Rate of decrease of myocardial O2 consumption due to cardiac arrest in anesthetized goats.

The rate of change of myocardial O2 consumption, MVO2, has been measured during the transition from beating to cardiac arrest. Cardiac arrest was achieved by destruction of the bundle of His by injection of formalin and induced by 25 s interruption of pacing. The left main coronary artery was perfused under constant pressure and the great cardiac vein was drained under controlled pressure. The arterio-venous O2 content difference, O2, and coronary arterial and venous flows, CAF resp CVF, were continuously measured. The MVO2 transient was calculated using the following equation based on a 3 compartment model: MVO2 = CAF . O2 - (Vc + Vv) . d[O2]v/dt - (Vc . Vv/CVF) . d2[O2]v/dt2 where Vc and Vv are the capillary and the venous blood volume as function of time and [O2]v is the venous oxygen content. A 7th order polynoma was fit to the [O2]v-data and the fitted equation was differentiated analytically to obtain the first and second order derivatives. The MVO2 decreased from 94 +/- 5 microliters O2/s/100 g (mean +/- SE) before cardiac arrest to 15.4 +/- 5 microliters O2/s/100 g after 15 s of cardiac arrest. The change in MVO2 (50% in 3.8 +/- 0.3 s) preceded the change in venous oxygen content (50% in 12.7 +/- 0.5 s) and the change in coronary resistance (50% in 14.9 +/- 0.9). These results are in accordance with the hypothesis that interstitial O2 concentration is a major determinant of coronary resistance.