Cardiorespiratory Fitness And Aortic Hemodynamics Are Associated With Brain Volume In Healthy Older Adults

Abstract

Cardiorespiratory fitness (CFR) is positively associated with greater brain volume in older adults; however, the mechanism is unknown. Improved structure and function of the large vessels supplying the brain due to habitual exercise may explain why CFR influences brain volume. PURPOSE: The purpose of this study was to determine if aortic hemodynamics modify the association between CFR and brain volume in both young and older adults. METHODS: Young (YA; n =27, age =25±5 y, women =15) and older (OA; n =23, age =64±5 y, women =11) healthy adults ranging from sedentary to exercise trained were studied. CFR was assessed using an incremental maximal exercise test on a cycle ergometer (VO2max). Total brain volume (gray matter + white matter) was determined using a T1 weighted scan on a 3T MRI scanner. Aortic hemodynamics were obtained from applanation tonometry (SphygmoCor) where the aortic pressure waveform was used to calculate aortic augmentation index (AIx). RESULTS: Young adults had a larger total brain volume (YA; 1.16±0.02 l vs. OA; 1.10±0.02 l, p<0.05), higher VO2 max (YA; 40±1 ml/kg/min vs. OA; 32±2 ml/kg/min, p<0.05), and lower AIx (YA; 2.9±2.5 % vs. OA; 19.2±2.4 %, p<0.05) compared with older adults. VO2max was not associated with AIx in young adults (p>0.05); however, VO2max was negatively associated with AIx in older adults (r =-0.61, p<0.05) such that older adults with higher CFR demonstrated lower aortic hemodynamics. There were no associations between VO2max, AIx, and total brain volume in young adults (p>0.05 for all). Conversely, both VO2max (r =0.51, p<0.05) and AIx (r =-0.64, p<0.05) were associated with total brain volume in older adults. When VO2max and AIx were entered into the model using multiple linear regression, VO2max was no longer a significant predictor of total brain volume in older adults (VO2max; p =0.41, AIx; p =0.03). CONCLUSIONS: High CFR and low aortic hemodynamics are associated with larger total brain volumes in older adults. Using multiple linear regression, aortic hemodynamics are a better predictor of total brain volume than CFR in older adults. Improved aortic hemodynamics may be a mechanism by which habitual exercise protects the brain from age-related volume decline. Supported by NIH grant HL118154.