title: Regulation of brain blood flow and oxygen delivery in elite breath-hold divers.
abstract: The roles of involuntary breathing movements (IBMs) and cerebral oxygen delivery in the tolerance to extreme hypoxemia displayed by elite breath-hold divers are unknown. Cerebral blood flow (CBF), arterial blood gases (ABGs), and cardiorespiratory metrics were measured during maximum dry apneas in elite breath-hold divers (n=17). To isolate the effects of apnea and IBM from the concurrent changes on ABG, end-tidal forcing ('clamp') was then used to replicate an identical temporal pattern of decreasing arterial PO2 (PaO2) and increasing arterial PCO2 (PaCO2) while breathing. End-apnea PaO2 ranged from 23 to 37 mm Hg (30 ± 7 mm Hg). Elevation in mean arterial pressure was greater during apnea than during clamp reaching +54 ± 24% versus 34 ± 26%, respectively; however, CBF increased similarly between apnea and clamp (93.6 ± 28% and 83.4 ± 38%, respectively). This latter observation indicates that during the overall apnea period IBM per se do not augment CBF and that the brain remains sufficiently protected against hypertension. Termination of apnea was not determined by reduced cerebral oxygen delivery; despite 40% to 50% reductions in arterial oxygen content, oxygen delivery was maintained by commensurately increased CBF.
authors.affiliation: Centre for Heart, Lung, and Vascular Health, School of Health and Exercise, Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Christopher 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-Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
authors.affiliation: University of Zagreb School of Kinesiology, Zagreb, Croatia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Drvis
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: David B
authors.initials: DB
authors.lastname: MacLeod
authors.affiliation: Centre for Heart, Lung, and Vascular Health, School of Health and Exercise, Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Bain
authors.affiliation: Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
authors.forename: Dennis
authors.initials: D
authors.lastname: Madden
authors.affiliation: Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
authors.forename: Petra Zubin
authors.initials: PZ
authors.lastname: Maslov
authors.affiliation: Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Dujic
mesh_terms: D000328:Adult; D001049:Apnea / Q000097:blood / Q000503:physiopathology; D001783:Blood Flow Velocity / Q000502:physiology; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000378:metabolism; D062485:Breath Holding; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004242:Diving / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology; D055815:Young Adult
chemical_list: D010100:Oxygen