Comparison of Pulmonary Functions at Onset of Ventilatory Insufficiency in Patients With Amyotrophic Lateral Sclerosis, Duchenne Muscular Dystrophy, and Myotonic Muscular Dystrophy

Airway Clearance Strategies and Secretion Management in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare, neurodegenerative motor neuron disease that affects voluntary muscle movement. Often, difficulty in coughing, breathing, and swallowing are sequela associated with the condition, and the presence of bulbar muscle predominant weakness results in deleterious effects on airway clearance and secretion management. This narrative review will provide practical guidance for clinicians treating this population. Cough insufficiency in this population typically manifests as a prolonged, slow, weak cough effort that impedes the clearability of secretions and airway protection. Dystussia and dysphagia frequently occur simultaneously in bulbar dysfunction, subsequently impacting respiratory health. Measures of respiratory strength should be obtained and monitored every 3-6 months, preferably in a multidisciplinary clinic setting. Cough augmentation, whether manual or mechanical techniques, should be sought as early in the disease progression as possible to adequately control secretions in the proximal airways. This airway clearance strategy can aid in the prevention and treatment of respiratory tract infections (RTIs), which can pose a significant clinical hurdle to those with ALS. The use of mechanical insufflation-exsufflation may be complicated by severe bulbar dysfunction rendering this technique ineffective. Though peripheral airway clearance strategies, such as high-frequency chest-wall compression, have the advantage of being less impacted by bulbar dysfunction, it is only recommended this modality be used in conjunction with, versus in lieu of, proximal strategies. Salivary secretion management includes the use of anticholinergics, botulinum toxin, and radiation therapy depending on severity and desire for relief.

Development of prediction models based on respiratory assessments to determine the need for non-invasive ventilation in patients with myotonic dystrophy type 1

INTRODUCTION

Myotonic dystrophy type 1 is a slowly progressive, multisystem, autosomal dominant disorder, in which the impairments of respiratory systems represent one of the main causes of death.

OBJECTIVE

The aim of our study is to develop prediction models to identify the most appropriate test(s) providing indication for NIV.

METHODS

DM1 patients attending the NEMO Clinical Center (Milan) between January 2008 and July 2020, who had been subjected to a complete battery of respiratory tests, were retrospectively recruited. Demographic, clinical, and anthropometric characteristics were collected, as well as arterial blood gas (ABG) analysis, spirometry, respiratory muscle strength, cough efficacy, and nocturnal oximetry as respiratory assessments. Patients were stratified in those requiring NIV and those with normal respiratory function.

RESULTS

Out of 151 DM1 patients (median age: 44 years [35.00-53.00]; male/female ratio: 0.80 (67/84)), 76 had an indication for NIV initiation (50.33%). ABG, spirometry, and nocturnal oximetry prediction models resulted in an excellent discriminatory ability in distinguishing patients who needed NIV from those who did not (AUC of 0.818, 0.808, and 0.935, respectively). An easy-to-use calculator was developed to automatically determine a score of NIV necessity based on the prediction equations generated from each aforementioned prediction model.

CONCLUSIONS

The proposed prediction models may help to identify which patients are at a higher risk of requiring ventilator support and therefore help in defining individual management plans and criteria for specific interventions early in the disease course.

Standardization of Air Stacking as Lung Expansion Therapy for Patients With Restrictive Lung Disease: A Pilot Study

OBJECTIVE

Although air stacking is a widely used lung expansion therapy essential for restrictive lung diseases, important details such as peak insufflation pressure (PIP) and number of squeezes have not been investigated. The purpose of this study was to standardize a method of air stacking to minimize problems with its application by identifying the optimal pressure and number of squeezes performed by professional physicians and investigating the current status of routine air stacking implementation in patients.

METHODS

This prospective cross-sectional test-retest study involved individuals who had neuromuscular disorders and had performed air stacking exercise for longer than 1 year. PIP and number of squeezes were measured to identify the differences between caregivers and physicians. Cases of incorrectly performed air stacking were investigated and categorized. The problems associated with air stacking were evaluated.

