Cardiorespiratory fitness modifies the relationship between arterial stiffness and cerebral blood flow independent of physical activity

Abstract

Introduction: Central arterial stiffness and cerebral blood flow (CBF) are inversely related. Poor cardiorespiratory fitness (CRF) and low physical activity (PA) are related to both higher arterial stiffness and lower CBF. The present study examined (i) whether CRF or PA moderate the relationship between arterial stiffness and CBF, and (ii) whether the intensity or the type of PA needs to be considered.

Methods: Participants (N = 78, Mean_AGE = 64.2±6.14, 72% female) from the Wisconsin Registry for Alzheimer's Prevention and the Wisconsin Alzheimer's Disease Research Center were categorized into low, average, and high fitness groups based on maximal graded exercise treadmill test performance. PA was assessed using the CHAMPS (Community Health Activities Model Program for Seniors) questionnaire. Based on hours/week, participants were classified as meeting the recommended 2.5 h of moderate intensity PA per week (PA Rec Met). Weekly hours of moderate and low intensity PA were calculated as activities of > 3 or < 3 metabolic equivalents, respectively. Activity type was categorized as exercise-, sports/leisure- and work-related. Arterial stiffness was measured as aortic pulse wave velocity (aoPWV) by 2D phase contrast magnetic resonance imaging (MRI). CBF was assessed by 4D flow MRI in the internal carotid arteries (ICAs), cavernous ICAs, middle cerebral arteries (MCAs), and via two composite measures of total and global flow.

Results: The association between aoPWV and CBF differed by fitness levels, with a negative relationship in the low fitness group and positive relationships in the average and high fitness groups (all Ps<0.05). Significant moderating effects on the relationships between aoPWV and CBF were also observed for PA Rec Met (all Ps<0.05), moderate intensity (p = 0.05), and exercise-related (all p's < 0.02) PA.

Discussion: Average or high fitness, meeting the PA guidelines, and more specifically, moderate intensity and exercise-related PA seem to attenuate the negative relationship between aoPWV on CBF.

Highlights: Higher cardiorespiratory fitness (CRF) reduces the negative impact of aortic pulse wave velocity (aoPWV) on cerebral blood flow (CBF)150 min of moderate physical activity (PA) also mitigates this impact, depending on activity typeInnovative methods: use of cardiac magnetic resonance imaging (MRI) for aoPWV assessmentInnovative methods: use of free-breathing acquisition during cardiac MRIInnovative methods: use of cranial 4D flow MRI for CBF assessment.

Keywords: Alzheimer's disease; aortic stiffness; cardiorespiratory fitness; cerebral hemodynamics; physical activity.

FIGURE 1

Physical activity scoring instructions. The community health activities model program for seniors (CHAMPS) Questionnaire items for each category are reflected in the figure. The intensity for each activity (METs) as well as total physical activity (hours/week) was calculated as the sum of all activities according to the original reference. Meeting the Physical Activity Recommendations (PA Rec Met; yes/no) was calculated as achieving ≥ 2.5 h (150 min) of moderate intensity activity in a week. Moderate‐intensity PA (hours/week) was defined as any PA ≥ 3 METs, while low‐intensity PA (hours/week) was defined as any PA < 3 METs. Of 52 participants who were classified as physically active, determined by moderate intensity activities, 25 also completed some level of vigorous intensity activity (≥6 METs). We opted to combine them under the moderate intensity grouping for analysis purposes because the low variation in vigorous activity rendered subgroups underpowered when modeling vigorous PA as a separate group. PA type (hours/week) was investigated as exercise, leisure/sports, and work‐related activities, and were classified as such based on the World Health Organization's “Global Recommendations on Physical Activity for Health”. Exercise‐related PA was defined as activities traditionally aimed at increasing a component of physical fitness, like cycling, swimming, running, walking, or strength training. Leisure/sports‐related activities were defined as leisure or recreational related sporting activities, like dancing, golf, basketball, soccer, racquetball, and gentle swimming, and work‐related activities were defined as tasks performed to maintain and manage a home or as part of an occupation.