Simultaneous invasive and noninvasive evaluations of baroreflex sensitivity with bolus phenylephrine technique

Estimation of baroreflex sensitivity (BRS) is receiving increasing attention in clinical and experimental cardiology. Until recently, in most studies BRS has been assessed on the basis of invasive blood pressure measurement, which limits its use in large-scale studies and in clinical practice. The development of continuous noninvasive blood pressure monitoring has made it possible to assess BRS noninvasively. We compared central invasive and peripheral noninvasive techniques in the assessment of BRS during cardiac catheterization in 40 patients with possible coronary artery disease. The correlation between noninvasive and invasive BRS was high (r = 0.92; p < 0.001). However, the noninvasive method resulted in significantly higher BRS values than did the invasive method (7.1 +/- 6.5 msec/mm Hg vs 5.1 +/- 4.3 msec/mm Hg, respectively; p < 0.001) because of the smaller increase in systolic blood pressure after phenylephrine injection by the noninvasive technique than by the invasive technique (18.9 +/- 6.8 mm Hg vs 25.2 +/- 7.8 mm Hg, respectively; p < 0.01). The difference between noninvasive and invasive BRS correlated positively with invasive BRS (r = 0.54; p < 0.001) and inversely with age (r = -0.39; p < 0.01) and resting systolic blood pressure (r = -0.30, p < 0.05). A noninvasive BRS value of < 4.0 ms/mm Hg showed a sensitivity of 94%, a specificity of 91%, and an accuracy of 93% in identifying cases of reduced invasive BRS (< 3.0 msec/mm Hg). Our findings encourage the use of finger-cuff method in the assessment of BRS. However, noninvasive BRS values were slightly but significantly higher than invasive BRS values, a difference that should be taken into account when BRS is measured by the noninvasive approach.