Respiratory Muscle Activations During Stable Threshold Load and Increasing Threshold Load Endurance Tests in COPD

Chronic obstructive pulmonary disease (COPD) is a common, preventable and treatable disease characterized by persistent respiratory symptoms and airway limitation due to airway and/or alveolar abnormality that is affected by many factors that cause abnormal lung development resulting from exposure to harmful gases or particles. COPD is known as the fourth most common cause of death in the world and is expected to rise to third place by the end of 2020. Physiopathological changes such as airflow limitation, bronchial fibrosis, increased airway resistance, ciliary dysfunction, gas exchange abnormalities and air trapping occur in COPD. While smoking is the most common risk factor in COPD; Occupational dust and chemicals, air pollution, lung growth and development, genetic predisposition such as age and gender, and exposure to environmental effects. Symptoms such as shortness of breath (dyspnea), cough, and sputum are common in COPD. In addition to pulmonary changes such as an increase in respiratory workload in individuals with COPD, there are also extrapulmonary changes such as respiratory muscle dysfunction.

respiratory muscle dysfunction; It is a decrease in respiratory muscle strength, endurance, or both, resulting from factors such as elongated diaphragm fibers, increased respiratory workload, changes in muscle mass and abdominal weight. Strength is defined as the muscle's capacity to produce power, while endurance is defined as the muscle's ability to sustain a given force over time (the capacity to resist fatigue). Loss of strength and/or endurance contributes to diaphragm weakness and impaired performance. Today, respiratory muscle strength parameters (MIP, MEP) are widely used in the evaluation of respiratory muscle function. However, evaluation of respiratory muscle endurance is more effective than respiratory muscle strength in the evaluation of submaximal respiratory muscle contraction, which is valid for daily activities, and in the clinical, functional and prognostic evaluation of respiratory muscles. Respiratory muscle endurance can be measured with constant threshold load and increased threshold load endurance tests. The imbalance between the function of the respiratory muscles and the respiratory workload they face chronically plays an important role in the formation of dyspnea and hypercapnia. Neural respiratory impulse (NRD), which is indirectly measured by electromyogram (EMG) of respiratory muscles, has attracted attention as a potential physiological marker indicating clinical deterioration due to imbalance between workload and capacity of respiratory muscles. The neural respiratory drive (NRD) is the output of the brainstem respiratory centers. NRD is not affected by the patient's will, is associated with symptoms such as dyspnea, and is usually increased in COPD.

Mechanical abnormalities such as airflow obstruction, static and dynamic hyperinflation, and intrinsic positive end-expiratory pressure increase the load on respiratory muscles in individuals with COPD. Inspiratory muscle contraction is impaired as a result of pressure changes, muscle shortening, increased contraction rate, change in geometry, and decreased compliance of the respiratory system. As a result, an increase in muscle activation and NRD is observed. Those with severe COPD require significantly higher muscle activations, both electrical and mechanical, to breathe and overcome the respiratory workload than those with mild to moderate COPD. In individuals with COPD, NRD increases when the load on the respiratory muscles increases as a result of an increase in respiratory workload, a decrease in capacity, or a combination of both. Studies have shown that, in addition to respiratory workload, workloads given with respiratory muscle training devices lead to an increase in the activation of respiratory muscles.

In the literature, it has been observed that there is an increase in respiratory muscle activity in individuals with COPD due to the increase in respiratory workload and in response to the loads given by respiratory muscle training devices. However, no study has been found in the literature comparing the activation of respiratory muscles during constant threshold load endurance test and increasing threshold load endurance test performed with respiratory muscle training devices, which are important for respiratory muscle function evaluation. With this planned study, it is aimed to contribute to the literature by examining the changes in muscle activation during the constant threshold load and increasing threshold load endurance tests where different workloads are given and by comparing these changes.