Diaphragm muscle fiber dysfunction in chronic obstructive pulmonary disease: toward a pathophysiological concept

The Application of Diaphragm Ultrasound in Chronic Obstructive Pulmonary Disease: A Narrative Review

Chronic Obstructive Pulmonary Disease (COPD) is a prevalent condition that poses a significant burden on individuals and society due to its high morbidity and mortality rates. The diaphragm is the main respiratory muscle, its function has a direct impact on the quality of life and prognosis of COPD patients. This article aims to review the structural measurement and functional evaluation methods through the use of diaphragmatic ultrasound and relevant research on its application in clinical practice for COPD patients. Thus, it serves to provide valuable insights for clinical monitoring of diaphragm function in COPD patients, facilitating early clinical intervention and aiding in the recovery of diaphragm function.

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Multi-task localization of the hemidiaphragms and lung segmentation in portable chest X-ray images of COVID-19 patients

Background

The COVID-19 can cause long-term symptoms in the patients after they overcome the disease. Given that this disease mainly damages the respiratory system, these symptoms are often related with breathing problems that can be caused by an affected diaphragm. The diaphragmatic function can be assessed with imaging modalities like computerized tomography or chest X-ray. However, this process must be performed by expert clinicians with manual visual inspection. Moreover, during the pandemic, the clinicians were asked to prioritize the use of portable devices, preventing the risk of cross-contamination. Nevertheless, the captures of these devices are of a lower quality.

Objectives

The automatic quantification of the diaphragmatic function can determine the damage of COVID-19 on each patient and assess their evolution during the recovery period, a task that could also be complemented with the lung segmentation.

Methods

We propose a novel multi-task fully automatic methodology to simultaneously localize the position of the hemidiaphragms and to segment the lung boundaries with a convolutional architecture using portable chest X-ray images of COVID-19 patients. For that aim, the hemidiaphragms' landmarks are located adapting the paradigm of heatmap regression.

Results

The methodology is exhaustively validated with four analyses, achieving an 82.31% ± 2.78% of accuracy when localizing the hemidiaphragms' landmarks and a Dice score of 0.9688 ± 0.0012 in lung segmentation.

Conclusions

The results demonstrate that the model is able to perform both tasks simultaneously, being a helpful tool for clinicians despite the lower quality of the portable chest X-ray images.

Effect of expiratory flow limitation on ventilation/perfusion mismatch and perioperative lung function during pneumoperitoneum and Trendelenburg position

BACKGROUND

Laparoscopic surgery and Trendelenburg position may affect the respiratory function and alter the gas exchange. Further the reduction of the lung volumes may contribute to the development of expiratory flow limitation (EFL). The latter is associated with an increased risk of postoperative pulmonary complications. Our aim was to investigate the incidence of EFL and to evaluate its effect on pulmonary function and intraoperative V/Q mismatch.

METHODS

This is a prospective study on patients undergoing elective laparoscopic gynecological surgery. We evaluated respiratory mechanics, V/Q mismatch and presence of EFL after anesthesia induction, during pneumoperitoneum and Trendelenburg position and at the end of surgery. Intraoperative gas exchange and hemodynamic were also recorded. Clinical data were collected until seven days after surgery to evaluate the onset of pulmonary postoperative complications (PPCs).

RESULTS

Among the 66 patients enrolled, 25/66 (38%) exhibited EFL during surgery, of whom 10/66 (15%) after anesthesia induction, and the remaining 15 patients after pneumoperitoneum and Trendelenburg position. Median PEEP able to reverse flow limitation was 7 [7-10] cmH2O after anesthesia induction and 9 [8-15] cmH2O after pneumoperitoneum and Trendelenburg position. Patients with EFL had significantly higher shunt (17 [2-25] vs. 9 [1-19]; P=0.05), low V̇/Q̇ (27 [20-70] vs. 15 [10-22]; P=0.05) and high V̇/Q̇ (10 [7-14] vs. 6 [4-7]; P=0.024). At the end of surgery, only high V/Q was significantly higher in EFL patients. Further, they exhibited higher incidence of postoperative pulmonary complication (48% (12/25) vs. 15% (6/41), P=0.005), hypoxemia and hypercapnia (80% [20/25] vs. 32% [13/41]; P<0.001).

CONCLUSIONS

Expiratory flow limitation is a common phenomenon during gynecological laparoscopic surgery associated with worsen gas exchange, increased V/Q mismatch and altered lung mechanics. Our study showed that patients experiencing EFL during surgery showed a higher risk for PPCs.

Emergency ultrasound of respiratory muscles: a promising tool for determining the outcomes of COPD exacerbations

BACKGROUND

The respiratory muscles of patients with chronic obstructive pulmonary disease (COPD) exhibit structural and functional changes that can be evaluated and monitored by ultrasonography.

METHODS

This single-center, prospective study was conducted in the emergency department (ED) of a tertiary care hospital over an eight-month period (September 2020-May 2021). Diaphragmatic excursions, end-expiratory thickness, and thickening fractions, as well as right and left intercostal muscle thicknesses, of all adult subjects manifesting COPD exacerbation, were assessed. The data were analyzed regarding ward/intensive care unit (ICU) hospitalization or discharge from the ED, mortality, and readmission within 15 days.

RESULTS

Sixty-three subjects were recruited for the study. Diaphragmatic excursion, end-expiratory diaphragmatic thickness, and intercostal muscle thickness measurements were significantly different between the ward, ICU, and discharge groups (p < 0.001) but lower in the deceased subjects (all p < 0.05). The diaphragmatic excursion value of 3.25 cm was the threshold value measured for distinguishing discharge from ED, and 1.82 cm was measured for admission to the ICU, both with 100% sensitivity and selectivity (AUC = 1).

DISCUSSION

Diaphragmatic excursion, diaphragmatic end-expiratory thickness, and right and left intercostal muscle thicknesses vary in the prognosis of subjects presenting with COPD exacerbation.

Maximal respiratory pressures: Measurements at functional residual capacity in individuals with different health conditions using a digital manometer

BACKGROUND

Measuring maximal respiratory pressure is a widely used method of investigating the strength of inspiratory and expiratory muscles.

OBJECTIVES

To compare inspiratory pressures obtained at functional residual capacity (FRC) with measures at residual volume (RV), and expiratory pressures obtained at FRC with measures at total lung capacity (TLC) in individuals with different health conditions: post-COVID-19, COPD, idiopathic pulmonary fibrosis (IPF), heart failure (CHF), and stroke; and to compare the mean differences between measurements at FRC and RV/TLC among the groups.

METHODS

Inspiratory and expiratory pressures were obtained randomly at different lung volumes. Mixed factorial analysis of covariance with repeated measures was used to compare measurements at different lung volumes within and among groups.

RESULTS

Seventy-five individuals were included in the final analyses (15 individuals with each health condition). Maximal inspiratory pressures at FRC were lower than RV [mean difference (95% CI): 11.3 (5.8, 16.8); 8.4 (2.3, 14.5); 11.1 (5.5, 16.7); 12.8 (7.1, 18.4); 8.0 (2.6, 13.4) for COVID-19, COPD, IPF, CHF, and stroke, respectively] and maximal expiratory pressures at FRC were lower than TLC [mean difference (95% CI): 51.9 (37.4, 55.5); 60.9 (44.2, 77.7); 62.9 (48.1, 77.8); 58.0 (43.9, 73.8); 57.2 (42.9, 71.6) for COVID-19, COPD, IPF, CHF, and stroke, respectively]. All mean differences were similar among groups.

CONCLUSION

Although inspiratory and expiratory pressures at FRC were lower than measures obtained at RV/TLC for the five groups of health conditions, the mean differences between measurements at different lung volumes were similar among groups, which raises the discussion about the influence of the viscoelastic properties of the lungs on maximal respiratory pressure.

Ultrasound assessment of the respiratory system using diaphragm motion-volume indices

Background

Although previous studies have determined limit values of normality for diaphragm excursion and thickening, it would be beneficial to determine the normal diaphragm motion-to-inspired volume ratio that integrates the activity of the diaphragm and the quality of the respiratory system.

Methods

To determine the normal values of selected ultrasound diaphragm motion-volume indices, subjects with normal pulmonary function testing were recruited. Ultrasound examination recorded diaphragm excursion on both sides during quiet breathing and deep inspiration. Diaphragm thickness was also measured. The inspired volumes of the corresponding cycles were systematically recorded using a spirometer. The indices were calculated using the ratio excursion, or percentage of thickening, divided by the corresponding breathing volume. From this corhort, normal values and limit values for normality were determined. These measurements were compared to those performed on the healthy side in patients with hemidiaphragm paralysis because an increase in hemidiaphragm activity has been previously demonstated in such circumstances.

Results

A total of 122 subjects (51 women, 71 men) with normal pulmonary function were included in the study. Statistical analysis revealed that the ratio of excursion, or percentage of thickening, to inspired volume ratio significantly differed between males and females. When the above-mentioned indices using excursion were normalized by body weight, no gender differences were found. The indices differed between normal respiratory function subjects and patients with hemidiaphragm paralysis (27 women, 41 men). On the paralyzed side, the average ratio of the excursion divided by the inspired volume was zero. On the healthy side, the indices using the excursion and the percentage of thickening during quiet breathing or deep inspiration were significantly increased comparedto patients with normal lung function. According to the logistic regression analysis, the most relevant indice appeared to be the ratio of the excursion measured during quiet breathing to the inspired volume.

Conclusion

The normal values of the diaphragm motion-volume indices could be useful to estimate the performance of the respiratory system. Proposed indices appear suitable in a context of hyperactivity.

Effect of respiratory training on respiratory failure secondary to unilateral phrenic nerve injury: A case report

INTRODUCTION

Diaphragm is one of the most important respiratory muscles dominated by the phrenic nerve. Phrenic nerve injury would induce a series of clinical symptoms, including respiratory failure. Respiratory training could assist in regular treatment in improving the respiratory function and daily ability of respiratory failure patients.

CASE PRESENTATION

A 71-years-old female was enrolled for the disorders of consciousness of 4.5 hours observed by her family and was diagnosed with respiratory failure secondary to unilateral phrenic nerve injury. The patient received basic therapy combined with rehabilitation training, including the training of aspirate muscle, limb resistance, thoracic loosening, aerobic training, electrical stimulation on respiratory nerves, and airway clearance. The combining therapeutic strategy significantly improved the daily ability and respiratory of the patient. The ultrasound showed that after therapy, the diaphragmatic muscles were thickened and the range of diaphragmatic movement was also enhanced. The pulmonary function was also improved after therapy.

CONCLUSION

The combination of rehabilitation is suitable for the treatment of respiratory failure patients with clear causes of phrenic nerve injury. For patients with unexplained causes, rehabilitation could also be performed before the diagnosis. Patients with irreversible injury need long-term and family rehabilitation prescriptions.

Role of Nrf2 and exercise in alleviating COPD-induced skeletal muscle dysfunction

Chronic obstructive pulmonary disease (COPD) is a complex chronic respiratory disease with cumulative impacts on multiple systems, exhibiting significant extrapulmonary impacts, and posing a serious public health problem. Skeletal muscle dysfunction is one of the most pronounced extrapulmonary effects in patients with COPD, which severely affects patient prognosis and mortality primarily through reduced productivity resulting from muscle structural and functional alterations. Although the detailed pathogenesis of COPD has not been fully determined, some researchers agree that oxidative stress plays a significant role. Oxidative stress not only catalyzes the progression of pulmonary symptoms but also drives the development of skeletal muscle dysfunction. Nuclear factor erythroid 2-related factor 2 (Nrf2), is a key transcription factor that regulates the antioxidant response and plays an enormous role in combating oxidative stress. In this review, we have summarized current research on oxidative stress damage to COPD skeletal muscle and analyzed the role of Nrf2 in improving skeletal muscle dysfunction in COPD through exercise. The results suggest that oxidative stress drives the occurrence and development of skeletal muscle dysfunction in COPD. Exercise may improve skeletal muscle dysfunction in patients with COPD by promoting the dissociation of Kelch-like ECH-associated protein 1 (Keap1) and Nrf2, inducing sequestosome1(p62) phosphorylation to bind with Keap1 competitively leading to Nrf2 stabilization and improving dynamin-related protein 1-dependent mitochondrial fission. Nrf2 may be a key target for exercise anti-oxidative stress to alleviate skeletal muscle dysfunction in COPD.

Effect of high-flow oxygen versus T-piece ventilation strategies during spontaneous breathing trials on weaning failure among patients receiving mechanical ventilation: a randomized controlled trial

BACKGROUND

A spontaneous breathing trial (SBT) is used to determine whether patients are ready for extubation, but the best method for choosing the SBT strategy remains controversial. We investigated the effect of high-flow oxygen versus T-piece ventilation strategies during SBT on rates of weaning failure among patients receiving mechanical ventilation.

METHODS

This randomized clinical trial was conducted from June 2019 through January 2022 among patients receiving mechanical ventilation for ≥ 12 h who fulfilled the weaning readiness criteria at a single-center medical intensive care unit. Patients were randomized to undergo either T-piece SBT or high-flow oxygen SBT. The primary outcome was weaning failure on day 2, and the secondary outcomes were weaning failure on day 7, ICU and hospital length of stay, and ICU and in-hospital morality.

RESULTS

Of 108 patients (mean age, 67.0 ± 11.1 years; 64.8% men), 54 received T-piece SBT and 54 received high-flow oxygen SBT. Weaning failure on day 2 occurred in 5 patients (9.3%) in the T-piece group and 3 patients (5.6%) in the high-flow group (difference, 3.7% [95% CI, - 6.1-13.6]; p = 0.713). Weaning failure on day 7 occurred in 13 patients (24.1%) in the T-piece group and 7 patients (13.0%) in the high-flow group (difference, 11.1% [95% CI, - 3.4-25.6]; p = 0.215). A post hoc subgroup analysis showed that high-flow oxygen SBT was significantly associated with a lower rate of weaning failure on day 7 (OR, 0.17 [95% CI, 0.04-0.78]) among those patients intubated because of respiratory failure (p for interaction = 0.020). The ICU and hospital length of stay and mortality rates did not differ significantly between the two groups. During the study, no serious adverse events were recorded.

CONCLUSIONS

Among patients receiving mechanical ventilation, high-flow oxygen SBT did not significantly reduce the risk of weaning failure compared with T-piece SBT. However, the study may have been underpowered to detect a clinically important treatment effect for the comparison of high-flow oxygen SBT versus T-piece SBT, and a higher percentage of patients with simple weaning and a lower weaning failure rate than expected should be considered when interpreting the findings. Clinical trial registration This trial was registered with ClinicalTrials.gov (number NCT03929328) on April 26, 2019.

The myokine Fibcd1 is an endogenous determinant of myofiber size and mitigates cancer-induced myofiber atrophy

Decline in skeletal muscle cell size (myofiber atrophy) is a key feature of cancer-induced wasting (cachexia). In particular, atrophy of the diaphragm, the major muscle responsible for breathing, is an important determinant of cancer-associated mortality. However, therapeutic options are limited. Here, we have used Drosophila transgenic screening to identify muscle-secreted factors (myokines) that act as paracrine regulators of myofiber growth. Subsequent testing in mouse myotubes revealed that mouse Fibcd1 is an evolutionary-conserved myokine that preserves myofiber size via ERK signaling. Local administration of recombinant Fibcd1 (rFibcd1) ameliorates cachexia-induced myofiber atrophy in the diaphragm of mice bearing patient-derived melanoma xenografts and LLC carcinomas. Moreover, rFibcd1 impedes cachexia-associated transcriptional changes in the diaphragm. Fibcd1-induced signaling appears to be muscle selective because rFibcd1 increases ERK activity in myotubes but not in several cancer cell lines tested. We propose that rFibcd1 may help reinstate myofiber size in the diaphragm of patients with cancer cachexia.

