title: Quantitative model of hematologic and plasma volume responses after ascent and acclimation to moderate to high altitudes.
abstract: Despite decades of research, the magnitude and time course of hematologic and plasma volume (PV) changes following rapid ascent and acclimation to various altitudes are not precisely described. To develop a quantitative model, we utilized a comprehensive database and general linear mixed models to analyze 1,055 hemoglobin ([Hb]) and hematocrit (Hct) measurements collected at sea level and repeated time points at various altitudes in 393 unacclimatized men (n= 270) and women (n= 123) who spent between 2 h and 7 days at 2,500-4,500 m under well-controlled and standardized experimental conditions. The PV change (ΔPV) was calculated from [Hb] and Hct measurements during a time period when erythrocyte volume is stable. The results are1) ΔPV decreases rapidly (~6%) after the 1st day at 2,500 m and [Hb] and Hct values increase by 0.5 g/dl and 1.5 points, respectively;2) ΔPV decreases an additional 1%, and [Hb] and Hct increase an additional 0.1 g/dl and 0.2 points every 500-m increase in elevation above 2,500 m after the 1st day;3) ΔPV continues to decrease over time at altitude, but the magnitude of this decrease and subsequent increase in [Hb] and Hct levels is dependent on elevation and sex; and4) individuals with high initial levels of [Hb] and Hct and older individuals hemoconcentrate less at higher elevations. This study provides the first quantitative delineation of ΔPV and hematological responses during the first week of exposure over a wide range of altitudes and demonstrates that absolute altitude and time at altitude, as well as initial hematologic status, sex, and age impact the response.
authors.affiliation: Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts; and beth.a.beidleman.civ@mail.mil.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Beidleman
authors.affiliation: Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts; and.
authors.forename: Janet E
authors.initials: JE
authors.lastname: Staab
authors.affiliation: Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts; and.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Muza
authors.affiliation: School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Michael N
authors.initials: MN
authors.lastname: Sawka
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000375:Aging / Q000502:physiology*; D000531:Altitude; D003198:Computer Simulation; D005260:Female; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D010953:Plasma Volume / Q000502:physiology*; D012727:Sex Characteristics; D055815:Young Adult
chemical_list: D006454:Hemoglobins
keywords: altitude acclimation; fluid shifts; hematocrit; hemoglobin; hypovolemia; plasma loss