Diaphragm Electromyographic Activity Research Articles

A novel method to quantify breathing effort from respiratory mechanics and esophageal pressure.

Breathing effort is important to quantify to understand mechanisms underlying central and obstructive sleep apnea, respiratory-related arousals, and the timing and effectiveness of invasive or non-invasive mechanically assisted ventilation. Current quantitative methods to evaluate breathing effort rely on inspiratory esophageal or epiglottic pressure swings or changes in diaphragm electromyographic (EMG) activity, where units are problematic to interpret and compare between individuals and to measured ventilation. This paper derives a novel method to quantify breathing effort in units directly comparable to measured ventilation by applying respiratory mechanics first principles to convert continuous transpulmonary pressure measurements into "attempted" airflow expected to have arisen without upper airway obstruction. The method was evaluated using data from eleven subjects undergoing overnight polysomnography, including 6 obese patients with severe obstructive sleep apnea (OSA), including one who also had frequent central events, and 5 healthy-weight controls. Classic respiratory mechanics showed excellent fits of airflow and volume to transpulmonary pressures during wake periods of stable unobstructed breathing (mean ± SD r² = 0.94 ± 0.03), with significantly higher respiratory system resistance in patients compared to healthy controls (11.2 ± 3.3 vs 7.1 ± 1.9 cmH2O·l-1·sec, P=0.032). Subsequent estimates of attempted airflow from transpulmonary pressure changes clearly highlighted periods of acute and prolonged upper airway obstruction, including within the first few breaths following sleep onset in patients. This novel technique provides unique quantitative insights into the complex and dynamically changing inter-relationships between breathing effort and achieved airflow during periods of obstructed breathing in sleep.

Optogenetic activation of the diaphragm

Impaired diaphragm activation is common in many neuromuscular diseases. We hypothesized that expressing photoreceptors in diaphragm myofibers would enable light stimulation to evoke functional diaphragm activity, similar to endogenous bursts. In a mouse model, adeno-associated virus (AAV) encoding channelrhodopsin-2 (AAV9-CAG-ChR2-mVenus, 6.12 × 1011 vg dose) was delivered to the diaphragm using a minimally invasive method of microinjection to the intrapleural space. At 8–18 weeks following AAV injection, mice were anesthetized and studied during spontaneous breathing. We first showed that diaphragm electromyographic (EMG) potentials could be evoked with brief presentations of light, using a 473 nm high intensity LED. Evoked potential amplitude increased with intensity or duration of the light pulse. We next showed that in a paralyzed diaphragm, trains of light pulses evoked diaphragm EMG activity which resembled endogenous bursting, and this was sufficient to generate respiratory airflow. Light-evoked diaphragm EMG bursts showed no diminution after up to one hour of stimulation. Histological evaluation confirmed transgene expression in diaphragm myofibers. We conclude that intrapleural delivery of AAV9 can drive expression of ChR2 in the diaphragm and subsequent photostimulation can evoke graded compound diaphragm EMG activity similar to endogenous inspiratory bursting.

Ampakines Stimulate Diaphragm Activity after Spinal Cord Injury.

Respiratory compromise after cervical spinal cord injury (SCI) is a leading cause of mortality and morbidity. Most SCIs are incomplete, and spinal respiratory motoneurons as well as proprio- and bulbospinal synaptic pathways provide a neurological substrate to enhance respiratory output. Ampakines are allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which are prevalent on respiratory neurons. We hypothesized that low dose ampakine treatment could safely and effectively increase diaphragm electromyography (EMG) activity that has been impaired as a result of acute- or sub-acute cervical SCI. Diaphragm EMG was recorded using chronic indwelling electrodes in unanesthetized, freely moving rats. A spinal hemi-lesion was induced at C2 (C2Hx), and rats were studied at 4 and 14 days post-injury during room air breathing and acute respiratory challenge accomplished by inspiring a 10% O2, 7% CO2 gas mixture. Once a stable baseline recording was established, one of two different ampakines (CX717 or CX1739, 5 mg/kg, intravenous) or a vehicle (2-hydroxypropyl-beta-cyclodextrin [HPCD]) was delivered. At 4 days post-injury, both ampakines increased diaphragm EMG output ipsilateral to C2Hx during both baseline breathing and acute respiratory challenge. Only CX1739 treatment also led to a sustained (15 min) increase in ipsilateral EMG output. At 14 days post-injury, both ampakines produced sustained increases in ipsilateral diaphragm EMG output and enabled increased output during the respiratory challenge. We conclude that low dose ampakine treatment can increase diaphragm EMG activity after cervical SCI, and therefore may provide a pharmacological strategy that could be useful in the context of respiratory rehabilitation.

