Effect of high negative inspiratory pressure on single breath CO diffusing capacity

Abstract

We measured the single breath diffusing capacity for carbon monoxide (DlcoSB) using a three-equation method to describe CO uptake in 10 normal seated subjects who eiter voluntarily inhaled slowly (0.5 L/sec) to total capacity (TLC), or inhaled slowly to TLC maximal effort through a high inspiratory which created high negative inspirator pressure. Subjects then performed in duplicate both with and without high negative inspiratory pressure while subjects were seated upright at reast and during steaty-state bicycle exercise. We found high negative inspiratory pressure increased DLcoSB by 10.5% ± 4.9% (mean ± SD) at rest P < 0.0001). In 7 sujects low level exercise alone increased DLcoSB by a similar 12.1 ± 7.3%; P = 0.0005). In six of the subjects there was a significanlt correlation between the increase in DLcoSB during high negative inspiratory pressure at rest and the increase in DLcoSB during steady-state exercise ( r = 0.89; P < 0.01). During steady-state exercise, high negative inspiratory pressure further increased DLcoSB 6.4 ± 6.3% compared to exercise alone ( P = 0.05). We conclude that the increase in DLcoSB with high negative inspiratory pressure at rest is a simple reproducible method of assessing recruitment of the pulmonary capillary bed in man.