RELATION OF 24-HOUR AMBULATORY BLOOD-PRESSURE AND SHORT-TERM BLOOD-PRESSURE VARIABILITY TO SEASONAL-CHANGES IN ENVIRONMENTAL-TEMPERATURE INSTAGE-I HYPERTENSIVE SUBJECTS - RESULTS OF THE HARVEST TRIAL

We investigated the seasonal changes in blood pressure (BP) and in sho rt-term BP variability determined using ambulatory blood pressure moni toring (ABPM). 1000 white subjects, who took part in the multicenter H ARVEST study, underwent ABPM with the A&D TM-2420 or the Spacelabs 902 07. Standard deviation of the mean daytime and nighttime BP was taken as an index of short-term BP variability (v). Maximal outdoor temperat ure (Tmax) during each ABPM was obtained from local Meteorological Cen ters. Subjects were divided according to season and to quartiles of Tm ax. A subgroup of 46 persons who repeated ABPM in Winter and Summer wa s also studied. We observed evident seasonal differences of office and ambulatory systolic BP (SEP) with a peak during Winter. Diastolic BP (DBP) and heart rate did not vary throughout the four seasons, Office SEP (p<0,01), 24-hour (p<0,002), daytime SEP (p<0,0001), both daytime SBPv (p<0,0001), DBPv (p<0,02) and nighttime SBPv (p<0,05), DBPv (p<0, 02) as well as norepinephrine (p<0,005) were significantly higher duri ng Winter than Summer. Similar differences were observed in subjects g rouped in quartiles of Tmax. In the subgroup daytime but not nighttime SEP was higher in the cold season. Average 24-hour SEP (p<0,05), dayt ime SEP (p<0,02), daytime SBPv (p<0,001) and DBPv (p<0,05) and norepin ephrine (p<0,0001) were significantly negatively correlated with Tmax in the whole population, BP is higher and subjected to wider oscillati ons during the cold season in patients with mild hypertension probably due to sympathetic activation. The assessment of a hypertensive subje ct may give different results according to the season.