Impact of expiratory strength training in amyotrophic lateral sclerosis

Introduction: We evaluated the feasibility and impact of expiratory muscle strength training (EMST) on respiratory and bulbar function in persons with amyotrophic lateral sclerosis (ALS). Methods: Twenty‐five ALS patients participated in this delayed intervention open‐label clinical trial. Following a lead‐in period, patients completed a 5‐week EMST protocol. Outcome measures included: maximum expiratory pressure (MEP); physiologic measures of swallow and cough; and penetration–aspiration scale (PAS) scores. Results: Of participants who entered the active phase of the study (n = 15), EMST was well tolerated and led to significant increases in MEPs and maximum hyoid displacement during swallowing post‐EMST (P < 0.05). No significant differences were observed for PAS scores or cough spirometry measures. Conclusions: EMST was feasible and well tolerated in this small cohort of ALS patients and led to improvements in expiratory force‐generating pressures and swallow kinematics. Further investigation is warranted to confirm these preliminary findings. Muscle Nerve 54 : 48–53, 2016     

Respiratory complications related to bulbar dysfunction in motor neuron disease

Bulbar dysfunction resulting from corticobulbar pathway or brainstem neuron degeneration is one of the most important clinical problems encountered in motor neuron disease (MND) and contributes to various respiratory complications which are major causes of morbidity and mortality. Chronic malnutrition as a consequence of bulbar muscle weakness may have a considerable bearing on respiratory muscle function and survival. Abnormalities of the control and strength of the laryngeal and pharyngeal muscles may cause upper airway obstruction increasing resistance to airflow. Bulbar muscle weakness prevents adequate peak cough flows to clear airway debris. Dysphagia can lead to aspiration of microorganisms, food and liquids and hence pneumonia. MND patients with bulbar involvement commonly display an abnormal respiratory pattern during swallow characterized by inspiration after swallow, prolonged swallow apnoea and multiple swallows per bolus. Volitional respiratory function tests such as forced vital capacity can be inaccurate in patients with bulbofacial weakness and/or impaired volitional respiratory control. Bulbar muscle weakness with abundant secretions may increase the risk of aspiration and make successful non-invasive assisted ventilation more difficult. We conclude that an evaluation of bulbar dysfunction is an essential element in the assessment of respiratory dysfunction in MND.     

Expiratory muscle strength training improves measures of pressure generation and cough strength in a patient with myotonic dystrophy type 1

Expiratory muscle strength training (EMST) exercise programmes aim to improve respiratory function by increasing the force generating capability of expiratory muscles by resistance training. In neuromuscular conditions, in which cough flow generation is often decreased, there is increasing interest in EMST as a therapeutic intervention. We present data showing efficacy of EMST in a patient with adult onset Myotonic Dystrophy Type 1 (DM1). A domiciliary training programme (5 days per week over 32 weeks) resulted in increases in maximum expiratory mouth pressure (from 15 cmH₂O to 38 cmH₂O) and peak cough flow (300 L/min to 390 L/min). Improvements were also seen in maximum inspiratory mouth pressure (26 cmH₂O to 52 cmH₂O) and sniff nasal inspiratory pressure (40 cmH₂O to 69 cmH₂O). No changes were detected in speech or swallowing. This novel study demonstrates that cough flow generation in DM1 may be increased by a programme of expiratory muscle training. A clinical trial of EMST in DM1 is warranted.     

Cardiopulmonary and metabolic responses to maximum exercise and aerobic capacity in hemiplegic patients

This study evaluated cardiopulmonary and metabolic responses to maximum exercise and aerobic capacity in hemiplegic patients and clarified the relationship between the resulting data and motor disability. Twenty patients with stroke and fifteen healthy controls were included in the study. Cardiopulmonary and metabolic responses to maximum exercise were investigated with an electronically braked arm crank ergometer. Vital capacity, forced expiratory volume in 1 second, peak expiratory flow rate, forced vital capacity, maximum voluntary ventilation, peak power output, respiratory exchange ratio, and exercise time were reduced in stroke patients when compared with the controls. No relationship was found between these data and motor disability. The hemiplegic patients showed a significant respiratory dysfunction and reduced exercise tolerance. These findings suggest that a program of ventilatory and aerobic training should be considered early after stroke to avoid cardiorespiratory problems and deconditioning.     

Ionotropic glutamate receptors mediate excitatory drive to caudal medullary expiratory neurons in the rabbit

Most of the neurons of the caudal ventral respiratory group (cVRG) are bulbospinal expiratory neurons that receive their main excitatory drive from more rostral, but not yet defined regions. This study was devoted to investigate the functional role of ionotropic excitatory amino acid (EAA) receptors in the excitatory drive transmission to cVRG expiratory neurons during eupnoeic breathing and some respiratory reflexes including cough induced by mechanical stimulation of the tracheobronchial tree. The experiments were performed on spontaneously breathing rabbits under pentobarbitone anesthesia making use of microinjections (30--50 nl) of EAA receptor antagonists into the cVRG. Phrenic nerve and abdominal muscle activities were recorded. Bilateral microinjections of 50 mM kynurenic acid (KYN), a broad-spectrum EAA antagonist, and 10 mM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA antagonist, or 5 mM 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (NBQX), a more specific non-NMDA antagonist, completely suppressed spontaneous rhythmic abdominal activity and reflex expiratory responses either to tracheal occlusion at end-inspiration (Breuer-Hering inflation reflex) or to expiratory threshold loading (5 cm H(2)O); they also suppressed both the inspiratory and expiratory components of the cough reflex. Spontaneous rhythmic abdominal activity and the reflex respiratory responses were strongly reduced, but not completely abolished by microinjections of 10 mM d(-)-2-amino-5-phosphonopentanoic acid (D-AP5), an NMDA antagonist. The results provide evidence that the excitatory drive to cVRG bulbospinal expiratory neurons during eupnoeic breathing and the investigated respiratory reflexes is mediated by EAA receptors. They also support the view that neurons located in the cVRG are not merely elements of the expiratory output system.     

Discharge of abdominal muscle alpha and gamma motoneurons during expiratory loading in cats

Expiratory responses were elicited in abdominal alpha and gamma motoneurons of anesthetized cats by continuous positive airway pressure, tracheal occlusion, lung inflation, or step-changes in expiratory airflow resistance. Abdominal alpha motoneurons were silent during quiet breathing but became rhythmically active whenever expiration was opposed. In addition, the responses of abdominal alpha motoneurons to an increase in expiratory airflow resistance included an increase in discharge frequency, an earlier firing time of individual neurons, recruitment of successively larger motor fibers, and an increased duration of discharge. Abdominal gamma motoneurons discharged continuously during quiet breathing and an increased frequency of discharge during the expiratory phase of the respiratory cycle was evident in approximately one-third of the fibers. This respiratory modulation was enhanced, or initiated if absent, by imposing a load during expiration. Bilateral cervical vagotomy abolished both the respiratory modulation of abdominal gamma motoneurons and expiratory activity in abdominal alpha motoneurons indicating the importance of supraspinal structures. Coactivation of abdominal alpha and gamma motoneurons during active expiration also suggests that a segmental reflex involving abdominal muscle spindles may be capable of providing automatic compensation for changes in expiratory load. In conclusion, both vagal and dorsal root information appear to contribute to the proprioceptive control of abdominal muscle expiratory activity.     

