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

• US 6,645,153 B2
• Filed: 02/07/2002
• Issued: 11/11/2003
• Est. Priority Date: 02/07/2002
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Bradley, Kerry, Kroll, Mark W.
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): MALLARI, PATRICIA C
• Application Number:
  US10/068,885
• Publication Number:
  US 20030149367A1
• Time in Patent Office: 642 Days
• Field of Search: 600/300-301, 600/481, 600/508-513, 600/547
• US Class Current: 600/481
• 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 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61B 5/145 Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissuemeasuring of blood pressure or blood flow A61B5/02; non-radiation detecting or locating of foreign bodies in blood A61B5/06
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy

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, a system comprising:

means for receiving signals representative of physiological parameters of the patient; and

means for determining a risk of mortality to congestive heart failure for the patient based on the signals;

wherein the means for determining the risk of mortality to congestive heart failure includes

means for determining ventilatory response for the patient based on the signals received from the sensors;

means for determining heart rate reserve for the patient as a function of the exertion level of the patient based on signals received from the sensors; and

means for combining the ventilatory response with the heart rate reserve as a function of the exertion level to yield a single congestive heart failure mortality risk metric.

2. In an implantable medical device for implant within a patient, the device comprising a plurality of sensors, a method comprising:

receiving signals from the sensors representative of physiological parameters of the patient;

determining a ventilatory response value and a heart rate reserve value from the received signals;

processing the ventilatory response value and the heart rate reserve value to generate a risk of mortality value;

comparing the risk of mortality value with a stored value; and

generating a warning signal if the risk of mortality value deviates from the stored value by at least a predetermined amount.

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;

determining a value representative of a risk of mortality for the patient to congestive heart failure based on the signals; and

comparing the value representative of risk of mortality with a threshold value and generating a warning signal if the value representative of risk of mortality exceeds the threshold value;

wherein the step of determining a value representative of risk of mortality to congestive heart failure includes the step of determining a ventilatory response for the patient based on the signal received from the sensors; and

wherein the step of determining ventilatory response for the patient is performed based on signals detected at sub-maximal exertion levels of the patient.

4. The method of claim 3:

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 0₂, Stroke Volume, Tidal Volume, and Respiration Rate; and

wherein the step of determining ventilatory response includes the step of calculating ventilatory response according to

5. The method of claim 4 wherein the coefficient a is about 1.14.

6. The method of claim 3:

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 determining ventilatory response includes the steps of inputting a Stroke Volume Constant and then calculating ventilatory response according to

7. The method of claim 6 wherein the Stroke Volume Constant is set to about 50 ml.

8. The method of claim 3:

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 determining ventilatory response includes the steps of inputting an Arterial Oxygen Saturation Constant and then calculating ventilatory response according to

9. The method of claim 8 wherein the Arterial O₂ Saturation Constant is about 0.95.

10. The method of claim 3 wherein the step of determining 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.

11. The method of claim 3 wherein the step of determining 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.

12. 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;

determining a value representative of a risk of mortality for the patient to congestive heart failure based on the signals; and

comparing the value representative of risk of mortality with a threshold value and generating a warning signal if the value representative of risk of mortality exceeds the threshold value;

wherein the step of determining a value representative of risk of mortality to congestive heart failure includes the step of;

determining 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 wherein the step of determining heart rate reserve based on the signals received from the sensors is performed using only signals detected at sub-maximal exertion levels of the patient.

14. The method of claim 12 wherein the step of determining heart rate reserve for the patient as a function of the exertion level includes the step of:

measuring actual patient heart rates at various exertion levels of the patient;

determining heart rate reserve at the various exertion levels of the patient based on the actual heart rates;

predicting the heart rate the patient would achieve if healthy at the various exertion levels; and

determining the slope of heart rate reserve as a function of the predicted heart rates.

15. The method of claim 14 wherein the step of predicting the heart rate the patient would achieve if healthy at the various exertion levels includes the steps of:

receiving signals from activity sensors representative of the current level of activity of the patient at the various exertion levels; and

converting the activity sensor signals to predicted heart rates using predetermined conversion values.

16. The method of claim 14 wherein the step of determining heart rate reserve at the various levels of exertion based on the actual heart rates includes the step of calculating:

17. The method of claim 14 wherein the step of determining the slope of heart rate reserve as a function of the predicted heart rate includes the steps of:

associating individual heart rate reserve values with contemporaneous predicted heart rates; and

calculating the slope of a straight line that best fits the heart rate reserve values as a function of the contemporaneous predicated heart rates.

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

means for receiving signals representative of physiological parameters of the patient; and

means for determining a risk of mortality to congestive heart failure for the patient based on the signals;

wherein the means for determining the risk of mortality to congestive heart failure includes means for determining heart rate reserve for the patient as a function of exertion level.

19. The system of claim 18 wherein the means for determining the risk of mortality to congestive heart failure further includes means for determining ventilatory response for the patient.

20. The system of claim 18 further including means for comparing the value representative of risk of mortality with a threshold value and generating a warning signal if the value representative of risk of mortality exceeds the threshold value.

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

a plurality of physiological sensors; and

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;

wherein the CHF risk determination unit is operative to determine heart rate reserve for the patient as a function of exertion level and to determine the risk of mortality to CHF based on heart rate reserve for the patient as a function of exertion level.

22. The system of claim 21 wherein plurality of sensors comprise:

a heart rate detector, an arterial oxygen saturation sensor, a right ventricular 0₂ sensor, a stroke volume sensor, a tidal volume sensor, and a respiration rate sensor.

23. The system of claim 21 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.

24. 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;

determining a value representative of a risk of mortality for the patient to congestive heart failure based on the signals; and

comparing the value representative of risk of mortality with a threshold value and generating a warning signal if the value representative of risk of mortality exceeds the threshold value;

wherein the step of determining a value representative of risk of mortality to congestive heart failure includes the step of;

determining ventilatory response for the patient based on the signals received from the sensors;

determining heart rate reserve for the patient as a function of the exertion level of the patient based on signals received from the sensors; and

combining the ventilatory response with the heart rate reserve as a function of the exertion level to yield a single congestive heart failure mortality risk metric.