Abstract: A variable orifice flow sensor includes a flow conduit member defining a flow orifice and fluidly connecting first and second fluid flow ports, a flapper of magnetizable sheet metal that is mounted in the conduit member by a hinge portion so that the flapper angularly deflects out of the plane of the orifice in response to fluid flow through the conduit member to vary the effective fluid flow cross-sectional area of the orifice in proportion to the flow rate of fluid through the conduit member, and a pressure sensing tap on either side of the flapper. A deflection-limiting surface is provided in the conduit member adjacent the hinge portion. The hinge portion abuts against the deflection-limiting surface when the flapper experiences an angular deflection at least equal to a predefined angle in response to a fluid flow rate that is at least equal to a predetermined value, whereby overstressing of the hinge portion is minimized.

Abstract: A pressure-limited, time-cycled pulmonary ventilator includes a pressurized gas system that supplies respiratory gas to a patient at a selected inspiratory flow rate; an exhalation valve that (a) opens an expiratory flow path in response to the elapsing of a selected inspiratory time period, and (b) maintains a selected proximal pressure limit during the inspiratory time period; and a volume-cycle override system that actuates the exhalation valve so as to open the expiratory flow path if the patient's tidal volume reaches or exceeds a selected volume limit during the inspiratory time period. The volume-cycle override system includes a flow sensor that outputs an inhalation flow rate signal. The flow rate signal is integrated to derive a measured tidal volume signal. An operator control produces a volume limit signal, indicating a selected volume limit, that is compared with the measured tidal volume signal to yield a difference signal.

Abstract: A system for measuring the flow rate of gas includes a flow head having a sensor thermoresistor mounted transversely to the flow of gas, and a reference thermoresistor mounted parallel to the flow of gas, both thermoresistors having equal resistance versus temperature functions. Each thermoresistor is connected in a feedback control circuit, in which each thermoresistor is separately supplied with current to heat it, the current first passing through a fixed resistance in series with each of the thermoresistors. The current supplies are servo controlled to equalize the resistance of each thermoresistor with that of its associated fixed resistance. The power consumed by each thermoresistor at its equilibrium resistance is measured to provide a power indicative signal associated with each thermoresistor. The two power indicative signals are compared to generate a delta power signal. An empirically-derived flow rate-versus-delta power curve is stored as a look-up table in a computer memory.

Abstract: A system including the method employed, for controlling the flow of a pressurized gas through a variable orifice flow control valve in a pressurized gas conduit system, such as a ventilator, in response to either a desired flow rate/volume input signal, a desired pressure signal or both. With respect to the flow rate input signal, the system generates a flow signal indicative of the actual flow rate of gas through the flow control valve by measuring the pressure drop across the valve and using the actual orifice area based on a control valve position signal given to the valve. This flow signal is compared to the flow rate input signal to give a correction signal which is used to form a volume flow reference signal. With respect to the desired pressure signal, a signal indicative of the effective pressure at a set location in the system is compared to the desired pressure signal and processed to give a pressure flow reference signal.

Abstract: A gas flow sensor system, using hot wire flow and temperature sensors, compensates and corrects for various factors, such as water vapor content and gas composition in the measured gas, gas temperature, physical differences in the sensors, ambient atmospheric pressure, and nonlinearities in the system. Physical differences in the sensors are corrected by adjusting the magnitude of the constant current flowing to the temperature sensor. Water vapor content and gas temperature corrections are made by modifying a flow temperature signal based on the resistance of the temperature sensor to form a flow reference signal indicative of a desired resistance difference between the resistances of the temperature and flow sensors, which resistance difference varies with the flow temperature signal. The flow reference signal is compared to a flow resistance signal (indicative of the resistance of the flow sensor) and the resulting flow correction signal is used to control the current flow to the flow sensor.

Abstract: A ventilator control system is responsive to a flow rate signal from a flow rate sensor that senses the flow rate of gas to a ventilated patient. The ventilator control system provides an episode signal to a ventilator to actuate the ventilator to provide an assisted breath. The ventilator control system has an interactive control panel for providing an operator selectable duration signal scaled to define a selected time interval between breaths. An operator also selects a flow rate threshold signal scale to define the flow rate that must be exceeded to qualify a breath from a patient as a valid breath. Episode signal circuitry responds to the flow rate signal, the flow-rate threshold signal, and the duration signal to generate an episode signal in response to the flow rate signal failing to exceed the flow rate threshold signal within the selected time interval.

