and other inputs via a user input device 133, the master controller 125 determines when (or to what level) to energize the heater plate 131 to heat the volume of water 130 in the humidification chamber 129.

[0079] As previously mentioned, any suitable patient interface can be used for the patient interface. The temperature probe 135 can be connected to the inlet conduit 103 near the patient interface 115, or the temperature probe 135 can be connected to the patient interface 115. The temperature probe 135 can be incorporated within the inlet conduit 103. The temperature probe 135 detects the temperature near or at the patient interface 115. A signal reflective of the temperature can be provided by the temperature probe 135 to an electronic, analog, or digital master controller 125. A heating element (not shown) can be used to regulate the temperature of the patient interface 115, raising the temperature of the patient interface 115 above a saturation temperature, thereby reducing the chance of unwanted condensation. A heating element 145 can also be used to regulate the temperature of the inlet conduit 103, raising the temperature of the inlet conduit 103 above a saturation temperature, thereby reducing the chance of unwanted condensation.

[0080] 1A, exhaled humidified gases are returned from the patient interface 115 to the gas source 105 via an expiratory tube 117. The expiratory tube 117 may comprise a vapor-permeable material, which will be described in more detail below. The vapor-permeable expiratory tube may be corrugated.

[0081] The expiratory tube 117 may have a temperature probe and / or heating element, as described above with respect to the inhalation tube 103, to reduce the chance of condensation reaching the gas source 105. The expiratory tube 117 does not need to return the exhaled gases to the gas source 105. The exhaled humidified gases may flow directly to the ambient environment or to other ancillary equipment, such as an air scrubber / filter (not shown).

[0082] In FIG. 1A, the intake pipe 103 includes or comprises a conduit having a smooth bore. The smooth bore results in the intake pipe 103 having a lower RTF than a conduit of comparable size having a corrugated bore. The smooth bore provides lower resistance to flow, thereby allowing the bore (i.e., diameter or cross-sectional area) to be reduced, resulting in a smaller compressible volume compared to a corrugated pipe with comparable resistance to flow. The intake conduit may be a composite conduit. A composite conduit may be generally defined as a conduit including two or more individual sections, or more specifically, two or more components, that define an interconnected conduit. A composite conduit may be spirally wound. A composite conduit may be spirally wound in a manner such that two or more components are helically twisted together or connected side-by-side to form a helix.

[0083] The expiratory tube 117 includes or comprises a conduit, at least a portion of which is vapor permeable. Vapor permeability facilitates moisture removal. At least the vapor permeable portion of the expiratory tube 117 can be corrugated. The corrugations can be on the inside of the tube. The corrugations increase the inner surface area of ​​the tube. The amount of vapor that can diffuse through a vapor permeable material is a function of the surface area of ​​the material that is in direct contact with the vapor. The corrugations also increase the turbulence of the gas within the expiratory tube. Increased turbulence means that the gas is better mixed, which causes water vapor to migrate to the outer wall of the expiratory tube 117. Increased turbulence can increase localized retention within the corrugations within the expiratory tube, which, when combined with the vapor permeability attribute, further improves moisture removal. The increased residence time in the corrugations causes the gases swirling within each corrugation "pocket" to have a lower temperature compared to that of a comparable sized smooth-bore tube, thereby increasing the relative humidity of these gases compared to that of a comparable sized smooth-bore tube. The increased relative humidity causes a higher vapor pressure gradient across the walls of the expiratory tube 117 compared to that of a comparable sized smooth-bore tube, which therefore increases the diffusion of vapor through the walls of the corrugated expiratory tube compared to that of a comparable sized smooth-bore tube.

[0084] The vapor-permeable corrugated conduit may be at least partially formed from a foamed polymer that is permeable to water vapor and substantially impermeable to the bulk flow of liquid water and gas. The expiratory tube 117 may include a wall that defines a space within the expiratory tube 117. At least a portion of the wall may be formed from a vapor-permeable foam material configured to allow water vapor to pass through but substantially prevent the passage of liquid water and the bulk flow of gas.

[0085] The vapor-permeable expiratory tube 117 can be formed from a non-foaming material. The non-foaming material can include a spirally wound vapor-permeable tape. The corrugation of the expiratory tube 117 can be achieved using a non-foaming material. The non-foaming material can include beads of different diameters arranged in an alternating pattern to form a corrugated interior surface.

[0086] The inlet tube 103 comprises a smooth-bore conduit. Smooth-bore conduits can be heated and insulated to minimize condensation and maximize moisture transport. Reducing condensation formation within the inlet tube allows for more vapor to be delivered to the patient in the humidified gas. Several factors affect condensation formation within the inlet tube 103, including the diameter of the inner bore, the degree of smoothness of the inner bore, the level of insulation of the tube, the presence of a heating element 145 (such as a wire or element) associated with the tube 103, and the location of the heating element within the tube 103, i.e., whether the heating element is within the inner bore of the tube 103 or within the wall of the tube 103. Specifically, reducing the diameter of the inner bore of the inlet tube 103 increases the velocity of gas as it travels within the inlet tube 103. Increasing the smoothness of the bore reduces turbulence and creates a more parabolic wavefront across the lumen. Therefore, by reducing the diameter of the inner bore and making the inner bore smooth, the higher velocity gas near the center of the tube transfers less heat to the slower velocity gas near the wall of the tube. Smooth bore tubes do not provide pockets where vapor can become trapped or condensation can accumulate, as occurs in corrugated tubes. Gas-borne vapors are therefore more likely to exit the tube and be delivered to the patient.

