Figure 1

Schematic overview of the Jespersen&Østergaard¹³ model of CTTH effect on brain oxygenation. The upper thread refers to arterial tone adjustment in neurovascular coupling during functional activation, representing as functional hyperemia in observation with excessive increase of CBF (relative to the increase of CMRO²). The lower thread represents microcirculatory adjustment during functional activation involving capillary flow homogenization. In this work, capillary flow dynamics are modeled with capillary transit time τ distribution in gamma function h(τ), where MTT is determined by the mean αβ of the gamma function and CTTH is determined by the standard deviation \(\sqrt{\alpha }\beta \). The OEF of the entire capillary bed is calculated from a single capillary contribution Q(τ) weighted by distribution h(τ). During cortical activation, assuming CBV’ = CBF·MTT is constant according to the central volume theorem, the inherent reduction of OEF due to decreased MTT must be accompanied by CTTH reduction (capillary homogenization) in order to secure adequate level of oxygenation to achieve OEF ^max during functional hyperemia.