title: Retrograde arterial leg blood flow during tilt-back from a head-up posture: importance of capacitive flows when arterial pressure changes.
abstract: The windkessel function of the arterial system converts the intermittent action of the heart into more continuous microcirculatory blood flow during diastole via the return of elastic energy stored in the walls of the arteries during systole. Might the same phenomenon occur regionally within the arterial system during tilting owing to regional differences in local arterial pressure imposed by gravity? We sought to test the hypothesis that during tilt-back from a head-up posture, the return of stored elastic energy in leg arteries would work to slow, or perhaps transiently reverse, the flow of blood in the femoral artery. Femoral artery blood flow and arterial pressure were recorded during tilt back from a 30 degrees head-up posture to supine (approximately 0.5 G) in young, healthy subjects (n = 7 males and 3 females) before and during clonidine infusion. During control (no drug) conditions femoral artery blood flow ceased for an entire heart beat during tilt-back. During clonidine infusion femoral artery blood flow reversed for at least one entire heart beat during tilt-back, i.e., blood flow in the retrograde direction in the femoral artery from the leg into the abdomen. Thus substantial capacitive effects of tilting on leg blood flow occur in humans during mild changes in posture.
authors.affiliation: 1Department of Integrative Physiology, The University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Don D
authors.initials: DD
authors.lastname: Sheriff
authors.forename: Inger Helene
authors.initials: IH
authors.lastname: Nådland
authors.forename: Karin
authors.initials: K
authors.lastname: Toska
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000008:administration & dosage; D003187:Compliance; D004562:Electrocardiography; D005260:Female; D005263:Femoral Artery / Q000000981:diagnostic imaging / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D018470:Gravity, Altered; D006339:Heart Rate; D006801:Humans; D007262:Infusions, Intravenous; D017078:Laser-Doppler Flowmetry; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D011187:Posture; D012039:Regional Blood Flow; D016683:Supine Position; D018667:Tilt-Table Test; D013997:Time Factors; D014463:Ultrasonography; D055815:Young Adult
chemical_list: D000316:Adrenergic alpha-Agonists; D003000:Clonidine