Patent GB-1383958-A (GB)
Title: Signal processing apparatus for achilles tendon reflex testing
IPC: A61B5/11
Filed: 1972-03-24
Abstract: 1383958 Achilles tendon reflex testing SEARLE MEDIDATA Inc 24 March 1972 [24 March 1971] 13836/72 Heading A5K Apparatus is provided for use in testing the Achilles-tendon reflex in a patient and for operation with a motion-sensor of the type having an optical path between a light source and a light detector 36 with the optical path occluded by the patient's foot to a varying degree as a result of reflexing of the Achilles tendon induced by a hammer blow, the apparatus comprising means for receiving the varying detector signal, means for detecting first and second points on said signal and providing an indication of the time between said points, the first point being the point 28a, Fig. 2A, at which the hammer blow is first felt by the patient and the second point 30d corresponding to a predetermined degree of induced Achilles-tendon reflex relaxation, and means for displaying a composite signal formed by the varying detector signal with an indication of the first and second points thereon. Detector signals from a low-pass filter 40, eliminating effects of artificial ambient light interference, pass to a circuit 44 having a two state output, Fig. 2E, with transitions between first and second states occuring with each change in the filter output signal from a zero slope to a positive or negative slope. The output of circuit 44 causes a pulse generator 48 to generate a sequence of four pulses in each normal reflex, Fig. 2F, corresponding to points 28a, 28b, 28c and 30c, Fig. 2A, of a normal reflex, the occurence of the third pulse being delayed, however, by a delay circuit 52 so that it occurs after any spastic contraction lobes 32, Fig. 2C, have occured to prevent such lobes producing further pulses in said sequence. The generator 48 output passes to a four-bit counter 50 having a fourth count output passing to a gate 69 and acting as a control for a detector 42, and a first court output passing to a monostable multivibrator 70 which resets the apparatus after each reflex test after a fixed time which is sufficiently long as to terminate after any trailing response lobe 34, Fig. 2D. A 100 Hz or 1 kHz counter 64 is controlled via a gate 60 to count only when a flip-flop 56 is in a set-state, caused by the first pulse from generator 48, flip-flop 56 being reset either by the output of detector 42 or by the output of multi-vibrator 70, the detector 42 sensing and giving an output when the signal from filter 40 has decreased by a predetermined amount, e.g. half, from the peak at point 30C, Fig. 2A. The circuit 44 also acts to differentiate an input thereto from flip-flop 56 to provide pulses which are added to the input from filter 40 to give said composite signal, Fig. 2I, which passes via an amplifier 94 to a visual recorder 96. The amplifier 94 is only operational during the timing interval of the multivibrator 70 and an operator control 106 initiates operation of the apparatus. The output, Fig. 2I, of recorder 96 is used by the operator to determine when a normal reflex has occurred, the operator then activating an entry circuit 66 to record the count in counter 64 in a computer or other data processor 68.