Effect of Parkinson’s Disease on Cardio-postural Coupling During Orthostatic Challenge, 2022, Rabie Fadil et al

Materials and Methods
Experimental Protocol
We recruited PD patients from the Movement Disorders Clinic at Sanford Health in Fargo, ND. All PD patients met at least two of the four diagnostic criteria for PD: bradykinesia, tremor, rigidity, and postural instability, and were DOPA responders. We also recruited healthy controls from the community. PD patients and healthy controls were excluded if they had severe neurological or medical conditions, such as multiple sclerosis, stroke, epilepsy, COPD, congestive heart failure, or renal failure.

Participants were also excluded if they had any implanted devices (e.g., deep brain stimulation, pacemaker). We excluded PD patients if they had a Montreal Cognitive Assessment [MOCA (Nasreddine et al., 2005)] score <21. Healthy controls were excluded if they met the criteria for mild cognitive impairment (MOCA <26). The IRB at Sanford Health and the University of North Dakota approved the protocol (IRB #1445). We obtained written informed consent from all participants. The study was conducted following the declaration of Helsinki.

Conclusion
In this study, we investigated the involvement of the cardiac baroreflex and cardio-postural coupling—a hypothesized blood pressure reflex involving the skeletal muscle-pump–in maintaining blood pressure in Parkinson’s disease patients and healthy controls.

We also studied the mechanical effect of the heart and leg muscles contractions on blood pressure. The results support the previous research suggesting that the cardiac baroreflex is impaired in PD patients and is likely driven by sympathetic and parasympathetic dysfunction.

Furthermore, our study demonstrated novel findings that Parkinson’s disease patients exhibited higher cardio-postural coupling gain but lower cardio-postural coupling active time during supine, tilt, and standing. In addition, the effect of leg muscle activation to maintain blood pressure was lower in Parkinson’s patients during supine, tilt, and standing.

We argue that PD-related rigidity, muscle weakness, and delayed muscle responses contribute to PD patients engaging dyssynchronous and ineffective leg muscles contractions without seeing an impactful benefit on blood pressure control. This would suggest PD patients experience a mechanical muscle pump impairment and cardio-postural coupling dysfunction which both could lead to dizziness resulting in an unexpected fall.

We have also found that the cardiac baroreflex has a limited effect on blood pressure during standing as lower limb muscles contract to pump blood back to the venous circulation, increasing cardiac output and blood pressure via the muscle-pump mechanism.

In conclusion, we found several factors that contribute to poor blood pressure regulation in PD. These factors have meaningful interaction that can contribute to dizziness, fainting, and falls in PD patients. It is imperative to recognize that the findings in this study are not limited to cardiac autonomic dysfunction alone but reflect a greater system entailing lower leg involvement in blood pressure regulation.

Finally, causality analysis and wavelet-derived metrics of fraction time active (FTA), gain, and active gain for quantitative evaluation of blood pressure control in Parkinson’s disease indicate a potential to use this methodology for the development of effective interventions to reduce falls in Parkinson’s disease by monitoring the cardiac baroreflex and cardio-postural coupling and their role in maintaining blood pressure and postural stability.

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