Objective: Cold exposure is associated with increased blood pressure (BP) levels and indoor temperature significantly influences BP fluctuations. However, no studies have examined the reproducibility of hypertensive status across seasons or explored the clinical implications of seasonal variations in indoor temperature on hypertensive status. Therefore, we aimed to investigate those associations in a general practice population. Design and method: This was a longitudinal analysis of the Prediction of ICT-Home Blood Pressure Variability (PREDICT) study. The PREDICT study is a practitioner-based, multicenter, prospective, observational trial conducted in Japan, which enrolled 618 high cardiovascular-risk participants who measured their home BP for over 2 years (mean SD age: 70.3 10.5 years; 52.1% men; 85.4% on antihypertensive medications). The participants measured their home BP using an automatic Information and Communication Technology-based validated device based on the cuff-oscillometric principle. Winter hypertension and summer hypertension were defined as participants with hypertension (morning systolic BP over 135 mmHg and/or morning diastolic BP over 85 mmHg) in winter (from December to February) and summer (from June to August) of each year, respectively. Sustained winter hypertension was defined as participants who met the criteria for hypertension in winter in both the first and second years. Restricted cubic splines were used to examine the potential non-linear associations between indoor temperature differences and the risks for sustained winter hypertension. Results: Moderate reproducibility was observed between consecutive summers and winters over a 2-year period; Kappa statistics (95% confidence interval CI) 0.650 (0.571–0.729) in winter hypertension, 0.575 (0.496–0.654) in summer hypertension. Participants shifting from summer normotension to winter hypertension showed lower reproducibility; 0.415 (0.336–0.494). In multivariate logistic regression analysis, the indoor temperature difference between summer and winter was significantly associated with sustained winter hypertension (n=184) (odds ratio 1.258 95% CI 1.118–1.425), even after adjusting for covariates including the average indoor temperature and mean HBP levels. The risk of sustained winter hypertension linearly increased, as the indoor temperature difference increased. Conclusions: Long-term home BP monitoring throughout the year are important for the management of hypertension and reducing seasonal indoor temperature difference may reduce the risk of BP increase in winter.
Fujiwara et al. (Fri,) studied this question.