PHYSIOLOGICAL BEHAVIOR OF RESPIRATORY MUSCLE DURING DIFFERENT TESTS OF RESPIRATORY ENDURANCE IN HEALTHY SUBJECTS
fatigue, respiratory muscles and plethysmography
INTRODUCTION: Fatigue, in general, is characterized when the muscle presents a decrease in its capacity to generate force and / or velocity, being this phenomenon due to a muscular activity under load and that is reversible by rest. Inspiratory muscle fatigue (IMF) has been classified as central fatigue, when it is induced by changes in the neural drive, or peripheral fatigue that is characterized by changes in the contractile properties of the inspiratory musculature resulting from the imposition of high loads. OBJECTIVES: 1) To evaluate and comparing the contraction and relaxation properties of the inspiratory muscles in healthy subjects after the induction of respiratory fatigue through two tests: normocapnic hyperpnea and inspiratory resistive load. 2) Evaluate and compare the shortening velocity of the inspiratory and diaphragmatic muscles after the induction of respiratory muscle fatigue 3) Evaluate and compare the tissue oxygenation of the sternocleidomastoid muscle after the induction of respiratory muscle fatigue 4) Evaluate the responses of the electrical activity of the sternocleidomastoid muscles , scalene, parasternal and rectus abdominis in both tests. METHODOLOGY: The research is a crossover type study with quantitative approach, in which healthy individuals of both genders were studied. The subjects were submitted initially to the pulmonary function test and to evaluate the strength of the respiratory muscles. Then, 10 nasal inspiratory pressure maneuvers (SNIP) were performed before the test, followed by the endurance test and 10 post SNIP maneuvers. The test was performed with the Powerbreathe valve at 80% of the maximum inspiratory pressure and with the Spirotiger at 70% of the maximum voluntary ventilation test (VVM), respecting a time of 7 days between the performance of each test and the order of its accomplishment was randomized. During the protocol the subject was monitored by optoelectronic plethysmography, surface electromyography and NIRS to evaluate the tissue oxygenation of the sternocleidomastoid muscle. From the SNIP maneuvers, the variables related to the relaxation and contraction properties were extracted. RESULTS: A total of 6 subjects participated in the study, being 3 men and 3 women, aged 25 (23-26.5) years, BMI 23.10 kg / m² (21.39-24.90). For the test with the powerbreathe the load used was 86.50 (67-90) CmH2O and for the spirotiger a minute volume of 116.4 (92-378) L / s. A decrease in the peak pressure (CmH2O) of the SNIP post maneuvers in relation to the pre-maneuver in both tests was observed. The maximum relaxation rate (MRR) decreased in all maneuvers of SNIP powders with the powerbreathe valve, except in the third maneuver. As for the spirotiger test, only the first post-maneuver showed a decrease. The maximum rate of pressure development (MRPD) decreased in all post maneuvers in relation to pre in both tests. Regarding the shortening velocity of the global inspiratory muscles (ΔVCW / Ti), there was a decrease in the first 5 post-test maneuvers in relation to the pre-value for both tests. However, the diaphragm shortening velocity (ΔVAB / Ti) only decreased in the maneuvers after the spirotiger test. The electrical activity of the respiratory muscles was calculated as a percentage of the pre-maneuver and a decrease in the activation (RMS) was observed in the post maneuvers in all the muscles studied for the spirotiger test. Already in the powerbreathe test, there was a decrease in all post maneuvers in all muscles, except in the rectus abdominis muscle. The duration of the tests was divided into intervals (20%, 60%, 80%, 100%) for analysis of tissue oxygenation variables. There was an increase in the concentration of oxygenated hemoglobin (HO2B), deoxygenated hemoglobin (HHB), and total hemoglobin (THB) in all percentages of test duration for both valves. This increase was more evident in the last test interval (100% ).