title: Influence of high altitude on cerebral blood flow and fuel utilization during exercise and recovery.
abstract: We examined the hypotheses that: (1) during incremental exercise and recovery following 4-6 days at high altitude (HA) global cerebral blood flow (gCBF) increases to preserve cerebral oxygen delivery (CDO2) in excess of that required by an increasing cerebral metabolic rate of oxygen ( CM RO2); (2) the trans-cerebral exchange of oxygen vs. carbohydrates (OCI; carbohydrates = glucose + ½lactate) would be similar during exercise and recovery at HA and sea level (SL). Global CBF, intra-cranial arterial blood velocities, extra-cranial blood flows, and arterial-jugular venous substrate differences were measured during progressive steady-state exercise (20, 40, 60, 80, 100% maximum workload (Wmax)) and through 30 min of recovery. Measurements (n = 8) were made at SL and following partial acclimatization to 5050 m. At HA, absolute Wmax was reduced by ∼50%. During submaximal exercise workloads (20-60% Wmax), despite an elevated absolute gCBF (∼20%, P < 0.05) the relative increases in gCBF were not different at HA and SL. In contrast, gCBF was elevated at HA compared with SL during 80 and 100% Wmax and recovery. Notwithstanding a maintained CDO2 and elevated absolute CM RO2 at HA compared with SL, the relative increase in CM RO2 was similar during 20-80% Wmax but half that of the SL response (i.e. 17 vs. 27%; P < 0.05 vs. SL) at 100% Wmax. The OCI was reduced at HA compared with SL during 20, 40, and 60% Wmax but comparable at 80 and 100% Wmax. At HA, OCI returned almost immediately to baseline values during recovery, whereas at SL it remained below baseline. In conclusion, the elevations in gCBF during exercise and recovery at HA serve to maintain CDO2. Despite adequate CDO2 at HA the brain appears to increase non-oxidative metabolism during exercise and recovery.
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada kurt.smith@ubc.ca.
authors.forename: K J
authors.initials: KJ
authors.lastname: Smith
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA.
authors.forename: D
authors.initials: D
authors.lastname: MacLeod
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
authors.forename: C K
authors.initials: CK
authors.lastname: Willie
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
authors.forename: N C S
authors.initials: NC
authors.lastname: Lewis
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
authors.forename: R L
authors.initials: RL
authors.lastname: Hoiland
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA.
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
authors.forename: M M
authors.initials: MM
authors.lastname: Tymko
authors.affiliation: University of Otago, Dunedin, New Zealand University Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
authors.forename: J
authors.initials: J
authors.lastname: Donnelly
authors.affiliation: Department of Biology, Mount Royal Univeristy, Calgary, AB, Canada.
authors.forename: T A
authors.initials: TA
authors.lastname: Day
authors.affiliation: Carolina Friends School, Durham, NC, USA.
authors.forename: N
authors.initials: N
authors.lastname: MacLeod
authors.affiliation: University of Otago, Dunedin, New Zealand University of Birmingham, Birmingham, UK.
authors.forename: S J E
authors.initials: SJ
authors.lastname: Lucas
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
authors.forename: P N
authors.initials: PN
authors.lastname: Ainslie
mesh_terms: D000328:Adult; D000531:Altitude; D001921:Brain / Q000098:blood supply / Q000378:metabolism* / Q000502:physiology; D050260:Carbohydrate Metabolism; D002560:Cerebrovascular Circulation; D015444:Exercise; D006801:Humans; D008297:Male; D010101:Oxygen Consumption