The heart of vertebrates is autonomous and so it generates the stimulus for the own heart beat. Despite that, such a heart is not independent and operates under tonic and concomitant modulation of both sympathetic and parasympathetic divisions of the autonomic nervous system. That modulation provides adjustments of the cardiac work in order to match cardiac output and metabolic demand; and also, provides cyclical adjustments on heart rate (fH) according to blood pressure variations, body temperature change, ventilation cycles, and other parameters. Hence, all vertebrates would have mechanisms to provide cardiorespiratory interactions enabling coordination of fH variations according to ventilation. Heart rate variability (HRV), similar to respiratory sinus arrhythmia (RSA), has been demonstrated on rattlesnakes. That HRV would be modulated only by the parasympathetic influences on the heart since that was abolished by atropine injection. If so, that would be reduced or absent when fH is high due spontaneous activity, handling or during recovering after instrumentation. If such assertion was experimentally validated we would have an interesting too for monitoring SNA recover and possibly, stress. Therefore, the aim of this project is to describe normal HRV in rattlesnakes and test if it is possible to use it for monitoring autonomic recovery after anaesthesia and/or surgical procedures, handling, or for detecting the factors important for stress conditions.
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