Particle Deposition In Human Lungs:Mechanisms And Factors

Abstract:Both the epidemiological and toxicological studies indicate that particulate air pollution can cause adverse health effect. Deposition of inhaled particles in human lung is an essential factor to reveal the correlation between particle exposure and mortality or morbidity and to assess the toxicity of particle. The completely exposure-dose-response relationship could provide scientific support for the development of air quality standards to control particulate pollution in relation to atmospheric and occupational environments. And knowledge on particle deposition in human lung is important to minimize the health risks associated with exposure to particulate pollution. On the other hand, therapeutic drug delivery by inhalation receives more and more attention for the treatment of respiratory diseases or other therapeutic purposes. The research of particle deposition can evaluate the efficacy of therapeutic drug. Furthermore, it would be utilized to optimize the drug deposition and reduce the dose and associated side effects by targeting the specific-sites within the lung.Weibel A symmetric lung model was adopted as the basic lung structure and then it was simplified as a trumpet model with varying cross-area. The transport of air and particles in human lung is governed by mass conservation equations. A one-dimensional dynamic model was used to calculate particles transport and deposition. The deposition fractions were obtained for the whole lung, regional lung and each airway generation. In this study, the effect of the particle sizes and densities, the breathing physiology, and the lung morphology on deposition was analyzed. The contribution of each deposition mechanism was also analyzed. In addition, deposition patterns for normal man under different activities were calculated and therapeutic drug delivery by inhalation was optimized.The results showed that the effect of particle size on deposition is significant. For a certain particle size, only one or two deposition mechanisms usually play a dominant role. The influence of particle density on deposition is dependent on the dominant mechanism. Deposition due to Brownian diffusion is independent on density. However, deposition due to impaction and sedimentation is enhanced by density increase. Breathing physiology is also important for particle deposition. The action of deposition mechanisms is not only related to particle size and density, but also associated with breathing physiology. The action of impaction is enhanced and the influence of sedimentation and diffusion is weakened with the increase of air flow rate. The site of particles deposited in the lung is affected by particle size, density, and breathing physiology. To deliver as more as possible amount of drug by inhalation to the targeted-site, the optimal particle size and breathing physiology should be used by patients. If the side effect of the therapeutic drug is severe, deposition in other area should be simultaneously considered.