Lymph flow in instrumented dogs varies with exercise intensity.

Abstract Background: Although it is generally accepted that exercise accelerates lymph flow, no study has directly measured lymph flow as a function of exercise intensity. In this study, we have measured flow in the thoracic lymph duct of five instrumented dogs while they ran on a treadmill. Methods and Results: Dogs were surgically instrumented with an ultrasonic flow transducer on the thoracic lymph duct and a catheter in the descending thoracic aorta. After recovery from surgery, the dogs ran on a treadmill at speeds which varied stepwise from 0 to 10 mph and from 10 to 0 mph. Dogs ran for 1 min at each speed with 15 min rest between each exercise. Heart rate increased significantly during exercise, whereas mean aortic pressure did not change. Resting lymph flow was 1.7 ± 0.2 ml/min. Exercise at 1.5 mph significantly increased lymph flow to 3.9 ± 0.6 ml/min (P < 0.01), 121% higher than resting flow. Lymph flow was further elevated at higher treadmill speeds, reaching 9.0 ± 1.6 ml/min (P < 0.01) at 10 m...