Transients in myocardial O2 consumption after abrupt changes in perfusion pressure in goats.

The dynamic oxygen content differences were analyzed in the present study. The left main coronary artery of the anesthetized, open-chest goat was perfused at constant pressure (Pp). Pp(t), arterial flow [Qa(t)], and the arteriovenous oxygen content difference [a-vO2(t)] were averaged per beat. The a-vO2 signal was corrected for mixing processes in the capillaries and transport time from capillaries to the venous measuring site [a-vO2(t)]. A change in Pp of 20 mmHg induced a temporary change in MVO2, referred to as the dynamic Gregg effect. With an increase in Pp, the maximal change of myocardial oxygen consumption [MVO2(t) = Qa(t).a-vO2(t)] was 15.0 +/- 3.6% (means +/- SE) during control and 31.3 +/- 2.3% with glibenclamide. With a decrease in Pp these changes were 16.3 +/- 2.9 and 21.0 +/- 1.1%. During control, the half-time for the rate of return of the MVO2 response was 4.2 +/- 0.8 s for an increase and 4.0 +/- 1.0 s for a decrease in Pp. With glibenclamide these values were 16.9 +/- 2.2 and 22.6 +/- 2.0 s. This study confirms that during steady state the Pp-induced MVO2 (steady-state Gregg effect) is diminished by autoregulation. However, it is concluded that during transients following abrupt changes in Pp, large changes in MVO2 occur depending on the rate of regulation (dynamic Gregg effect).