Assessment of autonomic regulation to heart rate variability by the method of complex demodulation

Complex demodulation of heart-rate variability was used to analyze changes in the autonomic regulation of dog heart rate during differential classical conditioning before and after autonomic blockade. This method tracked the rapid withdrawal of parasympathetic tone following the onset of the warning signal and detected a later rise in low-frequency power that was tentatively identified as a sympathetic increase. Results during drug blockade supported the analysis in intact conditions. It is concluded that complex demodulation of heart-rate variability provides a powerful tool for noninvasive assessment of autonomic changes in response to environmental or physiological challenges