Brazilian studies on pulmonary function in COPD patients: what are the gaps?

Abstract

Background: COPD is a major cause of death and morbidity worldwide, and is characterized by persistent airflow obstruction. The evaluation of obstruction is critically dependent on sensitive methods for lung-function testing. A wide body of knowledge has been accumulated in recent years showing that these methods have been significantly refined and seems promising for detection of early disease.

Objectives: This review focuses on research on pulmonary function analysis in COPD performed in Brazil during this century.

Materials and methods: The literature was searched using a systematic search strategy limited to English language studies that were carried out in Brazil from the year 2000 onward, with study objectives that included a focus on lung function.

Results: After we applied our inclusion and exclusion criteria, 94 articles addressed our stated objectives. Among the new methods reviewed are the forced-oscillation technique and the nitrogen-washout test, which may provide information on small-airway abnormalities. Studies investigating the respiratory muscles and thoracoabdominal motion are also discussed, as well as studies on automatic clinical decision-support systems and complexity measurements. We also examined important gaps in the present knowledge and suggested future directions for the cited research fields.

Conclusion: There is clear evidence that improvements in lung-function methods allowed us to obtain new pathophysiological information, contributing to improvement in our understanding of COPD. In addition, they may also assist in the diagnosis and prevention of COPD. Further investigations using prospective and longitudinal design may be of interest to elucidate the use of these new methods in the diagnosis and prevention of COPD.

Keywords: COPD; automatic clinical decision-support systems; complexity measurements; dynamic lung hyperinflation; oscillation mechanics; thoracoabdominal motion.

Figure 1

Schematic representation of the scope of the current review.

Figure 2

Examples of results for the resistance (R_rs; A) and reactance (X_rs; B) obtained in normal subjects and patients with COPD classified according to the GOLD criteria. Abbreviation: GOLD, Global Initiative for Chronic Obstructive Lung Disease.

Figure 3

Differences in the diagnostic performance of FOT and spirometric parameters, calculated by the difference between AUCs. Notes: Note the higher AUC values in the FOT parameters. The significance is shown at the top of the bars: 5, P<0.05; 1, P<0.01. Adapted from Faria et al, under creative commons license: http://creativecommons.org/licenses/by/2.0/. Abbreviations: FOT, forced-oscillation technique; AUCs, areas under the curve; Z_4Hz, absolute value of respiratory impedance; C_dyn, dynamic compliance; X_m, mean reactance; R_m, mean resistance; R₀, resistance at the intercept; FEF, forced expiratory flow; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; S, slope of resistance; Fr, resonance frequency.

Figure 4

Mean Z_rs values during the ventilatory cycle in the studied groups. Notes: *P<0.002; **P<0.0001. Groups were healthy subjects, smokers with normal spirometry, and patients with mild, moderate, severe, or very severe COPD. Adapted with permission from Silva KK, Faria AC, Lopes AJ, de Melo PL. Within-breath respiratory impedance and airway obstruction in patients with chronic obstructive pulmonary disease. Clinics (Sao Paulo). 2015;70(7):461–469. Abbreviations: Z_rs, respiratory impedance; GOLD, Global Initiative for Chronic Obstructive Lung Disease; ns, not significant; Z_bi, impedance at beginning of inspiration; Z_i, impedance during inspiration; Z_be, impedance at beginning of expiration; Z_e, impedance during expiration.

Figure 5

Comparisons of the diagnostic accuracy (area under the ROC curve) obtained using the best FOT parameter (BFP) and FOT + best ML methods. Note: All: all COPD patients; G1: mild airway obstruction; G2: moderate; G3: severe; G4: very severe airway obstruction. Abbreviations: FOT, forced-oscillation technique; ML, machine learning; ROC, receiver-operating characteristic.