Geographical Variations in Blood Pressure Level and Seasonality in Hemodialysis Patients

Abstract

Seasons and climate influence the regulation of blood pressure (BP) in the general population and in hemodialysis patients. It is unknown whether this phenomenon varies across the world. Our objective was to estimate BP seasonality in hemodialysis patients from different geographical locations. Patients from 7 European countries (Spain, Italy, France, Belgium, Germany, United Kingdom, and Sweden) participating in the DOPPS (Dialysis Outcomes and Practice Patterns Study) on years 2005 to 2011 were studied. Factors influencing pre- and postdialysis systolic BP and diastolic BP levels were analyzed by mixed models. There were 9655 patients (median age, 68; 59% male) from 263 facilities, seen every 4 months during a median duration of 1.3 years. Pre- and postdialysis systolic BP increased by a mean estimate of 5.1 mm Hg (95% confidence interval [CI], 3.7-6.4 mm Hg) and 4.4 mm Hg (95% CI, 2.9-5.9 mm Hg) for each 10° increase in latitude (1111 km to the North). In the longitudinal analysis, predialysis systolic BP was lower in summer and higher in winter (difference, 1.7 mm Hg; 95% CI, 1.3-2.2 mm Hg), with greater differences in southern locations (=0.04). Predialysis systolic BP was inversely associated with outdoor temperature (-0.8 mm Hg/7.2°C; 95% CI, -1.0 to -0.5 mm Hg/7.2°C), with steeper slopes in southern locations (=0.005). Results were similar for predialysis diastolic BP. In conclusion, there is a geographical and seasonal gradient of BP in European hemodialysis patients. There is a need to consider these effects when evaluating and treating BP in this population and potentially in others.

Blood Pressure Seasonality in Hemodialysis Patients from Five European Cities of Different Latitudes

“…We observed that increasing outdoor temperatures and longer sunshine duration were consistently associated with lower pre-dialysis BP, while humidity and rainfall were associated with increasing BP. Comfortingly, these results confirm those of our recent study which had similar objectives but different methods [8]. The influence of climate may occur through direct effect such as temperature-induced vasoconstriction and sweating [19].…”

“…It varies notably with climate and more specifically with temperature, humidity, rainfall and daylight span [5][6][7]. Recently, we observed for the first time a link between geographical location, BP level and BP seasonality in HD patients [8] which is in agreement with results from the general population [9,10]. Subjects living closer to the poles generally had higher BP and limited BP seasonal variations.…”

“…Increasing temperature triggers sweating to evacuate body heat, but this is limited in humid environments possibly due to skin saturation in water [21]. This is consistent with the direct association between humidity and BP level that we observed in the present and in earlier studies [7,8]. While the seasonal pattern was present and similar in the different facilities, it could not be clearly confirmed in Umea.…”

“…The average intra-individual change from summer (July) to winter (November) was 4 mmHg and 2 mmHg for pre-dialysis SBP and DBP respectively. It is now established that BP decreases of a significant amount in summer, although this may not occur in all populations, nor all locations [5,6,8,14,15]. The magnitude of seasonal cycles was greater in older, normotensive or diabetic HD patients.…”

“…Subjects living closer to the poles generally had higher BP and limited BP seasonal variations. In the EURODOPPS study, we analyzed a large population of representative samples from 7 European countries, but longitudinal data collection was performed only every four months, preventing to precisely estimate the magnitude of seasonal changes [8]. The objectives of the present study were to evaluate and quantify the seasonal change in BP in HD patients from 5 European cities located at different latitudes with greater precision.…”