A hemodynamic model representation of the dog lung

The published morphometric data from human, catt, and dog lungs suggest that the power-law relationships beiween the numbers (N(a) and N(v)) and diameters (D(a) and D(v)) of arteries and veins and between the lengths (L(a) and L(v)) and diameters of the arteries and veins could be used as scaling rules for assigning dimensions and numbers to the intrapulmonary vessels of the arterial and venous trees of the dog lung. These rules, along with the dimensions of the extrapulmonary arteries and capillary sheet and the distensibility coefficients of the vessels obtained from the literature, were used to construct a steady-state hemodynamic model of the dog lung vascular bed. The model can be characterized approximately by 15 orders of arteries with N(a) ~ 2.07 D(a)^-2.58 and 13 orders of veins with N(v) ~ 2.53 D(v)^-2.61. For the intrapulmonary vessels (orders 1-12), L(a) ~ 4.85 D(a)^1.01, and L(v) ~ 6.02 D(a)^1.07. The average ratio of the numbers of vessels in consecutive orders is ~3.2 for the arteries and veins. These arterial and venous trees are connected by the capillary sheet with an undistended thickness of ~3.5 μm and an area of 33 m². The average distensihility (% increase in diameter over the undistended diameter/Torr increase in transmural pressure) for the model arteries and veins is ~2.4% /Torr,and the distensibility of the capillary sheet (% increase in thickness over the undistended thickness/Torr increase in transmural pressure) is ~3.6% /Torr. The calculated arterial-capillary-venous volumes and compliances of the model agree well with experimental estimates of these variables in dogs. In addition, the model appears consistent with certain aspects of the pressure-flow relationships measured in dog lungs. The model appears to be a useful summary of some of the available data on pulmonary morphometry and vessel properties. It is anticipated that the model will provide the basis for dynamic modeling of the dog lung in the future.