title: Cerebral and muscle tissue oxygenation in acute hypoxic ventilatory response test.
abstract: Eight men were exposed to progressive isocapnic hypoxia for 10 min to test the hypothesis that (i) cerebral and muscle tissue would follow similar deoxygenation profiles during an acute hypoxic ventilatory response (AHVR) test; and (ii) strong cerebrovascular responsiveness to hypoxia would be related to attenuated cerebral deoxygenation. End-tidal O(2) concentration was reduced from normoxia (approximately 102 mmHg) to approximately 45 mmHg while arterial oxygen saturation (SpO2 %) declined from 98+/-1% to 77+/-7% (P<0.001). Near-infrared spectroscopy (NIRS)-derived local cerebral tissue (frontal lobe) deoxyhemoglobin increased 5.55+/-2.22 microM, while oxyhemoglobin and tissue oxygenation index decreased 2.57+/-1.99 microM and 6.2+/-3.4%, respectively (all P<0.001). In muscle (m. vastus lateralis) the NIRS changes from the initial normoxic level were non-significant. Cerebral blood velocity (V(mean), transcranial Doppler) in the middle cerebral artery increased from 53.4+/-10.4 to 60.6+/-11.6 cms(-1) (P<0.001). In relation to the decline in SpO2 % the mean rate of increase of V(mean) and AHVR were 0.33+/-0.19 cms(-1)%(-1) and 0.52+/-0.20l min(-1)%(-1), respectively. We conclude that cerebral, but not muscle, tissue shows changes reflecting a greater deoxygenation during acute hypoxia. However, the changes in NIRS parameters were not related to cerebrovascular responsiveness or ventilatory chemosensitivity during graded hypoxia.
authors.affiliation: Unit for Sports and Exercise Medicine, Institute of Clinical Medicine, University of Helsinki, Helsinki, Finland. juha.peltonen@helsinki.fi
authors.forename: Juha E
authors.initials: JE
authors.lastname: Peltonen
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
authors.forename: Darren S
authors.initials: DS
authors.lastname: DeLorey
authors.forename: Gregory R
authors.initials: GR
authors.lastname: duManoir
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Petrella
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000208:Acute Disease; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D001923:Brain Chemistry / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D002534:Hypoxia, Brain / Q000503:physiopathology; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology; D019265:Spectroscopy, Near-Infrared; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D006454:Hemoglobins; D002245:Carbon Dioxide; D010100:Oxygen