Mechanical performance of an in situ perfused heart from the turtle Chrysemys scripta during normoxia and anoxia at 5°C and 15°C

We developed an in situ perfused turtle (Chrysemys scripta) heart preparation to study its intrinsic mechanical properties at 5 degrees C and 15 degrees C using normoxic and anoxic perfusion conditions. The in situ preparation proved durable and stable. At 15 degrees C and a spontaneous heart rate of 23.4 beats min(-1), maximum stroke volume was 2.54 mlkg(-1) body mass, maximum cardiac output was 62.5 mlmin(-1) kg(-1) and maximum cardiac myocardial power output was 1.50 mW g(-1) ventricular mass. There was good agreement between these values and those previously obtained in vivo. Furthermore, since the maximum stroke volume observed here was numerically equivalent to that observed in ventilating C. scripta in vivo, it seems likely that C. scripta has little scope to increase stroke volume to a level much beyond that observed in the resting animal through intrinsic mechanisms alone. The ability of the perfused turtle heart to maintain stroke volume when diastolic afterload was raised (homeometric regulation) was relatively poor