No further decrease in blood pressure when the interval between readings exceeds one hour

OBJECTIVE: The assessment of blood pressure (BP) in individuals is traditionally based on a few BP readings obtained at intervals of just a few minutes. We examined if increasing intervals between BP readings on one visit would have an impact on the BP estimates. METHODS: We conducted an examination survey of cardiovascular risk factors in the general population aged 25-64 years in Seychelles (Indian Ocean), attended by 1255 of 1565 eligible participants. BP was measured once shortly after participants' arrival to the study centers (BP1) and twice before discharge, 15-351 min later (BP2, BP3; separated by 2 min). RESULTS: Mean (standard error) BP1 was 135.1 (0.7)/87.9 (0.4) mmHg, BP2: 130.7 (0.6)/85.1 (0.4) mmHg and BP3: 128.4 (0.6)/83.9 (0.3) mmHg. The difference in BP between the first and the last measurements (DeltaBP1-BP3) was, respectively, 5.8 (1.3)/2.6 (0.9) mmHg for a time interval between BP1 and BP3 of 15-60 min, 6.3 (0.5)/3.9 (0.3) mmHg for 61-120 min, 6.9 (0.6)/4.1 (0.4) mmHg for 121-240 min and 7.4 (0.7)/4.3 (0.5) mmHg for 241-351 min (P-trend for systolic/diastolic BP: 0.15/0.49). In multivariate analysis, both systolic and diastolic DeltaBP were associated with the initial BP level and the female sex but not with time (in minutes) between BP readings (for systolic/diastolic BP, P=0.12/0.34). CONCLUSION: The decrease in subsequent BP readings obtained did not differ whether the time interval between BP measurements was larger or smaller than 1 h. This indirectly suggests that extending the time interval between repeated BP readings on one single visit is unlikely to be a valid, alternative strategy to the recommendation of gathering BP readings on several, separate visits to define hypertension.