Patent GB-923936-A (GB)
Title: Sphyg momanometer
IPC: A61B5/021
Filed: 1962-01-03
Abstract: 923,936. Sphygmomanometers. E. B. GREENSPAN. Jan. 3, 1962 [Jan. 10, 1961], No. 232/62. Class 81 (2). A self-recording sphygmomanometer associated with an inflatable cuff has means responsive to the pressure within the cuff for producing a train of pulses which, as the cuff pressure is reduced, commences at the systolic blood pressure and terminates at the diastolic blood pressure and further means for setting pressure indicators in response to the commencement and end of the train of pulses. The functioning of the apparatus is based on the fact that the passage of blood past the cuff at each heart beat, between the systolic and diastolic pressures, causes a corresponding pulse of pressure within the cuff. The cuff 12, Fig. 1, is inflated by a bulb 18 and gradually deflated by opening a bleed valve 24 and the instantaneous pressure within the cuff is communicated through a tube 16 to a pressure indicator and to the opposite ends of a pulse generating device 28. The latter device comprises a hollow casing divided by a flexible diaphragm 38, Fig. 3, into two chambers 34, 36 both of which are connected, through nipples 44, 48 to the interior of the cuff. The duct through the nipple 44 is, however, restricted by a choke orifice 50 so that the rapid fluctuations in pressure caused by the patient's pulse are not communicated to the chamber 34. Apart from this, however, the pressures in the two chambers 34, 36 are maintained equal and thus, irrespective of the slowly changing pressure in the cuff, the pulse beats are detected by movement of the diaphragm 38. These movements, in turn, are caused to complete an electrical circuit by means of a contact 52 on the diaphragm engaging an adjustable fixed contact 54. In the recording mechanism, Fig. 4, an aneroid 74, connected to the cuff through a nipple 76, is coupled through suitable gearing to a spindle 108 carrying a pointer 114 which consequently continuously indicates the pressure in the cuff. In addition, there are systolic 120 and diastolic 122 pointers, mounted concentric with the spindle 108, which tend to follow the pointer 114, by means of spring wire connections 140, 146, unless prevented from doing so by pawls 156, 178 engaging corresponding ratchet wheels 134, 136. In using the instrument, the cuff is placed in position and inflated above systolic pressure, this being indicated by the pointer 114. A rod 162 is then depressed, by means of an external knob, until it is latched by a detent 116 engaging behind a recess 164. This action also disengages the pawls 156, 178 by means of a common bail 160 and consequently the pointers 120,122 are  free to take up the same position as the pointer 114. The downward movement of the bail 160 also actuates a changeover switch 190 to connect a battery through the pulse sensing contacts 52, 54, Fig. 3, to a magnet 168, Fig. 4. All three pointers consequently move back with the decreasing pressure until the first systolic pulse is detected, whereupon the magnet 168 is energized and withdraws the detent 166, thereby allowing the pawls to rise and arrest the movement of the pointers 120, 122. This additionally actuates the changeover switch 190 whereby the pulse-sensing contacts are now connected to a second magnet 182 the armature 184 of which is connected through a link 186 to the pawl 178. Consequently although the pointer 120 is continuously held at the systolic pressure by its pawl 156 each succeeding pulse energizes the magnet 182 so as to disengage the pawl 178 and allow the pointer 122 to continue to follow the decreasing pressure. However, when the diastolic pressure is reached no further pulses are received and the pointer 122 remains set at this pressure.