Hydraulic model of myogenic autoregulation and the cerebrovascular bed: the effects of altering systemic arterial pressure.

Systemic arterial (Ps), cerebrospinal fluid (Pcsf), and sagittal sinus (Pss) pressures were measured in 39 dogs divided into eight groups in which Ps was altered pharmacologically or by bleeding. The pharmaceuticals used were norepinephrine (N-EP), dopamine (DOP), sodium nitroprusside (SNP), and nitroglycerin (NTG). SNP and NTG were examined with and without methohexital (MHX) anesthesia and during chronic infusion and bolus injection. The various pressures were subjected to systems analysis in accordance with a previously published model of myogenic autoregulation. Myogenic autoregulation seemed to be impaired only during infusions of N-EP, DOP, and SNP without MHX and during hypovolemic hypotension. The various observed changes in Pcsf are explained by using a hydraulic model of the cerebrovascular bed in which Pcsf represents the pressure drop across the outflow resistance of the bridging veins and lateral lacunae and myogenic autoregulation at the arteries and arterioles represents the major inflow resistance. Impaired myogenic autoregulation is associated with a rise in Pcsf. In addition, variation in pulse pressure is demonstrated to be related to the arterial pulse pressure and the degree of arterial and arteriolar vasodilation.