The autoregulatory capability of Galen's rete cerebri and its connections.

The rete, a vascular system between the extra- and intracerebral arteries of certain animals, may have a variety of functions in different species. The calibres of the vessels of the rete and its arteries of supply have been measured under different conditions of blood pressure and PaCO2. It has been shown that the rete and its afferent arteries behave in an autoregulatory fashion down to a blood pressure of 60 mmHg. They also dilate with a rise in PaCO2. It has also been found that some parts of the system dilate even when the blood pressure drops lower than 60 mmHg. It is suggested that this autoregulatory capacity of extradural vessels limits the requirement for CSF spaces to change with blood pressure changes. A general rule has been sought which would link the known facts about cerebral autoregulation and the possession of extra- to intracranial anastomoses with the bodily shape and posture of the particular animal.