## 4 Discussion  
The aim of our study was to investigate potential differences in cardiopulmonary parameters and cognitive function in patients with OSA after 4 weeks of respiratory muscle training compared with CPAP treatment. Our findings showed different adjustments in  
Figure 3: Results before and after the intervention period between the groups in the domains of the Montreal Cognitive Assessment (MoCA) questionnaire. Abbreviations: \(\square\) Baseline RMTgroup; \(\square\) After 4-week RMTgroup; \(\square\) Baseline CPAPgroup; \(\square\) After 4-week CPAPgroup. \(\ast\)\(p\) < 0.05 between baseline and after 4-week. cardiopulmonary parameters, cognitive function, and sleep quality in both groups before and after the intervention period. [PERSON] et al. [7; 16; 17; 22; 36; 37; 38] have shown that exercise programs improve cardiopulmonary indicators in patients with chronic respiratory diseases. The current study showed that RMTgroup after the 4-week intervention period improved the lower limb strength via a 30 s StS test by 7% (CPAPgroup \(\uparrow\) 6.5%) and reduced the MAP after a 30 s StS test by 8.7% (CPAPgroup \(\uparrow\) 6.8%). OSA is associated with impaired hemodynamic and chronotropic responses during exercise, with the main causative factor being impaired cardiovascular autonomic function resulting from structural downregulation of cardiac \(\beta\)-receptors and/or altered baroreflex set-point [39]. The increased MAP is related to sympathetic vasoconstriction, endothelial dysfunction, or a blunted response to beta-2 receptor stimulation, mechanisms that have been shown to be active in patients with sleep-disordered breathing [27]. After the intervention period and 30 s StS test, opposite MAP responses were observed in the two groups. Changes in MAP affected systemic vascular resistance and cardiac output, resulting in blood vessels being influenced by both local mediators and the autonomic nervous system and the endothelial cells respond to vasoactive depending on the body's needs [28]. According to [PERSON] and [PERSON] [28] when MAP is elevated, a decrease in sympathetic output and an increase in parasympathetic tone will decrease myocardial chronotropy and dromotropy, resulting in a decrease in cardiac output and a subsequent decrease in MAP. In the current study, the oxygen uptake after a 30 s StS test was approximately at 55% of predicted values of maximal oxygen uptake in both groups before and after the intervention period while the RMTgroup after the intervention period showed higher values in RMS by 12.5% (CPAPgroup \(\uparrow\) 3.1%). Respiratory muscle training may improve the respiratory muscle function during submaximal exercise and promote benefits for cardiac autonomic control [40]. According to [PERSON] et al. [40], the effects of RMT on cardiac autonomic control are related to the respiratory metaboreflex, and the generated strengthening of the respiratory musculature can increase the threshold of metaboreflex activation, reducing limiting factors (e.g., dyspnea, peripheral fatigue) and improving physical performance, while the effects on the autonomic nervous system reflex control systems involve the main barooreceptors and chemoreceptors [41], embedding the theory of competitiveness between the diaphragm and the quadriceps muscle. The autonomic nervous system also plays a vital role in regulating MAP via the baroreceptor reflex and vagus nerve, determining the sympathetic or parasympathetic tone to either raise or lower MAP [28]. In the current study, the intervention period consisted of 4 weeks of daily training of approximately 35 min at 80-90% of MIP and MEP (submaximal interval exercise). Our results showed an increase in performance (repetitions in the 30 s StS test) and changes in respiratory function with the RMTgroup having lower breath frequency values at the end of the 30 s StS and after the intervention period (\(\downarrow\) 17%) compared to the CPAPgroup (\(\downarrow\) 8%).