[0087] Increasing the degree of tubing insulation reduces heat loss through the walls of the inspiratory tubing 103, thereby minimizing condensation formation and maximizing moisture delivery. Further increasing the insulation of the inspiratory tubing 103 reduces the extent to which the heating element must work to maintain the target temperature and humidity, and also makes the breathing circuit 100 more efficient, since the insulated tubing is better able to maintain the temperature and absolute humidity of the gases traveling through the tubing.

[0088] Adding a heating element to the inspiratory conduit 103 also maximizes humidification and reduces condensation. Locating one or more heating elements within the wall of the inspiratory conduit 103 maximizes humidification and minimizes condensation formation, contributing to the efficiency of the inspiratory conduit 103, breathing circuit 100, or humidification system. When positioned within the wall of the inspiratory conduit 103, the heating element heats the wall and does not directly heat the gas. Heating the wall reduces the relative humidity of the gas near the wall (heating the gas increases its temperature, which reduces its relative humidity). Locating a heating element on the lumen side of the inner wall of the insulating "bubble" (defined below) of the inspiratory conduit 103 (described in more detail below) can further reduce outward heat loss through the wall of the inspiratory conduit 103, which therefore maximizes humidification while minimizing condensation formation.

[0089] The expiratory tube 117 can include a corrugated conduit to maximize vapor removal while minimizing condensation formation and increasing local residence time within the corrugations. The expiratory tube 117 can include a vapor-permeable conduit to maximize vapor removal while minimizing condensation formation. The expiratory tube 117 can include a corrugated, vapor-permeable, and / or heated conduit to maximize vapor removal while minimizing condensation formation and increasing local residence time within the corrugations. Reducing condensation formation in the expiratory tube 117 allows more vapor to diffuse through the walls of the expiratory tube 117. The presence of the heating element 155 can keep the relative humidity of the gas below 100% (i.e., keep the gas temperature above the dew point saturation temperature). By positioning the heating element 155 near or within the walls of the expiratory tube 117, the heating element 155 primarily heats the gas near the walls of the expiratory tube 117. Condensation formation is avoided or limited by maintaining the gas temperature near the walls of the expiratory tube 117 above the dew point. The inspiratory tube 103 and expiratory tube 117 are described in much greater detail elsewhere herein.

[0090] It has been recognized that by incorporating an inspiratory tube 103 having a smaller diameter smooth bore conduit along with an expiratory tube 117 having a corrugated conduit, the expiratory tube 117 can be made larger in diameter and / or longer than would otherwise be possible while maintaining the compressible volume of the overall system. Additionally or alternatively, the combination of a smaller diameter smooth bore inspiratory tube 103 with a larger diameter corrugated expiratory tube 117 can maintain the overall pressure drop. Additionally or alternatively, the combination of a smaller diameter smooth bore inspiratory tube 103 with a larger diameter corrugated expiratory tube 117 can maintain the resistance to flow (RTF) of the breathing circuit 100 at a desired level. Increasing the length of the conduit typically undesirably increases the compressible volume of the conduit and therefore the compressible volume of the overall breathing circuit. Increasing the length of the conduit typically undesirably increases the RTF of the conduit and therefore the RTF of the overall breathing circuit. On the other hand, if the conduit is vapor permeable, increasing the length advantageously improves the ability of the conduit to remove vapors from the exhaled gases. It has been found that the combination of an inspiratory tube 103 having a smaller diameter smooth bore and an expiratory tube 117 having a larger diameter corrugated vapor permeable conduit increases the ability of the expiratory tube 117 to remove water vapor from the breathing circuit without increasing the compressible volume, pressure drop, and / or RTF of the overall system.

[0091] It has further been recognized that by incorporating an inspiratory tube 103 having a smooth bore conduit, along with an expiratory tube 117 having a corrugated conduit, the humidifier 107 improves humidity performance and provides therapeutic benefit to the patient while also approaching fully saturated gas without increasing the risk of liquid damage to the gas source 105 or condensate backflow to the patient.

[0092] An inlet tube 103 having a smooth-bore, spirally wound conduit can be paired with an expiratory tube 117 having a corrugated vapor-permeable conduit. As previously mentioned, the smooth bore of the inlet tube 103 has a lower RTF than a comparably sized corrugated bore. It can also have a smaller inner diameter than the corrugated conduit. Typically, a smaller inner diameter reduces the compressible volume, undesirably increasing the RTF of the inlet tube. However, the characteristics of the smooth bore can be selected such that the reduced RTF associated with the smooth bore of the inlet tube 103 outweighs the increased RTF due to the smaller inner diameter of the inlet tube 103. This selection of a smaller diameter inlet tube 103 also reduces the compressible volume of the inlet tube 103. This selection allows for a longer corrugated expiratory tube 117 paired with a smooth-bore inlet tube 103 without increasing the overall system pressure drop and / or compressible volume. Lengthening the expiratory tube 117 typically undesirably increases the tube's RTF and compressible volume. However, increasing the length also improves the vapor-permeable tube's ability to remove vapor from exhaled gases. In this configuration, pairing a smooth-bore inspiratory tube 103 with a corrugated expiratory tube 117 improves the expiratory tube's performance. The system pressure drop of the breathing circuit that may exist from the ventilator outlet to the ventilator inlet can be affected by the pressure characteristics (RTF) of each element in the circuit. Referring again to FIG. 1A , assuming constant pressure characteristics of the supply tubing from the ventilator to the humidifier, humidification chamber, interface tubing, and interface body, the primary factors contributing to the system pressure drop are the resistance to flow and the dimensions (length and diameter) of the expiratory tube 103 and expiratory tube 117. Any change in one of these factors should be balanced with the others to advantageously avoid increasing the system's pressure drop, RTF, and / or compressible volume. As described herein, the primary factors contributing to the compressible volume are the tube profile, compliance, and dimensions (length and diameter or cross-sectional area) of the inspiratory tube 103 and expiratory tube 117. A trade-off can be made between reducing the compressible volume of the inspiratory tube 103 and increasing the compressible volume of the expiratory tube 117, while preserving the compressible volume of the breathing circuit.As described herein, increasing the compressible volume of the expiratory tube 117 is beneficial for vapor permeability at the expiratory rim.

