Time of day to monitor ambulatory blood pressure affects the outcome

Objectives: The reproducibility of blood pressure variables from ambulatory blood pressure monitoring (AMBP) initiated at the same time of day (SAME: 1700-1900 h) was compared with the reproducibility of blood pressure variables when monitoring was initiated at opposite times of day (OPP: randomized, morning = 0700-0900 h and evening = 1700-1900 h). It was hypothesized that the reproducibility for SAME (n = 18) would be no different than the reproducibility for OPP (n = 13). Methods: The order of AMBP sessions was randomized. The Accutracker II was used to determine average blood pressures, Crest (CrBP), Trough (TrBP), and TrBP:CrBP ratio; Averages were divided into 24-h, daytime (0600-2200 h), and night-time (2200-0600 h) for both systolic and diastolic blood pressures. A paired t-test with an intraclass correlation was used to determine the reproducibility of AMBP for both SAME and OPP. A chi-square was used to compare the distribution of reproducible AMBP variables between SAME and OPP. Significance was at P < 0.05. Results: The reproducibility of AMBP variables for SAME and OPP was a significantly different for systolic blood pressure. All of the ambulatory systolic variables measured in the SAME group were reproducible except for the TrBP:CrBP, whereas only the systolic night-time averages of the OPP group were reproducible. Similarly all of the ambulatory diastolic variables measured in the SAME group were reproducible except for TrBP:CrBP, whereas 24-h, night-time averages, and TrBP were reproducible in the OPP group. Conclusions: Ambulatory blood pressure variables were consistently higher when the monitoring session began in the morning hours. © 2005 Lippincott Williams & Wilkins.