Prolonged Mechanical Ventilation: Outcomes and Management

The number of patients requiring prolonged mechanical ventilation (PMV) is increasing worldwide, placing a burden on healthcare systems. Therefore, investigating the pathophysiology, risk factors, and treatment for PMV is crucial. Various underlying comorbidities have been associated with PMV. The pathophysiology of PMV includes the presence of an abnormal respiratory drive or ventilator-induced diaphragm dysfunction. Numerous studies have demonstrated that ventilator-induced diaphragm dysfunction is related to increases in in-hospital deaths, nosocomial pneumonia, oxidative stress, lung tissue hypoxia, ventilator dependence, and costs. Thus far, the pathophysiologic evidence for PMV has been derived from clinical human studies and experimental studies in animals. Moreover, recent studies have demonstrated the outcome benefits of pharmacological agents and rehabilitative programs for patients requiring PMV. However, methodological limitations affected these studies. Controlled prospective studies with an adequate number of participants are necessary to provide evidence of the mechanism, prognosis, and treatment of PMV. The great epidemiologic impact of PMV and the potential development of treatment make this a key research field.

Iron Supplementation Improves Skeletal Muscle Contractile Properties in Mice with CKD

Background

Patients with chronic kidney disease (CKD) frequently have compromised physical performance, which increases their mortality; however, their skeletal muscle dysfunction has not been characterized at the single-fiber and molecular levels. Notably, interventions to mitigate CKD myopathy are scarce.

Methods

The effect of CKD in the absence and presence of iron supplementation on the contractile function of individual skeletal muscle fibers from the soleus and extensor digitorum longus muscles was evaluated in 16-week-old mice. CKD was induced by the adenine diet, and iron supplementation was by weekly iron dextran injections.

Results

Maximally activated and fatigued fiber force production was decreased 24%-52% in untreated CKD, independent of size, by reducing strongly bound myosin/actin cross-bridges and/or decreasing myofilament stiffness in myosin heavy chain (MHC) I, IIA, and IIB fibers. Additionally, myosin/actin interactions in untreated CKD were slower for MHC I and IIA fibers and unchanged or faster in MHC IIB fibers. Iron supplementation improved anemia and did not change overall muscle mass in CKD mice. Iron supplementation ameliorated CKD-induced myopathy by increasing strongly bound cross-bridges, leading to improved specific tension, and/or returning the rate of myosin/actin interactions toward or equivalent to control values in MHC IIA and IIB fibers.

Conclusions

Skeletal muscle force production was significantly reduced in untreated CKD, independent of fiber size, indicating that compromised physical function in patients is not solely due to muscle mass loss. Iron supplementation improved multiple aspects of CKD-induced myopathy, suggesting that timely correction of iron imbalance may aid in ameliorating contractile deficits in CKD patients.

The immediate effect of thoracolumbar manipulation and diaphragmatic release on inspiratory muscle strength in healthy smokers: A randomized clinical trial

BACKGROUND

Diaphragmatic release technique and thoracolumbar manipulation have been found effective in restoring normal diaphragmatic movement in healthy and diseased populations. Smoking has deleterious effects on human systems, including the musculoskeletal system.

OBJECTIVE

The current study aimed to investigate the immediate effects of diaphragmatic release technique and thoracolumbar manipulation on diaphragm muscle strength in healthy smokers.

METHODS

A double-blinded randomized clinical trial was conducted on 30 asymptomatic healthy smokers randomly assigned into two groups [intervention group (IG) and sham group (SG)] with 15 participants each. The IG received thoracolumbar manipulation and diaphragmatic release techniques, while the SG received no active treatment. The outcome measure was sniff nasal inspiratory pressure (SNIP).

RESULTS

The IG showed a significant increase in the SNIP with a mean difference of 20.13 cmH2O (95% CI: 13.62-26.64; P< 0.001), while the SG had a reduction in the SNIP value -3.27 cmH2O (95% CI: -0.65 to -5.89; P= 0.02). Diaphragmatic release technique and thoracolumbar manipulation significantly improved SNIP values immediately after the intervention, with a between-group difference of 31.07 cmH2O (95% CI: 15.26-46.87; P< 0.001).

CONCLUSIONS

Diaphragmatic release technique and thoracolumbar manipulation increased the diaphragm strength in healthy adult smokers, suggesting its potential utility in the management of participants with reduced respiratory muscle strength.

Evaluation of Diaphragm Thickness and Stiffness Using Ultrasound and Shear-Wave Elastography

ABSTRACT

The purposes of this study are to measure the thickness and stiffness of diaphragm in association with the respiratory cyclus and to assess the reproducibility of these measurements. Forty individuals who are volunteered for participating diaphragm evaluation were included in the study. Two radiologists with 14 and 15 years of experiences in abdominal ultrasound performed all examinations independently. Furthermore, 8 chronic obstructive pulmonary disease (COPD) patients were examined by only the first radiologist. Gray scale and shear-wave elastography imaging of only the right hemidiaphragm of all participants were performed. Thickness and stiffness of diaphragm were measured at the peak inspiration and end expiration phases. Intraclass correlation coefficients test was used to assess the interobserver agreement. The thickness and stiffness of diaphragm significantly increased with inspiration (P < 0.001). The mean ± SD stiffness of diaphragm in peak inspiration and end expiration phases was 51.84 ± 16.83 kPa and 38.49 ± 9.42 kPa, respectively, for the first radiologist and 49.61 ± 13.83 kPa and 37.52 ± 10.71 kPa, respectively, for the second radiologist. Intraclass correlation coefficient values for diaphragm stiffness were 0.667 and 0.736 in peak inspiration and end expiration phases, respectively. In COPD patients, there was no significant difference between stiffness measurements of respiratory phases. In conclusion, the current study revealed that diaphragm thickness and stiffness increase at inspiration, and these measurements are slightly more reproducible at the end of expiration. However, diaphragm stiffness changes between respiratory phases may not be valid for COPD patients, and this may be related to loss of force-generating capacity of diaphragm in COPD patients.

Ultrasound Shear Wave Elastography for Evaluation of Diaphragm Stiffness in Patients with Stable COPD: A Pilot Trial

OBJECTIVES

Skeletal muscle dysfunction is one of the most common comorbidities in chronic obstructive pulmonary disease (COPD). The occurrence of respiratory failure in COPD is common and leads to the patient's death. The diaphragm is the most important muscle in the respiratory system and plays a key role in the onset of respiratory failure. This study explores the feasibility of ultrasound shear wave elastography (SWE) to measure diaphragmatic stiffness and evaluates its changes in COPD patients.

METHODS

In total, 77 participants (43 patients with stable COPD and 34 healthy controls) were enrolled. All subjects underwent complete diaphragmatic ultrasound SWE measurements and pulmonary function tests. The diaphragmatic stiffness was indicated via diaphragmatic shear wave velocity (SWV) at functional residual capacity (FRC). A trained operator performed the ultrasound SWE examinations of the first 15 healthy controls thrice to assess the reliability of diaphragmatic SWE.

RESULTS

A good to excellent reliability was found in diaphragmatic SWV at FRC (ICC = 0.93, 95%CI 0.82-0.98). As compared to the control group, the diaphragmatic SWV at FRC was considerably high in the COPD group (median 2.5 m/s versus 2.1 m/s, P = .008). Diaphragmatic SWV at FRC was linked to forced expiratory volume in one second (r = -0.30, P = .009), forced vital capacity (r = -0.33, P = .003), modified Medical Research Council score (r = 0.30, P = .001), and COPD assessment test score (r = 0.48, P < .001).

CONCLUSIONS

Ultrasound SWE may be employed as an effective tool for quantitative evaluation of diaphragm stiffness and can help in personalized management of COPD, such as treatment guidance and follow-up monitoring.

