Author(s): RABERIN, A., NARANG, B.J.2,3, REMEC, K.2, LEPLA, M.2, KOVACIC, A.2, KAVCIC, K.2, DEBEVEC, T.2,3, MILLET, G.P.1, Institution: UNIVERSITÉ DE LAUSANNE: UNIVERSITE DE LAUSANNE, Country: SWITZERLAND, Abstract-ID: 1422

INTRODUCTION:
Exposure to hypoxia triggers hyperventilation and hypoxic pulmonary vasoconstriction (HPV) which may influence lung diffusing capacity (DL) by modifying pulmonary capillary blood volume (Vc) and/or membrane diffusion (Dm) [1]. These mechanisms are known to affect pulmonary gas exchange. However, their respective time courses during acclimatization, and in particular the relative contributions of Vc versus Dm to changes in DL, remain incompletely characterized, especially in women. Therefore, this study aimed to characterize the changes in pulmonary diffusing capacity and its determinants across 10 days of altitude exposure in women.
METHODS:
Fifteen healthy young female lowlanders were exposed to normobaric hypoxia (inspired O2 partial pressure: 98 mmHg; ~3500 m) for 10 days. DL was assessed at rest before (pre) and after (post) the exposure, as well as upon arrival (D0), and at day 2 (D2), 4 (D4), 9 (D9) during exposure. DL was also evaluated during steady-state exercise (6-min bouts at 40% of maximal power output) at pre, post and D2, D4, and D9. DL was assessed using the single-breath method with nitric oxide (DLNO) and carbon monoxide corrected for hemoglobin concentration (DLCO) (HypAir, MGC Diagnostics, Saint Paul, MN), following standardized procedures.
RESULTS:
At rest, alveolar volume (VA) and DLNO remained stable across all time points. Resting DLCO was higher at D9 vs. pre (27.3 ± 3.4 vs 25.6 ± 3.2 mL/min/mmHg, p = 0.022). Vc was greater at D0 (71.3 ± 17.6 mL), D2 (63.8 ± 10.8 mL), and D9 (68.2 ± 12.8 mL) compared with pre (53.2 ± 9.4 mL) and post (51.2 ± 7.9 mL; all p < 0.045). Conversely, DmCO was lower at D4 and D9 (134 ± 21 and 128 ± 17 mL/min/mmHg) compared with pre and post (172 ± 49 and 195 ± 45 mL/min/mmHg, all p < 0.037).
During exercise, VA and DLNO did not differ across time points. In contrast, DLCO values were higher at D4 and D9 (36.9 ± 5.3 and 37.6 ± 5.2 mL/min/mmHg) compared with both pre and post (32.0 ± 3.6 and 31.7 ± 2.8 mL/min/mmHg; all p < 0.015). Changes in Vc during exercise followed a similar pattern, while DmCO was lower at D4 and D9 (150 ± 27 and 148 ± 28 mL/min/mmHg) compared with pre- and post-exposure (213 ± 68 and 214 ± 60 mL/min/mmHg, all p < 0.017). There were no differences at rest or during exercise between the normoxic pre-post timepoints.
CONCLUSION:
Exercising DLCO demonstrated specific acclimatization kinetics across ten days in continuous hypoxia. DL improved after several days, driven by Vc increases that outweighed DmCO reductions. These adaptations likely reflected HPV-mediated elevations in perfusion pressure, leading to capillary distension and recruitment. Collectively, these findings suggest that moderate altitude exposure maintains or slightly enhances DL via Vc increases; an adaptation not maintained upon return to normoxia.

1 Martinot et al. (2013) J Appl Physiol. doi: 10.1152/japplphysiol.01455.2012.