Pathophysiological mechanisms of exertional breathlessness in chronic obstructive pulmonary disease and interstitial lung disease

Breathlessness dimensions should be evaluated in relation to the level of exertion: A clinical study

BACKGROUND/AIM

Exertional breathlessness is a dominating symptom in cardiorespiratory disease, limiting exercise capacity. Multidimensional measurement has been proposed to capture breathlessness, but it is unknown whether it is useful to differentiate people with abnormal vs normal exertional breathlessness intensity.

METHODS

This was a secondary analysis of a randomized controlled trial of outpatients aged ≥ 18 years performing a symptom-limited cycle incremental exercise test (IET). Breathlessness sensations at end of IET were identified using the multidimensional dyspnea profile (MDP) 30-min post-exercise and compared between people with abnormally high breathlessness (Borg 0-10 rating > upper limit of normal [ULN]) and people within normal ranges (≤ ULN) in relation to the percentage of predicted peak power output defined by normative reference equations.

RESULTS

Of 92 participants, 20 (22 %) had abnormally high breathlessness. Compared with those with normal breathlessness (n = 72 [78 %]), the abnormal group reported higher symptom intensity at peak exercise (7.9 ± 1.7 vs 6.3 ± 1.4 Borg units; p < 0.001) and had lower peak power output 129 ± 52 W vs 167 ± 55 W; p < 0.001). Differences between those with normal, and abnormal exertional breathlessness regarding MDP ratings were not statistically significant (all p > 0.05): overall unpleasantness, 4.1 ± 2.3 vs 4.7 ± 1.6; immediate perception, 10.9 ± 2.8 vs 11.5 ± 1.8; and emotional response, 4.1 ± 7.6 vs 3.2 ± 7.5. MDP ratings had no relation to peak power output.

CONCLUSION

Breathlessness dimensions are similar at the peak of a standardized IET and cannot differentiate between people with normal and abnormally high exertional breathlessness.

Effects of home-based telerehabilitation-assisted inspiratory muscle training in patients with idiopathic pulmonary fibrosis: A randomized controlled trial

BACKGROUND AND OBJECTIVE

There are few studies that have used inspiratory muscle training (IMT) as an intervention for patients with isolated idiopathic pulmonary fibrosis (IPF). This study aimed to investigate and interpret the effects of home-based telerehabilitation-assisted IMT in patients with IPF.

METHODS

Twenty-eight participants with IPF took part in the study. Lung function tests, functional exercise capacity by 6-min walk distance (6MWD), dyspnoea perception by modified medical research council dyspnoea scale (mMRC), and inspiratory muscle strength by maximal inspiratory pressure (MIP) were assessed. IMT was performed twice a day, 7 days/week, for 8 weeks. The intervention group (n = 14) performed IMT at 50% of their baseline MIP while the control group (n = 14) performed IMT without applied resistance. Loading intensity was progressed by keeping the load at 4-6 on a modified Borg scale for the highest tolerable perceived respiratory effort for each patient.

RESULTS

Dyspnoea based on mMRC score (p < 0.001, η2 effect size = 0.48) significantly decreased within the intervention group compared with the control group. There were significant increases in the intervention group compared to the control group based on 6MWD (p < 0.001, η2 effect size = 0.43), MIP (p = 0.006, η2 effect size = 0.25) and MIP % predicted (p = 0.008, η2 effect size = 0.25).

CONCLUSION

The findings of this study suggest that an 8-week home-based telerehabilitation-assisted IMT intervention produced improvements in inspiratory muscle strength, leading to improvements in functional exercise capacity and dyspnoea.

Effect of breathing exercises on patients with interstitial lung disease: A systematic review and meta-analysis

PURPOSE

This study was designed to synthesize the efficacy and safety of breathing exercises in interstitial lung disease (ILD) patients by reviewing the literature and comparing the impact of different control group types, ILD subtypes, breathing exercise action modes or methods, and intervention durations on clinical efficacy.

