Breathtaking heights: Lung mechanics and pulmonary extravascular fluid accumulation in female climbers during the K2 expedition

Female physiological responses to hypoxia remain underexplored, despite growing participation in mountaineering expeditions. Pulmonary interstitial oedema described during acute hypobaric hypoxia can be exacerbated by prolonged physical exercise. It is unclear whether these factors alter the mechanical properties of the respiratory system. We tested the hypothesis that prolonged exercise at terrestrial high altitude would result in interstitial oedema, quantified as B-lines by lung ultrasound, decreased respiratory reactance (X_rs) and lower respiratory resistance (R_rs), probably owing to reduced air density. Seven women, participating in the 2024 K2 female expedition, underwent respiratory oscillometry at Skardu (2228 m), Goro II (4319 m) and K2 Base Camp (5100 m) at 6 h post-arrival (K2BC1), after 24 h (K2BC2) and post-descent from camp I-II (K2BCPC; 6060 and 6654 m). The B-lines and systolic pulmonary artery pressure were assessed at Skardu, K2BC2 and K2BCPC. The inspiratory component of X_rs became more negative with increasing altitude (e.g., Skardu vs. K2BC1, -1.42 ± 0.25 vs. -1.62 ± 0.27 cmH₂O·s/L; P = 0.003), indicating reduced lung compliance. Both B-lines (1.0 ± 1.4 vs. 11.9 ± 9.3; P = 0.039) and systolic pulmonary artery pressure (21.9 ± 6.7 vs. 33.0 ± 2.7 mmHg; P < 0.001) increased significantly from Skardu to K2BCPC. The inspiratory component of R_rs decreased from Skardu to K2BC2 (2.88 ± 0.69 vs. 2.34 ± 0.82 cmH₂O·s/L; P = 0.003). In women, prolonged exercise at high altitude promotes the development of interstitial oedema (shown by the increase in B-lines), which is accompanied by a reduction in inspiratory X_rs, indicative of increased lung stiffness.