The effect of air temperature and barometric pressure on nighttime and daytime ambulatory blood pressure

Most studies which investigated the effect of weather conditions on blood pressure prevalently considered the effect of air temperature. Typically, there is a clear seasonal pattern with a higher values in cold than in hot months. This seasonal variation in blood pressure (BP) has been directly attributed to changes in air temperature, while less known is the effect of barometric pressure. In the present research both air temperature and atmospheric pressure effects on blood pressure were studied in a population of subjects who underwent non invasive ambulatory blood pressure monitoring during all the 24 hours. All outpatients referred to the Hypertension Clinic of the University of Florence, from January 1997 to December 2002, were considered for the study (n=3,764). For the same 6-year period, daily air temperature (°C) and barometric pressure (hPa) data were obtained by the urban weather station located in the centre of Florence. The influence of weather on mean and variability of systolic and diastolic blood pressure and heart rate over daytime (from 08:00 to 20:00 hours), nighttime (and from 01:00 to 06:00 hours) and the entire 24-hour period was assessed by regression analyses and analysis of variance. Comparison between class means was tested by Bonferroni test. A clear seasonal trend of systolic and diastolic BP was observed and both air temperature and barometric pressure showed significant relationships according to age. The different effects of air temperature and barometric pressure on BP are discussed. These information could contribute to improve the modulation of antihypertensive treatment, especially for subjects ≥65 yrs.