Augmented diffusion in the airways can support pulmonary gas exchange

Abstract

Bohn et al. (J Appl. Physiol.: Respirat. Environ. Exercise Physiol, 48: 710-716, 1980) reported that paralyzed beagle dogs maintained normal gas exchange for 6 h or more when small tidal volumes at high breathing rates were maintained at the airway opening (15 ml tidal volume at 15 breaths/s). These tidal volumes were 25% of dead space and thereby were too small to permit convective gas exchange with pulmonary air spaces. I have used a semiempirical analysis to show that augmented diffusion in the central airways, akin to Taylor's turbulent dispersion (Proc. R. Soc. Ser. A 223: 446-468, 1954) combined with molecular diffusion in the periphery of the lung, can account for most if not all of the observed gas transport during small tidal volume, high-frequency ventilation. Ventilation efficiency (alveolar ventilation/minute ventilation) is approximately 2-5% and is insensitive to the combination of frequency and tidal volume giving rise to the minute ventilation.