Patent ID: 8033998

Claim:
An implantable medical device, comprising: a first sensor for sensing a first signal in a patient correlated to a first physiological condition; a second sensor for sensing a second signal in the patient corresponding to a second physiological condition; a third sensor for sensing a third signal in the patient corresponding to a third physiological condition responsive to the second physiological condition; and control circuitry for receiving the first, second and third signals and being configured to determine a relationship between the second signal and the third signal, detect a change in the relationship between the second signal and the third signal, determine a threshold in response to detecting the change in the relationship between the second signal and the third signal, and detect an event in response to the first signal crossing the determined threshold; wherein the first sensor signal is correlated to a thoracic fluid level, the second sensor signal is correlated to patient activity, and the third sensor signal is correlated to respiration rate, and wherein detecting a change in the relationship between the second and third signals includes determining an activity level in response to sensing an increase in thoracic fluid level and sensing an increase in a respiration rate response to activity level compared to a previously measured respiration rate response, and wherein determining the threshold includes determining a first sensor signal level corresponding to the increase in the respiration rate response.