Atividade elétrica de músculos respiratórios e locomotores em indivíduos com doença respiratória obstrutiva durante teste de campo

Abstract

Introduction: Differently from calm breathing, during physical exercise, respiratory muscles are recruited as attempt to maintain adequate pulmonary ventilation and blood gas values within normal limits. In patients with expiratory airflow limitations, such as asthma and chronic obstructive pulmonary disease (COPD), the load offered by the respiratory system on the inspiratory muscles is increased mainly by changes in ventilatory mechanics. Thus, the respiratory muscle work that must be sustained beyond pre-existing changes in peripheral muscles puts at risk the development of muscle fatigue and impairment of exercise tolerance in this population. There are still gaps in the literature on how respiratory and peripheral muscles are activated and recruited during field tests that simulate everyday activities in this population, and the use of surface electromyography (EMGs) can be a useful tool in better understanding muscle behavior during the exercise. Aim: To evaluate the electrical signals of EMGs in the levels of activation and muscle fatigue of respiratory and locomotor muscles during field tests in subjects with obstructive respiratory diseases, and compare them to healthy ones. Methods: This is a case-control study. We evaluated 17 individuals diagnosed with asthma (Asthma group) (age: 34.76 ± 11.18; FEV1%: 91.41 ± 13.6) and 15 with COPD (COPD group) (age: 65.6 ± 7 .84; FEV1%: 63.46 ± 13.73) and 32 healthy matched for age, sex and body mass index (17 in the asthma control group and 15 in the COPD control group). All patients underwent the ISWT and the distance walked, cardiorespiratory variables, and reported symptoms were recorded. During the ISWT, the EMGs of the sternocleidomastoid (ECOM), the scalene (ESC), and the rectus femoris (RF) muscles were recorded and the electrical signals analyzed in the time and frequency domains, to extract the signal amplitude data, respectively, at 3 times (33%, 66%, and 100%) of the ISWT, in addition to the power spectrum density throughout the test. For statistical analysis, the GraphPad Prism 6.0 software was used with a significance level of p <0.05. Shapiro-Wilk test was applied to verify data normality. T-test was used for the analysis of anthropometric data, lung function, and performance on the ISWT. Mann-Whitney test was used to compare cardiorespiratory variables, dyspnea and fatigue symptoms in lower limbs, and EMG data. The Friedman test with Dunns post-hoc was used for intragroup analysis in the ISWT. Regression analyzes were performed to extract the coefficients of determination (r2) and slopes during the ISWT, for the variables of median frequency (FM), high-frequency and low-frequency contents, and H/L ratio. Regression slopes were compared between groups using the F test. Results: The distance walked on the ISWT was significantly shorter for the Asthma group compared to the respective Control group (p = 0.0007), with no differences between the COPD group and its control group. The amplitude of the EMGs of the assessed muscles was significantly higher in the initial stages of the ISWT in both Asthma groups (ECOM [33%: p= 0.0005 and 66%: p= 0.004], ESC [33%: p= 0.001 and 66 %: p= 0.03], and RF [33%: p= 0.02 and 66%: p= 0.004]) and COPD (ECOM [33%: p=0.009, 66%: p=0.02 and 100%: p=0.02], ESC [33%: p= 0.006, 66%: p= 0.008 and 100%: p= 0.01] and RF [33%: p= 0.03 and 66%: p=0.04]), compared to the matched control groups. The median frequency (FM) decreased considerably in the Asthma group for ESC (p = 0.01) and RF (p < 0.0001) compared to the Control group. In the COPD group, there was a linear decrease in FM for ECOM and RF, with significant values for ECOM (p < 0.0001), compared to the Control group. The H/L ratio dropped considerably for RF (p = 0.002) compared to the Control group. Conclusion: Our findings suggest that in asthma and COPD there is a increase in the electrical activity of respiratory muscles during ISWT, and this is accompanied by increased activation of the locomotor muscle, compared to healthy, to the detriment of poor functional performance, especially in asthma. Furthermore, we can suggest that respiratory and locomotor muscles are susceptible to muscle fatigue in obstructive respiratory diseases, with greater impacts on dyspnea and fatigue in lower limbs symptoms in patients with COPD during exercise.