Optogenetic diaphragm muscle activation in mice

Breathing impairments are the leading cause of morbidity and mortality across all forms of neuromuscular disease. When voluntarily diaphragm activation is insufficient, clinical options include mechanical ventilation or electrical stimulation via intramuscular wires. Here we tested the hypothesis that an optogenetic approach would enable light to serve as an adequate stimulus for inducing diaphragm contraction to sustain breathing during neuromuscular impairments. Wild type, C57/bl6 mice (n=10) received an intrapleural injection of an adeno-associated virus (AAV) construct containing the transgene for the light activated ion channel channelrhodopsin-2 (34 µl, AAV9-ACAGW-ChR2-mVenus, titer: 1.8x1013 vg/ml). After allowing 8-10 weeks for transgene expression, electromyography (EMG) and pneumotachography were measured during spontaneous breathing under isoflurane anesthesia. To test optogenetic activation, a high-power, 472 nm, micro-LED was directed at the inferior diaphragm surface. Stimulus pulse durations (PD) ranging from 0.1-1.0 ms and interpulse intervals (IPI) of 0.1, 0.5, 1.0, and 5.0 ms were tested. Directing light at the diaphragm evoked clearly discernable EMG activity in 10 of 10 animals treated with the AAV9 vector. The 5 ms IPI induced the largest EMG activation, occurring at a level comparable to endogenous diaphragm bursts. Stimulation with a 0.1 ms PD / 0.1 ms IPI, and 1 ms PD / 5 ms IPI both were able to generate robust increases in respiratory airflow. Optogenetic stimulation was repeated following an acute unilateral phrenic nerve section which abolished ipsilateral diaphragm EMG. The contralateral diaphragm inspiratory EMG signal was then used to “trigger” the light stimulation of the paralyzed hemi-diaphragm. This procedure enabled a robust, bilateral diaphragm activation in all mice that received the unilateral phrenicotomy (n= 5). Histology confirmed robust expression of mVenus in diaphragm myofibers in mice treated with the vector. Directing light at the diaphragm of non-AAV treated control mice caused no discernible impact on diaphragm EMG activity (n=2). We conclude that intrapleural AAV9-ACAGW-ChR2-mVenus injection effectively drives transgene expression in the diaphragm, and this approach can be used to enable robust optogenetic activation of this critically important respiratory muscle. To our knowledge, this is the first demonstration of light activation of the diaphragm, and this success opens up new directions for therapeutic targeting of diaphragm paralysis and respiratory insufficiency.

Surface respiratory electromyography and dyspnea in acute heart failure patients.

Dyspnea is the most common symptom among hospitalized patients with heart failure (HF) but besides dyspnea questionnaires (which reflect the subjective patient sensation and are not fully validated in HF) there are no measurable physiological variables providing objective assessment of dyspnea in a setting of acute HF patients. Studies performed in respiratory patients suggest that the measurement of electromyographic (EMG) activity of the respiratory muscles with surface electrodes correlates well with dyspnea. Our aim was to test the hypothesis that respiratory muscles EMG activity is a potential marker of dyspnea severity in acute HF patients. Prospective and descriptive pilot study carried out in 25 adult patients admitted for acute HF. Measurements were carried out with a cardio-respiratory portable polygraph including EMG surface electrodes for measuring the activity of main (diaphragm) and accessory (scalene and pectoralis minor) respiratory muscles. Dyspnea sensation was assessed by means of the Likert 5 questionnaire. Data were recorded during 3 min of spontaneous breathing and after breathing at maximum effort for several cycles for normalizing data. An index to quantify the activity of each respiratory muscle was computed. This assessment was carried out within the first 24 h of admission, and at day 2 and 5. Dyspnea score decreased along the three measured days. Diaphragm and scalene EMG index showed a positive and significant direct relationship with dyspnea score (p<0.001 and p = 0.003 respectively) whereas pectoralis minor muscle did not. In our pilot study, diaphragm and scalene EMG activity was associated with increasing severity of dyspnea. Surface respiratory EMG could be a useful objective tool to improve assessment of dyspnea in acute HF patients.

