Assessment of sympathetic index from the Valsalva maneuver

Abstract

Objective: Blood pressure (BP) decline and recovery during the Valsalva maneuver (VM) are used to evaluate the degree of sympathetic failure (SF) but a reliable sympathetic index (SI) derived from VM is lacking.

Methods: Patients with mild (n=20), moderate (n=65), and severe (n=60) SF and 23 healthy controls were evaluated using a standardized battery of autonomic tests. SF was defined as mild (associated with reduced sudomotor volumes at distal leg); moderate (associated with a fall in systolic BP ≥10< 30 mm Hg during the tilt test); and severe (associated with a fall in systolic BP ≥30 mm Hg during the tilt test). Six SIs were compared: SI1 (BP fall during phase 2), SI2 (BP recovery during phase 2), SI3 (the difference in BP between baseline and the end of phase 2), SI4 (the magnitude of phase 4), SI5 (BP recovery time), and SI6 (baroreflex sensitivity index).

Results: All indexes showed overall significant differences among tested groups (p<0.05). Only SI3 differentiated all subject groups. Compared to other SIs, SI3 correlated the most with orthostatic hypotension (OH; r=0.62, p < 0.05) during the tilt.

Conclusions: SI3 is the optimal method for calculation of SI since it 1) easily differentiates between healthy controls and those with SF; 2) correlates with the OH, a proxy for a sympathetic failure; 3) tracks the full spectrum of SF (mild-moderate-severe). SI3 expands the utility of quantitative autonomic testing.

Figure 1. Valsalva maneuver in a healthy subject and in severe sympathetic failure

A typical 4-phase blood pressure (BP) profile evoked by Valsalva maneuver in a healthy subject (A, B). Local BP minimum during phase 2 separates the early phase from the late phase. Note absence of BP recovery during the late phase 2 in a subject with severe sympathetic failure (C, D). Clear border separating the early phase from the late phase 2 is missing in C and D. MBP = mean BP.

Figure 2. Schematic of calculation of the sympathetic indexes 1–3

Indexes 1–3 are calculated from phase 2 of Valsalva maneuver. Note that indexes 1 (A) and 3 (C) merge in the case of severe sympathetic failure.

Figure 3. Representative examples of Valsalva maneuver in graded sympathetic failure (SF)

MBP = mean blood pressure.

Figure 4. Performance of sympathetic indexes

Comparison of sympathetic indexes I1–I6 (A). Comparison of dynamic ranges of indexes I3 and I1 (B). Dynamic range of I3 (DR_I3) exceeds the dynamic range of I1 (DR_I1). All values are expressed as mean ± standard error. MBP = mean blood pressure; SF = sympathetic failure.