"The reason for that is probably because these patients have had very difficult asthma for a long time and their lung capacity gets reduced because of that," o 'byrne said.

奥拜恩称，“之所以这样可能是因为，这些患者长期患有严重哮喘，导致其肺容量下降”。

youdao

High stress levels have been found to cause asthma attacks that make it difficult to breathe.

VOA: special.2009.03.24

Professor Martyn Partridge, chief medical adviser to Asthma UK, said it had previously been difficult to show that smoking causes asthma as it only needed a few patients with lung disease to be wrongly classified as having asthma to skew the results.

BBC: Women seem to be more at risk

The search is difficult because doctors, scientists and patients aren't used to thinking of rheumatoid arthritis, asthma and Alzheimer's disease as having the same root cause.

FORBES: Magazine Article

These cause all the features of asthma, including swelling and narrowing of the bronchi and secretion of thick mucus which make it difficult for patients to breathe.

BBC: Asthma vaccine hope