Respiratory symptoms frequent in smokers despite normal spirometry: The SPIROMICS study

1. Symptomatic smokers with preserved spirometric measurements had a significantly higher rate of respiratory exacerbations than both asymptomatic smokers with preserved spirometric measures and non-smoker controls.

2. Although many smokers have normal spirometric measurements, which excludes them from a diagnosis of COPD, a significant proportion of those who are symptomatic demonstrate an increased rate of exacerbations and activity limitation.

Evidence Rating Level: 2 (Good)

Study Rundown: A key diagnostic criterion in the diagnosis of COPD is a measured FEV₁:FVC ratio after bronchodialator use <0.70. However, large numbers of smokers report symptoms of COPD, such as chronic cough and dyspnea, despite an FEV₁: FVC after bronchodilator use greater than or equal to the cutoff for the diagnosis of COPD.

The Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) compared symptomatic smokers with preserved pulmonary function to asymptomatic smokers with preserved pulmonary function for risk of respiratory exacerbations, abnormalities on high resolution chest CT scans, and 6-minute walk distances.

The rate of respiratory exacerbations was significantly higher among symptomatic smokers with preserved pulmonary function than both asymptomatic smokers with preserved pulmonary function and nonsmokers. The 6-minute walk distance was shorter between symptomatic smokers with preserved pulmonary function and asymptomatic smokers with preserved pulmonary function and also between symptomatic smokers with preserved pulmonary function and nonsmokers. Symptomatic smokers with preserved pulmonary function did not significantly differ from asymptomatic smokers with preserved pulmonary function on high resolution CT scan, but did demonstrate significantly greater airway-wall thickening.

Click to read the study, published today in NEJM

Relevant Reading: The clinical impact of non-obstructive chronic bronchitis in current and former smokers

In-Depth [prospective cohort]: This multicenter, prospective cohort study compared symptomatic smokers with preserved pulmonary function to both asymptomatic smokers with preserved pulmonary function and nonsmokers for risk of respiratory exacerbations, abnormalities on high resolution chest CT scans, and 6-minute walk distances.

Respiratory exacerbation was defined as prescription of antibiotics and/or systemic glucocorticoids, any health care utilization, hospitalization, or ED visits. Over the course of the prospective analysis (median period followed=829 days), the rate of exacerbations was higher among symptomatic smokers with preserved pulmonary function than asymptomatic smokers with preserved pulmonary function (0.27±0.67 vs. 0.08±0.31, p<0.001) and nonsmokers (0.27±0.67 vs. 0.03±0.21, p<0.001). A p-value was not reported in the comparisons 6-minute walk distance was shorter among symptomatic smokers with preserved pulmonary function. Symptomatic smokers with preserved pulmonary function had a 6-minute walk distance that was 79.8±19.2% of the predicted value vs. 89.3±18.8% for asymptomatic smokers with preserved pulmonary function and 89.2±19.3% in nonsmokers. Symptomatic smokers with preserved pulmonary function did not significantly differ from asymptomatic smokers with preserved pulmonary function on high resolution CT scan (1.6±2.2% vs. 2.0±2.1%, p=0.99) but did demonstrate significantly greater airway-wall thickening (3.73±0.09 vs. 3.70±0.09, p=0.002).

Image: PD

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