The heart and the cold.

This review presents current epidemiological evidence indicating that a cold environment contributes to increased cardiovascular, especially coronary heart disease, morbidity and mortality, and examines the factors which might explain these findings. Most epidemiological studies have revealed a peak in the coronary morbidity and mortality during the cold season, and a strong negative correlation between the air temperature or its drop and the occurrence of coronary heart disease. These associations could be apparent, indirect or causative. A small part of the increased coronary morbidity and mortality could be due to, for example erroneous recording of cause of death (eg. death due to respiratory diseases). Part of the increased coronary manifestations of cold seem to be due to changes in living circumstances and habits associated with cold. The gradual development of hypothermia among people living in poor socio-economic conditions may lead to a disastrous chain of events. Snowfalls and storms associated with cold weather may increase the incidence of cardiac complications by exposing people to exceptional physical efforts and circumstances. Some of the effects of cold are direct: cold increases the myocardial oxygen demand by increasing sympathetic stimulation, systolic blood pressure and cardiac diastolic pressure and volume. At the same time the myocardial oxygen supply may be impeded by coronary vasoconstriction especially in vessels damaged by atherosclerosis. In addition to these short term effects cold may augment atherosclerosis for example by increasing blood pressure and the blood concentration of cholesterol, catecholamines, corticoids and thrombocytes during the cold season.(ABSTRACT TRUNCATED AT 250 WORDS)