METHODS

Systematic searches were conducted across 9 electronic databases, including PubMed, to retrieve English and Chinese studies reporting on ILD patients from inception to February 12, 2024. Study selection and data extraction were independently conducted by two researchers. The quality of the included studies was assessed using the Cochrane risk of bias tool. The data were analysed using RevMan 5.4 and STATA 17.0 software.

RESULTS

The search identified 25 studies. Compared to the control group, the breathing exercise group exhibited significantly improved lung function (FVC%pred: MD  =  3.46, 95%CI = 1.04 to 5.88; DLCO%pred: MD = 3.20, 95% CI = 2.91 to 3.48), dyspnoea (MRC or mMRC scale: MD = - 0.50, 95%CI = - 0.77 to - 0.22), exercise capacity (6MWD: MD = 32.65, 95% CI = 14.77 to 50.53), and HRQoL (SGRQ: MD = - 6.53, 95% CI = - 8.72 to - 4.34) in ILD patients. According to the subgroup analysis, significant improvements consistent with the overall results were observed in the control group with usual treatment. Compared with the control group, breathing exercises had varying degrees of improvement in the mixed diagnostic group, known-cause group, and fibrotic group of ILD patients; breathing exercises alone significantly improved DLCO%pred, MRC (or mMRC), and SGRQ; and the improvement in breathing exercises as part of pulmonary rehabilitation (PR) was more notable. Different durations of breathing exercise could promote the efficacy of different aspects of treatment for ILD patients.

CONCLUSIONS

Compared with usual treatment, breathing exercises can improve lung function, exercise capacity, and HRQoL in ILD patients, particularly without high requirements for intervention duration. The efficacy of breathing exercises varies for different ILD subtypes, and incorporating breathing exercises as part of PR can be more beneficial for ILD patients. No studies have shown significant risks for ILD patients engaging in breathing exercises.

Differences of ventilatory muscle recruitment and work of breathing in COPD and interstitial lung disease during exercise: a comprehensive evaluation

Introduction

COPD and interstitial lung disease (ILD) are significant chronic respiratory disorders, impacting quality of life. Respiratory muscle roles and differences remain not entirely clear. The objective of the present study was to evaluate the degree of recruitment of the respiratory muscles and the work of breathing in COPD and ILD during exercise.

Methods

We compared the sensory-mechanical relationships in COPD, ILD and healthy controls (n=20 each). They performed pulmonary function, noninvasive and invasive respiratory muscle strength, surface electromyography and work-of-breathing assessments.

Results

COPD and ILD did not show lower static muscle strength compared to controls, but did show poor performance in the exercise test with increased transdiaphragmatic pressure (P di). In ILD, there was a higher increase in oesophageal pressure and a lower gastric pressure (P ga) on inspiration; in COPD, there was a significant increase in P ga on inspiration. In ILD, there is greater recruitment of accessory inspiratory muscles, whereas in COPD, there is marked use of both inspiratory and expiratory muscles. The neuromechanical inefficiency (increased neural respiratory drive without the corresponding tidal volume) was found in both diseases. In COPD, there is a considerable increase in elastic work to overcome intrinsic positive end-expiratory pressure (PEEPi) and expiratory work of breathing, whereas in ILD, non-PEEPi elastic work of breathing is the highest part of the total work of breathing.

Conclusions

Early and increased activity of the respiratory muscles and work-of-breathing components significantly contribute to dyspnoea, exercise intolerance and neuromechanical inefficiency of ventilation in COPD and ILD. The mechanisms of P di generation were different between diseases.

