Indicator dilution lung water and capillary blood volume in prolonged heavy exercise in normal men

The indicator dilution quantity of extravascular water in the lung (idQwl) increases in exercise, but whether it is a real accumulation of fluid or is due to increased distribution of blood flow to previously unperfused regions of alveolar walls is unsettled. In 9 well-trained young men, we compared idQwl and the pulmonary capillary blood volume, as measured by the carbon monoxide diffusing capacity procedure, at rest and after 10 and about 50 min of heavy work (150 watts) on a bicycle ergometer. From rest to 10-min exercise, we observed the following changes. Heart rate 72 +/- 15 beats per min (mean +/- SD) to 151 +/- 23; cardiac output 6.0 +/- 1 liter per min to 17.7 +/- 4.1; carbon monoxide diffusing capacity, 46 +/- 10 ml per min per Hg to 65 "/- 11. These all remained constant between 10- and 50-min exercise. The idQwl increased from 178 +/- 37 ml at rest to 219 +/- 46 ml at 10 min and 233 +/- 43 ml at 50 min, and pulmonary capillary blood volume increased from 140 +/- 52 ml at rest to 220 +/- 106 and 206 +/- 98 at 10 and 50 min of exercise, respectively. All of the changes from rest to early exercise were significant (P less than 0.05) by paired t test. There were no significant changes between early and late exercise. We concluded that the early exercise increase in idQwl was due to redistribution of blood flow among and within alveolar walls. The absence of any increase in idQwl between early and late exercise is evidence against accumulation of lung fluid.