Measuring instrument for intracardial acquisition of the blood oxygen saturation of a patient for controlling the pacing rate of a heart pacemaker

An instrument for intracardial acquisition of blood oxygen saturation using a measuring probe having two leads in a sequence including making a reference signal measurement and a useful signal measurement, said instrument comprising:

• a light transmitter connected in said measuring probe between said leads;
• a measuring current path in said measuring probe connected between said leads including a light-sensitive diode and a resistor connected in series therewith;
• a normally open switch having a conducting path connected between said leads and a control terminal connected to a junction between said light-sensitive diode and said resistor;
• a capacitor connected in parallel with said light-sensitive diode between said junction and one of said leads;
• and
• an evaluation circuit connected to said leads which supplies a pulse to said measuring probe for each sequence and which measures the voltage across said leads,
• whereby said pulse initially energizes said light transmitter with said normally open switch being non-conducting for making said reference signal measurement and charging said capacitance by the action of said light from said transmitter on said light sensitive diode reflected by the blood oxygen, said normally open switch closing upon attainment of said selected charge on said capacitance for making said useful signal measurement.

An instrument for intracardial acquisition of blood oxygen saturation using a measuring probe having two leads in a sequence including making a reference signal measurement and a useful signal measurement, said instrument comprising:

• a first switch having a conducting path connected between said leads and a control electrode connected to one of said leads;
• a light transmitter connected in series with a conducting path of a second switch between said leads, said second switch having a control electrode;
• a voltage divider connected in parallel with said conducting path of said first switch and having a tap connected to said control electrode of said second switch;
• a light receiver connected between said leads, said light receiver disposed for receiving light from said light transmitter reflected by said blood oxygen and generating a current proportional thereto;
• and
• an evaluation circuit connected to said leads which supplies a continuously rising signal to said measuring probe and which measures the voltage across said leads,
• whereby said first and second switches are respectively responsive to said continuously rising signal such that said first switch is initially closed and said second switch is initially open during said reference signal measurement, and said first switch is thereafter opened and said second switch is thereafter closed for making said useful signal measurement.