Medical ventilators

Claim 2

In a medical ventilator of the constant volume type including a variable volume reservoir for storing respiratory gas during each expiration period of a repetitive respiratory cycle and from which reservoir gas is passed to a patient during each inspiration period of the cycle, an electrical position-sensing element operable with the reservoir to give an indication of the instantaneous volume of the reservoir over the variable range of the latter, an adjustable electrical volume-control element settable to the required volume of gas to be passed to the patient, actuating means for expanding and contracting the reservoir so as to perform the storage and passage functions of the latter, and a comparator for comparing the said indication of the instantaneous volume with the setting of the control element, the comparator being arranged to give an output signal when equality of the comparison is achieved, the improvement comprising means for terminating operation of the actuating means to expand the reservoir during each expiration period when said output signal is given and further comprising an electronic multivibrator having two states and individual adjustment means for determining the dwell times of each of said two states, and having respective signal outputs, and means for operating the actuating means to initiate the expiratory and the inspiratory periods in response to said respective outputs.

Claim 3

A medical ventilator according to claim 1 wherein the actuating means comprises a pneumatically operated piston and cylinder arrangement, the piston being mechanically connected to the reservoir, a first gas control solenoid means for passing actuating gas to one side of the piston during each inspiratory period so as to cause the piston to move in such a direction as to decrease the volume of the reservoir, and a second gas control solenoid means for passing actuating gas to the other side of the piston during each expiratory period so as to cause movement of the piston in the opposite direction and, hence, to increase the volume of the reservoir; and means for operating the first and second gas control solenoid means by the multivibrator outputs corresponding to the inspiratory and expiratory periods respectively.

Claim 4

A medical ventilator according to claim 2 including an AND-gate and wherein the expiratory period signal output of the multivibrator is connected to one input of the AND-gate and the comparator output is connected to a further input of the AND-gate, and wherein the output of the AND-gate is connected to and controls the said second gas control solenoid means.

Claim 5

A medical ventilator according to claim 1 comprising a second presettable electrical control set to a position indicative of the empty or minimum-volume condition of the reservoir, a second comparator having onE comparison input connected to the position sensing element and the other comparison input connected to the second presettable control, the output of the comparator thereby indicating that the reservoir has reached its minimum volume state and, hence, that the required quantity of gas has been passed to the patient during the inspiration period.

Claim 6

A medical ventilator according to claim 4, further comprising means, operable if the patient tries to inhale during an expiratory period, for switching the multivibrator immediately from its expiration signal state to its inspiration signal state thereby causing the ventilator to revert to the inspiration period.

Claim 7

A medical ventilator according to claim 5 wherein said means for switching comprises detecting means for detecting the reduced pressure, in the airway connecting the ventilator to the patient, caused by the attempted inhalation.

Claim 8

A medical ventilator according to claim 4 comprising a third settable volume control element settable to an alternative volume of gas to be passed to the patient, adjustable timing control means for setting the inspiration period to any desired value, and gating means, operative at the next instant of changeover from an inspiratory period to an expiratory period after receipt of an over-ride signal, for over-riding the existing setting of the volume and inspiration time by settings dependent on the set position of the third volume control element and of the timing control means.

Claim 9

A medical ventilator according to claim 7 comprising pulse generator means for providing the over-ride signal at regular intervals.

Claim 10

A medical ventilator according to claim 8 wherein the pulse generator means comprises a counter and a clock pulse source feeding the counter which gives an over-ride pulse after receipt of a predetermined number of clock pulses, after which the counter resets to zero.

Claim 11

A medical ventilator according to claim 9 comprising means for providing a manual over-ride signal to said gating means, which signal becomes operative on the next subsequent changeover from an expiratory period to an inspiratory period.

Claim 12

A medical ventilator according to claim 10 comprising means for resetting the counter to zero on release of the manual over-ride signal.

Claim 13

In a medical ventilator of the constant volume type including a variable-volume reservoir for storing respiratory gas during each expiration period of a repetitive respiratory cycle and from which reservoir gas is passed to a patient during each inspiration period of the cycle, an electrical position sensing element operable with the reservoir to give an indication of the instantaneous volume of the reservoir over the variable range of the latter, an adjustable, electrical volume-control element settable to the required volume of gas to be passed to the patient, actuating means for expanding and contracting the reservoir so as to perform the storage and passage functions of the latter, a comparator for comparing the said indication of the instantaneous volume with the setting of the control element, the comparator being arranged to give an output signal when equality of the comparison is achieved, the improvement comprising means for terminating operation of the actuating means to expand the reservoir during each expiration period when the said output signal is given and further comprising a further comparator having one comparison input connected to the position sensing element and the other comparison input connected to a presettable electrical control set to a position indicative of the empty or minimum-volume condition of the reservoir, the output of the further comparator thereby indicating that the reservoir has reached its minimum volume state and, hence, that the required quantity of gas has been passed to the patient during the inspiration period, and gating means whereby an alarm signal is given at the commencement of the next subsequent expiration period if no output signal indicating that the reServoir has returned to its minimum volume state is given by the said further comparator.

Claim 14

In a medical ventilator of the constant volume type including a variable-volume reservoir for storing respiratory gas during each expiration period of a repetitive respiratory cycle and from which reservoir gas is passed to a patient during each inspiration period of the cycle, an electrical position sensing element operable with the reservoir to give an indication of the instantaneous volume of the reservoir over the variable range of the latter, an adjustable, electrical volume-control element settable to the required volume of gas to be passed to the patient, actuating means for expanding and contracting the reservoir so as to perform the storage and passage functions of the latter, a comparator for comparing the said indication of the instantaneous volume with the setting of the control element, the comparator being arranged to give an output signal when equality of the comparison is achieved, the improvement comprising means for terminating operation of the actuating means to expand the reservoir during each expiration period when the said output signal is given and further comprising a further comparator having one comparison input connected to the position sensing element and the other comparison input connected to a presettable electrical control set to a position indicative of the empty or minimum-volume condition of the reservoir, the output of the further comparator thereby indicating that the reservoir has reached its minimum volume state and, hence, that the required quantity of gas has been passed to the patient during the inspiration period, and gating means whereby an alarm signal is given at the commencement of the next subsequent expiration period if no output signal indicating that the reServoir has returned to its minimum volume state is given by the said further comparator.