Mechanisms, Pathophysiology and Currently Proposed Treatments of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the leading global causes of morbidity and mortality. A hallmark of COPD is progressive airflow obstruction primarily caused by cigarette smoke (CS). CS exposure causes an imbalance favoring pro- over antioxidants (oxidative stress), leading to transcription factor activation and increased expression of inflammatory mediators and proteases. Different cell types, including macrophages, epithelial cells, neutrophils, and T lymphocytes, contribute to COPD pathophysiology. Alteration in cell functions results in the generation of an oxidative and inflammatory microenvironment, which contributes to disease progression. Current treatments include inhaled corticosteroids and bronchodilator therapy. However, these therapies do not effectively halt disease progression. Due to the complexity of its pathophysiology, and the risk of exacerbating symptoms with existing therapies, other specific and effective treatment options are required. Therapies directly or indirectly targeting the oxidative imbalance may be promising alternatives. This review briefly discusses COPD pathophysiology, and provides an update on the development and clinical testing of novel COPD treatments.

Ultrasound Evaluation of Diaphragm Force Reserve in Patients with Chronic Obstructive Pulmonary Disease

Rationale: Diaphragm function is a key determinant of dyspnea in chronic obstructive pulmonary disease (COPD); however, it is rarely assessed in clinical practice. Lung hyperinflation can also impair diaphragm function. Ultrasound can assess the activity, function, and force reserve of the diaphragm.Objectives: To compare diaphragm activity, function, and force reserve among patients with COPD and healthy control subjects.Methods: Patients with stable COPD (n = 80) and healthy control subjects (n = 20) were enrolled (97% of them were men). Ultrasound was used to measure the thickening fraction of the diaphragm during tidal breathing and maximum volitional effort. Outcome measures were as follows: 1) the difference in diaphragm force reserve, activity, and function between patients with COPD and control subjects; 2) the correlation between lung volumes and diaphragm force reserve, activity, and function; and 3) the relationship between diaphragm force reserve and the rate of moderate to severe exacerbation of COPD.Results: The tidal thickening fraction of the diaphragm during resting breathing (TFdi-tidal) was higher in patients with COPD than in control subjects (P = 0.002); it was approximately twice as high in patients with severe COPD than in control subjects. Patients with COPD had poorer diaphragm function than control subjects as assessed by the maximal thickening fraction of the diaphragm during Muller maneuver (P < 0.01). Diaphragm force reserve ratio assessed by 1-(tidal thickening fraction of the diagphragm during resting breathing/maximal thickening fraction of the diaphragm) was lower in patients with COPD than in control subjects, and it fell with increasing Global Initiative for Chronic Obstructive Lung Disease stages (P < 0.001); it correlated with inspiratory capacity (r = 0.46) and the body mass index, airflow obstruction, dyspnea, exercise capacity (BODE) index, a multidimensional scoring system (r = -0.49). Patients who developed exacerbation during the following 2 years had less force reserve than patients without exacerbation (P = 0.024).Conclusions: Male patients with COPD have increased diaphragm workload, impaired diaphragm function, and reduced force reserve compared with healthy subjects. Ultrasound assessment of the diaphragm in COPD provides important functional information.Clinical trial registered with the Thai Clinical Trials Registry (TCTR20160411001). Registered 31 April 5, 2016.

Diaphragm Morphology Assessed by Computed Tomography in Chronic Obstructive Pulmonary Disease

Rationale: Chronic obstructive pulmonary disease (COPD) is associated with abnormal skeletal muscle morphology and function. Objectives: To test the hypothesis that in vivo diaphragm muscle morphology assessed by computed tomography (CT) imaging would be associated with COPD severity, exacerbations, health status, and exercise capacity. Methods: The COPD Morphometry Study is a cross-sectional study that enrolled a clinical sample of smokers with COPD. Spirometry was performed and COPD severity was defined according to guidelines. Three-dimensional left hemidiaphragm morphology was segmented from contiguous axial CT images acquired at maximal inspiration, yielding quantitative measures of diaphragm CT density in Hounsfield units, dome height, and muscle volume. Exacerbations prompting pharmacotherapy or hospitalization in the preceding 12 months and St. George's Respiratory Questionnaire for COPD were assessed. Incremental symptom-limited cycle ergometry quantified peak oxygen uptake ([Formula: see text]o_2Peak). Associations were adjusted for age, sex, body height, body mass index, and smoking status. Results: Among 65 smokers with COPD (75% male; [mean ± standard deviation (SD)] 56 ± 26 pack-years; forced expiratory volume in 1 second [FEV₁] percentage predicted 55 ± 23%), mean diaphragm CT density was 3.1 ± 10 Hounsfield units, dome height was 5.2 ± 1.3 cm, and muscle volume was 57 ± 24 cm³. A 1-SD decrement in the diaphragm CT density was associated with 8.3% lower FEV₁, 3.27-fold higher odds of exacerbation history, 9.7-point higher score on the St. George's Respiratory Questionnaire for COPD, and 2.5 ml/kg/min lower [Formula: see text]o_2Peak. A 1-SD decrement in dome height was associated with 11% lower FEV₁ and 1.3 ml/kg/min lower [Formula: see text]o_2Peak. There were no associations with diaphragm volume observed. Conclusions: CT-assessed diaphragm morphology was associated with COPD severity, exacerbations, impaired health status, and exercise intolerance. The mechanisms and functional impact of lower diaphragm CT density merit investigation.

Effect of Oxidative Stress on Diaphragm Dysfunction and Exercise Intervention in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) can cause extrapulmonary injury such as diaphragm dysfunction. Oxidative stress is one of the main factors causing diaphragm dysfunction in COPD. Exercise plays a positive role in the prevention and treatment of diaphragm dysfunction in COPD, and the changes in diaphragm structure and function induced by exercise are closely related to the regulation of oxidative stress. Therefore, on the basis of the review of oxidative stress and the changes in diaphragm structure and function in COPD, this article analyzed the effects of exercise on oxidative stress and diaphragm dysfunction in COPD and explored the possible mechanism by which exercise improves oxidative stress. Studies have found that diaphragm dysfunction in COPD includes the decline of muscle strength, endurance, and activity. Oxidative stress mainly affects the structure and function of the diaphragm in COPD through protein oxidation, protease activation and calcium sensitivity reduction. The effects of exercise on oxidative stress level and diaphragm dysfunction may differ depending on the intensity, duration, and style of exercise. The mechanism of exercise on oxidative stress in the diaphragm of COPD may include improving antioxidant capacity, reducing oxidase activity and improving mitochondrial function.

The Investigation of Falls and Balance from the Perspective of Activities of Daily Living in Patients with COPD

The aim of this study was (1) to compare the activities of daily living (ADLs), perceived falling risk and balance in chronic obstructive pulmonary disease (COPD) patients with or without falling history and (2) to investigate the relationship between ADLs and balance. Fourteen patients with COPD with a history of falling whose mean falling frequency was 2.64 ± 0.74 times in the last 12-months (fallers) and 14 age and sex-matched patients with COPD with no history of falling (non-fallers) were included. The outcome measures were the London Chest Activity of Daily Living (LCADL) scale, Activities-Specific Balance Confidence (ABC) scale, Berg Balance Scale (BBS), 6-minute walking test, and quadriceps-femoris strength. Fallers reported increased dyspnoea perception in ADLs, decreased balance confidence, and disturbed balance compared with non-fallers (p < 0.05). A strong correlation was found between the LCADL scale item score (dressing the upper body) and the BBS total score (rho = -0.81, p = 0.001) in fallers. The LCADL scale item score (going out socially) was significantly correlated with the total score of the ABC scale (rho = -0.61, p = 0.001). Moderate correlations were found between the LCADL scale item scores (dressing the upper body, washing hair, and walking up stairs) and the BBS total score (p < 0.003). This study demonstrated that increased severity of dyspnoea perception during ADLs is associated with impaired balance and poor balance confidence, regardless of functional capacity and peripheral muscle strength in patients with COPD. The balance confidence was low in functional mobility-based activities in patients with COPD with a history of falling.

Tailoring the Sleep Laboratory for Chronic Respiratory Failure

"Many seemingly mundane aspects of the sleep laboratory can have outsized effects on the quality of polysomnographic data obtained from, and care provided to, patients. This is particularly true when performing polysomnography on patients with chronic respiratory failure due to various causes. This article uses a disease-based approach to review physical and protocol-based accommodations that should be considered when performing polysomnography on this patient population."

