Mechanical mixture due to pulmonary flow, in contrast to mixing by molecular diffusion within the respiratory spaces, has been studied directly using aerosol inhalation. The technique uses particles, about ½ μ in diameter, which are fairly stable in the respiratory tract, and measures the concentration of aerosol during expiration with a continuous and rapid detector of scattered light and, simultaneously, the expiratory volume flow. The flow component of pulmonary ventilation is described in terms of the fractions of tidal air (Vx) and functional residual air (Vr) which participate in the ventilatory exchange of aerosol. Aerosol clearance experiments on three apparently healthy subjects show these two newly defined mixing volumes (Vx and Vr) to be much smaller than their analogous volumes measured by gas clearance: less than one-third for the fraction of tidal air and less than one-tenth for the fraction of functional residual air. These results demonstrate quantitatively the major role of molecular diffusion in ventilation. This approach provides a new method for the measurement of the mechanical component of intrapulmonary mixing. Submitted on November 3, 1958
The volume of the dead space in breathing and the mixing of gases in the lungs of man
