Selective brain cooling: role of angularis oculi vein and nasal thermoreception

We have measured blood flows in the angularis oculi (AOV), facial, and jugular veins and temperatures in the carotid artery and near the hypothalamus in three Lightly anesthetized sheep while body and nasal mucosal (T-nm) temperatures were varied independently. Above a threshold hypothalamic temperature (T-hyp) of 39 degrees C both selective brain cooling (SEC) and AOV blood flow increased. For a given T-hyp, the increase in AOV flow and SEC was inversely proportional to T-nm: low T-nm resulted in high AOV flow and SBC, whereas increasing T-nm attenuated both AOV flow and SBC. This decrease in AOV flow results in submaximal SBC, which does not concur with the hypothesis that SBC functions to protect a thermally vulnerable brain. The trigger for these changes in AOV blood flow was T-nm. Occlusion of the AOV during SBC showed that AOV flow accounted for over 80% of SBC. We conclude that SBC is not only a mechanism for reducing brain temperature but may also be a means of adjusting T-hyp to facilitate the appropriate thermoregulatory responses.