Oxygen sensing pacemaker

Claim 1

In a demand heart pacemaker for providing stimulating pulses to the heart at a predetermined rate in the absence of naturally occurring heartbeats, of the type comprising: sensing means for sensing naturally occurring heart signals and generating a reset signal; pulse generator means for generating stimulating pulses at a minimum pacing rate, including first timing means for providing each stimulating pulse separated by an escape interval corresponding to the pacing rate and reset means responsive to a reset signal for resetting said timing means and restarting the escape interval; means for measuring blood oxygen level and for providing an escape interval modifying signal; means responsive to the escape interval modifying signal for adjusting the escape interval to provide pacing pulses on demand at a minimum rate correlated to the cardiac output requirements of the patient; the improvement wherein said blood oxygen level measuring means comprises: a sensor capsule means for location in the bloodstream, including a first light source generating light at a first wavelength, a second light source generating light at a second wavelength and a light responsive means for generating a light level signal indicative of the intensity of the light impinging upon said light responsive means, said first and second light sources and said light responsive means mounted within said sensor capsule means, said sensor capsule means at least partially transparent such that light generated by said first and second light sources may pass through said capsule body into said bloodstream and such that light reflected by said bloodstream may pass through said sensor capsule means to impinge upon said light responsive means; second timing means coupled to said sensing means and to said pulse generator means for determining a first time interval following said reset signals and following said stimulating pulses, for determining a second time interval following said first time interval, for generating a first sampling signal during said first time period and for generating a second sampling signal during said second time period; light source driving means coupled to said second timing means and to said first and second light sources for activating said first light source during said first time interval and for activating said second light source during said second time interval; first sample and hold means coupled to said second timing means and to said light responsive means, responsive to said first sampling signal for sampling said light level signal and for holding a first value derived from said sampled light level signal; and second sample and hold means coupled to said second timing means and to said light responsive means, responsive to said second sampling signal for sampling said light level signal and for holding a second value derived from said sampled light level signal; and wherein said adjusting means is coupled to said first and second sample and hold means and wherein said adjusting means adjusts said escape interval in response to said first and second values stored in said first and second sample and hold means.