She said Francis' main challenge will be to keep his remaining full lung healthy.

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As well as squeezing fluid out of the lungs, it may promote the release of hormones that encourage healthy lung function.

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Viewers are shown close-ups of a healthy lung next to a blackened emphysemic lung, and the loop of a transplant scar that runs under Ms Laffin's arm and across her back.

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People are generally able to survive with one lung (as evidenced by Pope Francis) and live active, healthy and productive lives.

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The CDC said that people with heart and lung disease, children and older adults are most vulnerable, but even healthy adults can suffer symptoms when smoke levels are high enough.

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Trained dogs were asked to sniff out a study group that included lung cancer patients, chronic obstructive pulmonary disease (COPD) patients, and healthy volunteers.

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Most of the data we have on the effects of lung resection are from cancer patients, and Francis, having been young and otherwise healthy, probably did better than older, sicker patients.

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Chairman of the British Lung Foundation, Dr Mark Britton, said the research provided more "exciting evidence" of a link between a healthy diet and healthy lungs.

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