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

Background: 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 remains unclear, particularly in older adults. Methods: Eighteen elderly individuals (62-79 years, 11 males) were randomly assigned to either an IHC (n=8) or control group (CTL, n=10). Both groups underwent 24 sessions (3 sessions/week) 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 months after (Post 2) intervention cessation. Results: 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 to 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; p=0.739). Conclusion: 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.