Fluid mechanics of the pulmonary circulation.

Assessment of the fluid mechanics of the pulmonary circulation has been hindered by the relative inaccessibility of the pulmonary vascular bed. Current understanding is based largely on analyses of mathematical models which have been used to simulate hemodynamic characteristics within an architectural representation of that bed. These representations have ranged from simple, lumped parameter structures to anatomically realistic structures based on measurements of casts of the irregular branching network of pulmonary arteries and veins. Nonlinear models have been studied to determine the effects of vessel taper and within beat geometrical variations as cross-sectional shapes change from circular to elliptical and small vessels undergo recruitment, distention, and collapse as a result of the shifting balance in alveolar, pleural, and capillary pressures. This article reviews current concepts of pulmonary circulatory fluid mechanics focusing on mathematical models and relevant hemodynamic studies.