title: Impact of body position on central and peripheral hemodynamic contributions to movement-induced hyperemia: implications for rehabilitative medicine.
abstract: This study used alterations in body position to identify differences in hemodynamic responses to passive exercise. Central and peripheral hemodynamics were noninvasively measured during 2 min of passive knee extension in 14 subjects, whereas perfusion pressure (PP) was directly measured in a subset of 6 subjects. Movement-induced increases in leg blood flow (LBF) and leg vascular conductance (LVC) were more than twofold greater in the upright compared with supine positions (LBF, supine: 462 ± 6, and upright: 1,084 ± 159 ml/min, P < 0.001; and LVC, supine: 5.3 ± 1.2, and upright: 11.8 ± 2.8 ml·min⁻¹ ·mmHg⁻¹, P < 0.002). The change in heart rate (HR) from baseline to peak was not different between positions (supine: 8 ± 1, and upright: 10 ± 1 beats/min, P = 0.22); however, the elevated HR was maintained for a longer duration when upright. Stroke volume contributed to the increase in cardiac output (CO) during the upright movement only. CO increased in both positions; however, the magnitude and duration of the CO response were greater in the upright position. Mean arterial pressure and PP were higher at baseline and throughout passive movement when upright. Thus exaggerated central hemodynamic responses characterized by an increase in stroke volume and a sustained HR response combined to yield a greater increase in CO during upright movement. This greater central response coupled with the increased PP and LVC explains the twofold greater and more sustained increase in movement-induced hyperemia in the upright compared with supine position and has clinical implications for rehabilitative medicine.
authors.affiliation: Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah, USA. joel.trinity@utah.edu
authors.forename: Joel D
authors.initials: JD
authors.lastname: Trinity
authors.forename: John
authors.initials: J
authors.lastname: McDaniel
authors.forename: Massimo
authors.initials: M
authors.lastname: Venturelli
authors.forename: Anette S
authors.initials: AS
authors.lastname: Fjeldstad
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Ives
authors.forename: Melissa A H
authors.initials: MA
authors.lastname: Witman
authors.forename: Zachary
authors.initials: Z
authors.lastname: Barrett-O'Keefe
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
authors.forename: D Walter
authors.initials: DW
authors.lastname: Wray
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D000328:Adult; D002302:Cardiac Output / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D006940:Hyperemia / Q000209:etiology* / Q000503:physiopathology*; D007866:Leg / Q000098:blood supply; D008297:Male; D009068:Movement / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D016896:Treatment Outcome