Cerebral Blood Flow Dynamics in Neurogenic Orthostatic Hypotension: A Systematic Review and Meta-Analysis.

Background: Neurogenic orthostatic hypotension (nOH) causes pathological falls in standing blood pressure that may or may not be symptomatic. nOH also raises the risk of poor neurological outcomes irrespective of symptom presence, possibly reflecting subclinical cerebral hypoperfusion. Dynamic changes in cerebral blood flow velocity (CBFv) help infer how blood pressure fluctuations influence CBFv and cerebral autoregulation. Whether CBFv is impacted in nOH relative to related conditions without nOH and healthy controls (HC) remains unresolved. Whether nOH symptoms reflect greater CBFv falls is also unclear. This review aimed to compare CBFv between nOH and HC, nOH and disease-matched controls (eg, Parkinson disease±nOH), and between symptomatic and asymptomatic nOH.

Methods: Embase and MEDLINE were searched up to April 2024. Means, SDs, and sample sizes for supine and upright CBFv were extracted to generate standardized effect sizes (Hedge g). Random-effects modeling compared postintervention between-group effect sizes.

Results: Seventeen studies were included for review. Thirteen studies were suitable for meta-analysis comparing nOH to HC, 2 comparing disease-matched controls to nOH and to HC, and 3 for symptomatic comparisons. Compared with HC, nOH had larger drops in CBFv (Hedge g, -0.64 [95% CI, -0.85 to -0.44]; P<0.001). CBFv falls between nOH and disease-matched controls were similar (P=0.17). Symptomatic nOH had larger CBFv drops (Hedge g, 0.84 [95% CI, 0.212-1.461]; P=0.009) than asymptomatic nOH.

Conclusions: nOH causes significant orthostatic reductions in CBFv compared with HC, and symptomatic patients experience greater falls in CBFv than asymptomatic patients. Recognizing the clinical implications of CBFv in nOH is crucial for mitigating adverse outcomes.