Discharge properties of human diaphragm motor units with ageing.

Ageing is associated with changes in the respiratory system including in the lungs, rib cage and muscles. Neural drive to the diaphragm, the principal inspiratory muscle, has been reported to increase during quiet breathing with ageing. We demonstrated that low-threshold motor units of the human diaphragm recruited during quiet breathing have similar discharge frequencies across age groups and shorter discharge times in older age. With ageing, motor unit action potential area increased. We propose that there are minimal functionally significant changes in the discharge properties of diaphragm motor units with ageing despite remodelling of the motor unit in the periphery. There are changes in the skeletal, pulmonary and respiratory neuromuscular systems with healthy ageing. During eupnoea, one study has shown relatively higher crural diaphragm electromyographic activity (EMG) in healthy older adults (>51years) than in younger adults, but these measures may be affected by the normalisation process used. A more direct method to assess neural drive involves the measurement of discharge properties of motor units. Here, to assess age-related changes in neural drive to the diaphragm during eupnoea, EMG was recorded from the costal diaphragm using a monopolar needle electrode in participants from three age groups (n≥7 each): older (65-80years); middle-aged (43-55years) and young (23-26years). In each group, 154, 174 and 110 single motor units were discriminated, respectively. A mixed-effects linear model showed no significant differences between age groups for onset (group mean range 9.5-10.2Hz), peak (14.1-15.0Hz) or offset (7.8-8.5Hz) discharge frequencies during eupnoea. The motor unit recruitment was delayed in the older group (by ∼15% of inspiratory time; p=0.02 cf. middle-aged group) and had an earlier offset time (by ∼15% of inspiratory time; p=0.04 cf. young group). However, the onset of multiunit activity was similar across groups, consistent with no global increase in neural drive to the diaphragm with ageing. The area of diaphragm motor unit potentials was ∼40% larger in the middle-aged and older groups (P<0.02), which indicates axonal sprouting and re-innervation of muscle fibres associated with ageing, even in middle-aged participants.

Awake teeth grinding in participants with canine guidance or group function: Effect on diaphragm EMG activity, heart rate, and oxygen saturation

ABSTRACT Objective: To compare the effect of canine guidance or group function on diaphragm activity, heart rate, and oxygen saturation during awake teeth grinding at different body positions. Methods: Fifty healthy participants, 25 with canine guidance and 25 with group function, were included. Bilateral electromyographic (EMG) recordings of the diaphragm (DIA) during awake teeth grinding were performed in standing, seated upright, and right lateral decubitus positions. Simultaneously, heart rate and oxygen saturation were measured. Results: EMG activity of the DIA muscle was similar in the working side and non-working side between participants with canine guidance and group function in the different body positions studied. The heart rate and oxygen saturation showed no significant differences between the two groups. Conclusion: EMG activity of the DIA muscle, the heart rate, and oxygen saturation during teeth grinding are not significantly influenced by the type of laterotrusive occlusal scheme.

Respiratory EMG Activity between Subjects with Costo-diaphragmatic, Upper Costal or Mixed Breathing Type

