Diaphragmatic Compound Muscle Action Potentials Recorded From Over the Sternum and Lateral Chest Wall: a Comparative Study

Objectives:To report normative data for diaphragmatic compound muscle action potentials (DCMAPs) recorded from over the sternum and lateral chest wall (LCW).Method:The phrenic nerve of seventy-three healthy subjects was bilaterally stimulated at the posterior border of the sternocleidomastoid muscle. DCMAPs from over the sternum and LCW were recorded (inspiration/expiration). Results: Normative values of sternal and LCW DCMAPs were presented. Significant differences were found between sternal and LCW potentials in the mean latency, amplitude, and area (p<0.001). The duration did not differ between the two sites. Differences were found between inspiration and expiration, right and left sides, and men and women. Regression analysis showed a relation between latency of sternal and LCW potentials and age. Latency (LCW potentials) and amplitude and area (sternal/LCW potentials) were related to gender. Amplitude (LCW potentials/inspiration) and area (sternal potentials/inspiration) were related to chest circumference (p=0.023 and 0.013 respectively). Area (sternal potentials/expiration) was related to the BMI (p=0.019). Conclusions: Our normative values for sternal and LCW DCMAPs are provided. Notable differences in the DCMAPs parameters were detected between the two recording sites, inspiration and expiration, right and left, and men and women. Significance:The technique of phrenic nerve should be standardized.

May the Force and Mass Be With You—Evidence-Based Contribution of Mechano-Biological Descriptors of Resistance Exercise

Skeletal muscle is one of the most important tissues of the human body. It comprises up to 40% of the body mass and is crucial to survival. Hence, the maintenance of skeletal muscle mass and strength is pivotal. It is well-established that resistance exercise provides a potent anabolic stimulus to increase muscle mass and strength in men and women of all ages. Resistance exercise consists of mechano-biological descriptors, such as load, muscle action, number of repetitions, repetition duration, number of sets, rest interval between sets, frequency, volitional muscular failure, and range of motion, which can be manipulated. Herein, we discuss the evidence-based contribution of these mechano-biological descriptors to muscle mass and strength.

The Promising Application of a New Ulnar Nerve Compound Muscle Action Potential Measurement Montage in Amyotrophic Lateral Sclerosis

Objective Detecting peripheral nerve damage by electrophysiology examination accurately and sensitively is important for the follow-up evaluation of amyotrophic lateral sclerosis(ALS). In this study, we applied a new proximal E2 electrode in the ulnar motor nerve conduction study with E1 on abductor digiti minimi(ADM), and investigated its effect on the compound muscle action potential(CMAP) of the ulnar nerve. Methods We included 64 ALS patients and 64 age- and sex- matched controls. Patients characteristics were collected for phenotype, symptom duration and site of onset. The revised ALS Functional Rating Scale(ALSFRS-R) was evaluated at the time of administration to assess the severity of ALS. The ulnar nerve CMAP was recorded using an E1 electrode on the muscle belly and an E2 electrode on distal tendon(traditional montage, CMAP-dE2) and proximal tendon(new montage, CMAP-pE2) respectively. Results The waveform of CMAP-pE2 was steadier presenting a uniform unilobed pattern. In the controls, there were no significant differences between the amplitudes of CMAP-dE2 and CMAP-pE2(p=0.96). In ALS patients, the amplitude of CMAP-pE2 was significantly lower than that of CMAP-dE2(p<0.01), especially for patients with ADM spontaneous activity and muscular atrophy. Using the new method, the damaged axons were more likely to be stratified into more severe decreased levels. Furthermore, the decline of CMAP-pE2 was significantly correlated with ALSFRS-R(p<0.01). Conclusions The new electrode configuration in the ulnar nerve conduction test could reflect the degree of axonal injury much more sensitively after the presence of ulnar nerve degeneration and was more suitable for the evaluation of disease progression.

Effects of muscle shortening on single-fiber, motor unit, and compound muscle action potentials

Even under isometric conditions, muscle contractions are associated with some degree of fiber shortening. The effects of muscle shortening on extracellular electromyographic potentials have not been characterized in detail. Moreover, the anatomical, biophysical, and detection factors influencing the muscle-shortening effects have been neither identified nor understood completely. Herein, we investigated the effects of muscle shortening on the amplitude and duration characteristics of single-fiber, motor unit, and compound muscle action potentials. We found that, at the single-fiber level, two main factors influenced the muscle-shortening effects: (1) the electrode position and distance relative to the myotendinous zone and (2) the electrode distance to the maxima of the dipole field arising from the stationary dipole created at the fiber-tendon junction. Besides, at the motor unit and muscle level, two additional factors were involved: (3) the overlapping between the propagating component of some fibers with the non-propagating component of other fibers and (4) the spatial spreading of the fiber-tendon junctions. The muscle-shortening effects depend critically on the electrode longitudinal distance to the myotendinous zone. When the electrode was placed far from the myotendinous zone, muscle shortening resulted in an enlargement and narrowing of the final (negative) phase of the potential, and this enlargement became less pronounced as the electrode approached the fiber endings. For electrode locations close to the myotendinous zone, muscle shortening caused a depression of both the main (positive) and final (negative) phases of the potential. Beyond the myotendinous zone, muscle shortening led to a decrease of the final (positive) phase. The present results provide reference information that will help to identify changes in MUPs and M waves due to muscle shortening, and thus to differentiate these changes from those caused by muscle fatigue. Graphical abstract

Myasthenia gravis and coronavirus disease 2019: A report from Iran

Background: Coronavirus disease 2019 (COVID-19) is spreading rapidly and has affected millions of people worldwide. Comorbid diseases have complicated the course of infection and increased mortality. Myasthenia gravis (MG) affects the neuromuscular junctions (NMJs) and can compromise respiratory muscle action, leading to worse clinical outcomes in individuals infected with the COVID-19 theoretically. In this study, the aim is to assess the pattern of COVID-19 infection in patients with MG based on several factors. Methods: This was a prospective cohort study following 150 patients with MG over a six-month period. The patients were monitored for the development of signs and symptoms of the COVID-19 infection. Results: Comparison of the patients infected with COVID-19 with MG and those not infected was performed independently based on age, duration since MG diagnosis, status of thymectomy, and current clinical status of MG disease. Data analysis did not reveal increased susceptibility or increased severity of COVID-19 illness based the criteria assessed. Conclusion: COVID-19 related deaths and susceptibility were not related to age, thymectomy status, and disease duration in patients with MG.

A novel mutation of the COLQ gene causes congenital myasthenic syndromes: A case report

Congenital myasthenic syndromes (CMS) are a group of heterogeneous disorders of the neuromuscular junctions, characterised by fluctuating and fatigable weakness with an early onset. Endplate acetylcholinesterase deficiency (EAD) due to mutations in COLQ is a subtype of CMS whose key clue for diagnosis is repetitive compound muscle action potential (R-CMAP) under nerve conduction studies. In light of the significant overlap of clinical symptoms, misdiagnosis is common for CMS, causing delayed or incorrect treatments. Here, we report a case of CMS due to a novel mutation in COLQ with a typical R-CMAP and discuss the significance of R-CMAP for diagnosis.