title: Cerebrovascular reactivity to hypercapnia is unimpaired in breath-hold divers.
abstract: Hypercapnic cerebrovascular reactivity is decreased in obstructive sleep apnoea and congestive heart disease perhaps as a result of repeated apnoeas. To test the hypothesis that repeated apnoeas blunt cerebrovascular reactivity to hypercapnia, we studied breath hold divers and determined cerebrovascular reactivity by measuring changes in middle cerebral artery velocity (MCAV, cm s(-1)) per mmHg change in end-tidal partial pressure of CO2(PET,CO2 ) in response to two hyperoxic hypercapnia rebreathing manoeuvres (modified Read protocol) in elite breath-hold divers (BHD, n=7) and non-divers (ND, n=7). In addition, ventilation and central (beat-to-beat stroke volume measurement with Modelflow technique) haemodynamics were determined. Ventilatory responses to hypercapnia were blunted in BHD versus ND largely due to lower breathing frequency. Cerebrovascular reactivity did not differ between groups (3.7 +/- 1.4 versus 3.4 +/- 1.3% mmHg(-1) in BHD and ND, respectively; P=0.90) and the same was found for cerebral vascular resistance and MCAV recovery to baseline after termination of the CO2 challenge. Cardiovascular parameters were not changed significantly during rebreathing in either group, except for a small increase in mean arterial pressure for both groups. Our findings indicate that the regulation of the cerebral circulation in response to hypercapnia is intact in elite breath-hold divers, potentially as a protective mechanism against the chronic intermittent cerebral hypoxia and/or hypercapnia that occurs during breath-hold diving. These data also suggest that factors other than repeated apnoeas contribute to the blunting of cerebrovascular reactivity in conditions like sleep apnoea.
authors.affiliation: Department of Physiology, University of Split School of Medicine, Soltanska 2, 21000 Split, Croatia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ivancev
authors.forename: Ivan
authors.initials: I
authors.lastname: Palada
authors.forename: Zoran
authors.initials: Z
authors.lastname: Valic
authors.forename: Ante
authors.initials: A
authors.lastname: Obad
authors.forename: Darija
authors.initials: D
authors.lastname: Bakovic
authors.forename: Niki M
authors.initials: NM
authors.lastname: Dietz
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Dujic
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide; D002319:Cardiovascular System / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D004242:Diving; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D018496:Hyperoxia / Q000503:physiopathology; D020768:Middle Cerebral Artery / Q000503:physiopathology; D010313:Partial Pressure; D012119:Respiration; D015656:Respiratory Mechanics; D014655:Vascular Resistance
chemical_list: D002245:Carbon Dioxide