The effect of nitrate on the oxygen availability during exercise in effort angina pectoris.

Respiratory responses during exercise were observed to determine whether improvement of oxygen availability in working skeletal muscle is attributable to increased aerobic capacity after administration of nitrate in patients with effort angina. After isosorbide dinitrate (ISDN) administration, the aerobic capacity increased 3.3 ml/min/Kg (20%) as compared with the control test (p less than 0.001), but the anaerobic threshold (AT), a good indicator of oxygen availability, was unchanged, and the respiratory quotient at the peak of exercise was elevated. These findings suggest that oxygen availability in skeletal muscle was not altered after ISDN, and increased exercise load accompanied increased anaerobic glycolysis. It was concluded that the nitrate-induced increase in aerobic capacity was not dependent upon the change in oxygen availability in skeletal muscle but rather upon the elevated anginal threshold.