Reactivity of Cerebral Blood Flow to CO 2 in Patients With Transient Cerebral Ischemic Attacks

Cerebral blood flow and its ability to increase in response to inhalation of 6% CO2 was measured in six patients with a history of transient ischemic attacks in the internal carotid distribution and in ten normal control subjects. Flow was measured with a method which uses time concentration curves made with intravenously injected radioactive indicator and externally placed radiation detectors. It permits measurement of flow, expressed in arbitrary units as a flow index, within the range of a detector placed against the side of the head. Resting flow indices and the increases in flow indices in response to CO2 inhalation did not differ significantly between the TIA patients and the normal control subjects. These results are discussed in terms of possible mechanisms of TIA, and it is concluded that the preserved CO2 responsiveness of the flow indices in these six patients is in support of the theory that intermittent platelet microembolization is an important cause of TIA.