Forward and backward transmission of pressure waves in the pulmonary vascular bed of the dog.

Pressures were measured in lobar pulmonary arteries, veins, and left atria of anesthetized open-chest dogs. Observations were made before and after snaring the lobar vessels and before and after infusing dextran to raise the mean pressure. Pressure waves were subjected to harmonic analysis. Forward (artery to vein) and backward (vein to artery) transmission (output/input pressure) and transmission ratios (forward/backward transmission) were calculated for each harmonic. At low frequencies, forward transmission was increased by dextran, but backward transmission was unaffected. At low frequencies and high mean pressures the bed was nonsymmetrical, forward transmission being several times greater than backward at the same mean pressure (transmission ratio > 1 ) . The findings were analyzed with the aid of simple models. Nonsymmetry at low frequencies and high mean pressures appears to be due to arterial exceeding venous compliance. The findings and resulting theory are pertinent to the understanding of the shape and amplitude of arterial "wedge"-pressure traces. ADDITIONAL