Quantitative indices of baroreflex-sympathoneural function: application to patients with chronic autonomic failure.

PURPOSE: Chronic autonomic failure syndromes such as Parkinson disease with orthostatic hypotension (PD + OH), multiple system atrophy (MSA), and pure autonomic failure (PAF) typically feature arterial baroreflex failure. Identifying baroreflex-sympathoneural failure from hemodynamic responses to the maneuver usually has been qualitative. We report quantitative methods for evaluating baroreflex-sympathoneural function, based on beat-to-beat systolic blood pressure (BPs) responses to the Valsalva maneuver.

METHOD: Using the trapezoid rule, we calculated the area under the curve (baroreflex area, BRA) between baseline systolic blood pressure (BPs) and the BPs for each beat in Phase II (BRA-II) and Phase IV (BRA-IV) in 136 autonomic failure patients and 171 controls. The sum of the areas was defined as total BRA (BRA-T). We compared individual values by the BRA approach with those by other measures.

RESULTS

Mean values for log BRA-II, BRA-IV, and BRA-T were higher in PD + OH, PAF, and MSA than in controls (p < 0.001 each). The log of BRA-T correlated negatively with the fractional orthostatic change in total peripheral resistance (r = -0.41, p < 0.001), fractional orthostatic change in plasma norepinephrine (r = -0.27, p < 0.001), orthostatic change in BPs (r = -0.62, p < 0.001), fall in BPs in Phase II of the Valsalva (r = 0.58, p < 0.001), and log of baroreflex-cardiovagal slope (r = -0.40, p < 0.001). Areas under receiver operating characteristic curves were 0.85 for BRA-T and 0.89 for BRA-IV (p < 0.001).

CONCLUSION

The BRA approach provides quantitative measures of baroreflex-sympathoneural function. Chronic autonomic failure syndromes entail deficiencies of both the cardiovagal and sympathoneural limbs of the arterial baroreflex.