Determinants of maximal expiratory flow and density dependence in normal humans

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Abstract
There is a large variability in maximal expiratory flow (.ovrhdot.V) and density dependence (DD) in normal humans. Lung mechanics and flow-volume curves were obtained in 40 normal males while they breathed air or He-O2 (80-20%). Static lung recoil (Pst) at 50% vital capacity, total lung capacity and pulmonary resistance each correlated (P < 0.05) with airflow at 50% vital capacity. The relationship of .ovrhdot.V and Pst was described by Pst = 1/2 .rho. .ovrhdot.V2/A2 + R.ovrhdot.V, where .rho. is gas density, A is the critical area at the flow-limiting site and R is peripheral resistance. At constant Pst and R, this simplified equation predicts an inverse relation between DD and airflow, which was found at recoil pressures of 8 and 7 cm H2O (P < 0.05). If peripheral losses are small, subjects with smaller flow-limiting airways would have lower airflows but higher DD than subjects with larger airways. Apparently, lungs display dysanaptic growth and the central airways play a significant role in determining .ovrhdot.V and DD in normal humans.

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