[0093] The smooth bore of the inhalation tube 103 reduces resistance to flow (compared to a corrugated inhalation tube), reducing the overall system pressure drop. This allows any or all of the other three factors (resistance to flow of the corrugated expiratory tube 117 or the dimensions of the respective tubes) to be modified to increase system pressure drop. The inner diameter of the inhalation tube can be smaller than that of a comparable corrugated inhalation tube, which desirably increases the velocity of gas flowing through the inhalation tube 103. However, a smaller diameter also increases resistance to flow to some extent. As long as the increase in RTF due to the smaller diameter is sufficiently smaller than the decrease in RTF resulting from the use of a smooth bore, the length of the corrugated expiratory tube 117 can be increased without increasing system pressure drop. Increasing the length of the expiratory tube 117 increases the surface area of ​​the expiratory tube 117 wall. The amount of vapor that can diffuse through a vapor-permeable material is a function of the material's surface area. Increasing the length of the expiratory tube 117 increases the surface area of ​​the walls of the expiratory tube 117 and also increases the residence time of gas in the expiratory tube 117. The amount of vapor that can diffuse through a permeable material is also related to the length of time that the vapor-carrying gas is in contact with the material.

[0094] The compressible volume of the breathing circuit (the cumulative volume of the entire gas flow path) can be balanced in a similar manner. For example, a change in the dimensions (cross-sectional area or diameter, length) of the inspiratory tube 103 can be offset by a change in the dimensions (cross-sectional area or diameter, length) of the corrugated expiratory tube 117. As described herein, decreasing the diameter of the inspiratory tube 103 can reduce the compressible volume. This reduction in compressible volume can increase the accuracy of the delivered tidal volume. As described herein, a decrease in the diameter of the inspiratory tube 103 can offset an increase in the diameter and / or length of the expiratory tube 117. As described herein, changing the dimensions of the expiratory tube 117 can enhance the function of the expiratory tube 117, for example, by increasing the vapor permeability of the expiratory tube 117. Because changing the tube diameter affects both the system pressure drop and the system compressible volume, advantageously, both equations should be balanced or selected simultaneously during the change. Reducing the diameter of the inhalation tube 103 can both increase resistance to flow and decrease compressible volume, resulting in a faster average gas velocity through the tube. Increasing the length of the corrugated exhalation tube 117 increases resistance to flow and also increases compressible volume. Table 1 (discussed above) summarizes the effect of various features on these two system metrics.

[0095] Pairing a corrugated expiratory tube 117 with a smooth-bore inspiratory tube 103 can enhance the performance of the inspiratory tube 103. Pairing a larger-diameter expiratory tube 117 with a smaller-diameter inspiratory tube 103 is net-neutral with respect to compressible volume but can increase the function of the breathing circuit (e.g., increased vapor diffusion in the expiratory tube 117). In this configuration, the smooth-bore inspiratory tube 103 minimizes condensation and therefore maximizes moisture delivery. The overall compressible volume can be reduced by changing the dimensions, e.g., the diameter and length, of the inspiratory tube 103 and expiratory tube 117. In some configurations, the inspiratory tube 103 is insulated, which helps make the humidifier 107 and / or heating elements, such as the heater plate 131, more efficient at generating moisture delivered to the patient 101. The heater plate 131 does not need to operate as hard because it does not have to generate a high target temperature at the humidification chamber port 111, and because the heated and insulated intake tube 103 better maintains the absolute humidity of the gas flowing from the humidification chamber port 111 through the intake tube 103.

[0096] Locating the heater wire 145 within the wall of the intake tube 103 also increases the efficiency of the intake tube 103 in maintaining the relative humidity of the gas. The heater wire can heat the wall of the intake tube 103 and not the gas flowing through the lumen of the intake tube 103, thereby reducing the relative humidity of the gas near the wall of the intake tube 103. If the intake tube 103 includes a composite conduit having a spirally wound hollow body, or "bubble" tube (described in more detail below), the heater wire 145 is below the insulating bubble (on the lumen side of the inner wall), thereby reducing heat loss outward through the wall of the intake tube 103.

[0097] The smooth bore intake tube 103 promotes laminar gas flow, which creates a more parabolic wavefront across the lumen of the intake tube 103, with gas closer to the center of the lumen having a higher velocity relative to gas closer to the walls of the intake tube 103. In this configuration, the higher velocity gas has less time to transfer heat to the adjacent lower velocity gas traveling from the inlet 109 to the outlet 113. This arrangement, along with the inward direction of the heat generated by the heater wire, helps to further increase the heat retained by the gas flow.

[0098] The smooth bore intake tube 103 also does not provide pockets where vapor can become trapped or condensation can accumulate, as corrugated tubes do. Gas-borne vapors therefore remain in the vapor phase and are more likely to exit the intake tube 103 and be delivered to the patient 101.

