Submitted on June 9, 2004
Accepted on August 3, 2004
EFFECT OF SMALL FLOW REVERSALS ON AEROSOL MIXING IN THE ALVEOLAR REGION OF THE HUMAN LUNG
Chantal Darquenne1* and G. Kim Prisk1
1 Department of Medicine, University of California, San Diego, La Jolla, CA, USA
* To whom correspondence should be addressed. E-mail: cdarquenne{at}ucsd.edu.
It has been suggested that irreversibility of alveolar flow combined with a stretched and folded pattern of streamlines can lead to a sudden increase in mixing in the lung. To determine whether this phenomenon is operative in the human lung in vivo, we performed a series of bolus studies with a protocol designed to induce complex folding patterns. Boli of 0.5 and 1 µm-diameter particles were inhaled at penetration volumes (Vp) of 300 and 1200ml in eight subjects during short periods of microgravity aboard the NASA Microgravity Research Aircraft. Inspiration was from residual volume (RV) to one liter above 1G functional residual capacity. This was followed by a 10-sec breath hold, during which up to seven 100ml flow reversals (FR) were imposed at Vp = 300 ml and up to four 500ml FR at Vp = 1200ml, and by an expiration to RV. Bolus dispersion and deposition were calculated from aerosol concentration and flow rate continuously monitored at the mouth. There was no significant increase in dispersion and deposition with increasing FR except for dispersion between zero and 7 FR at Vp=300ml with 0.5 µm-diameter particles, and this increase was small. This suggested that either the phenomenon of stretch and fold did not occur within the number of FR we performed, or that it had already occurred during the one breathing cycle included in the basic maneuver. We speculate that the phenomenon occurred during the basic maneuver which is consistent with the high degree of dispersion and deposition observed previously in microgravity.
