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Putting blood pressure on the map—literally

New study shows the importance of considering local temperature and geography when measuring cardiovascular health

Outdoor temperatures can sway blood pressure readings significantly for residents in warmer cities like Miami.

How can new technology change the way we monitor health? Researcher Jennifer Radin explains what her team learned from a study across six U.S. cities. The results were published recently in the journal Blood Pressure Monitoring.

By Jennifer Radin, PhD, assistant professor at the Scripps Translational Science Institute

One day you are outside enjoying sunny 70º F weather, and the next day temperature drops down to a cool 50º F and you have to grab your sweater on the way to work. Luckily, these large temperature fluctuations don’t happen often here in San Diego, but even small day-to-day temperature drops can potentially raise your blood pressure through vasoconstriction or tightening of your blood vessels in response to cooler weather. Warm weather does the opposite and causes vasodilation or widening of blood vessels.

Several studies have identified seasonal fluctuations in blood pressure, with higher blood pressure seen in colder months. Winter months have also been associated with higher rates of heart attacks and strokes, probably in part because of temperature induced blood pressure increases. However, less is known about how day-to-day changes in outdoor temperature impact a population’s daily mean blood pressure and heart rate, especially when it is measured indoors, in a temperature controlled environment. Additionally, few studies have compared its impact on populations living in climatically different geographies.

Our study evaluated the relationship between daily mean temperature data with daily mean blood pressure and heart rate data—collected from kiosks called higi health stations in six U.S. cities. Higi stations give users the ability to accurately measure their blood pressure and heart rate, weight and BMI at over 11,500 food, drug and retail locations across the country. Because this service is free and conveniently located, higi has collected one of the largest biometric databases with over 122 million blood pressure readings since 2012.

We found an inverse correlation between average daily mean temperature and a city’s mean blood pressure, meaning that when temperature went up, blood pressure went down. However, we found that changes in daily temperature had no impact on daily mean pulse. Interestingly, we also found that exposure to large temperature variability may result in some adaptation: We found that populations in warm, less temperature variable cities, like Miami, had a greater blood pressure response to a 1ºC temperature change than those in colder, more variable climates, like Boise and Chicago. Future, prospective studies evaluating differences in a city’s mean temperature and temperature variability, while controlling for population differences such as age, BMI, and co-morbidities, will help us to further evaluate and understand this relationship.

Numerous personal characteristics and behaviors such as weight, age, gender, genetics, stress, exercise, and smoking may impact an individual’s blood pressure. Our study suggests that environmental changes such as temperature and even geography should also be added to this list. In the future, taking into account a person’s individualized environment when diagnosing someone with hypertension or tailoring their treatment may help improve health outcomes. Improved access to free screening stations, like higi, and the development of new technology, such as continuous blood pressure watches, will allow even greater insight into the relationship of a person’s continuously changing environment and vital signs.

Read the study

This study was supported in part by the National Institutes of Health (NIH)/National Center for Advancing Translational Sciences (grant UL1TR001114) and a grant from the Qualcomm Foundation. The study included authors at Higi SH LLC.

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