PHYSIOLOGICAL BEHAVIOR OF RESPIRATORY MUSCLE DURING DIFFERENT TESTS OF RESPIRATORY ENDURANCE IN HEALTHY SUBJECTS
fatigue, respiratory muscles and plethysmography
INTRODUCTION: Fatigue is generally characterized when the muscle has a decrease in its ability to generate force and / or speed, this phenomenon is due to a muscle activity under load and is reversible upon rest. Inspiratory muscle fatigue (IMF) has been classified as central fatigue when it is induced by changes in neural drive, or peripheral fatigue that is characterized by changes in inspiratory muscle contractile properties from the imposition of high loads. OBJECTIVE: To evaluate and compare the physiological behavior of respiratory muscles during two respiratory endurance tests, normocapnic hyperpnea and inspiratory pressure threshold load in healthy subjects. METHODOLOGY: The research is a crossover study with a quantitative approach, in which healthy individuals of both genders were studied. The subjects were initially submitted to pulmonary function test and respiratory muscle strength evaluation. Then two respiratory endurance tests were performed. The protocol consisted of 10 pre sniff maneuvers, endurance test and 10 post sniff maneuvers. The test was performed with the Powerbreathe valve at 80% of maximal inspiratory pressure and Spirotiger at 70% of the maximum voluntary ventilation test, respecting a time period of 7 days between each test. During the protocol the subject was monitored by optoelectronic plethysmography, surface electromyography and NIRS for evaluation of tissue oxygenation of the sternocleidomastoid muscle. RESULTS: A total of 18 subjects participated in the study, 9 men and 9 women, with a mean age 23.94 ± 1.70 years, BMI 22.63 ± 1.95 kg / m². For the CLPI test, the load used was around 85.64 ± 15.78 CmH2O and a mean duration of the test was 157s, while for the HN test the subjects had a minute volume of 105, 1 ± 19.91 L / s and a time of 197s. In the intragroup comparison, regarding the BORG effort scale, there was an increase in the post value compared to the pre for both groups (p <0.0001), while in the intergroup comparison there was no difference (p> 0.05). Regarding the relaxation variables obtained from the sniff curve, in the intragroup comparison in relation to the pre values, there was a statistically significant increase only in the time finding (τ) in the first and third maneuver post test with NH, (p = 0 , 0067 and p = 0.0049), respectively. In the CLPI test, there was also an increase in the time constant (τ) in the first four post-test maneuvers (p <0.005). Regarding the other relaxation variables (MRR and 1 / 2RT) there was no statistically significant difference in the intragroup comparison in both test modalities. The contraction variables, also obtained from the sniff test, showed no statistical difference in the intragroup comparison of post-pre (P> 0.05) maneuvers. Regarding intergroup comparisons, no variable showed any difference. During the CLPI test there was a decrease in the median frequency, obtained from the surface electromyography of the inspiratory muscles, with a slope of -0.013 and r2 = 0.055. In the HN test there was also a fall of this variable with slope of -0.035 and r2 = 0.025. CONCLUSION: From the results found, it can be stated that inspiratory muscles behave similarly in relation to these different endurance test modalities. Additionally, inspiratory muscle fatigue causes changes in the relaxation variables, especially in the time constant rather than in the contraction variables.