Action of the sympathetic and parasympathetic nervous system on cardiovascular dynamics revealed by blocking drugs

The effect of the drugs atropine (a parasympathetic blocker) and propranolol (a sympathetic blocker) is investigated. In the experiment, the subjects were measured under an experimental protocol that used saline controls, with both spontaneous and paced breathing as well as apnea. The recorded data included an electrocardiogram, end tidal CO₂, blood pressure and a direct measurement of the muscle sympathetic nerve activity. The signals were analysed using time-frequency methods and an information theory approach, revealing information about the change in coupling and coherence that has not previously been studied. The results show that atropine strongly reduces the power in the signals and also removes the coupling and coherence between cardiovascular oscillations. The effects occur across a wide range of frequencies and provide insight into the neurophysiological mechanisms involved in the regulation of the cardiovascular system.