Aging blunts hyperventilation-induced hypocapnia and reduction in cerebral blood flow velocity during maximal exercise

Cerebral blood flow (CBF) increases from rest to ∼60% of peak oxygen uptake (VO2peak) 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 VO2peak. 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 VO2peak. 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 PCO2 (PETCO2) were monitored continuously. Blood pressure (BP) was monitored intermittently. From rest to 50% of VO2peak, 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 70% of VO2peak, the hyperventilation-induced declines in both PETCO2 (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% VO2peak), elevations in CBF are reduced in OA and (2) age-related declines in hyperventilation during maximal exercise result in less hypocapnic-induced cerebral vasoconstriction.