Author's reply to letters on death in heat waves
http://www.100md.com
《英国医生杂志》
EDITOR—Although air movement alone will not always prevent heat stroke in air close to body temperature if the air is saturated1 or if sweating is impaired—for example, by drugs with anticholinergic actions2—air movement is an essential component in preventing heat stroke. Recent advice specifically related to heat stress in Britain over the next decade included not only a fan but moistening of clothing, open windows, light clothing, and avoidance of physical exertion.3
Moistening clothing substitutes for sweat. In moving air this allows evaporative cooling even of people with impaired sweating and in air warmer than body core temperature. In British (and most other) heat waves outdoor air is well short of saturation. Relative humidity was 22% near Faversham when the record temperature of 38.5 °C was recorded there last summer.
Air conditioning can virtually eliminate heat related mortality even in a subtropical climate.4 However, its capital cost and energy consumption are high, and it is not widely installed in countries such as Britain, where high temperatures are infrequent. Once heat stress does occur, cool baths are effective, but repeated immersion is less likely to be acceptable to elderly and ill people than moistening exposed skin and air movement from an open window. In case of doubt a simple test will show whether this or any other measure is helping: if it makes people feel cooler and more comfortable, it almost certainly is.
The design and management of buildings for hot weather is a different, but important, issue. As Pauleau points out,5 buildings can warm more slowly than outdoor air during the day, and closing windows for part of the day will then help. However, solar radiation and heat production by people and cooking can make buildings warm faster than outside air. Closed windows then accelerate the warming, as well as letting humidity rise.
Sunlight entering through windows, high occupancy, and low thermal mass and insulation are major factors promoting rapid warming. A lounge with picture windows and full of elderly people on a sunny day is a particular risk, even if the people are shaded from direct sunlight. Incidentally, outdoor slatted shutters are more effective than indoor curtains against solar heating. The shutters prevent radiation entering the building to produce greenhouse warming, while indoor curtains do not.
William R Keatinge, professor emeritus
Medical Sciences Building, Barts and the London School of Medicine, Queen Mary and Westfield College, London E1 2AD w.r.keatinge@qmul.ac.uk
Competing interests: None declared.
References
Wolfe RM. Death in heat waves. BMJ 2003;327: 1228. (22 November.)
Kilbourne EM, Choi K, Jones TS, Thacker SB, and the field investigation team. Risk factors for heat stroke: a case control study. JAMA 1982;247: 3332-6.
Keatinge WR. Death in heat waves. BMJ 2003;327: 512-3. (6 September.)
Donaldson GC, Keatinge WR, Nayha S. Changes in summer temperature and heat related mortality since 1971 in North Carolina, South Finland and Southeast England. Environ Res 2003;91: 1-7.
Pauleau A. Death in heat waves. BMJ 2003;327: 1228-9. (22 November.)
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Air conditioning can virtually eliminate heat related mortality even in a subtropical climate.4 However, its capital cost and energy consumption are high, and it is not widely installed in countries such as Britain, where high temperatures are infrequent. Once heat stress does occur, cool baths are effective, but repeated immersion is less likely to be acceptable to elderly and ill people than moistening exposed skin and air movement from an open window. In case of doubt a simple test will show whether this or any other measure is helping: if it makes people feel cooler and more comfortable, it almost certainly is.
The design and management of buildings for hot weather is a different, but important, issue. As Pauleau points out,5 buildings can warm more slowly than outdoor air during the day, and closing windows for part of the day will then help. However, solar radiation and heat production by people and cooking can make buildings warm faster than outside air. Closed windows then accelerate the warming, as well as letting humidity rise.
Sunlight entering through windows, high occupancy, and low thermal mass and insulation are major factors promoting rapid warming. A lounge with picture windows and full of elderly people on a sunny day is a particular risk, even if the people are shaded from direct sunlight. Incidentally, outdoor slatted shutters are more effective than indoor curtains against solar heating. The shutters prevent radiation entering the building to produce greenhouse warming, while indoor curtains do not.
William R Keatinge, professor emeritus
Medical Sciences Building, Barts and the London School of Medicine, Queen Mary and Westfield College, London E1 2AD w.r.keatinge@qmul.ac.uk
Competing interests: None declared.
References
Wolfe RM. Death in heat waves. BMJ 2003;327: 1228. (22 November.)
Kilbourne EM, Choi K, Jones TS, Thacker SB, and the field investigation team. Risk factors for heat stroke: a case control study. JAMA 1982;247: 3332-6.
Keatinge WR. Death in heat waves. BMJ 2003;327: 512-3. (6 September.)
Donaldson GC, Keatinge WR, Nayha S. Changes in summer temperature and heat related mortality since 1971 in North Carolina, South Finland and Southeast England. Environ Res 2003;91: 1-7.
Pauleau A. Death in heat waves. BMJ 2003;327: 1228-9. (22 November.)
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