Document Detail

Does cerebral oxygen delivery limit incremental exercise performance?
MedLine Citation:
PMID:  21921244     Owner:  NLM     Status:  MEDLINE    
Previous studies have suggested that a reduction in cerebral oxygen delivery may limit motor drive, particularly in hypoxic conditions, where oxygen transport is impaired. We hypothesized that raising end-tidal Pco(2) (Pet(CO(2))) during incremental exercise would increase cerebral blood flow (CBF) and oxygen delivery, thereby improving peak power output (W(peak)). Amateur cyclists performed two ramped exercise tests (25 W/min) in a counterbalanced order to compare the normal, poikilocapnic response against a clamped condition, in which Pet(CO(2)) was held at 50 Torr throughout exercise. Tests were performed in normoxia (barometric pressure = 630 mmHg, 1,650 m) and hypoxia (barometric pressure = 425 mmHg, 4,875 m) in a hypobaric chamber. An additional trial in hypoxia investigated effects of clamping at a lower Pet(CO(2)) (40 Torr) from ∼75 to 100% W(peak) to reduce potential influences of respiratory acidosis and muscle fatigue imposed by clamping Pet(CO(2)) at 50 Torr. Metabolic gases, ventilation, middle cerebral artery CBF velocity (transcranial Doppler), forehead pulse oximetry, and cerebral (prefrontal) and muscle (vastus lateralis) hemoglobin oxygenation (near infrared spectroscopy) were monitored across trials. Clamping Pet(CO(2)) at 50 Torr in both normoxia (n = 9) and hypoxia (n = 11) elevated CBF velocity (∼40%) and improved cerebral hemoglobin oxygenation (∼15%), but decreased W(peak) (6%) and peak oxygen consumption (11%). Clamping at 40 Torr near maximal effort in hypoxia (n = 6) also improved cerebral oxygenation (∼15%), but again limited W(peak) (5%). These findings demonstrate that increasing mass cerebral oxygen delivery via CO(2)-mediated vasodilation does not improve incremental exercise performance, at least when accompanied by respiratory acidosis.
Andrew W Subudhi; J Tod Olin; Andrew C Dimmen; David M Polaner; Bengt Kayser; Robert C Roach
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2011-09-15
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  111     ISSN:  1522-1601     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2011 Dec 
Date Detail:
Created Date:  2011-12-14     Completed Date:  2012-04-30     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1727-34     Citation Subset:  IM    
Altitude Research Center, Department of Emergency Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
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MeSH Terms
Anoxia / physiopathology
Bicycling / physiology
Blood Flow Velocity
Brain / metabolism
Carbon Dioxide / blood
Cerebrovascular Circulation / physiology*
Exercise / physiology*
Exercise Test
Oxygen / blood
Oxygen Consumption / physiology*
Young Adult
Grant Support
Reg. No./Substance:
124-38-9/Carbon Dioxide; 7782-44-7/Oxygen

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