Normative Reference Equations for Breathlessness Intensity during Incremental Cardiopulmonary Cycle Exercise Testing

Rationale: Cardiopulmonary exercise testing (CPET) is the gold standard to evaluate exertional breathlessness, a common and disabling symptom. However, the interpretation of breathlessness responses to CPET is limited by a scarcity of normative data. Objectives: We aimed to develop normative reference equations for breathlessness intensity (Borg 0-10 category ratio) response in men and women aged ⩾40 years during CPET, in relation to power output (watts), oxygen uptake, and minute ventilation. Methods: Analysis of ostensibly healthy people aged ⩾40 years undergoing symptom-limited incremental cycle CPET (10 W/min) in the CanCOLD (Canadian Cohort Obstructive Lung Disease) study. Participants had smoking histories <5 pack-years and normal lung function and exercise capacity. The probability of each Borg 0-10 category ratio breathlessness intensity rating by power output, oxygen uptake, and minute ventilation (as an absolute or a relative value [percentage of predicted maximum]) was predicted using ordinal multinomial logistic regression. Model performance was evaluated by fit, calibration, and discrimination (C statistic) and externally validated in an independent sample (n = 86) of healthy Canadian adults. Results: We included 156 participants (43% women) from CanCOLD; the mean age was 65 (range, 42-91) years, and the mean body mass index was 26.3 (standard deviation, 3.8) kg/m2. Reference equations were developed for women and men separately, accounting for age and/or body mass. Model performance was high across all equations, including in the validation sample (C statistic for men = 0.81-0.92, C statistic for women = 0.81-0.96). Conclusions: Normative reference equations are provided to compare exertional breathlessness intensity ratings among individuals or groups and to identify and quantify abnormal breathlessness responses (scores greater than the upper limit of normal) during CPET.

Home-based respiratory muscle training on quality of life and exercise tolerance in long-term post-COVID-19: Randomized controlled trial

OBJECTIVE

To evaluate the effects of a home-based respiratory muscle training programme (inspiratory [IMT] or inspiratory/expiratory muscles [RMT]) supervised by telerehabilitation on quality of life and exercise tolerance in individuals with long-term post-COVID-19 symptoms. The secondary objective was to evaluate the effects of these programmes on respiratory muscle function, physical and lung function, and psychological state.

METHODS

88 individuals with long-term symptoms of fatigue and dyspnoea after COVID-19 diagnosis were randomly (1:1 ratio) assigned to IMT, IMT_sham, RMT or RMT_sham groups for an 8-week intervention (40min/day, 6 times/week). Primary outcomes were quality of life (EuroQol-5D questionnaire) and exercise tolerance (Ruffier test). Secondary outcomes were respiratory muscle function (inspiratory/expiratory muscle strength; inspiratory muscle endurance), physical function (lower and upper limb strength [1-min Sit-to-Stand and handgrip force]), lung function (forced spirometry), and psychological status (anxiety/depression levels and post-traumatic stress disorder). All outcomes were measured pre-, intermediate- (4^th week), and post-intervention.

RESULTS

At post-intervention, there was a statistically significant and large (d>0.90) improvement in quality of life, but not in exercise tolerance, in the RMT group compared with the RMT_sham group. Both of the real training groups produced a statistically significant and large increase in inspiratory muscle strength and endurance (d≥0.80) and in lower limb muscle strength (d≥0.77) compared with the 2 sham groups. Expiratory muscle strength and peak expiratory flow showed a statistically significant and large (d≥0.87) increase in the RMT group compared with the other 3 groups.

CONCLUSION

Only an 8-week supervised home-based RMT programme was effective in improving quality of life, but not exercise tolerance, in individuals with long-term post-COVID-19 symptoms. In addition, IMT and RMT programmes were effective in improving respiratory muscle function and lower limb muscle strength, but had no impact on lung function and psychological status.

