Cardiorespiratory synchrony in turtles

Abstract

Many reptiles, particularly diving species, display characteristic cardiovascular changes associated with lung ventilation (cardiorespiratory synchrony). Previous studies on freshwater turtles show that heart rate and pulmonary blood flow rate (Q̇(pul)) increase two- to fourfold during ventilation compared with breath-holding, and some studies report concomitant decreases in systemic blood flow rate (Q̇(sys)). The primary aim of this study was to provide a detailed description of cardiorespiratory synchrony in free-diving and fully recovered turtles (Trachemys scripta). During breath-holds lasting longer than 5 min, Q̇(pul) averaged 15 ml min-1 kg-1 and increased more than threefold to a maximum value of 50 ml min-1 kg-1 during ventilation. Q̇(sys) also increased during ventilation compared with during breath-holds lasting longer than 5 min (from 44 to 73 ml min-1 kg-1 during ventilation). Neither Q̇(pul) nor Q̇(sys) was affected by the number of breaths in the ventilatory periods. Changes in Q̇(pul) and Q̇(sys) were accomplished entirely through a significant increase in heart rate during ventilation, while total stroke volume (systemic + pulmonary) remained constant. Irrespective of the ventilatory state, Q̇(sys) exceeded Q̇(pul) by 20-30 ml min-1 kg-1. Nevertheless, because Q̇(pul) increased relatively more than Q̇(sys) during ventilation, Q̇(pul)/Q̇(sys) increased from 0.29 during apnoea to 0.80 during long ventilation. This study confirms cardiorespiratory synchrony in the turtle Trachemys scripta but, in contrast to earlier studies, a net right-to-left cardiac shunt prevailed regardless of ventilatory state.