Stroke is a major cause of long-term disability and mortality worldwide, often resulting in impairments not only in motor and cognitive functions but also in autonomic nervous system (ANS) regulation. Among the physiological markers that reflect ANS activity, heart rate variability (HRV) has emerged as a promising biomarker for assessing stroke severity and predicting recovery outcomes. HRV quantifies the temporal fluctuations between heartbeats and is traditionally analyzed through time- and frequency-domain measures. More recent approaches have introduced non-linear metrics such as approximate entropy, sample entropy, and detrended fluctuation analysis to capture complex heart rate dynamics. In this narrative review, we address the role of both linear and non-linear HRV parameters in the context of stroke, highlighting their relevance for understanding autonomic dysfunction and guiding rehabilitation. Evidence shows that reduced HRV is associated with poorer functional outcomes, higher mortality, and increased risk of complications post-stroke. Moreover, HRV trends can provide valuable insights into treatment effectiveness and individual recovery trajectories. We also discuss practical considerations for HRV measurement, including device selection, preprocessing strategies, and the need for methodological standardization. Finally, we outline interventional strategies that may enhance HRV and promote better recovery. Together, these findings support the integration of HRV analysis into stroke care as a non-invasive, accessible tool to guide prognosis and tailor interventions.

Introduction: Brain-derived neurotrophic factor (BDNF) is a neurotrophin expressed in the central nervous system, where it supports synaptic plasticity, neuronal survival, and dendritic remodeling. Reduced circulating BDNF levels have been reported in several neurological and psychiatric disorders, increasing evidence links BDNF to post-stroke recovery. However, because BDNF is also produced and stored in platelets- the main peripheral reservoir- its measurement is highly sensitive to preanalytical handling. Improper sample preparation may trigger platelet degranulation and cause substantial variability in serum and plasma BDNF levels. Content: This scoping review examined preanalytical procedures used for BDNF quantification in clinical studies involving adult stroke patients. Following PRISMA-ScR guidelines, we systematically searched Pubmed, Embase, Web of Science, and the Cochrane Library for English-language clinical trials, randomized controlled trials, and observational studies measuring BDNF in blood derivatives. The search was completed on February 3rd, 2025. Summary: From 11,030 records identified, 8,696 underwent screening after removing duplicates and excluding records concerning populations other than stroke, 49 studies met inclusion criteria. 74.4 % reported associations between circulating BDNF levels and clinical features or outcomes, though significant heterogeneity across study designs limited comparability. Serum was used in 36 studies, but key preanalytical parameters (such as clotting time, transport temperature) were frequently unreported. Similar inconsistencies emerged for plasma preparation, including anticoagulant type and management of platelet content. Outlook: These findings reveal major gaps in the reporting of preanalytical methods for BDNF measurement in stroke research and emphasize the need for standardized procedures to ensure reliable and comparable biomarker data.