The influence of thoracic gas compression and airflow density dependence on the assessment of pulmonary function at high altitude. Issue 6 (29th March 2018)

• Record Type: Journal Article
• Authors: Cross, Troy J.; Wheatley, Courtney; Stewart, Glenn M.; Coffman, Kirsten; Carlson, Alex; Stepanek, Jan; Morris, Norman R.; Johnson, Bruce D.
• Is Part Of: Physiological reports. Volume 6:Issue 6(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-03-29
• Subjects: Airflow density dependence -- forced expiratory flows -- high altitude -- thoracic gas compression; Physiology -- Periodicals; 571
• DOI: 10.14814/phy2.13576
• Languages: English
• ISSNs: 2051-817X

Abstract

Abstract: The purpose of this report was to illustrate how thoracic gas compression (TGC) artifact, and differences in air density, may together conflate the interpretation of changes in the forced expiratory flows (FEFs) at high altitude (>2400 m). Twenty‐four adults (10 women; 44 ± 15 year) with normal baseline pulmonary function (>90% predicted) completed a 12‐day sojourn at Mt. Kilimanjaro. Participants were assessed at Moshi (Day 0, 853 m) and at Barafu Camp (Day 9, 4837 m). Typical maximal expiratory flow‐volume (MEFV) curves were obtained in accordance with ATS/ERS guidelines, and were either: (1) left unadjusted; (2) adjusted for TGC by constructing a "maximal perimeter" MEFV curve; or (3) adjusted for both TGC and differences in air density between altitudes. Forced vital capacity (FVC) was lower at Barafu compared with Moshi camp (5.19 ± 1.29 L vs. 5.40 ± 1.45 L, P < 0.05). Unadjusted data indicated no difference in the mid‐expiratory flows (FEF25–75% ) between altitudes (∆ + 0.03 ± 0.53 L sec −1 ; ∆ + 1.2 ± 11.9%). Conversely, TGC‐adjusted data revealed that FEF25–75% was significantly improved by sojourning at high altitude (∆ + 0.58 ± 0.78 L sec −1 ; ∆ + 12.9 ± 16.5%, P < 0.05). Finally, when data were adjusted for TGC and air density, FEFs were "less than expected" due to the lower air density at Barafu compared with Moshi camp (∆–0.54 ± 0.68 L sec −1 ; ∆–10.9 ± 13.0%, P < 0.05), indicating a mild obstructive defect had developed on ascent to high altitude. These findings clearly demonstrate the influence that TGC artifact, and differences in air density, bear on flow‐volume data; consequently, it is imperative that future investigators adjust for, or at least acknowledge, these confounding factors when comparing FEFs between altitudes. Abstract : The reported changes in forced expiratory flows (FEFs) in response to high‐altitude exposure are variable in the literature. This variability may be due, at least in part, to the confounding influences of thoracic gas compression artifact, and airflow density dependence, on the FEFs recorded at high altitude. In this study, FEFs were collected at 853 m (Moshi) and 4837 m (Barafu) during a 12‐day sojourn at Mt Kilimanjaro and were either left unadjusted, adjusted for differences in air density, and/or thoracic gas compression (TGC). Unadjusted data indicated little change in FEFs between altitudes, while adjusting for TGC revealed that mid‐expiratory flows improved by sojourning at the higher elevation. When data were further adjusted for airflow density dependence, FEFs at Barafu were "less than expected" compared with those at Moshi. These findings underscore the importance of adjusting FEFs for TGC and differences in air density when interpreting changes in pulmonary function across different altitudes.