Optical sensor and method for detecting a patient condition
An implantable medical device for monitoring tissue perfusion that includes a light source emitting a light signal and a light detector receiving emitted light scattered by a volume of body tissue. The light detector emits a signal having an alternating current component corresponding to the pulsatility of blood flow in the body tissue volume. A processor receives the current signal and determines a patient condition in response to the alternating component of the current signal.
1. An implantable medical device for monitoring blood flow pulsatility in a volume of body tissue in a patient, the device comprising:
at least two electrodes for sensing a cardiac electrical signal;
a light source for emitting a modulated light signal;
a filter for filtering the wavelengths of the modulated light signal scattered by the volume of body tissue;
a light detector for receiving the filtered modulated light signal and emitting a current signal having an alternating current component correlated to pulsatility of blood flow within the volume of body tissue;
a processor for receiving the cardiac electrical signal, detecting an arrhythmia in response to the cardiac electrical signal, receiving the light detector signal, determining a pulsatility metric in response to the alternating current component of the light detector signal, comparing the pulsatility metric to a heart rate determined from the cardiac electrical signal, confirming the arrhythmia in response to the comparison, and detecting T-wave oversensing in response to the cardiac electrical signal being greater than the pulsatility metric, wherein the pulsatility metric is a frequency of the alternating current component and; and
a therapy control module coupled to the processor and delivering an anti-arrhythmia therapy in response to the arrhythmia confirmation.
2. The device of claim 1 , wherein the processor is further configured to detect T-wave undersensing in response to the pulsatility metric being greater than the cardiac electrical signal.
3. The device of claim 1 , wherein the processor confirms the arrhythmia in response to the pulsatility metric being approximately equal to the cardiac electrical signal.
4. The device of claim 1 , further comprising a signal modulator modulating the emitted light signal wherein the processor demodulates light detector signal.
5. The device of claim 4 wherein the emitted light signal is modulated at a carrier frequency of approximately 100 to 10,000 Hz.
6. The device of claim 1 , wherein the light detector is a photo darlington device.
7. The device of claim 1 , wherein the processor determines one of a frequency of the alternating current component and a peak-to-peak amplitude difference of the alternating current component.
8. The device of claim 7 wherein the processor determines a heart rate from the cardiac electrical signals and compares the determined heart rate to the frequency of the alternating current component.
9. The device of claim 1 , wherein the processor further determines the presence of a motion artifact in the light detector signal.