[0099] The corrugated expiratory tube 117 maximizes vapor removal and minimizes condensation. The expiratory tube 117 can be vapor permeable, which promotes vapor diffusion through the walls of the expiratory tube 117 and into the external atmosphere. In some configurations, the expiratory tube 117 is vapor permeable and heated, and controlled heating along the tube promotes vapor diffusion through the walls of the expiratory tube 117 and into the external atmosphere. Vapor transported to the external atmosphere is not delivered to the gas source 105. The corrugated expiratory tube 117 creates turbulence in the gas flow adjacent to the walls of the expiratory tube 117, which increases the residence time of gas adjacent to the walls of the corrugations. Increasing residence time increases the opportunity for vapor diffusion through the walls of the expiratory tube 117. Increasing residence time also reduces the temperature of gases swirling within each corrugation "pocket," thereby increasing the relative humidity of these gases. Higher relative humidity increases the vapor pressure gradient across the wall of the expiratory tube 117, which therefore increases the diffusion of vapor through the wall.

[0100] As described below, the expiratory tube 117 can include a heater wire 155 wound near the center of the lumen of the expiratory tube 117. When positioned in this manner, the heater wire increases turbulence in the gas flow while minimizing condensation formation. Increased turbulence means better mixing of the gas, which causes water vapor to migrate to the outer wall of the expiratory tube 117. The corrugated expiratory tube 117 also provides corrugation "pockets," which have the advantage of collecting any liquid that condenses from the vapor. Liquid that accumulates in the corrugations is liquid that is not delivered to the gas source 105. In other configurations, the heater wire can be positioned within the wall of the expiratory tube. The presence of the heater wire 155 within the expiratory tube 117 also reduces condensation formation within the expiratory tube.

[0101] The combination of a smooth bore inspiratory tube 103 and a corrugated expiratory tube 117 allows the humidifier 107 to enhance humidity performance. In both invasive and non-invasive ventilation, there is a contribution from the patient and bias flow. In both, the expiratory tube 117 can function to reduce the amount of humidity returned to the gas source 105. The function of the expiratory tube 117 can be to significantly reduce the amount of humidity returned to the gas source 105.

[0102] The function of the expiratory tube allows the humidifier 107 and inhalation tube 103 to deliver more moisture to the patient 101. If the expiratory tube 117 is unable to sufficiently reduce the amount of moisture returned to the gas source 105, then the ability of the humidifier 107 and inhalation tube 103 to deliver more moisture to the patient 101 must be reduced or reversed because some of the excess moisture will be carried through the expiratory tube 117 to the gas source 105.

[0103] The inspiratory tube 103 and the expiratory tube 117 are described in more detail below.

[0104] intake pipe FIG. 2A shows a side view of a section of an intake conduit 201. Generally, the conduit 201 includes a first elongate member 203 and a second elongate member 205. Member is a broad term and is given its ordinary and accustomed meaning to those skilled in the art (i.e., it is not limited to a specific or dedicated meaning), including, but not limited to, an integral part, an integral component, and a separate component. The first elongate member 203 has a "bubble" shape, while the second elongate member 205 is a structural support or reinforcing member that adds structural support to the hollow body. As used herein, all references to a "bubble" refer to an elongate hollow body having a shape defined by a wall in cross section with a hollow space therein. Such shapes can include an oval or "D" shape, with reference to FIG. 2B. Such shapes can include an "O" shape and other symmetrical and asymmetrical regular and irregular shapes. In this description, the term "bubble" can refer to the cross-sectional shape of the elongate wrap or turn of the first elongate member 203 in a transverse cross section through the wrap or turn, as shown, for example, in FIG. 2B. The hollow body and structural support member can have a helical configuration as described herein. The conduit 201 can be used to form the intake tube 103 described above, the coaxial tube described below, or any other tube described elsewhere in this disclosure.

[0105] The first elongate member 203 includes a hollow body that is spirally wound to at least partially form an elongate tube having a longitudinal axis LA-LA and a lumen 207 extending along the longitudinal axis LA-LA. A portion 211 of the first elongate member 203 forms at least a portion of the inner wall of the lumen 207. The first elongate member 203 may be a tube. Preferably, the first elongate member 203 is flexible. Flexible refers to the ability to bend. Additionally, the first elongate member 203 is preferably transparent, or at least translucent or partially opaque. A degree of optical transparency allows a caregiver or user to inspect the lumen 207 for blockages or contamination or to identify the presence of moisture (i.e., condensation). Various plastics, including medical-grade plastics, are suitable for the body of the first elongate member 203. Suitable materials include polyolefin elastomers, polyether block amides, thermoplastic copolyester elastomers, EPDM-polypropylene blends, and thermoplastic polyurethanes.

[0106] The hollow body structure of the first elongate member 203 contributes to the insulating properties of the conduit 201. An insulated conduit is desirable because, as previously mentioned, it prevents heat loss, allowing the conduit 201 to deliver gas from the humidifier 107 to the patient 101 while maintaining a conditioned state of the gas with minimal energy expenditure.

[0107] The second elongate member 205 is also spirally wound and is coupled to the first elongate member 203 between adjacent turns of the first elongate member 203. The second elongate member 205 forms at least a portion of the lumen 207 of the elongate tube. The second elongate member 205 serves as structural support for the first elongate member 203. The second elongate member 205 can be wider at the base (closer to the lumen 207) and narrower at the top. The second elongate member can be generally triangular, generally T-shaped, or generally Y-shaped. However, any shape that matches the contour of the corresponding first elongate member 203 is suitable.

