SHORT-TERM REPRESENTATIVES OF DAYTIME AND NIGHTTIME AMBULATORY BLOOD PRESSURES

Objective: To see whether measurements of ambulatory blood pressure during short-term daytime and night-time periods can represent complete daytime and night-time pressures accurately. Design: Short-term measurements would be less uncomfortable for patients, easier to perform and could lead to fewer missing values, outliers or artefacts than full-day measurements, especially when repeated monitorings are required. Method: Ambulatory blood pressure was measured every 15 min for 24 h in 254 subjects with normal or borderline office blood pressure. Each pressure profile included at least 80 valid readings. Mean blood pressures for different l-, 2-, 3-, 4-, 5- and 6-h spans were calculated and compared with mean daytime and night-time values using paired Student's t-test. Results: One or two-hour spans of daytime blood pressure poorly represented mean daytime pressure. In contrast, 4-h readings, selected between 1000-2200 h represented daytime blood pressure with good accuracy. Over the total sample, 4-h mean blood pressure readings from 1000 2200 h differed from daytime readings by < 2 mmHg and 2-h mean readings from 0300-0700 h differed from mean night-time readings by < 1 mmHg. Conclusion: We suggest that 4-h measurements of ambulatory blood pressure during the daytime and 2-h measurements at night (with time spans selected as indicated as above) may be of value.