Factors predicting the fall in clinic blood pressure on repeated measurements

OBJECTIVE: Clinic blood pressure (BP) is only an approximate measure of the true blood pressure. It tends to decrease towards the true value on repeated measurements. The aim of this analysis was to identify the factors related to the change in systolic and diastolic BP on repeated measurements. METHODS: Data on BP and other clinical characteristics were obtained from the National Health and Nutrition Examination Survey (NHANES) database. In 2007-8, there were 4943 participants aged 20 years or over with repeated BP measurements. Repeated measurements analysis of variance was used to identify variables related to the change in BP with time. RESULTS: As expected, BP was significantly related to age, gender, and body mass index (all P < 0.001). Systolic and diastolic BP both decreased significantly with time (all P < 0.001), but was not related to body weight, arm dimension, triceps skinfold thickness, cuff size, and consumption of food, coffee and tobacco in the preceding 30 minutes. For systolic BP, the decrease was also negatively related to the pulse rate (P < 0.001). CONCLUSION: Older persons and those with high systolic BP had a larger fall in BP on repeated measurements. Therefore, adequate inflation of cuff and repeated measurements in the elderly are key factors for accurate measurement of clinic BP