[0108] Preferably, the second elongate member 205 is flexible to facilitate bending of the tube. Desirably, the second elongate member 205 is less flexible than the first elongate member 203. This enhances the ability of the second elongate member 205 to provide structural support to the first elongate member 203. The second elongate member 205 can be solid or mostly solid.

[0109] The second elongate member 205 can house or contain a conductive material such as a filament, specifically a filament used to generate heat or transmit information from a sensor (not shown). The heating element can include a filament to minimize cold surfaces on which condensation from moist gases can form. The heating element can also be used to change the temperature distribution of gas within the lumen 207 of the conduit 201. Various polymers and plastics, including medical-grade plastics, are suitable for the body of the second elongate member 205. Suitable materials include polyolefin elastomers, polyether block amides, thermoplastic copolyester elastomers, EPDM-polypropylene blends, and thermoplastic polyurethanes. The first elongate member 203 and the second elongate member 205 can be fabricated from the same material.

[0110] FIG. 2B shows a longitudinal cross-section of the upper portion of the conduit 201 of FIG. 2A. FIG. 2B is in the same orientation as FIG. 2A. The first elongate member 203 can have a hollow body shape. The first elongate member 203 can form a plurality of hollow bubbles in the longitudinal cross-section. A portion 209 of the first elongate member 203 overlaps an adjacent covered portion of the second elongate member 205. A portion 211 of the first elongate member 203 forms at least a portion of the wall of the lumen 207 (tube bore). Adjacent bubbles can be separated by a gap 213. A T-shaped second elongate member 205 can facilitate maintaining the gap 213 between adjacent bubbles, as shown in FIG. 2B.

[0111] The first elongate member 203 defines a plurality of hollow bubbles in longitudinal cross section.

[0112] One or more conductive materials can be placed within the second elongated member 205 for heating or sensing the gas flow. Two heating elements 215 can be housed within the second elongated member 205, one on each side of the longitudinal portion of the "T." The heating elements 215 comprise a conductive material, such as an aluminum (Al) and / or copper (Cu) alloy or a conductive polymer. Preferably, the material forming the second elongated member 205 is selected so as not to react with the metal of the heating element 215 when the heating element 215 reaches its operating temperature. The heating elements 215 can be spaced apart from the lumen 207 so that the elements are not exposed to the lumen 207. At one end of the composite tube, a pair of elements can be formed into a connected loop. Multiple filaments can be placed within the second elongated member 205.

[0113] Table 2 shows a non-limiting sample of dimensions for two composite conduits described herein, one for infants and the other for adults, as well as some non-limiting sample ranges for these dimensions. Dimensions refer to the transverse cross-section of the tube. In these tables, lumen diameter refers to the inner diameter of the tube. Pitch refers to the distance between two repeat points measured axially along the tube, i.e., the distance between the tips of adjacent vertical "T" portions of the second elongate member 205. Bubble width refers to the width (maximum outer diameter) of the bubble. Bubble height refers to the height of the bubble from the tube lumen. Bead height refers to the maximum height of the second elongate member 205 from the tube lumen (e.g., the height of the vertical "T"). Bead width refers to the maximum width of the second elongate member 205 (e.g., the width of the horizontal "T"). Bubble thickness refers to the thickness of the bubble wall.

[0114] [Table 2]

[0115] Tables 3 and 4 show the properties of a composite tubing described herein (designated "A") having a heating element embedded within the second elongated member 205. For comparison, properties are also shown for Fisher & Paykel model RT100 (designated "B"), a disposable corrugated tubing having a heating element helically wound inside the tubing bore.

[0116] Resistance to flow (RTF) measurements were performed in accordance with Annex A of ISO 5367:2000(E). This publication provides a standard equipment list, procedural steps, and units for expressing the resistance to flow test results as a measurement of the pressure rise at rated flow rate through the breathing tube. It includes variances for testing breathing tubes supplied ready-to-use or 1-meter lengths of breathing tubing supplied to be cut to length, as well as variances for testing each limb individually of a dual-limb circuit containing a pair of breathing tubes connected together in a Y-piece. The test result is the difference in pressure measured in the reservoir with and without a breathing tube attached to the reservoir opening.

[0117] The results are summarized in Table 3. As can be seen below, the RTF of the composite pipe is lower than the RTF of a comparable sized Model RT100 pipe.

[0118] [Table 3]

[0119] Condensation or "rainout" within the tube refers to the weight of condensation collected per day at a gas flow rate of 20 L / min and a room temperature of 18°C. Humidified air flows continuously from the chamber through the tube. The weight of the tube is recorded before and after each test day. Three consecutive tests are performed, with the tube allowed to dry between tests. The results are shown in Table 4 below. The results show that rainout is significantly lower for the composite tube than for a comparable sized Model RT100 tube.

[0120] [Table 4]

[0121] The composite tube 201 can include one or more heating filaments 215 disposed in the gas path. The heating filaments can be disposed helically on the wall of the lumen (the tube bore). The one or more heating filaments 215 can be disposed on the wall of the lumen through bonding, embedding, or otherwise, such that the heating filaments are formed on a surface of the second elongate member 205 that, when assembled, forms the wall of the lumen. Thus, the method can include disposing one or more heating filaments 215 on the wall of the lumen.

[0122] Other details regarding a composite conduit suitable for the intake pipe 103 are disclosed in the specifications and drawings of U.S. Patent Application Publication No. 14 / 123,485, published as U.S. Patent Application Publication No. 2014 / 0202462 A1, and U.S. Patent Application Publication No. 14 / 649,801, published as U.S. Patent Application Publication No. 2015 / 0306333 A1, which are incorporated herein by reference in their entirety for all that they contain.

