Transvascular fluid flux from the pulmonary vasculature at rest and during exercise in horses

Abstract

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 (J V−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.

Changes in arterial, mixed venous and intraerythrocytic ion concentrations during prolonged exercise

“…Vengust et al . (2006) reported that horses undergoing intense exercise experience a loss of fluid from the pulmonary capillaries into the lung interstitium, which is probably due to increased pulmonary microvascular pressures and a decreased colloid osmotic gradient in response to fluid release from erythrocytes secondary to high O 2 tension in the lungs.…”

“…This occurrence seems unlikely in our study as the lost fluid would have to be hypertonic with respect to sodium and protein in order to explain our results. However, it is possible that during the course of exercise, movement of water or other nonprotein containing fluid from erythrocytes (Vengust et al . 2006) and/or surrounding tissues into the pulmonary microvasculature contributed to the small, but significant, observed differences between pl[Na + ] a and pl[Na + ] v and [TP] a and [TP] v .…”

Effect of frusemide on transvascular fluid fluxes across the lung in exercising horses

“…Within 2 min of the onset of heavy exercise in horses, approximately 12 l/min or 4% of cardiac output moves from the pulmonary circulation into the pulmonary interstitium (Vengust et al . 2006a).…”

“…2001). During our previous study we have shown that erythrocytes are major contributors to pulmonary transvascular fluid fluxes (Vengust et al . 2006a).…”

Effects of chronic acetazolamide administration on gas exchange and acid‐base control in pulmonary circulation in exercising horses

“…1997; Juel et al . 1999), which is evident as the erythrocyte regulatory volume decrease in peripheral tissues, and by the erythrocyte regulatory volume increase across the lung (Vengust et al . 2006a,b).…”