Moderate intermittent hypoxic conditioning to enhance cerebrovascular function in the elderly: a randomized controlled trial

Aging is associated with cerebrovascular impairment, increasing the risk for neurovascular and degenerative diseases. Intermittent hypoxic conditioning (IHC) has been proposed as a valuable strategy to enhance vascular health. However, its effects in cerebrovascular territories remain unclear, particularly in older adults. Eighteen elderly individuals (62-79 yr, 11 males) were randomly assigned to either an IHC (<i>n</i> = 8) or a control group (CTL, <i>n</i> = 10). Both groups underwent 24 sessions (3 sessions/wk) of passive moderate exposure to either intermittent hypoxia (targeted oxygen saturation by pulse oximetry = 75%-80%) or sham hypoxia. Middle cerebral artery (MCA) reactivity to hypo- (hyperventilation task) and hypercapnia (carbon dioxide ramp administration) was assessed using transcranial Doppler ultrasound. Cerebrovascular reactivity to carbon dioxide (CVR_CO2) was evaluated in both absolute and relative changes in MCA blood velocities (MCAv), before (Pre), 3-4 days after (post 1), and 2 mo after (post 2) intervention cessation. As expected, MCAv decreased during hypocapnia (CTL = -15.7 ± 7.0 cm/s; IHC = -15.9 ± 6.0 cm/s) and increased during hypercapnia (CTL = 20.7 ± 8.4 cm/s; IHC = 18.2 ± 11.1 cm/s) at all time points in both groups. However, compared with CTL, IHC did not significantly improve any CVR_CO2 parameters (e.g., relative CVR_CO2 to hypercapnia, Pre: CTL = 4.3 ± 1.9, IHC = 3.1 ± 2.0; post 1: CTL = 4.1 ± 1.6, IHC = 3.4 ± 1.6; post 2: CTL = 4.7 ± 2.0, IHC = 3.5 ± 1.7 cm/s/mmHg; <i>P</i> = 0.739). The present work does not support the potential benefits of IHC on cerebrovascular function. However, future studies are required to confirm these preliminary results and may consider a more comprehensive appraisal of the cerebral hemodynamic control.<b>NEW & NOTEWORTHY</b> This study is the first to investigate the effects of IHC on CVR_CO2 over the short- and mid-term in elderly individuals. Contrary to our initial hypothesis, 8 wk of moderate IHC did not enhance CVR_CO2 at any time point.