Respiratory sinus arrhythmia is a major component of HRV in undisturbed, remotely monitored rattlesnakes, Crotalus durissus

Abstract

An implanted telemetry device transmitted ECG from the South American rattlesnake, Crotalus durissus, held under stable conditions without restraining cables or interaction with researchers. Mean heart rate (fH) recovered rapidly (<24h) from anaesthesia and operative procedures. This anticipated a more gradual development of heart rate variability (HRV), with instantaneous fH increasing during each lung ventilation cycle. Atropine injection increased mean fH and abolished HRV. Complete autonomic blockade revealed a parasympathetic tonus on the heart of 55% and an adrenergic tonus of 37%. Power spectral analysis of HRV identified a peak at the same frequency as ventilation. Such correlation is sustained after temperature change and that is clear when ventilation is less episodic. This HRV peak is homologous to that observed in mammals and termed respiratory sinus arrhythmia - RSA. Evidence for instantaneous control of fH implied rapid conduction of activity in the cardiac efferent nervous supply, supported by the description of myelinated fibres in the cardiac vagus. Establishment of HRV 10 days after surgical intervention seems a reliable indicator of the re-establishment of control of integrative functions by the autonomic nervous system. We suggest that this criterion could be applied to other animals exposed to natural or imposed trauma, thus improving protocols involving animal handling, including veterinarian procedures.