The effects of inspiratory resistive training on respiratory muscle function in patients with muscular dystrophy

The effects of inspiratory resistive training on respiratory muscle function was evaluated in 11 patients with Duchenne, limb-girdle, and facio-scapulo-humeral (FSH) type muscular dystrophy. Muscle training consisted of breathing against an inspiratory resistance for two 15-minute sessions each day while at home. Following 6 weeks of training, there were significant increases in the maximum resistance that could be tolerated for at least 5 minutes (P < 0.01) and also in the maximum duration that ventilations equal to 30%, 50%, 70%, and 90% of the maximum voluntary ventilation could be sustained (P < 0.05). In six patients who trained for an additional 6-week period, respiratory muscle endurance increased even further. The degree of improvement in respiratory muscle endurance was positively correlated with baseline vital capacity (r = 0.84, P < 0.05) and maximal inspiratory pressure (r = 0.76, P < 0.05). Spirometry, functional residual capacity, and maximal inspiratory and expiratory pressures were not affected by training. We conclude that inspiratory resistive training improves respiratory muscle endurance in muscular dystrophy patients. Improvement in respiratory muscle function may serve to delay the onset of respiratory complications in patients with muscular dystrophy.     

Relationships between spinal deformities and respiratory function in patients with severe motor and intellectual disabilities syndrome

The term severe motor and intellectual disabilities syndrome (SMIDS) refers to describe a heterogeneous group of disorders with severe physical disabilities and profound mental retardation. Many patients with SMIDS have spinal deformities such as spinal rotation and scoliosis. On the other hand, they often have respiratory dysfunction, resulting in high mortality from respiratory failure. Therefore, we hypothesized that spinal abnormalities might affect respiratory dysfunction, and analyzed the correlation between spinal abnormalities (Cobb angles (CA) and spinal rotation scores (SRS)) and respiratory parameters (observed during tidal breathing at static supine posture) in 10 patients with SMIDS (M: F 2:8, age 29.0 +/- 7.3 years). The patients inability to make effort in spirometry prevented us from evaluating vital capacity and forced expiratory volume. We measured respiratory rate, tidal volume, and expiratory gas during tidal breathing for 10 minutes. There was no patient with the athethotic type of CP. CA and SRS were found to be correlated with each other (r = 0.81, p < 0.01). CA was inversely correlated with tidal volume (both Vt and Vt/Height;r = -0.69, p < 0.05). Both CA and SRS correlated with respiratory rate (r = 0.67 and 0.69, respectively). Moreover, the slope of the regression lines of the VO2-VCO2 plots (V-slope) was correlated with CA (r = 0.86, p < 0.01). Contrary to our expectation, none of the respiratory parameters showed significant correlations with BMI. Moreover, we found no relationship between the spinal deformity (CA or SRS) and BMI. These observations suggest that the spinal abnormalities affect respiratory patterns in a restrictive manner and increase the respiratory change rate during tidal breathing in patients with SMIDS.     

Phrenic nerve involvement and respiratory muscle weakness in patients with Charcot‐Marie‐Tooth disease 1A

Diaphragm weakness in Charcot‐Marie‐Tooth disease 1A (CMT1A) is usually associated with severe disease manifestation. This study comprehensively investigated phrenic nerve conductivity, inspiratory and expiratory muscle function in ambulatory CMT1A patients. Nineteen adults with CMT1A (13 females, 47 ± 12 years) underwent spiromanometry, diaphragm ultrasound, and magnetic stimulation of the phrenic nerves and the lower thoracic nerve roots, with recording of diaphragm compound muscle action potentials (dCMAP, n = 15), transdiaphragmatic and gastric pressures (twPdi and twPgas, n = 12). Diaphragm motor evoked potentials (dMEP, n = 15) were recorded following cortical magnetic stimulation. Patients had not been selected for respiratory complaints. Disease severity was assessed using the CMT Neuropathy Scale version 2 (CMT‐NSv2). Healthy control subjects were matched for age, sex, and body mass index. The following parameters were significantly lower in CMT1A patients than in controls (all P < .05): forced vital capacity (91 ± 16 vs 110 ± 15% predicted), maximum inspiratory pressure (68 ± 22 vs 88 ± 29 cmH₂O), maximum expiratory pressure (91 ± 23 vs 123 ± 24 cmH₂O), and peak cough flow (377 ± 135 vs 492 ± 130 L/min). In CMT1A patients, dMEP and dCMAP were delayed. Patients vs controls showed lower diaphragm excursion (5 ± 2 vs 8 ± 2 cm), diaphragm thickening ratio (DTR, 1.9 [1.6‐2.2] vs 2.5 [2.1‐3.1]), and twPdi (8 ± 6 vs 19 ± 7 cmH₂O; all P < .05). DTR inversely correlated with the CMT‐NSv2 score (r = ?.59, P = .02). There was no group difference in twPgas following abdominal muscle stimulation. Ambulatory CMT1A patients may show phrenic nerve involvement and reduced respiratory muscle strength. Respiratory muscle weakness can be attributed to diaphragm dysfunction alone. It relates to neurological impairment and likely reflects a disease continuum.     

