Krassimira Stoeva 1 , Klara Dokova 1 , Nevijana Feschieva 1 ,Philip Kirov 2 , Stefka Petrova 3 ,

1. 384Marked seasonal variation in blood pressure and in proportions hypertensive… in north-east Bulgaria Krassimira Stoeva1, Klara Dokova1,Nevijana Feschieva1,Philip Kirov2,Stefka Petrova3, Ioto Iotov4, M Adela Sanz5,John Powles6(1) Dept of Social Medicine, Medical University, Varna, Bulgaria, (2)Stroke Unit, University Hospital, Varna, Bulgaria,  (3) National Centre for Hygiene, Medical Ecology and Nutrition, Sofia,(4) Cardiology Department, Medical University , Varna, Bulgaria, (5) Department of Preventive Medicine and Public Health, University of the Basque Country, Bilbao (6)Dept of Public Health and Primary Care, University of Cambridge 4. Conclusions 1. Introduction 3. Results 159 subjects participated in both cycles of fieldworkand had a total of at least 6 blood pressure measurements on at least 3 occasions. Of the 11 subjects with fewer than 8 blood pressure readings, 2 had 7 and 9 had 6. All missing readings were from the second visit in the winter cycle. Data quality rated moderate by digit preference and optimal by the proportion of odd blood pressure readings and the proportion of identical/duplicate results. There were marked falls in the means of the usual blood pressures from winter to summer, averaging 12 mmHg systolic and 7 mmHg diastolic. The finding that room temperature at the time of measurement did not account statistically for the variation in blood pressures by season does not exclude an effect of temperature operating mainly over time periods longer than an hour or so. Variation in blood pressure by season has been reported by many authors. The main interest in the data reported here lies in the magnitude of the seasonal variation. In a clinical context, individuals could be misclassified if season of measurement is not taken into account. In a public health context, information on blood pressure distributions may be difficult to interpretif season of measurement and room temperatures at the time of measurement are not reported. For example, when our results for mean systolic pressures at ages 45 to 64 are compared with those for 41 MONICA populations6, our male populations (urban plus rural combined) would rank 2nd highest on the basis of their winter measurements, but around the median using the measurements made in summer. For females the corresponding rankings would shift from around the median to the lowest quintile. Such widely differing rankings make it difficult to assess the potential contribution of local blood pressure distributions to the high stroke incidence in this region. Ranking of populations aged 45 to 64 by mean systolic blood pressures: study populations in Varna, Bulgaria compared to 41 MONICA populations separately on the basis of measurements made in winter and in summer. A seasonal variation in blood pressure has been reported from many countries, often with recommendations that either season of measurement or room temperatures at the time of blood pressure measurement should be noted1,2,3. Despite this, blood pressure findings from risk factor surveys continue to be reported without mention either of seasonal conditions or of ambient temperatures. We present here seasonal blood pressure data from Bulgaria, a lower middle income country with a high incidence of stroke4. In our study populations,access to central heating in winter or to cooling in summer has been limited by the economic difficulties of ‘transition’. Mean blood pressures at ages 45 to 74 (age standardised) by season Place holder 2. Methods 81 rural residents and 78 urban residents aged 45 to 74, divided approximately equally by sex and age-strata, took part in a validation study of dietary measurement in 2000. Each subject participated for one week of data collection in winter and one week during the summer. Blood pressure was measured in the subject’s home, on two days in the winter and two days in the summer cycles. On each occasion, two measurements were made, after 5 minutes rest in a sitting position. The 4 measurements within each season were made by the same fieldworker. The indoor temperature at the time of measurement was recorded. Data quality was monitored using digit preference and other published guides5. Subjects were deemed to meet the pressure criteria for hypertension if they had a usual systolic blood pressure (SBP) greater than 140 mmHg or a usual diastolic blood pressure (DBP) greater than 90 mmHg, where ‘usual’ refers to the mean of available readings for either winter or summer or of both combined. Because the data were unbalanced, least square means and their variances were estimated using proc glm in SAS ver 8.2. These were used for the calculation of group means, variances and confidence intervals. Data were age standardised using 5 year age groups and world standard weights. The proportion with usual blood pressures in the hypertensive range fell from 69% in winter to 47% in summer. Room temperatures at the time of measurement were an average of 7 degrees higher in summer (25.5º vs 18.5º). During the winter cycle of fieldwork, room temperatures were below 18º on 30 % of occasions. In regression models for systolic and diastolic pressures including both room temperature and season, the coefficient for temperature became statistically insignificant. References [1]Brennan PJ, Greenberg G, Miall WE, Thompson SG. Seasonal variation in arterial blood pressure. BMJ 1982, 285:919-923. [2] Rose G. Seasonal variation in blood pressure in man. Nature 1961, 189-235. [3]Woodhouse PR, Khaw KT, Plummer M. Seasonal variation of blood pressure and its relation to ambient temperature in an elderly population. J Hypertens 1993, 11: 1267-1274. [4]Powles J, Kirov P, Feschieva N, Stanoev M, Atanasova V.Stroke in urban and rural populations in north-east Bulgaria: incidence and case fatality findings from a 'hot pursuit' study . BMC-Public Health 2002;2(1):24. [5] Bennett S. Blood pressure measurement error: its effect on cross-sectional and trend analyses.J.Clin.Epidemiol. 1994; 47: 293-301. [6]Wolf HK, Tuomilehto J, Kuulasmaa K, Domarkiene S, Cepaitis Z, Molarius A,Sans S, Dobson A, Keil U, Rywik S. Blood pressure levels in the 41 populations of the WHO MONICA Project. J.Hum.Hypertens. 1997; 11 (11) :733-42. Funding source * standardised by age using the world standard weights Web address: http://www.phpc.cam.ac.uk/varna/stroke/index.html