The hazard of rounding Cape Horn: is it changing?

Abstract

…he who goes the oftenest round Cape Horn goes the most circumspectly.Herman Melville, "White-Jacket", 1850Notwithstanding the range of strategies to help one cope with the cold weather, most countries experience mortalities in excess of 5-30% in winter, brought on mainly by cerebrovascular events. 1 This variability is mainly attributed to the population being able to keep themselves warm, both indoors and outdoors, necessitated by the mean cold temperature. Policies and measures to increase efficient use of energy indoors, coupled with advice to citizens suggesting to wear adequate warm protective clothing and to keep themselves active when out in the open, have been thus promoted. The elderly are aware of the risks, and traditionally perceive winter as a rounding of Cape Horn.Consequently, the result of exposure to acute cold may trigger vasoconstriction, with a rise in blood pressure (BP), and myocardial ischaemia in patients with coronary artery disease. This acute response is considered in all guidelines on BP measurement which recommend the importance of standardised room temperature when assessing BP values. However, a negative relationship between outdoor temperature and BP values was consistently observed even when measurements were taken in comfortably warm rooms. 2 In the French Three-City study 3 that prospectively investigated 8801 participants over the age of 65 years, average systolic BP was 5 mm Hg higher in winter than in summer. This variation was independent of anthropometric data and baseline BP values, but rather related to the subjects' age. Variations in BP were greater in subjects 80 years of age or older, than in younger participants. In the reanalysis of data collected in the World Health Organization Monica Project (monitoring trends and determinants in cardiovascular disease) risk factors surveys, 4 including 25 populations in 16 countries (115 434 participants aged 35-64 years) the effect of outdoor temperature remained after controlling for indoor temperature, as a 1°C increase in outdoor temperature reducing BP values by 0.14 mm Hg (95% Cl −0.23 to −0.05, adjusted for indoor temperature). Conversely, the effects of the winter season disappeared after controlling for outdoor temperature, suggesting that a major component of the seasonal change in BP was the direct result of temperature. 4 As physicians, we often have to deal with the effects of temperature in treating hypertensive patients even during summer, when we encounter the potential implications of falls or acute renal failure caused by a marked reduction in BP especially in the elderly. As a consequence, (although not considered in hypertension guidelines) physicians often resort to seasonal adaptation of antihypertensive drugs in their clinical practice.The influence of temperature, or at least seasonality, is conversely less considered in epidemiological studies investigating the burden of risk factors in populations. The importance of conducting an epidemiological study throughout a whole year, or at least to declare the...

Factors affecting seasonal changes in blood pressure in North India: A population based four-seasons study

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