Patent GB-1327622-A (GB)
Title: Detecting means eg for measuring blood pressure
IPC: A61B5/0215
Filed: 1970-09-29
Abstract: 1327622 Measuring maxima & minima SIEMENS A G 29 Sept 1970 [2 Oct 1969 30 July 1970] 46368/70 Heading G1N and G1U Maximum and/or minimum amplitudes of a continuously varying amplitude voltage wave, e.g. a blood pressure or respiration voltage wave, are determined by utilizing a maximum valve capacitor C Max 1 which charges to the maxima of the wave and a minimum valve capacitor C Min 1 which charges to the minima of the wave, each capacitor being at least partly discharged respectively at an instant lying in a period extending from a succeeding non-spurious minimum to a new non- spurious maximum and at an instant lying in a period extending from a succeeding non-spurious maximum to a new non-spurious minimum. This instant may be determined by the R-wave of an ECG, at the instant of the succeeding non-spurious minimum or maximum respectively, or at the instant when the wave, approaching a succeeding non-spurious maximum or minimum respectively, reaches a level which is within 30% of the previous non-spurious maximum or minimum respectively. As shown in Fig.1, capacitor C Max 1 and a second capacitor C Max 2, which is charged concurrently with C Max 1, are charged to voltage Max 1 and the value Max 1 is indicated by an instrument connected to C Max 2. At the instant Max 1 (detected by rate of charging of C Max 1 =0), capacitor C Min 1 is discharged to 30% the difference between Min 1 and Max 1. C Max 1 retains its charge until the instant Min 2 (detected by rate of charging of C Min 1 = 0), and at this instant C Max 1 is discharged to 50% the difference between Max 1 and Min 2 and a capacitor C Min 2 is discharged to the value Min 2 which is indicated by an instrument connected to C Min 2. At the occurrence of the next max, max 2 ( detected by rate of charging of C max 1 = 0), C max 2 is discharged to the value Max 2 which is indicated by the instrument connected to C Max 2. The values Min 3 and Max 3 may be indicated in the same manner. The values 30% and 50% may be detected using a voltage divider. If measurements are taken in the region of the heart, a number of spurious maxima and minima occur, which may be detected as actual values if the method described above is utilized. In such a case, Fig.4 (not shown), C max 2 is discharged to the value of Max 2 only when the voltage curve reaches 30% of the last detected minimum, Min 2, in relation to max 1, C Min 1 also being discharged at this constant. The valve Max 2 is thus indicated by the instrument connected to C Max 2. In the same manner C min 2 is only discharged to the value min 2 when the voltage curve reaches 30% of the last detected maximum, max 1, in relation to the value min 1, C Max 1 also being discharged at this instant. The value Min 2 is thus indicated by the instrument connected to C min 2. As shown in Fig.5, C max 2 and C min 2 are connected to a voltage divider 1, 2, 3 divided in the ratio 30:40:30, the tapping points 4, 5 being connected to operational amplifiers 8, 9 which compare the tapped voltages with the voltage curve. The outputs of 8, 9 are connected through diodes 12, 13 to a bi-stable multi-vibrator which in one state discharges the capacitors C Max 2 and C Min 1, and in the other state discharges the capacitors C max 1 and C min 2. The above apparatuses may also be used to monitor respiration.