This study aimed to compare the electromyographic (EMG) activity among participants with costo-diaphragmatic, mixed or upper costal breathing type. Forty male were classified according to their breathing type into three groups: costo-diaphragmatic, upper costal and mixed breathing type. EMG activity of diaphragm (DIA), external intercostal (EIC), sternocleidomastoid (SCM) and latissimus dorsi (LAT) muscles was recorded in the dorsal, left lateral and ventral decubitus positions, during the following tasks: 1) quiet breathing, 2) speaking, 3) swallowing, and 4) sustained maximal inspiration. DIA activity was higher in upper costal than in costo-diaphragmatic breathing in all tasks and body positions; was higher in mixed than in costo-diaphragmatic breathing in all tasks in the dorsal and ventral decubitus positions and only in task 4 in the left lateral decubitus position; was similar between upper costal and mixed breathing in all tasks and body positions. EIC activity was significantly higher in mixed than costodiaphragmatic breathing in all tasks in the dorsal decubitus position and only in task 4 in the left lateral decubitus position. SCM activity did not show significant differences. LAT activity was only higher in upper costal than costodiaphragmatic breathing in task 4 in the dorsal decubitus position, in tasks 1, 2 and 4 in the left lateral decubitus position, and in tasks 2, 3 and 4 in the ventral decubitus position. EMG activity of the DIA was the only muscle that allows to differentiate between upper costal or mixed breathing than costo-diaphragmatic in all tasks in the dorsal and ventral decubitus positions.

Effect of breathing type on electromyographic activity of respiratory muscles during tooth clenching at different decubitus positions

Objective: To compare the effect of breathing type on electromyographic (EMG) activity of respiratory muscles during tooth clenching at different decubitus positions.Methods: Forty young men participants were included, 11 with upper costal, 9 with mixed, and 20 with costo-diaphragmatic breathing type. EMG recordings of diaphragm (DIA), external intercostal (EIC), sternocleidomastoid (SCM), and latissimus dorsi (LAT) muscles during tooth clenching in the intercuspal position were performed in dorsal, left lateral, and ventral decubitus positions.Results: DIA EMG activity was higher in subjects with upper costal or mixed than with costodiaphragmatic breathing type (p = 0.006; 0.021, respectively), whereas it was similar between upper costal and mixed breathing types. EIC, SCM, and LAT activity was similar among breathing types.Conclusion: Higher DIA activity would be a risk factor to exceed the adaptive capability of healthy subjects with upper costal or mixed breathing type.

Compensatory effects following unilateral diaphragm paralysis

Injury to nerves innervating respiratory muscles such as the diaphragm muscle results in significant respiratory compromise. Electromyography (EMG) and transdiaphragmatic pressure (Pdi) measurements reflect diaphragm activation and force generation. Immediately after unilateral diaphragm denervation (DNV), ventilatory behaviors can be accomplished without impairment, but Pdi generated during higher force non-ventilatory behaviors is significantly decreased. We hypothesized that 1) the initial reduction in Pdi during higher force behaviors after DNV is ameliorated after 14 days, and 2) changes in Pdi over time after DNV are associated with concordant changes in contralateral diaphragm EMG activity and ventilatory parameters. In adult male rats, the reduced Pdi during occlusion (∼40% immediately after DNV) was ameliorated to ∼20% reduction after 14 days. Contralateral diaphragm EMG activity did not significantly change immediately or 14days after DNV compared to the pre-injury baseline for any motor behavior. Taken together, these results suggest that over time after DNV compensatory changes in inspiratory related muscle activation may partially restore the ability to generate Pdi during higher force behaviors.

Contribution of 5-HT2A receptors on diaphragmatic recovery after chronic cervical spinal cord injury

Unilateral C2 spinal cord hemisection (C2Hx) interrupts bulbospinal respiratory pathways innervating ipsilateral phrenic motoneurons, resulting in cessation of ipsilateral diaphragm motor output. Plasticity within the spinal neural circuitry controlling the diaphragm can induce partial recovery of phrenic bursting which correlates with the time-dependent return of spinal serotonin (5-HT) immunoreactivity in the vicinity of phrenic motoneurons. The 5-HT2A receptor subtype is present on phrenic motoneurons and its expression is up-regulated after cervical spinal cord injury; however the functional role of these receptors following injury has not been clearly defined. The present study evaluated the functional role of 5-HT2A receptors by testing the hypothesis that pharmacologic blockade would attenuate diaphragm activity in rats with chronic cervical spinal cord injury. Bilateral diaphragm electromyography (EMG) was performed in vagal-intact and spontaneously breathing rats before and after intravenous administration of the 5-HT2A receptor antagonist Ketanserin (1mg/kg). Intravenous ketanserin significantly attenuated ipsilateral diaphragm EMG activity in C2Hx animals but had no impact on diaphragm output in uninjured animals. We conclude that 5-HT2A receptor activation contributes to the recovery of ipsilateral phrenic motor output after chronic cervical spinal cord injury.

