Characterization of Middle Cerebral Artery Velocity Kinetics in Response to Isometric Handgrip Exercise in Healthy Adults

Abstract

Cerebral blood flow (CBF) is known to increase in response to both dynamic and isometric exercise. However, middle cerebral artery blood velocity (MCAv) kinetics in response to small-muscle isometric exercise, and sex differences in this kinetic response, require further investigation. Previous work suggests that MCAv response times to stressors may be indicative of cerebrovascular function, so the kinetics of this response to isometric exercise would add to the understanding of cerebrovascular health. The objective of this study was to characterize MCAv kinetics in response to isometric handgrip exercise and investigate potential sex differences in the response. We expected that MCAv at baseline would be higher in females than in males. However, we hypothesized that this sex difference would disappear during isometric handgrip exercise. In addition, we hypothesized that the time constant (τ) would be shorter in females compared with males, with a higher maximum response amplitude in females compared with males. Twenty-six healthy older adults with an average age of 56.8 ± 5.0 years (11 male (M) – aged 59.4 ± 4.8 years; 15 female (F) – aged 54.6 ± 4.1 years) completed an isometric handgrip exercise protocol. The exercise protocol consisted of the following: 1) performing a maximum voluntary contraction (MVC) with a handgrip device in the participants’ left hand (on a separate visit); 2) performing a sustained contraction until failure at 40% of the participant’s MVC. MCAv was continuously measured at rest and during handgrip exercise. The time constant was calculated as 63% of the time until steady-state MCAv during handgrip exercise. There was a trend for higher MCAv at baseline (57.8 ± 11.0 cm/s) in females (61.5 ± 11.2 cm/s) compared with males (53.6 ± 9.6 cm/s) that did not reach significance (p=0.08). There were no significant differences between the sexes for max amplitude of MCAv response to isometric handgrip exercise (M: 20.7 ± 11.1 cm/s; F: 15.4 ± 10.0 cm/s; p = 0.24) or time constant (M: 20.5 ± 9.8 sec; F: 18.6 ± 11.3 sec; p = 0.65). These results suggest no significant differences in MCAv between males and females at baseline. There also appear to be no significant sex differences in the kinetic response of MCAv to handgrip exercise. Future work could model MCAv kinetics in response to isometric handgrip exercise. The relationship between age and MCAv kinetics could also be investigated, along with the effect of menopause on MCAv kinetics in females. American Heart Association (19IPLOI34680015; JNB); American Heart Association COVID Supplement (19IPLOI34680015; JNB). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.