Body position and ventilation-perfusion relationships in unilateral pulmonary disease.

The effect of positional change (right vs left lateral decubitus) on the distribution of ventilation and perfusion ratios was determined in four patients with respiratory failure and chest roentgenographic findings of unilateral pulmonary disease. In these patients with a unilateral interstitial pattern, improvement in oxygenation which occurred when the "good" side was dependent (down) was associated with changes in the patterns of ventilation-perfusion distribution; two patients showed a predominant decrease in right-to-left intrapulmonary shunt, and two showed an improvement in ventilation-perfusion equality. Therefore, when unilateral interstitial pulmonary disease was present, positional change resulted in changes in right-to-left intrapulmonary shunt or low ventilation-perfusion ratios or both. Variability between patients can be explained by the nonhomogeneity of pulmonary disease in patients with respiratory failure.