Diaphragm electromyographic activity following unilateral midcervical contusion injury in rats.

The present study shows that unilateral contusion injury at C4 results in substantial loss of phrenic motoneurons but increased diaphragm muscle activity across a range of ventilatory and higher force, nonventilatory behaviors. Measures of neural drive indicate increased descending input to phrenic motoneurons that was more pronounced during higher force, nonventilatory behaviors. These findings reveal novel, complex adaptations in neuromotor control following injury, suggestive of increased recruitment of more fatigable, high-threshold motor units.

BDNF effects on functional recovery across motor behaviors after cervical spinal cord injury.

This study demonstrates that after unilateral C2 spinal cord hemisection (SH), there are differences in the spontaneous recovery of diaphragm (DIAm) electromyographic activity during ventilatory compared with more forceful, nonventilatory motor behaviors. Furthermore, we show that intrathecal delivery of brain-derived neurotrophic factor (BDNF) at the level of the phrenic motor neuron pool enhances recovery of ipsilateral DIAm activity following SH, exerting main effects on recovery of ventilatory but not higher force, nonventilatory behaviors.

The interaction between breathing and swallowing in amyotrophic lateral sclerosis.

The aim of the study is to determine the association between respiratoryswallow patterns in amyotrophic lateral sclerosis (ALS) patients. Furthermore, it aims to clarify the role of the dysphagia limit in defining the relationship between swallowing disorders and respiratory disorders. Functional rating scales were used to describe swallowing and respiratory function. Swallowing was observed using the dysphagia limit. Dysphagia limit is the volume at which a second or more swallows are required to swallow the whole bolus. Laryngeal and chest movement sensors, pulmonary function tests, submental, and diaphragm electromyography activity were used to evaluate the relationship between swallowing and respiratory phase. Of the 27 patients included in the study, 14 were dysphagic and 13 were non-dysphagic. Tests showed normal respiratory function in 11 of the non-dysphagic patients and 3 of the dysphagic patients. There was a high correlation between the dysphagia limit and Amyotrophic Lateral Sclerosis Functional Rating Scale swallowing parameters. Non-dysphagic patients were able to swallow during inspiration but only six patients in the dysphagic group were able to swallow during inspiration. The occurrence of dysphagia in ALS is related to piecemeal deglutition and respiration consistency during swallowing. Detecting the timingof disturbances in the relationship betweenswallowing and respirationmay be a way of identifying dysphagia. Dysphagia limit may be a useful, complementary test for assessing swallowing disturbances in amyotrophic lateral sclerosis.

Utility of a Novel Biofeedback Device for Within-Breath Modulation of Heart Rate in Rats: A Quantitative Comparison of Vagus Nerve vs. Right Atrial Pacing.

In an emerging bioelectronics era, there is a clinical need for physiological devices incorporating biofeedback that permits natural and demand-dependent control in real time. Here, we describe a novel device termed a central pattern generator (CPG) that uses cutting edge analog circuitry producing temporally controlled, electrical stimulus outputs based on the real time integration of physiological feedback. Motivated by the fact that respiratory sinus arrhythmia (RSA), which is the cyclical changes in heart rate every breath, is an essential component of heart rate variability (HRV) (an indicator of cardiac health), we have explored the versatility and efficiency of the CPG for producing respiratory modulation of heart rate in anesthetized, spontaneously breathing rats. Diaphragmatic electromyographic activity was used as the input to the device and its output connected to either the right cervical vagus nerve or the right atrium for pacing heart rate. We found that the CPG could induce respiratory related heart rate modulation that closely mimicked RSA. Whether connected to the vagus nerve or right atrium, the versatility of the device was demonstrated by permitting: (i) heart rate modulation in any phase of the respiratory cycle, (ii) control of the magnitude of heart rate modulation, and (iii) instant adaptation to changes in respiratory frequency. Vagal nerve pacing was only possible following transection of the nerve limiting its effective use chronically. Pacing via the right atrium permitted better flexibility and control of heart rate above its intrinsic level. This investigation now lays the foundation for future studies using this biofeedback technology permitting closer analysis of both the function and dysfunction of RSA.

