Pressure Transmission in Pulmonary Arteries Related to Frequency and Geometry

The propagation of the pulse wave through the canine pulmonary arterial tree has been evaluated by means of harmonic analysis. The apparent phase velocity varied both with frequency and distance as one would expect in the presence of reflected waves. The phase velocity was about 230 cm/sec for the inflated and 325 cm/sec for the deflated lung. Theoretical considerations as well as experimental results indicate that the major branches represent the primary reflection site for the pulse wave. The pulse pressure is transmitted across the pulmonary capillary bed, although at a high attenuation, and the transmission varies markedly with lung volume. The dimensions of the pulmonary arterial tree were evaluated from casts. Data for the length and cross sections of the various branches are given. The volume of the arterial tree as represented by the casts was 24 ml. The cross section of the various branches represents an ellipse rather than a circle, and the cross section ratios of the major branch points is considerably less than those postulated for optimal energy transfer. The implications of the geometrical findings for the relation between pressure gradient and flow are briefly discussed.