RESULTS

A total of 45 participants were included. PIP was 41.4 (SD = 4.2; range = 34.8-50.0) cm H2O, and optimal number of squeezes was 3.1 (SD = 0.5; range = 2-4). When the air stacking methods used by caregivers were evaluated, 19 of 45 caregivers (42.2%) used methods inappropriately. Higher PIP and larger number of squeezes were observed with caregiver implementation. Thirty caregivers (66.7%) experienced finger or wrist pain; this problem was observed especially in female caregivers, who tended to incorrectly perform air stacking.

CONCLUSIONS

This pilot study showed that the optimal pressure of air stacking was 35 to 50 cm H2O. Caregivers often perform air stacking inappropriately, leading to complications without achieving the purpose of air stacking. The introduction of a new method, such as manometry, can be helpful for achieving optimal air stacking.

IMPACT

Optimal pressure of air stacking can be measured with inexpensive, simple, and commercially available digital manometry. This approach enables air stacking to be performed and taught more accurately and efficiently and reduces complications in both patients and caregivers.

Relationship between Eating and Digestive Symptoms and Respiratory Function in Advanced Duchenne Muscular Dystrophy Patients

Background:

Duchenne muscular dystrophy (DMD) patients can have various issues that affect their quality of life, including eating and digestive conditions.

Objective:

We sought to identify the relationship between respiratory function and various eating and digestion related symptoms in patients with advanced Duchenne muscular dystrophy (DMD).

Methods:

Eating and digestive symptoms, including loss of appetite, nausea, vomiting, diarrhea, constipation, swallowing difficulty, mastication difficulty, early satiety, and aspiration, were evaluated among patients with advanced DMD who were nonambulatory and required noninvasive mechanical ventilatory support. In addition, various respiratory function parameters were measured, including forced vital capacity (FVC), maximal insufflation capacity (MIC), peak cough flow (PCF), assisted PCF (APCF), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP). We then analyzed the relationship between gastrointestinal symptoms and respiratory function parameters.

Results:

A total of 180 patients (age, 22.3±5.0 years) were included in the analysis. Loss of appetite and early satiety showed no correlation with any of the respiratory function parameters. Constipation was correlated with MEP; swallowing difficulty was correlated with MIC, APCF, MIP and MEP; and mastication difficulty was correlated with FVC, PCF, APCF, MIP, and MEP. Notably, age did not correlate with any gastrointestinal symptoms.

Conclusions:

Eating and digestive symptoms are more closely correlated with respiratory function than with age in patients with DMD. We think this correlation is mainly caused by the skeletal muscle strength, which is major determinant of both digestive and respiratory function.

Utility of maximum inspiratory and expiratory pressures as a screening method for respiratory insufficiency in slowly progressive neuromuscular disorders

The aim of this study was to assess whether different cut-offs of maximum inspiratory and/or expiratory pressure (MIP/MEP) are valuable screening parameters to detect restrictive respiratory insufficiency. Spirometry, MIP, MEP and capillary blood gas analysis were obtained from patients with confirmed neuromuscular disorders. We calculated regression analysis, sensitivity, specificity and predictive values. We enrolled 29 patients with myotonic dystrophy type 1 (DM1), 19 with late-onset Pompe disease (LOPD), and 24 with spinal muscular atrophy type 3. Moderate to high reduction in manometry was exclusively found in LOPD and DM1 patients. Significant associations were found between manometry and spirometry. Highest adjusted r² was found for MIP % predicted and forced vital capacity (FVC) % predicted. Manometry predicted abnormal FVC and forced expiratory volume 1 s (FEV1). MEP > 80 cmH₂O predicted normal FVC and FEV1, regardless of cut-off values. MIP and MEP did not positively predict alterations in capillary blood gas analysis. Disease-specific cut-offs of manometry did not increase the prediction rate of patients with abnormal FVC and FEV1. Predicted values should be calculated for a more comprehensive interpretation of manometry results. MIP and MEP can serve as a screening parameter for patients with neuromuscular disorders, but parallel testing of both MIP and MEP needs to be performed to increase the positive prediction probability across disease groups.

