Background. A failure to effectively denervate the renal sympathetic nerves has been
proposed as a possible explanation for the lack of effect on BP in the SYMPLICITY
HTN-III trial. However, no mechanisms of BP regulation were assessed, making it difficult
to determine if the procedure reduced sympathetic nerve activity (SNA). Aim. To assess
SNA and key regulators of BP in participants from the SYMPLICITY HTN-III study. Methods.
Nine patients (55.6±7.2yrs, n=8 male) with Resistant Hypertension, treated with 4.9±1.2
antihypertensive drugs were studied after completion of their participation in SYMPLICITY
III. After 20 min of quiet rest cardiac output (C2H2 rebreathing method, Qc), heart rate (ECG) and BP (auscultatory) were measured. Total
peripheral resistance (TPR) was calculated from mean arterial pressure and Qc. SNA
was measured using the microneurography technique (muscle SNA), and the 24hr urine
excretion of norepinephrine (renal SNA) and epinerphrine (sypathoadrenal function).
Investigators involved in data collection and analysis were blinded to group allocation.
We have not broken the blinding as 6 more subjects will be studied. Results. In patients
with a systolic BP of <140mmHg, Qc and MSNA burst frequency were lower than patients with systolic BP of
≥140mmHg (Table 1). TPR, and urinary norepinephrine and epinephrine excretion were similar between
groups. Burst incidence was higher in the group with lower systolic BP because heart
rate was lower. Conclusions. These preliminary findings suggest that SNA remains elevated
despite improved BP control in some patients. Lower BP was associated with lower Qc,
indicating blood volume may be lower through pressure natriuresis.
Table 1Comparison of HTN-III patients with normal and elevated BP.
Systolic BP <140mmHg, n=4 | Systolic BP ≥140mmHg, n=5 | |
---|---|---|
Systolic BP, mmHg | 121±17 | 151±10 |
Diastolic BP, mmHg | 72±14 | 90±8 |
Qc, l/min indexed to BSA | 2.2±0.3 | 2.8±0.4 |
Heart Rate, bpm | 70±21 | 78±11 |
TPR, dyn.s.cm5 | 1364±268 | 1405±241 |
Burst frequency, burst min | 40.3±5.8 | 46.7±21.4 |
Burst incidence, burst/100HB | 69.9±25.6 | 57.3±28.1 |
Norepinephrine, μg/g creatinine | 33.8±4.8 | 33.0±16.7 |
Epinephrine, μg/g creatinine | 2.0±0.0 | 3.0±0.6 |
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© 2015 Published by Elsevier Inc.