Effect of gravity on aerosol dispersion and deposition in the human lung after periods of breath holding

Abstract

Darquenne, Chantal, Manuel Paiva, and G. Kim Prisk. Effect of gravity on aerosol dispersion and deposition in the human lung after periods of breath holding. J Appl Physiol 89: 1787-1792, 2000.-To determine the extent of the role that gravity plays in dispersion and deposition during breath holds, we performed aerosol bolus inhalations of 1-m-diameter particles followed by breath holds of various lengths on four subjects on the ground (1G) and during short periods of microgravity (G). Boluses of ϳ70 ml were inhaled to penetration volumes (V p ) of 150 and 500 ml, at a constant flow rate of ϳ0.45 l/s. Aerosol concentration and flow rate were continuously measured at the mouth. Aerosol deposition and dispersion were calculated from these data. Deposition was independent of breath-hold time at both V p in G, whereas, in 1G, deposition increased with increasing breath hold time. At V p ϭ 150 ml, dispersion was similar at both gravity levels and increased with breath hold time. At V p ϭ 500 ml, dispersion in 1G was always significantly higher than in G. The data provide direct evidence that gravitational sedimentation is the main mechanism of deposition and dispersion during breath holds. The data also suggest that cardiogenic mixing and turbulent mixing contribute to deposition and dispersion at shallow V p . aerosol bolus; cardiogenic mixing AEROSOL BOLUS INHALATIONS have largely been used to study deposition and mixing processes in specific volumetric regions of the lung (3,4,13,19). Particles are transported in the respiratory tract by the carrier gas, and they deviate from the streamlines mainly by diffusion, sedimentation, and inertia. Of these mechanisms, sedimentation is the only mechanism that is directly affected by a change in the gravity (G) level. The deposition and dispersion of aerosol boluses inhaled in microgravity (G) therefore differ from those inhaled in normal gravity (1G) because sedimentation plays a role in these processes. This has been shown by our group in previous studies (7,8), in which aerosol bolus inhalations with no breath hold before the subsequent exhalation were performed in G, 1G, and 1.6G. In these studies, both aerosol deposition (DE) and dispersion (H) increased with increasing G level, and this effect was more pronounced in the alveolar region of the lung than in the large airways.In the present study, we performed bolus inhalations of 1-m-diameter particles, followed by breath holds of various lengths, up to 5 s. The tests were performed on the ground (1G) and during short periods of G aboard the NASA Microgravity Research Aircraft, to determine the extent of the role that gravity plays in DE and H during breath holds. We show that gravitational sedimentation is the principal mechanism of DE during breath holding. The data also suggest that cardiogenic mixing contributes to DE and H and that the effect is larger in the central airways than in the alveolar region. METHODS Equipment.Aerosol bolus data were collected with the same equipment used in previous studies (7,8). The eq...

Aerosols in the study of convective acinar mixing

“…While the data were suggestive although not definitive of the concept, we speculated that the phenomenon of stretch and fold already occurred during one single flow reversal in the lung. This conclusion was consistent with the high degree of dispersion and deposition previously observed with single bolus inhalations in microgravity (Darquenne et al, 1998(Darquenne et al, , 1999(Darquenne et al, , 2000 and the complex mixing pattern seen in polymer filled rat lungs after a single breathing cycle (Tsuda et al, 2002).…”

“…All the mechanisms of particle movements, except Brownian diffusion that are involved in this transfer are usually referred to as convective mixing. Factors contributing to convective mixing include non-reversibility of velocity profiles within the airspaces, airway and alveolar geometries asymmetries between inspiratory and expiratory flows (Scherer and Haselton, 1982), non-homogeneous ventilation of the lung (Darquenne et al, 1999;Rosenthal, 1993), cardiogenic mixing (Darquenne et al, 2000;Scheuch and Stahlhofen, 1991) and the phenomenon of "stretch and fold" (Butler and Tsuda, 1998;Darquenne and Prisk, 2004). It should be noted that in this context, the term convective mixing not only include mechanisms that are specific to convection itself but also mechanisms, such as inertia and gravitational sedimentation that result in particle crossing streamlines.…”

Aerosol Deposition in the Human Lung in Reduced Gravity

“…To further assess the potential effect of cardiogenic mixing, aerosol bolus tests that included a breath hold after the inhalation of the bolus were performed both in lG and in 1G. (5,13) Data were obtained with 1-lm particles at a penetration volume of 150 and 500 mL and breath holds of 0, 3, and 5 sec (5) and with 0.5-lm particles at a penetration volume of 300 and 1,200 mL and breath holds of 0, 5, and 10 sec (13) (Fig. 4).…”

“…Indeed, a significant fraction of particles that would + Significant differences between breath holds in both lG and 1G ( p < 0.05). Modified from Darquenne et al (5) and Prisk et al, (13) with permission from Elsevier for the latter.…”

“…It was not until the mid-1990s that more extensive measurements of aerosol deposition in reduced gravity were made. (5)(6)(7)(8)(9)(10)(11)(12)(13)(14) To date, all experimental studies on aerosol inhalation in reduced gravity have been performed during short periods of reduced gravity achieved during parabolic flights. The aim of this article is to review these experimental studies and highlight the role of gravity in the transport and deposition of inhaled particles in the human lung.…”