The trough: peak ratio and the smoothness index in the evaluation of control of 24 h blood pressure by treatment in hypertension

Stefano Omboni, Gianfranco Parati, Giuseppe Mancia

Research output: Contribution to journalArticlepeer-review

Abstract

The duration and homogeneity of the antihypertensive effect of a drug are commonly quantified by computation of the trough:peak ratio (T/P) from 24 h ambulatory blood pressure recordings [i.e. the ratio of the reduction in blood pressure at the end of the interval between doses (trough) and the reduction in blood pressure at the time of the maximal effect of a drug (peak)]. Although it is widely employed, this index has a lot of limitations: it makes use of only a small portion of a 24 h blood pressure recording; individual T/P values do not have a normal distribution, unless responders at peak are selected; it bears no relation to 24 h blood pressure variability; peak changes in blood pressure are affected by a placebo effect and thus T/P needs correction for effects of placebo; peak and trough changes in blood pressure are reproducible over time but T/P is not; and, finally, it was shown in the SAMPLE study that T/P is not correlated to changes in left ventricular mass induced by treatment, and thus has a limited clinical value. To overcome these limitations our group has recently proposed the 'smoothness index', which allows one to assess the homogeneity of the antihypertensive effect by using all the 24 h blood pressure data (i.e. it is obtained by dividing the average of the 24 hourly reductions in blood pressure with treatment by its SD). In our experience smoothness index has many advantages over T/P: individual values have a normal distribution and there are no erratic values (thus smoothness index can be expressed as mean ± SD and is subject to parametric statistics); it has a greater reproducibility than does T/P both with medium- and long-term treatment; it has a significant and inverse relationship with variability of 24 h blood pressure (i.e. the greater the smoothness index the smaller the blood pressure variability during treatment); it has a significant and positive relation to treatment-induced regression of left ventricular hypertrophy; and, finally, placebo has a negligible effect on it, so that, in principle, it does not need a correction for effects of placebo, in contrast to T/P. In conclusion a large body of evidence indicates that T/P has a limited ability to quantify the homogeneity of the 24 h blood pressure effect of an antihypertensive drug, whereas the smoothness index seems to provide a better description of this homogeneity.

Original languageEnglish
Pages (from-to)201-204
Number of pages4
JournalBlood Pressure Monitoring
Volume3
Issue number3
Publication statusPublished - 1998

Keywords

  • Ambulatory blood pressure monitoring
  • Antihypertensive treatment
  • Smoothness index
  • Trough:peak ratio

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine
  • Internal Medicine

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