Studies were carried out to assess (1) the statistical and clinical meaning of the trough: peak ratio and (2) the value of self-measurement of blood pressure at home in monitoring the duration of action of antihypertensive drugs in individual patients and in groups of patients.Patients and methods
Data from previous single-blind trials in 44 individual patients were reanalysed. The trough:peak ratio was calculated from mean blood pressure values.Results
There are two major limitations in using this method. (1) Estimates of the trough: peak ratio are biased by the inclusion of non-responders. These patients have the usual random variations in blood pressure, and small differences can result in a spuriously high trough: peak ratio which may lead to an overestimate of the actual ratio. (2) The standard deviation of the trough: peak ratio is large; for a given mean trough: peak ratio some patients have the required 24-h drug cover, whereas others do not. The large standard deviation is partly a result of statistical problems, since four different blood pressure values are used to calculate the ratio. It is therefore essential to increase the precision of the measurement to decrease the standard deviation.Conclusions
Self-measurement of blood pressure at home might be a useful and inexpensive way of estimating the trough: peak ratio. As repeated measurements of blood pressure can be carried out at home under standardized conditions, this method increases the precision of each measurement. It is possible, therefore, to calculate individual trough: peak ratios and the drug regimen (once or twice a day) can be individualized.