This can include second cancers, coronary artery disease, heart failure, lung problems and endocrine disorders (growth function and slow or delayed sexual development).

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By studying the climbers, six of whom reached the summit, the researchers hope to gain insight into heart failure, lung disease and sleep apnea all conditions related to a low-oxygen, or hypoxic, state.

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Last week, a government spokesman said Chavez was battling a severe lung infection that has caused respiratory failure.

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"Once you are in your 70s, 80s or 90s, or if you have chronic disease like heart failure, rheumatoid arthritis, chronic lung and kidney disease, a larger body size gives you longevity, " he said.

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The data show that, after failure of second-line chemotherapy, lung-cancer patients rarely get any added survival time from further treatments and often suffer significant side effects.

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People with heart failure often have a lower quality of life than arthritis, chronic lung disease or angina sufferers.

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The study, of patients with non-small cell lung cancer who were also receiving chemotherapy, showed an increase in "local failure, " meaning cancer cells at the radiation site either weren't killed or began growing.

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But Professor Peter Sever, of the National Heart and Lung Institute at Imperial College London, said there were already effective drugs for heart failure and that Viagra's action was not unique.

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However, if patients living with one lung have diabetes, coronary artery disease, chronic lung disease or are immunosuppressed, they may also be more vulnerable to develop complications such as respiratory distress or failure if they develop an upper respiratory infection such as bronchitis or pneumonia.

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