Dispersion of aerosol boluses in the human lung: dependence on lung
volume, bolus volume, and gender.
Brown, James S., Timothy R. Gerrity, William D. Bennett, Chong S. Kim,
and Dennis E. House.
Center for Environmental Medicine and Lung Biology, University of
North Carolina at Chapel Hill; Clinical Research Branch, Human
Studies Division, Health Effects Research Laboratory, US
Environmental Protection Agency
APStracts 2:0308A, 1995.
The dispersion of aerosol boluses in the human lungs has been studied
in health and disease usually as a means of investigating convective
mixing. However, there are only limited data on the roles played in
dispersion by critical factors such as the volume of inhaled boluses,
lung inflation, and gender. To examine these factors we measured the
difference in volume variance between exhaled and inhaled boluses
([sigma]V2) of a 0.5 [mu]m aerosol in 11 healthy male and 12 healthy
female subjects as a function of tidal volume (Vt=1000 and 1500 ml in
females, and 1000 and 2000 ml in males), bolus penetration volume (i
at 250 ml increments over each Vt), and bolus volume (target VBol=75,
150, and 300 ml). Analysis of variance showed marginally significant
gender effects (p=0.073) on [sigma]V2, with [sigma]V2 greater in
males than in females. There was also a significant effect of VBol on
[sigma]V2 (p<0.001). A i dependent mean volume shift between
inhaled and exhaled boluses (_) was observed at all i except 500 ml.
The observation of gender and VBol effects and the existence of a
non-zero _ suggest convective mixing mechanisms other than
longitudinal dispersion alone occur in the healthy lung. The lack of
Vt dependence suggests a minimal role of lung inflation above FRC on
dispersion. The dependence of [sigma]V2 on i2 up to 1750 ml and
minimal VBol effects demonstrates that convective mixing processes
continue far into the gas exchange regions of the lung and support a
significant role for axial streaming.
Received 31 January 1995; accepted in final form 29 June 1995.
APS Manuscript Number A96-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.