Noninvasive Ventilation in Chronic Obstructive Pulmonary Disease

The role of noninvasive positive pressure ventilation (NIV) in severe chronic obstructive pulmonary disease (COPD) has been controversial. Over the past two decades, data primarily obtained from Europe have begun to define the clinical characteristics of patients likely to respond, the role of high-intensity NIV, and the potential best timing of initiating therapy. These approaches, however, have not been validated in the context of the U.S. healthcare delivery system. Use of NIV in severe COPD in the United States is limited by the practicalities of doing in-hospital titrations as well as a complex system of reimbursement. These systematic complexities, coupled with a still-emerging clinical trial database regarding the most effective means to deliver NIV, have led to persistent uncertainty regarding when in stable severe COPD treatment with NIV is actually appropriate. In this review, we propose an assessment algorithm and treatment plan that can be used in clinical practice in the United States, but we acknowledge that the absence of pivotal clinical trials largely precludes a robust evidence-based approach to this potentially valuable therapy.

Impact of experimental obesity on diaphragm structure, function, and bioenergetics

Obesity is associated with bioenergetic dysfunction of peripheral muscles; however, little is known regarding the impact of obesity on the diaphragm. We hypothesized that obesity would be associated with diaphragm dysfunction attributable to mitochondrial oxygen consumption and structural and ultrastructural changes. Wistar rat litters were culled to 3 pups to induce early postnatal overfeeding and consequent obesity. Control animals were obtained from unculled litters. From postnatal day 150, diaphragm ultrasound, computed tomography, high-resolution respirometry, immunohistochemical, biomolecular, and ultrastructural histological analyses were performed. The diaphragms of obese animals, compared with those of controls, presented changes in morphology as increased thickening fraction, diaphragm excursion, and diaphragm dome height, as well as increased mitochondrial respiratory capacity coupled to ATP synthesis and maximal respiratory capacity. Fatty acid synthase gene expression was also higher in obese animals, suggesting a source of energy for the respiratory chain. Myosin heavy chain-IIA was increased, indicating shift from glycolytic toward oxidative muscle fiber profile. Diaphragm tissue also exhibited ultrastructural changes, such as compact, round, and swollen mitochondria with fainter cristae and more lysosomal bodies. Dynamin-1 expression in the diaphragm was reduced in obese rats, suggesting decreased mitochondrial fission. Furthermore, gene expressions of peroxisome γ proliferator-activated receptor coactivator-1α and superoxide dismutase-2 were lower in obese animals than in controls, which may indicate a predisposition to oxidative injury. In conclusion, in the obesity model used herein, muscle fiber phenotype was altered in a manner likely associated with increased mitochondrial respiratory capability, suggesting respiratory adaptation to increased metabolic demand.NEW & NOTEWORTHY Obesity has been associated with peripheral muscle dysfunction; however, little is known about its impact on the diaphragm. In the current study, we found high oxygen consumption in diaphragm tissue and changes in muscle fiber phenotypes toward a more oxidative profile in experimental obesity.

circSamd4 represses myogenic transcriptional activity of PUR proteins

By interacting with proteins and nucleic acids, the vast family of mammalian circRNAs is proposed to influence many biological processes. Here, RNA sequencing analysis of circRNAs differentially expressed during myogenesis revealed that circSamd4 expression increased robustly in mouse C2C12 myoblasts differentiating into myotubes. Moreover, silencing circSamd4, which is conserved between human and mouse, delayed myogenesis and lowered the expression of myogenic markers in cultured myoblasts from both species. Affinity pulldown followed by mass spectrometry revealed that circSamd4 associated with PURA and PURB, two repressors of myogenesis that inhibit transcription of the myosin heavy chain (MHC) protein family. Supporting the hypothesis that circSamd4 might complex with PUR proteins and thereby prevent their interaction with DNA, silencing circSamd4 enhanced the association of PUR proteins with the Mhc promoter, while overexpressing circSamd4 interfered with the binding of PUR proteins to the Mhc promoter. These effects were abrogated when using a mutant circSamd4 lacking the PUR binding site. Our results indicate that the association of PUR proteins with circSamd4 enhances myogenesis by contributing to the derepression of MHC transcription.

Diaphragm thickening assessed by ultrasonography is lower than healthy adults in patients with chronic obstructive pulmonary disease

BACKGROUND

Ultrasound imaging has been widely used for imaging of the diaphragm thickness (Tdi) and thickening. Few studies assessed the Tdi using ultrasonography in patients with chronic obstructive pulmonary disease (COPD). We measured the Tdi and thickening in patients with COPD compared with healthy younger and healthy older adults to reveal the influence of ageing and/or COPD.

METHODS

Thirty-eight male patients with COPD (age 72 ± 8 years), 15 healthy younger (age 22 ± 1 years) and 15 healthy older (age 72 ± 5 years) male volunteers were recruited. We measured Tdi at total lung capacity (Tdi_TLC ), functional residual capacity (Tdi_FRC ) and residual volume (Tdi_RV ) using B-mode ultrasonography. We calculated the change ratio of Tdi_TLC and Tdi_RV (ΔTdi%). We used a one-way analysis of variance and multiple comparison test for the comparison analysis.

RESULTS

The Tdi_TLC and the ΔTdi% were significantly lower in patients with COPD compared to the healthy adults. There was no significant difference in these values with age. There was no between group difference in the Tdi_FRC or Tdi_RV .

CONCLUSIONS

Our results indicate significant differences in Tdi_TLC and ΔTdi% between patients with COPD and healthy adults. Therefore, diaphragm ultrasonography can assess diaphragm dysfunction associated with COPD. We suggest that it is better to use Tdi_TLC and ΔTdi% (not only Tdi at rest) to assess diaphragm function.

Salidroside mitigates skeletal muscle atrophy in rats with cigarette smoke-induced COPD by up-regulating myogenin and down-regulating myostatin expression

OBJECTIVES

The present study aimed at investigating the therapeutic effect of Salidroside on skeletal muscle atrophy in a rat model of cigarette smoking-induced chronic obstructive pulmonary disease (COPD) and its potential mechanisms.

METHODS

Male Wistar rats were randomized, and treated intraperitoneally (IP) with vehicle (injectable water) or a low, medium or high dose of Salidroside, followed by exposure to cigarette smoking daily for 16 weeks. A healthy control received vehicle injection and air exposure. Their lung function, body weights and gastrocnemius (GN) weights, grip strength and cross-section area (CSA) of individual muscular fibers in the GN were measured. The levels of TNF-α, IL-6, malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) in serum and GN tissues as well as myostatin and myogenin expression in GN tissues were measured.

RESULTS

In comparison with that in the healthy control, long-term cigarette smoking induced emphysema, significantly impaired lung function, reduced body and GN weights and CSA values in rats, accompanied by significantly increased levels of TNF-α, IL-6 and MDA, but decreased levels of SOD and GSH in serum and GN tissues. Furthermore, cigarette smoking significantly up-regulated myostatin expression, but down-regulated myogenin expression in GN tissues. Salidroside treatment decreased emphysema, significantly ameliorated lung function, increased antioxidant, but reduced MDA, IL-6 and TNF-α levels in serum and GN tissues of rats, accompanied by decreased myostain, but increased myogenin expression in GN tissues.

CONCLUSION

Salidroside mitigates the long-term cigarette smoking-induced emphysema and skeletal muscle atrophy in rats by inhibiting oxidative stress and inflammatory responses and regulating muscle-specific transcription factor expression.

Ultrasound Assessment Of Diaphragmatic Function During Acute Exacerbation Of Chronic Obstructive Pulmonary Disease: A Pilot Study

Purpose

Impairment of diaphragmatic function is one of the main pathophysiological mechanisms of chronic obstructive pulmonary disease (COPD) and is known to be related to acute exacerbation. Ultrasonography (US) allows for a simple, non-invasive assessment of diaphragm kinetics. The purpose of this study was to investigate the changes in diaphragmatic function during acute exacerbation of COPD, by US.

