Baroreflex function in Parkinson's disease: Insights from the modified-Oxford technique.

Non-motor symptoms are common in Parkinson's disease (PD) and they include dysregulation of cardiovascular system, which adversely affects quality of life. Recent studies provide indirect evidence that baroreflex dysfunction may be one of the mechanisms of cardiovascular dysregulation in PD. Herein, we tested the hypothesis that the baroreflex gain, assessed across an extensive range of the reflex arc by eliciting rapid changes in blood pressure (BP) induced by sequential boluses of vasoactive drugs (modified-Oxford technique), would be attenuated in middle-aged patients with PD. Beat-to-beat heart rate (electrocardiography) and BP (finger photoplethysmography) were obtained during 10-min of supine rest preceding the modified-Oxford [bolus of nitroprusside followed by phenylephrine 1-min afterwards] in eleven patients with PD (51±6yr) and seven age-matched controls (47±6yr). The resulting systolic BP and R-R interval responses were plotted and fitted with segmental linear regression and symmetric sigmoid model. Spontaneous indices obtained via sequence technique were also used to estimate baroreflex gain. Compared to controls, the estimated gains measured by segmental linear regression (patients: 3.83±2.6 ms/mmHg vs. controls: 7.78±1.7 ms/mmHg; P=0.003) and symmetric sigmoid model (patients: 12.36±6.9 ms/mmHg vs. controls: 32.02±19.0 ms/mmHg; P=0.009) were lower in patients with PD. The operating range of BP was larger in patients with PD compared to controls (13±7 mmHg vs. controls: 7±3 mmHg; P=0.032). Of note, the gain obtained from spontaneous indices was similar between groups. These data indicate that baroreflex gain was reduced by >50% in PD, thereby providing clear and direct evidence that cardiovagal baroreflex dysfunction occurs in PD.