Assessment of the thigh cuff technique for measurement of dynamic cerebralautoregulation

Background and Purpose-Dynamic methods of measuring cerebral autoregulation have become an accepted alternative to static evaluation. This article aim s to describe a set of data collected from healthy volunteers by a dynamic method, the purpose being to qualify and quantify expected results for thos e who may be designing a study using this technique. Methods-Cerebral blood flow velocity (CBFV) (measured by transcranial Doppl er) and arterial blood pressure (Finapres) were recorded in 16 normal subje cts before, during, and after the induction of a blood pressure drop (relea se of bilateral thigh cuffs). This procedure was repeated 6 times for each subject. A mathematical model was applied to the data to generate an autore gulatory index (ARI) with values between 0 and 9. Results-The ARI values for this sample population follow a normal distribut ion, with a mean+/-SD of 4.98+/-1.06 (n=15). Analysis of the cumulative mea n ARI values of all subjects showed an exponential-type convergence of ARI: toward the sample mean as the number of test iterations increased. The pop ulation average blood pressure drop on thigh cuff release was 26.4+/-7.1 mm Hg (n=16), occurring in 4.6+/-1.7 seconds. The corresponding population av erage drop for CBFV was 15.6+/-5.8 cm/s, taking 2.5+/-1.0 seconds. No signi ficant trend was noted in the measurements as the number of test iterations increased. The correlation between the predicted and actual CBFV, having a mean value of 0.76+/-0.19, showed evidence of a nonlinear relationship to ARI values. Significant correlation was also found between ART and (1) arte rial blood pressure before cuff release and (2) the magnitude of the drop i n CBFV on cuff release. Conclusions-The distribution of ART values is not significantly different f rom normal. At least 3 iterations of the test procedure should be performed and averaged to obtain the mean ARI for each subject. There is no signific ant evidence of physiological accommodation as the number of test iteration s increases. The effects of mean blood pressure and the magnitude of the ch ange in CBFV should be considered as possible covariates when ARI data are analyzed.