Patent GB-322530-A (GB)
Title: An improved sphygmometer or instrument for measuring blood pressure and fluctuations thereof
IPC: A61B5/022
Filed: 1928-09-08
Abstract: 322,530. Paterson, W. D. Sept. 8, 1928. Sphygmographs.-A sphygmometer, of the kind in which the blood pressure is measured by means of the fluctuations produced in a counter-pressure applied to an artery by a pneumatically inflated cuff, has a throttled permanent air passage between both sides of the differential pressure detector, and one compartment of the latter is large enough to dissipate any appreciable counterimpulse transmitted to it. An airtight chamber 32 of metal, glass, or other suitable material, is closed by a screw cap, stopper, or cover 33, through which pass three pipes 9, 23, 35 of glass or metal; the pipe 9 connects the interior of the differential pressure detector 41 to the hollow rubber armlet 27, and the other pipes 23 and 35 connect the pressure chamber 32 to the armlet 26 through the valve 21 and to the main air supply pipe 15, respectively. When the two overlapping cuffs are employed, the pipe 9 is connected to both of them through the pipes 20 and 22, and 25. The pipes 22 and 25 may be flexible. The differential pressure chamber 41 is closed by a rubber or other flexible diaphragm 7 which is attached by a light plate 8 to the shorter arm 3 of the light pivoted lever 2, 3 of the recording pen 1. The lever 3 passes through and is pivoted on a polished, hollow metal spindle 42, Fig. 3, which is housed in the metal block 4 and is lubricated so that an airtight film is formed between the pressure chamber 32 and the outside air. Countersunk portions 6 allow the lever to vibrate without appreciable leakage from the chamber 32. The manometer, which may consist of a mercury U-tube 18, has a scale 19 for direct reading and a float connected to a recording pen. A throttle valve 11 controlling the leak from one side of the diaphragm 7 to the other is connected to the pressure chamber 32 through pipes 14, 35 and to the pipe 9 through the narrower pipe 10. The setting of this valve is regulated by the handle 12 and indicated by the scale or pointer 13. A two-way valve 21, which can disconnect either of the pipes 9 or 23 from the cuff 26, may be replaced by a spring clip or like device if the pipes are of flexible rubber tubing. The rubber cuffs 26, 27 are kept in position around the upper arm by a non-distensible or leather cover with straps. To inflate the apparatus to the same pressure throughout the taps 11 and 31 are opened, the valve 21 preferably opened to all three ports, the screw-adjusted release valves 24 and 29, 24 being slow-acting and 29 quick-acting, are closed, and the pressure raised by means of the bulb pump or compressor 28. If the valve 11 is now closed and the valve 21 moved to close the pipe 23 and to connect together pipes 22 and 20, vibrations in the cuffs will cause the diaphragm 7 to vibrate provided that the average counterpressure lies within certain limits. To avoid any leak through the pump 28 after the apparatus has been inflated, the valve 31 may be closed. Lower pressures may be obtained by opening the release valve 24, or the valves 31 and 29, and the throttle valve 11 to equalize the pressure throughout the apparatus. Records may be taken during a continuous fall or rise in the average pressure in the apparatus, a fall in pressure being obtained by adjusting the throttle valve 11 and opening one of the release valves until the pen 1 traces a horizontal line. As the pressure falls between certain limits, the pen will record the pulsations of blood pressure by means of upward strokes, and an index of the minimum blood pressure is given on such a record. A smaller record giving an index of both the maximum and minimum blood pressures is obtained from the cuff 27 alone by closing the throttle valve 11 to slightly more than before and by turning the valve 21 to connect pipes 22 and 23 together and to close pipe 20. A continuous rise in average counter-pressure is obtained by substituting a collapsable chamber for the bulb 28 or by admitting compressed air through a central valve. The apparatus is deflated by opening tap 31, release valve 29, and valve 21 to all three ports. The record strip may be flat or cylindrical and may be wound on the cylinder 38 to be driven by the clockwork motor 36. A time marker may be fitted to the lug 34. and a recording manometer may also be fitted to the pipe 15. The apparatus may be constructed in a portable form. A friction brake, operated electrically or otherwise, may be fitted to the manometer float if more accurate visual readings of the average pressure are desired. It is stated in the Provisional Specification that the lower armlet 27 is the larger.