Components of the pressure required to breathe dense gases

To elucidate the impact of high gas density on airway flow (during inspiration and expiration) and on gas acceleration (at end-inspiration and end-expiration), I simulated pressures for breathing in man with a) an equation of motion of the respiratory system, b) the assumption that pressure to accelerate gas is directly proportional to density, and c) five different assumptions concerning the relationships among lung volume, density, and the pressure for flow. The results show that accelerative pressure is not an important fraction of the total pressure with attainable densities, tidal volumes, and frequencies when it is assumed that lung volume changes as a sine-wave function of time. High accelerative pressure has a minor effect of making intrapleural pressure tend to be in phase with flow, as it is with high flow resistance. Alternate assumptions about pressure to cause flow led to small changes in the patterns of pressure with time, but had little effect on the overall picture.

Effects of lung volume and density on flow pressure can be characterized successfully in several ways, and the large density effect on flow pressure dominates the energy requirement for breathing in dense-gas environments.