[0123] expiratory tube As previously described with respect to FIG. 1 , a breathing circuit can utilize a vapor-permeable (i.e., breathable) expiratory tube to handle exhaled gases with high relative humidity. Breathability is desirable to increase vapor diffusion and thus prevent rainout (condensation) in these components. Therefore, a breathing circuit can include a vapor-permeable expiratory tube. Generally, the expiratory tube includes an inlet (for receiving exhaled gases), an outlet (for discharging the received gases), and an enclosing wall defining at least one gas passageway between the inlet and the outlet, at least a portion of which is a vapor-permeable material that allows water vapor to pass through but substantially prevents the passage of liquid water and the bulk flow of respiratory gases. The expiratory tube can terminate with a first connector at the inlet and a second connector at the outlet, providing only one gas passageway along the length between the inlet and outlet connectors.

[0124] By virtue of its breathability or vapor permeability, the wall provides a water vapor pathway from the gas space within the tube to the area on the other side of the wall, which may be the outside air. Preferably, the vapor permeable portion of the enclosing wall is formed from a foam material. The tube may comprise an extruded corrugated conduit.

[0125] It has been found that an expiratory tube comprising a vapor-permeable foamed polymer advantageously possesses both breathability and strength. The expiratory tube can include a wall defining a space therein, at least a portion of which is made of a vapor-permeable foam material that allows vapor from gas within the space to pass through but prevents liquid water from passing through. The entire surrounding wall can be formed of a foam material. Preferably, the wall is also impermeable to the bulk flow of gas within the space, including breathing gas. Due to its vapor permeability, the wall provides a pathway for water vapor from the gas space to the region on the opposite side of the wall.

[0126] Reference is now made to Figures 3A and 3B, which illustrate an expiratory tube conduit 301. Figure 3A shows a side view of conduit 301, and Figure 3B shows a cross-section of conduit 301 along the same side view as Figure 3A. In both Figures 3A and 3B, the horizontal axis is indicated by line 303-303. The wall of the conduit, shown as wall 305 in Figure 3B, is a vapor-permeable foam material. As shown, conduit 301 is corrugated. The wall of the tube, shown as wall 305 in Figure 3B, is a breathable foam material, as described above.

[0127] Because the tube is a type of component, the details of the components discussed above also apply to the tube discussed herein. At least a portion of the surrounding wall can include a breathable foam material that allows water vapor to pass through but substantially prevents liquid water and the bulk flow of breathing gases from passing through. The tube can be an extruded corrugated tube. The medical circuit tube can be used as a breathing tube or conduit, or as a tube or conduit for a limb of an air delivery system. For example, the tube can be used as an expiratory breathing tube or an exhaust conduit, respectively. The tube can be part of a patient interface. The conduit 301 can be used as the expiratory tube 117 as described above, a coaxial tube as described below, or any other tube described elsewhere in this disclosure.

[0128] By incorporating highly breathable or vapor-permeable foam materials, components can be manufactured to have both relatively high bending stiffness and high breathability. Because of their high vapor permeability (breathability), foamed polymers allow water vapor to diffuse rapidly from them. This reduces condensation formation in the expiratory tract by allowing water vapor to permeate from the humidified gas in the expiratory tract to the surrounding ambient air or other drier gases on the other side of the component. However, components formed from these foamed polymers can be rigid, self-supporting, and compression-resistant, or even semi-rigid, offering relatively high resistance to compression and buckling, and even eliminating the need for additional reinforcement. Foamed polymers are useful for forming components of medical circuits because they allow water vapor from gases to permeate but prevent the permeation of liquid water. They are also substantially impermeable to bulk gas flow, allowing them to be used to form components for delivering humidified gases. The foamed polymer can be selected so that, without additional reinforcement, the "bulk" properties (thickness, material, material mix, modulus of elasticity, breathability, and / or bulk hardness) meet the requirements of the ISO 5367:2000(E) standard (i.e., the test for increased resistance to flow) and still be vapor permeable. ISO 5367:2000(E) is incorporated herein by reference in its entirety.

[0129] Preferably, the foamed polymer is a vapor-permeable foamed thermoplastic polymer. The vapor-permeable thermoplastic polymer can be a foamed thermoplastic elastomer (or TPE as defined by ISO 18064:2003(E)), such as (1) a copolyester thermoplastic elastomer (e.g., ARNITEL®, a copolyester thermoplastic elastomer with polyether soft segments, or other TPC or TPC-ET materials as defined by ISO 18064:2003(E)), or (2) a polyether block amide (e.g., PEBAX®, a polyamide thermoplastic elastomer with polyether soft segments, or other TPA-ET materials as defined by ISO 18064:2003(E)), or (3) a thermoplastic polyurethane (a TPU material as defined by ISO 18064:2003(E)), or (4) a foamed polymer blend, such as a TPE / polybutylene terephthalate (PBT, e.g., DURANEX® 500FP) blend. It has been found that the vapor-permeable TPE ARNITEL® VT3108 may be particularly suitable for foaming and forming components. For this material, the breathability-to-strength relationship can be significantly improved by foaming the material as it is formed into a product or component. When the breathable thermoplastic polymer is an expanded TPE / PBT blend, the blend preferably contains 80%-99% (or about 80%-99%) TPE by weight and 20%-1% (or about 20%-1%) PBT by weight. The void fraction of the foamed material can be greater than 25% (or about 25%), e.g., 25-60% (or about 25-60%), or 30-50% (or about 30-50%). The foamed material can be configured so that no more than 5% (or about 5%) of the voids in the foamed material are greater than 500 μm in diameter.