Cough following low thoracic hemisection in the cat

A function of the abdominal expiratory muscles is the generation of cough, a critical respiratory defense mechanism that is often disrupted following spinal cord injury. We assessed the effects of a lateral T9/10 hemisection on cough production at 4, 13 and 21 weeks post-injury in cats receiving extensive locomotor training. The magnitudes of esophageal pressure as well as of bilateral rectus abdominis electromyogram activity during cough were not significantly different from pre-injury values at all time points evaluated. The results show that despite considerable interruption of the descending pre-motor drive from the brainstem to the expiratory motoneuron pools, the cough motor system shows a significant function by 4 weeks following incomplete thoracic injury.     

Pulmonary function tests and diaphragmatic compound muscle action potential in patients with sporadic amyotrophic lateral sclerosis

Sathyaprabha TN, Pradhan C, Nalini A, Thennarasu K, Raju TR. Pulmonary function tests and diaphragmatic compound muscle action potential in patients with sporadic amyotrophic lateral sclerosis.
Acta Neurol Scand: 2010: 121: 400–405.
© 2010 The Authors Journal compilation © 2010 Blackwell Munksgaard. Background – Respiratory failure is the primary cause of death in patients with amyotrophic lateral sclerosis (ALS). Diaphragmatic compound muscle action potentials (DCMAP) are valid parameters to assess the respiratory muscle innervation. Aim – In this study we propose to establish evidence of pulmonary dysfunction in patients with ALS and its relation to DCMAP parameters among patients with sporadic ALS. Materials and methods – Twenty nine patients (M‐20, F‐9) diagnosed to have sporadic ALS by El. Escorial criteria, without symptoms of pulmonary dysfunction, and able to perform the PFT satisfactorily, were studied. Thirty controls (M‐20, F‐10) were selected from patient’s relatives. Forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), peak expiratory flow rate (PEFR) and maximum voluntary ventilation (MVV) were measured by spirometry. Maximum expiratory pressure (MEP) was measured by digital peak pressure monitor. Right phrenic nerve conductions (DCMAP) were performed and the latencies and amplitude of diaphragmatic com‐pound action potential (DCMAP) was recorded in controls and ALS patients. Results – The mean age of patients was 51.41 ± 10.72 years (37–82) and control was 53.57 ± 8.85 years (30–68). None of the patients had symptoms or clinical evidence of respiratory dysfunction. The FVC, FEV1, PEFR, MVV, MIP and MEP were significantly (P < 0.001) reduced in ALS. The mean DCMAP amplitude was reduced among patients (610 ± 506.231 μv) as compared to controls (1303.33 ± 584.56, P < 0.001) and mean latency was increased in patients (9.73 ± 2.57 ms) compared to controls (7.69 ± 0.87, P = 0.001). There was significant negative correlation between PFTs and latencies of DCMAP. Amplitude of DCMAP did not correlate with PFTs. Conclusion – There is significant negative correlation between DCMAP latencies and PFTs suggesting early loss of myelinated fibres and diaphragmatic dysfunction. DCMAP latencies may be a good indicator of early respiratory muscle involvement and also of disease progression in ALS.     

