(555.19) Intracranial Cerebrovascular Reactivity by Traditional and Novel Methods in Young, Middle, and Old Aged Healthy Males and Females

Poster Board Number: E79

Jodie Koep (University of Queensland, University of Queensland), Jeff Coombes (University of Queensland), Alan Barker (University of Exeter), Chloe Taylor (Western Sydney University), Faith Pizzey (University of Queensland), Stefanie Ruediger (University of Queensland), Bert Bond (University of Exeter), Tom Bailey (University of Queensland, University of Queensland)

Objective: Lower cerebrovascular reactivity (CVR) to hypercapnia is associated with increased risk of age-related cognitive decline and all-cause mortality. Despite the important clinical implications of CVR, evidence of the physiological changes across the healthy adult lifespan is conflicting, with limited findings in females. The aim of this study was to assess the effect of age and sex on CVR. We hypothesized: 1) CVR to be lower in middle-aged and older compared to young adults, and 2) a higher CVR in young females compared with young males, and a higher CVR in older males than older females.

Methods: Young (n=25, 12 female, age 27±1.5y), middle-age (n=31, 18 female, age 54±7.3y) and older healthy participants (n=20, 10 female, age 70±2.5y) completed CVR via inhalation of 5% carbon dioxide (CO2) for 5 minutes. Traditional CVR was characterized by the peak middle cerebral artery velocity (MCAv) response per mmHg increase in end-tidal CO2 (traditional cm/s-1mmHg), and using a novel mono-exponential model to characterize the dynamic onset response of the MCAv. Independent samples ANOVA was used to compare main and interaction effects of age and sex.

Results: Traditional CVR was not different between young, middle and older groups (2.0±0.7 vs 1.8±0.9 vs 1.9±0.9 cm/s-1mmHg; P=0.102). Dynamic onset (novel) responses revealed the time constant of the MCAv response was significantly slower in older and middle-aged compared to young adults (29±16 vs 27±20 vs 14±9 seconds, P=0.03). No effects of sex were observed for traditional or novel CVR (P≥0.14), but young females had a higher baseline MCAv than young males (70.8 vs 78.6 cm/s-1 P=0.04), which was not observed in middle and older age adults.

Conclusions: CVR is preserved in ageing adults, but the speed of the MCAv response is blunted in older and middle-aged adults compared to young adults. Utilizing dynamic onset responses reveal underlying differences in cerebral regulation with healthy ageing that were not detected by traditional methods.