The Prognostic Performance of Lung Diffusing Capacity in Preserved Ratio Impaired Spirometry: An Observational Cohort Study

Abstract

Purpose

Similar to chronic obstructive pulmonary disease (COPD), the diffusing capacity of the lung (D_LCO) might be decreased and associated with poor prognosis in preserved ratio impaired spirometry (PRISm), a clinical entity as a prodromal phase of COPD. The aims of the present study were to evaluate the distributions of D_LCO and to assess the association between D_LCO and mortality among subjects with PRISm.

Patients and Methods

We conducted an observational cohort study at the National Hospital Organization Fukuoka National Hospital. We classified the 899 patients ≥ 40 years of age with an assessment of D_LCO into five groups based on spirometry: preserved spirometry, PRISm, mild COPD, moderate COPD, and severe/very severe COPD. The prevalence of low D_LCO (< 80% per predicted) was compared among the five groups. Using PRISm patients with follow-up data, we further investigated the association of low D_LCO with all-cause mortality.

Results

The prevalence of low D_LCO in the PRISm group (58.8%) was significantly higher than that in the preserved-spirometry group (21.8%), the mild-COPD group (23.5%), and the moderate-COPD group (36.0%) (all P < 0.01), and it was comparable to that in the severe/very severe-COPD group (63.2%). The results remained unchanged after adjusting for potential confounders. Among the PRISm subjects, the overall survival rate was significantly lower in the low-D_LCO group than in the preserved-D_LCO group (P < 0.01). The multivariable-adjusted hazard ratio (HR) for all-cause mortality was significantly higher in the low-D_LCO group than in the preserved-D_LCO group (HR = 10.10 (95% confidence interval 2.33–43.89)).

Conclusion

Diffusing capacity was more impaired in PRISm subjects than in those with preserved spirometry or mild to moderate COPD. Regarding PRISm, low D_LCO was a significant risk factor for all-cause mortality. Clinicians should assess D_LCO in the management of PRISm to predict the future risk of overall death.

Keywords:

• preserved ratio impaired spirometry
• chronic obstructive pulmonary disease
• diffusing capacity of the lungs
• all-cause mortality

Abbreviations

PRISm, preserved ratio impaired spirometry; COPD, chronic obstructive pulmonary disease; D_LCO, diffusing capacity of the lung for carbon monoxide; BD, bronchodilator; FEV₁/FVC, forced expiratory volume in 1 second to forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; % pred, percent predicted; V_A, alveolar volume; ATS/ERS, American Thoracic Society/European Respiratory Society; BMI, body mass index; SVC, slow vital capacity; ANOVA, analysis of variance; OR, odds ratio; 95% CIs, 95% confidence intervals; HR, hazard ratio.

Data Sharing Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Ethics Approval and Informed Consent

This study was approved by the National Hospital Organization Fukuoka National Hospital Institutional Review Board for Clinical Research (#F4-2). Given the retrospective nature of the study, written informed consent was not requested by the ethics committee.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests in this work.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.