Scalene muscle activity during progressive inspiratory loading under pressure support ventilation in normal humans

Intermittent neck flexion induces greater sternocleidomastoid deoxygenation than inspiratory threshold loading

PURPOSE

To compare deoxygenation of the sternocleidomastoid, scalenes, and diaphragm/intercostals (Dia/IC) during submaximal intermittent neck flexion (INF) versus submaximal inspiratory threshold loading (ITL) in healthy adults.

METHODS

Fourteen participants performed a randomized, cross-over, repeated measures design. After evaluation of maximal inspiratory pressures (MIP) and maximum voluntary contraction (MVC) for isometric neck flexion, participants were randomly assigned to submaximal ITL or INF until task failure. At least 2 days later, they performed the submaximal exercises in the opposite order. ITL or INF targeted 50 ± 5% of the MIP or MVC, respectively, until task failure. Near-infrared spectroscopy (NIRS) was applied to evaluate changes of deoxy-hemoglobin (ΔHHb), oxy-hemoglobin (ΔO2Hb), total hemoglobin (ΔtHb), and tissue saturation of oxygen (StO2) of the sternocleidomastoid, scalenes, and Dia/IC. Breathlessness and perceived exertion were evaluated using Borg scales.

RESULTS

Initially during INF, sternocleidomastoid HHb slope was greatest compared to the scalenes and Dia/IC. At isotime (6.5-7 min), ΔtHb (a marker of blood volume) and ΔO2Hb of the sternocleidomastoid were higher during INF than ITL. Sternocleidomastoid HHb, O2Hb, and tHb during INF also increased at quartile and task failure timepoints. In contrast, scalene ΔO2Hb was higher during ITL than INF at isotime. Further, Dia/IC O2Hb and tHb increased during ITL at the third quartile and at task failure. Borg scores were lower at task failure during INF compared to ITL.

CONCLUSION

Intermittent INF induces significant metabolic activity of the sternocleidomastoid and a lower perception of effort, which may provide an alternative inspiratory muscle training approach for mechanically ventilated patients.

Dyspnoea in acutely ill mechanically ventilated adult patients: an ERS/ESICM statement

This statement outlines a review of the literature and current practice concerning the prevalence, clinical significance, diagnosis and management of dyspnoea in critically ill, mechanically ventilated adult patients. It covers the definition, pathophysiology, epidemiology, short- and middle-term impact, detection and quantification, and prevention and treatment of dyspnoea. It represents a collaboration of the European Respiratory Society and the European Society of Intensive Care Medicine. Dyspnoea ranks among the most distressing experiences that human beings can endure. Approximately 40% of patients undergoing invasive mechanical ventilation in the intensive care unit (ICU) report dyspnoea, with an average intensity of 45 mm on a visual analogue scale from 0 to 100 mm. Although it shares many similarities with pain, dyspnoea can be far worse than pain in that it summons a primal fear response. As such, it merits universal and specific consideration. Dyspnoea must be identified, prevented and relieved in every patient. In the ICU, mechanically ventilated patients are at high risk of experiencing breathing difficulties because of their physiological status and, in some instances, because of mechanical ventilation itself. At the same time, mechanically ventilated patients have barriers to signalling their distress. Addressing this major clinical challenge mandates teaching and training, and involves ICU caregivers and patients. This is even more important because, as opposed to pain which has become a universal healthcare concern, very little attention has been paid to the identification and management of respiratory suffering in mechanically ventilated ICU patients.

Dyspnoea in acutely ill mechanically ventilated adult patients: an ERS/ESICM statement

This statement outlines a review of the literature and current practice concerning the prevalence, clinical significance, diagnosis and management of dyspnoea in critically ill, mechanically ventilated adult patients. It covers the definition, pathophysiology, epidemiology, short- and middle-term impact, detection and quantification, and prevention and treatment of dyspnoea. It represents a collaboration of the European Respiratory Society (ERS) and the European Society of Intensive Care Medicine (ESICM). Dyspnoea ranks among the most distressing experiences that human beings can endure. Approximately 40% of patients undergoing invasive mechanical ventilation in the intensive care unit (ICU) report dyspnoea, with an average intensity of 45 mm on a visual analogue scale from 0 to 100 mm. Although it shares many similarities with pain, dyspnoea can be far worse than pain in that it summons a primal fear response. As such, it merits universal and specific consideration. Dyspnoea must be identified, prevented and relieved in every patient. In the ICU, mechanically ventilated patients are at high risk of experiencing breathing difficulties because of their physiological status and, in some instances, because of mechanical ventilation itself. At the same time, mechanically ventilated patients have barriers to signalling their distress. Addressing this major clinical challenge mandates teaching and training, and involves ICU caregivers and patients. This is even more important because, as opposed to pain which has become a universal healthcare concern, very little attention has been paid to the identification and management of respiratory suffering in mechanically ventilated ICU patients.