Respiratory Muscle Activity During Simultaneous Stationary Cycling and Inspiratory Muscle Training.

Inspiratory muscle training (IMT) strengthens the muscles of respiration, improves breathing efficiency, and increases fitness. The IMT is generally performed independently of aerobic exercise; however, it is not clear whether there is added benefit of performing the IMT while simultaneously performing aerobic exercise in terms of activating and strengthening inspiratory muscles. The purpose of our study was to determine the effect of IMT on respiratory muscle electromyography (EMG) activity during stationary cycling in the upright and drops postures as compared with that when the IMT was performed alone. Diaphragm and sternocleidomastoid EMG activity was measured under different resting and cycling postures, with and without the use of the IMT at 40% maximal inspiratory pressure (n = 10; mean age 37). Cycling in an upright posture while simultaneously performing the IMT resulted in a significantly greater diaphragm EMG activity than while performing the IMT at rest in upright or drops postures (p ≤ 0.05). Cycling in drops postures while performing the IMT had a significantly greater diaphragm EMG activity than when performing the IMT at rest in either upright or drops postures (p ≤ 0.05). Sternocleidomastoid muscle activity increased with both cycling and IMT, although posture had little effect. These results support our hypothesis in that the IMT while cycling increases respiratory EMG activity to a significantly greater extent than when performing the IMT solely at rest, suggesting that the combination of IMT and cycling may provide an additive training effect.

Diaphragmatic Reinnervation in Ventilator-Dependent Patients with Cervical Spinal Cord Injury and Concomitant Phrenic Nerve Lesions Using Simultaneous Nerve Transfers and Implantable Neurostimulators

Patients who are ventilator dependent as a result of combined cervical spinal cord injury and phrenic nerve lesions are generally considered to be unsuitable candidates for diaphragmatic pacing due to loss of phrenic nerve integrity and denervation of the diaphragm. There is limited data regarding efficacy of simultaneous nerve transfers and diaphragmatic pacemakers in the treatment of this patient population. A retrospective review was conducted of 14 consecutive patients with combined lesions of the cervical spinal cord and phrenic nerves, and with complete ventilator dependence, who were treated with simultaneous microsurgical nerve transfer and implantation of diaphragmatic pacemakers. Parameters of interest included time to recovery of diaphragm electromyographic activity, average time pacing without the ventilator, and percent reduction in ventilator dependence. Recovery of diaphragm electromyographic activity was demonstrated in 13 of 14 (93%) patients. Eight of these 13 (62%) patients achieved sustainable periods (> 1 h/d) of ventilator weaning (mean = 10 h/d [n = 8]). Two patients recovered voluntary control of diaphragmatic activity and regained the capacity for spontaneous respiration. The one patient who did not exhibit diaphragmatic reinnervation remains within 12 months of initial treatment. Surgical intervention resulted in a 25% reduction (p < 0.05) in ventilator dependency. We have demonstrated that simultaneous nerve transfers and pacemaker implantation can result in reinnervation of the diaphragm and lead to successful ventilator weaning. Our favorable outcomes support consideration of this surgical method for appropriate patients who would otherwise have no alternative therapy to achieve sustained periods of ventilator independence.

