Twenty-five minutes between blood pressure readings: the influence on prevalence rates of isolated systolic hypertension.

The aim of the present study was to investigate the influence of a 25-min time interval between the first and the last reading of a series of six, on systolic (SBP) and Phase V diastolic (DBP) blood pressure and its implications for prevalence rates of hypertension. Readings were taken from 5999 persons (2889 men and 3110 women) by two observers using a Hawksley random-zero sphygmomanometer. The first reading was taken 5 min after entering the examining room. The study showed a considerable fall in mean SBP (men, 10.3 mmHg; women, 10.4 mmHg) and hardly a difference in mean DBP (men, 0.8 mmHg; women, 0.1 mmHg) between the first and sixth reading. The fall in SBP was independent of observer and sex and hardly correlated with age or Quetelet's index. The study also showed the implications for the classification of hypertension. Prevalence rates of isolated systolic hypertension dropped remarkably (men, 4.0 to 0.5%; women, 0.9 to 0.1%) between both readings while prevalence rates of severe, moderate and mild diastolic hypertension were nearly similar for the first and sixth reading.