Barometric Pressure at High Altitude: Revisiting West's Prediction Equation, and More.

Apte, Chandrashekhar V. Barometric pressure at high altitude: revisiting West's prediction equation, and more. High Alt Med Biol. 24:85-93, 2023. Introduction: Since an earlier prediction equation to calculate barometric pressure at a given altitude had been tested against limited barometric pressure observations, its accuracy needed to be re-validated against additional pressure observations. Methods: Five-year (2016-2020) barometric pressure and altitude data were downloaded from an open-source website for 25 select locations. The calculated predicted pressure was compared with mean 5-year, mean monthly, and mean daily pressures. Percent prediction error and root mean square errors were used to assess accuracy of the prediction equation. Results: The original prediction equation was accurate to within 1% for locations only within 22° latitude. It was increasingly inaccurate at higher latitudes and also for means based on shorter time spans (e.g., mean monthly and daily pressures). A new prediction equation was proposed by developing a model using downloaded data. The new equation resulted in more accurate predictions for all latitudes and all time spans. The new equation also performed well when tested at seven new locations. Conclusions: Ideally, medical professionals at high altitude should rely on actual barometric pressure observations to assess hypoxic risk. In the absence of actual measurements, the suggested new prediction equation may be used to estimate, with some limitations, the ambient barometric pressure at latitudes below 47° and altitudes up to about 4,700 m.

The maximum expiratory flow-volume loop in natives of Ladakh and acclimatized lowlanders.

Differences in static and dynamic volumes may exist between high altitude residents of Indian Himalayas and their South American counterparts, as well as with acclimatized lowlander sojourners. Maximum expiratory flow-volume loops were recorded in healthy native highlanders of Ladakh (NH, N = 75) and in healthy acclimatized lowlanders (AL, N = 32) at an altitude of 3450 m in the western Indian Himalayas. The forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1), both corrected for a height of 168 cm, were significantly higher in NH [FVC: 5.02 (0.51) vs. 3.89 (0.45) L, p < 0.0001; FEV1: 4.27 (0.47) vs. 3.44 (0.37) L, p < 0.0001]. The flow rates at larger lung volumes (PEFR, FEF25, and FEF50) were similar in the two groups. The NH showed significantly higher flow rates at low lung volumes, that is, FEF75 and FEF75-85% [FEF75: 2.03 (0.69) vs. 1.70 (0.52) L/s, p = 0.0092; FEF75-85%: 1.42 (0.54) vs. 1.06 (0.35) L/s, p = 0.0001]. The exact mechanisms allowing the higher flow rates at low lung volumes remain to be elucidated, but it is possible that these findings may indicate an inherited adaptive response in the Ladakhi highlander.