Decoupling the neurovascular axis: autonomic and hemodynamic determinants of intracranial pulse wave morphology via principal component analysis

Purpose This study investigated the integrated relationship between systemic hemodynamics, autonomic modulation, and non-invasive intracranial pulse wave morphology (P2/P1 ratio) across na adult age range under basal seated resting conditions. Methods Two hundred ninety-nine healthy volunteers (137 males, 162 females; mean age 48.74 ± 24 years) were evaluated. Blood pressure, heart rate, symbolic heart rate variability (0 V, sympathetic; 2UV, parasympathetic), and P2/P1 ratio via scalp extensometry were recorded. Principal Component Analysis (PCA) with Varimax rotation was applied to eight normalized variables (Age, HR, SBP, DBP, PP, 0 V, 2UV, and P2/P1). Results Four components explained 85.81% of variance. PC1 (34.04%) comprised age (loading 0.802), PP (0.824), SBP (0.883), and P2/P1 (0.647), representing an age-pulsatile axis. PC2 (25.46%) captured autonomic dynamics, dominated by 0 V and 2UV. PC3 (13.93%) was dominated by DBP, whereas PC4 (12.38%) showed a P2/P1 loading (0.560). Spearman analysis showed associations of age with P2/P1 (ρ = 0.623, p < 0.05), PP (ρ = 0.479, p < 0.05), and SBP (ρ = 0.472, p < 0.05). P2 > P1 morphology was more frequent among older participants and higher PP. Conclusion Under basal seated resting conditions, P2/P1 was associated with age and pulsatile hemodynamics, particularly PP, while autonomic modulation represented a partially distinct component. The P2/P1 variance in PC4 suggests additional factors not captured by the systemic variables examined. These findings support this non-invasive framework as an exploratory approach for studying cerebrovascular and craniospinal dynamics across adulthood, but do not establish causality or equivalence with invasive measurements.