Noninvasive Assessment of Neuromechanical and Neuroventilatory Coupling in COPD

This study explored the use of parasternal second intercostal space and lower intercostal space surface electromyogram (sEMG) and surface mechanomyogram (sMMG) recordings (sEMGpara and sMMGpara, and sEMGlic and sMMGlic, respectively) to assess neural respiratory drive (NRD), neuromechanical (NMC) and neuroventilatory (NVC) coupling, and mechanical efficiency (MEff) noninvasively in healthy subjects and chronic obstructive pulmonary disease (COPD) patients. sEMGpara, sMMGpara, sEMGlic, sMMGlic, mouth pressure (Pmo), and volume (Vi) were measured at rest, and during an inspiratory loading protocol, in 16 COPD patients (8 moderate and 8 severe) and 9 healthy subjects. Myographic signals were analyzed using fixed sample entropy and normalized to their largest values (fSEsEMGpara%max, fSEsMMGpara%max, fSEsEMGlic%max, and fSEsMMGlic%max). fSEsMMGpara%max, fSEsEMGpara%max, and fSEsEMGlic%max were significantly higher in COPD than in healthy participants at rest. Parasternal intercostal muscle NMC was significantly higher in healthy than in COPD participants at rest, but not during threshold loading. Pmo-derived NMC and MEff ratios were lower in severe patients than in mild patients or healthy subjects during threshold loading, but differences were not consistently significant. During resting breathing and threshold loading, Vi-derived NVC and MEff ratios were significantly lower in severe patients than in mild patients or healthy subjects. sMMG is a potential noninvasive alternative to sEMG for assessing NRD in COPD. The ratios of Pmo and Vi to sMMG and sEMG measurements provide wholly noninvasive NMC, NVC, and MEff indices that are sensitive to impaired respiratory mechanics in COPD and are therefore of potential value to assess disease severity in clinical practice.

Effect of Automated Oxygen Titration during Walking on Dyspnea and Endurance in Chronic Hypoxemic Patients with COPD: A Randomized Crossover Trial

The need for oxygen increases with activity in patients with COPD and on long-term oxygen treatment (LTOT), leading to periods of hypoxemia, which may influence the patient’s performance. This study aimed to evaluate the effect of automated oxygen titration compared to usual fixed-dose oxygen treatment during walking on dyspnea and endurance in patients with COPD and on LTOT. In a double-blinded randomised crossover trial, 33 patients were assigned to use either automated oxygen titration or the usual fixed-dose in a random order in two walking tests. A closed-loop device, O2matic delivered a variable oxygen dose set with a target saturation of 90–94%. The patients had a home oxygen flow of (mean ± SD) 1.6 ± 0.9 L/min. At the last corresponding isotime in the endurance shuttle walk test, the patients reported dyspnea equal to median (IQR) 4 (3–6) when using automated oxygen titration and 8 (5–9) when using fixed doses, p < 0.001. The patients walked 10.9 (6.5–14.9) min with automated oxygen compared to 5.5 (3.3–7.9) min with fixed-dose, p < 0.001. Walking with automated oxygen titration had a statistically significant and clinically important effect on dyspnea. Furthermore, the patients walked for a 98% longer time when hypoxemia was reduced with a more well-matched, personalised oxygen treatment.

Inspiratory muscle training in interstitial lung disease: a systematic scoping review

Inspiratory muscle training (IMT) has been described as one of the components of the treatment of chronic lung conditions such as obstructive and restrictive lung diseases. Although the number of studies showing results of IMT in patients with interstitial lung disease (ILD) is scarce when compared with studies in patients with COPD, evidence points to benefits of IMT in this population. This scoping review aimed to explore the role and the rationale of IMT in patients with ILD and to gather recent evidence on the effects of IMT in this population. The studies included in this review showed improvements in respiratory muscle function, quality of life, exercise capacity and dyspnea after ILD patients participated in programs that included stand-alone IMT or combined with pulmonary rehabilitation. There is still a gap in the literature to allow a clear conclusion on the indications of IMT as part of ILD treatment because of poor research design and small numbers of participants. Therefore, although IMT seems to have a positive effect in patients with ILD, current evidence prevents us from drawing a definite conclusion. Further studies need to be conducted using better research methodology to demonstrate and confirm the positive effects of IMT.