Rate adaptive cardiac rhythm management device using transthoracic impedance
First Claim
1. A method of determining transthoracic impedance in a cardiac rhythm management device, the method comprising:
- repeatedly delivering a multiple phase stimulus to a thorax region of a patient; and
demodulating more than one phase of the multiple phase stimuli to obtain sample points of a response signal including transthoracic impedance information.
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Abstract
A cardiac rhythm management (CRM) device detects transthoracic impedance, extracts ventilation or other information, and adjusts a delivery rate of the CRM therapy accordingly. A four-phase sequence of alternating direction current pulse stimuli is periodically delivered to a patient'"'"'s thorax. A transthoracic impedance signal is extracted using a weighted demodulation. Signal processing extracts ventilation information and removes cardiac stroke information using an adaptive lowpass filter. The adaptive filter cutoff frequency is based on the patient'"'"'s heart rate; a higher cutoff frequency is provided for higher heart rates. Peak/valley detection indicates tidal volume, which is integrated to extract minute ventilation (MV). Short and long term averages are formed and compared to establish a MV indicated rate. Rate adjustment ignores MV information when a noise-measurement exceeds a threshold. An interference avoidance circuit delays delivery of the stimuli when telemetry pulses or other interfering signals are detected.
117 Citations
20 Claims
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1. A method of determining transthoracic impedance in a cardiac rhythm management device, the method comprising:
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repeatedly delivering a multiple phase stimulus to a thorax region of a patient; and
demodulating more than one phase of the multiple phase stimuli to obtain sample points of a response signal including transthoracic impedance information. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification