Abstract: An expiration cassette is removably insertable in a receiving section of a ventilator and contains a gas passage, an expiratory valve and a flow meter. The expiratory cassette also has a locking mechanism for locking and unlocking interaction with a receiving section in the ventilator.

Abstract: An arrangement for passive gas sampling in a breathing system has a conduit having a venturi-nozzle for passively generating pressure variations in the conduit dependent on a flow of breathing gas in the conduit, and a first port and a second port terminating in the conduit and connected to a measurement chamber. The first port and the second port are arranged relative to the venturi-nozzle such that the pressure variations force a flow of breathing gas through the first port into the measurement chamber and out through the second port.

Abstract: An arrangement for passive gas sampling of a breathing gas in a breathing system has an element disposed in a tube for the passive diversion of a portion of the flow of breathing gas to a measurement chamber.

Abstract: Devices for the measurement of volumetric flow rate of a gas in a conduit are described. A vane arrangement is subjected to airflow and is displaced I response thereto. The vane arrangement forms a light guide, and one end of the vane arrangement receives an encoded light source, the encoding being over the range of displacement of the vane. In one form, the encoding can be achieved by a light source and a mask, the mask being shaped to provide for variance of the light transmitted therethrough as a function of the vane displacement range. One form of mask can be a tapered arrowhead. Embodiments of the flow rate measurement device offer good dynamic response. The measuring device can be incorporated in CPAP or ventilatory assist devices for the control thereof.

Abstract: In a method for assessing pulmonary stress, a volume of respiratory gas is received from the lungs of a subject, an ensuing pressure is measured and the pressure-volume (P-V) relationship is analyzed. The analysis includes a determination of the profile of the pressure-volume (P-V) relationship. The profile is straight when no stress is present, convex when there is a risk for over-distension and concave when alveolar units are opened up. Implemented in a breathing apparatus the method can be used to assist an operator in diagnostic and therapeutic considerations in relation to a patient.

Abstract: An oxygen mask assembly including an oxygen dilutor assembly with air inlet apertures located in a top wall thereof for diluting the oxygen flowing therethrough. In one embodiment, the mask assembly additionally includes an air reservoir bag assembly, a one-way inhalation valve for maintaining continuous positive airway pressure in the mask and a pressure valve on the mask for adjusting the air pressure in the mask.

Abstract: In an apparatus and method for examining the pulmonary mechanics of a respiratory system, in order to obtain information about the mechanical properties of the respiratory system's lungs, during an expiration of a flow of gas streaming out of the respiratory system is modulated, the volume of gas streaming out of the respiratory system is determined, the variation in pressure in the respiratory system is determined, and an expiratory pressure-volume relationship is determined from the expiratory volume and the expiratory variation in pressure.

Abstract: Apparatus (1) for relieving dyspnoea in an ambulatory exercising subject comprises a housing (3) to be worn on the subject, and within which a variable speed air blower motor (5) is located for delivering an air supply to the subject through a mouthpiece (10) at a pressure similar to average intrinsic positive end-expiratory pressure of the subject. A pressure transducer (25) in the mouthpiece (10) monitors the pressure during breathing cycles of the subject, and a control circuit (22) determines the average intrinsic positive end-expiratory pressure of the subject over five breathing cycles. The control circuit (22) operates the air blower motor (5) for delivering the air supply to the subject at a pressure similar to the determined average intrinsic positive end-expiratory pressure.

Abstract: According to this process, there is supplied to the passengers a first fraction of air enriched in oxygen from independent supply elements, in particular high pressure cylinders (16), during a descent phase of the aircraft between a normal cruising altitude and an intermediate rerouting altitude. There is moreover compressed air taken from a source of compressed air belonging to the aircraft, to produce (in 2) a second fraction of the air enriched in oxygen which is delivered to the passengers, at least during a phase of stabilized flight of the aircraft, adjacent the re-routing altitude, greater than 5,500 meters.

Abstract: A new method and a device are disclosed to determine physiologic parameters of a subject by analyzing it's breathing gas with an electrochemical sensor. The measured components of the breathing gas allow for many conclusions about the condition of the subjects's pulmonary system. It is therefore an objective of this invention to determine physiologic parameters from measuring the partial pressure of oxygen in the mainstream of the breathing gas. According to the invention the measurement can be performed non invasive and allows for conclusions about the respiratory and metabolic system of a subject. The invention makes a continuous measurement of the oxygen partial pressure possible, that almost shows no time delay. The invention allows for instance the determination of parameters like the oxygen concentration in the breathing gas, the oxygen consumption of the subject, the heart frequency, the respiratory quotient, the compliance of the pulmonary tract and other physiologic parameters.

