Study the mechanical pulmonary changes in patients with congestive heart failure (CHF) by impulse oscillometry

Respiratory system reactance reflects communicating lung volume in chronic obstructive pulmonary disease

Respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) is theoretically and experimentally related to lung volume. In chronic obstructive pulmonary disease (COPD), the absolute volume measured by body plethysmography includes a proportion that is inaccessible to pressure oscillations applied via the mouth, that is, a "noncommunicating" lung volume. We hypothesized that in COPD the presence of noncommunicating lung would disrupt the expected Xrs-volume relationship compared with plethysmographic functional residual capacity (FRC_pleth). Instead, Xrs would relate to estimates of communicating volume, namely, expiratory reserve volume (ERV) and single-breath alveolar volume (Va_SB). We examined FOT and lung function data from people with COPD (n = 51) and from healthy volunteers (n = 40). In healthy volunteers, we observed an expected inverse relationship between reactance at 5 Hz (X5) and FRC_pleth. In contrast, there was no such relationship between X5 and FRC_pleth in COPD subjects. However, there was an inverse relationship between X5 and both ERV and Va_SB. Hence the theoretical Xrs-volume relationship is present in COPD but only when considering the communicating volume rather than the absolute lung volume. These findings confirm the role of reduced communicating lung volume as an important determinant of Xrs and therefore advance our understanding and interpretation of FOT measurements in COPD. NEW & NOTEWORTHY To investigate the determinants of respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) in chronic obstructive pulmonary disease (COPD), we examine the relationship between Xrs and lung volume. We show that Xrs does not relate to absolute lung volume (functional residual capacity) in COPD but instead relates only to the volume of lung in communication with the airway opening. This communicating volume may therefore be fundamental to our interpretation of FOT measurements in COPD and other pulmonary diseases.

Finding the best thresholds of FEV1 and dyspnea to predict 5-year survival in COPD patients: the COCOMICS study

Background

FEV₁ is universally used as a measure of severity in COPD. Current thresholds are based on expert opinion and not on evidence.

Objectives

We aimed to identify the best FEV₁ (% predicted) and dyspnea (mMRC) thresholds to predict 5-yr survival in COPD patients.

Design and Methods

We conducted a patient-based pooled analysis of eleven COPD Spanish cohorts (COCOMICS). Survival analysis, ROC curves, and C-statistics were used to identify and compare the best FEV₁ (%) and mMRC scale thresholds that predict 5-yr survival.

Results

A total of 3,633 patients (93% men), totaling 15,878 person-yrs. were included, with a mean age 66.4±9.7, and predicted FEV₁ of 53.8% (±19.4%). Overall 975 (28.1%) patients died at 5 years. The best thresholds that spirometrically split the COPD population were: mild ≥70%, moderate 56–69%, severe 36–55%, and very severe ≤35%. Survival at 5 years was 0.89 for patients with FEV₁≥70 vs. 0.46 in patients with FEV₁ ≤35% (H.R: 6; 95% C.I.: 4.69–7.74). The new classification predicts mortality significantly better than dyspnea (mMRC) or FEV₁ GOLD and BODE cutoffs (all p<0.001). Prognostic reliability is maintained at 1, 3, 5, and 10 years. In younger patients, survival was similar for FEV₁ (%) values between 70% and 100%, whereas in the elderly the relationship between FEV₁ (%) and mortality was inversely linear.

Conclusions

The best thresholds for 5-yr survival were obtained stratifying FEV₁ (%) by ≥70%, 56–69%, 36–55%, and ≤35%. These cutoffs significantly better predict mortality than mMRC or FEV₁ (%) GOLD and BODE cutoffs.