Abstract
Abstract only In a healthy brain, the cerebral microvessels respond to increased metabolic demand by vasodilating to increase blood flow. Reduced cerebrovascular responses to stimuli are indicative of impaired cerebrovascular functioning, and this mismatch may be a mechanism underlying age‐related reductions in cognition. The purpose of this study was to investigate how the cerebral blood flow (CBF) response to a metabolic stimulus differs between young and older participants. It has been shown that older adults have lower CBF response to chemical stimuli compared to young adults, and we hypothesized there would also be age‐associated differences in the CBF response to metabolic stimuli. We evaluated 15 young (25±1 y) and 11 older (64±1 y) habitual exercisers. Participants were instrumented with a transcranial Doppler ultrasound to measure middle cerebral artery velocity (MCAv) and a Finometer to measure beat‐to‐beat mean arterial pressure (MAP) at baseline and during two difficulty levels of the n‐back memory test. Cerebrovascular conductance index (CVCi) was calculated as MCAv/MAP. There were no group differences in BMI or resting heart rate. The older adults had a significantly higher MAP at rest compared with young adults (96±4 mmHg vs. 86±2 mmHg, respectively; p<0.05). There were no differences in MCAv at baseline. However, baseline CVCi was lower in the older adults compared with young adults (0.55±0.04 cm/s/mmHg vs. 0.70±0.06 cm/s/mmHg respectively; p<0.05). There were no differences in MCAv during either level of the test. During the level 1 test, older adults had higher MAP compared with young adults (111±6 mmHg vs. 96±3 mmHg respectively; p<0.05). During the level 2 test, the older adults again demonstrated augmented MAP compared with young adults (108±5 mmHg vs. 94±3 mmHg; p<0.05). Interestingly, older adults had a greater percent increase in CVCi compared with young adults during the level 2 test (13±3% vs. 7±2% respectively; p<0.05). Thus, while older adults had lower baseline CVCi and lower CVCi during the test, they had a greater increase in CVCi during the higher difficulty test. In summary, there were no age‐associated differences in baseline MCAv or change in MCAv during the cognitive tests, yet MAP was higher in the older adults. Therefore, our results suggest that the CBF response to an acute cognitive challenge is similar in young and older adults, but the regulatory mechanism may be different. Support or Funding Information Supported by National Institute of Health grant HL118154, and the American Physiological Society Undergraduate Research Excellence Fellowship. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .