GB745646A - Improvements in or relating to apparatus for oximetric measurement - Google Patents

Abstract

745,646. Blood testing apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Dec. 7, 1953 [Dec. 5, 1952], No. 30932/52. Class 81(2). [Also in Group XL(b)] The invention relates to apparatus for measuring the oxygen content of blood in the human ear, of the type comprising an ear attachment having a lamp mounting, a photocell mounting carrying a pair of photo-cells one provided with a filter having different absorption coefficients for oxidised and unoxidised haemoglobin and the other with a filter with the same absorption coefficient for both, a pair of transparent pressure members, between the lamp mounting and photo-cells and means for adjusting the pressure applied to the ear. According to the invention the transparent member furthest from the lamp mounting, the photo-cells and the colour filter are so disposed as to permit visual and photo-metric observations to be made simultaneously. As shown, the lamp 2 is mounted in a housing the end portion 5 of which acts as a transparent pressure member. The housing is mounted on a parallel motion linkage comprising four strips 12 of spring steel mounted vertically near one end of the base. The photo-cells 18 on red sensitive with a red filter and the other infra-red sensitive with an infra-red filter, are mounted on one face of a prism 13 another face 15 of which forms the other pressure member while a third face 20 is directed downwardly and enables visual observation of the ear to be made. An overcentre spring 1 and toggle 3 enable the lamp housing to be biased towards the prism thus clamping the ear and rendering it bloodless. Circuit. The photo-cells 18 are connected with their negative terminals, common and positive terminals to opposite ends of a resistance chain comprising potentiometer P2, rheostats P1 and register R1, The difference voltage developed by the cells is rendered alternating by a vibrating contact SV and are fed through a transformer, the primary of which is tuned to the vibration frequency, to the grid of the first stage of a two stage resistance capacity coupled amplifier comprising triodes V1, V2. A continuously variable gain control potentiometer is provided in the second stage of the amplifier which feeds a nicroammeter and bridge-type rectifier M. The gain of the amplifier may be reduced by 60 per cent. by means of switch S2 which tops the anode load of valve V1. Milliameter M may be used for measuring the voltage applied to the lamp 2 by changing over a switch S3 and thus putting the milliameter and its associated rectifier in series with a resister R1. A jack J is provided to enable recording apparatus to be connected, the recorder comprising a pentode amplifier, a voltage doubler detector, a smoothing network, a current amplifier and a pen-type recorder. Details of the setting up of the apparatus are given in the Specification.