title: Short-term intermittent hypoxia enhances sympathetic responses to continuous hypoxia in humans.
abstract: Short-term intermittent hypoxia leads to sustained sympathetic activation and a small increase in blood pressure in healthy humans. Because obstructive sleep apnea, a condition associated with intermittent hypoxia, is accompanied by elevated sympathetic activity and enhanced sympathetic chemoreflex responses to acute hypoxia, we sought to determine whether intermittent hypoxia also enhances chemoreflex activity in healthy humans. To this end, we measured the responses of muscle sympathetic nerve activity (MSNA, peroneal microneurography) to arterial chemoreflex stimulation and deactivation before and following exposure to a paradigm of repetitive hypoxic apnea (20 s/min for 30 min; O(2) saturation nadir 81.4 +/- 0.9%). Compared with baseline, repetitive hypoxic apnea increased MSNA from 113 +/- 11 to 159 +/- 21 units/min (P = 0.001) and mean blood pressure from 92.1 +/- 2.9 to 95.5 +/- 2.9 mmHg (P = 0.01; n = 19). Furthermore, compared with before, following intermittent hypoxia the MSNA (units/min) responses to acute hypoxia [fraction of inspired O(2) (Fi(O(2))) 0.1, for 5 min] were enhanced (pre- vs. post-intermittent hypoxia: +16 +/- 4 vs. +49 +/- 10%; P = 0.02; n = 11), whereas the responses to hyperoxia (Fi(O(2)) 0.5, for 5 min) were not changed significantly (P = NS; n = 8). Thus 30 min of intermittent hypoxia is capable of increasing sympathetic activity and sensitizing the sympathetic reflex responses to hypoxia in normal humans. Enhanced sympathetic chemoreflex activity induced by intermittent hypoxia may contribute to altered neurocirculatory control and adverse cardiovascular consequences in sleep apnea.
authors.affiliation: Division of Cardiology, MC H047, Heart & Vascular Institute, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, P.O. Box 850, Hershey, PA 17033, USA. uleuenberger@psu.edu
authors.forename: Urs A
authors.initials: UA
authors.lastname: Leuenberger
authors.forename: Cynthia S
authors.initials: CS
authors.lastname: Hogeman
authors.forename: Sadeq A
authors.initials: SA
authors.lastname: Quraishi
authors.forename: Sadeq
authors.initials: S
authors.lastname: Quraishi
authors.forename: Latoya
authors.initials: L
authors.lastname: Linton-Frazier
authors.forename: Kristen S
authors.initials: KS
authors.lastname: Gray
mesh_terms: D000328:Adult; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D018496:Hyperoxia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D010100:Oxygen