Method and apparatus for determining respiratory effort in a medical device

A method of determining respiratory effort in a medical device, comprising:

• sensing cardiac pressure signals;
• sensing cardiac signals and determining a heart rate in response to the sensed cardiac signals;
• filtering the sensed pressure signals in response to the determined heart rate to generate a heart-rate dependent frequency response;
• deriving a filtered signal in response to the heart rate dependent frequency response;
• generating sample points in response to the derived filtered signal;
• detecting an inspiration in response to a first predetermined number of sample points corresponding to the sensed pressure signals being less than a detection threshold;
• detecting an expiration in response to a second predetermined number of sample points corresponding to the sensed pressure signals, occurring subsequent to the first predetermined number of sample points, being greater than the detection threshold;
• detecting a breath in response to the detected inspiration and the detected expiration;
• and
• determining the respiratory effort in response to the detected breath.