Exploring relationships between middle cerebral artery blood velocity waveform morphological features and cerebrovascular hemodynamics

Sex and hormonal fluctuations play a critical role in cerebrovascular physiology, yet their influence on middle cerebral artery blood velocity (MCAv) waveform morphology remains poorly understood. While males generally have larger cerebral arteries, females often exhibit enhanced vascular function, potentially mediated by chronic exposure to gonadal hormones such as estrogen. Across the menstrual cycle, acute fluctuations in estrogen and progesterone further modulate cerebrovascular regulation, with estrogen promoting vasodilation and arterial compliance, and progesterone exerting counteractive effects. In this study, we examined MCAv waveform morphology alongside standard physiological measures in 34 healthy adults (16 males, 17 early follicular (EF) females, 11 mid-luteal (ML) females) at rest. Using transcranial Doppler ultrasonography, carotid artery duplex imaging, and continous blood pressure, we extracted morphological features from the MCAv including: slopes, angles, integrals, peak/valley prominence, curvature, skewness, and kurtosis. Morphological features were compared across sexes and menstrual cycle phases, and correlated with physiological variables. Results demonstrated clear sex specific differences in MCAv waveform morphology. Males exhibited greater right skewness and higher kurtosis, consistent with stiffer or less distensible arteries. While females showed waveform characteristics indicative of higher vascular compliance. Within females, ML phase waveforms displayed intermediate features between males and EF phase females, suggesting cyclical modulation of cerebrovascular mechanics. Importantly, waveform morphology revealed subtle, physiologically meaningful differences not captured by traditional time-averaged MCAv measures.