Respiratory muscle activation and action during voluntary cough in healthy humans

Fecal incontinence patients categorized based on anal pressure and electromyography: Anal sphincter damage and clinical symptoms

BACKGROUND

Disruption of external anal sphincter muscle (EAS) is an important factor in the multifactorial etiology of fecal incontinence (FI).

OBJECTIVES

We categorize FI patients into four groups based on the location of lesion in neuromuscular circuitry of EAS to determine if there are differences with regards to fecal incontinence symptoms severity (FISI) score, age, BMI, obstetrical history, and anal sphincter muscle damage.

METHODS

Female patients (151) without any neurological symptoms, who had undergone high-resolution manometry, anal sphincter EMG, and 3D ultrasound imaging of the anal sphincter were assessed. Patients were categorized into four groups: Group 1 (normal)-normal cough EMG (>10 μV), normal squeeze EMG (>10 μV), and normal anal squeeze pressure (>124 mmHg); Group 2 (cortical apraxia, i.e., poor cortical activation)-normal cough EMG, low squeeze EMG, and low anal squeeze pressure; Group 3 (muscle damage)-normal cough EMG, normal squeeze EMG, and low anal squeeze pressure; and Group 4 (pudendal nerve damage)-low cough EMG, low squeeze EMG, and low anal squeeze pressure.

RESULTS

The four patient groups were not different with regards to the patient's age, BMI, parity, and FISI scores. 3D ultrasound images of the anal sphincter complex revealed significant damage to the internal anal sphincter, external anal sphincter, and puborectalis muscles in all four groups.

CONCLUSION

The FI patients are a heterogeneous group; majority of these patients have significant damage to the muscles of the anal sphincter complex. Whether biofeedback therapy response is different among different patient groups requires study.

Analysis and applications of respiratory surface EMG: report of a round table meeting

Surface electromyography (sEMG) can be used to measure the electrical activity of the respiratory muscles. The possible applications of sEMG span from patients suffering from acute respiratory failure to patients receiving chronic home mechanical ventilation, to evaluate muscle function, titrate ventilatory support and guide treatment. However, sEMG is mainly used as a monitoring tool for research and its use in clinical practice is still limited-in part due to a lack of standardization and transparent reporting. During this round table meeting, recommendations on data acquisition, processing, interpretation, and potential clinical applications of respiratory sEMG were discussed. This paper informs the clinical researcher interested in respiratory muscle monitoring about the current state of the art on sEMG, knowledge gaps and potential future applications for patients with respiratory failure.

Diaphragm pacing and independent breathing in individuals with severe Pompe disease

Introduction

Pompe disease is an inherited disease characterized by a deficit in acid-α-glucosidase (GAA), an enzyme which degrades lysosomal glycogen. The phrenic-diaphragm motor system is affected preferentially, and respiratory failure often occurs despite GAA enzyme replacement therapy. We hypothesized that the continued use of diaphragm pacing (DP) might improve ventilator-dependent subjects' respiratory outcomes and increase ventilator-free time tolerance.

Methods

Six patients (3 pediatric) underwent clinical DP implantation and started diaphragm conditioning, which involved progressively longer periods of daily, low intensity stimulation. Longitudinal respiratory breathing pattern, diaphragm electromyography, and pulmonary function tests were completed when possible, to assess feasibility of use, as well as diaphragm and ventilatory responses to conditioning.

Results

All subjects were eventually able to undergo full-time conditioning via DP and increase their maximal tolerated time off-ventilator, when compared to pre-implant function. Over time, 3 of 6 subjects also demonstrated increased or stable minute ventilation throughout the day, without positive-pressure ventilation assistance.

Discussion

Respiratory insufficiency is one of the main causes of death in patients with Pompe disease. Our results indicate that DP in Pompe disease was feasible, led to few adverse events and stabilized breathing for up to 7 years.

