title: Aging blunts hyperventilation-induced hypocapnia and reduction in cerebral blood flow velocity during maximal exercise.
abstract: Cerebral blood flow (CBF) increases from rest to ∼60% of peak oxygen uptake (VO(2peak)) and thereafter decreases towards baseline due to hyperventilation-induced hypocapnia and subsequent cerebral vasoconstriction. It is unknown what happens to CBF in older adults (OA), who experience a decline in CBF at rest coupled with a blunted ventilatory response during VO(2peak). In 14 OA (71 ± 10 year) and 21 young controls (YA; 23 ± 4 years), we hypothesized that OA would experience less hyperventilation-induced cerebral vasoconstriction and therefore an attenuated reduction in CBF at VO(2peak). Incremental exercise was performed on a cycle ergometer, whilst bilateral middle cerebral artery blood flow velocity (MCA V (mean); transcranial Doppler ultrasound), heart rate (HR; ECG) and end-tidal PCO(2) (P(ET)CO(2)) were monitored continuously. Blood pressure (BP) was monitored intermittently. From rest to 50% of VO(2peak), despite greater elevations in BP in OA, the change in MCA V(mean) was greater in YA compared to OA (28% vs. 15%, respectively; P < 0.0005). In the YA, at intensities >70% of VO(2peak), the hyperventilation-induced declines in both P(ET)CO(2) (14 mmHg (YA) vs. 4 mmHg (OA); P < 0.05) and MCA V(mean) (-21% (YA) vs. -7% (OA); P < 0.0005) were greater in YA compared to OA. Our findings show (1), from rest-to-mild intensity exercise (50% VO(2peak)), elevations in CBF are reduced in OA and (2) age-related declines in hyperventilation during maximal exercise result in less hypocapnic-induced cerebral vasoconstriction.
authors.affiliation: Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, Canada.
authors.forename: K R
authors.initials: KR
authors.lastname: Marsden
authors.forename: M J
authors.initials: MJ
authors.lastname: Haykowsky
authors.forename: J D
authors.initials: JD
authors.lastname: Smirl
authors.forename: H
authors.initials: H
authors.lastname: Jones
authors.forename: M D
authors.initials: MD
authors.lastname: Nelson
authors.forename: Luis A
authors.initials: LA
authors.lastname: Altamirano-Diaz
authors.forename: J C
authors.initials: JC
authors.lastname: Gelinas
authors.forename: Y C
authors.initials: YC
authors.lastname: Tzeng
authors.forename: K J
authors.initials: KJ
authors.lastname: Smith
authors.forename: C K
authors.initials: CK
authors.lastname: Willie
authors.forename: D M
authors.initials: DM
authors.lastname: Bailey
authors.forename: P N
authors.initials: PN
authors.lastname: Ainslie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D006985:Hyperventilation / Q000150:complications* / Q000000981:diagnostic imaging / Q000503:physiopathology; D016857:Hypocapnia / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D005082:Physical Exertion / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology*; D017585:Ultrasonography, Doppler, Transcranial; D014661:Vasoconstriction; D055815:Young Adult