Simultaneous comparison of tracheobronchial and right duct lymph dynamics in dogs

The simultaneous responses of lymph flow and protein concentration were compared using lymph from the right duct (RD) and small afferent tracheobronchial (TB) lymphatics cannulated in the same dog. Lymph was collected during a base-line period and following steady-state left atrial pressure (Pla) elevations. For a mean increase in Pla of 14.8 cmH2O, RD flow increased 1.1 times control and TB flow by 2.5 times control. Total protein lymph-to-plasma ratios decreased significantly for TB lymph but not for RD lymph. Assuming TB represented pure lung lymph, the right duct was estimated to drain 4% of the total lung lymph and consist of 11% lung lymph with 89% extrapulmonary lymph at normal lymph flows. The lung lymph contribution to RD flow increased to 24% with increased Pla. Equivalent capillary pore dimensions calculated using endogenous protein fractions in both RD and TB lymph resulted in small pores of 100 and 90 A and large pores of 220 and 225 A, respectively. The fraction filtered through the large-pore population estimated using RD lymph was half that predicted using TB lymph. These data indicate that RD lymph data cannot accurately reflect pulmonary vascular permeability, since extrapulmonary lymph provided a major component of RD lymph flow at both base-line and increased filtration states.