Predictors of Peak Expiratory Cough Flow in Individuals with Amyotrophic Lateral Sclerosis

Dystussia is prevalent in individuals with amyotrophic lateral sclerosis (ALS), leading to a diminished physiologic capacity to effectively defend the airway. We aimed to identify predictors of peak expiratory cough flow rate in individuals with ALS. One hundred and thirty-four individuals with a confirmed diagnosis of ALS (El-Escorial criteria revised) completed the ALS Functional Rating Scale-Revised (ALSFRS-R) and underwent pulmonary function and cough spirometry testing. Pearson's correlation coefficients and hierarchical multiple regression modeling were conducted to determine predictors of voluntary cough peak expiratory flow rate (p < 0.05). The full model including age, bulbar disease, cough spirometry metrics, and respiratory parameters had a marginal R² = 0.635, F (7, 126) = 30.241, p < 0.0005, adjusted R² = 0.61. Maximum expiratory pressure, compression phase, and vital capacity did not contribute and were therefore removed (p < 0.05). The most parsimonious predictive model included age, bulbar disease, peak inspiratory flow rate and duration, peak expiratory rise time, and inspiratory pressure generation with a marginal R² = 0.543. Although expiratory pressure generation has historically served as the therapeutic target to improve dystussia in ALS, the current dataset highlighted that the inability to quickly and forcefully inspire during the inspiratory phase of voluntary cough places patients at a mechanical disadvantage to generate subsequent high-velocity expiratory airflow to clear the airway. Thus, therapeutic training programs that include both inspiratory and expiratory strength targets may optimize airway clearance capacity in this challenging patient population.

Characterizing Expiratory Respiratory Muscle Degeneration in Duchenne Muscular Dystrophy Using MRI

BACKGROUND

Expiratory muscle weakness and impaired airway clearance are early signs of respiratory dysfunction in Duchenne muscular dystrophy (DMD), a degenerative muscle disorder in which muscle cells are damaged and replaced by fibrofatty tissue. Little is known about expiratory muscle pathology and its relationship to cough and airway clearance capacity; however, the level of muscle replacement by fat can be estimated using MRI and expressed as a fat fraction (FF).

RESEARCH QUESTION

How does abdominal expiratory muscle fatty infiltration change over time in DMD and relate to clinical expiratory function?

STUDY DESIGN AND METHODS

Individuals with DMD underwent longitudinal MRI of the abdomen to determine FF in the internal oblique, external oblique, and rectus abdominis expiratory muscles. FF data were used to estimate a model of expiratory muscle degeneration by using nonlinear mixed effects and a cumulative distribution function. FVC, maximal inspiratory and expiratory pressures, and peak cough flow were collected as clinical correlates to MRI.

RESULTS

Forty individuals with DMD (aged 6-18 years at baseline) participated in up to five visits over 36 months. Modeling estimated the internal oblique progresses most quickly and reached 50% replacement by fat at a mean patient age of 13.0 years (external oblique, 14.0 years; rectus abdominis, 16.2 years). Corticosteroid-untreated individuals (n = 4) reached 50% muscle replacement by fat 3 to 4 years prior to treated individuals. Individuals with mild clinical dystrophic phenotypes (n = 3) reached 50% muscle replacement by fat 4 to 5 years later than corticosteroid-treated individuals. Internal and external oblique FFs near 50% were associated with maximal expiratory pressures < 60 cm H₂O and peak cough flows < 270 L/min.

INTERPRETATION

These data improve understanding of the early phase of respiratory compromise in DMD, which typically presents as airway clearance dysfunction prior to the onset of hypoventilation, and links expiratory muscle fatty infiltration to pulmonary function measures.

Comparison of physical properties of voluntary coughing, huffing and swallowing in healthy subjects

Coughing, huffing and swallowing protect the airway from aspiration. This study was conducted to compare the physical properties of voluntary coughing, huffing and swallowing in healthy subjects. Ten healthy men were asked to huff, cough and swallow repeatedly. Electromyograms (EMGs) were recorded from the left side of the external oblique (EO), sternocleidomastoid, suprahyoid (SH) and thyrohyoid muscles. Airflow was recorded using a face mask with two-way non-rebreathing valves. The expiratory velocity of huffing and coughing and the SH EMG of all actions presented high intraclass correlation coefficients (> 0.8). The inspiratory and expiratory velocities did not differ significantly between coughing and huffing. The expiratory acceleration of coughing was significantly higher than that of huffing, whereas the expiratory volume of coughing was significantly smaller than that of huffing. The EO EMG of coughing and huffing were significantly larger than that of swallowing. The EO EMG activity during the expiratory phase was significantly higher than that of the other phases of both coughing and huffing. The SH EMG of coughing and huffing were significantly smaller than that of swallowing. Correlation analysis revealed that the expiratory velocity of coughing was strongly positively correlated with that of huffing. The expiratory volume of huffing was significantly positively correlated with hand grip strength. These results suggest that EO and SH muscle activities during huffing or coughing differ those during swallowing, and huffing and coughing may work similarly in expiratory function.