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.

Interventions Relieving Dyspnea in Intubated Patients Show Responsiveness of the Mechanical Ventilation-Respiratory Distress Observation Scale

Rationale: Breathing difficulties are highly stressful. In critically ill patients, they are associated with an increased risk of posttraumatic manifestations. Dyspnea, the corresponding symptom, cannot be directly assessed in noncommunicative patients. This difficulty can be circumvented using observation scales such as the mechanical ventilation-respiratory distress observation scale (MV-RDOS). Objective: To investigate the performance and responsiveness of the MV-RDOS to infer dyspnea in noncommunicative intubated patients. Methods: Communicative and noncommunicative patients exhibiting breathing difficulties under mechanical ventilation were prospectively included and assessed using a dyspnea visual analog scale, MV-RDOS, EMG activity of alae nasi and parasternal intercostals, and EEG signatures of respiratory-related cortical activation (preinspiratory potentials). Inspiratory-muscle EMG and preinspiratory cortical activities are surrogates of dyspnea. Assessments were conducted at baseline, after adjustment of ventilator settings, and, in some cases, after morphine administration. Measurements and Main Results: Fifty patients (age, 67 [(interquartile interval [IQR]), 61-76] yr; Simplified Acute Physiology Score II, 52 [IQR, 35-62]) were included, 25 of whom were noncommunicative. Relief occurred in 25 (50%) patients after ventilator adjustments and in 21 additional patients after morphine administration. In noncommunicative patients, MV-RDOS score decreased from 5.5 (IQR, 4.2-6.6) at baseline to 4.2 (IQR, 2.1-4.7; P < 0.001) after ventilator adjustments and 2.5 (IQR, 2.1-4.2; P = 0.024) after morphine administration. MV-RDOS and alae nasi/parasternal EMG activities were positively correlated (ρ = 0.41 and 0.37, respectively). MV-RDOS scores were higher in patients with EEG preinspiratory potentials (4.9 [IQR, 4.2-6.3] vs. 4.0 [IQR, 2.1-4.9]; P = 0.002). Conclusions: The MV-RDOS seems able to detect and monitor respiratory symptoms reasonably well in noncommunicative intubated patients. Clinical trial registered with www.clinicaltrials.gov (NCT02801838).

Surface electromyographic (sEMG) activity of the suprahyoid and sternocleidomastoid muscles in pitch and loudness control

Purpose: This study set out to determine the contributions of the suprahyoid and sternocleidomastoid (SCM) muscles in changing pitch and loudness during phonation among vocally healthy populations. Method: Thirty-nine participants were first recruited, and twenty-nine of them who passed the screening test (Voice Handicap Index [VHI]-10 score ≤11, auditory-perceptual voice rating score ≤2) were finally selected (mean age = 28.2 years). All participants were measured for their surface electromyographic (sEMG) activity collected from the bilateral suprahyoid and SCM muscles when producing the vowel /a/, /i/, and /u/ in natural (baseline) and at different pitch (+3, +6, -3, -6 semitones) and loudness (+5, +10, -5 dB) levels. Linear mixed-effects models were performed to determine the influencing factors on the root-mean-square percentage of maximal voluntary contraction (RMS %MVC) value of the sEMG signals. Results: Compared with the baseline, a significant decrease of RMS %MVC was found in the suprahyoid muscles during overall phonations of lower pitches (-3 and -6 semitones) and loudness (-5 dB). However, no significant change was detected when producing speech at higher pitch (+3 and +6 semitones) and loudness (+5 and +10 dB) levels. Among the three vowels, /i/ demonstrated significantly higher RMS %MVC than those of /a/ and /u/. The SCM muscles, however, did not show any significant change in the RMS %MVC values among different vowels in relation to the pitch and loudness changes. When the muscles were compared across the two sides, significantly higher RMS %MVC was found in the right side of the suprahyoid (in pitch and loudness control) and SCM (in pitch control) when compared to the left side. Conclusions: The suprahyoid muscle activities were significantly decreased when producing lower pitches and intensities compared to the natural baselines. The production of sustained /i/ required significantly more suprahyoid muscle activities than those of /a/ and /u/. The SCM muscles did not show much sEMG activity in any of the pitch and loudness levels, which could be used potentially as the calibration or normalization of peri-laryngeal sEMG measurement. The findings also showed a tendency for bilateral asymmetry in the use of suprahyoid and SCM muscles.

The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise

NEW FINDINGS

What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

ABSTRACT

We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P < 0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P = 0.151) but was significantly lower during medium (25%, P = 0.02) and high (36%, P < 0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P < 0.05). The EMGdi was significantly lower in medium and high PAV conditions (P = 0.035 and P < 0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r = 0.61, P = 0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

Dyspnea and the electromyographic activity of inspiratory muscles during weaning from mechanical ventilation

Rationale

Dyspnea, a key symptom of acute respiratory failure, is not among the criteria for spontaneous breathing trial (SBT) failure. Here, we sought (1) to determine whether dyspnea is a reliable failure criterion for SBT failure; (2) to quantify the relationship between dyspnea and the respective electromyographic activity of the diaphragm (EMGdi), the parasternal (EMGpa) and the Alae nasi (EMGan).

Methods

Mechanically ventilated patients undergoing an SBT were included. Dyspnea intensity was measured by the Dyspnea-Visual Analogic Scale (Dyspnea-VAS) at the initiation and end of the SBT. During the 30-min SBT or until SBT failure, the EMGdi was continuously measured with a multi-electrode nasogastric catheter and the EMGan and EMGpa with surface electrodes.

Results

Thirty-one patients were included, SAPS 2 (median [interquartile range]) 53 (37‒74), mechanically ventilated for 6 (3‒10) days. Seventeen patients (45%) failed the SBT. The increase in Dyspnea-VAS along the SBT was higher in patients who failed (6 [4‒8] cm) than in those who passed (0 [0‒1] cm, p = 0.01). The area under the receiver operating characteristics curve for Dyspnea-VAS was 0.909 (0.786–1.032). The increase in Dyspnea-VAS was significantly correlated to the increase in EMGan (Rho = 0.42 [0.04‒0.70], p < 0.05), but not to the increase in EMGpa (Rho = − 0.121 [− 0.495 to − 0.290], p = 0.555) and EMGdi (Rho = − 0.26 [− 0.68 to 0.28], p = 0.289).

Conclusion

Dyspnea is a reliable criterion of SBT failure, suggesting that Dyspnea-VAS could be used as a monitoring tool of the SBT. In addition, dyspnea seems to be more closely related to the electromyographic activity of the Alae nasi than of the diaphragm.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01025-5.

Accessory and Expiratory Muscles Activation During Spontaneous Breathing Trial: A Physiological Study by Surface Electromyography

Background

The physiological and prognostical significance of accessory and expiratory muscles activation is unknown during a spontaneous breathing trial (SBT). We hypothesized that, in patients experiencing weaning failure, accessory and expiratory muscles are activated to cope with an increased respiratory workload.

Purpose

To describe accessory and expiratory muscle activation non-invasively by surface electromyography (sEMG) during an SBT and to assess differences in electrical activity (EA) of the inspiratory and expiratory muscles in successful vs. failing weaning patients.

Methods

Intubated patients on mechanical ventilation for more than 48 h undergoing an SBT were enrolled in a medical and surgical third-level ICU of the University Teaching Hospital. Baseline characteristics and physiological variables were recorded in a crossover physiologic prospective clinical study.

Results

Of 37 critically ill mechanically ventilated patients, 29 (78%) patients successfully passed the SBT. Rapid shallow breathing index (RSBI) was higher in patients who failed SBT compared with the successfully weaned patients at baseline and over time (group-by-time interaction p < 0.001). EA of both the diaphragm (EAdi_surf) and of accessory muscles (ACC_surf) was higher in failure patients compared with success (group-by-time interaction p = 0.0174 and p < 0.001, respectively). EA of expiratory muscles (ESP_surf) during SBT increased more in failure than in weaned patients (group-by-time interaction p < 0.0001).

