Flow Dynamics in Human Respiratory and Circulatory Systems

Abstract

Inhalation toxicology requires an understanding of fluid dynamics within airways because particles are transported by inhaled air. That is, since particles are entrained in airstreams, their trajectories will reflect the character of the fluid carrying them. We have addressed how airflow research can benefit from the rich tradition of blood-flow studies available in the literature. The salient point is that the Navier-Stokes and mass conservation equations governing fluid dynamics are applicable to the motion of liquids (e.g., blood flow in the circulatory system) and gases (e.g., airflow in the respiratory system). The sources cited herein suggest the study of blood flow to be more advanced than airflow, historically having received considerably more attention. Theoretical investigations of the circulatory system have been (1) more elegant and rigorous from mathematical perspectives and (2) more biologically realistic regarding considerations of complex elements such as transient motion, three-dimensional simulations, and morphological effects. Perhaps attributable to that advanced state of modeling, it has been well documented that fluid dynamics factors such as velocity gradients and mechanical stresses on tubular surfaces play important, direct roles in the actual manifestation of heart diseases, specifically atherosclerosis. Alternatively, perhaps the clear cause-and-effect relationship has resulted in the more sophisticated level of blood flow studies. We have examined the literature with regard to the feasibility of extrapolating results from analyses of the circulatory system to the respiratory system. Our findings indicate that, although caution must be exercised when making comparisons, blood-flow studies can indeed shed valuable insight on the behavior of airflow. This suggests that a new library of information is available for inhalation toxicologists interested in particle dosimetry and risk assessment issues.