After a very bad winter, the warmth of summer will provide a welcome relief. However, too hot a summer can be a health hazard for seniors, particularly during heat waves. There are different definitions for what constitutes a heat wave, one of which is a temperature of five degrees Celsius over the normal maximum for several consecutive days. In the U.S. A., it is defined as over 90 degrees Fahrenheit (32.2 degrees Celsius) for three or more days. In Toronto, a heat alert is declared, when, based on calculations of temperature, humidity and air mass, there is a 65 percent likelihood of increased mortality. Montreal has developed a heat map which shows localized temperature variations due to asphalt and concrete replacing trees and green spaces, which is very helpful in identifying areas of greatest heat intensity. Excess deaths amongst seniors were a major issue in the heat waves in Europe in 2003 and in Chicago in 1995, so the impact of heat waves on seniors is not to be taken lightly.

The body's temperature is kept at a level of 38 degrees Celsius (98.4 degrees Fahrenheit) by a fine balance between heat production by the body's metabolism, physical exercise, and the ambient temperature, and heat loss due to evaporation, conduction and convection. Heat loss in hot weather is increased by sweating, dilatation of blood vessels near the skin, and increased output by the heart, with a redirection of blood from the internal organs to the skin. In seniors, these methods may not be as effective as in younger adults due to decreased sweating, less effective blood flow to the skin and a smaller increase in heart output. Within several days peo-ple adapt better to the heat. Seniors with chronic respiratory diseases and heart disease are at greater risk. The risks for all seniors are increased when the air quality deteriorates and causes smog, which is often the case in large cities during heat waves. Medications such as antidepressants, other psychiatric medications, anti Parkinson medication and diuretics add to the risks.

When heat production exceeds heat loss, the body's temperature rises and can lead to heat cramps, with painful spasms of the legs or the stomach muscles. More serious heat exhaustion may cause loss of appetite, nausea, vomiting, and weakness. Headaches, lightheadedness and fainting may be present. In more advanced cases, heat stroke can occur with an absence of sweating, confusion, agitation, hallucinations, and seizures. Treatment consists of cooling the patient and replacing fluids and electrolytes.

Seniors with chronic diseases and the very young are at greatest risk. Young athletes and workers who undertake energetic physical exercise during heat waves also may run into difficulties.

Precautions should be taken during heat waves to prevent problems. Fluid and salt replacement is important as is appropriate loose, light clothing. Advantage should be taken of an air-conditioned environment when possible. If not available in the seniors' homes, use can be made of public libraries, community centers, shopping malls and cinemas. Homes should be kept cool with fans and drawn curtains on the sunny side of the building are important measures. Reduced use of stoves or ovens is advisable. Windows may be opened wide at night, if this may be done safely. Avoiding exercise, heavy meals and decreasing the intake of alcohol and caffeine are all helpful measures. Cool showers and cool sponging are also of value. Seniors should avoid going out in the maximum heat of the day if possible.

In summary, heat waves pose a threat to seniors because of physiological changes. Seniors with chronic diseases and on multiple medications are at higher risk. Preventive measures and an early response to symptoms by taking measures to keep cool and replacing lost fluids will be effective in ensuring a safe as well as an enjoyable summer.

Rory Fisher, Geriatrician, Sunnybrook Health Science Centre, Toronto