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

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.

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.

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).

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.