title: Myogenic responses occur on a beat-to-beat basis in the resting human limb.
abstract: Investigations of human myogenic responses typically use maneuvers that evoke robust changes in transmural pressure. Although this strategy has demonstrated peripheral myogenic responsiveness in the limbs, particularly in glabrous skin of the hand or foot, it has not considered the potential influence of the myogenic mechanism in beat-to-beat blood flow (BF) control during unprovoked rest. In the present study, we examined the interactions of spontaneous beat-to-beat mean arterial pressure (MAP; Finapres) with BF (Doppler ultrasound) supplying the forearm (brachial artery), lower leg (popliteal artery), and hand (ulnar artery) during 10 min of supine rest in healthy young men. Cross-correlation analyses revealed a negative association between MAP and BF, which was more prominent in the forearm than lower leg. The strongest correlation resulted when a -2-heart beat offset of MAP was applied (R=-0.53±0.04 in the forearm and -0.23±0.05 in the leg, P<0.05), suggesting an ∼2-s delay from instances of high/low MAP to low/high BF. Negatively associated episodes (high MAP/low BF and low MAP/high BF) outnumbered positively associated data (P<0.05). BF during low MAP values was greater than the steady-state average BF and vice versa. Wrist and ankle occlusion blunted the strength of correlations, homogenized the incidence of MAP and BF pairings, and reduced the magnitude of deviation from steady-state values. In contrast, these relationships were matched or accentuated for hand BF. Overall, these results suggest that myogenic responses are present and occur rapidly in human limbs during rest, overwhelm perfusion pressure gradient influences, and are primarily mediated by the distal limb circulation.
authors.affiliation: Department of Biomedical Sciences, University of Missouri, Columbia, Missouri;
authors.forename: Seth T
authors.initials: ST
authors.lastname: Fairfax
authors.affiliation: Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri; Department of Child Health, University of Missouri, Columbia, Missouri; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri;
authors.forename: Jaume
authors.initials: J
authors.lastname: Padilla
authors.affiliation: Department of Physical Education, University of Brasilia, Brasilia, Brazil.
authors.forename: Lauro C
authors.initials: LC
authors.lastname: Vianna
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and.
authors.forename: Seth W
authors.initials: SW
authors.lastname: Holwerda
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Davis
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and fadelp@health.missouri.edu.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Fadel
mesh_terms: D000328:Adult; D062186:Arterial Pressure; D001783:Blood Flow Velocity; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D005542:Forearm / Q000098:blood supply*; D006225:Hand / Q000098:blood supply*; D006339:Heart Rate; D006706:Homeostasis; D006801:Humans; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D008955:Models, Cardiovascular; D011150:Popliteal Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D012039:Regional Blood Flow; D012146:Rest; D013997:Time Factors; D017535:Ulnar Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D018608:Ultrasonography, Doppler
keywords: blood flow; brachial artery; popliteal artery; vascular regulation