A nonlinear fluid model for pulmonary blood circulation.

In this paper, we apply a quasi-one-dimensional unsteady nonlinear fluid model to study human pulmonary circulation. Eighteen generations of blood vessels composed of the branching arterial, capillary and venous distensible vessel segments make up the complete pulmonary circulation. The numerical result gives satisfactory agreement with the physiological experimental data: a dramatic pressure drop occurs in the arterioles and postcapillaries, a negative transmural pressure is shown in the postcapillary and small venous segments, a large reverse flow occurs in the main pulmonary artery during the diastolic period, and the reverse flow decreases gradually along the pulmonary tree. In the microgravity case where g = 180 cm s-2, the computation illustrated the effect of gravity force on the blood distribution in the different parts of the pulmonary circulation. The effect of gravity on the total output is not obvious. The effect of local factors which initiate the variations of the geometrical or pulmonary circulation can be stimulated quantitatively by this model. The proposal model can be very useful for clinical practice and for studying the extreme cases which are very difficult to investigate by experiments.