Vascular Reactivity to Rhythmic Handgrip at Altitude

• Author / Creator

  Maier, Lauren

• Background: During exercise, there is an increase in sympathetic activity, causing vasoconstriction and reduced blood flow. However, to maintain blood flow and oxygen delivery to the exercising skeletal muscle, a phenomenon known as sympatholysis occurs, which is the reduction in sympathetic vasoconstriction. Evidence suggests that young males and females regulate peripheral blood flow differently in response to stressors, including exercise, but the underlying mechanisms for these differences are unclear. Further, the influence of hypoxia on this relationship is poorly understood. Therefore, the purpose of this thesis was to examine the sympathetic control of the vasculature during rhythmic handgrip exercise and explore any sex-based differences.
  Methods: 8 young, healthy participants (4M/4F) were tested at both low (Kelowna, BC; 344m) and high (Barcroft Station, White Mountain; 3800m) altitude during early acclimatization (days 3-11). A larger set of participants were tested at low (n=10; 4M/6F) and high (n=14; 8M/6F) altitude and will be reported separately. Participants performed 3 minutes of rhythmic handgrip exercise at 25% of their maximal voluntary contraction during local infusions of saline, propranolol (beta-blockade), and propranolol plus phentolamine (combined alpha-beta-blockade). Doppler ultrasound was used to examine brachial artery blood flow (FBF) and calculate forearm vascular conductance (FVC).
  Results: There was a main effect of condition on FBF (p=0.01), but no effect of altitude exposure (p=0.99) [low altitude (control, 0.18 ± 0.06; beta-blockade, 0.21 ± 0.07; alpha-beta-blockade, 0.26 ± 0.05 mL/min/100mL FAV), high altitude (control, 0.16 ± 0.04; beta-blockade, 0.27 ± 0.06; alpha-beta-blockade, 0.31 ± 0.07 mL/min/100mL FAV)]. Condition had a main effect on the change in FVC (p=0.02), but altitude exposure did not (p=0.50). The change in FVC during exercise at low altitude was significantly less during alpha-beta-blockade (3 ± 5 a.u.) compared to beta-blockade (14 ± 3 a.u.), but not control (10 ± 7 a.u.). At altitude FVC response during exercise was less during alpha-beta-blockade (5 ± 5 a.u.) compared to control (11 ± 4 a.u.), but not beta-blockade (13 ± 5 a.u.). Sex had an effect on FVC during exercise at high altitude (p=0.02), but not at low altitude (p=0.94). Males showed a greater FVC during exercise at altitude compared to females.
  Conclusions: This study demonstrated the importance of alpha-adrenergic receptors in the blood flow response to exercise. It showed that there was no difference in the blood flow response with altitude exposure, suggesting exercise hyperemia is preserved in mild-moderate exercise during early acclimatization. However, males and females may respond differently to an exercise stimulus during high altitude hypoxia exposure; this study suggests males have a greater blood flow response at altitude. Indeed, there may be an interaction between exercise and hypoxia that differentiates how males and females regulate exercising blood flow.

• Subjects / Keywords

  • altitude
  • blood flow
  • exercise

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-3tkg-qm82

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.