Abstract: A endotracheal tube for patient ventilation is modified to permit measurement of pressure at the patient trachea by providing a chamber in the end of the ET tube to be located in the patient, airway. This chamber has a highly pliant external wall with a degree of redundancy and is connected to a pressure measuring device exterior of the patient by a lumen in the wall of the ET tube. In addition, apparatus for controlling airway pressure during exhalation comprises valve means connected via a first inlet to an exhalation tube from a patient airway, connected to a source of negative pressure through an outlet and having a second inlet with a variable flow control means for controlling the flow of gas therethrough. Gas pressure is controlled within the valve by varying the pressure gradient between the upstream and downstream sides of the second inlet so that it equals the pressure gradient between the patient airway and the downstream side of the second inlet.

Abstract: Method and apparatus for non-invasively determining the time onset (Tonset) and end (Tend) of patient inspiratory efforts. A composite pressure signal is generated comprising the sum of an airway pressure signal, a gas flow pressure signal obtained by applying a gain factor (Kf) to a signal representing gas flow rate and a gas volume pressure signal obtained by applying a gain factor (Kv) to a signal representing volume of gas flow. Kf and Kv values are adjusted to result in a desired linear trajectory of composite pressure signal baseline in the latter part of the exhalation phase. The current composite pressure signal is compared with (i) selected earlier composite pressure signal values and/or (ii) value expected at current time based on extrapolation of composite pressure signal trajectory at specified earlier times and/or (iii) the current rate of change in the composite pressure signal with a selected earlier rates of change.

Abstract: Method and apparatus are described for determining respiratory system resistance (R) in a patient receiving gas from a ventilator. A negative pulse in the pressure and/or flow output of the ventilator during selected inflation cycles is generated and Paw, V dot and V are measured at a point (T0) near the beginning of the pulse, at a point (T1) near the trough of the negative pulse and at a point (T−1) preceding T0. The value of R is calculated from the difference between Paw. V dot and V at TO and at TI and where the change in patient generated pressure (Pmus) in the interval TO−TI is estimated by extrapolation from the different between Paw, V dot and V and T0 and at T−I, in accordance with Equation 8.

Abstract: Passive elastic and resistance values for a particular patient are estimated during proportional assist ventilation and other forms of assisted ventilation to permit reliable adjustment for volume-related and flow-related assist gains to meet continuously varying patient muscle pressure. Independent but simultaneous procedures are effected to determine the respective values. The pressure-volume relationship is determined by a modification of the inspiratory hold technique while the pressure-flow relationship is determined by deliberately introducing brief perturbations in pressure, flow and volume and observing the effects obtained.

Abstract: Improvements in piston-based ventilator design and operation are described. In one aspect, individual compensation of force dissipation within the gas delivery system is effected, so that the desired gas pressure is delivered to the patient airway without the necessity for monitoring the actual pressure and using it as feedback. In another aspect, a piston is dimensioned slightly less than the chamber wall of the pump to define a gap through which an acceptable amount of gas may leak but which eliminates the need for a physical seal, thereby minimizing the frictional resistance within the pump.

Abstract: An endotracheal tube for patient ventilation is modified to permit measurement of pressure at the patient trachea by providing a chamber in the end of the ET tube to be located in the patient airway. This chamber has a highly pliant external wall with a degree of redundancy and is connected to a pressure measuring device exterior of the patient by a lumen in the wall of the ET tube. In addition, apparatus for controlling airway pressure during exhalation comprises valve means connected via a first inlet to an exhalation tube from a patient airway, connected to a source of negative pressure through an outlet and having a second inlet with a variable flow control means for controlling the flow of gas therethrough. Gas pressure is controlled within the valve by varying the pressure gradient between the upstream and downstream sides of the second inlet so that it equals the pressure gradient between the patient airway and the downstream side of the second inlet.

Abstract: Ventilation to a patient is provided in response to patient effort. The free flow of gas from a piston, or similar air source, in response to patient inhalation is detected, the instantaneous rate and volume of flow are measured and the measurements are used as control signals to a drive motor for the piston to move the piston to generate a pressure which is proportional to the sum of measured and suitably amplified rate and volume of flow signals. Since the command signal to the pressure generator only changes subsequent to, and not in advance of, a change in flow and volume, the ventilator is subservient to the patient and provides a proportional assist to patient ongoing breathing effort during inspiration (Proportional Assist Ventilation, PAV).

Abstract: A novel ventilating apparatus for the delivery of air or a desired gas mixture to a patient by displacement of an electric motor actuated piston in a chamber to expel such gas while electronic control ensures that the force applied to the piston is of a pattern and magnitude. In one preferred embodiment, the ventilating apparatus provides a proportional assist to the breathing pattern of the patient.