Until we start to cough, wheeze or feel like we have an elephant sitting on our chest, most of us usually take the health of our lungs for granted, say respiratory specialists.
Breath after breath, day and night, our hard-working lungs filter dust, bacteria and chemicals from up to eight litres of air each minute extracting life-giving oxygen and neutralising toxic threats, without us giving the process a second thought.
During exercise that workload could increase five-fold to 40-60 litres each minute.
Often it wasn't until there was a lot of damage and deterioration in function that we registered a problem, said respiratory physician Philip Thompson, director of the Lung Institute of WA.
But, while not getting the headlines that heart disease and cancer attract, lung diseases as a group are the third most common cause of death in Australia and for GPs, make up the largest part of their day.
"It is the most common thing they deal with - almost 22 per cent of presentations involve a respiratory problem," Professor Thompson said.
The slow progression of some lung diseases such as emphysema and asthma and the large capacity provided by two lungs meant people could have deteriorating lung capacity well before symptoms were evident, he said.
"So if you took one lung out on the spot you would end up in the emergency department but if you took it out over 10 years, you could sit there and say you were perfectly well."
He said some cancers, depending on where they were located in the lungs, could remain "hidden" and not produce symptoms until more advanced, or pressing on other tissues.
Respiratory physician Christine Jenkins, of The Australian Lung Foundation said most people were good at explaining away breathlessness with exertion, and persistent cough and sputum. They often adapted their everyday activities to avoid becoming short of breath, making it the commonest warning sign that is easily overlooked.
But such strategies and self-explanation could be damaging because by the time everyday activities such as walking up stairs and hills or household tasks such as washing the car, vacuuming and gardening caused breathlessness, up to 50 per cent of lung function could already be lost, she warned.
Other signs of lung disease included having a persistent cough with phlegm - present for three months of the year for two or more years in succession or for protracted periods associated with wheezing and tightness following a cold or chest infection.
Professor Jenkins said many smokers wrongly accepted the symptoms as part of their habit, or out of guilt delayed seeking medical advice until they had succeeded in quitting.
"These symptoms of cough and sputum and breathlessness are easily explained away and that is the problem with them - everyone has their own explanation when in fact the explanation may be underlying lung disease," she said.
If you were puffing after climbing three flights of stairs, ask why, Professor Jenkins said.
"You might be in trouble with your heart, your lungs or with a lack of fitness and that is something a doctor should sort out for you."
Professor Thompson suggested a simple breathing test each year, similar to regular blood pressure checks.
"Chronic deterioration in lung function is like going down a slope towards a cliff edge - you can be right on the edge and think you are totally safe but one tiny push, like a 2 per cent change in your lung capacity, and you are over the edge and can't breathe," he said.The delicate internal lining of the lungs was "unforgiving" he said. Once damaged there was a greater likelihood of recurrence of disease or of developing subsequent complications.
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