Patent GB-1466620-A (GB)
Title: Method and apparatus for controlling the pressure variation of a respirator
IPC: A61M16/00
Filed: 1974-10-15
Abstract: 1466620 Artificial respiration F HOFFMANN-LA-ROCHE & CO AG 15 Oct 1974 [21 Nov 1973] 44682/74 Heading A5T A device, used in conjunction with respiration apparatus, for reducing the pressure of the gas supplied to a patient during the propagation period of a blood-pulse wave in the pulmonary alveolar blood-flow path comprises timing means which respond to blood-pulsesynchronised electrical signals, and pressurecontrol means controlled by said timing means to operate during said propagation period. In a first embodiment (Fig. 1) blood-pulsesynchronised electrical signals are generated by an electracardiograph 8 and fed to a timing circuit 9. The blood-pulse-synchronised signal triggers a first timing signal having a duratior correspondng to the length of time required for said blood-pulse wave to reach the pulmon ary alveolar blood system. The termination of the first timing signal triggers a second timing signal !having a duration corresponding to said blood-pulse-wave propagation period. The second timing signal is fed from timing circuit 9 to an amplifier 10 and is then used to oper. ate the pressure-control means whch comprises a two-way valve 4 in a gas duct 3 connecting a respirator 2 with a patient 1. When the valve 4 is in position I (Fig. 1) the lungs of the patient are connected with the resiprator 2 For the duration of the second timing signal the valve 4 is in position II (Fig. 1), the lungs of the patient then being in communication with the ambient atmosphere, thus causing a pressure decrease in the lungs. Termination of the second timing signal returns the valve 4 to position I. Instead of connecting the lungs of the patient to the ambient atmosphere during the second timing pulse, a vacuum chamber 18 and/or pump 19 may alternatively be used. In a second embodiment (Fig. 4, not shown) the valve 4 is replaced by a pump (20) which draws gas from the duct between the patient and the respirator for the duration of the second timing signal and returns said gas at the end of said signal. In a third embodiment (Fig. 5 not shown) the respiratory frequency is controlled by the heart-beat frequency. The respirator in this embodiment comprises a source (21) of gas at elevated pressure, a valve (22) for regulating flow of gas and a pneumatic switch (23) which discharges exhaled air. Blood-pulse-synchronised signals are fed via conductor (31) to control device (28) which operates valve (22) to give inhalation and exhalation times which are multiples of the heart-beat period and which generates timing pulses to operate valve (22) during said blood-pulse-wave propagationperiod. A measuring head (26) generates signals, representing gas flow and/or pressure, which are fed to control device (28) which controls these parameters to set levels. An embodiment is described in which the patient (an infant) is subjected to an overall constant pressure which is reduced for the duration of said blood-pulse-wave propagation-period. The blood-pulse-synchronised signal may be obtained by direct or indirect means for determining stresses of the heart or blood pressure, flow, flow velocity or flow acceleration. In all the embodiments described the duration of both the first and the second timing signals are variable for use with different patients or blood-pulse-signal generating means. Specification 1432572 is referred to.