Nimodipine does not affect the cerebral autoregulatory response in the anesthetized pig

The effect of the calcium blocker nimodipine on the cerebral blood flow (CBF) and cerebral autoregulatory responses was examined in seven fentanyl/N2O/anesthetized pigs. CBF was measured continuously from the sagittal sinus by a venous outlet flow technique. Cerebral autoregulation tests were performed before, after 30 min of nimodipine infusion (0.5 microgram.kg-1.min-1), and at 30 min after the infusion. The autoregulatory response to a gradual blood pressure increase was tested by infusion of angiotensin, and to a gradual blood pressure decrease was tested by caval block. The slope of the relationship between the regional cerebral vascular resistance (rCVR) and mean arterial blood pressure (MABP) was used as a measure of the autoregulatory capacity. The lower limit of autoregulation was determined as the MABP at which rCVR did not further decrease. An i.v. bolus dose (10 micrograms.kg-1) of nimodipine resulted in a transient increase in rCBF during 3 min, together with an MABP reduction. After 1 h of nimodipine infusion, MABP was reduced (19%), while rCBF, rCVR, and cerebral metabolism were unaffected. In the control condition, a preserved cerebral autoregulatory response to the increase of MABP (+30 mm Hg) was indicated by an unaffected rCBF and determined by the slope of the rCVR/MABP regression line (0.053), not different from the slope during blood pressure decrease (0.063). The cerebral autoregulatory responses to increase or decrease in MABP were not attenuated by nimodipine infusion. The lower limit of autoregulation (48 +/- 6 mm Hg) was not altered by nimodipine.