177 EFFECT OF ISCHEMIA ON MECHANICAL FUNCTION IN THE NEONATAL RABBIT HEART

Abstract

This study was designed to evaluate the effect of ischemia and reperfusion on myocardial mechanical function in the neonate. Newborn (NB,n=14) and adult (A,n=14) rabbit hearts were studied utilizing the isolated arterially perfused septal preparation that was maintained at 27°C or 33°C and paced at 90 beats/minute. The muscle was perfused initially with an oxygenated Krebs-Henseleit solution. After stabilization of mechanical function, 60 minutes of global ischemia was induced and then the muscle was reperfused with oxygenated solution. The muscle was kept in a humidified, warm, oxygen-poor atmosphere. Developed tension (DT), maximal rate of tension development (+dT/dt) and resting tension (RT) were recorded continuously. The changes in DT and +dT/dt were similar. During ischemia, +dT/dt declined hyperbolically at the same rate in all groups, and the values after 60 minutes of ischemia were not significantly different from zero. During ischemia, the RT increased significantly in both groups and the increase in the A was significantly (P < 0.001) greater than in the NB. After 60 minutes of reperfusion, the recovery of +dT/dt (97 ± 5% of control at 27°C; 48 ± 12% at 33°C) in the NB was significantly (P<0.001) greater than in the A (58 ± 6% at 27°C; 16 ± 6% at 33°C). After reperfusion, the RT returned to control in the NB, but not in A. These data indicate that the NB myocardium is more resistant to ischemia than the A myocardium.