Research Report
Population: Adult
Nathan Forrest Johnson, DPT, PhD, Assistant Professor, University of Kentucky nathan.johnson@uky.edu
Brian Gold, PhD, Associate Professor, University of Kentucky brian.gold@uky.edu
Alison Bailey, M.D., Director of Ambulatory and Preventive Cardiology, University of Kentucky Alison.bailey@uky.edu
Jody Clasey, PhD, Professor, University of Kentucky jlclas0@email.uky.edu
David Powell, PhD, Research Faculty, University of Kentucky david.k.powell@uky.edu
Keywords: Prevention, Cardiorespiratory Fitness, Cerebral Blood Flow, Aging
Title: Cardiorespiratory Fitness Modifies the Relationship between Cardiac Function and Cerebral Blood Flow in Older Adults
Purpose: A growing body of evidence indicates that cardiorespiratory fitness attenuates some age-related cerebral declines. However, little is known about the role that cardiac function plays in this relationship. Brain regions with high resting metabolic rates, such as the default mode network (DMN), may be especially vulnerable to age-related declines in cardiac functions affecting cerebral blood flow (BF). This study explored the relationship between a measure of myocardial mechanics, global longitudinal strain (GLS), and BF to the DMN. In addition, we explored how cardiorespiratory affects this relationship.
Subjects: Forty-two community dwelling healthy volunteers (14 males) participated in this study. Of these forty-two participants five did not complete the treadmill test because they were either currently taking a beta-blocker, they reported a history of cardiac ablation, or the supervising cardiologist terminated the test due to an abnormal EKG. One participant voluntarily terminated the test due to mouthpiece discomfort and another participant was unable to complete the MRI scan due to the presence of a scleral buckle. Finally, five participants were excluded because they failed to achieve VO2 peak. The 30 remaining participants (9 males) ranged in age from 59 to 69 (mean age = 63.73 years, SD = 2.8).
Materials/Methods: To assess GLS a limited study transthoracic echocardiogram was obtained on each participant adhering to American Society of Echocardiography (ASE) criteria. All participants completed a physician-supervised maximal graded exercise test (Max GXT) to assess VO2 peak. MRI data were collected on a 3 Tesla Siemens TIM scanner at the University of Kentucky. Intrinsic connectivity during resting state fMRI was assessed via independent component analysis (ICA). Cerebral blood flow was assessed using arterial spin labeling (ASL) MRI.
Results: Results indicated that superior cardiorespiratory fitness and myocardial mechanics were positively associated with DMN BF. Moreover, results of a mediation analysis revealed that the relationship between GLS and DMN BF was accounted for by individual differences in fitness.
Conclusions: Findings suggest that benefits of healthy cardiac function to brain function are modified by cardiorespiratory fitness.
Clinical Relevance: Physical inactivity is a significant risk factor for many chronic diseases and conditions. The benefits associated with regular physical activity extend well beyond the cardiovascular system. Maintaining or improving cardiorespiratory fitness as an older adult can have a significant impact on age-related cerebral declines. Physical therapists are in a unique position to transform society by assuming a leadership role to improve the health of our population via movement optimization.
Citation:
Johnson, Nathan Forrest, DPT, PhD; Gold, Brian T., PhD; Bailey, Alison L., M.D.; Clasey, Jody L., PhD; Powell, David K., PhD. Cardiorespiratory Fitness Modifies the Relationship between Cardiac Function and Cerebral Blood Flow in Older Adults.. Poster Presentation. IV STEP Conference, American Physical Therapy Association, Columbus, OH, July 17, 2016. Online. https://u.osu.edu/ivstep/poster/abstracts/105_johnson-et-al/