Abstract: A diagnostic medical device which monitors physiological parameters during sleep is disclosed. The device includes mask means (2) adapted to fit over the nose and mouth of a patient being monitored, and an acquisition unit (5) is adapted to be removeably fitted to the mask means (2). The mask means (2) has inlet means (3) to allow the patient to breath, sensor means (8) which monitor physiological conditions and which provide physiological signals thereto for storage or real time data transmission to external devices.

Abstract: A pressure support system having enhanced noise reduction and a valve assembly for use in pressure support system. The pressure support system includes a pressure generator having an inlet and an outlet. A first conduit defining a tortuous path is coupled between a gas source and the inlet of the pressure generator. A second conduit coupled to the outlet of the pressure generator delivers the flow of gas from the pressure generator to a patient. A valve assembly communicates gas from the second conduit to the first conduit to control the pressure or a rate of the flow of gas in the second conduit. By communicating gas from the second conduit to the first conduit, the noise associated with exhausting gas from the second conduit is muffled by the tortuous path of the first conduit.

Abstract: A portable oxygen concentrator system adapted to be readily transported by a user includes a rechargeable energy source and a concentrator powered by the energy source. The concentrator converts ambient air into concentrated oxygen gas for the user and includes a plurality of adsorption beds and a rotary valve assembly. The rotary valve assembly is relatively rotatable with respect to the plurality of adsorption beds to provide valving action for selectively transferring fluids through the plurality of adsorption beds for converting ambient air into concentrated oxygen gas for the user. The ratio of adiabatic power to oxygen flow for the concentrator is in the range of 6.2 W/LPM to 23.0 W/LPM.

Abstract: A system and method of performance testing an aircraft's oxygen supply system where demand is assured by in use performance testing and monitoring by a controller and monitor for the partial pressure of oxygen necessary to meet demand in a pressurized aircraft. The system and method utilizing a predetermined performance test signal sent out at pre-programmed intervals of time during use, receiving, evaluation and responding to performance test signal control data received in response to the performance test signal and adjusting the partial pressure of oxygen to meet demand if necessary.

Abstract: The invention concerns a patient's ventilation with breathing mixture The installation comprises a ventilating assembly (10) for delivering said breathing mixture provided with a sensor for measuring the pressure (26) of the delivered mixture and a sensor for measuring the flow rate (28) of the delivered mixture; an inhalation conduit (12); and a device (30) for detecting accidental disconnection of the ventilation circuit comprising processing means (32, 34) for calculating, for each ventilating cycle, an apparent coefficient of the patient's compliance based on the measurements carried out by said pressure and flow rate sensors, using a predetermined formula; means (32, 34) for determining the sign of said compliance coefficient; means (32, 34) for comparing said compliance coefficient to a predetermined positive value; and means (40) for triggering a warning (42, 44) if the compliance coefficient is negative or if the compliance coefficient is higher than said predetermined value.

Abstract: A respiration assistor (10) for use in an anaesthesia breathing system. The respiration assistor is intended to provide respiratory assistance for a patient (14) who is breathing spontaneously under anaesthesia in order that the patient's end-expired CO2 will be maintained at or near the normal physiological level. For this purpose, the respiration assistor incorporates a blower (15) which is located in series with a gas flow detector (20 or 39) and an electric control circuit (19) is provided for activating the blower (15) when inspired gas flow is detected by the detector (20 or 39). Also, the respiration assistor incorporates an expiratory valve (23) that is actuated to a closed condition when the blower is activated.

Abstract: A system controls and manages administration of a therapeutic gas, such as NO, O2, or the like, to a spontaneously breathing, non-ventilated patient such that concentrated NO is as low as reasonably possible while delivering the desired amount of NO to the distal portions of the lungs. The system includes an entrainment cell that provides remote, turbulent mixing with low temporal latency and can be used with a nasal cannula or a mask. The entrainment cell uses room air to dilute the therapeutic gas; however, supplementary gases can also be used. A baffle can be included to promote mixing and a flow sensor can also be used if desired. Multiple ports can be included in the entrainment cell. An equalizing valve is also disclosed.

Abstract: A system and method for automatically blending gases, comprising an input device for receiving predetermined mixed gas concentration data from the user, a plurality of gas inlet valves which allow a plurality of gas flows to enter a homogenizing chamber for mixing the plurality of gas flows into a mixed gas, at least one gas sensor for detecting the concentration of one or more components of the mixed gas and generating at least one output signal representative thereof; and a manager for receiving the at least one output signal and comparing the at least one output signal with the predetermined mixed gas concentration data and in response generating a signal to at least one gas inlet valve to modify the plurality of gas flows to maintain the desired mixed gas concentration. The system and method may further be used for the production of breathing gases for divers, such as Nitrox or Trimix, which significantly extend bottom time and reduce required decompression.

Abstract: An apparatus, method and system for non-invasive breathing assistance to a patient. The apparatus comprises a hose or other gas conduit with a valve. Proximity of the patient to a sensor causes the valve to open, directing a pressurized stream of air or other gas at the patient's mouth, assisting the patient in breathing.

Abstract: The present invention is directed to a portable oxygen concentrator system adapted to be transported by a user. The portable oxygen concentrator system includes an energy source, an air separation device powered by the energy source and adapted to convert ambient air into concentrated oxygen gas for the user, at least one sensor adapted to sense one or more conditions indicative of the oxygen gas needs of the user, and a control unit interrelated with the air separation device and the at least one sensor to control the air separation device so as to supply an amount of oxygen gas equivalent to the oxygen gas needs of the user based at least in part upon the one or more conditions sensed by the at least one sensor.

Abstract: An interactive pressure support system and method employing a pressure generating system that provides a pressure therapy to the pulmonary system of a patient and an interactive system associated with the pressure generating system to enable the patient to interact with the pressure support system, for example, to monitor the effectiveness of the treatment provided by the pressure support system. The interactive system includes an output device that provides first information to the patient, an input device that allows the patient to provide second information that is based on the first information and a control unit that controls the operation of the output device to present the first information and collection of the second information via the input device. In a further embodiment, the operation of the pressure generating system is controlled based on the second information provided by the patient.

Abstract: The present invention relates to systems and methods for automatically and continuously regulating the level of nasal pressure to an optimal value during OSA treatment. OSA therapy is implemented by a device which automatically re-evaluates an applied pressure and continually searches for a minimum pressure required to adequately distend a patient's pharyngeal airway. For example, this optimal level varies with body position and stage of sleep throughout the night. In addition, this level varies depending upon the patient's body weight and whether or not alcohol or sleeping medicine has been ingested.

Abstract: An apparatus for controlling dispensing of medical gases, comprising a unit for supplying medical gas, connected hermetically by way of a tube to a gas dispenser connected to a patient, a detector located along the tube for detecting correct respiration of the patient with at least one pressure sensor that detects cyclic pressure increases inside the dispenser caused by patient expirations, binary output signals being conveyed by the sensor to the detector which compares periodicity of the signals with a reference physiological periodicity, and an alarm indicator controlled by the detector and activated if the periodicity does not occur.

Abstract: The present invention pertains to a pressure support system in which a flow or volume of gas is measured without using a dedicated flow element used in a conventional flow meter. Instead, the present invention provides a tortuous gas flow path in which a pressure differential is created between two points in the tortuous path. This pressure differential created by the gas flow path provides the necessary pressure drop for measuring the gas flow and/or gas volume passing through the pressure support system.

Abstract: An ambient pressure control ventilation apparatus for mechanical ventilation of a patient comprising a sealable chamber (5) adapted to accommodate a whole body of a patient, a pump (2) fluidly connected to the chamber adapted to alternatively compress and decompress a ventilating gas within the chamber, a relief valve (14) fluidly connected to the chamber and a control unit (1) adapted to control the pump and the relief valve to facilitate a periodic regime of alternating compression and decompression of the ventilating gas within the chamber about a predetermined baseline.

Abstract: A process is provided for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it as well as to a corresponding control device. The respiration pressure, the breathing gas flow generated by the respirator as well as the respiration rate may be used as parameters. The process presents the advantage that the control of the current respiration needs of the patient are taken into account by the muscle pressure (PMUS), i.e., the percentage of the airway pressure caused by the patient's own effort, being maintained at a value close to zero. An airway pressure (PAWC) is first calculated for this purpose from previously measured values for the airway pressure (PAW) and the breathing gas flow (d/dt V) and the mechanical parameters resistance (RL) and compliance (C) of the patient's lungs, which were determined therefrom, and this is subsequently compared with the actually measured value for the airway pressure (PAW).

Abstract: An apparatus (10) for supplying breathable gas is disclosed. The apparatus (10) includes a main housing (12), a sub-housing (14), having a gas flow path (28) between a gas inlet (16) and a gas outlet (18), a motive power source (22) within the main housing (12) and an impeller (30) within the sub-housing (14) in fluid communication between the gas inlet (16) and the gas outlet (18). The impeller (30) is adapted to releaseably engage the motive power source (22) external the gas flow path (28) and the sub-housing (14) is releasably connectable to said main housing. Also disclosed is a method of cleaning, sterilising or disinfecting the gas flow path (28) of the breathable gas supply apparatus (10). The method of cleaning comprising the steps of removing the sub-housing (14) from the main housing (12) cleaning, sterilising, disinfecting or replacing the sub-housing (14) and connecting the sub-housing (14) to the main housing (12).

Abstract: The present invention is directed to a portable oxygen concentrator system adapted to be transported by a user. The portable oxygen concentrator system includes an energy source, an air separation device powered by the energy source and adapted to convert ambient air into concentrated oxygen gas for the user, at least one sensor adapted to sense one or more conditions indicative of the oxygen gas needs of the user, and a control unit interrelated with the air separation device and the at least one sensor to control the air separation device so as to supply an amount of oxygen gas equivalent to the oxygen gas needs of the user based at least in part upon the one or more conditions sensed by the at least one sensor.

Abstract: A method and a device for switching to the inspiration or expiration phase during CPAP therapy are disclosed. By means of a first high threshold value and a second low threshold value non-specific influences on the first derivative of the gas flow curve are suppressed in the corresponding breathing phase and the transition to the corresponding following gas phase is determined with high sensitivity. The invention further relates to methods for recognizing and suppressing the influence of the pulse or for switching to the inspiration phase in case of shallow breathing. The advantages of the invention are greater switching accuracy and improved safety for the patient.

Abstract: The gas-supply system for the inhalation treatment of humans or mammals, entailing controlled dosing of at least one gas, characterized by a tidal volume-dependent regulation of the gas dosing.

Abstract: A pressure support system having enhanced noise reduction and a valve assembly for use in pressure support system. The pressure support system includes a pressure generator having an inlet and an outlet. A first conduit defining a tortuous path is coupled between a gas source and the inlet of the pressure generator. A second conduit coupled to the outlet of the pressure generator delivers the flow of gas from the pressure generator to a patient. A valve assembly communicates gas from the second conduit to the first conduit to control the pressure or a rate of the flow of gas in the second conduit. By communicating gas from the second conduit to the first conduit, the noise associated with exhausting gas from the second conduit is muffled by the tortuous path of the first conduit.

Abstract: An oxygen conserver having sensing and delivery ports simultaneously connected with a patient by a dual cannula. Inhalation by a patient produces a partial vacuum to move a sensing diaphragm to a venting position and cause a delivery diaphragm to move to an open position for supplying oxygen to the patient through the delivery port. A manually operable control valve enables continuous oxygen flow through the delivery port independently of operation of the sensing diaphragm.

Abstract: A respiratory nitric oxide meter includes a respiratory connector designed to be supported in contact with a subject and to pass respiratory gases as the subject breathes. A flow pathway receives and passes the respiration gases. One end of the pathway is in fluid communication with the respiratory connector, and the other end is in fluid communication with a reservoir of respiratory gases. A nitric oxide concentration sensor generates electrical signals as a function of the instantaneous fraction of nitric oxide as the respiration gases pass through the flow pathway.

Abstract: A small breath-activated, microprocessor controlled device that can be used with any drug formulation appropriate for pulmonary delivery is disclosed. A fixed-resistor housing incorporates a microprocessor and pressure transducer to detect pressure changes associated with patient derived airflow across the device. The microprocessor determines the flow rate and tidal volume over several breaths and averages them. Depending on where in the brocho-pulmonary tree the drug is to be administered, the microprocessor will precisely meter the drug in the appropriate phase of the respiratory cycle and deliver small aliquots of the formulation over several breaths until the total dose is administered.

