FARMER, C.G.: Myocardial Oxygenation and the Evolution of the Vertebrate Cardiopulmonary System

For many vertebrates, there are no other normal stresses to which the cardiopulmonary system is exposed that come close to the extreme stresses of heavy exercise. Hence it is expected that the demands of exercise have exerted strong selection pressures on the evolution of vertebrate cardiopulmonary system. I have been examining the importance of air-breathing during exercise in several fishes as a potential mechanism of myocardial oxygenation. Similarly, I have been investigating the importance of the intracardiac shunt of reptiles in myocardial oxygenation during exercise. This research has employed a variety of techniques (ECG, blood gas, blood pressure, and blood flow measurements). Although preliminary, my findings suggest that myocardial oxygenation is not adequate in some air-breathing fishes when exercising in well oxygenated water but denied access to air. Furthermore, when the potential benefits to myocardial oxygenation of the intracardiac shunt are removed by exercising turtles under hypoxic conditions, cardiac function is perturbed. Hence, the necessity of an adequate supply of oxygen to the heart during activity may have influenced the evolution of the vertebrate lung and the intracardiac shunt.