In lung function laboratories, statistical responses after bronchodilators (Bd) administration are widely used in patients with airflow limitation. However, their clinical relevance is debatable. Objective: To determine which spirometric parameters best reflect improvement in both exercise tolerance and exertional dyspnea in response to bronchodilators in obstructive lung diseases. Methods: Fifty patients with persistent asthma and/or COPD (FEV1/FVC = 41 ± 11%) were submitted to slow and forced vital capacity testing, MVV and a six-minute walking test (6 MW) following practice, before and after a 400 mug dose of salbutamol was given by MDI. Responses to Bd were expressed in absolute values and considered as increments to the initial values and predicted values. Responses to Bd were considered clinically significant if distance was longer than 30 m in the 6 MW test and/or if there was a 2-point decrease in the Borg scale in the walking distance. Results: 32 patients were responsive (R) to Bd and 18 were non-responsive (NR). As deltaMW correlated with age, (rs = --0.38 <FONT FACE=Symbol>¾</FONT> p < 0.01) an analysis on spirometric data, including age as covariant, was performed and expressed as x ± SE. No difference in FEV1 was observed between the groups (R = 255 ± 57 ml; NR = 256 ± 43 ml). The same occurred regarding MVV (R = 11± 2 L/min; NR = 10 ± 2 L/min.). The best separation (p < 0.01) was given by changes in inspiration capacity (IC) followed by changes in slow vital capacity (SVC): IC% of initial R = 23 ± 3% and NR = 3 ± 4%; absolute IC = 411 ± 58 ml and NR = 163 ± 77 ml; predicted IC%: R = 19 ± 3% and NR = 3 ± 4%. For SVC, the values were: % initial -- R = 18 ± 2% and NR = 9 ± 3%; absolute changes -- R = 448 ± 52 ml and NR = 256 ± 70 ml. Increases in IC > 15% of the initial values and 0.3 L and increases in SVS > 15% of the initial values and 0.4 L determined responsive patients with positive predicted values as approximately 90%. Conclusion: Variations in FEV1, FVC and MVV do not predict improvement in exercise capacity after Bd. This is best reflected by 15% of increases in IC and/or in the SVC initial values.
Obstructive lung diseases; Spirometry; Predictive value of tests; Bronchodilator agents; Exercise tolerance; Dyspnea
