Interstitial lung fluid balance in healthy lowlanders exposed to high-altitude

•We aimed to assess lung fluid balance before and after gradual ascent to 5,150 m.•Lung diffusing capacity increased from sea-level to high-altitude;.•Alveolar-capillary membrane conductance also increased from sea-level to high-altitude;.•Gradual non-significant reduction in ultrasound lung comets with altitude;.•Evidence of a decrease in interstitial lung fluid relative to at sea-level with gradual ascent to high-altitude.

We aimed to assess lung fluid balance before and after gradual ascent to 5150 m. Lung diffusion capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (DmCO) and ultrasound lung comets (ULCs) were assessed in 12 healthy lowlanders at sea-level, and on Day 1, Day 5 and Day 9 after arrival at Mount Everest Base Camp (EBC). EBC was reached following an 8-day hike at progressively increasing altitudes starting at 2860 m. DLCO was unchanged from sea-level to Day 1 at EBC, but increased on Day 5 (11 ± 10%) and Day 9 (10 ± 9%) vs. sea-level (P ≤ 0.047). DmCO increased from sea-level to Day 1 (9 ± 6%), Day 5 (12 ± 8%), and Day 9 (17 ± 11%) (all P ≤ 0.001) at EBC. There was no change in ULCs from sea-level to Day 1, Day 5 and Day 9 at EBC. These data provide evidence that interstitial lung fluid remains stable or may even decrease relative to at sea-level following 8 days of gradual exposure to high-altitude in healthy humans.