J Physiol Volume 570, Number 2, 397-405, January 15, 2006 DOI: 10.1113/jphysiol.2005.098723
Transvascular fluid flux from the pulmonary vasculature at rest and during exercise in horses
Modest Vengust1,
Henry Staempfli2,
Laurent Viel2 and
George Heigenhauser3
1 Veterinary Faculty, University of Ljubljana, Ljubljana SI-1115, PO Box 3425, Slovenia
2 Department of Clinical Studies, University of Guelph, Ontario, Canada N1G 2W1
3 Department of Medicine, McMaster University Medical Centre Hamilton, Ontario, Canada L8N 3Z5
Exercise causes changes in pulmonary haemodynamics through redistribution of blood flow, increase in the pulmonary surface area, and increase in pulmonary vascular pressures. These changes contribute to the increase in fluid exchange across the alveolar–capillary barrier. To determine the extent of the fluid exchange across the alveolar–capillary barrier at rest and during exercise, six horses were exercised on a high-speed treadmill until fatigue. Arterial and mixed venous blood were sampled at rest and during exercise and recovery. Blood volume changes across the lung (
BV; measured in percentage) were calculated from changes in plasma protein and haemoglobin concentration, and haematocrit. Cardiac output (Q) was calculated using the Fick equation. Fluid flux (JV–A; measured in l min–1) across the alveolar–capillary barrier was then quantified based on Q and BV. At rest, no fluid movement occurred across the pulmonary vasculature (0.6 ± 0.6 l min–1). During exercise, the amount of fluid moved from the pulmonary circulation was 8.3 ± 1.3 l min–1 at 1 min, 6.4 ± 2.9 l min–1 at 2 min, 10.1 ± 1.0 l min–1 at 3 min, 12.9 ± 2.5 l min–1 at 4 and 9.6 ± 1.5 l min–1 at fatigue (all P < 0.0001). Erythrocyte volume decreased by 6% (P < 0.01) across the lungs, which decreased the colloid osmotic gradient in the pulmonary vasculature. Decrease colloid osmotic gradient along with increased hydrostatic forces in the pulmonary vasculature would enhance displacement of fluid into the pulmonary interstitium. In conclusion, exercise caused large increases in transpulmonary fluid fluxes in horses. Here, we present a simple method to calculate transpulmonary fluid fluxes in different species, which can be used to elucidate mechanisms of lung fluid balance in vivo.
(Received 14 September 2005;
accepted after revision 1 November 2005;
first published online 3 November 2005)
Corresponding author M. Vengust: Veterinary Faculty, University of Ljubljana, Ljubljana SI-1115, PO Box 3425, Slovenia. Email: modest.vengust{at}vf.uni-lj.si
Copyright © 2006 The Physiological Society.
