Effect of a deep breath on gas mixing and diffusion in the lung

Abstract

We examined the effect of a previous deep breath on both inert gas mixing and the single breath diffusing capacity (D L CO SB) during submaximal single breath maneuvers in normal subjects. Single breath washouts were performed either immediately after a deep breath or after breathing tidally for 10 min. Maneuvers consisted of inhaling test gas from functional residual capacity of 50% inspiratory capacity and, after either 0 or 6 s of breath holding, exhaling slowly back to residual volume. We measured the Fowler dead space, the Phase III slope of the alveolar plateau of the He washout (ΔHe/L), the amplitude of the cardiogenic oscillations (Oc), closing capacity, mixing efficiency (Emix) and D L CO SB using the three equation method. For maneuvers immediately after a deep breath we found that ΔHe/L was steeper and the Oc were larger for washouts with 6 s but not 0 s of breath holding, while Emix was significantly lower and D L CO SB significantly higher for both the 0 s and the 6 s breath holding maneuvers. We conclude that a deep breath increases D L CO SB but simultaneously also increases convective-dependent inhomogeneity in the lung.