Correlation of Bone Mineral Density with Pulmonary Function in Advanced Duchenne Muscular Dystrophy

BACKGROUND

A relationship between bone mineral density (BMD) and physical function has been revealed in the general population and various diseases. However, there is a lack of research investigating the correlation between BMD and respiratory function, one of few measurable physical parameters in patients with advanced Duchenne muscular dystrophy (DMD).

OBJECTIVE

To determine whether pulmonary function parameters, including respiratory muscle strength, are related to BMD.

DESIGN

Retrospective observational study.

SETTING

A tertiary university hospital.

PATIENTS

DMD patients who were over 20 years of age, nonambulatory, and supported by mechanical ventilators.

METHODS

The patients' age, weight, and pulmonary function as well as the BMD of the first and the fourth lumbar vertebra were assessed. Pulmonary function includes forced vital capacity (FVC), unassisted and assisted peak cough flow (UPCF and APCF), maximal expiratory pressure (MEP), and maximal inspiratory pressure (MIP).

MAIN OUTCOME MEASURES

A bivariate correlation for BMD and other pulmonary parameters was calculated, and hierarchical regression analysis was used to determine predictors of spine Z-score.

RESULTS

It was observed that the decrease in the spine BMD was not significantly correlated with age. However, the body mass index (BMI) and all parameters of pulmonary function were correlated with BMD. Partial correlation analysis adjusted by BMI showed that UPCF and APCF were powerful predictors of spine BMD.

CONCLUSIONS

The BMD of the lumbar spine correlated with BMI and PCF in patients with DMD at an advanced stage.

Consensus-Based Care Recommendations for Pulmonologists Treating Adults with Myotonic Dystrophy Type 1

PURPOSE OF REVIEW

Myotonic dystrophy type 1 (DM1) is a severe, progressive genetic disease that affects approximately 1 in 2,500 individuals globally [Ashizawa et al.: Neurol Clin Pract 2018;8(6):507-20]. In patients with DM1, respiratory muscle weakness frequently evolves, leading to respiratory failure as the main cause of death in this patient population, followed by cardiac complications [de Die-Smulders et al.: Brain 1998;121(Pt 8):1557-63], [Mathieu et al.: Neurology 1999;52(8):1658-62], [Groh et al.: Muscle Nerve 2011;43(5):648-51]. This paper provides a more detailed outline on the diagnostic and management protocols, which can guide pulmonologists who may not have experience with DM1 or who are not part of a neuromuscular multidisciplinary clinic. A group of neuromuscular experts in DM1 including pulmonologists, respiratory physiotherapists and sleep specialists discussed respiratory testing and management at baseline and during follow-up visits, based on their clinical experience with patients with DM1. The details are presented in this report.

RECENT FINDINGS

Myotonic recruited 66 international clinicians experienced in the treatment of people living with DM1 to develop and publish consensus-based care recommendations targeting all body systems affected by this disease [Ashizawa et al.: Neurol Clin Pract. 2018;8(6):507-20]. Myotonic then worked with 12 international respiratory therapists, pulmonologists and neurologists with long-standing experience in DM respiratory care to develop consensus-based care recommendations for pulmonologists using a methodology called the Single Text Procedure. This process generated a 7-page document that provides detailed respiratory care recommendations for the management of patients living with DM1. This consensus is completely based on expert opinion and not backed up by empirical evidence due to limited clinical care data available for respiratory care management in DM patients. Nevertheless, we believe it is of relevance for professionals treating adults with myotonic dystrophy because it addresses practical issues related to respiratory management and care, which have been adapted to meet the specific issues in patients with DM1.

