ABSTRACT
Many reptiles, particularly diving species, display characteristic cardiovascular changes associated with lung ventilation (cardiorespiratory synchrony). Previous studies on freshwater turtl.es show that heart rate and pulmonary blood flow rate (Q̇pul) increase two-to fourfold during ventilation compared with breath-holding, and some studies. report concomitant decreases in systemic blood flow rate (Q̇sys). The primary aim of this study was to provide a detailed description of cardiorespiratory synchrony in free-diving and fully recovered turtles (Trachemys scrip.ta). During breath-holds lasting longer than 5 min, Q̇pul 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. Q̇sys 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 Q̇pul nor Q̇sys was affected by the n. umber of. breaths in the ventilatory periods. Changes in Q̇pul and Q̇sys were accomplished entirely through a significant increase in heart rate during ventilation, while total stroke volume (systemic + pulmonary) remain.ed constant. Irre.spective of the ventilatory state, Q̇sys exceeded Q̇pul by 20–30 ml min-1 kg-1. Nev.ertheless, because Q̇pul in.creas.ed relatively more than Q̇sys during ventilation, Q̇pul/Q̇sys increased from 0.29 during apnoea to 0.80 during lung 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.
