title: Lower vascular tone and larger plasma volume in Parkinson's disease with orthostatic hypotension.
abstract: The pathophysiology of orthostatic hypotension in Parkinson's disease (PD) is incompletely understood. The primary focus has thus far been on failure of the baroreflex, a central mediated vasoconstrictor mechanism. Here, we test the role of two other possible factors: 1) a reduced peripheral vasoconstriction (which may contribute because PD includes a generalized sympathetic denervation); and 2) an inadequate plasma volume (which may explain why plasma volume expansion can manage orthostatic hypotension in PD). We included 11 PD patients with orthostatic hypotension (PD + OH), 14 PD patients without orthostatic hypotension (PD - OH), and 15 age-matched healthy controls. Leg blood flow was examined using duplex ultrasound during 60° head-up tilt. Leg vascular resistance was calculated as the arterial-venous pressure gradient divided by blood flow. In a subset of 9 PD + OH, 9 PD - OH, and 8 controls, plasma volume was determined by indicator dilution method with radiolabeled albumin ((125)I-HSA). The basal leg vascular resistance was significantly lower in PD + OH (0.7 ± 0.3 mmHg·ml(-1)·min) compared with PD - OH (1.3 ± 0.6 mmHg·ml(-1)·min, P < 0.01) and controls (1.3 ± 0.5 mmHg·ml(-1)·min, P < 0.01). Leg vascular resistance increased significantly during 60° head-up tilt with no significant difference between the groups. Plasma volume was significantly larger in PD + OH (3,869 ± 265 ml) compared with PD - OH (3,123 ± 377 ml, P < 0.01) and controls (3,204 ± 537 ml, P < 0.01). These results indicate that PD + OH have a lower basal leg vascular resistance in combination with a larger plasma volume compared with PD - OH and controls. Despite the increase in leg vascular resistance during 60° head-up tilt, PD + OH are unable to maintain their blood pressure.
authors.affiliation: Department of Physiology, Radboud University Nijmegen Medical Centre, PO BOX 9101, 6500 HB Nijmegen, The Netherlands. j.groothuis@fysiol.umcn.nl
authors.forename: J T
authors.initials: JT
authors.lastname: Groothuis
authors.forename: R A J
authors.initials: RA
authors.lastname: Esselink
authors.forename: J P H
authors.initials: JP
authors.lastname: Seeger
authors.forename: M J H
authors.initials: MJ
authors.lastname: van Aalst
authors.forename: M T E
authors.initials: MT
authors.lastname: Hopman
authors.forename: B R
authors.initials: BR
authors.lastname: Bloem
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000627:therapeutic use; D001794:Blood Pressure / Q000502:physiology; D001808:Blood Vessels / Q000503:physiopathology*; D015259:Dopamine Agents / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007024:Hypotension, Orthostatic / Q000209:etiology / Q000503:physiopathology*; D007866:Leg / Q000098:blood supply; D008297:Male; D008875:Middle Aged; D009129:Muscle Tonus / Q000502:physiology*; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology*; D010953:Plasma Volume / Q000502:physiology*; D019275:Radiopharmaceuticals; D012039:Regional Blood Flow / Q000502:physiology; D012711:Serum Albumin, Radio-Iodinated; D018667:Tilt-Table Test; D014655:Vascular Resistance / Q000502:physiology
chemical_list: D000978:Antiparkinson Agents; D015259:Dopamine Agents; D019275:Radiopharmaceuticals; D012711:Serum Albumin, Radio-Iodinated