Cerebrovascular responses to incremental exercise during hypobaric hypoxia: effect of oxygenation on maximal performance

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 294; no. 1; pp. H164 - H171
• Main Authors: Subudhi, Andrew W, Lorenz, Matthew C, Fulco, Charles S, Roach, Robert C
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.01.2008
• Subjects: Acute Disease; Adult; Blood Flow Velocity; Blood pressure; Cerebrovascular Circulation; Chronic Disease; Exercise; Exhalation; Fatigue; Frontal Lobe - blood supply; Frontal Lobe - metabolism; Frontal Lobe - physiopathology; Heart; Humans; Hyperoxia - metabolism; Hyperoxia - physiopathology; Hypoxia; Hypoxia - metabolism; Hypoxia - physiopathology; Inhalation; Male; Middle Cerebral Artery - physiopathology; Muscle Contraction; Muscle Fatigue; Oxygen; Oxygen Consumption; Physical Exertion; Quadriceps Muscle - metabolism; Quadriceps Muscle - physiopathology; Respiratory Mechanics; Spectroscopy, Near-Infrared; Spectrum analysis; Ultrasonography, Doppler, Transcranial
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.01104.2007

1 University of Colorado Altitude Research Center, Denver, Colorado; 2 University of Colorado at Colorado Springs, Colorado Springs, Colorado; and 3 United States Army Research Institute of Environmental Medicine, Natick, Massachusetts Submitted 24 September 2007 ; accepted in final form 19 November 2007 We sought to describe cerebrovascular responses to incremental exercise and test the hypothesis that changes in cerebral oxygenation influence maximal performance. Eleven men cycled in three conditions: 1 ) sea level (SL); 2 ) acute hypoxia [AH; hypobaric chamber, inspired P O 2 (P I O 2 ) 86 Torr]; and 3 ) chronic hypoxia [CH; 4,300 m, P I O 2 86 Torr]. At maximal work rate ( max ), fraction of inspired oxygen (F I O 2 ) was surreptitiously increased to 0.60, while subjects were encouraged to continue pedaling. Changes in cerebral (frontal lobe) (C OX ) and muscle (vastus lateralis) oxygenation (M OX ) (near infrared spectroscopy), middle cerebral artery blood flow velocity (MCA V mean ; transcranial Doppler), and end-tidal P CO 2 (P ET CO 2 ) were analyzed across % max (significance at P < 0.05). At SL, P ET CO 2 , MCA V mean , and C OX fell as work rate rose from 75 to 100% max . During AH, P ET CO 2 and MCA V mean declined from 50 to 100% max , while C OX fell from rest. With CH, P ET CO 2 and C OX dropped throughout exercise, while MCA V mean fell only from 75 to 100% max . M OX fell from rest to 75% max at SL and AH and throughout exercise in CH. The magnitude of fall in C OX , but not M OX , was different between conditions (CH > AH > SL). F I O 2 0.60 at max did not prolong exercise at SL, yet allowed subjects to continue for 96 ± 61 s in AH and 162 ± 90 s in CH. During F I O 2 0.60, C OX rose and M OX remained constant as work rate increased. Thus cerebral hypoxia appeared to impose a limit to maximal exercise during hypobaric hypoxia (P I O 2 86 Torr), since its reversal was associated with improved performance. altitude; near infrared spectroscopy; cerebral blood flow; fatigue; muscle oxygenation Address for reprint requests and other correspondence: A. W. Subudhi, Dept. of Biology, Univ. of Colorado at Colorado Springs, 1420 Austin Bluffs Parkway, Colorado Springs, Colorado 80918 (e-mail: asubudhi{at}uccs.edu )