Abstract: A method for analyzing the concentration of selected constituent gases in the expiratory gas streams from a patient. The method includes the steps of: (a) measuring the flow rate of the expiratory gas stream to provide a flow rate signal; (b) generating a tidal volume signal in response to the flow rate signal; (c) generating a sample control signal in response to the tidal volume signal and the flow rate signal to mark an interval within the end tidal periods of several successive expiratory gas streams; (d) extracting a sample of each of the several successive expiratory gas streams during the marked interval in response to the sample control signal; (e) accumulating each extracted sample in a variable volume reservoir; (f) transferring the accumulated gas samples within the variable volume reservoir into a sample cell in response to the variable volume reaching a predetermined limit; and (g) measuring the concentration of the selected constituent gas in the volume of gas contained in the cell.

Abstract: A gas blending system for use with a medical ventilator blends a pressurized gas with ambient air for delivery to the ventilator in response to the ventilator's demand for gas during the gas intake phase of its cycle. The system comprises a demand valve that discharges a flow of the pressurized gas in proportion to the demand applied to its outlet. The demand valve outlet is coupled to a first inlet of a blending valve, a second inlet of which is open to the atmosphere. The blending valve has a blended gas outlet adapted to be coupled to the ventilator. The total demand applied by the ventilator to the blended gas outlet is transmitted to the first and second inlets. A proportioning mechanism in the blending valve adjusts the demand that is transmitted to the demand valve outlet through the blending valve first inlet as a percentage of the total demand applied to the blended gas outlet.

Abstract: A humidifier system including a humidifier chamber and heater assembly, microprocessor based control circuitry, and a housing for the control circuitry. The humidifier system is adapted to provide air at nearly 100 percent relative humidity and at a predetermined temperature (e.g. 35.degree. C.) to a medical (e.g. critical care) patient. The humidifier chamber includes a continuous spiral heat exchange path which extends between a vapor storage chamber and an outlet of the humidifier chamber at which an air heating tube is connected, so that outgoing air can be delivered to the patient. The vapor storage chamber is interfaced with a ventilator source of incoming air and a relatively small reservoir in which a supply of water is boiled by the heater assembly for providing vapor saturated air from the vapor storage chamber to the heat exchange path.

Abstract: A gas blending system includes a proportional mixing valve having a valve element movable between first and second limits of travel corresponding to a minimum and maximum percentage, respectively, of one of the gases in the blended mixture. The position of the valve element is detected by a detection mechanism, producing a position signal inputted to a microcomputer. The microcomputer also receives a control signal representing a desired percentage of one of the gases to be blended. The microcomputer calculates a desired valving element position as a function of the value of the control signal, and generates a drive signal as a function of a comparison made by the microcomputer between the detected valve element position and the desired position. A motor drives the valve element to the desired position in response to the drive signal.

Abstract: A volume ventilator is disclosed which has a balloon valve type exhalation valve for permitting release of gases to the ambient environment during the exhalation period of artificial ventilation or spontaneous breathing, or when there is excess proximal pressure in the ventilator system. A pressure transducer continuously senses the proximal pressure in the ventilator system and sends to a microcomputer controller and associated circuitry of the ventilator system a signal indicative of the instantaneous proximal pressure. The pressure in the balloon, which is the pilot pressure of the exhalation valve, is regulated through a jet venturi type pressure controller which is connected to a source of pressurized gas. The gas flows through the jet venturi, wherein its flow rate is regulated by a ball valve moving against a suitable valve seat. The ball valve is controlled by a stepper motor through a cam follower.

Abstract: An external, self-contained laryngeal prosthesis is adapted for use by a tracheostomized patient having a surgically-formed "pseudoglottis" separating the trachea and the hypopharynx. The prosthesis includes a housing and a fitting for attaching the housing to the tracheostoma formed in the patient's neck. The housing contains an inhalation valve to allow inhaled air to pass through a first conduit into the trachea, and an exhalation valve for directing exhaled air from the first conduit into the housing downstream from the inhalation valve toward a second conduit. The second conduit is adapted for communicating between the housing and the hypopharynx through the fitting and through an incision in the pseudoglottis. Downstream from the exhalation valve is a tone-generating mechanism responsive to air pressures in a range normally produced by a speech effort.

Abstract: A pneumatic speech simulator has a vibratory tone-generating element which produces an audible tone in response to the flow of pressurized air within a predetermined pressure range, said tone being transmitted to a patient's pharyngeal region by a conduit, such as a nasal catheter. The simulator includes a pressure compensation valve, upstream from the tone-generating element, which maintains the pressure experienced by the tone-generating element within its operating range as the pneumatic resistance of tone-transmitting conduit is increased due to partial or total blockage.

Abstract: A gas flow measuring system employs an oscillating chopper valve alternately to deliver a flow head-generated pressure and a reference pressure to a pressure transducer. The chopper valve is driven by a stepping motor under the control of a microcomputer. The stepping motor drives the valve, with an oscillatory frequency determined by the microcomputer, between a first detented position, in which the flow head-generated pressure is delivered to the transducer, and a second detented position, in which the reference pressure is delivered to the transducer. The electrical signal produced by the transducer is fed to a sample-and-hold circuit, also under the control of the microcomputer, whereby the microcomputer controls the sampling rate of the sample-and-hold circuit. The microcomputer can thus establish an optimal sampling rate in accordance with the oscillatory frequency of the valve. In this manner, very fast sampling rates can be established, thereby minimizing the effects of zero drift in the transducer.

