Ventilation-Perfusion Variations Within the Lung

Abstract

Lobarspirometry was performed in nine normal men and four tuberculous patients in the supine and the erect position. With this technique, the distribution of O₂ uptake and ventilation to the upper lobe, the lower lobe and the whole of the opposite lung may be measured simultaneously. In the normal subject, the distribution of ventilation between lobes and lungs was the same whether he was erect or supine. When supine, an individual may show lobar ventilation-perfusion-ratio (Va/Q) variations, but with no significant preference for one lobe. In the erect position, the upper lobe O₂ uptake fraction decreased while that in the lower lobe increased. Erect man consistently has higher Va/Q in the upper lobe than in the lower lobe as a result of the redistribution of pulmonary blood flow favoring the lower lobe. These lobar Va/Q differences described underestimate the magnitude of the over-all variations within the lungs. As the result of these considerations, the measurement of any physiological parameter that involves the assumption of equality between arterial Pco₂ and alveolar Pco₂ will be in error. Submitted on April 23, 1957