title: Arterial diameter during central volume depletion in humans.
abstract: The luminal diameter of the radial artery was followed by high frequency ultrasound during 50 degrees head-up tilt-induced central volume depletion in ten healthy subjects of whom six were tilted twice and pretreated with the serotonin receptor antagonist methysergide or placebo following a double-blind randomized design. Eight subjects without active treatment experienced presyncopal symptoms after 16-45 (mean 32 min). Central volume depletion was indicated by an increase in mean thoracic electrical impedance [from 31.5 (SEM 1.6) to 33.4 (SEM 1.7) omega; P < 0.05]. Cardiac output decreased [from 4.1 (SEM 0.3) to 2.2 (SEM 0.3) 1.min-1] and heart rate [HR, from 64 (SEM 3) to 100 (SEM 7) beats.min-1], mean arterial pressure (MAP, from 77 (SEM 4) to 89 (SEM 2) mmHg [10.3 (SEM 0.53 to 11.9 (SEM 0.27) kPa]) and total peripheral resistance (TPR, from 19 (SEM 2) to 34 (SEM 4) mmHg.min.1-1 [2.5 (SEM 0.27) to 4.5 (SEM 0.53) kPa.min.1-1]) increased; but with the appearance of presyncopal symptoms, HR, MAP and TPR were reduced to 65 (SEM 8) beats.min-1, 46 (SEM 4) mmHg [6.1 (SEM 0.53) kPa] and 18 (SEM 3) mmHg.min.1-1 [2.4 (SEM 0.4) kPa.min-1.1-1], respectively (P < 0.05). Vascular resistance was reflected in the arterial diameter which decreased from 2.42 (SEM 0.17) to 2.27 (SEM 0.14) mm during head-up tilt and increased to 2.71 (SEM 0.14) mm with the appearance of presyncopal symptoms (P < 0.05). Methysergide reduced the resting radial (15 +/- 2%) and temporal artery diameters (10 +/- 3%) (P < 0.05); however, it affected neither tilt-tolerance nor the central cardiovascular response to tilt. The results suggested a serotonergic influence on arterial tone at rest, and demonstrated that vessels as large as the radial artery participated in vascular control during central volume depletion independent of such a serotonergic influence.
authors.affiliation: Department of Neurology, University of Copenhagen, Denmark.
authors.forename: H K
authors.initials: HK
authors.lastname: Iversen
authors.forename: P
authors.initials: P
authors.lastname: Madsen
authors.forename: S
authors.initials: S
authors.lastname: Matzen
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001810:Blood Volume / Q000502:physiology*; D002302:Cardiac Output; D004311:Double-Blind Method; D017097:Electric Impedance; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008784:Methysergide; D010919:Placebos; D011187:Posture; D017534:Radial Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D012702:Serotonin Antagonists; D014463:Ultrasonography; D014655:Vascular Resistance
chemical_list: D010919:Placebos; D012702:Serotonin Antagonists; D008784:Methysergide