System and method for evaluating risk of mortality due to congestive heart failure using physiologic sensors

• US 20030149453A1
• Filed: 02/07/2002
• Published: 08/07/2003
• Est. Priority Date: 02/07/2002
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Bradley, Kerry, Kroll, Mark W.
• Granted Patent: US 6,961,615 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61N 1/36514 controlled by a physiological quantity other than heart potential, e.g. blood pressure controlled by two or more physical parameters A61N1/36585
• CPC Class Codes: A61N 1/368 comprising more than one electrode co-operating with different heart regions A61N1/3622, A61N1/3627 take precedence
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: G16H 40/63 for local operation
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

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 O₂, 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.

Claims

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.

2. The method of claim 1:

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 O₂, 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 O₂ Saturation−

Right Ventricular O₂)×

(Heart Rate)×

(Stroke Volume)).

3. The method of claim 2 wherein the coefficient α

is about 1.14.

4. The method of claim 1:

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 O₂, 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 O₂ Saturation−

Right Ventricular O₂)×

(Heart Rate)×

(Stroke Volume Constant)).

5. The method of claim 4 wherein the Stroke Volume Constant is set to about 50 ml.

6. The method of claim 1:

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 O₂, 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 O₂ Saturation Constant−

Right Ventricular O₂)×

(Heart Rate)×

(Stroke Volume)).

7. The method of claim 6 wherein the Arterial O₂ Saturation Constant is about 0.95.

8. The method of claim 1 wherein the step of estimating ventilatory response for the patient includes the steps of:

receiving signals representative of ventilation amplitude, ventilation rate, and sinus rate; and

determining ventilatory response by multiplying the ventilation amplitude by the ventilation rate and correlating with the sinus rate.

9. The method of claim 1 wherein the step of estimating ventilatory response for the patient includes the steps of:

receiving signals representative of the current level of activity of the patient, sinus rate and minute ventilation; and

determining ventilatory response by dividing minute ventilation by the current level of activity of the patient and correlating with the sinus rate.

10. The method of claim 1 further including the step of determining a value representative of a risk of mortality to congestive heart failure based on the estimated ventilatory response.

11. The method of claim 10 wherein the step of controlling at least one function of the device includes the step of comparing the value representative of risk of mortality with a threshold value and, if it exceeds the threshold value, controlling a telemetry device to output a warning signal.

12. The method of claim 10 further including the step of also determining a value representative of a risk of mortality to congestive heart failure based on heart rate reserve as a function of the exertion level of the patient based on signals received from the sensors.

13. The method of claim 12 further including the step of combining the value representative of a risk of mortality determined based on ventilatory response with the value representative of a risk of mortality determined based on heart rate reserve as a function of the exertion level to yield a single congestive heart failure mortality risk metric.

14. The method of claim 1 wherein the step of controlling at least one function of the device includes the step of controlling a memory device to store the estimated ventilatory response as diagnostic information.

15. In an implantable medical device for implant within a patient, a system comprising:

a plurality of physiological sensors; and

a ventilatory response estimation unit operative to estimate the ventilatory response of the patient at maximum exertion based on the signals detected by the physiological sensors at sub-maximal exertion levels.

16. The system of claim 15 further wherein the ventilatory response estimation unit is part of a congestive heart failure (CHF) risk determination unit operative to process signals from the sensors and to determine the risk of mortality to CHF for the patient.

17. The system of claim 16 wherein the CHF risk determination unit also includes a heart rate reserve estimation unit operative to determine heart rate reserve as a function of exertion level and to determine the risk of mortality to CHF based on both heart rate reserve and ventilatory response.

18. The system of claim 16 wherein the CHF risk determination unit is further operative to compare the risk of mortality with a threshold risk level and to generate a warning signal if the risk of mortality exceeds the threshold risk level.

19. The system of claim 15 wherein plurality of sensors comprise:

a heart rate detector, an arterial oxygen saturation sensor, a right ventricular O₂ sensor, a stroke volume sensor, a tidal volume sensor, and a respiration rate sensor.

20. In an implantable medical device for implant within a patient, a system comprising:

means for determining that the patient is at a sub-maximal exertion level;

means for detecting one or more physiological parameters of the patient at the sub-maximal exertion level; and

means for estimating the ventilatory response of the patient at maximum exertion based on the signals detected at the sub-maximal exertion level.

21. The system of claim 20 further comprising means for determining a risk of mortality to congestive heart failure for the patient based on the estimated ventilatory response.

22. The system of claim 21 wherein the means for determining the risk of mortality to congestive heart failure comprises means for determining heart rate reserve for the patient as a function of exertion level and for determining the risk of mortality to CHF based on both heart rate reserve and ventilatory response.

23. The system of claim 22 wherein the means for determining the risk of mortality to congestive heart failure compares the value representative of risk of mortality with a threshold value and, if it exceeds the threshold value, generates a warning signal.

24. The system of claim 20 further comprising means for storing the estimated ventilatory response as diagnostic information.