title: Interaction between central-peripheral chemoreflexes and cerebro-cardiovascular control.
abstract: We investigated the interaction between hypoxia and hypercapnia on ventilation and on cerebro-cardio-vascular control. A group of 12 healthy subjects performed rebreathing tests to determine the ventilatory response to hypoxia, at different levels of carbon dioxide (CO(2)), and to normoxic hypercapnia. Oxygen saturation (SaO(2)), end-tidal CO(2) (et-CO(2)), minute ventilation, blood pressure, R-R interval and mid-cerebral artery flow velocity (MCFV) were continuously recorded. The hypoxic ventilatory response significantly increased under hypercapnia and decreased under hypocapnia (slopes L/min/% Sa O(2): -0.33 +/- 0.05, -0.74 +/- 0.02 and -1.59 +/- 0.3, p < 0.0001, in hypocapnia, normocapnia and hypercapnia, respectively). At similar degrees of ventilation, MCFV increased more markedly during normocapnic hypoxia than normoxic hypercapnia; the slopes linking MCFV to hypoxia remained unchanged at increasing levels of et-CO(2), whereas the regression lines were shifted upward. The R-R interval decreased more markedly during normocapnic hypoxia than normoxic hypercapnia and the arterial baroreflex sensitivity was decreased only by hypoxia. Cardiovascular responses to hypoxia were not affected by different levels of et-CO(2). We conclude that concomitant hypoxia and hypercapnia, while increasing ventilation synergistically, exert an additive effect on cerebral blood flow. Increased sympathetic activity (and reduced baroreflex sensitivity) is one of the mechanisms by which hypoxia stimulates cardiac sympathetic activity.
authors.affiliation: Dept. of Internal Medicine, University of Catania, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Spicuzza
authors.forename: Cesare
authors.initials: C
authors.lastname: Porta
authors.forename: Alfina
authors.initials: A
authors.lastname: Bramanti
authors.forename: Mara
authors.initials: M
authors.lastname: Maffeis
authors.forename: Gaia
authors.initials: G
authors.lastname: Casucci
authors.forename: Nadia
authors.initials: N
authors.lastname: Casiraghi
authors.forename: Luciano
authors.initials: L
authors.lastname: Bernardi
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D012123:Pulmonary Ventilation / Q000502:physiology