Efeito do uso de salbutamol nas propriedades mecânicas do sistema respiratório de indivíduos saudáveis, tabagistas e portadores de doença pulmonar obstrutiva crônica

Abstract

Chronic obstructive pulmonary disease (COPD) is characterized by partially reversible flow limitation, classified by the post-bronchodilator level of airway obstruction. There is abundant evidence that FEV1 alone is not able to show bronchodilation in COPD patients, even in patients with clinical improvement. The forced oscillation technique (FOT) has shown high sensitivity for early detection of mechanical changes in COPD. However, the bronchodilator effect on respiratory impedance is still unclear. Objective to evaluate the utility of FOT in the diagnosis of different stages of airway obstruction, (2) to investigate the response to salbutamol in healthy, smoking and COPD patients in different degrees of severity. We evaluated 25 healthy subjects with no history of smoking, 24 smokers and 151 COPD patients classified into grades I, II, III and IV of severity. All subjects were assessed by the FOT followed by spirometry before and after the use of salbutamol spray. The resistance and reactance curves showed change at all stages of airway obstruction after the use of salbutamol. The smoking group showed similar mechanical changes to the mild group (p=ns). The parameters R0, Rm, Csr,din and Z4Hz presented adequate diagnostic accuracy (AUC>0.85) in all stages of disease severity. All FOT and spirometry parameters showed decreased after salbutamol use. Healthy individuals showed a small decrease compared with the subgroups of COPD. The variations of the impedance module (ΔZ4Hz) and resistance parameters, (ΔR0, ΔRm, Δs) were significant (p<0.0001, p<0.003, p<0.04 and p<0.0002, respectively) with increased bronchial obstruction. Mean reactance (ΔXm) increased with disease severity (p<0.0002). The ΔCrs,dyn showed no significant change with the severity of COPD. In percentage terms, FOT parameters showed significant variation in ΔRm% (p<0.02), Δs (p<0.02) and ΔXm% (p<0.004) with increased airway obstruction. ΔR0% ΔCrs,dyn% and ΔZ4Hz% did not vary between different stages of COPD. The association between bronchodilation in the airways and lung impedance was weak between ΔXm vs ΔFVC (r=0.32, p<0.0001) and ΔZ4Hz% vs ΔFEV1% vs ΔFVC% (r=0.28, p<0.0005, r=0.29, p<0.0003, respectively). The FOT is useful in the evaluation of the mechanical changes at different levels of airway obstruction in COPD. We demonstrate the benefit of a bronchodilator, quantifying the improvement of ventilation through the FOT. The respiratory impedance decreases in all stages of COPD. This suggests that the impedance changes are not dependent on lung volume as in spirometry and that bronchodilation occurs at all stages of the progression of COPD.