To evaluate the usefulness of maximum-minimum difference (MMD) of BP in a month compared to standard deviation (SD), as an index of BP variability.Design and Method:
Study-1: Twelve patients (age 65.9 ± 12.1 y/o) were enrolled. Measurements of home systolic (S) BP were required in the morning. The 12 months consecutive data and at least 3 times measurements a month were required for including. (Mean 29.0 ± 4.5 times/month in the morning). We checked the correlation between MMD and SD. Study-2: Six hemodialized patients monitored with i-TECHO system (J of Hypertens 2007: 25: 2353–2358) for longer than one year were analyzed. As in study-1, we analyzed the correlation between SD and MMD of SBP. Measurements: 17.4 ± 11.9 times per month. Study-3: The data from our previous study (FUJIYAM study Clin. Exp Hypertens 2014: 36:508–16) were extracted. 1524 patient-month morning BP data were calculated as in study-1. Picking up data measuring more than 24 times a month, 517 patient-month BP data were analyzed. We compared the ratio to 25 times measured data of SD and MMD, in the setting 5, 10, 15, 20 times measured data.Results:
Study-1: In SBP, DBP, pulse, MMD were correlated very well to SD (p < 0.0001, R = 0.923 in SBP). Equation of SBPSD = 1.275 + 0.208xMMD. Study-2: R = 0.884 (P < 0.0001) SBPSD = 2.17 + 0.22xMMD. Study-3: If data were extracted (measurements >24 times), correlation was 0.927 (P < 0.0001). The equation of SBPSD = 1.520 + 0.201xMMD. As in study 1, the correlations between MMD and SD were very strong either in SBP, BP, pulse. The ratios of SD to 25 times were as follows; 0.956 in 5 times, 0.956 in 10, 0.979 in 15, 0.991 in 20 times. The ratios of MMD to 25 times were as follows; 0.558 in 5, 0.761 in 10, 0.874 in 15, 0.944 in 20.Conclusions:
SD is easily assumed by MMD as an index of day-by-day BP variability of a month.