When heat waves become killers

As the southern states of Australia head in to winter, it’s hard to recall the oppressive heat wave that killed more than 200 hundred people in South Australia and Victoria last summer.

While we are acutely aware that our infrastructure may buckle or shut down under high temperatures, we underestimate the power of heat waves to quickly kill those most vulnerable: the elderly living alone, the mentally ill and the very young.

The number of heat wave deaths in South Australia and Victoria was directly linked to the number of elderly people living alone, who were not monitored by family or friends. Global warming did not cause the high death rate as some environmental groups have said. It was neglect.

Unlike many communal Asian cultures where the elderly are revered, in Australia our attitude to the elderly must take some of the blame for the high death rate.

According to Dr Monika Nitschke, the principal scientific officer at the South Australian Department of Health, medications such as diuretics and anti-hypertensive drugs used to lower blood pressure, may inhibit the ability to sweat or interfere with the reduction of temperature regulation mechanism in the central nervous system.

“An overheated core causes an inflammatory response through out the body, which, in combination with other mechanisms, can inhibit the body's natural mechanism for cooling down. You get hotter and hotter,” she said.

“Elderly people here (SA) died very quickly in unconditioned houses, - especially if they had no one to look after them.

“We need heat wave action plans and prevention plans which extend to the type of houses we live in, we can make cities and suburbs more livable under heat stress.”

Heat and the body

Think of the body as a thermostat. It operates best at its core temperature of 37C. Walk outside on a hot day and the central nervous system immediately starts working to cool you down. It diverts blood away from the internal organs and towards your skin. The blood carries the heat to the extremities.

Meanwhile, the sweat glands start to release water, which cools as it evaporates on the skin. On a very hot and humid day, it's harder to radiate heat away from your body due to the high water content in the air.

Infants and small children have a very slow sweat response, and their hearts aren't always strong. Obese people can't dissipate heat quickly and may have fewer sweat glands. Mentally ill and elderly patients sometimes take drugs that inhibit perspiration.

The heart does much of the hard mechanical work. That's OK if you're 16 but it's not good if you're 86. It can lead to arrhythmia or to a heart attack. As Dr Nitschke said, some medications for high blood pressure won't let the heart beat faster, which means it can't push blood away from the core organs quickly enough.