HINDLIMB AND LUNG LYMPH FLOWS DURING PROLONGED EXERCISE

We performed experiments to determine the effect of 2 h of exercise on hindlimb lymph flow (QL) and protein concentration in sheep. We compared these results with the lung QL response to long-term exercise. Eleven sheep with catheters in an efferent duct of a prefemoral lymph node and 12 sheep with chronic lung lymph catheters exercised at 2.5-3.0 km/h for up to 2 h (lung lymph: range 45-120 min, mean 80 min; hindlimb lymph: range 75-120 min, mean 110.5 min). Cardiac output approximately doubled. Pulmonary vascular resistance decreased by 42%, and systemic vascular resistance decreased by 35%. There were small increases in calculated pulmonary microvascular and arterial pressures. During steady-state exercise, lung QL doubled and the lung lymph-to-plasma protein concentration ratio decreased by 16%. There was an immediate fivefold increase in hindlimb QL, and the hindlimb lymph-to-plasma protein concentration ratio decreased by 26%. Hindlimb QL decreased to a constant 130% above baseline during the last 30 min of exercise. We conclude that the marked increase in hindlimb QL early in exercise is secondary to a massaging effect in working muscles. The steady-state increases in QL toward the end of the exercise period in both lung and hindlimb are secondary to both increased surface area and pressure in the pulmonary and systemic microvascular circulations. Our data suggest that in the lung the major factor determining QL is increased vascular surface area.