PT Schumacker, JS Soble and T Feldman
Section of Cardiology, University of Chicago, IL 60637.

Previous studies have reported finding supply-dependent O2 uptake (VO2) in patients with the adult respiratory distress syndrome, sepsis, chronic obstructive lung disease, sleep apnea, and other cardiopulmonary diseases. A common element among these diverse conditions is the potential to reduce systemic O2 delivery (QO2 = cardiac output.arterial O2 content). The aim of the present study was to determine whether patients with aortic stenosis also exhibit increases in VO2 when O2 delivery is increased after valvuloplasty. Fifty-six patients were studied while breathing room air in the supine position. Expired gases for determination of O2 uptake (VO2 [measured]), cardiac output (thermodilution), arterial and mixed venous blood gases, and hemodynamic measurements were obtained immediately before and within 30 min after aortic valvuloplasty. After valvuloplasty, VO2 (measured) increased from 3.03 +/- 0.51 to 3.24 +/- 0.62 ml/min/kg (p < 0.0001). However, O2 extraction ratio did not change from baseline levels (32.16 +/- 10.1%) after valvuloplasty (32.21 +/- 8.25%, p = not significant). These results could have occurred only if O2 delivery had also increased. Accordingly, Fick- derived Q and corresponding QO2 (Fick) both increased significantly, suggesting the presence of O2 supply-dependent VO2. However, neither Q (thermodilution) nor QO2 (thermodilution) changed significantly, and regression of VO2 (measured) against QO2 (thermodilution) failed to detect a relationship. We conclude that patients with aortic stenosis exhibit increases in O2 delivery and uptake after valvuloplasty, although this may or may not reflect covert tissue hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

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