[0130] For any known material, the permeability and coefficient can be calculated using the equation: ln(P) = 0.019(ln(M)) 2It was found that there was no difference beyond line 201, which shows -0.7ln(M)) + 6.5, where P is the permeability of the material in g·mm / m2 / day measured according to ASTM E96 Procedure A (dry method at 23°C and 90% relative humidity), and M is the Young's modulus of the material in MPa.

[0131] The breathing circuit can include an expiratory tube comprising a non-foam-based, corrugated, and / or vapor-permeable material. In some non-limiting configurations, the inner wall of the expiratory tube can comprise a spirally wrapped vapor-permeable tape. In some configurations, the inner wall of the expiratory tube comprises a series of beads of different diameters. The beads of different diameters can be arranged along the inner wall of the expiratory tube to create a wave pattern.

[0132] The wall may also include at least one reinforcing rib or at least one area of ​​localized thickening to stiffen the wall. The tube may include a plurality of reinforcing ribs disposed about the periphery of the surrounding wall. These ribs may be co-extruded with the tube and generally aligned with the longitudinal axis of the tube. Preferably, there are between 3 and 8 reinforcing ribs, more particularly between 3 and 5 reinforcing ribs.

[0133] 4A and 4B, which illustrate a portion of a conduit 301 that can be used to form the expiratory tube 117. The conduit 301 can be manufactured from a foamed vapor-permeable material as described herein. The conduit 301 further includes a plurality of reinforcing ribs 403 that can be co-extruded with the conduit 301. The ribs 403 can be formed from the same foamed polymer as the conduit 301. Alternatively, the ribs 403 can be made from a different material than the conduit 301. This can be achieved by co-extrusion. As shown in FIG. 4A, the conduit 301 can be extruded with the ribs 403 in place and then corrugated to form the "dot" structure shown in FIG. 4B. The conduit 301 can include between three and eight reinforcing ribs, for example, between three and five reinforcing ribs.

[0134] In particular, the ribs can be disposed around the circumference of the tubing, the ribs can be disposed circumferentially around the interior surface of the tubing, or the ribs can be generally longitudinally aligned along the length of the tubing between the inlet and outlet.

[0135] 5A and 5B, which show a configuration for a corrugated, ribbed vapor permeable conduit 301. In Figure 5, raised ribs 403 are visible within the spaces between the interior ridges of conduit 301.

[0136] In addition to the above, a heater such as a resistive heater wire may be provided within the passageway of the conduit 301, within the wall of the conduit 301, or around the exterior of the outer wall surface of the conduit 301 to reduce or eliminate condensation formation within the tube. Figure 6 is a schematic diagram of a corrugated foamed polymer conduit 301 incorporating a heater wire 601 within the passageway of the conduit 301. Figure 7 is a schematic diagram of a corrugated foamed polymer conduit 301 incorporating a heater wire 601 around the exterior of the outer wall surface of the conduit 301. Figure 8 includes a schematic diagram of an expiratory tube 117 incorporating a heater wire 601 within the tube wall.

[0137] Other details regarding the expiratory tube are disclosed in the specification and drawings of U.S. Patent Application Publication No. 13 / 517,925, published as U.S. Patent Application Publication No. 2013 / 0098360 A1, which are incorporated herein by reference in their entirety for all that they contain.

[0138] With further reference to Figure 8, this shows a breathing circuit including an inspiratory tube 103 and an expiratory tube 117. The characteristics of the inspiratory tube 103 and the expiratory tube 117 are similar to those described above with respect to Figures 1-7. The inspiratory tube 103 has an inlet 109 in communication with a humidifier 107 and an outlet 113 from which humidified gas is delivered to the patient 101. The expiratory tube 117 also has an inlet 109 for receiving exhaled gas from the patient 101 and an outlet 113. As described above with respect to Figure 1, the outlet 113 of the expiratory tube 117 may discharge exhaled gas to the atmosphere, to the gas source 105, to an evacuator / filter (not shown), or to any other suitable location.

[0139] As discussed above with respect to Figures 1, 6, and 7, a heated wire 215 may be included in the inspiratory tube 103 and / or a heated wire 601 may be included in the expiratory tube 117 to raise the temperature of the gas (primarily the gas near the tube wall) above the saturation temperature, thereby reducing the risk of condensation formation within the tube. It should be understood that the heated wire may desirably include a coiled or helical configuration and is shown as straight for conceptual interpretation. The breathing circuit may include connectors (Y-connectors or wye-pieces 801) for connecting the inspiratory tube 103 and the expiratory tube 117 to a patient interface (not shown). Of course, it should be understood that other breathing circuit configurations are within the scope of this disclosure.

[0140] The foregoing description includes preferred forms of the present invention. Modifications may be made thereto without departing from the scope of the invention. Various modifications in construction and various embodiments and applications of the invention will occur to those skilled in the art to which the invention pertains without departing from the scope of the invention, as defined in the appended claims. The disclosures and descriptions herein are purely illustrative and are not intended to be in any way limiting.

Claims

1. An inspiratory tube configured to receive a humidified inhaled gas flow from a humidifier and to supply this humidified exhaled gas flow to a patient interface, wherein the inspiratory tube includes an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore, the inspiratory central bore being smooth, An exhalation tube configured to receive an exhaled gas flow from a patient, comprising an exhalation inlet, an exhalation outlet, and a wall surrounding an exhalation center bore, wherein the wall of the exhalation tube is permeable to water vapor and substantially impermeable to a bulk flow of liquid and exhaled gas flowing through the exhalation tube, and A device equipped with a breathing circuit.