Oropharyngeal dysphagia may occur in late-onset Pompe disease,implicating bulbar muscle involvement

Late-onset Pompe disease (presenting after 12 months of age) often presents with limb-girdle and respiratory weakness, but oropharyngeal dysphagia has not been reported previously. A retrospective review of all late-onset Pompe disease patients evaluated in the neuromuscular clinic at Duke University Medical Center from 1999–2010 was performed. Twelve patients were identified and 3 had symptoms of oropharyngeal dysphagia. The medical record was reviewed, including the results of electromyography, videofluroscopic swallow examinations, and motor speech examination including instrumental assessment of lingual force with the Iowa Oral Performance Instrument. Oropharyngeal dysphagia was mild in two cases and severe in one. One of the two patients with mild severity demonstrated oral stage swallow signs; in the other, residual material was observed in the area of the cervical esophagus. In the patient with severe oropharyngeal dysphagia, both the oral and pharyngeal stages of swallowing were affected with penetration and aspiration documented. The degree of swallowing impairment appeared to correlate with overall physical strength and function. Oropharyngeal dysphagia may occur in patients with late-onset Pompe disease, implicating bulbar muscle involvement. Screening for symptoms of dysphagia may help reduce morbidity and mortality, while improving understanding of the late-onset Pompe disease phenotype. Further studies, including examination of the relationship between lingual weakness and oropharyngeal dysphagia, are warranted.     

Safety and effectiveness of resistance training in patients with late onset Pompe disease - a pilot study

Pompe disease is a progressive myopathy resulting from deficiency in lysosomal enzyme acid α-glucosidase (GAA), which leads to glycogen accumulation in lysosomes primarily in skeletal and cardiac muscle. Enzyme replacement therapy (ERT) with recombinant human (rh) GAA works well in alleviating the cardiomyopathy; however, many patients continue to have progressive muscle weakness. The purpose of this study was to evaluate the effectiveness of a respiratory training combined with 24-week supervised resistance training program on muscle strength (measured by Biodex)), and respiratory function including maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP) in subjects with late onset Pompe disease receiving ERT. Ten subjects participated in a 24-week resistance exercise program, three times per week, in addition to respiratory muscle exercise training six days per week. Overall, at the end of the resistance training program, as measured by Biodex dynamometry, the leg extensor strength improved by 10.5 ± 3.2Nm. (<p 0.01), leg flexors improved by 12.1 ± 4.1Nm (p < 0.01), the elbow flexors improved by 5.1 ± 2.3Nm (p = 0.03), and the elbow extensor strength improved by a mean of 4.5 ± 1.9Nm. (p = 0.02). MIP improved by 8.5 ± 3.7 cm H₂O (p = 0.03) and the MEP by 6.4 ± 4.4 (p = 0.16). The exercise training significantly improved the trajectories of MIP and 6 MWT outcomes but not FVC when compared with the natural history data available in 6 individuals. These pilot results indicate that resistance training combined with respiratory training and ERT had a positive effect on muscular strength, functional capacity, and respiratory function in patients with late-onset Pompe disease and might be considered as a potential adjunct therapy in this population.     

Respiratory muscle performance and the Perception of dyspnea in Parkinson's disease

BACKGROUND: Pulmonary and respiratory muscle function impairment are common in patients with Parkinson's disease (PD). However, dyspnea is not a frequent complaint among these patients, although it is well documented that the intensity of dyspnea is related to the activity and the strength of the respiratory muscles. PATIENTS AND METHODS: We studied pulmonary function, respiratory muscle strength and endurance and the perception of dyspnea (POD) in 20 patients with PD (stage II and III Hoehn and Yahr scale) before and after their first daily L-dopa dose. Respiratory muscle strength was assessed by measuring the maximal inspiratory and expiratory mouth pressures (PImax and PEmax), at residual volume (RV) and total lung capacity (TLC) respectively. The POD was measured while the subject breathed against progressive load and dyspnea was rated using a visual analog scale. RESULTS: Respiratory muscle strength and endurance were decreased and the POD was increased during the off medication period compared to normal subjects. There was a nonsignificant trend to an increase in Plmax, PEmax and endurance after L-dopa intake. The POD of PD patients decreased (p<0.05) following medication, although, it remained increased (p<0.01) as compared to the normal subjects. Even if patients had spirometry data showing a mild restrictive pattern, before medication, both forced vital capacity (FVC) and forced expiratory volume (FEV)1 remained almost identical after L-dopa intake. CONCLUSIONS: Patients with PD have higher POD, compared to normal subjects and this increased perception is attenuated when the patients are on dopaminergic medication. The change in the POD is not related to changes in respiratory muscle performance or pulmonary functions. A central effect or a correction of uncoordinated respiratory movements by L-dopa may contribute to the decrease in POD following L-dopa treatment.     

