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, the authors evaluated by both methods a group of 40 patients 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 (/spl alpha/LF) and high frequency (/spl alpha/HF) bands; the mean /spl alpha/ was also computed. PHE followed immediately, with at least 3 injections during rest and one during CB. /spl alpha/LF could not be measured during both rest and CB in 40% of patients. The PHE slope could not be found in 7% of patients during rest and in 10% during CB. Regression analysis of the PHE slope vs /spl alpha/LF (r=0.61), /spl alpha/ HF (r=0.63) and /spl alpha/(r=0.67) showed a weak correlation during rest. No correlation was found during CB.