Asthma and bronchiectasis exacerbation

Subjects

Data were collected retrospectively from inpatients diagnosed with bronchiectasis with or without asthma at the Shanghai Pulmonary Hospital (Shanghai, China) between January 2013 and December 2014. Patients who had not received a chest HRCT scan examination or who had indecipherable HRCT scan images were excluded. Patients with other diseases (e.g. chronic obstructive pulmonary disease, allergic bronchopulmonary aspergillosis, α₁-antitrypsin deficiency, significant immunodeficiencies and respiratory carcinomas) were also excluded. All aspects of the study were performed in accordance with relevant guidelines and regulations.

Diagnosis of bronchiectasis and asthma

Diagnosis of bronchiectasis was performed using chest HRCT scans in suspected patients with coughing and expectoration, or long durations of haemoptysis. High-resolution images were obtained during full inspiration at 1-mm collimation and 10-mm intervals from the apex to the base of the lungs. The presence of bronchiectasis was confirmed based on the following criteria: 1) lack of tapering in the bronchi; 2) dilation of the bronchi where the internal diameter was larger than that of the adjacent pulmonary artery; or 3) visualisation of the peripheral bronchi within 1 cm of the costal pleural surface or the adjacent mediastinal pleural surface [6, 7]. An exacerbation is defined as the patient reporting four or more of the following symptoms: change in sputum production, increased dyspnoea, increased cough, fever >38°C, increased wheezing, decreased exercise tolerance, fatigue, malaise, lethargy, reduced pulmonary function, changes in chest sounds or radiographic changes consistent with a new infectious process [3]. The type of bronchiectasis was defined morphologically. Patients with small areas of bronchiectasis only visible in a single pulmonary segment were excluded, because this sign can appear in a large proportion of the healthy population [8].

Asthma diagnosis was confirmed according to the Global Initiative for Asthma (GINA) guideline at the time of diagnosis. Asthma was diagnosed for patients with symptoms such as episodic breathlessness, wheezing, cough and chest tightness, and whose spirometry showed bronchial reversibility of 12% and 200 mL from the prebronchodilator value or airway hyperresponsiveness as a 20% decrease in forced expiratory volume in 1 s (FEV₁) caused by a provocative histamine with a cumulative dose <2.4 mg [9, 10]. In accordance with the GINA guidelines, asthma symptom control assessment was based on the frequency of daytime and night-time asthma symptoms, reliever use and activity limitation.

Variables

The variables collected in this study included the following: general and anthropometric information (i.e. age, sex, body mass index and smoking history); history of respiratory illness (i.e. pertussis, tuberculosis and anaphylactic rhinitis); lung signs (moist or dry rales); serological indicators (e.g. C-reactive protein, erythrocyte sedimentation rate, albumin and immunoglobulin (Ig)); pulmonary function test results (e.g. predicted and absolute values of FEV₁ and forced vital capacity (FVC) and FEV₁/FVC ratio); and microbiological detection of sputum samples. Sputum samples were accepted if they contained <10 squamous epithelial cells and >25 leukocytes per low-powered field. Bronchiectasis exacerbations were recorded in patients within 1 year of their discharge from the hospital, using telephone or face-to-face interviews.

Statistics

The statistical packages SPSS (version 19.0; SPSS, Chicago, IL, USA) and GraphPad Prism (version 5; GraphPad Software, San Diego, CA, USA) were used for statistical analysis and drawing graphs, respectively. The data were tabulated as mean±sd in the case of quantitative variables and as absolute numbers and percentages in the case of qualitative variables. The Kolmogorov–Smirnov test was used to analyse the distribution of variables. In the bivariate analysis, the t-test for independent variables was used to analyse variables that were normally distributed and the Mann–Whitney U-test was used to analyse variables that were non-normally distributed. Qualitative variables were compared using the Chi-squared test. In multiple comparisons, quantitative variables were compared using one-way ANOVA. If a variable was found to be significant, the Student–Newman–Keuls q-test was used to analyse the comparison among groups in multiple comparisons. Depending on whether variables were normally or non-normally distributed, either a Spearman or a Pearson coefficient was calculated to assess the correlation between variables. In the case of elevated collinearity between two variables (Spearman correlation test >0.6), the variable with greater clinical significance was included in the final regression equation. A logistic regression model was used to determine the factors that were independently associated with bronchiectasis exacerbation. The variables that presented statistically significant differences (p<0.05) in the bivariate analysis and were of clinical interest were included as the independent variables in the first model. The forward stepwise technique (i.e. the Wald test) was then used to remove any variables with p>0.1 from the final model. The odds ratio and 95% confidence interval were calculated for the independent variables, with p≤0.05 considered to be significant.