Heat Waves, Aging, and Human Cardiovascular Health
Heat Waves, Aging, and Human Cardiovascular Health
This brief review is based on a President's Lecture presented at the Annual Meeting of the American College of Sports Medicine in 2013. The purpose of this review was to assess the effects of climate change and consequent increases in environmental heat stress on the aging cardiovascular system. The earth's average global temperature is slowly but consistently increasing, and along with mean temperature changes come increases in heat wave frequency and severity. Extreme passive thermal stress resulting from prolonged elevations in ambient temperature and prolonged physical activity in hot environments creates a high demand on the left ventricle to pump blood to the skin to dissipate heat. Even healthy aging is accompanied by altered cardiovascular function, which limits the extent to which older individuals can maintain stroke volume, increase cardiac output, and increase skin blood flow when exposed to environmental extremes. In the elderly, the increased cardiovascular demand during heat waves is often fatal because of increased strain on an already compromised left ventricle. Not surprisingly, excess deaths during heat waves 1) occur predominantly in older individuals and 2) are overwhelmingly cardiovascular in origin. Increasing frequency and severity of heat waves coupled with a rapidly growing at-risk population dramatically increase the extent of future untoward health outcomes.
The earth's climate is warming, with global mean temperature increasing by 0.74°C from between the years of 1906 and 2005. Humans are tropical animals and are therefore capable of surviving in, and adapting to, such relatively small changes in mean ambient temperatures. However, as mean global temperature rises, the frequency, severity, and relative length of heat waves increase. Heat waves can be functionally defined as an extended number of days with higher than normal temperatures. Prolonged exposure to high ambient temperatures induces a substantial stress on the human cardiovascular system, and although human beings are capable of withstanding extremely high temperatures for short periods, the cardiovascular strain induced by prolonged heat exposure contributes negatively to health outcomes. Indeed, during a heat wave, most of the excess morbidity and mortality are not directly heat related but are cardiovascular in origin, brought about by the increased cardiovascular challenge associated with thermoregulatory responses to heat stress.
Elderly individuals, even in the absence of overt cardiovascular disease, are the most vulnerable population during prolonged environmental heat exposure, experiencing significantly worse health outcomes than any other age cohort. Individuals older than 65 yr comprise most of the extra emergency room visits and deaths during heat waves. The global population of aged individuals is rapidly growing, meaning that an increasingly larger subset of the population will be susceptible to illness and death as climatic temperature continues to rise.
To defend against increasing core temperature, humans increase skin blood flow and sweat rate to dissipate heat. These effector responses are necessary for thermoregulation but place a great demand on the cardiovascular system by necessitating a relatively large increase in cardiac output. Decrements in skin blood flow are also observed and compounded with pathologies including hypertension and hypercholesterolemia as well as with common medications used in the primary and secondary prevention of cardiovascular disease. Even healthy aging is associated with an attenuated rise in skin blood flow and decreased sweat gland output in response to heat stress, but the integrated response to heat stress still places a great burden on a compromised (i.e. decreased adrenergic responsiveness) left ventricle.
The purpose of this review is to discuss the effect of heat stress on the aging cardiovascular system and, within that context, the projected effects of global warming on human cardiovascular health. This brief review was based on a President's Lecture presented at the 60th Annual Meeting of the American College of Sports Medicine in 2013.
Abstract and Introduction
Abstract
This brief review is based on a President's Lecture presented at the Annual Meeting of the American College of Sports Medicine in 2013. The purpose of this review was to assess the effects of climate change and consequent increases in environmental heat stress on the aging cardiovascular system. The earth's average global temperature is slowly but consistently increasing, and along with mean temperature changes come increases in heat wave frequency and severity. Extreme passive thermal stress resulting from prolonged elevations in ambient temperature and prolonged physical activity in hot environments creates a high demand on the left ventricle to pump blood to the skin to dissipate heat. Even healthy aging is accompanied by altered cardiovascular function, which limits the extent to which older individuals can maintain stroke volume, increase cardiac output, and increase skin blood flow when exposed to environmental extremes. In the elderly, the increased cardiovascular demand during heat waves is often fatal because of increased strain on an already compromised left ventricle. Not surprisingly, excess deaths during heat waves 1) occur predominantly in older individuals and 2) are overwhelmingly cardiovascular in origin. Increasing frequency and severity of heat waves coupled with a rapidly growing at-risk population dramatically increase the extent of future untoward health outcomes.
Introduction
The earth's climate is warming, with global mean temperature increasing by 0.74°C from between the years of 1906 and 2005. Humans are tropical animals and are therefore capable of surviving in, and adapting to, such relatively small changes in mean ambient temperatures. However, as mean global temperature rises, the frequency, severity, and relative length of heat waves increase. Heat waves can be functionally defined as an extended number of days with higher than normal temperatures. Prolonged exposure to high ambient temperatures induces a substantial stress on the human cardiovascular system, and although human beings are capable of withstanding extremely high temperatures for short periods, the cardiovascular strain induced by prolonged heat exposure contributes negatively to health outcomes. Indeed, during a heat wave, most of the excess morbidity and mortality are not directly heat related but are cardiovascular in origin, brought about by the increased cardiovascular challenge associated with thermoregulatory responses to heat stress.
Elderly individuals, even in the absence of overt cardiovascular disease, are the most vulnerable population during prolonged environmental heat exposure, experiencing significantly worse health outcomes than any other age cohort. Individuals older than 65 yr comprise most of the extra emergency room visits and deaths during heat waves. The global population of aged individuals is rapidly growing, meaning that an increasingly larger subset of the population will be susceptible to illness and death as climatic temperature continues to rise.
To defend against increasing core temperature, humans increase skin blood flow and sweat rate to dissipate heat. These effector responses are necessary for thermoregulation but place a great demand on the cardiovascular system by necessitating a relatively large increase in cardiac output. Decrements in skin blood flow are also observed and compounded with pathologies including hypertension and hypercholesterolemia as well as with common medications used in the primary and secondary prevention of cardiovascular disease. Even healthy aging is associated with an attenuated rise in skin blood flow and decreased sweat gland output in response to heat stress, but the integrated response to heat stress still places a great burden on a compromised (i.e. decreased adrenergic responsiveness) left ventricle.
The purpose of this review is to discuss the effect of heat stress on the aging cardiovascular system and, within that context, the projected effects of global warming on human cardiovascular health. This brief review was based on a President's Lecture presented at the 60th Annual Meeting of the American College of Sports Medicine in 2013.
