Dynamic sampling
Dynamic sampling of physiological parameters based on the next anticipated occurrence of a relatively periodic physiological event. Embodiments of the invention may be used to increase the battery life or effective data storage capacity of implantable medical devices while retaining or improving measurement resolution.
1. A method of operating an implantable medical device, comprising:
sensing a physiological parameter of a patient and producing a representative signal thereof, the physiological parameter including a periodically repeating physiological event;
sampling the sensed signal at a selected sampling frequency to produce digital samples representative of the sensed signal;
detecting the physiological events based on the digital samples;
determining an expected time period between the physiological events; and
setting the selected sampling frequency, the selected sampling frequency being increased ahead of an expected time of each physiological event based on the expected time period between physiological events, the selected sampling frequency being decreased following detection of each event.
2. A method according to claim 1 , further comprising delivering a therapy to the patient at the expected time of each physiological event.
3. A method according to claim 1 , further comprising delivering a therapy to the patient after detection of each physiological event.
4. A method according to claim 3 , wherein the therapy includes electrical stimulation of upper airway muscles of the patient.
5. A method according to claim 1 , wherein the physiological parameter includes an intrathoracic pressure in the patient.
6. A method according to claim 1 , wherein the periodically repeating physiological event includes respiratory inspiration.
7. A method according to claim 1 , wherein the determining the expected time period is based on the detection of the physiological events.
8. A method according to claim 1 , further including detecting the frequency that the sensor signal crosses a measurement threshold value, the determining the expected time period between the physiological events being based on the frequency that the sensor signal crosses the measurement threshold value.
9. A method according to claim 1 , wherein the increase of the selected sampling frequency includes increasing the sample frequency linearly with respect to time on the approach of the expected time of each physiological event.
10. A method according to claim 1 , wherein the increase of the selected sampling frequency includes increasing the sample frequency exponentially with respect to time on the approach of the expected time of each physiological event.
11. A method according to claim 1 , wherein the increase of the selected sampling frequency includes rapidly increasing the sampling frequency on the approach of the expected time of each physiological event.
12. A method according to claim 1 , wherein the selected sampling frequency consists of first and second sampling frequencies, the second sampling frequency being higher than the first sampling frequency, then setting the sampling frequency being between the first and second sampling frequencies.