Am. J. Respir. Crit. Care Med.,
Volume 163, Number 3, March 2001, 614-618
Clearance of Filtered Fluid from the Lung
during Exercise
Role of Hyperpnea
TOMONOBU
KOIZUMI,
ROBERT J.
ROSELLI,
RICHARD E.
PARKER,
CASILDA I.
HERMO-WEILER,
MUKUL
BANERJEE,
and
JOHN H.
NEWMAN
Center for Lung Research, Department of Medicine, and Department of Biomedical Engineering, Vanderbilt University School of Medicine,
Nashville, Tennessee; Department of Physiology, Meharry Medical College, Nashville, Tennessee; and First Department of Medicine,
Shinshu University, Matsumoto, Japan
During strenuous exercise in sheep, lung lymph flow increases
within seconds and rises to levels 7- to 10-fold over baseline. Concomitant with the flow increase, the lymph protein content rapidly decreases to levels consistent with severe capillary hypertension. This pattern of clearance of filtered fluid is quite different than is seen with the passive capillary hypertension that results from mechanical obstruction of the mitral valve. In passive capillary hypertension, the increase in lymph flow and reduction in
lymph protein content develop over several hours. The purpose of
this study was to discover if these observed differences in edema
clearance are related to the hyperpnea that accompanies exercise.
Sheep were instrumented for continuous measurement of pulmonary arterial, left atrial, and systemic pressures, cardiac output by
ultrasound, lung lymph flow, and ventilation. First, hemodynamics, ventilatory, and lymph clearance variables were measured during
moderate exercise at 2.8 mph on a treadmill. Second, on a separate occasion, sheep were induced to hyperventilate to the same
minute ventilation as during exercise, using modest CO2 stimulation. Lymph flow and hemodynamics were unaffected by this hyperpnea. The third arm of the experiment was to raise pulmonary
microvascular pressure at rest to the level seen with exercise by
means of a balloon catheter placed in the mitral valve. Lymph flow
rose and protein content decreased slowly and to a lower degree
than seen with exercise despite a comparable microvascular pressure. Finally, left atrial hypertension and induced hyperpnea were
combined in sheep at rest, and the resulting lymph flow and protein
content were the same as seen with exercise at similar pressures and
ventilation. We conclude that hyperpnea is a major mechanism of
interstitial liquid clearance during exercise, and may be largely responsible for preventing pulmonary edema that might occur at the
high microvascular pressures of strenuous exercise.
