GRADING OF CEREBRAL DYNAMIC AUTOREGULATION FROM SPONTANEOUS FLUCTUATIONS IN ARTERIAL BLOOD-PRESSURE

Background and Purpose-Assessment of cerebral autoregulation has been traditionally performed with static changes in arterial blood pressure . Newer dynamic methods require the induction of sudden drops in arter ial blood pressure with the sudden release of bilateral thigh cuffs. A n alternative method is proposed, based on the spontaneous variability of arterial blood pressure that does not require its manipulation. We compared this method with the established thigh cuff method in patien ts with carotid artery stenosis. Methods-Cerebral blood flow velocity (determined by transcranial Doppler) and arterial blood pressure (dete rmined by noninvasive servo-controlled plethysmograph) were recorded i n 20 patients with carotid artery stenosis and 18 age-matched controls . At rest, grading of dynamic autoregulation was estimated from the im pulse response of the blood pressure-velocity dynamic relationship. Th is was compared with the autoregulatory index (ARI) provided by the th igh cuff method and with the degree of stenosis. The critical closing pressure was derived from the fitted models and was also correlated wi th degree of stenosis. Results-The 2 ARIs were significantly correlate d (r=0.76) and reduced in subjects with carotid stenosis (baseline ART , 3.65 +/- 3.11 versus 6.68+/-1.88, P<0.0001; thigh cuff ART, 3.78+/-2 .32 versus 6.35+/-1.06, P<10(-5)). The critical closing pressure (rela tive to mean arterial blood pressure) was also significantly reduced ( -0.24+/-1.06 versus 0.50+/-0.31, P<0.0001) and correlated with the thi gh cuff ARI (r=0.68). Both the baseline ARI and critical closing press ure were correlated with degree of stenosis (P<10(-6)). Conclusions-Gr ading of dynamic autoregulation with the use of undisturbed recordings of arterial blood pressure and cerebral blood flow velocity might pro vide a safer technique for assessment of patients in whom a sudden dro p of arterial blood pressure is not desirable, such as patients with h eart or autonomic failure.