Dear Editor,
We have with interest taken note of the letter from Cinara Stein and Rodrigo Della Méa Plentz, in which they express their concerns regarding the methodology, results and generalized conclusion of our study “Antihypertensive effect of low-frequency transcutaneous electrical nerve stimulation (TENS) in comparison with drug treatment” (Blood Press. 2012;Early Online:1–5).
The subjects in our study were as stated all Caucasian. The duration of hypertension is important for the prognosis and response to treatment, but since hypertension very often goes without symptoms it is always hard to evaluate the duration of the hypertensive state even though the date of diagnosis is known. Lifestyle factors are important and the impact of these is not disputed. The level of physical activity and the type of pre-study treatment differed, as did body weight, even though the mean BMI corresponds to overweight. In our crossover design, the subjects served as their own control, minimizing the impact of difference of the subjects.
The required sample size was 31 subjects and we intended to recruit 41 subjects to compensate for subjects lost to follow-up. Before inclusion, a registered nurse prepared 41 unmarked envelopes of which 21 contained a note reading “TENS”, and 20 reading “felodipin”. This type of randomization with sealed envelopes is in line with many other randomized trials, for example the Simplicity HTN-2-Trial (Citation1). At the time of inclusion, the nurse picked one of the shuffled envelopes deciding the initial treatment.
The main purpose of our study was to evaluate the antihypertensive effect of low-frequency TENS from a clinical point of view. Even if not entirely comprehensive, we present a background of electrical stimulation in various settings. As referred to, there are studies and findings supporting different effects of electrical stimulation. We do not dispute these findings, although most often the endpoints of these studies are not of proven clinical value. The study of baroreflex sensitivity by Gademan et al. (Citation2) mentioned by Stein and Della Méa Plentz presents no change of systolic blood pressure. In particular we referred to the also mentioned investigations by Jacobsson et al (Citation3) and Kaada et al (Citation4), and commented the limitations and results of these calling for confirming investigations.
That the studied form of stimulation was so-called low-frequency should be clear and our conclusions naturally regard this type of electrical stimulation only. We believe that, in comparison with previous investigations, our study is better designed to evaluate blood pressure reducing capacity of low-frequency TENS and the clinical feasibility of the treatment. We conclude that our study does not demonstrate any solid evidence of BP reduction, since we found no evidence supporting this.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References
- Symplicity HTN-2 InvestigatorsEsler MD, Krum H, Sobotka PA, Schlaich MP, Schmieder RE, Böhm M, et al. Renal sympathetic denervation in patients with treatment- resistant hypertension (The Symplicity HTN-2 Trial): A randomised controlled trial. Lancet. 2010;376:1903–1909.
- Gademan MG, Sun Y, Han L, Valk VJ, Schalij MJ, van Exel HJ, et al. Rehabilitation: Periodic somatosensory stimulation increases arterial baroreflex sensitivity in chronic heart failure patients. Int J of Cardiol. 2011;152:237–241.
- Jacobsson F, Himmelmann A, Bergbrant A, Svensson A, Mannheimer C. The effect of transcutaneous electric nerve stimulation in patients with therapy-resistant hypertension. J Hum Hypertens. 2000;14:795–798.
- Kaada B, Flatheim E, Woie L. Low-frequency transcutaneous nerve stimulation in mild/moderate hypertension. Clin Physiol. 1991;11:161–168.