title: Can a combination of handgrip exercise and prolonged forearm occlusion elicit a maximal brachial artery FMD response?
abstract: BACKGROUND
  The upper limit of brachial artery (BA) flow-mediated dilation (FMD) has not been thoroughly interrogated, and long duration occlusion + handgrip exercise may create larger shear stress stimuli than previous manipulations.
  
  
  OBJECTIVE
  To determine whether novel combinations of occlusion + handgrip exercise can extend the range of FMD stimulus-response relationship characterization and permit identification of a BA-FMD response ceiling.
  
  
  METHODS
  Ten healthy subjects performed eight reactive hyperemia (RH) FMD trials: 5, 10, and 15 min of occlusion (5RH, 10RH, 15RH); 5, 10 and 15 min of occlusion + 3-min ischemic exercise (IE) (5IE, 10IE, 15IE); 10 and 15 min of occlusion + 3-min IE + 4-min post-occlusion exercise (PE) (10IEPE, 15IEPE). Shear stress was estimated as shear rate (SR = blood velocity/BA diameter; (ultrasound assessment)) (SR stimulus = area under the curve (AUC) until peak diameter). Data are mean ± SE.
  
  
  RESULTS
  There were no differences in SR-AUC among IE and IEPE trials (p > 0.70), however, IE consistently increased the SR-AUC (IE + IEPE trial average 17,845.1 ± 2,023.3 a.u.) vs. the 5RH and 10RH trials (4,943.0 ± 428.4 a.u., 6,800.6 ± 805.9 a.u.) (p < 0.05). The %FMD ranged from 7.3 ± 0.8% (5RH) to 19.1 ± 2.0% (15IEPE) (p < 0.001) with no differences among IE and IEPE trials (p > 0.16). FMD increased with increasing SR-AUC (all subjects, all trials: r(2) 0.36, p < 0.001) CONCLUSIONS: The stimulus created by brief (5 min) occlusion + ischemic exercise was not significantly enhanced by prolonging occlusion or continuing to exercise post-occlusion. The FMD response did not clearly plateau with increasing stimulus magnitude; however, the FMD capacity was shown to be more than double the FMD magnitude that was elicited with a standard 5-min occlusion test.
authors.affiliation: Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, Kingston, ON, K7L 3N6, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Ku
authors.forename: Alana
authors.initials: A
authors.lastname: McEvoy
authors.forename: Kyra E
authors.initials: KE
authors.lastname: Pyke
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001916:Brachial Artery / Q000502:physiology*; D015444:Exercise; D005260:Female; D005542:Forearm / Q000098:blood supply / Q000502:physiology*; D018737:Hand Strength; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D008297:Male; D011930:Reaction Time; D012039:Regional Blood Flow; D014664:Vasodilation