Heart rate spectral analysis, cardiac norepinephrine spillover, and muscle sympathetic nerve activity during human sympathetic nervous activation and failure.

Abstract

HRV at 0.1 Hz depends on factors in addition to cardiac sympathetic nerve firing rates, including multiple neural reflexes, cardiac adrenergic receptor sensitivity, postsynaptic signal transduction, and electrochemical coupling, and is not directly related to cardiac norepinephrine spillover, which is a more direct measure of the sympathetic nerve firing rate.