Peripheral vascular responses to an orthostatic challenge and plasma volume in Parkinson's disease patients with orthostatic hypotension

Abstract

Orthostatic hypotension (OH) is present in 50% of Parkinson's disease (PD) patients. A reduced peripheral vasoconstriction and an inadequate plasma volume may contribute to OH in these patients. Indeed, plasma volume expansion is considered as an effective therapy. The objective was to compare baseline plasma volume and peripheral vascular responses to an orthostatic challenge in PD patients with OH (PD+OH, n=15) with PD patients without OH (PD‐OH, n=17) and controls (C, n=15). We examined superficial femoral artery blood flow using duplex ultrasound during a 60° head‐up tilt (HUT). Leg vascular resistance (LVR) was calculated. In a subset (9 PD+OH, 9 PD‐OH and 8 C), we determined plasma volume by indicator dilution method with radio‐labeled albumin. We found a lower baseline LVR in PD+OH (0.6±0.3 mmHg/ml/min) compared with PD‐OH (1.2±0.6 mmHg/ml/min) and C (1.3±0.5 mmHg/ml/min). LVR increased during 60° HUT to a similar magnitude in all groups (PD+OH +0.3 to 0.9±0.1; PD‐OH +0.5 to 1.7±0.3; C +0.7 to 2.1±0.3 mmHg/ml/min). Plasma volume was larger in PD+OH (62±3 ml/kg) compared with PD‐OH (54±6 ml/kg) and C (54±8 ml/kg). In conclusion, PD+OH have a lower LVR in combination with a higher plasma volume compared with PD‐OH and C. Although PD+OH increase LVR during 60° HUT to a similar extend as the other groups, they are unable to maintain their blood pressure in an upright position, possibly due to the attenuated basal LVR.