Effect of Heart Rate on Aerosol Recovery and Dispersion in Human Conducting Airways After Periods of Breathholding

Journal of Applied Physiology

Paiva

Prisk

2000

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...

Section: Dementioning

confidence: 88%

Section: Dementioning

confidence: 99%

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

Journal of Applied Physiology

Paiva

Prisk

2000

“…Such an increase is compatible with an effect of cardiogenic mixing on deposition as suggested by Scheuch and Stahlhofen. (26) Indeed, as there was no inspiratory or expiratory flow in the airways during the breath holds, neither impaction nor flow irreversibility could have caused the observed increase in deposition. Sedimentation was not a factor either because of the absence of gravity.…”

Section: Regional Deposition In Reduced Gravitymentioning

confidence: 97%

“…(6) Other potential contributors to aerosol deposition may include mixing induced by the nonreversibility of the flow in the airways and/or by cardiogenic mixing resulting from the physical motion of the heart that generates an oscillating motion of air in the lungs. (23)(24)(25) The effect of cardiogenic mixing on aerosol bolus behavior was previously investigated by Scheuch and Stahlhofen, (26) who performed bolus inhalations of 1-lm-diameter particles on a subject at rest and after exercise when the heart rate was increased by more than a factor of 2. They showed that the motion of the heart increased aerosol deposition and that this increase was more obvious at shallow penetration volumes.…”

Section: Regional Deposition In Reduced Gravitymentioning

confidence: 99%

Aerosol Deposition in the Human Lung in Reduced Gravity

Journal of Aerosol Medicine and Pulmonary Drug Delivery

2014

The deposition of aerosol in the human lung occurs mainly through a combination of inertial impaction, gravitational sedimentation, and diffusion. For 0.5-to 5-lm-diameter particles and resting breathing conditions, the primary mechanism of deposition in the intrathoracic airways is sedimentation, and therefore the fate of these particles is markedly affected by gravity. Studies of aerosol deposition in altered gravity have mostly been performed in humans during parabolic flights in both microgravity (lG) and hypergravity (*1.6G), where both total deposition during continuous aerosol mouth breathing and regional deposition using aerosol bolus inhalations were performed with 0.5-to 3-lm particles. Although total deposition increased with increasing gravity level, only peripheral deposition as measured by aerosol bolus inhalations was strongly dependent on gravity, with central deposition (lung depth < 200 mL) being similar between gravity levels. More recently, the spatial distribution of coarse particles (mass median aerodynamic diameter & 5 lm) deposited in the human lung was assessed using planar gamma scintigraphy. The absence of gravity caused a smaller portion of 5-lm particles to deposit in the lung periphery than in the central region, where deposition occurred mainly in the airways. Indeed, 5-lm-diameter particles deposit either by inertial impaction, a mechanism most efficient in the large and medium-sized airways, or by gravitational sedimentation, which is most efficient in the distal lung. On the contrary, for fine particles (*1 lm), both aerosol bolus inhalations and studies in small animals suggest that particles deposit more peripherally in lG than in 1G, beyond the reach of the mucociliary clearance system.

“…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.…”

Section: Introductionmentioning

confidence: 99%

Aerosols in the study of convective acinar mixing

Respiratory Physiology & Neurobiology

Prisk

2005

Convective mixing (CM) refers to the different transport mechanisms except Brownian diffusion that irreversibly transfer inspired air into resident air and can be studied using aerosol bolus inhalations. This paper provides a review of the present understanding of how each of these mechanisms contributes to CM. Original data of the combined effect of stretch and fold and gravitational sedimentation on CM are also presented. Boli of 0.5 μm-diameter particles were inhaled at penetration volumes (V p ) of 300 and 1200 ml in eight subjects. Inspiration was followed by a 10-s breath hold, during which small flow reversals (FR) were imposed, and expiration. There was no physiologically significant dependence in dispersion and deposition with increasing FR. The results were qualitatively similar to those obtained in a previous study in microgravity in which it was speculated that the phenomenon of stretch and fold occurred during the first breathing cycle without the need of any subsequent FR.