Dynamic Windkessel autoregulation for optical hemodynamic imaging: quantifying microcirculation, oxygen diffusion, and vascular autoregulation from low-frequency hemodynamic oscillations

Hemodynamic-based neuroimaging and non-neuroimaging techniques are widely used in neuroscience and functional studies. Probing spontaneous or induced hemodynamic oscillations by light, such as coherent hemodynamics spectroscopy (CHS), has emerged as an effective approach for quantifying cerebral microcirculation and vascular autoregulation. We introduce dynamic Windkessel autoregulation, which enables noninvasive quantification of microcirculation, oxygen diffusion rates, and vascular autoregulation from low-frequency oscillations (LFOs). The model incorporates arteriole vasomotor responses to blood pressure variations and quantifies autoregulatory capacity using a dimensionless autoregulation gain index <i>n</i>, which decreases with impaired autoregulation. The model accurately reproduced observed microcirculation and arterial blood flow and volume LFO responses, enabling straightforward quantification of vascular autoregulation. Furthermore, we integrate the model into WK-PIPE CHS and demonstrate recovery of key hemodynamic parameters, including the local tissue oxygen diffusion rate (α=0.179 ± 0.049s^-1) and vascular autoregulation (<i>n</i> = 4.68 ± 0.59) on five healthy human subjects imaged with visible structured light under paced breathing. Dynamic Windkessel autoregulation, as a mechanistic framework for vascular autoregulation, offers potential applications in monitoring cerebrovascular and cardiovascular health and early detection of their dysfunction using optical hemodynamic imaging.