System and method for evaluating risk of mortality due to congestive heart failure using physiologic sensors
A congestive heart failure (CHF) mortality risk metric is automatically generated using an implantable medical device and, if it exceeds a predetermined threshold, a warning signal is issued indicating a significant risk of mortality due to CHF, perhaps necessitating more aggressive medical therapy. The CHF mortality risk metric is calculated based on a combination of estimated ventilatory response values and the slope of heart rate reserve as a function of predicted heart rates. Ventilatory response is estimated based on detected values of actual heart rate, arterial oxygen saturation, right ventricular O 2 , stroke volume, tidal volume, and respiration rate. Heart rate reserve values are derived from the actual heart rate along with patient age and rest heart rate. The predicted heart rates, which represent the heart rates the patient would achieve if healthy, are derived from activity sensor signals. The CHF mortality risk metric is then calculated as a ratio of ventilatory response and the slope of the heart rate reserve. If the CHF mortality risk metric exceeds a critical threshold value, such as 90, the warning signal is generated. Also described herein are various techniques for estimating ventilatory response.
1. In an implantable medical device for implant within a patient, the device having a plurality of sensors and a control unit for processing signals from the sensors, a method performed by the control unit comprising:
receiving signals from the sensors representative of physiological parameters of the patient detected at sub-maximal exertion levels;
estimating the ventilatory response of the patient at maximum exertion based on the signals detected at sub-maximal exertion levels; and
controlling at least one function of the device based on the estimated ventilatory response.
wherein the step of receiving signals representative of physiological parameters of the patient includes the step of receiving signals representative of Heart Rate, Arterial Oxygen Saturation, Right Ventricular O 2 , Stroke Volume, Tidal Volume, and Respiration Rate; and
wherein the step of estimating ventilatory response includes the step of calculating
VR =(Tidal Volume−Respiratory Rate) /(α×(Arterial O 2 Saturation−Right Ventricular O 2 ) ×(Heart Rate)×(Stroke Volume)).
2. The method of claim 1 , wherein the coefficient α is about 1.14.
3. In an implantable medical device for implant within a patient, the device having a plurality of sensors and a control unit for processing signals from the sensors, a method performed by the control unit comprising:
receiving signals from the sensors representative of physiological parameters of the patient detected at sub-maximal exertion levels;
estimating the ventilatory response of the patient at maximum exertion base on the signals detected at sub-maximal exertion levels; and
controlling at least one function of the device based on the estimated ventilatory resoonse;
wherein the step of receiving signals representative of physiological parameters of the patient includes the step of receiving signals representative of Heart Rate, Arterial Oxygen Saturation, Right Ventricular O 2 , Tidal Volume, and Respiration Rate; and
wherein the step of estimating ventilatory response includes the steps of inputting a Stroke Volume Constant and then calculating
VR =(Tidal Volume−Respiratory Rate)/(α×(Arterial O 2 Saturation−Right Ventricular O 2 ) ×(Heart Rate)×(Stroke Volume Constant)).
4. The method of claim 3 wherein the Stroke Volume Constant is set to about 50 ml.
5. In an implantable medical device for implant within a patient, the device having a plurality of sensors and a control unit for processing signals from the sensors, a method performed by the control unit comprising:
receiving signals from the sensors representative of physiological parameters of the patient detected at sub-maximal exertion levels;
estimating the ventilatory response of the patient at maximum exertion based on the signals detected at sub-maximal exertion levels; and
controlling at least one function of the device based on the estimated ventilatory response;
wherein the step of receiving signals representative of physiological parameters of the patient includes the step of receiving signals representative of Heart Rate, Right Ventricular O 2 , Stroke Volume, Tidal Volume, and Respiration Rate; and
wherein the step of estimating ventilatory response includes the steps of inputting an Arterial Oxygen Saturation Constant and then calculating
VR =(Tidal Volume−Respiratory Rate) /(α×(Arterial O 2 Saturation Constant−Right Ventricular O 2 ) ×(Heart Rate)×(Stroke Volume)).
6. The method of claim 5 wherein the Arterial O 2 Saturation Constant is about 0.95.