SUMMARY

The resulting recommendations are intended to improve respiratory care for the most vulnerable of DM1 patients and lower the risk of untoward respiratory complications and mortality by providing pulmonologist who are less experienced with DM1 with practical indications on which tests and when to perform them, adapting the general respiratory knowledge to specific issues related to this multiorgan disease.

Clinical implication of maximal voluntary ventilation in myotonic muscular dystrophy

Patients with myotonic muscular dystrophy type 1 (DM1) tend to exhibit earlier respiratory insufficiency than patients with other neuromuscular diseases at similar or higher forced vital capacity (FVC). This study aimed to analyze several pulmonary function parameters to determine which factor contributes the most to early hypercapnia in patients with DM1.We analyzed ventilation status monitoring, pulmonary function tests (including FVC, maximal voluntary ventilation [MVV], and maximal inspiratory and expiratory pressure), and polysomnography in subjects with DM1 who were admitted to a single university hospital. The correlation of each parameter with hypercapnia was determined. Subgroup analysis was also performed by dividing the subjects into 2 subgroups according to usage of mechanical ventilation.Final analysis included 50 patients with a mean age of 42.9 years (standard deviation = 11.1), 46.0% of whom were male. The hypercapnia was negatively correlated with MVV, FVC, forced expiratory volume in 1 second (FEV1), and their ratios to predicted values in subjects with myotonic muscular dystrophy type 1. At the same partial pressure of carbon dioxide, the ratio to the predicted value was lowest for MVV, then FEV1, followed by FVC. Moreover, the P values for differences in MVV and its ratio to the predicted value between ventilator users and nonusers were the lowest.When screening ventilation failure in patients with DM1, MVV should be considered alongside other routinely measured parameters.

How to Interpret Abnormal Findings of Spirometry and Manometry in Myotonic Dystrophies?

BACKGROUND/AIM

Pulmonary function tests are used for screening respiratory insufficiency in patients with myotonic dystrophy (DM). We analysed the agreement between two different approaches in assessment of abnormal findings of forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP), in DM patients.

METHODS

We used Cohen's κ- and Bangdiwala's B- statistic to compare the agreement between different cut-off values recommended by experts (ENMC) and the cut-off values based on the reference range (RR). We further analysed their sensitivity (Sn) and specificity (Sp) in detecting symptoms associated with respiratory insufficiency.

RESULTS

The observed agreement was: 1) for FVC: κ= -0.002, B = 0.406; 2) for FEV1: κ= 0.944, B = 0.946; 3) for MIP: κ= 0.625, B = 0.674; and 4) for MEP: κ= 0.241, B = 0.373. Overall, RR cut-off values showed higher sensitivity, whereas the ENMC values showed higher specificity in detecting symptoms of respiratory involvement.

CONCLUSIONS

The two approaches showed perfect agreement in assessment of FEV1, substantial agreement for MIP, and weak agreement for FVC and MEP. RR is an established method of assessment for spirometry and should be favoured because it takes variability within the population into account. Further development and validation of regression equations for RR calculations of predicted maximal respiratory pressures, with corresponding lower limits of normal, is required.The B statistic is more robust in assessing agreement between two diagnostic methods, resolving the issue of the κ paradox.

Respiratory dysfunction in myotonic dystrophy type 1: A systematic review

Myotonic dystrophy type 1 (DM1) is one of the most common muscular dystrophies in adults. This review summarises the current literature regarding the natural history of respiratory dysfunction in DM1, the role of central respiratory drive and peripheral respiratory muscle involvement and its significance in respiratory function, and investigates the relationship between genetics (CTG repeat length) and respiratory dysfunction. The review included all articles that reported spirometry on 10 or more myotonic dystrophy patients. The final review included 55 articles between 1964 and 2017. The major conclusions of this review were (1) confirmation of the current consensus that respiratory dysfunction, predominantly a restrictive ventilatory pattern, is common in myotonic dystrophy and is associated with alveolar hypoventilation, chronic hypercapnia, and sleep disturbance in the form of sleep apnoea and sleep related disordered breathing; (2) contrary to commonly held belief, there is no consensus in the literature regarding the relationship between CTG repeat length and severity of respiratory dysfunction and a relationship has not been established; (3) the natural history and time-course of respiratory functional decline is very poorly understood in the current literature; (4) there is a consensus that there is a significant involvement of central respiratory drive in this alveolar hypoventilation however the current literature does not identify the mechanism for this.

