Previous studies have reported finding supply-dependent O2 uptake (V̇O2) 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 (Q̇O2 = cardiac output · arterial O2 content). The aim of the present study was to determine whether patients with aortic stenosis also exhibit increases in V̇O2 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 (V̇O2 [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, V̇O2 (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 Q̇ and corresponding Q̇O2 (Fick) both increased significantly, suggesting the presence of O2 supply-dependent V̇O2. However, neither Q̇ (thermodilution) nor Q̇O2 (thermodilution) changed significantly, and regression of V̇O2 (measured) against Q̇O2 (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. The inability to detect this relationship when V̇O2 (measured) was plotted against Q̇O2 (thermodilution) can be explained by the large measurement error in thermodilution Q̇ determinations, relative to the change in output produced by valvuloplasty.
|Original language||English (US)|
|Number of pages||9|
|Journal||American journal of respiratory and critical care medicine|
|State||Published - May 1994|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Critical Care and Intensive Care Medicine