Abstract: The present invention discloses both a method of operating CPAP apparatus, and the apparatus itself in which a breathable gas delivery device, or mask (1), is connected to a gas supply pump (14) via a conduit which includes a restriction to gas flow such as a small bore portion (3). A pressure transducer (11) is used to sense the gas pressure at the patient's nose and the transducer output is used to servo-control the pump (14) to maintian the sensed pressure substantially constant.

Abstract: An on demand supplemental oxygen delivery system that is self-calibrating includes a tank containing a supply of oxygen and a nasal cannula through which the oxygen may be provided to a patient when the system solenoid valve is in the open condition. When the valve is in the closed condition, the cannula communicates with a pressure transducer via a transducer line. An orifice is formed in the line so that the pressure within the transducer line goes to atmospheric pressure when the valve is in the open condition. When the valve is in the open condition, the pressure transducer reads the atmospheric pressure and directs it to a system controller where it is stored as a reference pressure. When the valve is in the closed condition, the pressure transducer monitors the pressure in the nasal cannula.

Abstract: A device and method of ventilating a patient reduces the bias flow relative to existing oscillatory ventilators. The device has a gas flow circuit comprising an oscillating line, a patient line and an exhalation or a return line. A gas supply line is and an outlet valve are in pneumatic communication with the gas flow circuit. One or more CO2 scrubbers and one or more check valves are provided in the circuit. A method of ventilating using such a device is also disclosed.

Abstract: An improved methodology and systems for delivery of breathing gas such as for the treatment of obstructive sleep apnea through application of alternating high and low level positive airway pressure within the airway of the patient with the high and low airway pressure being coordinated with the spontaneous respiration of the patient, and improved methods and apparatus for triggering and for leak management in such systems.

Abstract: Methods and systems for supplying supplemental oxygen to patients for use in sub-acute care which maintains healthy blood oxygen content in the patients by controlled dosing of oxygen with a measured response to the patient's actual blood oxygen content are disclosed. The dosing can be provided by simple ON/OFF control over the delivery of oxygen or the amount of oxygen delivered to the patient with each inhalation can be varied in response to the patient's need as determined by a more sophisticated control scheme, such as a PID loop control algorithm, that utilizes the difference between the patient's actual blood oxygen content and a target blood oxygen content and/or trends in the blood oxygen content. The systems and methods are particularly directed at patients receiving supplemental oxygen in a sub-acute care environment.

Abstract: The gas-supply system entailing controlled dosing of at least one gas or at least one aerosol is characterized by a control means for a dosing whereby the feed of the gas or aerosol into a breathing gas starts at a defined point in time during the expiration of a patient.

Abstract: A flow diverter valve is used in controlling the pressure and/or flow rate of a breathable gas supplied to the airways of a patient by a breathable gas flow generator supply apparatus during, for example, ventilatory assistance treatments such as non-invasive positive pressure ventilation and nasal Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea. The flow diverter valve includes a vane and a housing. The housing has an inlet port, an outlet port, and an exhaust port. The exhaust port opens to atmosphere, and the inlet port is in fluid communication with the flow generator. The outlet port is in fluid communication with a patient mask via a conduit. The vane is configured with respect to the housing such that a blower associated with the CPAP apparatus remains substantially unchoked, regardless of whether the vane is in the open or closed position.

Abstract: A device and method is disclosed for delivering NO to a patient. The device utilizes a single controller that controls two separate flow controllers to deliver an oxygen-containing gas and a NO-containing gas to the patient. The flow profiles of the oxygen-containing gas and the NO-containing gas are controlled by the controller. In one aspect of the invention, the flow profile of the NO-containing gas is proportional to the flow profile of the oxygen-containing gas throughout patient inspiration. In this regard, the patient receives a steady concentration of NO. In another aspect of the invention, the flow profile of the NO-containing gas is quasi-proportional to the flow profile of the oxygen-containing gas. In this regard, the NO-containing gas flow profile is altered to provide an increased concentration of NO either at the beginning or end of inspiration. In one aspect, the delivery device is used with mechanically-ventilated patients.

Abstract: A gas delivery system, having a gas identification, by which a gas supplied to the gas delivery system is identified, a blender, blending oxygen and the gas to provide a gas mixture with an oxygen flow rate set up by an operator, and at least one flow sensor, to measure a flow rate of the gas mixture. The blender is driven by an actuator motor to various blender positions with the blender positions being calibrated based on the specific heat ratio and the gas constant of the gas. The flow sensor can be installed at the inspiratory circuit, the proximal circuit and the expiratory circuit of the gas delivery system. The flow sensor output is corrected based on the actual conditions, including the temperature, pressure and humidity, and characteristics of the gas mixture.

Abstract: A ventilator supplies a plurality of volumes of fluid to a patient during a like plurality of inhalations by the patient. Each volume of fluid is supplied at an inspiratory positive airway pressure during a corresponding inhalation by the patient. A volume of fluid received by the patient is determined for each of the plurality of inhalations by the patient and an average volume of fluid received by the patient during each of the plurality of inhalations is determined. The average volume of fluid received by the patient during each inhalation is compared to a predetermined target volume and the inspiratory positive airway pressure each volume of fluid is supplied to the patient is adjusted as a function of the comparison.

Abstract: A portable anesthesia administering system which includes a compact, lightweight unit that does not require a source of electrical power to provide regulated pressurized anesthesia gas to a patient. The operating elements include a disposable carbon dioxide absorber, a charcoal scavenger absorber, an oxygen pressure sensor and alarm for detecting a drop in the oxygen pressure below a pre-selected level. The unit utilizes an anesthesia vaporizer and regulator, an airway pressure limiting valve and airway inlet and outlet control valves to provide a gaseous anesthesia agent in pre-selected amounts. Attached to the disposable carbon dioxide absorber is a manifold block which provides for a plurality of anesthesia regulating and control elements to facilitate the administration of the anesthesia. Connected to the manifold block is an external breathing bag for assisting in the breathing of the patient.

Abstract: Device for scuba diving consisting of at least a processor and of at least a manometer, both housed within a sheath, said manometer being connected to one or more bottles containing compressed air. The said processor includes a corresponding central unit for data processing, operatively connected to the manometer by means of connecting elements which allow said processor and said manometer to exchange information flows and also to be positioned within the housing sheath independently one from the other, so as to obtain a device for scuba diving with a modular structure.

Abstract: A device with a gas sensor for measuring a breathing gas component in a breathing gas line is improved such that a pressure correction of the gas concentration measurement can be performed without appreciably affecting the respiration pressure. Provisions are made for branching off a first measuring gas line (23) with a first electrochemical measuring cell (28) from the breathing gas line (7). A first throttling point (26) is arranged in the course of the first measuring gas line (23) between the first electrochemical measuring cell (28) and the breathing gas line (7). A first pressure sensor (29), for the pressure correction, is located downstream of the first electrochemical measuring cell (28).

Abstract: A method to maintain isocapnia for a subject. A fresh gas is provided to the subject when the subject breathes at a rate less than or equal to the fresh gas flowing to the subject. The fresh gas flow equal to a baseline minute ventilation minus a dead space gas ventilation of the subject contains a physiological insignificant amount of CO2. An additional reserve gas is provided to the subject when the subject breathes at a rate more than the fresh gas flowing to the subject. The reserve gas has a partial pressure of carbon dioxide equal to an arterial partial pressure of carbon dioxide of the subject. A breathing circuit is applied to the method to maintain isocapnia for a subject. The breathing circuit has an exit port, a non-rebreathing valve, a source of fresh gas, a fresh gas reservoir and a reserve gas supply.

Abstract: A differential Fick technique including a first phase in which baseline breathing parameters may be established and a second phase in which a change in the effective ventilation of a patient is induced. The durations of the first and second phases may be substantially the same, and may be abbreviated relative to the durations of comparable phases of previously known differential Fick techniques. The disclosed differential Fick technique also lacks a recovery period in which the respiratory parameters of a patient are permitted to return to “normal” levels.

Abstract: An indirect calorimeter operative to measure the respiratory oxygen consumption per unit time of a subject includes a respiratory connector operative to be supported in contact with a subject, so as to pass respiratory gases as the subject breathes into the respiratory connector, and a bi-directional flow meter having an ultrasonic flow transducer that bi-directionally transmits and receives ultrasonic signals to the transducer to generate a signal as a function of the volume of gases passing through the flow meter. The indirect calorimeter also includes a gas concentration sensor operative to generate a signal as a function of an instantaneous carbon dioxide content of gases passing by the gas concentration sensor.