Autoregulatory response of pial vessels in the cat

Pial vessel responses to mean arterial pressures (MAP) between 40 and 160 mmHg, induced by withdrawal and reinfusion of blood, were studied in twelve cats under barbiturate- and N2O-anaesthesia, using the cranial window technique and videoangiometry. Very minor changes of pial arterial calibres were noted between MAP 80 and 120 mmHg. During further reduction of MAP, small arteries dilated more than large arteries and measured 43 +/- 4.6% and 30 +/- 1.9% at MAP 40 mmHg, respectively. When MAP was elevated to 140 mmHg, large arteries constricted more than small ones; at MAP 160 mmHg, however, they started to redilate, while small arteries continued to constrict to -13 +/- 2.3%. Within the autoregulatory range, pial veins remained unchanged; at MAPs of 40 and 160 mmHg, venous calibre variations remained below 10%.