Objective: To investigate if impairments in muscle contraction affects blood pressure (BP) regulation in PD.

Background: Orthostatic hypotension (OH) contributes to unexpected falls in PD. PD patients show deficits in cardiac baroreflex and slowed muscle activation. The contraction of leg muscles, known as the skeletal muscle-pump, helps maintain BP by forcing pooled venous blood to return to the heart and prevent OH.

Method: Simultaneous BP, electrocardiogram, and electromyogram (EMG) of the bilateral tibialis anterior (TA), lateral and medial gastrocnemius (LG, MG), and soleus (SOL) were recorded from 13 PD patients in ON state (M = 65.4 ± 5.2; H & Y: 1.3 ± .6) in supine (5 minutes), head-up tilt test (15 minutes), and standing positions (5 minutes). Wavelet transform coherence (WTC) was used to examine the interaction between blood pressure with heart RR intervals and muscle EMG during stand. PD patients were administered the MDS-UPDRS, Orthostatic Hypotension Questionnaire (OHQ), and Scales for Outcomes in Parkinson’s disease – Autonomic Dysfunction (SCOPA-AUT). No PD patients met the clinical diagnostic criteria for OH. Therefore, a median-split was performed on the OHQ scores to create two groups: PD patients with OH symptoms (n = 7) and those without (n = 6).

Results: Preliminary WTC results showed that PD participants with OH symptoms have lower cardiac baroreflex fraction time active (0.13 ± 0.09 vs 0.44 ± 0.2, p = 0.02) compared to their counterparts. However, muscle-pump baroreflex fraction time active was higher in PD patients with OH symptoms compared to the ones without (0.09 ± 0.04 vs 0.03 ± 0.04, p = 0.02), driven by significant differences in plantar flexion muscle activation (LG, MG, SOL; ps = 0.05), with greater muscle activation in PD patients with OH symptoms.

Conclusion: Our data suggests that PD patients without OH symptoms show more active cardiac baroreflex, whereas PD patients with OH symptoms show a more active skeletal muscle pump to regulate blood pressure. Although PD patients with OH symptoms did not show clinical OH, our findings suggest that early signs of compromised autonomic function results in increased leg muscle activation to compensate for deficits in cardiac baroreflex. The study findings highlighted the impairment of cardiac baroreflex in PD patients with OH symptoms and their reliance on muscle-pump baroreflex to maintain blood pressure.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/leg-muscle-contractions-compensate-for-declining-cardiac-baroreflex-in-pd-patients/