Relationship of air trapping to increased lung recoil pressure induced by chest cage restriction

Chest cage restriction was produced in 13 normal male subjects. We could not detect trapped air during restriction by comparing lung volumes determined by nitrogen washout with those determined by plethysmography. However, 3 subjects did have definite evidence of trapping because they released small amounts of air (mean, 61 ml) when the restriction was removed. Two subjects had suggestive evidence of trapping. Yet there was no correlation between trapping and the degree of increase in static lung recoil associated with restriction. Seven subjects had chest restriction produced while they were breathing air and again while they were breathing 100 per cent oxygen, in an attempt to reveal the presence of airway closure. In only one subject was oxygen breathing clearly associated with a greater then expected increase in lung recoil after restriction; suggestive changes were seen in 2 other subjects. However, there was no definite correlation between unusual increases in lung recoil induced by restriction while breathing oxygen and the presence of air trapping. We conclude that trapping, hence airway closure, is not required for the increase in static lung recoil that occurs with chest cage restriction.