Abstract
The efficiency in autoregulation of regional cerebral blood flow (CBF) was compared in the carotid and vertebral arterial systems. A newly developed photoelectric method was used with 6 rhesus monkeys to measure the mean transit time of blood (t), together with the cerebral blood volume (CBV) in the tissue of the parietotemporal area supplied by the carotid artery and of the cerebellar tonsil supplied by the vertebral artery. From values of t and CBV, the CBF was calculated using the Stewart-Hamilton equation. During continuous recording of CBV and frequent determination of t in both territories simultaneously, various levels of hypotension were induced by stepwise exsanguination through a femoral vein. As had been expected, CBF tended to decrease when blood pressure fell below a certain threshold. However, the author found that the mode of the decreases in CBF in the two arterial systems was quite different. The CBF in the carotid arterial system tended to be preserved even when the blood pressure fell below 60 mmHg while that in the vertebral arterial system started to decrease from as high as 70 mmHg of blood pressure. In addition, the decrease in the vertebral arterial system became more marked in accordance with the progress of hypotension. The difference in the CBF decreases in the two arterial systems at blood pressure less than 60 mmHg was statistically significant (p<0.05).
From these data, the author concluded that the efficiency in autoregulation of regional blood flow in the vertebral arterial system was inferior to that in the carotid arterial system.
