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Studies of the lymphatic drainage of dog lungs
Abstract:
The lymphatic system of the lungs has proved difficult to study and characterize because it is technically complex to investigate, its properties are difficult to quantitate, and anatomically it is extraordinarily variable. This study was part of a more comprehensive effort to understand the nature of lymphatic permeation by extrinsic materials (e.g., dusts) arising from alveolar deposition, and had three main objectives; (1) to develop a reliable surgical approach for the collection of lymph from the right duct; (2) to investigate some of the inconsistencies in lymphatic structure and function, especially the relationship of the right lymph duct (RLD) and thoracic lymph duct (TLD) outflows to the pulmonic lymph; and (3) to begin a systematic investigation of lymphatic uptake of administered materials by varying their physicochemical parameters. Ultimately, we utilized a modification of the surgical approach of Meyer, which we believe is less prone to blood contamination than the venous-sac procedure of Leeds and Uhley and provides purer pulmonic lymph. By this means we obtained average RLD flow rates of 4.5 ml/h or 0.35 ml/h . kg body weight in 24 dogs, which are comparable to those in the recent literature. For demarcation of the pulmonic drainage in relation to the RLD and TLD, we found in 13 dogs that 75% or more of the lung lymph returned to the venous circulation through the RLD, wheras less than 3% of the thoracic lymph entered the RLD. Radioactive tracers were administered by intralymphatic, intrabronchial, inhalation, and intravenous routes to obtain these findings and the uptake data. Lymphatic uptake values for iron, cadmium, and lead were obtained principally after intrabronchial administration. The uptake data, while preliminary, indicate that both the chemical species and their physical states are important in affecting alveolar permeation into the pulmonic lymph. Evidence for varying lymphatic roles in the alveolar retention of these heavy metals is also presented.