Inter-individual differences are observed in the response to conditions that entrain an increase in microvascular filtration, such as increase in cardiac output and hypoxia. We characterized these differences considering ventilatory response, lung diffusion and fluid balance. 23 subjects, 37,4±7,2 (SD) years, 5 females, 17 males, performed an incremental exercise test until exhaustion on cyclo-ergometer at sea level (SL) and after 6h at 3300m (HA). Variables measured included: total lung diffusion (DLCO) and subcomponents (capillary volume, Vc; membrane diffusion, Dm;), gas exchanges, pulmonary ventilation, heart rate, pulse oxymetry, respiratory impedance (IOS). Based on ventilatory response to exercise in HA, subjects were divided into "high"(HR) and "low" (LR) responder. No difference in arterial saturation in both groups at SL (99%) and in HA (91.6%). Vc was greater in HR at rest at SL, and decreased during work at SL, and in HA ( both at rest and during work). In LR, Vc increased in the same conditions. Work and hypoxia increased respiratory impedance in HR, suggesting a perturbation in lung fluid balance. The decrease in Vc in HR may be interpreted as a protective mechanism to buffer the development of edema.