Conclusion

Non-invasive respiratory muscle monitoring by sEMG was feasible during SBT. Respiratory muscles EA increased during SBT, regardless of SBT outcome, and patients who failed the SBT had a higher increase of all the inspiratory muscles EA compared with the patients who passed the SBT. Recruitment of expiratory muscles—as quantified by sEMG—is associated with SBT failure.

Effect of Test Interface on Respiratory Muscle Activity and Pulmonary Function During Respiratory Testing in Healthy Adults

Purpose

The mouthpiece is the standard interface for spirometry tests. Although the use of a mouthpiece can be challenging for patients with orofacial weakness, maintaining a proper seal with a facemask can be an issue for healthy individuals during forceful efforts. We compared respiratory muscle activity and tests using a mouthpiece and facemask in healthy adults to investigate whether they can be used interchangeably.

Methods

In this observational study, subjects (n=12) completed forced vital capacity, maximal respiratory pressure, and peak cough flow with a mouthpiece and facemask. Root mean square values of the genioglossus, diaphragm, scalene, and sternocleidomastoid were compared between conditions.

Results

When switching from a mouthpiece to a facemask, significantly higher values were seen for peak cough flow (average bias= -54.36 L/min, p<0.05) and the difference seen with MEP and MIP were clinically significant (average bias: MEP=27.33, MIP=-5.2). Additionally, submental activity was significantly greater when MIP was conducted with a mouthpiece. No significant differences were seen in respiratory muscle activity during resting breathing or spirometry.

Conclusion

There are clinically significant differences with cough and MEP tests and neck muscles are activated differently based on interface. Considering the small sample size, our findings suggest a facemask may be used to complete some PFTs.

The physiology and pathophysiology of exercise hyperpnea

In health, the near-eucapnic, highly efficient hyperpnea during mild-to-moderate intensity exercise is driven by three obligatory contributions, namely, feedforward central command from supra-medullary locomotor centers, feedback from limb muscle afferents, and respiratory CO₂ exchange (V̇CO₂). Inhibiting each of these stimuli during exercise elicits a reduction in hyperpnea even in the continuing presence of the other major stimuli. However, the relative contribution of each stimulus to the hyperpnea remains unknown as does the means by which V̇CO2 is sensed. Mediation of the hyperventilatory response to exercise in health is attributed to the multiple feedback and feedforward stimuli resulting from muscle fatigue. In patients with COPD, diaphragm EMG amplitude and its relation to ventilatory output are used to decipher mechanisms underlying the patients' abnormal ventilatory responses, dynamic lung hyperinflation and dyspnea during exercise. Key contributions to these exercise-limiting responses across the spectrum of COPD severity include high dead space ventilation, an excessive neural drive to breathe and highly fatigable limb muscles, together with mechanical constraints on ventilation. Major controversies concerning control of exercise hyperpnea are discussed along with the need for innovative research to uncover the link of metabolism to breathing in health and disease.

Surface EMG cross talk quantified at the motor unit population level for muscles of the hand, thigh, and calf

Cross talk is an important source of error in interpreting surface electromyography (EMG) signals. Here, we aimed at characterizing cross talk for three groups of synergistic muscles by the identification of individual motor unit action potentials. Moreover, we explored whether spatial filtering (single and double differential) of the EMG signals influences the level of cross talk. Three experiments were conducted. Participants (total 25) performed isometric contractions at 10% of the maximal voluntary contraction (MVC) with digit muscles and knee extensors and at 30% MVC with plantar flexors. High-density surface EMG signals were recorded and decomposed into motor unit spike trains. For each muscle, we quantified the cross talk induced to neighboring muscles and the level of contamination by the nearby muscle activity. We also estimated the influence of cross talk on the EMG power spectrum and intermuscular correlation. Most motor units (80%) generated significant cross-talk signals to neighboring muscle EMG in monopolar recording mode, but this proportion decreased with spatial filtering (50% and 42% for single and double differential, respectively). Cross talk induced overestimations of intermuscular correlation and has a small effect on the EMG power spectrum, which indicates that cross talk is not reduced with high-pass temporal filtering. Conversely, spatial filtering reduced the cross-talk magnitude and the overestimations of intermuscular correlation, confirming to be an effective and simple technique to reduce cross talk. This paper presents a new method for the identification and quantification of cross talk at the motor unit level and clarifies the influence of cross talk on EMG interpretation for muscles with different anatomy.NEW & NOTEWORTHY We proposed a new method for the identification and quantification of cross talk at the motor unit level. We show that surface EMG cross talk can lead to physiological misinterpretations of EMG signals such as overestimations in the muscle activity and intermuscular correlation. Cross talk had little influence on the EMG power spectrum, which indicates that conventional temporal filtering cannot minimize cross talk. Spatial filter (single and double differential) effectively reduces but not abolish cross talk.

