The sympathetic nervous system in hypertension: assessment by blood pressure variability and ganglionic blockade

Objective: To determine if the contribution of the sympathetic nervous system to blood pressure could be evidenced by low-frequency oscillations of systolic blood pressure (LF(SBP)), reflecting vascular sympathetic modulation, or by the decrease in blood pressure after autonomic blockade. Design: We studied multiple system atrophy (MSA) patients, in whom supine hypertension is maintained by residual sympathetic tone (`positive controls'); pure autonomic failure (PAF) patients, in whom supine hypertension is largely independent of sympathetic tone (`negative controls'); essential hypertensive patients (HTN) and normotensive subjects (NTN). Results: Supine systolic blood pressure (SBP) was 204 ± 8, 185 ± 6, 177 ± 9 and 130 ± 4 mmHg in MSA, PAF, HTN and NTN, respectively. LF(SBP) was higher in MSA and HTN (5.7 ± 1.5 and 5.8 ± 1.4 mmHg(2)) compared to NTN and PAF (3.3 ± 0.5 and 1.1 ± 0.5 mmHg(2)). Trimethaphan 2–4 mg/min induced complete autonomic blockade and lowered SBP below 125 mmHg in all NTN and all but one MSA (to 111 ± 3 and 97 ± 9 mmHg). SBP remained elevated in PAF (164 ± 7 mmHg). Responses in HTN were variable; SBP decreased below 125 mmHg in three and remained elevated in four patients. The decrease in LF(SBP) correlated with the reduction in SBP, with a steeper slope in MSA and HTN compared to NTN (29.0 ± 5.5, 8.4 ± 1.6 and 3.6 ± 1.2 mmHg/mmHg(2), respectively). Conclusion: Ganglionic blockade, alone or coupled to LFSBP, discriminated between human models of sympathetic-dependent (MSA) and independent (PAF) hypertension. This approach may aid in assessing the contribution of the sympathetic nervous system in essential hypertension, in which sympathetic dependence is variably expressed.