| 摘要 |
1,142,880. Measuring blood pressure. INTERNATIONAL BUSINESS MACHINES CORP. 19 Sept., 1966 [20 Oct., 1965], No. 41653/66. Heading ASK. [Also in Division G3] A blood pressure measuring system includes a circuit for periodically establishing a predetermined voltage for a predetermined period across a device such as a thermistor or, as shown, a photocell 12, the circuit comprising a series transistor Tl connected to control the photocell current, a capacitor C for applying a variable control voltage starting at a datum level to the transistor Tl, and a detector, e.g. a Schmitt trigger 20, operable when the voltage across the photocell 12 is equal to the said predetermined voltage to prevent further variation of the control voltage. In the embodiment shown the photoelectric cell 12 is incorporated in a blood pressure measuring transducer 10, 11 and the current in photocell 12 is set to give the desired voltage output prior to each blood pressure measurement. Thus, under the control of circuit elements 15 to 19 the capacitor C is initially discharged to produce minimum current through the photocell 12; after a predetermined time delay a transistor T2 is rendered conductive and the capacitor C commences to charge, the voltage on capacitor C being applied over a double emitter follower T3, T4 to the base of transistor T1 which thus controls the current through the photocell 12. When the voltage on the photocell reaches the predetermined value the Schmitt trigger switches and applies a signal to element 19 which operates to stop the charging of capacitor C; the then voltage level on capacitor C continues to be applied to the base of transistor T1 so that the said predetermined voltage is maintained across photocell 12 whilst blood pressure measurements are made. The cycle for discharging capacitor C and then charging it to a desired level is repeated at desired time intervals under the control of signals generated by the control element 15. The photocell is included in a cuff used to occlude blood flow in a patients finger and, when the pressure exerted by the cuff is allowed to decrease linearly, the photocell, by registering the amount of light transmitted through the finger, indicates when blood is beginning to flow. |
