Noxious stimulation reduces blood pressure but not flow in the internal carotid artery as measured in rabbits.

The purpose of this study was to examine effects on blood flow by alteration of blood pressure resulting from noxious stimuli. The experiment was carried out in anesthetized and paralyzed rabbits. Blood pressure was measured through a teflon catheter inserted in the common carotid artery (CCA). Blood flow at the CCA, internal carotid artery (ICA), or external carotid artery (ECA) was measured using an electromagnetic flowmeter placed at the CCA. The effects of pinching and electrical stimuli upon the blood pressure and flow were tested. Blood pressure at all three arteries decreased transiently from these noxious stimulations. There were no statistical changes in the blood flows respectively. However, different mechanism could exist between ECA and ICA because blood flow of ECA was decreased and that of ICA was increased or had no change. We concluded that vascular resistance reduction in the ICA against the arterial pressure decrement produced by noxious stimuli may be a control mechanism to keep cerebral blood flow constant. In contrast, there may be no such mechanism in the ECA circulation.