Effects of cardiorespiratory fitness and exercise training on cerebrovascular blood flow and reactivity: a systematic review with meta-analyses

• Published in: American journal of physiology. Heart and circulatory physiology 2021-07, Vol.321 (1), p.H59-H76
• Main Authors: Smith, Emily C, Pizzey, Faith K, Askew, Christopher D, Mielke, Gregore I, Ainslie, Philip N, Coombes, Jeff S, Bailey, Tom G
• Format: Article
• Language: English
• Subjects: Athletes; Blood flow; Cardiorespiratory fitness; Cerebral blood flow; Confidence intervals; Fitness training programs; Magnetic resonance imaging; Physical fitness; Physical training; Quality; Reactivity; Reviews; Systematic review; Training; Ultrasound
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00880.2020

We address two aims; Aim 1 (Fitness Review) compare the effect of higher cardiorespiratory fitness (CRF) (e.g. endurance athletes) with lower CRF (e.g. sedentary adults) on cerebrovascular outcomes, including middle cerebral artery velocity (MCAv) as assessed by Transcranial Doppler (TCD) or Magnetic Resonance Imaging (MRI). Aim 2 (Exercise Training Review) determine the effect of exercise training on cerebrovascular outcomes. Systematic review of studies with meta-analyses where appropriate. Certainty of evidence was assessed by Grading of Recommendations Assessment, Development and Evaluation (GRADE). Twenty studies (18 using TCD) met the eligibility criteria for Aim 1 and 14 studies (8 using TCD) were included for Aim 2. There was a significant effect of higher compared with lower CRF on cerebrovascular resistance index (effect size, 95% confidence interval), (-0.54, -0.91 to -0.16) and cerebrovascular reactivity (0.98, 0.41 to 1.55). Studies including males only demonstrated a greater effect of higher CRF on cerebrovascular resistance index than mixed or female studies (male only: -0.69, -1.06 to -0.32, mixed and female studies (0.10, -0.28 to 0.49). Exercise training did not increase MCAv (0.05, -0.21 to 0.31), although there was a small improvement trending to significant in cerebrovascular reactivity (0.60, -0.08 to 1.28; p=0.09). Exercise training showed heterogeneous effects on regional, but little effect on global cerebral blood flow as measured by MRI. High CRF positively effects cerebrovascular function, including decreased CVRi and increased CVR however, global cerebral blood flow and MCAv is primarily unchanged following an exercise intervention in healthy and clinical populations.