Dyspnea and respiratory muscles ultrasound to predict extubation failure

This study investigated dyspnea intensity and respiratory muscles ultrasound early after extubation to predict extubation failure.It was conducted prospectively in two intensive care units in France and Canada. Patients intubated for at least 48 h were studied within 2 h after an extubation following a successful spontaneous breathing trial. Dyspnea was evaluated by the Dyspnea-Visual Analog Scale from 0 to 10 cm (VAS) and the Intensive Care - Respiratory Distress Observational Scale (range 0-10). The ultrasound thickening fraction of the parasternal intercostal and the diaphragm were measured; limb muscle strength was evaluated using the Medical Research Council score (MRC) (range 0-60).Extubation failure occurred in 21 of the 122 enrolled patients (17%). Dyspnea-VAS and Intensive Care - Respiratory Distress Observational scale were higher in patients with extubation failure versus success: 7 (5-9) cm versus 3 (1-5) cm respectively (p<0.001) and 4.4 (2.5-6.5) versus 2.4 (2.1-2.8) respectively (p<0.001). The ratio of intercostal muscle to diaphragm thickening fraction was significantly higher and MRC was lower in patients with failure (0.9 [0.4-3.0] versus 0.3 [0.2-0.5], p<0.001, and 45 [36-50] versus 52 [44-60], p=0.012). The thickening fraction of the intercostal and its ratio to diaphragm thickening showed the highest area under the receiver operating characteristic curves for an early prediction of extubation failure (0.81). Areas under the receiver operating characteristic curves of Dyspnea-VAS and Intensive Care - Respiratory Distress Observational scale reached 0.78 and 0.74 respectively.Respiratory muscle ultrasound and dyspnea measured within 2 h after extubation predict subsequent extubation failure.

Are there differences in muscular activation to maintain balance between individuals with chronic obstructive pulmonary disease and controls?

BACKGROUND

The mechanisms underlying impaired balance in chronic obstructive pulmonary disease (COPD) are poorly understood, which makes it difficult to choose the best therapeutic approaches. Therefore, this study aimed to investigate patterns of muscular activation to maintain balance and its determinants in this population.

METHODS

Thirty-three subjects with COPD and 33 controls were assessed by a force platform in four tasks: standing with eyes opened (FHEO) and closed (FHEC); standing on unstable surface (SUS) and one-legged stance (OLS). Electromyographic activity of lower limb, trunk and neck muscles was concomitantly recorded. To asses functional balance, Brief-balance evaluation systems and timed up & go (TUG) tests were applied. Lung function, exercise capacity and muscle force were also assessed.

RESULTS

Subjects with COPD presented worse balance and higher scalene activation than controls in OLS (mean difference 23.0 [95%CI 1.7-44.3] _%Δ μV_RMS; P = 0.034), besides presenting also higher activation of gluteus medius during FHEC task (mean difference 1.5 [95%CI 0.2-2.8] _%Δ μV_RMS; P = 0.023) and taking longer to complete the TUG (mean difference 0.6 [95%CI 0.1-1.2] seconds; P = 0.042). Exercise capacity and peripheral muscle force were determinants of functional balance (r² = 0.505), whereas age (OR = 1.24; 95%CI 1.02-1.52) and total lung capacity (OR = 2.42; 95%CI 1.05-5.56) were determinants of static balance.

CONCLUSION

Individuals with COPD have worse static and functional balance in comparison with controls, besides presenting higher activation of scalene and gluteus medius during static balance tasks. Exercise capacity and peripheral muscle force emerged as determinants of functional balance, whereas age and lung hyperinflation contributed to poor static balance.

