While health concerns about bushfire smoke are focused mainly on respiratory conditions, there is an emerging concern about the impact the smoke can have on the heart and circulatory system.
Although this impact is not immediately obvious and may remain hidden, recent evidence suggests the smoke can cause cardiovascular problems and complicate existing ones.
This is significant because, in Sydney alone, the air quality is now three times poorer than it has been in the previous five bushfire seasons.
Given Australia is facing a record hot and dry summer, with high fire risks, people with cardiovascular issues are advised to take precautions in the weeks ahead.
If they live in smoke-affected areas, Professor Garry Jennings, chief medical adviser of Australia’s Heart Foundation, recommends they refrain from outdoor activities.
“Don’t allow yourself to get unnecessarily exposed. Give your daily walk or exercise a miss and make it up when the smoke has gone.”
People prone to respiratory conditions are advised to wear masks outdoors, and Professor Jennings said people with a history of heart disease may consider doing the same.
Although past studies have produced inconsistent findings, Professor Jennings said there was now an emerging consensus about the increased risk of heart failure, heart attacks, strokes, pulmonary embolism and high blood pressure, during and in a few days after exposure to bushfire smoke.
The evidence shows the denser the smoke, the higher the risk.
Professor Jennings, a cardiologist, says the problem arises from fine particles in the smoke that are smaller than 2.5 micrometres in diameter, a fraction the width of human hair.
These particles have the capacity to travel deep into the lung, into its smallest branches, where they can cross over into the bloodstream.
“Loaded with active ingredients, they can incite inflammation and other problems,“ he said.
“There is also a suggestion they make the blood a little more coagulable, which may explain the raised risk of stroke and pulmonary embolism.”
Others suggest these particles can also affect the autonomic nervous system, which in turn may contribute to instability in blood pressure or increase the heart rate.
A study published in the Journal of the American Heart Association last year looked at over a million emergency room visits across California during 2015 wildfires.
It found a 10 per cent increased risk of presentation with heart attacks, strokes, worsened heart failure symptoms and irregular heart rhythms.
On dense smoke days, emergency department visits for these ailments jumped, particularly among elderly patients.
The study looked at other diseases too, such as appendicitis, and found no increase in hospital presentation.
Professor Jennings said the smoke can accelerate pre-existing cardiovascular conditions. “Nobody gets a heart attack from the last five days. They’ve set themselves up to have it and the smoke might just bring it forward.”
Evidence on the cardiovascular impact of bushfire smoke is currently only available for the short term.
In the meantime, Professor Jennings said having a heart check was better insurance than wearing a mask or staying inside.