Randomized control trial of effects of a 10-week inspiratory muscle training program on measures of pulmonary function in persons with multiple sclerosis

Pulmonary impairments have long been recognized as major causes of morbidity and mortality in individuals with advanced multiple sclerosis (MS). This study was designed to determine if a 10-week home exercise inspiratory training program in community-dwelling persons with MS improves pulmonary muscle strength and endurance. Forty-six ambulatory individuals with clinically diagnosed MS [Expanded Disability Status Scale (EDSS) 2.0-6.5, intervention group mean = 3.96 and control group mean = 3.36] were randomly assigned to an intervention group that received 10 weeks of inspiratory muscle strength training (IMT) or a nontreatment control group. Twenty-one subjects in the control group and 20 subjects in the intervention group completed the study. The intervention group demonstrated significantly greater improvement than the control group in maximal inspiratory pressure (P < 0.001). When compared to the control group, no significant differences were noted for maximal expiratory pressure or maximal ventilation volume after training in the intervention group. Baseline and postexercise training comparison of secondary pulmonary expiratory outcomes were significant in the intervention group for forced expiratory volume at one second (FEV1) (P = 0.014), forced vital capacity (FVC) (P = 0.041), and midexpiratory flow rate(FEF(25-75%)) (P = 0.011). No significant changes were noted for the control group. Thus, IMT significantly increased inspiratory muscle strength and resulted in generalized improvements in expiratory pulmonary function in persons with MS who have minimal to moderate disability. Future studies are needed that focus on the long-term effects of IMT with increased resistance and the impact it has on increasing pulmonary function and functional performance.     

Pitfalls of intramuscular electromyographic recordings from the human costal diaphragm.

OBJECTIVE: Techniques for intramuscular recordings from the costal diaphragm have been described. This report describes procedures to assist with precise placement of these electrodes using ultrasound imaging and describes several sources of error that must be excluded when interpreting recordings made with intramuscular electrodes. METHODS: Fine-wire electrodes were inserted into the left costal diaphragm under the guidance of ultrasound imaging in 17 healthy volunteers. Various respiratory maneuvers were performed to confirm the accuracy of the electromyographic (EMG) recordings and the electrode placement was confirmed with intercostal nerve blocks in one subject. RESULTS: EMG recordings can be made from the costal diaphragm. However, despite precise electrode placement and use of intramuscular electrodes with small receptive areas, the EMG recording could be contaminated by cross-talk (discrete motor unit activity) from the adjacent internal intercostal muscle and from movement of the electrode relative to the muscle fibers during breathing. Furthermore, it is necessary to distinguish between expiratory intercostal muscle activity and units in the diaphragm that discharge tonically throughout expiration. CONCLUSIONS: While ultrasound guidance of intramuscular electrode insertion can assist with accurate electrode placement in the diaphragm, confirmation of the stability of the recording and absence of cross-talk is critical to avoid misinterpretation of diaphragm function.     

