Meeting Abstract
Galagos, lorises, and tarsiers, have the unique ability to rotate their heads ~180°. In most other primates, such extended head rotation results in transient loss of consciousness from decreased cerebral arterial perfusion. Mechanisms for maintaining consciousness during head-turning in primates are unknown. Here, we hypothesize that an internal carotid arterial meshwork known as the carotid rete facilitates this behavior. Retia are uncommon among primates and have dramatically different hemodynamic properties than singular vessels. Modified from Ohm’s law, vascular resistance is modeled after series and parallel electrical circuits. Contiguous arteries are conceptualized as vessels in series, and retia are modeled in parallel, which decreases resistance by providing numerous avenues for blood flow. We develop 2 hemodynamics models: 1) vascular resistance of the carotid rete in its standard anatomical orientation, and 2) the vascular resistance when the branches that form the carotid rete are reduced by 50%, stimulating head turning. We based these models on digital 3D renderings of the arterial pattern constructed from microCT scans of cadaveric galago specimens injected with radiopaque latex . We find that, because of the carotid rete’s many interconnecting branches, the reciprocal resistance of this parallel circuit reduces resistance and maintains flow, even when retial branch lumen is decreased by half. Thus, we provide evidence that the carotid rete may help to continually supply blood to the brain through a mechanism of decreased resistance by providing multiple routes for blood to flow during the commonly observed behavior of extreme cervical rotation in galagos.
