Effect of variation in environmental temperature on blood pressure: is it important?

OBJECTIVES: To study the effect of variation in environmental temperature on blood pressure and pulse. DESIGN: Repeated blood pressure and pulse measurements in volunteers on two days when environmental temperatures differed by 10 degrees C. SETTING: Part of an ongoing community based study. SUBJECTS: 25 Black subjects (23 males and two females) volunteered from a population cohort participating in an ongoing longitudinal study examining cardiovascular risk factors in an urban African Black environment. MAIN OUTCOME MEASURE: Mean systolic and diastolic blood pressures and pulse rates. RESULTS: The systolic and diastolic blood pressures were significantly higher when recorded at 15 degrees C than at 25 degrees C, mean difference 32.2 +/- 4.2, p < 0.001 and 19.5 +/- 3.0 p < 0.001) for systolic and diastolic blood pressures respectively. The pulse rate per minute at 15 degrees C was significantly lower than at 25 degrees C (mean difference 11.1 +/- 3.2 p = 0.002). CONCLUSIONS: A decrease in environmental temperature by 10 degrees C appears to increase blood pressure. Awareness of this phenomenon is important, especially when surprisingly high blood pressures are observed during low ambient temperatures, to avoid over diagnosis of hypertension. This phenomenon, together with that already established of the white coat hypertension, may lead to the erroneous diagnosis of hypertension.