Shock reduction using absolute calibrated tissue oxygen saturation and total hemoglobin volume fraction
First Claim
1. A method, comprising:
- sensing cardiac depolarization signals;
detecting an arrhythmia in response to the depolarization signals;
controlling an optical sensor to emit light in response to the detected arrhythmia;
detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths;
computing a measure of tissue oxygenation from the optical sensor output signal, wherein computing the measure of tissue oxygenation comprises;
computing a light attenuation for each of the at least four wavelengths;
computing a second derivative of the light attenuation with respect to two different wavelengths;
computing a measure of tissue oxygen saturation independent of total hemoglobin as a ratio of the second derivatives at the two different wavelengths;
computing a measure of total hemoglobin volume fraction using the second derivative of a selected one of the two different wavelengths;
detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation, wherein the measure of tissue oxygenation is computed responsive to at least one of the measure of tissue oxygen saturation independent of total hemoglobin and the measure of total hemoglobin volume fraction;
computing the measure of tissue oxygenation as a weighted combination of the measure of oxygen saturation and the measure of total hemoglobin volume fraction;
determining if one of the measure of oxygen saturation and the measure of total hemoglobin volume fraction is out of a respective acceptable range; and
adjusting a weighting factor used to compute the weighted combination in response to one of the measures of oxygen saturation and total hemoglobin volume fraction being out of a respective acceptable range.
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Accused Products
Abstract
An implantable medical device for detecting and treating an arrhythmia includes an optical sensor adapted for positioning adjacent to a blood-perfused tissue volume. In one embodiment for controlling arrhythmia therapies delivered by the device, the optical sensor is controlled to emit light in response to detecting an arrhythmia, detect light scattered by the volume of blood perfused tissue including measuring an optical sensor output signal corresponding to the intensity of scattered light for at least four spaced-apart wavelengths, and compute a volume-independent measure of tissue oxygen saturation from the detected light. The hemodynamic status of the arrhythmia is detected in response to the measure of tissue oxygen saturation.
113 Citations
29 Claims
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1. A method, comprising:
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sensing cardiac depolarization signals; detecting an arrhythmia in response to the depolarization signals; controlling an optical sensor to emit light in response to the detected arrhythmia; detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths; computing a measure of tissue oxygenation from the optical sensor output signal, wherein computing the measure of tissue oxygenation comprises; computing a light attenuation for each of the at least four wavelengths; computing a second derivative of the light attenuation with respect to two different wavelengths; computing a measure of tissue oxygen saturation independent of total hemoglobin as a ratio of the second derivatives at the two different wavelengths; computing a measure of total hemoglobin volume fraction using the second derivative of a selected one of the two different wavelengths; detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation, wherein the measure of tissue oxygenation is computed responsive to at least one of the measure of tissue oxygen saturation independent of total hemoglobin and the measure of total hemoglobin volume fraction; computing the measure of tissue oxygenation as a weighted combination of the measure of oxygen saturation and the measure of total hemoglobin volume fraction; determining if one of the measure of oxygen saturation and the measure of total hemoglobin volume fraction is out of a respective acceptable range; and adjusting a weighting factor used to compute the weighted combination in response to one of the measures of oxygen saturation and total hemoglobin volume fraction being out of a respective acceptable range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 22, 23, 24)
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11. An implantable medical device, comprising:
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a cardiac electrode for sensing cardiac depolarization signals; an optical sensor for providing a signal corresponding to light attenuation by a volume of blood perfused tissue; a control module coupled to the optical sensor controlling the light emitted by the optical sensor; a monitoring module receiving an optical sensor output signal and measuring light attenuation for at least four spaced-apart light wavelengths; and a processor coupled to the cardiac electrode and the monitoring module, the processor being configured to; detect an arrhythmia in response to the depolarization signals, compute a tissue oxygenation measurement in response to detecting the arrhythmia, compute an attenuation for each of the at least four wavelengths of detected light, compute a second derivative of the light attenuation with respect to two different wavelengths, compute a measure of tissue oxygen saturation independent of total hemoglobin as a ratio of the second derivatives at the two different wavelengths, compute a measure of total hemoglobin volume fraction using the second derivative of a selected one of the two different wavelengths; detect a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation, wherein the measure of tissue oxygenation is computed responsive to at least one of the measure of tissue oxygen saturation independent of total hemoglobin and the measure of total hemoglobin volume fraction; determine an attenuation for each of the at least four wavelengths at an episode onset time point of the arrhythmia detection; determine an onset measurement at the episode onset time point based on a weighted combination of the tissue oxygen saturation and the total hemoglobin volume fraction for the time of the arrhythmia detection; determine if one of the measure of oxygen saturation and the measure of total hemoglobin volume fraction is out of a respective acceptable range; and adjust a weighting factor used to compute the weighted combination in response to one of the measures of oxygen saturation and total hemoglobin volume fraction being out of a respective acceptable range. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A non-transitory computer readable medium having computer executable instructions for performing a method comprising:
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sensing cardiac depolarization signals; detecting an arrhythmia in response to the depolarization signals; controlling an optical sensor to emit light in response to the detected arrhythmia; detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths; computing a measure of tissue oxygenation from the optical sensor output signal, wherein computing the measure of tissue oxygenation comprises; computing a light attenuation for each of the at least four wavelengths; computing a second derivative of the light attenuation with respect to two different wavelengths; computing a measure of tissue oxygen saturation independent of total hemoglobin as a ratio of the second derivatives at the two different wavelengths; computing a measure of total hemoglobin volume fraction using the second derivative of a selected one of the two different wavelengths; and detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation, wherein the measure of tissue oxygenation is computed responsive to at least one of the measure of tissue oxygen saturation independent of total hemoglobin and the measure of total hemoglobin volume fraction; determine an attenuation for each of the at least four wavelengths at an episode onset time point of the arrhythmia detection; determine an onset measurement at the episode onset time point based on a weighted combination of the tissue oxygen saturation and the total hemoglobin volume fraction for the time of the arrhythmia detection; determining if one of the measure of oxygen saturation and the measure of total hemoglobin volume fraction is out of a respective acceptable range; and adjusting a weighting factor used to compute the weighted combination in response to one of the measures of oxygen saturation and total hemoglobin volume fraction being out of a respective acceptable range.
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25. An implantable medical device, comprising:
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a cardiac electrode for sensing cardiac depolarization signals; an optical sensor configured to produce a signal corresponding to light attenuation by a volume of blood perfused tissue; a control module coupled to the optical sensor and configured to control the light emitted by the optical sensor; a monitoring module coupled to the optical sensor and configured to receive an optical sensor output signal and determine light attenuation for at least four spaced-apart light wavelengths; and a processor electrically coupled to the cardiac electrode and the monitoring module and configured to receive the cardiac electrical signal, the processor being configured to; detect an arrhythmia in response to the cardiac electrical signal, determine an attenuation for each of the at least four wavelengths at an episode onset time point of the arrhythmia detection; determine a second derivative of the attenuation with respect to each of two different wavelengths of the four wavelengths for the episode onset time point of the arrhythmia detection; determine a tissue oxygen saturation independent of total hemoglobin based on a ratio of the two second derivatives determined with respect to each of the two different wavelengths for the episode onset time point; determine a total hemoglobin volume fraction based on a selected one of the two second derivatives determined for the episode onset time point; establish a first weighting factor applied to the tissue oxygen saturation and a second weighting factor applied to the total hemoglobin volume fraction; determine an onset measurement at the episode onset time point based on a weighted combination of the tissue oxygen saturation and the total hemoglobin volume fraction for the time of the arrhythmia detection using the established first and second weighting factors; compare the onset measurement to an onset detection threshold, detect a hemodynamically unstable status of the detected arrhythmia in response to the onset measurement being less than the onset detection threshold; determine if one of the tissue oxygen saturation and the total hemoglobin volume fraction is out of a respective acceptable range; and adjust one of the first weighting factor and the second weighting factor used to compute the weighted combination in response to one of the tissue oxygen saturation and the total hemoglobin volume fraction being out of the respective acceptable range. - View Dependent Claims (27, 28, 29)
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26. A method, comprising:
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sensing cardiac depolarization signals; detecting an arrhythmia in response to the depolarization signals; controlling an optical sensor to emit light in response to the detected arrhythmia; detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths; computing a measure of tissue oxygenation from the optical sensor output signal, wherein computing the measure of tissue oxygenation comprises; computing a light attenuation for each of the at least four wavelengths; computing a second derivative of the light attenuation with respect to two different wavelengths; computing a measure of tissue oxygen saturation independent of total hemoglobin as a ratio of the second derivatives at the two different wavelengths; computing a measure of total hemoglobin volume fraction using the second derivative of a selected one of the two different wavelengths; computing the measure of tissue oxygenation as a weighted combination of the measure of oxygen saturation and the measure of total hemoglobin volume fraction; determining if one of the measure of oxygen saturation and the measure of total hemoglobin volume fraction is out of a respective acceptable range; adjusting a weighting factor used to compute the weighted combination in response to one of the measures of oxygen saturation and total hemoglobin volume fraction being out of a respective acceptable range; and detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation.
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Specification