Lung volume and lung mechanics in infancy lateral or supine posture?

In 23 infants and young children aged from 3 wk to 2 1/2 years, lung volume, by plethysmography, dynamic lung compliance and total pulmonary resistance with air-filled balloons and pneumotachography, have been measured in the supine and right lateral postures in order to observe any possible systematic differences in either body position. Fourteen subjects were studied under light sedation, the remaining nine under general anaesthesia before elective surgery. In the sedated group, no significant differences were found between the two positions for lung mechanics. In the anaesthetised group the only measurement that varied with position was dynamic lung compliance, being lower in the supine posture (P less than 0.05). In one of the sedated infants with predominantly left sided lung disease, large position dependent changes in lung volume and lung mechanics were observed suggesting that care should be taken in interpreting lung function tests in infants with unilateral lung disease. In the anaesthetised subjects, the finding of reduced ratios of esophageal to mouth pressure change during brief airway occlusions, suggests that under these conditions pleural pressure changes were unequally distributed.