Self-monitored blood pressure measurements

I wish to make a few comments on a paper published in the September issue of the BJGP¹ that question its methodology and, therefore, the reliability of its conclusions.

First, the number of patients is small at 163 participants. This study is a secondary retrospective analysis of data from a failed clinical trial of a herbal product (asparagus) that was being tested for an antihypertensive effect.¹ The participants were not randomly selected from the population, but were recruited by advertisements and word of mouth. The assessments occurred in ‘a small city-centre clinic’.

Second, I have searched the British Hypertension Society list of validated home blood pressure measurement devices and cannot find the ‘Boso-Medicus Prestige’ device that was used in the trial. Is it possible that this machine has not been clinically validated and, therefore, may be inaccurate?

Third, I have not seen the coefficient of variation used in other blood pressure studies. I suspect that it was used here mainly to reduce the level of variability of the results and, therefore, help to get the figures to look more respectable.

Fourth, Table 3 is very difficult to understand with the columns showing duration of monitoring, and the rows displaying intervals.

Last, in the discussion section it is worrying to see that the authors try to explain their findings using a made up ‘example’ rather than using data from the trial to explain itself.

For all these reasons I do not believe that the unusual findings from this trial are real and applicable to my patients.