Instrumentation for monitoring blood circulation

Claim 1

Compact monitor apparatus for monitoring a blood circulation condition comprising: a source of infrared radiation, infrared sensor means mounted in spaced, side by side relation to said infrared source, said source and said sensor means being arranged whereby, when applied to a skin surface said source and said sensor means are exposed to spaced but immediately adjacent skin surface areas, oscillator means for energizing said infrared source to generate a series of pulses of infrared radiation at a relatively high frequency that is substantially greater than the power distribution frequency, whereby the pulsating blood flow immediately beneath the skin surface area significantly changes the transmission of infrared radiation as a function of the amount of blood in that region and thus imposes a modulation at a relatively low frequency that is substantially less than said power distribution frequency on the amplitude of the relatively high frequency pulses of infrared radiation emanating from the skin surface as sensed by said sensor means, band pass circuitry means connected to said sensor means and tuned to pass only signals in a frequency band that has a lower limit greater than said power distribution frequency and an upper limit less than three times said relatively high frequency, detector circuitry means connected to said band pass circuitry means for producing a series of output pulses as a function of the modulated pulse signals passed by said band pass circuitry means, low pass circuitry means, connected to said detector circuitry means and tuned to pass only signals at a frequency substantially less than said power distribution frequency, such that the relatively low frequency components of the output pulses from said detector circuitry means are passed and the relatively high frequency pulse components of said output pulses are blocked, pulse generator means connected to said low pass circuitry means to generate a pulse pf predetermined amplitude and duration in response to each output pulse from said low pass circuitry means, the repetition rate of said pulse generator being limited to a maximum rate of about three pulses per second, and output indicator means connected to respond to said pulses of predetermined amplitude and duration from said pulse generator means to produce an indication of the monitored blood circulation condition as a function of the modulation by said pulsating blood flow of the series of infrared radiation pulses as sensed by said infrared sensor.