Lymph flow in instrumented dogs varies with exercise intensity

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.

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 mph, 419% higher than resting flow. Regression analysis demonstrated a linear relationship between treadmill speed and the percent increase in lymph flow. Lymph flow returned to the resting rate 1-2 min post-exercise.

Lymph flow in the thoracic duct is positively correlated with exercise intensity.