The nature of respiratory muscle weakness in patients with late-onset Pompe disease

Late-onset Pompe disease (LOPD) causes myopathy of skeletal and respiratory muscles, and phrenic nerve pathology putatively contributes to diaphragm weakness. The aim of this study was to investigate neural contributions to diaphragm dysfunction, usefulness of diaphragm ultrasound, and involvement of expiratory abdominal muscles in LOPD. Thirteen patients with LOPD (7 male, 51±17 years) and 13 age- and gender-matched controls underwent respiratory muscle strength testing, ultrasound evaluation of diaphragm excursion and thickness, cortical and cervical magnetic stimulation (MS) of the diaphragm with simultaneous recording of surface electromyogram and twitch transdiaphragmatic pressure (twPdi; n = 6), and MS of the abdominal muscles with recording of twitch gastric pressure (twPgas; n = 6). The following parameters were significantly reduced in LOPD patients versus controls: forced vital capacity (p<0.01), maximum inspiratory and expiratory pressure (both p<0.001), diaphragm excursion velocity (p<0.05), diaphragm thickening ratio (1.8 ± 0.4 vs. 2.6 ± 0.6, p<0.01), twPdi following cervical MS (12.0 ± 6.2 vs. 19.4 ± 4.8 cmH₂O, p<0.05), and twPgas following abdominal muscle stimulation (8.8 ± 8.1 vs. 34.6 ± 17.1 cmH₂O, p<0.01). Diaphragm motor evoked potentials and compound muscle action potentials showed no between-group differences. In conclusion, phrenic nerve involvement in LOPD could not be electrophysiologically confirmed. Ultrasound supports assessment of diaphragm function. Abdominal expiratory muscles are functionally involved in LOPD.     

Respiratory muscle strength training: treatment and response duration in a patient with early idiopathic Parkinson's disease

The outcome of a 20 week expiratory muscle strength training program (EMST) is documented in a patient with early idiopathic Parkinson's disease. A pressure threshold device was utilized and training occurred in the home setting. The training was intensive with a physiologically challenging load specific to the expiratory muscles, adjusted weekly based on the participant's performance. Results indicated that strength, as indexed by the generation of maximum expiratory pressure (MEP), increased by 50% in the first 4 weeks of training, consistent with the average strength increase obtained in previous research. Strength increases continued beyond the traditional 4 weeks of training with a final improvement in MEP of 158% from baseline over the 20 weeks. When the EMST was discontinued for a period of 4 weeks, the participant's MEP decreased by 16% from the 20 week endpoint measurement. The strength training pattern of the expiratory muscles observed in this study was similar to the pattern previously reported for limb muscles.     

Episodic hypoxia exacerbates respiratory muscle dysfunction in DMD(mdx) mice

Many patients with Duchenne muscular dystrophy (DMD) are eventually diagnosed with sleep-disordered breathing (SDB). SDB is associated with reduced ventilation, decreased arterial oxygen tension, and increased respiratory muscle recruitment during sleep, factors that could be especially detrimental to respiratory muscles in DMD. To assess whether SDB impacts dystrophin-deficient respiratory muscle function and fibrosis, diaphragm strength, and collagen content were evaluated in dystrophic mice (Dmd(mdx)) exposed to experimental SDB. Diurnal exposure to episodic hypoxia resulted in a 30% reduction in diaphragm strength without affecting collagen content. Episodic hypoxia secondary to SDB can exacerbate respiratory muscle dysfunction in DMD.     

Pulmonary function and electromyographic study of respiratory muscles in myotonic dystrophy

Ten adult myotonic dystrophy patients underwent measurements of lung function, maximal dynamic and static ventilatory efforts, and respiratory muscle electromyography (EMG). EMG studies were performed during spontaneous breathing or when subjects breathed through high inspiratory or expiratory resistive loads. Present results show that (1) a moderate restriction of lung volumes with hypoxemia plus normocapnia is often observed; (2) patients sustain dynamic ventilatory efforts more easily than static work; and (3) abnormalities in respiratory muscle EMG exist with spontaneous expiratory and inspiratory intercostal activities during quiet breathing and changes in muscular response to resistive loads. Inspiratory loading evokes contraction of expiratory muscles, with a marked decrease in inspiratory activities. Expiratory resistive loads prolong the diaphragmatic contraction throughout the expiratory time, and in some patients, relaxation of the diaphragm does not occur during the loaded run. These EMG data suggest that the reciprocal inhibition among respiratory neurons is enhanced in myotonic dystrophy and that myotonia also occurs in the diaphragm when loads oppose its relaxation.