Respiratory Management of the Patient With Duchenne Muscular Dystrophy

In 2010, Care Considerations for Duchenne Muscular Dystrophy, sponsored by the Centers for Disease Control and Prevention, was published in Lancet Neurology, and in 2018, these guidelines were updated. Since the publication of the first set of guidelines, survival of individuals with Duchenne muscular dystrophy has increased. With contemporary medical management, survival often extends into the fourth decade of life and beyond. Effective transition of respiratory care from pediatric to adult medicine is vital to optimize patient safety, prognosis, and quality of life. With genetic and other emerging drug therapies in development, standardization of care is necessary to accurately assess treatment effects in clinical trials. This revision of respiratory recommendations preserves a fundamental strength of the original guidelines: namely, reliance on a limited number of respiratory tests to guide patient assessment and management. A progressive therapeutic strategy is presented that includes lung volume recruitment, assisted coughing, and assisted ventilation (initially nocturnally, with the subsequent addition of daytime ventilation for progressive respiratory failure). This revision also stresses the need for serial monitoring of respiratory muscle strength to characterize an individual's respiratory phenotype of severity as well as provide baseline assessments for clinical trials. Clinical controversies and emerging areas are included.

Respiratory involvement in neuromuscular disorders

PURPOSE OF REVIEW

In numerous neuromuscular disorders (NMDs), respiratory muscle weakness is present, and acute or chronic respiratory failure may evolve. Very often, respiratory involvement substantially adds to the burden of disease, impairs quality of life, or reduces life expectancy. This article summarizes new aspects of both diagnosis and management of respiratory muscle weakness in patients with NMDs.

RECENT FINDINGS

Drugs like deflazacort, ataluren, eteplirsen, and nusinersen are now approved treatments for Duchenne Muscular Dystrophy and Spinal Muscular Atrophy, and others are on their way in NMDs. Although observing how innovative drugs will change the natural history of these diseases, including respiratory function over time, adequate symptomatic treatment remains meaningful and is strongly recommended. Physicians should systematically take respiratory involvement into account to improve patients' quality of life and prognosis.

SUMMARY

First, it is outlined in which subtypes of NMD respiratory muscle dysfunction is particularly relevant. Second, new developments regarding diagnostic procedures, including respiratory muscle strength testing, spirometry, and sleep studies, are covered. Third, this article gives an overview on current concepts of ventilatory support and management of secretions in patients with NMD.

Semi-Automated Analysis of Diaphragmatic Motion with Dynamic Magnetic Resonance Imaging in Healthy Controls and Non-Ambulant Subjects with Duchenne Muscular Dystrophy

