Patent ID: 7676262

Claim:
In an implantable cardiac device, a method of determining a duration of activity for a patient, said method comprising: obtaining an activity threshold based on historical patient heart-rate data and historical patient activity data measured by the implantable cardiac device; obtaining a plurality of heart rate measurements measured by the implantable cardiac device; obtaining a plurality of activity level measurements measured by the implantable cardiac device; determining with the implantable cardiac device a plurality of activity correlation values (CORR current ) using the formula: CORR current =HRR×(ACT current −ACT offset ), wherein: CORR current is a current activity correlation value, HRR is heart rate reserve, ACT current is an activity measurement output by an activity sensor of the implantable cardiac device, and ACT offset is an activity offset parameter; and monitoring with the implantable cardiac device the amount of time correlation values exceed the activity threshold to determine the duration of activity.