Pain induces decrease of blood flow in the common carotid arteries in cluster headache attacks

Eighteen cluster headache patients and five controls were studied using ultrasound duplex techniques to measure blood flow in the common carotid arteries after nitroglycerin and placebo administration. Vessel diameter and blood flow tended to be greater before nitroglycerin in patients in the cluster headache period than in patients out of period and controls. Nitroglycerin tended to increase blood flow only in patients not in the cluster period and in controls. There was a significant decrease in common carotid blood flow and increase in vascular resistance related to maximum pain in both nitroglycerin-induced and spontaneous cluster headache attacks. Blood flow did not reach the initial flow values after the attack was over. In one patient a hyperventilation attack only temporarily decreased the pain. We suggest that the decrease in blood flow and increase in vascular resistance may be due to constriction of intracranial arteries by reflex activation of sympathetic efferents, rather than to decrease of arterial CO₂ tension.