The current study was the first to investigate different training protocols. The present study found that IMT with 30 and 60% of MIP similarly increases functional exercise capacity; the highest improvement in PA is seen in IMT with 30%; IMT increases QMS, HGS, MEP, respiratory functions, and balance, reduces dyspnoea and fatigue.
Different training protocols that varied from 40 to 70% were used for IMT in patients with CKD [6, 7, 29,30,31,32]. Both IMT studies with 50–70% MIP [7, 29, 32] and 40% MIP [30, 33] showed improvement in IMS. In addition, studies with IMT with 40% MIP (25.92 cmH2O) [30], IMT with 50% MIP (22.5 cmH2O) [29], and IMT with 70% MIP (23.4 cmH2O) [7] showed an increase in MIP compared with controls that were no resistance, very low resistance, or no training. In the current study, MIP improved in all three groups, but IMT with 30% (33.16 cmH2O) and 60% (30.95 cmH2O) MIP showed higher improvements than IMT with 10% MIP (19.08 cmH2O). A minimal load of 30% MIP was found to improve in patients with chronic obstructive pulmonary disease [34]. However, in the present study, the IMT group with 10% MIP showed an improvement. Medeiros et al., stated an improvement in MIP in both training (50% MIP) and control (minimum device load; 5 cmH2O) groups in patients with CKD hemodialysis [32]. Owing to different disease mechanisms, the effects of IMT might be diverse in patients with CKD [32, 34]. IMT with 30% MIP may be an effective protocol for patients with CKD who cannot tolerate high intensities.
Studies about the effects of IMT on MEP in patients with CKD are limited. Three studies showed an increase in MEP [29, 32, 33], two 50% MIP studies showed that improvement varies from 10.8 to 23.16 cmH2O [29, 32], and only one 40% MIP study found an increase in MEP (73.12 to 82.50 cmH2O) [33]. Although there was no significant difference, the highest increase was observed in the group treated with 30% MIP. Of note, including patients with respiratory muscle weakness may have led to a greater increase in MEP than in the current study [32].
A decrease in exercise capacity has been reported in patients with CKD [35]. A systematic review reported an 80 m increase in the 6-MWT distance after IMT in patients with CKD, compared with controls [6]. However, in two studies with 50–70% MIP, there was no improvement in the 6-MWT distance [7, 32]. In the present study, the 6-MWT distance was improved in all groups, but the group with 30% MIP (Group 2: ∆6-MWT 80.57 m) and the group with 60% MIP (Group 3: ∆6-MWT 73.68 m) showed more improvement than the group with 10% MIP (Group 1: ∆6-MWT distance 45.25 m). In addition, the increase in the 6-MWT distance was higher than the MCID (66.3 m) [20]. Due to the short training period [7] and viral infection [32], there was no improvement in the 6-MWT distance in the abovementioned studies. It is known that mortality is related to reduced exercise capacity, [3] and so IMT might be beneficial for the survival of patients with CKD. Thus, the effects of IMT on mortality should be investigated in further studies.
Improvement in respiratory functions was shown in previous studies in patients with CKD [29, 30, 32, 33]; FVC was increased in studies with 40–50% MIP [29, 30, 33], and PEF improved in one study with 50% MIP [32]. In the current study, FEV1, FVC, and PEF were improved only in the 30% MIP group. FEF25-75(%) was improved in all groups. To further investigate the effects of IMT, pulmonary function should be assessed in more detail, such as diffusion capacity.
The present study was the first to show that QMS and HGS improved after IMT in patients with CKD. In addition, 10, 30, and 60% MIP similarly improved QMS, and HGS. It was shown that IMT with 30% [36] 40% [37], 50%, and 70% [38] MIP improved QMS in patients with heart failure. In addition, it was known that IMT increased limb blood flow in patients with heart failure [39]. A reduction in muscle metaboreflex activity may be a factor in increased muscle strength [40], thus further studies are needed to identify the mechanisms underlying the effects of IMT on peripheral muscle strength in patients with CKD.
In the literature, only one IMT (40% MIP) study showed that dyspnoea was improved after eight weeks of IMT [30]; however, dyspnoea was reduced after IMT with 10, 30, and 60% MIP in the current study. A reduction in dyspnoea may be due to an improvement in exercise capacity and respiratory muscle strength, therefore, new studies are needed to investigate the effects of IMT on dyspnoea, as the presence of respiratory muscle weakness may have affected the results.
A reduction in fatigue after IMT was observed in only one study with a 50% MIP [29]; however, fatigue was assessed using a sub-scale of QoL assessment. In the present study, fatigue decreased in both groups with 10, 30, and 60% MIP. Improvements in respiratory and peripheral muscle strength may have led to reduced fatigue. In the literature, the effects of IMT on QoL are scarce in patients with CKD. Two studies after eight weeks of IMT with 40 and 50% MIP showed no differences [30, 32]. One IMT study with 50% MIP for ten weeks stated an improvement in QoL sub-scales of energy/fatigue, sleep, pain, and a list of symptoms/problems [29]. In the present study, the SF-36 physical and mental sub-scale scores were increased in the 30% MIP group. A recent systematic review/meta-analysis stated that the effect of respiratory muscle training on QoL was unclear in patients with CKD [8], thus the effects of different IMT training durations on QoL should be examined.
In the current study, total PA increased in all groups; however, the 30% MIP group showed a significant improvement in total PA. A study found that IMT with 30% and 50% similarly increased PA in patients with heart failure. They stated that an increase in PA could be due to patients feeling safe and a reduction in kinesiophobia [36]. In the current study, an increase in functional exercise capacity or patients feeling safe and confident [36] may be the reason for improvement in PA. The effects of IMT on kinesiophobia in patients with CKD should be investigated in future studies. Balance was improved in the 10 and 30% MIP groups after the IMT, and an increase in the QMS may improve balance. There is a high incidence of falls in patients with CKD [41], and IMT could be an option to prevent falls by improving balance.
Limitations
This study had a few limitations. Although the 6-MWT is a valid and reliable test for assessing functional exercise capacity [18], cardiopulmonary exercise tests have not been performed because of technical problems. Balance was evaluated using the BBS [25], therefore, computer-based systems should be used in future studies. Although the control group performed 10% MIP, an improvement was observed in this group, which may be due to daily low-load training, therefore, the control group should be sham without load, in future studies.
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- Source: https://bmcnephrol.biomedcentral.com/articles/10.1186/s12882-024-03610-1