Intense hypoxic cycle exercise does not alter lung density in competitive male cyclists

Abstract

We tested the hypothesis that intense short duration hypoxic exercise would result in an increase in extravascular lung water (EVLW), as evidenced by an increase in lung density. Using computed tomography (CT), baseline lung density was obtained in eight highly trained male cyclists (mean +/- SD: age = 28 +/- 8 years; height = 180 +/- 9 cm; mass = 71.6 +/- 8.2 kg; VO2max= 65.0 +/- 5.2 ml kg min(-1)). Subjects then completed an intense hypoxic exercise challenge on a cycle ergometer and metabolic data, HR and %S(p)O2 were recorded throughout. While breathing 15% O2, subjects performed five 3 km cycling intervals (mean power, 286 +/- 20 W; HR = 91 +/- 4% HRmax) separated by 5 min of recovery. From a resting hypoxic S(p)O2 of 92 +/- 4%, subjects further desaturated during exercise to 76 +/- 3%. CT scans were repeated 76 +/- 10 min (range 63-88 min) following the completion of exercise. There was no change in lung density from pre (0.18 +/- 0.02 g ml(-1)) to post-exercise (0.18 +/- 0.04 g ml(-1)). The substantial reduction in S(p)O2 may be explained by a number of potential mechanisms, including decreased pulmonary diffusion capacity, alveolar hypoventilation, reduced red cell transit time, ventilation/perfusion inequality or a temperature and pH induced rightward-shift in the oxyhaemoglobin dissociation curve. Alternatively, the integrity of the blood gas barrier may have been disrupted without any measurable increase in lung density.

Influence of sildenafil on lung diffusion during exposure to acute hypoxia at rest and during exercise in healthy humans

“…Interestingly, in the present study, alveolar–capillary membrane conductance, when considered alone or when corrected for differences in V c , returned to baseline values during recovery under all three exercise conditions. These findings are in agreement with previous studies by us and others which have recently demonstrated that normobaric hypoxic exercise may not be an adequate stimulus to increase lung water in normally-trained healthy humans (Gallagher et al 1988; Guenette et al 2007; Hanel et al 1994; Hodges et al 2007; MacNutt et al 2007; Snyder et al 2006). Therefore, as with previous studies, the present study provides no evidence that short-duration hypoxic exercise results in lung fluid accumulation in healthy but untrained subjects.…”

Cycling performance decrement is greater in hypobaric versus normobaric hypoxia

“…The change in PV from SL to HYP was similar in both HH and NH, and the change in PV during exercise was also similar in both environments. Previous research demonstrated compelling radiographic evidence of pulmonary edema in athletes exercising in HH [40], while other studies found no lung water accumulation in humans exercising in NH [41,42]. Differences in fluid circulation and the trans alveolar-capillary membrane flux [43] may induce greater pulmonary vasoconstriction in HH and decrease O 2 diffusion via a decreased pressure gradient [13].…”

Hypoxia induced changes in lung fluid balance in humans is associated with beta-2 adrenergic receptor density on lymphocytes

“…Additionally, one of the mechanisms by which hypoxia is thought to result in an increase in lung water is through an increase in pulmonary capillary pressures. Three relatively recent studies have demonstrated that exercise during hypoxia (even in trained individuals) does not result in an increase in lung water, although they likely had dramatic increases in pulmonary pressures given high cardiac outputs coupled with hypoxic pulmonary vasoconstriction (Guenette et al, 2007; Hodges et al, 2007; MacNutt et al, 2007). Of importance, three of our subjects (18%) demonstrated radiographic evidence for an increase in lung water with short-term hypoxic exposure which is in agreement with some previous estimates of the percentage of the population that is susceptible to high-altitude pulmonary edema.…”