title: Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude.
abstract: 1. To assess the effects of acute exposure to high altitude on baroreceptor function in man we evaluated the effects of baroreceptor activation on R-R interval and blood pressure control at high altitude. We measured the low-frequency (LF) and high-frequency (HF) components in R-R, non-invasive blood pressure and skin blood flow, and the effect of baroreceptor modulation by 0. 1-Hz sinusoidal neck suction. Ten healthy sea-level natives and three high-altitude native, long-term sea-level residents were evaluated at sea level, upon arrival at 4970 m and 1 week later.2. Compared with sea level, acute high altitude decreased R-R and increased blood pressure in all subjects [sea-level natives: R-R from 1002+/-45 to 775+/-57 ms, systolic blood pressure from 130+/-3 to 150+/-8 mmHg; high-altitude natives: R-R from 809+/-116 to 749+/-47 ms, systolic blood pressure from 110+/-12 to 125+/-11 mmHg (P<0.05 for all)]. One week later systolic blood pressure was similar to values at sea level in all subjects, whereas R-R remained elevated in sea-level natives. The low-frequency power in R-R and systolic blood pressure increased in sea-level natives [R-R-LF from 47+/-8 to 65+/-10% (P<0.05), systolic blood pressure-LF from 1.7+/-0. 3 to 2.6+/-0.4 ln-mmHg2 (P<0.05)], but not in high-altitude natives (R-R-LF from 32+/-13 to 38+/-19%, systolic blood pressure-LF from 1. 9+/-0.5 to 1.7+/-0.8 ln-mmHg2). The R-R-HF decreased in sea-level natives but not in high-altitude natives, and no changes occurred in systolic blood pressure-HF. These changes remained evident 1 week later. Skin blood flow variability and its spectral components decreased markedly at high altitude in sea-level natives but showed no changes in high-altitude natives. Neck suction significantly increased the R-R- and systolic blood pressure-LF in all subjects at both sea level and high altitude.3. High altitude induces sympathetic activation in sea-level natives which is partially counteracted by active baroreflex. Despite long-term acclimatization at sea level, high-altitude natives also maintain active baroreflex at high altitude but with lower sympathetic activation, indicating a persisting high-altitude adaptation which may be genetic or due to baroreflex activity not completely lost by at least 1 year's sea-level residence.
authors.affiliation: Department of Internal Medicine, University of Pavia, IRCCS San Matteo, 27100 Pavia, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Bernardi
authors.forename: C
authors.initials: C
authors.lastname: Passino
authors.forename: G
authors.initials: G
authors.lastname: Spadacini
authors.forename: A
authors.initials: A
authors.lastname: Calciati
authors.forename: R
authors.initials: R
authors.lastname: Robergs
authors.forename: R
authors.initials: R
authors.lastname: Greene
authors.forename: E
authors.initials: E
authors.lastname: Martignoni
authors.forename: I
authors.initials: I
authors.lastname: Anand
authors.forename: O
authors.initials: O
authors.lastname: Appenzeller
mesh_terms: D000328:Adult; D000368:Aged; D000531:Altitude; D001794:Blood Pressure; D002319:Cardiovascular System / Q000294:innervation*; D002346:Carotid Sinus; D004562:Electrocardiography; D006339:Heart Rate; D006801:Humans; D008833:Microcirculation; D008875:Middle Aged; D011311:Pressoreceptors / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D012867:Skin / Q000098:blood supply; D013396:Suction; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors