fig 4.

Temporal digital subtracted image of a cerebral angiogram obtained during CO₂ inhalation. The digital image obtained immediately before injection of contrast material into the brachiocephalic artery was subtracted from that obtained during the injection. The field of view was 20 × 20 mm.

A, Before CO₂ inhalation. The original image is the same as that shown in figure 2. Arrowheads indicate large branches of the circle of Willis, namely, the middle cerebral artery, the posterior cerebral artery, the anterior cerebellar artery, and the basilar artery; arrows, small branches of the circle of Willis; double arrowheads, the internal carotid artery; double arrows, anastomotic ramus (between the internal carotid artery and the external ophthalmic artery). The anterior cerebellar artery arises from the communicating artery in the dog. PaCO₂ was 34.9 mm Hg.

B, During CO₂ inhalation, PaCO₂ was 125.5 mm Hg.

C, 60 minutes after the completion of CO₂ inhalation, PaCO₂ was 30.2 mm Hg.