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

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Abstract
Respiratory responses during exercise were observed to determine whether improvement of O2 availability in working skeletal muscle is attributable to increasd 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 < 0.001), but the anaerobic threshold (AT), a good indicator of O2 availability, was unchanged and the respiratory quotient at the peak of exercise was elevated. O2 availability in skeletal muscle was not altered after ISDN. Increased exercise load accompanied increased anaerobic glycolysis. The nitrate-induced increase in aerobic capacity was not dependent upon the change in O2 availability in skeletal muscle but rather upon the elevated anginal threshold.