title: Effect of high altitude and exercise on microvascular parameters in acclimatized subjects.
abstract: The role of microvascular fluid shifts in the adaptation to hypobaric hypoxia and its contribution to the pathophysiology of AMS (acute mountain sickness) is unresolved. In a systematic prospective study, we investigated the effects of hypobaric hypoxia and physical exercise alone, and in combination, on microvascular fluid exchange and related factors. We used computer-assisted VCP (venous congestion plethysmography) on the calves of ten altitude-acclimatized volunteers. We investigated the effects of: (i) actively climbing to an altitude of 3196 m, (ii) airlifting these subjects to the same altitude, and (iii) exercise at low altitude. CFC (capillary filtration capacity), Pvi (isovolumetric venous pressure) and Qa (calf blood flow) were assessed before and after each procedure and then repeated after an overnight rest. Measurements of CFC showed no evidence of increased microvascular permeability after any of the procedures. Pvi was significantly decreased (P<0.001) from 20.3+/-4.4 to 8.9+/-4.3 mmHg after active ascent, and was still significantly lower (P=0.009) after overnight rest at high altitude (13.6+/-5.9 mmHg). No such changes were observed after the passive ascent (16.7+/-4.0 mmHg at baseline; 17.3+/-4.5 mmHg after passive ascent; and 19.9+/-5.3 mmHg after overnight rest) or after exercise at low altitude. After the active ascent, Qa was significantly increased. We also found a significant correlation between Qa, Pvi and the number of circulating white blood cells. In conclusion, we found evidence to support the hypothesis that increased microvascular permeability associated with AMS does not occur in acclimatized subjects. We also observed that the microvascular equilibrium pressure (Pvi) fell in inverse relation to the increase in Qa, especially in hypoxic exercise. We hypothesize that this inverse relationship reflects the haemodynamic changes at the microvascular interface, possibly attributable to the flow-induced increases in endothelial surface shear forces.
authors.affiliation: Clinic for Anaesthesiology, Ludwig-Maximilians University Munich, Marchioninistr. 15, 81377 Munich, Germany. andreas.bauer@med.uni-muenchen.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Bauer
authors.forename: Florian
authors.initials: F
authors.lastname: Demetz
authors.forename: Dirk
authors.initials: D
authors.lastname: Bruegger
authors.forename: Martin
authors.initials: M
authors.lastname: Schmoelz
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schroepfer
authors.forename: André
authors.initials: A
authors.lastname: Martignoni
authors.forename: Heiko
authors.initials: H
authors.lastname: Baschnegger
authors.forename: Josef
authors.initials: J
authors.lastname: Hoelzl
authors.forename: Manfred
authors.initials: M
authors.lastname: Thiel
authors.forename: Alexander
authors.initials: A
authors.lastname: Choukér
authors.forename: Klaus
authors.initials: K
authors.lastname: Peter
authors.forename: John
authors.initials: J
authors.lastname: Gamble
authors.forename: Frank
authors.initials: F
authors.lastname: Christ
mesh_terms: D000064:Acclimatization; D000328:Adult; D000531:Altitude; D000704:Analysis of Variance; D001794:Blood Pressure; D002199:Capillary Permeability; D015444:Exercise; D006339:Heart Rate; D006801:Humans; D007866:Leg / Q000098:blood supply; D008297:Male; D009051:Mountaineering; D010100:Oxygen / Q000097:blood; D010991:Plethysmography; D012039:Regional Blood Flow
chemical_list: D010100:Oxygen