Physiological Significance of Maximal Oxygen Intake in "Pure" Mitral Stenosis

Abstract

Acute circulatory and respiratory adjustments to mild through maximal upright exercise were studied in seven patients with "pure" mitral stenosis. Maximal oxygen uptake was determined objectively by demonstrating a plateau of oxygen uptake with increasing workloads. Time to reach a plateau of oxygen uptake was normal (2 to 3 minutes) at all workloads. At any given oxygen uptake, cardiac output and hepatic clearance of indocyanine green (ICG) were abnormally low while total arteriovenous (A-V) oxygen difference, heart rate, blood lactate, and ventilation were abnormally high. However, with respect to relative oxygen uptake (per cent of maximal oxygen uptake), the reduction in cardiac output was exaggerated, but A-V oxygen difference, heart rate, blood lactate, and hepatic clearance of ICG were essentially normal. RQ and VE/VOO2were quantitatively abnormal even with respect to relative oxygen uptake, but the pattern of changes from mild to maximal exercise was normal. Low maximal oxygen uptake defined the reduction in stroke volume while other circulatory responses were normal with respect to relative oxygen uptake.