Methods

This single-center, prospective study included patients with acute exacerbation of COPD symptoms. US measurements were performed within 72 hrs after exacerbation and after improvement of symptoms. Diaphragmatic excursion and its thickening fraction (TF) were measured as markers of diaphragmatic function. TF was calculated as (thickness at end inspiration – thickness at end expiration)/thickness at end expiration.

Results

Ten patients were enrolled. All patients were male, and the mean age was 79.8 years. The TF of the right diaphragm showed a significant increase from the initial to the follow-up values (80.1 ± 104.9 mm vs. 159.5 ± 224.6 mm, p = 0.011); however, the diaphragmatic excursion did not vary significantly between the initial and follow-up values (22 ± 6 mm vs 23 ±12 mm). The change in excursion between the stable and exacerbation periods was positively correlated with time to the next exacerbation and negatively correlated with the time taken to recover from the exacerbation.

Conclusion

These data support the possibility that a defect in diaphragm thickening is related to acute exacerbation of COPD.

Acute effects of photobiomodulation therapy applied to respiratory muscles of chronic obstructive pulmonary disease patients: a double-blind, randomized, placebo-controlled crossover trial

To investigate the effects of photobiomodulation applied to respiratory muscles on lung function, thoracoabdominal mobility, respiratory muscle strength, and functional capacity in COPD patients. This is a randomized double-blind crossover clinical trial. Twelve male COPD patients participated in the study. Participants were randomly allocated to receive two photobiomodulation sessions, 1 week apart: (1) an effective photobiomodulation session applied at the main respiratory muscles by means of a cluster with 69 light-emitting diodes (LEDs), containing 35 red (630 ± 10 nm; 10 mW; 0.2 cm²) and 34 near-infrared (830 ± 20 nm; 10 mW; 0.2 cm²) LEDs and (2) a sham photobiomodulation session, following the same procedures without emitting light. The primary outcomes were pulmonary function (spirometric indexes); thoracoabdominal mobility (cirtometry); respiratory muscle strength (maximal respiratory pressures), assessed at three moments: (1) baseline, (2) 1 h after intervention, and (3) 24 h after intervention; and the functional capacity, assessed by the 6-min walk test (6MWT) at baseline and 24 h after intervention. No significant interactions were found for spirometric variables, maximal respiratory pressures, and cirtometry. However, there was a Time × Condition interaction (F = 18.63; p = 0.001; η²_p = 0.62) in the walked distance on the 6MWT, with a significant increase after photobiomodulation intervention (p < 0.01) compared with the baseline. Photobiomodulation applied to respiratory muscles was effective in improving acute functional capacity in COPD patients. To the best of our knowledge, this is the first study assessing the effects of photobiomodulation applied to respiratory muscles in patients with COPD.

Skeletal Muscle Dysfunction in Chronic Obstructive Pulmonary Disease. What We Know and Can Do for Our Patients

Skeletal muscle dysfunction occurs in patients with chronic obstructive pulmonary disease (COPD) and affects both ventilatory and nonventilatory muscle groups. It represents a very important comorbidity that is associated with poor quality of life and reduced survival. It results from a complex combination of functional, metabolic, and anatomical alterations leading to suboptimal muscle work. Muscle atrophy, altered fiber type and metabolism, and chest wall remodeling, in the case of the respiratory muscles, are relevant etiological contributors to this process. Muscle dysfunction worsens during COPD exacerbations, rendering patients progressively less able to perform activities of daily living, and it is also associated with poor outcomes. Muscle recovery measures consisting of a combination of pulmonary rehabilitation, optimized nutrition, and other strategies are associated with better prognosis when administered in stable patients as well as after exacerbations. A deeper understanding of this process' pathophysiology and clinical relevance will facilitate the use of measures to alleviate its effects and potentially improve patients' outcomes. In this review, a general overview of skeletal muscle dysfunction in COPD is offered to highlight its relevance and magnitude to expert practitioners and scientists as well as to the average clinician dealing with patients with chronic respiratory diseases.

A randomised controlled trial to investigate the use of high-frequency airway oscillations as training to improve dyspnoea in COPD

Introduction

Chronic obstructive pulmonary disease (COPD) is characterised by expiratory flow limitation resulting in symptomatic dyspnoea, sputum retention and ventilation heterogeneity. Changes in breathing mechanics affect the ability of respiratory muscles to respond to the ventilatory demands, increasing the sensation of dyspnoea. A high-frequency airway oscillating device has been developed to combine respiratory muscle training and oscillations to improve dyspnoea and sputum retention within COPD.

Methods and analysis

Patients with symptomatic COPD (Medical Research Council Breathlessness scale grade ≥2) will be recruited to a double-blind, randomised, sham-controlled trial. Both groups will follow an 8-week intervention phase using the device three times per day for 5 min at a time. This will be recorded in a self-reported diary. The device applies a flow resistive load and oscillations for combined training. Those receiving the sham device will follow the same protocol; however, the mechanism of action will be removed from the device. Improvements in the Chronic Respiratory Questionnaire-Dyspnoea domain will be the primary outcome measure. Secondary outcomes will explore respiratory muscle function, health-related quality of life, exercise capacity and physical activity. The Lung Clearance Index will be an exploratory outcome. Outcomes will be explored using the most appropriate statistical test, dependent on the sample distribution. Focus groups will be an exploratory outcome and analysed by thematic analysis.

Ethics and dissemination

Ethical approval has been obtained from the East Midlands-Leicester South Research Ethics Committee and the trial has been registered through the ISRCTN Registry. The study results will be disseminated to the appropriate stakeholders through presentations, conferences and peer-reviewed journals.

A double-blind, placebo-controlled, randomised trial investigating the effects of high-frequency airway oscillations on dyspnoea, sputum, quality of life and exercise capacity in #COPD.http://bit.ly/2F8bQ6s

Endotoxin-Induced Emphysema Exacerbation: A Novel Model of Chronic Obstructive Pulmonary Disease Exacerbations Causing Cardiopulmonary Impairment and Diaphragm Dysfunction

Chronic obstructive pulmonary disease (COPD) is a progressive disorder of the lung parenchyma which also involves extrapulmonary manifestations, such as cardiovascular impairment, diaphragm dysfunction, and frequent exacerbations. The development of animal models is important to elucidate the pathophysiology of COPD exacerbations and enable analysis of possible therapeutic approaches. We aimed to characterize a model of acute emphysema exacerbation and evaluate its consequences on the lung, heart, and diaphragm. Twenty-four Wistar rats were randomly assigned into one of two groups: control (C) or emphysema (ELA). In ELA group, animals received four intratracheal instillations of pancreatic porcine elastase (PPE) at 1-week intervals. The C group received saline under the same protocol. Five weeks after the last instillation, C and ELA animals received saline (SAL) or E. coli lipopolysaccharide (LPS) (200 μg in 200 μl) intratracheally. Twenty-four hours after saline or endotoxin administration, arterial blood gases, lung inflammation and morphometry, collagen fiber content, and lung mechanics were analyzed. Echocardiography, diaphragm ultrasonography (US), and computed tomography (CT) of the chest were done. ELA-LPS animals, compared to ELA-SAL, exhibited decreased arterial oxygenation; increases in alveolar collapse (p < 0.0001), relative neutrophil counts (p = 0.007), levels of cytokine-induced neutrophil chemoattractant-1, interleukin (IL)-1β, tumor necrosis factor-α, IL-6, and vascular endothelial growth factor in lung tissue, collagen fiber deposition in alveolar septa, airways, and pulmonary vessel walls, and dynamic lung elastance (p < 0.0001); reduced pulmonary acceleration time/ejection time ratio, (an indirect index of pulmonary arterial hypertension); decreased diaphragm thickening fraction and excursion; and areas of emphysema associated with heterogeneous alveolar opacities on chest CT. In conclusion, we developed a model of endotoxin-induced emphysema exacerbation that affected not only the lungs but also the heart and diaphragm, thus resembling several features of human disease. This model of emphysema should allow preclinical testing of novel therapies with potential for translation into clinical practice.

