PURPOSE: To compare respiratory and lower limb muscle strength and exercise capacity in subjects with and without COPD and to identify factors associated with reduced walked distance.
METHODS: We studied 21 COPD patients (13 men, 63.4±6.7 years) and 21 subjects without COPD (13 men, 63.7± 6.6 years). All subjects performed spirometry and assessment of respiratory muscle strength. Quadriceps strength was evaluated by the one-repetition maximum test (1RM). Exercise capacity was assessed through the six-minute walk test (SMWT). We used ANOVA, Spearman test and linear regression to analyze data.
RESULTS: Mean forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and FVC/FEV1 were 71.9±15.9%, 41.9±17.5% and 47.1±12.6 in COPD patients and 106.8±22.1%, 105.7±21.4% and 79.7.2±4.8 in subjects without COPD, respectively. The maximal inspiratory pressure (PImax) and expiratory pressure (PEmax) were decreased in COPD (-76.5 ± 23.4 cmH2O and 100.1 ± 25.7 cmH2O) compared to control (-101.5 ± 18.2 cmH2O and 127.1 ± 23.3 cmH2O; p<0.001). The mean values of 1RM test were 16.6 ± 5.4 kg and 22.9 ± 3.5 kg, respectively in COPD and non COPD subjects (p=0.001). The walked distance was lower in patients compared to control (404.9 ± 76.2 m vs 539.1 ± 48.3 m; p=0.0001). FEV1 (r=0.822), PEmax (r=0.623), PImax (r=-0.605), lower limb muscle strength (r=0.644), dessaturation and symptoms during exercise were associated with the walked distance (all p value<0.01). A model adjusted by gender was constructed with the walked distance as dependent variable using all subjects. FEV1 and PImax were the predictors that remained in the model (r2=0.761; p<0.001).
CONCLUSIONS: COPD patients have reduced respiratory and lower limb muscle strength as well as impaired exercise capacity compared to control subjects. FEV1 and PImax, but not quadriceps muscle strength, were the main factors associated with the walked distance in SMWT.
CLINICAL IMPLICATIONS: Interventions that increase respiratory muscle strength could be useful to improve exercise capacity in COPD patients. Supported by FIPE HCPA.
DISCLOSURE: The following authors have nothing to disclose: Marli Knorst, Andréia Silva, Anelise Dumke, Adriane Pasqualoto, Daiane Falkembach, Sérgio Menna Barreto
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