2. The device according to claim 1, wherein the wall of the exhalation tube comprises a foamed polymer that is permeable to water vapor and substantially impermeable to liquid water and bulk flow of exhaled gas.

3. The intake pipe surrounds the heating element within the intake center bore, or The intake pipe includes a heating element attached to the wall of the intake pipe, or The intake pipe includes a heating element embedded in the wall of the intake pipe. The device according to claim 1 or 2.

4. The exhalation tube includes a heating element within the exhalation center bore, or The exhalation tube includes a heating element attached to the wall of the exhalation tube, or The exhalation tube includes a heating element embedded in the wall of the exhalation tube. The device according to any one of claims 1 to 3.

5. The device according to any one of claims 1 to 4, wherein the intake tube has a plurality of bubbles in a cross-section in the longitudinal direction, and each of the plurality of bubbles has a flat surface that forms at least a portion of the wall of the expiratory center bore.

6. The device according to claim 5, wherein the intake pipe includes at least one heating element, and the at least one heating element of the intake pipe is located between one of the plurality of bubbles and the intake center bore.

7. The device according to any one of claims 1 to 6, wherein the exhalation tube includes a plurality of reinforcing ribs, the plurality of reinforcing ribs are arranged circumferentially around the wall and are generally aligned longitudinally between the exhalation inlet and the exhalation outlet.

8. The device according to any one of claims 1 to 7, comprising a temperature probe.

9. The device according to claim 8, wherein the temperature probe is connectable to the intake pipe.

10. The device according to claim 8, wherein the temperature probe is built into the intake tube.

11. The device according to any one of claims 1 to 10, wherein the breathing circuit includes a humidifier configured to humidify the inspiratory gas flow to the patient, and the humidifier includes a humidifying chamber configured to store a volume of liquid and to be in fluid communication with the inspiratory gas flow.

12. The device according to claim 11, wherein the humidifier includes a heater configured to generate steam by heating the liquid in the humidifying chamber so that the intake gas flow is humidified by steam.

13. The device according to any one of claims 1 to 12, wherein the exhalation tube is terminated by a first connector at the exhalation inlet and by a second connector at the exhalation outlet, and the exhalation center bore is provided over the length between the first connector and the second connector.

14. It is a respiratory system, A humidifier configured to humidify the inhaled gas flow to the patient, An inspiratory tube configured to receive the humidified inspiratory gas flow from the humidifier and to supply the humidified inspiratory gas flow to a patient interface, comprising an inspiratory inlet, an inspiratory outlet, and a wall surrounding an inspiratory central bore, wherein the wall of the inspiratory central bore is smooth, An exhalation tube configured to receive an exhaled gas flow from the patient, comprising an exhalation inlet, an exhalation outlet, and an inner wall surrounding an exhalation center bore, wherein the wall of the exhalation tube is permeable to water vapor and substantially impermeable to the bulk flow of liquid and exhaled gas flowing through it, Respiratory system, including the respiratory system.

15. The respiratory apparatus according to claim 14, wherein the intake tube includes at least one heating element in the intake center bore.

16. The intake pipe includes at least one heating element attached to the wall of the intake pipe, or The intake pipe includes at least one heating element surrounded within the wall of the intake pipe, or The exhalation tube includes at least one heating element within the exhalation center bore. The respiratory apparatus according to claim 14 or 15.

17. The exhalation tube includes at least one heating element attached to the wall of the exhalation tube, or The exhalation tube includes at least one heating element embedded in the inner wall of the exhalation tube. The respiratory apparatus according to any one of claims 14 to 16.

18. The respiratory apparatus according to any one of claims 14 to 17, wherein the inhalation tube includes a helically wound member that forms a plurality of bubbles, each having a flat surface that forms at least a portion of the wall of the inhalation center bore in a cross-section in the longitudinal direction.

19. The respiratory apparatus according to claim 18, wherein the intake tube surrounds at least one heating element, and the at least one heating element of the intake tube is located between one of the plurality of bubbles and the intake center bore.

20. The respiratory apparatus according to any one of claims 14 to 19, wherein the wall of the exhalation tube comprises a foamed polymer.

21. The respiratory apparatus according to any one of claims 14 to 20, wherein the exhalation tube includes a plurality of reinforcing ribs, the plurality of reinforcing ribs are arranged circumferentially around the wall and are generally aligned longitudinally between the exhalation inlet and the exhalation outlet.

22. A respiratory device according to any one of claims 14 to 21, comprising a temperature probe.

23. The respiratory apparatus according to claim 22, wherein the temperature probe is connectable to the inspiratory tube.

24. The respiratory apparatus according to claim 22, wherein the temperature probe is built into the inhalation tube.

25. The respiratory device according to claim 22, comprising a patient interface, wherein the temperature probe detects the temperature at or near the patient interface.

26. The respiratory apparatus according to any one of claims 14 to 25, wherein the humidifier comprises a humidifying chamber configured to store a certain amount of liquid and to be in fluid communication with the intake gas flow.

27. The respiratory apparatus according to claim 26, wherein the humidifier comprises a heater configured to heat the liquid in the humidification chamber to generate steam, thereby humidifying the intake gas flow with the steam.

28. The respiratory apparatus according to any one of claims 14 to 27, wherein the exhalation tube is terminated by a first connector at the exhalation inlet and by a second connector at the exhalation outlet, and the central exhalation bore is provided over the length between the first connector and the second connector.

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