Comparison between spectral analysis and the phenylephrine method for the assessment of baroreflex sensitivity in chronic heart failure

Baroreflex sensitivity assessed by means of the phenylephrine test plays a prognostic role in patients with previous myocardial infarction, but the ne ed for drug injection limits the use of this technique. Recently, several n on-invasive methods based on spectral analysis of systolic arterial pressur e and heart period have been proposed, but their agreement with the phenyle phrine test has not been investigated in patients with heart failure. The t wo methods (phenylephrine test and spectral analysis) were compared in a gr oup of 49 patients with chronic congestive heart failure both at rest and d uring controlled breathing. The linear correlation and the limits of agreem ent between the phenylephrine test slope and the alpha-index [alpha(c); cor rected by the coherence function between the interbeat interval (RR interva l) and systolic arterial pressure] were evaluated. Only 16 patients had a m easurable alpha-index at rest in both the low-frequency (LF) and high-frequ ency (HF) bands; the alpha(c)-index allowed measurements in all patients. I t correlated moderately with the phenylephrine test slope at rest (r = 0.71 and P < 0.001 in LF; r = 0.57 and P < 0.001 in HF) and during controlled b reathing (r = 0.51 and P < 0.001 in LF; r = 0.63 and P < 0.001 in HF). Mult ivariate regression analysis showed that only alpha(c)LF during rest and al pha(c)HF during controlled breathing contributed significantly to barorefle x gain estimation. However, the agreement between methods was weak; the nor malized limits of agreement and bias were - 162 to 243% (0.46 ms/mmHg) for alpha(c)LF and - 185 to 151% (-0.99 ms/mmHg) for alpha(c)HF. Thus the compa rison between baroreflex sensitivity measurements obtained by the phenyleph rine test and spectral analysis showed a moderate correlation between the t wo methods; however, despite the linear association, a consistent lack of a greement between the two techniques was found. Because both systematic and random factors contribute to the difference, these two techniques cannot be considered as alternatives for the assessment of heart failure.