Diaphragm contractile weakness due to reduced mechanical loading: role of titin

The diaphragm, the main muscle of inspiration, is constantly subjected to mechanical loading. Only during controlled mechanical ventilation, as occurs during thoracic surgery and in the intensive care unit, is mechanical loading of the diaphragm arrested. Animal studies indicate that the diaphragm is highly sensitive to unloading, causing rapid muscle fiber atrophy and contractile weakness; unloading-induced diaphragm atrophy and contractile weakness have been suggested to contribute to the difficulties in weaning patients from ventilator support. The molecular triggers that initiate the rapid unloading atrophy of the diaphragm are not well understood, although proteolytic pathways and oxidative signaling have been shown to be involved. Mechanical stress is known to play an important role in the maintenance of muscle mass. Within the muscle's sarcomere, titin is considered to play an important role in the stress-response machinery. Titin is a giant protein that acts as a mechanosensor regulating muscle protein expression in a sarcomere strain-dependent fashion. Thus titin is an attractive candidate for sensing the sudden mechanical arrest of the diaphragm when patients are mechanically ventilated, leading to changes in muscle protein expression. Here, we provide a novel perspective on how titin and its biomechanical sensing and signaling might be involved in the development of mechanical unloading-induced diaphragm weakness.

Expiratory flow-limitation in mechanically ventilated patients: A risk for ventilator-induced lung injury?

Expiratory flow limitation (EFL), that is the inability of expiratory flow to increase in spite of an increase of the driving pressure, is a common and unrecognized occurrence during mechanical ventilation in a variety of intensive care unit conditions. Recent evidence suggests that the presence of EFL is associated with an increase in mortality, at least in acute respiratory distress syndrome (ARDS) patients, and in pulmonary complications in patients undergoing surgery. EFL is a major cause of intrinsic positive end-expiratory pressure (PEEPi), which in ARDS patients is heterogeneously distributed, with a consequent increase of ventilation/perfusion mismatch and reduction of arterial oxygenation. Airway collapse is frequently concomitant to the presence of EFL. When airways close and reopen during tidal ventilation, abnormally high stresses are generated that can damage the bronchiolar epithelium and uncouple small airways from the alveolar septa, possibly generating the small airways abnormalities detected at autopsy in ARDS. Finally, the high stresses and airway distortion generated downstream the choke points may contribute to parenchymal injury, but this possibility is still unproven. PEEP application can abolish EFL, decrease PEEPi heterogeneity, and limit recruitment/derecruitment. Whether increasing PEEP up to EFL disappearance is a useful criterion for PEEP titration can only be determined by future studies.

Expiratory Flow Limitation During Mechanical Ventilation

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Association between inspiratory muscle weakness and slowed oxygen uptake kinetics in patients with chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) may have poor inspiratory muscle function, which reduces minute and alveolar ventilation, leading to increased hypoxemia and slow pulmonary oxygen uptake kinetics. However, little is known about the effect of inspiratory muscle weakness (IMW) on oxygen uptake kinetics in patients with COPD. Thus, we tested the hypothesis that COPD patients with IMW have slowed oxygen uptake kinetics. An observational study was conducted that included COPD patients with moderate to severe airflow limitation and a history of intolerance to exercise. Participants were divided into 2 groups: (IMW+; n = 22) (IMW–; n = 23) of muscle weakness. The maximal inspiratory, expiratory, and sustained inspiratory strength as well as the maximal endurance of the inspiratory muscles were lower in IMW+ patients (36 ± 9.5 cm H2O; 52 ± 14 cm H2O; 20 ± 6.5 cm H2O; 94 ± 84 s, respectively) than in IMW– patients (88 ± 12 cm H2O; 97 ± 28 cm H2O; 82.5 ± 54 cm H2O; 559 ± 92 s, respectively; p < 0.05). Moreover, the 6-min walk test and peak oxygen uptake were reduced in the IMW+ patients. During the constant work test, oxygen uptake kinetics were slowed in the IMW+ compared with IMW– patients (88 ± 29 vs 61 ± 18 s, p < 0.05). Our findings demonstrate that inspiratory muscle weakness in COPD is associated with slowed oxygen uptake kinetics, and thus, reduced functional capacity.

Obesity modulates diaphragm curvature in subjects with and without COPD

Obesity is a common comorbidity of chronic obstructive pulmonary disease (COPD) and has been associated with worse outcomes. However, it is unknown whether the interaction between obesity and COPD modulates diaphragm shape and consequently its function. The body mass index (BMI) has been used as a correlate of obesity. We tested the hypothesis that the shape of the diaphragm muscle and size of the ring of its insertion in non-COPD and COPD subjects are modulated by BMI. We recruited 48 COPD patients with postbronchiodilator forced expiratory volume in 1 s (FEV1)-to-forced vital capacity (FVC) < 0.7 and 29 age-matched smoker/exsmoker control (non-COPD) subjects, who underwent chest computed tomography (CT) at lung volumes ranging from functional residual capacity (FRC) to total lung capacity (TLC). We then computed maximum principal diaphragm curvature in the midcostal region of the left hemidiaphragm at the end of inspiration during quiet breathing (EI) and at TLC. The radius of maximum curvature of diaphragm muscle increased with BMI in both COPD and non-COPD subjects. The size of diaphragm ring of insertion on the chest wall also increased significantly with increasing BMI. Surprisingly, COPD severity did not appear to cause significant alteration in diaphragm shape except in normal-weight subjects at TLC. Our data uncovered important factors such as BMI, the size of the diaphragm ring of insertion, and disease severity that modulate the structure of the ventilatory pump in non-COPD and COPD subjects.

Clinical importance of cross-sectional area of intercostal muscles in patients with chronic obstructive pulmonary disease

INTRODUCTION

Limb muscle wasting is one of main systemic manifestation of chronic obstructive pulmonary disease (COPD). However, the change of respiratory muscle is unclear.

OBJECTIVES

This study assessed the cross-sectional area (CSA) of the intercostal muscles (ICMs) in patients with COPD, using chest computed tomography (CT) and determined its association with the clinical characteristics of COPD.

METHODS

They retrospectively reviewed 60 patients with stable COPD and compared them with 30 controls. CSA (mm² ) of the ICM on chest CT was measured at the midline level of the lateral arch of the bilateral first rib with a 3-mm slice thickness by using CT histogram software. The association with the clinical characteristics of COPD and with the control groups was assessed.

RESULTS

CSA of the ICM and the CSA/body mass index (BMI) were lower in the COPD group than in the control group. Patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 4 had a significantly lower CSA of the ICM than patients with stage 1, 2, and 3. CSA of the ICM was positively associated with FEV₁ , %FEV₁ predicted, FEV₁ /FVC ratio, and BMI and negatively associated with age. However, there were no associations with PaO₂ , PaCO₂ , smoking status, 6-minute walk test, frequency of acute exacerbation of COPD, and serum C-reactive protein level.

CONCLUSION

Intercostal muscle atrophy occurs in COPD patients and is associated with severity of airway obstruction, BMI, and increasing age.

Respiratory muscle activity and patient-ventilator asynchrony during different settings of noninvasive ventilation in stable hypercapnic COPD: does high inspiratory pressure lead to respiratory muscle unloading?

Introduction

High-intensity noninvasive ventilation (NIV) has been shown to improve outcomes in stable chronic obstructive pulmonary disease patients. However, there is insufficient knowledge about whether with this more controlled ventilatory mode optimal respiratory muscle unloading is provided without an increase in patient–ventilator asynchrony (PVA).

Patients and methods

Ten chronic obstructive pulmonary disease patients on home mechanical ventilation were included. Four different ventilatory settings were investigated in each patient in random order, each for 15 min, varying the inspiratory positive airway pressure and backup breathing frequency. With surface electromyography (EMG), activities of the intercostal muscles, diaphragm, and scalene muscles were determined. Furthermore, pressure tracings were derived simultaneously in order to assess PVA.

