Effect of electrical forepaw stimulation on capillary transit time heterogeneity (CTH)
Functional hyperemia reduces oxygen extraction efficacy unless counteracted by a reduction of capillary transit time heterogeneity of blood. We adapted a bolus tracking approach to capillary transit time heterogeneity estimation for two photon microscopy and then quantified changes in plasma mean transit time and capillary transit time heterogeneity during forepaw stimulation in anesthetized mice (C57BL/6NTac) In addition, we analyzed transit time coefficient of variance capillary transit time heterogeneity/mean transit time, which we expect to remain constant in passive, compliant microvascular networks. Electrical forepaw stimulation reduced, both mean transit time (11.3% 1.3% and capillary transit time heterogeneity (24.1% 3.3% consistent with earlier literature and model predictions. We observed a coefficient of variance reduction (14.3% 3.5% during functional activation, especially for the arteriolar to venular passage. Such coefficient of variance reduction during functional activation suggests homogenization of capillary flows beyond that expected as a passive response to increased blood flow by other stimuli. This finding is consistent with an active neurocapillary coupling mechanism, for example via pericyte dilation. Mean transit time and capillary transit time heterogeneity reductions were consistent with the relative change inferred from capillary hemodynamics (cell velocity and flux) Our findings support the important role of capillary transit time heterogeneity in flow metabolism coupling during functional activation.
Journal of cerebral blood flow and metabolism official journal of the International Society of Cerebral Blood Flow and Metabolism