Seasonal effect on blood pressure variability in hypertensive patients assessed by different measurement methods

Objective: The seasonal variation in temperature is well known to affect the level of blood pressure (BP). However, its impact on BP variability is uncertain. This study investigated the seasonal variation in BP variability in hypertensive patients assessed using office and out-of-office BP measurements. Design and method: Adult hypertensives on stable antihypertensive drug treatment were assessed with office (OBP), home (HBP), and ambulatory BP (ABP) measurements in winter, next summer, and in the next winter. BP variability was quantified using the standard deviation (SD) and coefficient of variation (CV). Results: Fifty-eight participants had complete data for winter and summer (mean age 65.2±7.9 [SD], 64% males, 21% obese, 48% smokers, 11% diabetes, 18% cardiovascular disease, 28% on a single antihypertensive drug, 38% on 2 drugs, 34% on > 2 drugs). OBP, HBP and daytime ABP were lower in summer than in winter (P<0.01), whereas nighttime ABP was unchanged (P = NS) (Figure). SD and CV for systolic OBP were higher in winter than summer (P<0.01/<0.05, respectively). BP variability assessed by HBP and ABP measurement did not differ in winter and summer (Figure). Forty participants had complete data for winter-summer-next winter. OBP, HBP and daytime ABP were higher in the second winter compared with summer excluding any order effect. Respective CV values showed no difference (p = NS). Conclusions: These preliminary data suggest that despite the considerable impact of seasonal changes in temperature on the levels of BP, its variability is not affected. Thus, variability appears to be an intrinsic feature of the individual's BP behaviour, which is largely unaffected by extrinsic seasonal factors.