Patent GB-1288019-A (GB)
IPC: A61M16/00
Filed: 1971-08-19
Abstract: 1288019 Medical ventilator PHILIPS ELECTRONIC ASSOCIATED INDUSTRIES 19 Aug 1971 38978/71 Heading A5T A medical ventilator of the constant volume type comprises a variable-volume reservoir B1, B2 for storing respiratory gas, an electrical position-sensing element VR1 associated with said reservoir so arranged to give an indication of the instantaneous volume of the reservoir over the variable range of the reservoir, an adjustable, electrical volume control element (VR2), (Fig. 2 not shown) used to preset the required volume of gas to be passed to a patient, actuating means DC1 for expanding and contracting the reservoir, and a camparator device (CO1) for comparing the indication of the instantaneous volume with the setting of said control element, the comparator being arranged to give an output signal when equality of the comparison is achieved, and wherein operation of the actuating means is terminated when the signal is given. In operation, assuming that valve S1 is operational and that the bellows B1, B2 are already filled with the required volume of gas, driving gas from the inlet DG is passed via ports 1, 2 of valve Sl to the upper chamber of cylinder DC1, thus forcing the piston and ram downwards and thus expelling the respiratory gas from the bellows at a rate determined by the flow rate control FRC. A safety valve SV (not shown) guards against excess pressure in the tubing. The pressure in the inspiratory tubing holds valve NRV1 closed since the pressure is higher that atmospheric pressure on the other side of the valve. During the inspiratory period, expiration valve EV is held closed by solenoid DS2 which itself is energised during inspiratory period. This ensures that no inspiratory gas can escape via the expiratory path. At the end of the inspiratory period, valve S1 is released and valve S2 operated. Driving gas is then fed to port 2 of cylinder DC1, and a venting path to atmosphere is provided via port 1 and valve S1. The operation of the piston of cylinder DC1 upwards causes the pressure in bellows B1, B2 to be reduced thus opening non-return valve NRV1 and drawing respiratory gas into the bellows via inlet RG. Valve NRV2 is closed and NRV3 open so that the gas in the patient's lungs may be vented to atmosphere via the Y-piece, hoseline HL2, expiratory valve EV, volume meter VM, and non-return valve NRV3. The bellows are provided with a position-sensing device which is indicated as potentiometer VR1. A fixed d.c. voltage is applied to the potentiometer VR1 and the sensing signal output SS, which is proportional to the position of the bellows and hence the volume, is taken from the sliding contact. Thus, the tidal volume may be controlled by the signal output to any predetermined value with the control of the inspiration and expiration periods being made by a multivibrator (MV) (Figs. 2, 3 not shown). In order that the patient may inspire extra quantities of respiratory gas at required intervals ("sigh inspiration"), there is provided a sigh unit (Fig. 4 not shown) comprising an inspiration timer unit and an interval timer unit. This permits a sigh volume of respiratory gas to be passed to the patient for the duration of a sigh inspiration period; the normal controls of the apparatus being over-ridden for this particular period.