Convective mixing in human respiratory tract: estimates with aerosol boli

Convective gas mixing in the respiratory tract of 17 healthy male subjects was studied by an aerosol bolus technique. The monodisperse 1 micron di(2-ethylhexyl)sebacate droplets we used behaved as a nondiffusing gas. As the bolus was inspired to different depths and then expired, we measured the extent to which the bolus spread. We found that the deeper the bolus penetrated into the lungs, the more it became dispersed. The half-width of the expired bolus was a linear function of the volume to which the bolus penetrated at volumetric penetrations of 100-800 cm3. This suggests that convective mixing is not confined to central airways but can also occur in the lung periphery.