Among patients with chronic obstructive pulmonary disease (COPD), those with the lowest maximal inspiratory pressures experience greater breathing discomfort (dyspnea) during exercise. In such individuals, inspiratory muscle training (IMT) may be associated with improvement of dyspnea, but the mechanisms for this are poorly understood. Therefore, we aimed to identify physiological mechanisms of improvement in dyspnea and exercise endurance following inspiratory muscle training (IMT) in patients with COPD and low maximal inspiratory pressure (Pimax). The effects of 8 wk of controlled IMT on respiratory muscle function, dyspnea, respiratory mechanics, and diaphragm electromyography (EMGdi) during constant work rate cycle exercise were evaluated in patients with activity-related dyspnea (baseline dyspnea index <9). Subjects were randomized to either IMT or a sham training control group ( n = 10 each). Twenty subjects (FEV1 = 47 ± 19% predicted; Pimax  = -59 ± 14 cmH2O; cycle ergometer peak work rate = 47 ± 21% predicted) completed the study; groups had comparable baseline lung function, respiratory muscle strength, activity-related dyspnea, and exercise capacity. IMT, compared with control, was associated with greater increases in inspiratory muscle strength and endurance, with attendant improvements in exertional dyspnea and exercise endurance time (all P < 0.05). After IMT, EMGdi expressed relative to its maximum (EMGdi/EMGdimax) decreased ( P < 0.05) with no significant change in ventilation, tidal inspiratory pressures, breathing pattern, or operating lung volumes during exercise. In conclusion, IMT improved inspiratory muscle strength and endurance in mechanically compromised patients with COPD and low Pimax. The attendant reduction in EMGdi/EMGdimax helped explain the decrease in perceived respiratory discomfort despite sustained high ventilation and intrinsic mechanical loading over a longer exercise duration. NEW & NOTEWORTHY In patients with COPD and low maximal inspiratory pressures, inspiratory muscle training (IMT) may be associated with improvement of dyspnea, but the mechanisms for this are poorly understood. This study showed that 8 wk of home-based, partially supervised IMT improved respiratory muscle strength and endurance, dyspnea, and exercise endurance. Dyspnea relief occurred in conjunction with a reduced activation of the diaphragm relative to maximum in the absence of significant changes in ventilation, breathing pattern, and operating lung volumes.
J Appl Physiol (1985). 2018 Aug 1;125(2):381-392.
https://doi.org/10.1152/japplphysiol.01078.2017

INTRODUCTION: Inspiratory muscle function may be affected in patients with End-Stage Renal Disease (ESRD), further worsening the functional loss in these individuals. However, the impact of inspiratory muscle weakness (IMW) on the functional capacity (FC) of hemodialysis patients remains unknown. Thus, the present study aimed to evaluate the impact of IMW on FC in ESRD patients undergoing hemodialysis.
MATERIALS AND METHODS: ESRD patients on hemodialysis treatment for more than six months were evaluated for inspiratory muscle strength and FC. Inspiratory muscle strength was evaluated based on maximal inspiratory pressure (MIP). IMW was defined as MIP values less than 70% of the predicted value. FC was evaluated using the Incremental Shuttle Walk test (ISWT). Patients whose predicted peak oxygen uptake (VO2peak) over the distance walked during the ISWT was less than 16mL/kg/min were considered to have FC impairment. Associations between variables were assessed by linear and logistic regression, with adjustment for age, sex, body mass index (BMI), presence of diabetes and hemoglobin level. Receiver-operating characteristic (ROC) analysis was used to determine different cutoff values of the MIP for normal inspiratory muscle strength and FC.
RESULTS: Sixty-five ERSD patients (67.7% male), aged 48.2 (44.5-51.9) years were evaluated. MIP was an independent predictor of the distance walked during the ISWT (R2 = 0.44). IMW was an independent predictor of VO2peak < 16mL/kg/min. (OR = 5.7; p = 0.048) in adjusted logistic regression models. ROC curves showed that the MIP cutoff value of 82cmH2O had a sensitivity of 73.5% and specificity of 93.7% in predicting normal inspiratory strength and a sensitivity and specificity of 76.3% and 70.4%, respectively, in predicting VO2peak ≥ 16mL/kg/min.
CONCLUSIONS: IMW is associated with reduced FC in hemodialysis patients. Evaluation of the MIP may be important to functional monitoring in clinical practice and can help in the stratification of patients eligible to perform exercise testing.
PMID: 28278163 PMCID: PMC5344350 DOI: 10.1371/journal.pone.0173159

PURPOSE: The aim of this study was to investigate the effects of inspiratory muscle training (IMT) on respiratory muscle strength, exercise capacity, dyspnea, fatigue, quality of life, and daily living activities of asthmatic patients.
METHODS: Thirty-eight asthmatic patients, between 18 and 65 years of age, were enrolled in the study and randomly divided into 2 groups; IMT (n = 20) or control (n = 18). Participants in the IMT group performed 30 breaths using a patient-specific threshold pressure device, twice daily for 6 wk at 50% maximal inspiratory pressure (MIP), in addition to ""breathing training"" during this period. Participants in the control group performed only the ""breathing training"" (sham or no threshold pressure device). Outcome measurements, performed before and after the intervention, included pulmonary function test, respiratory muscle strength, 6-min walk test, modified Medical Research Council dyspnea scale, St George's Respiratory Questionnaire, Fatigue Severity Scale, and London Chest Activity of Daily Living scale.
RESULTS: Among the outcomes in the study, changes to key variables including MIP (P < .01); MIP, percent predicted (P < .01); maximal expiratory pressure (MEP), percent predicted (P < .01); 6-min walk test walking distance (P = .001); modified Medical Research Council scale (P =<.001); Fatigue Severity Scale (P = .03); St George's Respiratory Questionnaire symptoms (P = .03); London Chest Activity of Daily Living domestic (P = .03); and London Chest Activity of Daily Living leisure (P = .01) were significantly different in favor of IMT versus control.
CONCLUSION: These findings suggest that IMT may be an effective modality to enhance respiratory muscle strength, exercise capacity, quality of life, daily living activities, reduced perception of dyspnea, and fatigue in asthmatic patients.
PMID: 29652761 DOI: 10.1097/HCR.0000000000000318