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Am. J. Respir. Crit. Care Med., Volume 161, Number 6, June 2000, 1957-1962

Closing Volume Influences the Postural Effect on Oxygenation in Unilateral Lung Disease

KANG-HYEON CHOE, YONG-TAE KIM, TAE-SUN SHIM, CHAE-MAN LIM, SANG-DO LEE, YOUNSUCK KOH, WOO-SUNG KIM, DONG-SOON KIM, JIN-SOOK RYU, and WON-DONG KIM

Pulmonary and Critical Care Division, Department of Internal Medicine and Department of Nuclear Medicine, University of Ulsan College of Medicine, Seoul, Korea

In normal adults, both blood flow and ventilation are distributed preferentially to the dependent lung zones. In adults with unilateral lung disease, arterial oxygenation improves when they are positioned with their good lung down because of improved matching of ventilation and perfusion. When the closing volume is increased, dependent airways are closed during tidal breathing, so that reduced ventilation-perfusion ratio and hypoxia develops and ventilation is preferentially distributed to the upper lung zones. We undertook an observational study on the effects of lateral recumbency on arterial oxygenation in adult patients with unilateral lung disease and tested the hypothesis that oxygenation in lateral recumbency might be influenced by an increase in closing volume. Arterial blood gases were analyzed in the supine, right and left lateral decubitus positions and the AaPO2 was calculated in 44 randomly selected patients 49.9 ± 18.7 yr of age with unilateral pneumonia (23 cases) or pulmonary tuberculosis (21 cases). In 26 patients, individual PaO2 with the normal lung in the dependent position was higher than that with the diseased lung; the opposite was true for 18 patients. The difference in PaO2 and AaPO2 between the two positions was statistically significant in both groups. In 16 patients (10 men and six women 49.2 ± 18.2 yr of age), we measured closing volume and determined the fractional ventilation to each lung by 133Xe lung scan in the three positions. In these 16 patients, the difference in PaO2 between the normal and the diseased lung in the dependent position was related significantly to the difference in the fractional ventilation going to the normal lung between the dependent and the supine position (r = 0.642, p = 0.007). The latter was related significantly to the % predicted closing volume (CV/VC) (r = -0.597, p = 0.015). This study has shown that closing volume, as well as posture, might be involved in determining oxygenation in lateral recumbency in patients with unilateral lung disease.




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