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

Abstract

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 (n = 8) or a control group (CTL, n = 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 (CVRCO2) 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 CVRCO2 parameters (e.g., relative CVRCO2 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; P = 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. NEW & NOTEWORTHY This study is the first to investigate the effects of IHC on CVRCO2 over the short- and mid-term in elderly individuals. Contrary to our initial hypothesis, 8 wk of moderate IHC did not enhance CVRCO2 at any time point.