RELATIONSHIPS BETWEEN LYMPHATIC PUMP FLOW AND TOTAL LYMPH-FLOW IN THE SMALL-INTESTINE

Response of collecting lymphatics to acute elevations in lymph formation was studied in vivo. Mesentery of 33 rats was prepared for intravital microscopic study, and indexes of lymph propulsion (contraction frequency, stroke volume, and ejection fraction) were monitored. In 14 rats, total lymph flow was measured by cannulating the main intestinal lymph trunk. After a control period, lymph flow was increased by hemodilution with isotonic saline. Right atrial pressure did not significantly increase during the hemodilution period. Total lymph flow increased to approximately 25 times control. Lymph propulsion (the product of stroke volume and contraction frequency) decreased in five lymphangions (group I). In 22 lymphangions, lymph propulsion increased one to five times control (group II). The remaining six lymphangions increased lymph propulsion by greater than five times control (group III). Group I possessed the largest end-diastolic diameter, highest baseline contraction frequency, and did not dilate as lymphatic filling increased. Group III possessed the smallest initial end-diastolic diameter and lowest baseline contraction frequency, and end-diastolic diameter doubled as lymphatic filling increased. The characteristics of group II were between those of groups I and III. Total lymph flow and lymph propulsion by group III lymphangions tended to agree when lymph flow was less than five times control. In more edematous conditions, total lymph flow exceeded lymphatic pump flow. The characteristics of group II were between those of groups I and III. Analysis of the location of various sized lymphangions within the lymphatic network indicated that the smaller group III lymphangions were located nearer the intestinal wall, and the larger group I lymphangions were nearer the outflow from the mesentery. Incorporation of these data into a theoretical analysis suggests that the lymphatic pump accounts for the majority of the lymphatic safety factor against edema formation when the rate of lymph formation is less than five times control.