THE ROLE OF THE PERICARDIUM AND THE EFFECTS OF ADRENALINE AND CHANGESIN OXYGEN-TENSION ON THE PERFORMANCE OF AN IN-SITU PERFUSED CROCODILEHEART

An in situ perfused crocodile (Crocodylus porosus) heart preparation w as used to examine the mechanical responses of the heart to increases in adrenaline concentration, to a decrease in oxygen tension and to op ening of the pericardium. Starling and power curves were constructed b efore and after these experimental manipulations, Increasing adrenalin e concentration in the perfusate from 5 nmoll(-1) to 0.5 mu moll(-1) p roduced a significant increase in heart rate and a decrease in stroke volume, leaving cardiac output unchanged, With maximal adrenergic stim ulation, the left ventricle was able to generate greater power outputs at high right aortic output pressures; however, the right ventricle s howed a decrease in performance with increasing output pressure. Decre asing the Po-2 of the perfusate to 10 kPa resulted in a significant br adycardia. Both the flow and pressure-generating capabilities of the p erfused heart preparation were reduced, although the heart was able to maintain low work levels at this Po-2. Opening the pericardium permit ted greater movement/expansion of the cardiac chambers and resulted in an increase in heart rate, Higher flows were generated at low filling pressures during the input pressure challenge as a result of an incre ase in the sensitivity of the Starling response.