4. Discussion
The purposes of the study were to develop the respiratory device training (named TU-Breath Training version II) and examine the effect of the prototype on cardiorespiratory performance (i.e., respiratory muscle strength and functional capacity) and rate of dyspnea in hemodialysis patients. The study reported that use of respiratory prototype program could improve respiratory muscle strength, functional capacity and rate of dyspnea in hemodialysis patients. These results are in line with the previous studies 1, 5-8.
The study was revealed that an improvement in MIP, 6MWD and sensation of breathlessness were observed in inspiratory muscle training thought respiratory prototype (TU-Breath Training version II). Dysfunction in multiple systems (e.g., musculoskeletal, cardiovascular and respiratory systems) could be found in patients with CRF. The reduction of systemic protein and skeletal muscle mass leads to loss of muscle mass whether in type I or type II fibers in cross-sectional areas. Further, the proportion of show fibers and also in the size of the fast fibers can been improved inspiratory muscle training 9. Muscle atrophy in particular type II muscle fibers, results from a reduction of vascular and capillary blood flow 10. These results are part of uremic myopathy in relation to skeletal muscles including the diaphragm and intercostal muscle and may present in muscle weakness (decreased MIP) and poor functional capacity (i.e., 6-MWT)11. In addition, impaired respiratory muscle by the uremic neuropathy and myopathy could leads to increases the work of breathing and also the neuromuscular dissociation 11. Therefore, neuromuscular dissociation might provoke an increase in respiratory effort and perceived in breathlessness among patients with chronic renal failure 12. In addition, weakness of inspiratory muscle leads to increase respiratory effort during exercise or physical activity resulting to increase metabolic stress in respiratory muscle and metaboreflex stimulation 13. Thus, metaboreflex stimulus and uremic myopathy might partially explain why respiratory muscle training improved sensation of breathlessness and cardio-respiratory fitness (i.e., inspiratory muscle strength and 6-MWT).
Regarding to breathlessness, the study found a decrease of dyspnea after 8-week intervention program. Silva et al found an improvement in the sensation of breathlessness after inspiratory muscle training program in hemodialysis patients 8. Decreased dyspnea is reported in IMT, it might be a decreasing dynamic hyperinflation of rib cage and therefore increasing gas exchange 14. In addition, increased respiratory muscle strength can be enhancing the pattern of maximal thoraco-abodminal motion (14). Additionally, Patessio et al reported the relationship between the sensation of breathlessness and respiratory muscle strength 15. MIP less than 80 cmH20 has been defined as inspiratory muscle weakness3,16. In the present study, MIP was an average 68.32 cmH2O which is clinically important inspiratory muscle weakness. However, after training programme for 8-week, the improvement in inspiratory muscle rose to 82.55 cmH2O. Therefore, it might be, in part, inspiratory muscle training improved the inspiratory muscle strength and thereby decreased sensation of breathlessness.
Some limitations of the present study should be noted. A relative small sample size with quasi experimental design which is lack of a control group. Therefore, further study need to explore the effect of inspiratory muscle training with a large sample size and randomized control trails. In addition, the training protocol such as intensity, frequency and duration of the study should be a consideration that might affect the result of the study.