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1Division of Pulmonary and Critical Care Medicine, Department of Medicine, and 2Division of Physiology, Department of Environmental Health Sciences, The Johns Hopkins Medical Institutions, Baltimore, Maryland
Submitted 4 March 2005 ; accepted in final form 21 March 2005
Ventilation (
) increases lung lymph flow (
L), but the separate effects of tidal volume (VT) and frequency (f) and the role of
-induced changes in edema formation are poorly understood. An isolated, in situ sheep lung preparation was used to examine these effects. In eight sheep with f = 10 min1, results obtained during 30-min periods with VT = 5 or 20 ml/kg were compared with values obtained during bracketed 30-min control periods (VT = 12.5 ml/kg). Eight other sheep with constant VT (12.5 ml/kg) were studied at f = 5 or 20 min1 and compared with f = 10 min1. Three additional groups of six sheep were perfused for 100 min with control
(10 ml/kg, 10 min1). VT was then kept constant or changed to 20 or 3 ml/kg during a second 100-min period. Increases in VT or f increased
L and vice versa, without corresponding effects on the rate of edema formation. For the same change in
, changing VT had a greater effect on
L than changing f. The change in
L caused by an increase in VT was significantly greater after the accumulation of interstitial edema. The change in
L caused by a sustained increase in VT was transient and did not correlate with the rate of edema formation, suggesting that
altered
L through direct mechanical effects on edema-filled compartments and lymphatic vessels rather than through
-induced changes in fluid filtration.
pulmonary edema; sheep; lung fluid balance; lung interstitial space; edema clearance
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