DISCUSSION
Based on the findings, it can be suggested that the increase in inspiratory muscle strength, through inspiratory muscle training, was associated with decreased levels of cardiac anxiety in patients undergoing myocardial revascularization.
Anxiety and depression are interdependent variables and several studies have already shown a reduction in the intensity of these conditions in patients undergoing cardiac surgery exposed to physical exercise5,12,13. However, no studies were found to determine the impact of inspiratory muscle training on cardiac anxiety in this population.
A possible explanation for this result is the increase in levels of the brain-derived neurotrophic factor (FNDC), mainly in the hippocampus region14. The FNDC is of fundamental importance for the learning and consolidation of memory, which in turn, are responsible for the long-term effects of environmental stimuli as stressful life events15. Broman-Fulks and collaborators demonstrated a decrease in the self-reported feeling of fear or anxiety in patients undergoing an aerobic exercise program16.
Based on the results found in our study, it can be associated that inspiratory resistance training has the same effect on the FNDC protein, providing a behavioral change in these patients.
Another possibility for reducing anxiety is the increase in cerebral neurogenesis, which can be obtained through physical exercise. To achieve this change in brain structure, some conditions are associated, such as: increased endorphin B, vascular endothelial growth factor, FNDC and serotonin14.
In addition, Bettencourt and collaborators report that the ability to exercise has a direct influence on anxiety and depression17. The greater the capacity to perform activities, the lower the cardiac anxiety. Patients undergoing cardiothoracic surgery tend to have reduced physical capacity in the postoperative period8,9 and that IMT is a tool to increase functional capacity. Thus, the reduction in anxiety found in our study may have been influenced by the increase in functional capacity secondary to muscle training.
Tamuleviciute-Prasciene et al.18 concluded in their literature review that physical exercise enhances clinical and functional outcomes such as increased strength and muscle mass, mobility, cognition, activities of daily living and reduced anxiety. Most of these studies address aerobic exercises as part of phase I rehabilitation, in our study we increased the protocol with the IMT, achieving encouraging results.
During IMT there is a reduction in the diaphragmatic metaborreflex, generating a greater blood supply to appendicular muscles, thus improving performance in activities13,19, increasing the self-esteem of these patients, causing a reduction in cardiac anxiety.
A study entitled EUROASPIRE III demonstrated that regular physical exercise is associated with decreased levels of anxiety and depression in patients with coronary artery disease20. A similar result was found by Zheng and collaborators, but in patients after acute myocardial infarction21.
Pain related to the presence of drains and surgical incision leading to the avoidance of certain activities such as coughing, taking deep breaths and physical activity22, can generate a reduction in ventilatory muscle strength, thus increasing cardiac anxiety.
Another form of anxiety control resides in the pre and postoperative guidelines. It is based on the possibility of informing the patient what will happen during the entire operative period that extends from hospital admission to discharge home. These guidelines, in addition to reducing anxiety, are linked to improved quality of life, self-report, functional capacity and postoperative complications6,7. Orienting and making the patient aware of the need and benefits of inspiratory muscle training is of fundamental importance. Orienting and making the patient aware of the need and benefits of inspiratory muscle training is of fundamental importance.
According to our knowledge, this is the first study that correlates the direct impact of IMT on cardiac anxiety in patients undergoing CABG, therefore, we cannot consider that training was the main contributor to reducing the outcome variable.
Some limitations can be pointed out: (1) lack of sample calculation; (2) non-stratification for risk factors such as age, surgical risk and comorbidities; (3) not applying a pain scale, although all patients have protocol-guided analgesia.