Aerosol Deposition in the Human Lung Periphery Is Increased by Reduced-Density Gas Breathing

Abstract

Aerosol mixing resulting from turbulent flows is thought to be a major mechanism of deposition in the upper respiratory tract (URT). Because turbulence levels are a function of gas density, the use of a low-density carrier gas should reduce deposition in the URT allowing the aerosol to reach more peripheral airways of the lung. We performed aerosol bolus tests on 11 healthy subjects to investigate the effect of reduced gas density on regional aerosol deposition in the human lung. Using both air and heliox (80% helium, 20% oxygen) as carrier gas, boluses of 1 and 2 microm-diameter particles were inhaled to five volumetric lung depths (V(p)) between 150 and 1200 mL during an inspiration from residual volume (RV) to 1 liter above functional residual capacity at a constant flow rate of approximately 0.50 L/sec, which was immediately followed by an expiration to RV at the same flow rate. Aerosol deposition and axial dispersion were calculated from aerosol concentration and flow rate measured at the mouth. For 1 microm-diameter particles, deposition was significantly reduced by 29 +/- 28% (mean +/- SD, p < 0.05) when breathing heliox instead of air at shallow V(p) (150 mL) and significantly increased by 11 +/- 9% at deep V(p) (1200 mL). For 2 microm-diameter particles, deposition was significantly higher at V(p) = 500 mL by 6 +/- 7% and the predicted V(p) to achieve 100% deposition was significantly lower with heliox (834 +/- 146 mL) compared to air (912 +/- 128 mL) (p < 0.05). Despite a decrease in deposition at shallow V(p), there was no change in axial dispersion, suggesting that other factors such as radial turbulent mixing result in decreased aerosol deposition. Our results suggested that heliox reduces upper airway deposition of 1 and 2 microm-diameter particles allowing more particles to penetrate and subsequently deposit in the peripheral lung.

Role of carrier gases in enhancement of gas exchange and aerosol–drug delivery under invasive high frequency oscillatory ventilation

“…Despite this effect of the inertial impaction mechanism in both cases, the deposition under air was ≥ 40% higher than He (see Table 4). This is due the reduction in turbulence and flow resistance, which is in well agreement to the similar observations reported in different prior studies (Anderson et al, 1990;Ari et al, 2011;Darquenne and Prisk, 2004;Katz et al, 2014;Miyawaki et al, 2012;Peterson et al, 2008). Matida et al, (2006) and Ilie et al, (2008) in their study of particle deposition for cases with/without turbulence modeling, reported that turbulence mechanism is as important as the impaction mechanism.…”

“…A decreasing (increasing) gas density (kinematic viscosity) effectively minimizes the turbulence and flow resistance, which effectively reduces particle dispersion (Anderson et al, 1990;Ari et al, 2011;Darquenne and Prisk, 2004;I. Katz et al, 2014;Miyawaki et al, 2012;Peterson et al, 2008). Consequently, the particle deposition during the inspiration phase increases (decreases)…”

“…Carrier gas properties like density and viscosity plays an important role and can be tuned to enhance aerosol deposition for patients under therapy management (Peterson et al, 2008).…”

Delivery of helium–oxygen mixture during spontaneous breathing: evaluation of three high-concentration face masks

“…Owing to this unique physical property, He-O 2 mixtures may potentially be useful in the treatment of conditions such as increased upper airway resistance, asthma, and chronic obstructive pulmonary disease to decrease work of breathing and dyspnea [2][3][4]. The effects of He-O 2 mixtures can also be used for optimizing particle deposition in the human respiratory tract, but will depend on physical properties of the mixture such as density, viscosity, and mean free path [5][6][7]. The clinical efficacy of breathing an He-O 2 mixture, however, has not been firmly established [8].…”

Laser diffraction characterization of droplet size distributions produced by vibrating mesh nebulization in air and a helium–oxygen mixture

“…Further to its potential role as a therapeutic agent on its own, He/O 2 has been advocated as a carrier gas to better transport medical aerosols into obstructed lungs (Anderson & Svartegren, 1993;Corcoran & Gamard, 2004;Kim, Saville, Sikes, & Corcoran, 2006;Kress et al, 2002;Manthous et al, 1995;Peterson, Prisk, & Darquenne, 2008). In this application, it is important to assess the effects of varying gas properties not only on the mechanics of particle deposition in the respiratory tract, but also on aerosol production processes.…”