Mathematical analysis of the autonomic influence on the heart rate variability

The influence of arterial baroreceptor reflex on the heart rate variability is analysed by using a simple computer model of short-term autonomic regulation of heart activity. As basic mechanisms sufficient to elicit heart rate oscillations, the model incorporates: the systemic circulation, a non-pulsatile cardiac pump and a delayed non-linear negative-feedback simulating the arterial baroreceptor reflex. Short-term autonomic control of the cardiac pump is effected through sympathetic and parasympathetic divisions whose activities are modulated by afferent vagal tone. Model dynamics result high sensitive to changes of autonomic regulation parameters whose variations within a physiological range cause heart rate and arterial pressure to oscillate with frequencies within 0.1-0.4 Hz band. Simulation results reveal that because of the different latent periods characterising the sympathetic- and vagal-mediate controls two distinct oscillatory components with incommensurate frequencies may appear. Heart rate power spectrum exhibits a peak in LF band whose frequency diminishes form 0.17 to 0.12 Hz when efferent parasympathetic activity is partially depressed. Instead, an oscillatory component with high-frequency (0.4 Hz) appears when an enhancement of vagal activation or a partial inhibition of the sympathetic excitation is simulated.