Incremental bias in finapres estimation of baseline blood pressure levels over time

Finapres finger blood pressure monitoring appears to provide a reliable alternative to intra-arterial blood pressure measurement under many circumstances. However, few studies have focused on the limitations of Finapres assessment. In a previous pilot investigation, we observed that Finapres pressure following mental stressors failed to return to initial resting levels. Our objectives in the present study were to (1) replicate earlier findings, (2) examine whether local changes in the measured finger were responsible for the observed drift, and (3) test a method to facilitate the return of pressure to systemic baseline levels. We studied two groups of healthy subjects who underwent a protocol consisting of two mental stressors pre ceded and followed by baseline periods. In the control group, the Finapres continuously monitored pressure on a single finger for the entire protocol. The intervention group periodically had the Finapres cuff removed and the measured finger exercised to prevent local changes that might influence Finapres estimation of blood pressure. Comparisons indicated a group x baseline interaction effect for systolic and diastolic pressures (P < .0004 and P < .003, respectively). The group with the exercise intervention showed much greater recovery during the final baseline than the control group. Recovery of pressures in the control group but not the intervention group was inversely related to the stress level of blood pressure (r = .86, P < .0002), indicating a relationship between blood pressure rise and the degree of distortion of subsequent baseline values. On the basis of our results, we propose that in prolonged protocols, the measurement finger be exercised to facilitate accurate measurements of finger pressure with the Finapres.