Results

Compared to spontaneous breathing, the most pronounced decrease in EMG activity was achieved with the high-pressure settings. Adding a high breathing frequency did reduce EMG activity per breath, while the decrease in EMG activity over 1 min was comparable with the high-pressure, low-frequency setting. With high backup breathing frequencies less breaths were pressure supported (25% vs 97%). PVAs occurred more frequently with the low-frequency settings (P=0.017).

Conclusion

High-intensity NIV might provide optimal unloading of respiratory muscles, without undue increases in PVA.

Diaphragm Muscle Adaptation to Sustained Hypoxia: Lessons from Animal Models with Relevance to High Altitude and Chronic Respiratory Diseases

The diaphragm is the primary inspiratory pump muscle of breathing. Notwithstanding its critical role in pulmonary ventilation, the diaphragm like other striated muscles is malleable in response to physiological and pathophysiological stressors, with potential implications for the maintenance of respiratory homeostasis. This review considers hypoxic adaptation of the diaphragm muscle, with a focus on functional, structural, and metabolic remodeling relevant to conditions such as high altitude and chronic respiratory disease. On the basis of emerging data in animal models, we posit that hypoxia is a significant driver of respiratory muscle plasticity, with evidence suggestive of both compensatory and deleterious adaptations in conditions of sustained exposure to low oxygen. Cellular strategies driving diaphragm remodeling during exposure to sustained hypoxia appear to confer hypoxic tolerance at the expense of peak force-generating capacity, a key functional parameter that correlates with patient morbidity and mortality. Changes include, but are not limited to: redox-dependent activation of hypoxia-inducible factor (HIF) and MAP kinases; time-dependent carbonylation of key metabolic and functional proteins; decreased mitochondrial respiration; activation of atrophic signaling and increased proteolysis; and altered functional performance. Diaphragm muscle weakness may be a signature effect of sustained hypoxic exposure. We discuss the putative role of reactive oxygen species as mediators of both advantageous and disadvantageous adaptations of diaphragm muscle to sustained hypoxia, and the role of antioxidants in mitigating adverse effects of chronic hypoxic stress on respiratory muscle function.

Nasal high-flow therapy reduces work of breathing compared with oxygen during sleep in COPD and smoking controls: a prospective observational study

Patients with chronic obstructive pulmonary disease (COPD) endure excessive resistive and elastic loads leading to chronic respiratory failure. Oxygen supplementation corrects hypoxemia but is not expected to reduce mechanical loads. Nasal high-flow (NHF) therapy supports breathing by reducing dead space, but it is unclear how it affects mechanical loads of patients with COPD. The objective of this study was to compare the effects of low-flow oxygen and NHF therapy on ventilation and work of breathing (WOB) in patients with COPD and controls during sleep. Patients with COPD (n = 12) and controls (n = 6) were recruited and submitted to polysomnography to measure sleep parameters and ventilation in response to administration of oxygen and NHF. A subset of six patients also had an esophageal catheter inserted for the purpose of measuring WOB. Patients with COPD had similar minute ventilation (V̇e) but lower tidal volumes than matched controls. With oxygen, [Formula: see text]was increased and V̇e was reduced in both controls and patients with COPD, but there was an increase in transcutaneous CO₂ levels. NHF produced a greater reduction in V̇e and was associated with a reduction in CO₂ levels. Although NHF halved WOB, oxygen produced only a minor reduction in this parameter. We conclude that oxygen produced little change in WOB, which was associated with CO₂ elevations. On the other hand, NHF produced a large reduction in V̇e and WOB with a concomitant decrease in CO₂ levels. Our data indicate that NHF improves alveolar ventilation during sleep compared with oxygen and room air in patients with COPD and therefore can decrease their cost of breathing.

NEW & NOTEWORTHY

Nasal high-flow (NHF) therapy can support ventilation in patients with chronic obstructive pulmonary disease during sleep by decreasing the work of breathing and improving CO₂ levels. On the other hand, oxygen supplementation corrects hypoxemia, but it produces only a minimal reduction in work of breathing and is associated with increased CO₂ levels. Therefore, NHF can be a useful method to assist ventilation in patients with increased respiratory mechanical loads.

Contractile capability of the diaphragm assessed by ultrasonography predicts nocturnal oxygen saturation in COPD

BACKGROUND AND OBJECTIVE

Diaphragm function might be useful to predict nocturnal oxygen desaturation in COPD. Ultrasonography has been widely used for the assessment of the diaphragm. We aimed to investigate the relationship between the contractile capability of the diaphragm assessed by ultrasonography and the nocturnal percutaneous arterial oxygen saturation (NSpO₂ ) in COPD.

METHODS

Twenty-eight male patients with COPD (age, 73 ± 7 years; forced expiratory volume in 1 s (FEV₁ ), 54.2 ± 17.0% predicted) were included. The thickness of the diaphragm (Tdi) was assessed by ultrasonography. We calculated the change ratio of Tdi at the end of maximal inspiration and expiration (%ΔTdi). The mean value of NSpO₂ (NSpO_2mean ), the percentage of total sleep time (TST) with desaturation above 4% (DA4%) and the percentage of TST with saturation below 90% (SB90%) were measured by overnight oximetry. Daytime arterial oxygen pressure (PaO₂ ) and maximal inspiratory mouth pressure (PI_max ) were also measured.

RESULTS

All participants had mild or no daytime hypoxaemia (PaO₂ , 77.3 ± 8.6 mm Hg). The NSpO_2mean , DA4% and SB90% were significantly correlated with %ΔTdi, PaO₂ , %PI_max of the predicted value and the Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage. The %ΔTdi and PaO₂ were predictors of NSpO₂ mean by multiple regression analysis.

CONCLUSION

This study suggested a close relationship between the NSpO₂ and the contractile capability of the diaphragm assessed by ultrasonography in COPD. The %ΔTdi combined with PaO₂ might predict NSpO₂ in COPD patients with mild or no daytime hypoxaemia.

Manual evaluation of the diaphragm muscle

The respiratory diaphragm is the most important muscle for breathing. It contributes to various processes such as expectoration, vomiting, swallowing, urination, and defecation. It facilitates the venous and lymphatic return and helps viscera located above and below the diaphragm to work properly. Its activity is fundamental in the maintenance of posture and body position changes. It can affect the pain perception and emotional state. Many authors reported on diaphragmatic training by using special instruments, whereas only a few studies focused on manual therapy approaches. To the knowledge of the authors, the existing scientific literature does not exhaustively examines the manual evaluation of the diaphragm in its different portions. A complete evaluation of the diaphragm is mandatory for several professional subjects, such as physiotherapists, osteopaths, and chiropractors not only to elaborate a treatment strategy but also to obtain information on the validity of the training performed on the patient. This article aims to describe a strategy of manual evaluation of the diaphragm, with particular attention to anatomical fundamentals, in order to stimulate further research on this less explored field.

Role of Protein Carbonylation in Skeletal Muscle Mass Loss Associated with Chronic Conditions

Muscle dysfunction, characterized by a reductive remodeling of muscle fibers, is a common systemic manifestation in highly prevalent conditions such as chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), cancer cachexia, and critically ill patients. Skeletal muscle dysfunction and impaired muscle mass may predict morbidity and mortality in patients with chronic diseases, regardless of the underlying condition. High levels of oxidants may alter function and structure of key cellular molecules such as proteins, DNA, and lipids, leading to cellular injury and death. Protein oxidation including protein carbonylation was demonstrated to modify enzyme activity and DNA binding of transcription factors, while also rendering proteins more prone to proteolytic degradation. Given the relevance of protein oxidation in the pathophysiology of many chronic conditions and their comorbidities, the current review focuses on the analysis of different studies in which the biological and clinical significance of the modifications induced by reactive carbonyls on proteins have been explored so far in skeletal muscles of patients and animal models of chronic conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and physiological aging. Future research will elucidate the specific impact and sites of reactive carbonyls on muscle protein content and function in human conditions.