title: The impact of moderate-altitude staging on pulmonary arterial hemodynamics after ascent to high altitude.
abstract: Staged ascent (SA), temporary residence at moderate altitude en route to high altitude, reduces the incidence and severity of noncardiopulmonary altitude illness such as acute mountain sickness. To date, the impact of SA on pulmonary arterial pressure (PAP) is unknown. We tested the hypothesis that SA would attenuate the PAP increase that occurs during rapid, direct ascent (DA). Transthoracic echocardiography was used to estimate mean PAP in 10 healthy males at sea level (SL, P(B) approximately 760 torr), after DA to simulated high altitude (hypobaric chamber, P(B) approximately 460 torr), and at 2 times points (90 min and 4 days) during exposure to terrestrial high altitude (P(B) approximately 460 torr) after SA (7 days, moderate altitude, P(B) approximately 548 torr). Alveolar oxygen pressure (Pao(2)) and arterial oxygenation saturation (Sao(2)) were measured at each time point. Compared to mean PAP at SL (mean +/- SD, 14 +/- 3 mmHg), mean PAP increased after DA to 37 +/- 8 mmHg (Delta = 24 +/- 10 mmHg, p < 0.001) and was negatively correlated with both Pao(2) (r(2) = 0.57, p = 0.011) and Sao(2) (r(2) = 0.64, p = 0.005). In comparison, estimated mean PAP after SA increased to only 25 +/- 4 mmHg (Delta = 11 +/- 6 mmHg, p < 0.001), remained unchanged after 4 days of high altitude residence (24 +/- 5 mmHg, p = not significant, or NS), and did not correlate with either parameter of oxygenation. SA significantly attenuated the PAP increase associated with continuous direct ascent to high altitude and appeared to uncouple PAP from both alveolar hypoxia and arterial hypoxemia.
authors.affiliation: Massachusetts General Hospital, Boston, 02114, USA. abaggish@partners.org <abaggish@partners.org>
authors.forename: Aaron L
authors.initials: AL
authors.lastname: Baggish
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fulco
authors.forename: Stephen
authors.initials: S
authors.lastname: Muza
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rock
authors.forename: Beth
authors.initials: B
authors.lastname: Beidleman
authors.forename: Allen
authors.initials: A
authors.lastname: Cymerman
authors.forename: Kibar
authors.initials: K
authors.lastname: Yared
authors.forename: Peter
authors.initials: P
authors.lastname: Fagenholz
authors.forename: David
authors.initials: D
authors.lastname: Systrom
authors.forename: Malissa J
authors.initials: MJ
authors.lastname: Wood
authors.forename: Arthur E
authors.initials: AE
authors.lastname: Weyman
authors.forename: Michael H
authors.initials: MH
authors.lastname: Picard
authors.forename: N Stuart
authors.initials: NS
authors.lastname: Harris
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000532:Altitude Sickness / Q000097:blood / Q000503:physiopathology*; D004780:Environment, Controlled; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D009051:Mountaineering / Q000502:physiology*; D033281:Nontherapeutic Human Experimentation; D010101:Oxygen Consumption / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000502:physiology; D011651:Pulmonary Artery / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012016:Reference Values; D055815:Young Adult