The role of coronary flow and pressure as determinants of myocardial oxygen consumption in the presence or absence of vasomotor tone

When coronary flow was kept constant and coronary pressure increased by angiotensin or decreased by dipyridamole, myocardial oxygen consumption (MVO2) remained unchanged. When vasomotor tone was abolished by dipyridamole or was intact, changing coronary flow resulted in a change in MVO2 in the same direction as flow; this change in MVO2 was in part the result of a significant alteration in coronary oxygen extraction. These results suggest that coronary flow, but not coronary pressure is an important determinant of MVO2 both in the presence or absence of vasomotor tone. </jats:p

The relationship between oxygen extraction and extravascular mean transit time in the canine heart

A significant relationship was observed between myocardial oxygen extraction and the extravascular mean time transit time. This relationship implies that oxygen extraction by the myocardium is a time-dependent process, and emphasizes the critical link between blood flow and myocardial oxygen consumption. </jats:p

Effects of perhexiline maleate on coronary flow distribution in the ischemic canine myocardium.

Intravenous perhexiline maleate in a canine preparation with fixed coronary flow increases coronary diastolic pressure. It also redistributes coronary flow so as to preserve endocardial flow. Myocardial oxygen consumption was reduced and lactate uptake enhanced by the drug. It had no effect upon the threshold for ischemic-induced left ventricular failure.</jats:p

Effects of respiratory alkalosis on human skeletal muscle metabolism at the onset of submaximal exercise

The purpose of this study was to examine the effects of respiratory alkalosis on human skeletal muscle metabolism at rest and during submaximal exercise. Subjects exercised on two occasions for 15 min at 55 % of their maximal oxygen uptake while either hyperventilating (R-Alk) or breathing normally (Con). Muscle biopsies were taken at rest and after 1 and 15 min of exercise. At rest, no effects on muscle metabolism were observed in response to R-Alk. In the first minute of exercise, there was a delayed activation of pyruvate dehydrogenase (PDH) in R-Alk compared with Con, resulting in a reduced rate of pyruvate oxidation. Also, glycogenolysis was higher in R-Alk compared with Con, which was attributed to a higher availability of the monoprotonated form of inorganic phosphate (Pi), resulting in an elevated rate of pyruvate production. The mismatch between pyruvate production and its oxidation resulted in net lactate accumulation. These effects were not seen after 15 min of exercise, with no further differences in muscle metabolism between conditions. The results from the present study suggest that respiratory alkalosis may play an important role in lactate accumulation during the transition from rest to exercise in acute hypoxic conditions, but that other factors mediate lactate accumulation during steady-state exercise