T here is growing evidence that outdoor temperature is a major determinant of the observed seasonal fluctuations in blood pressure (BP) with higher and lower BP in winter and summer, respectively. [1][2][3][4][5][6] An inverse association between ambient temperature and BP has been observed in several studies.7-9 Thermoregulatory vasoconstriction, which increases arterial BP significantly, 10 is an adaptive response to provide enhanced circulatory function for the protective mechanisms that are activated to maintain temperature in cold weather (nonshivering thermogenesis and increased metabolic rate).
2,11Elevation of BP induced by a longer period of cold exposure is not reversible after return to a thermo-neutral temperature in animal studies 12 and may result in cold-induced hypertension. Although several studies explored the effects of seasonal variations on BP, few studies have looked at longitudinal BP changes in relation to fluctuations in weather patterns. To our knowledge, there are no studies that examined the role of sunshine, rain, or air frost on BP. It is unclear whether BP response to weather parameters like temperature, rainfall, frost, and sunshine is similar in everybody. If there is heterogeneity in weather-related BP response, it would be important to know whether intraindividual and interindividual responsiveness to weather changes can predict long-term risk. The aim of this study was to determine the within-subject changes in BP in response to a range of weather patterns and test whether individual BP response to the weather is predictive of long-term mortality and BP control in a large hypertensive cohort.
Methods
Study PopulationThe Glasgow Blood Pressure Clinic provides secondary and tertiary level service to individuals with hypertension from the West of Scotland. The details of the study population and settings, clinical Abstract-Very few studies have looked at longitudinal intraindividual blood pressure responses to weather conditions.There are no data to suggest that specific response to changes in weather will have an impact on survival. We analyzed >169 000 clinic visits of 16 010 Glasgow Blood Pressure Clinic patients with hypertension. Each clinic visit was mapped to the mean West of Scotland monthly weather (temperature, sunshine, rainfall) data. Percentage change in blood pressure was calculated between pairs of consecutive clinic visits, where the weather alternated between 2 extreme quartiles (Q 1 -Q 4 or Q 4 -Q 1 ) or remained in the same quartile (Q n -Q n ) of each weather parameter. Subjects were also categorized into 2 groups depending on whether their blood pressure response in Q 1 -Q 4 or Q 4 -Q 1 were concordant or discordant to Q n -Q n . Generalized estimating equations and Cox proportional hazards model were used to model the effect on longitudinal blood pressure and mortality, respectively. Q n -Q n showed a mean 2% drop in blood pressure consistently, whereas Q 4 -Q 1 showed a mean 2.1% and 1.6% rise in systolic and diastolic blood pressure, respectively. However,...