Grading of cerebral dynamic autoregulation from spontaneous fluctuations in arterial blood pressure

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 arterial blood pressure with the sudden release of bilateral thigh cuffs. An 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 patients with carotid artery stenosis.

Cerebral blood flow velocity (determined by transcranial Doppler) and arterial blood pressure (determined by noninvasive servo-controlled plethysmograph) were recorded in 20 patients with carotid artery stenosis and 18 age-matched controls. At rest, grading of dynamic autoregulation was estimated from the impulse response of the blood pressure-velocity dynamic relationship. This was compared with the autoregulatory index (ARI) provided by the thigh cuff method and with the degree of stenosis. The critical closing pressure was derived from the fitted models and was also correlated with degree of stenosis.

The 2 ARIs were significantly correlated (r=0.76) and reduced in subjects with carotid stenosis (baseline ARI, 3.65+/-3.11 versus 6.68+/-1.88, P<0. 0001; thigh cuff ARI, 3.78+/-2.32 versus 6.35+/-1.06, P<10(-5)). The critical closing pressure (relative 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 thigh cuff ARI (r=0.68). Both the baseline ARI and critical closing pressure were correlated with degree of stenosis (P<10(-6)).

Grading of dynamic autoregulation with the use of undisturbed recordings of arterial blood pressure and cerebral blood flow velocity might provide a safer technique for assessment of patients in whom a sudden drop of arterial blood pressure is not desirable, such as patients with heart or autonomic failure.