Is dynamic cerebral autoregulation impaired in idiopathic Parkinson’s disease?

Background: Cerebral autoregulation (CA) refers to the ability of the brain to maintain a relatively constant cerebral blood flow (CBF) in response to significant changes in cerebral perfusion pressure. CA is governed by several key mechanisms, which can be described as neurogenic, myogenic and metabolic. Idiopathic Parkinson’s disease (PD) is a common neurodegenerative disease with a significant autonomic component, and it has been hypothesised that CA in PD may therefore be impaired. However, to date, the literature on this subject has been limited in its scope, of uneven quality and has yielded conflicted findings. Objective: This Thesis aimed to determine if dynamic CA is impaired in patients with idiopathic PD, compared to healthy control subjects, and if dynamic CA varies between the ‘on’ and ‘off’ states of PD. Methods: CA was assessed by means of continuous non-invasive monitoring of arterial blood pressure (BP) and velocities in the middle cerebral arteries bilaterally using transcranial Doppler ultrasound. A cohort of patients with idiopathic Parkinson’s disease were studied in both their clinically ‘on’ and ‘off’ states, and their data were compared to that obtained from age- and sex-matched healthy controls. In addition to assessing the CA response to spontaneous fluctuations in BP, a variety of paradigms were used to induce changes in mean cerebral blood flow velocity and BP, including passive arm movement and hyperventilation. Results: This study has demonstrated that CA responses to spontaneous fluctuations in BP do not differ significantly between the on and off states of PD, but do differ significantly between PD patients and healthy controls, ultimately suggesting that CA is altered, but not necessarily impaired, in idiopathic PD. CBF velocity responses to passive arm movement and hyperventilation did not differ significantly between the on and off states of PD, or between PD patients and healthy controls.