Inotropic and intracellular acid-base changes during metabolic acidosis

Experiments in isolated, Ringer-perfused isovolumic rabbit hearts showed that metabolic acidosis resulted in a decrease in peak left ventricular pressure and dP/dt. Concomitantly, the decrease in extracellular pH from 7.28 plus or minus 0.02 to 6.82 plus or minus 0.02 at constant PaCO2 was associated with a negative av HCO3- difference that lasted throughout the duration of acidosis. This negative av HCO3- difference indicated that either HCO3- moved into the intravascular space or H+ moved in the opposite direction during acidosis. During perfusion with normal pH solution av HCO3- was not significantly different from zero. Washout of the extracellular space with the acid solution can account for only 32 percent of the total amount of HCO3-recovered in the venous perfusate during the 30 min of acidosis. The remaining 68 percent (10.7 plus or minus 3.1 mmol times kg-1 of cardiac tissue) must then have originated in the cellular fluid. When intracellular fluid volume is taken into account, it can be calculated that 21.3 plus or minus 6.1 mmol of HCO3- moved into the vascular space per liter of intracellular water. The magnitude of this HCO3- flux suggests that significant myocardial cellular acid-base changes are associated with metabolic acidosis.