Resting Breathing Instability During Wakefulness as a Predictor of Clinical Outcome in COPD

Abstract

BACKGROUND:

Dyspnea is a common symptom in patients with COPD. It causes physical inactivity and impaired health-related quality of life. Although optimal breathing methods alleviate dyspnea, it is unclear whether breathing instability has a clinical impact on patients with COPD. This study aimed to investigate whether resting breathing instability during wakefulness was associated with dyspnea assessed by the modified Medical Research Council (mMRC) dsypnea scale and whether breathing instability can be a novel predictor of clinical outcomes.

METHODS:

Forty-four subjects with stable COPD were enrolled (mean age, 71.0 y). Resting breathing was monitored for 15 min by using respiratory inductance plethysmography. Breathing instability was evaluated with the coefficient of variation for breath-by-breath respiratory duration and tidal volume ( ${\mathbf{\text{V}}}_{\mathbf{\text{T}}}$ ) by using an artifact-free respiratory signal for 5 min. Pulmonary function testing and blood gas analysis were performed (mean FEV₁ percent of predicted, 68.5%). Questionnaires with regard to dyspnea and health-related quality of life were also completed. Exacerbations were recorded prospectively for 1 year after the initial assessment.

RESULTS:

The coefficients of variation for ${\mathbf{\text{V}}}_{\mathbf{\text{T}}}$ were significantly higher in the subjects with an mMRC dyspnea scale score ≥ 2 versus those with an mMRC dyspnea scale score < 2 (26.4 ± 7.4% vs 20.3 ± 6.4%, P = .006) . The coefficients of variation for respiratory duration and V_T were not associated with age, body mass index, and pulmonary function variables. In multivariate analysis, FEV₁ percent of predicted and coefficient of variation for ${\mathbf{\text{V}}}_{\mathbf{\text{T}}}$ remained significant predictors for an mMRC dyspnea scale score ≥ 2 (P = .004 and P = .01, respectively). Coefficient of variation values were also correlated with several health-related quality of life domains. The exacerbation frequency was associated with the coefficient of variation for ${\mathbf{\text{V}}}_{\mathbf{\text{T}}}$ .

CONCLUSIONS:

Resting breathing pattern during wakefulness is a novel assessment tool for severity of dyspnea, which can be one of the predictors for exacerbation in patients with COPD.