Do alpha-index and phenylephrine test provide similar measurements of baroreflex sensitivity in cardiac patients with chronic heart failure?

To verify whether the phenylephrine test (PHE) and spectral analysis (alpha-index) provide similar measures of baroreflex sensitivity in patients with chronic heart failure due to left ventricular dysfunction, we evaluated by both methods a group of 40 pts during rest and controlled breathing (CB). R-R interval (RR), blood pressure (BP) and respiration were recorded in both conditions (600 heart beats), and bivariate spectral analysis was carried out. The alpha-index was measured when the magnitude squared coherence (MSC) between RR variability and systolic BP variability was > 0.5 in the low frequency (alpha LF) and high frequency (alpha HF) bands; the mean alpha was also computed. PHE followed immediately, with a least 3 injections during rest and one during CB. alpha LF could not be measured during both rest and CB in 40% of pts. The PHE slope could not be found in 7% of pts during rest and in 10% during CB. Regression analysis of the PHE slope vs alpha LF (r=0.61), alpha HF (r=0.63) and alpha(r=0.67) showed a weak correlation during rest. No correlation was found during CB.