Lung Mechanics and Physiologic Shunt During Spontaneous Breathing in Normal Subjects

Abstract

The mechanics of breathing, lung compliance, and AaDo2 during air and oxygen breathing were studied in 16 normal subjects. In 5 subjects, the effect of intravenously administered morphine sulfate on the same parameters was also investigated. Compliance and AaDo2 (shunt) varied little in the individual subjects during spontaneous breathing. Spontaneous sighing was not followed by changes in lung mechanics or compliance; similarly, almost complete absence of sighing for periods from 60-90 min. following administration of morphine sulfate was not associated with changes in lung mechanics or shunt. The transient increase in compliance that followed maximal inspiration is thought to be the result of changes in surface tension properties of the lungs and not to decreases in the number of perfused but unventilated (atelectatic) alveoli. We propose that lung mechanics and ventilation-perfusion relations during spontaneous breathing are regulated on a breath to breath basis and that sighing does not play a significant part in this regulation.