Subjects with Duchenne Muscular Dystrophy (DMD) suffer from progressive muscle damage leading to diaphragmatic weakness that ultimately requires ventilation. Emerging treatments have generated interest in better characterizing the natural history of respiratory impairment in DMD and responses to therapy. Dynamic (cine) Magnetic Resonance Imaging (MRI) may provide a more sensitive measure of diaphragm function in DMD than the commonly used spirometry. This study presents an analysis pipeline for measuring parameters of diaphragmatic motion from dynamic MRI and its application to investigate MRI measures of respiratory function in both healthy controls and non-ambulant DMD boys. We scanned 13 non-ambulant DMD boys and 10 age-matched healthy male volunteers at baseline, with a subset (n = 10, 10, 8) of the DMD subjects also assessed 3, 6, and 12 months later. Spirometry-derived metrics including forced vital capacity were recorded. The MRI-derived measures included the lung cross-sectional area (CSA), the anterior, central, and posterior lung lengths in the sagittal imaging plane, and the diaphragm length over the time-course of the dynamic MRI. Regression analyses demonstrated strong linear correlations between lung CSA and the length measures over the respiratory cycle, with a reduction of these correlations in DMD, and diaphragmatic motions that contribute less efficiently to changing lung capacity in DMD. MRI measures of pulmonary function were reduced in DMD, controlling for height differences between the groups: at maximal inhalation, the maximum CSA and the total distance of motion of the diaphragm were 45% and 37% smaller. MRI measures of pulmonary function were correlated with spirometry data and showed relationships with disease progression surrogates of age and months non-ambulatory, suggesting that they provide clinically meaningful information. Changes in the MRI measures over 12 months were consistent with weakening of diaphragmatic and inter-costal muscles and progressive diaphragm dysfunction. In contrast, longitudinal changes were not seen in conventional spirometry measures during the same period. Dynamic MRI measures of thoracic muscle and pulmonary function are, therefore, believed to detect meaningful differences between healthy controls and DMD and may be sensitive to changes in function over relatively short periods of follow-up in non-ambulant boys with DMD.

[Update on the respiratory management of patients with chronic neuromuscular disease]

BACKGROUND

Neuromuscular diseases include a wide range of conditions that may involve potentially life-threatening respiratory complications (infection, respiratory failure).

SURVEILLANCE AND PULMONARY FUNCTION TESTS

For patients with neuromuscular diseases, clinical assessment of respiratory function and regular pulmonary function tests are needed to screen for nocturnal respiratory disorders, weakness of the diaphragm and potential restrictive disorders and/or chronic hypercapnic respiratory insufficiency, possibly with couch deficiency. MANAGEMENT OF NOCTURNAL RESPIRATORY DISORDERS AND CHRONIC RESPIRATORY FAILURE: Nocturnal respiratory assistance is an important phase of care for nocturnal respiratory disorders and chronic respiratory failure. This may involve continuous positive airway pressure, adaptative servo-ventilation or non-invasive ventilation with a facial or nasal mask. As needed, diurnal assistance may be proposed by mouthpiece ventilation. Should non-invasive ventilation prove insufficient, or if significant swallowing disorders or recurrent bronchial obstruction develop, or in case of prolonged intubation, tracheotomy may be required.

LOWER AIRWAY OBSTRUCTION

In case of lower airway infection with ineffective cough, physical therapy, associated with air stacking, intermittent positive pressure breathing or mechanical in-exsufflation may be proposed.

PATIENT-CENTERED MANAGEMENT

Care for swallowing disorders, nutritional counseling (cachexia, obesity), vaccinations and therapeutic education are integral elements of patient-centered management aiming to prevent the negative impact of infection and to manage respiratory failure of chronic neuromuscular disease.

Respiratory complications, management and treatments for neuromuscular disease in children

PURPOSE OF REVIEW

To summarize current literature describing the respiratory complications of neuromuscular disease (NMD) and the effect of respiratory interventions and to explore new gene therapies for patients with NMD.

RECENT FINDINGS

Measurements of respiratory function focus on vital capacity and maximal inspiratory and expiratory pressure and show decline over time. Management of respiratory complications includes lung volume recruitment, mechanical insufflation-exsufflation, chest physiotherapy and assisted ventilation. Lung volume recruitment can slow the progression of lung restriction. New gene-specific therapies for Duchenne muscular dystrophy and spinal muscular atrophy have the potential to preserve respiratory function longitudinally. However, the long-term therapeutic benefit remains unknown.

SUMMARY

Although NMDs are heterogeneous, many lead to progressive muscle weakness that compromises the function of the respiratory system including upper airway tone, cough and secretion clearance and chest wall support. Respiratory therapies augment or support the normal function of these components of the respiratory system. From a respiratory perspective, the new mutation and gene-specific therapies for NMD are likely to confer long-term therapeutic benefit. More sensitive and standard tools to assess respiratory function longitudinally are needed to monitor respiratory complications in children with NMD, particularly the youngest patients.