Effects of Tracheal Distension on Upper Airway Reflex Responsiveness in Cat

A tracheostomy cuff is used in patients to ensure no material enters the lower airway. To clinically determine whether a patient is ready for cuff‐deflation airway protective reflexes are tested, often while the cuff is actively distending the trachea. We hypothesized that tracheal distension alters normal sensory feedback and decreases airway protective reflex efficacy. In adult cats, a balloon was inflated at the 4th cartilaginous ring of the trachea, and electromyography (EMG) activities from the diaphragm, internal oblique, crycoarytenoid and mylohyoid muscles were recorded. Cough was stimulated by mechanical stimulation of the intrathoracic trachea. Swallow was elicited by a water bolus to the oropharynx. The presence of the deflated balloon in the trachea greatly promoted the number of swallows (105±60%). Moderate tracheal distention decreased diaphragm (~20%) and internal oblique (~30%) EMG activity compared to baseline during cough, and partially recovered 10 minutes after distension was removed. Cough number decreased by 52±13% during tracheal distension. No significant effect on crycoarytenoid or mylohyoid (~4%) EMG activity during swallow was observed. However, large tracheal distensions induced depression in swallow EMG magnitude and number. These results indicate that tracheal distension in the physiological range alters sensory feedback that is important in the production of cough but not swallow, although the production of swallow can be negatively affected by distensions that increase the risk of mechanical or ischemic damage to tracheal tissue. Therefore, clinical assessments of cough when a tracheal cuff is or recently has been present may not represent a metric of normal function. Supported by HL 103425.

Assessment of Diaphragm EMG Activity Recovery Following Upper Cervical Spinal Cord Injury

Motor units are normally recruited in an orderly manner in order to accomplish ventilatory behaviors. The duration of non‐stationarity in electromyographic (EMG) bursts provides an estimate of the period of motor unit recruitment. Motor unit recruitment also reflects central drive, which can be estimated by the root‐mean‐squared (RMS) EMG value 75 ms after the EMG burst onset (RMS75). Following unilateral diaphragm muscle (DIAm) paralysis induced by upper cervical spinal cord hemisection at C2 (SH), there is gradual spontaneous recovery of ipsilateral EMG activity. Increased activity of the contralateral (uninjured) DIAm is sufficient to maintain ventilation following SH. We hypothesized that changes in central drive can be estimated by the period of non‐stationarity and RMS75 from the contralateral DIAm EMG following ipsilateral paralysis and spontaneous recovery of DIAm EMG activity. We found that the duration of non‐stationarity increased to a greater extent in rats that did not recover ipsilateral EMG activity by 14 days post‐SH (D14) compared to those that did. In addition, we found that RMS75 values following SH were reduced in rats displaying recovery of ipsilateral DIAm EMG activity compared to rats that did not. Collectively, these results suggest that the duration of non‐stationarity and RMS75 can be used to evaluate recovery of ipsilateral DIAm function following spinal cord injury.

Effect of Body Position on Respiratory Muscle Activity in Subjects with Upper Costal or Costo-diaphragmatic Breathing Type

Effect of body position on electromyographic (EMG) activity has been studied in the cranio-cervical-mandibular muscles, but its effect on the activity of respiratory muscles in subjects with different breathing types has not yet been elucidated. This study included two groups of twenty male subjects each, one with upper costal and the other with costo-diaphragmatic breathing type. EMG activity was recorded using bipolar surface electrode technique. Electrodes were placed on the sternocleidomastoid (SCM), diaphragm (DIA), and external intercostal (EIC) and Latissimus dorsi (LAT) muscles. EMG activity was recorded in standing and lateral decubitus positions, during the following tasks: [1] Normal quiet breathing; [2] speaking the word “Mississippi”; [3] forced deep breathing. EMG activity of DIA and EIC muscles was higher in the standing than in the lateral decubitus position during all tasks in both breathing groups (p<0.05), excepting DIA activity during task 2 in the costo-diaphragmatic group. EMG activity of LAT muscle was higher in the standing than in the lateral decubitus position during task 3 in both breathing groups (p<0.05). EMG activity of DIA activity was higher in subjects with upper costal than in subjects with costo-diaphragmatic breathing type in the standing position during all tasks and also in the lateral decubitus position during tasks 1 and 2 (p<0.05). EMG activity of ECM, EIC and LAT muscles was not significantly different between both breathing types in the studied body positions. The higher EMG activity observed in the standing than in the lateral decubitus positions in both breathing groups, suggests differences in the respiratory effort depending on the body position. The higher EMG activity observed in DIA muscle of subjects with upper costal than costo-diaphragmatic breathing types, suggests differences in the respiratory effort depending on the breathing type.