Cerebrovascular response to elevation of ventricular pressure.

The behaviour of Pial vessels to levels of CSF-pressure between 10 and 100 mmHg induced by vetricular infusion of mock CSF, was observed in 6 cats under barbiturate and N2O anaesthesia, using the cranial window technique and videoangiometry. Supratentorial pressure (STP) equaled infratentorial pressure in the cisterna magna (CMP) throughou. No changes in pial arterial calibres were noted up to a CMP of 13 mmHg (i.e. a cerebral perfusion pressure (CPP) of 100 mmHg). Further increase of CMP to 45 mmHg induced significant arterial dilatation of 40 +/- 3.4%. With a further rise of ventricular fluid pressure (VFP) no marked further arterial dilatation occurred. Dilatation of arteries up to 100 um resting diameter and arteries between 100 and 250 um resting diameter and arteries between 100 and 250 um was not significantly different. When CPP approached 40 mmHg, arteries were still 47 +/- 3.6% dilated. Pial venous calibre did not vary by more than 20% during elevation of VFP. At CPP 47 mmHg, small and large veins were dilated by 14%. Single venous segments were compressed by crossing pial arteries and caused upstream venous congestion and distension.