A new study entitled “Fixed airways obstruction among patients with severe asthma: findings from the Singapore General Hospital-Severe Asthma Phenotype Study” identified risk factors associated with fixed obstruction airways in patients with severe asthma in Singapore. The study was published in the journal BMC Pulmonary Medicine.

Asthma is a chronic inflammatory disease of the airways and is characterized by reversible airflow obstruction in response to bronchodilators or inhaled corticosteroids. The most severe cases, accounting for 5% of all asthma cases, are associated with higher mortality and morbidity rates. These usually exhibit an irreversible obstruction of the airways due to a failure of responding to standard therapeutics, such as inhaled corticosteroids or bronchodilators.

Identifying the causes for the fixed obstruction in asthma is crucial, however, studies performed with populations from distinct regions (Americans, Canadians, Europeans and Asians) identified distinct risk factors for disease severity. In this new study, the authors aimed to identify the factors responsible for the fixed obstruction in patients with severe asthma from Singapore.

To this end, they analyzed 245 patients previously acknowledged to be treatment-resistant severe asthma patients, according to the criteria established by the World Health Organization, which defines these as patients who require a combination of high-dose inhaled corticosteroids and long-acting beta agonists. The patients were part of the Singapore General Hospital-Severe Asthma Phenotype Study (SGH- SAPS). According to their performance on the test for forced expiratory volume in one second (after treatment with bronchodilator) prediction (PostBDFEV1 % predicted), patients were divided into two different groups – the group with equal or more than 70% and those with less than 70%, each reflecting the non-fixed obstruction and a fixed-obsctruction, respectively.

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The authors identified patients in the fixed-obstruction group were recognized as more frequent smokers, either in the past or currently, with high pack consumption yearly. However, the negative impact of this feature to the PostBDFEV1 % predicted was small. As expected, the values for all pulmonary function tests, including the PostBDFEV1 % predicted, the FEV1/FVC ratio and the FVC % predicted (Forced vital capacity) were significantly decreased in patients with fixed-obstruction. Other features, including atopy and allergen sensitization, or even symptoms and medication were similar between both groups.

Thus, the authors found smoking to be a risk factor associated with fixed obstruction, and this to be a consequence of obstruction of either lungs’ small and large airways.