Abstract: A mechanism is provided for a respiratory ventilator by which the gas-delivery mechanism of the ventilator can be caused to deliver gas to the patient either at a predetermined flow rate or at a rate directly controlled by the patient's instantaneous demand. The mechanism includes a pressure-responsive device adapted to produce an analog signal indicative of the difference between a reference pressure and the patient's airway proximal pressure. The analog signal has a first polarity when the proximal pressure is less than the reference pressure in response to an inhalation effort, and a second polarity when the proximal pressure is greater than the reference pressure in response to an exhalation effort. A first control mechanism is provided which causes the gas-delivery system to deliver gas at a rate which is proportional to the absolute value of the analog signal when the signal has the first polarity and an absolute value at least equal to a predetermined threshold value.

Abstract: A patient adaptor fitting for a medical ventilator includes a jet pump having a nozzle receiving breathing gas from the inspiratory leg of the patient circuit, and a throat in communication with the expiratory leg of the patient circuit. Gas flows from the nozzle to the throat through a chamber in communication with the patient's breathing passages. The nozzle and the throat are dimensioned so as to produce a pressure drop in the chamber which balances the pressure drop through the expiratory leg of the patient circuit, thereby minimizing residual positive end expiratory pressure (PEEP) caused by the pneumatic resistance in the expiratory leg. The throat and nozzle dimensions are also selected so that the minimization of the residual PEEP occurs over a relatively wide range of flow rates into the nozzle.

Abstract: A gas flow rate control device for a medical ventilator includes a variable-orifice valve for adjustment of the peak flow rate, and a waveform regulator which supplies controlled gas pressure to the orifice. The regulator maintains a fixed pressure differential between the upstream side of the orifice and a reference pressure. The reference pressure is variable between atmospheric pressure and a pressure which is essentially patient airway proximal pressure. When the reference pressure is patient airway proximal pressure, a constant pressure differential is maintained across the orifice so that a uniform flow rate is maintained. When the reference pressure is atmospheric pressure, a constant pressure is supplied to the upstream side of the orifice, so that the flow rate from the orifice decreases as patient airway proximal pressure on the downstream side of the orifice increases.

Abstract: A servo-type gas pressure relief valve for regulating air pump pressure to pneumatic components of a medical ventilator or similar equipment utilizes a small diaphragm-type bleed or pilot valve to control the action of a main diaphragm valve. A small amount of inlet gas from the bottom side of the large diaphragm is passed through a restricted orifice to the top side of the large diaphragm. The bleed valve bleeds this gas to the atmosphere at a selected pressure, said bleeding action creating a pressure differential across the diaphragm of the main valve, which is thereby opened to exhaust gas to the atmosphere. A screw adjustment exerts tension on a spring which, in turn, exerts a force on the upper part of the bleed valve diaphragm. By adjusting the tension on the spring, the pressure at which air is bled to the atmosphere can be controlled, thereby accurately controlling the pressure at which the main valve opens.

Abstract: A directional sensor for the detection of a very feeble effort to breathe on the part of a patient whose breathing needs are under the influence and control of a mechanical ventilator. A self-heated thermistor assembly is mounted in a small diameter sensor tube. A diaphragm and chamber arrangement provides a low volume flow of air in the sensor tube past the thermistor assembly at a high velocity, so that a very small effort to breathe will draw a limited volume of air past the thermistor assembly at a high velocity, causing rapid cooling. The air will flow past the thermistor assembly in a first direction in response to an inhalation effort, and in a second direction in response to an exhalation effort. A heating element is arranged in the tube so that a first temperature-related voltage change is produced across the thermistor assembly when air flow is in the first direction, and a second such temperature-related voltage change is produced when air flow is in the second direction.

Abstract: A system for sequentially providing a volume of gas containing a high frequency oscillation to a proximal airway. In a preferred embodiment a control means periodically drives in synchronism both inhalation and exhalation means into an inspiratory phase of an oscillatory cycle and then into an expiratory phase of the oscillatory cycle. The inhalation means during the inspiratory phase delivers a volume of fresh gas to the proximal airway of a patient, and during the expiratory phase refills itself from a source of low pressure gas while simultaneously blocking therefrom expired gas from the proximal airway. The exhalation means during the inspiratory phase vents to atmosphere expired gas withdrawn from the proximal airway during the previous expiratory phase and simultaneously blocks therefrom fresh gas from said inhalation means and during the expiratory phase extracts the expired volume of gas from the proximal airway.