Cardiorespiratory responses of snakes to experimental hemorrhage

Abstract

Cardiovascular, respiratory and ventilatory responses were measured simultaneously in yellow rat snakes (Elaphe obsoleta quadrivittata) subjected to acutely graded experimental hemorrhage. Unanesthetized snakes maintained arterial pressure and normal or greater levels of oxygen uptake during cumulative losses of whole blood averaging 90.3%. Oxygen delivery during hemorrhage was usually associated with high levels of arterial saturation, increased ventilation, increased arterialPO2, and stability of arterial pH and blood pressure. Arterial pressure eventually declined with increasing blood loss, but patterns were variable and some snakes maintained pressure at blood volume deficits exceeding 100% of the estimated prehemorrhage value. At severe blood losses (typically exceeding 50–80%) arterial pressure fell precipitously and at levels below 15–10 Torr was paralleled by arterial pH. Initially, blood levels of lactic acid were as low as a few mg% but increased dramatically (1–2 orders of magnitude) after severe blood loss when cardiorespiratory performance diminished. Snakes survived the experiments when allowed to drink water, in spite of significant levels of anemia. The observed relationships reflect well developed abilities of these reptiles to control hemodynamic and respiratory functions.