Scalene and sternocleidomastoid activation during normoxic and hypoxic incremental inspiratory loading

The purpose of this study was to examine scalene (SA) and sternocleidomastoid (SM) activation during normoxic (norm-ITL; FIO2  = 21%) and hypoxic (hyp-ITL; FIO2  = 15%) incremental inspiratory threshold loading (ITL). Thirteen healthy participants (33 ± 4 years, 9 female) performed two ITL tests breathing randomly assigned gas mixtures through an inspiratory loading device where the load was increased every two minutes until task failure. SA and SM root mean square (RMS) electromyography (EMG) were calculated and expressed as a percentage of maximum (RMS%max ) to reflect muscle activation intensity. Myoelectric manifestations of fatigue were characterized as decreased SA or SM EMG median frequency during maximum inspiratory pressure maneuvers before and after ITL. Dyspnea was recorded at baseline and task failure. Ventilatory parameters and mouth pressure (Pm) were recorded throughout the ITL. SA,RMS%max and SM,RMS%max increased in association with ITL load (p ≤ .01 for both). SA,RMS%max was similar between norm-ITL and hyp-ITL (p = .17), whereas SM,RMS%max was greater during the latter (p = .001). Neither SA nor SM had a decrease in EMG median frequency after ITL (p = .75 and 0.69 respectively). Pm increased in association with ITL load (p < .001) and tended to be higher during hyp-ITL compared to norm-ITL (p = .05). Dyspnea was similar during both conditions (p > .05). There was a trend for higher tidal volumes during hyp-ITL compared to norm-ITL (p = .10). Minute ventilation was similar between both conditions (p = .23). RMS,%max of the SA and SM increased linearly with increasing ITL. The presence of hypoxia only increased SM activation. Neither SA nor SM presented myoelectric manifestations of fatigue during both conditions.

Recruitment pattern of the diaphragm and extradiaphragmatic inspiratory muscles in response to different levels of pressure support

Background

Inappropriate ventilator assist plays an important role in the development of diaphragm dysfunction. Ventilator under-assist may lead to muscle injury, while over-assist may result in muscle atrophy. This provides a good rationale to monitor respiratory drive in ventilated patients. Respiratory drive can be monitored by a nasogastric catheter, either with esophageal balloon to determine muscular pressure (gold standard) or with electrodes to measure electrical activity of the diaphragm. A disadvantage is that both techniques are invasive. Therefore, it is interesting to investigate the role of surrogate markers for respiratory dive, such as extradiaphragmatic inspiratory muscle activity. The aim of the current study was to investigate the effect of different inspiratory support levels on the recruitment pattern of extradiaphragmatic inspiratory muscles with respect to the diaphragm and to evaluate agreement between activity of extradiaphragmatic inspiratory muscles and the diaphragm.

Methods

Activity from the alae nasi, genioglossus, scalene, sternocleidomastoid and parasternal intercostals was recorded using surface electrodes. Electrical activity of the diaphragm was measured using a multi-electrode nasogastric catheter. Pressure support (PS) levels were reduced from 15 to 3 cmH₂O every 5 min with steps of 3 cmH₂O. The magnitude and timing of respiratory muscle activity were assessed.

Results

We included 17 ventilated patients. Diaphragm and extradiaphragmatic inspiratory muscle activity increased in response to lower PS levels (36 ± 6% increase for the diaphragm, 30 ± 6% parasternal intercostals, 41 ± 6% scalene, 40 ± 8% sternocleidomastoid, 43 ± 6% alae nasi and 30 ± 6% genioglossus). Changes in diaphragm activity correlated best with changes in alae nasi activity (r² = 0.49; P < 0.001), while there was no correlation between diaphragm and sternocleidomastoid activity. The agreement between diaphragm and extradiaphragmatic inspiratory muscle activity was low due to a high individual variability. Onset of alae nasi activity preceded the onset of all other muscles.

Conclusions

Extradiaphragmatic inspiratory muscle activity increases in response to lower inspiratory support levels. However, there is a poor correlation and agreement with the change in diaphragm activity, limiting the use of surface electromyography (EMG) recordings of extradiaphragmatic inspiratory muscles as a surrogate for electrical activity of the diaphragm.

Abnormal Activity of Neck Inspiratory Muscles during Sleep as a Prognostic Indicator in Chronic Obstructive Pulmonary Disease

Rationale: In patients with chronic obstructive pulmonary disease (COPD), increased activity of neck inspiratory muscles has been reported as a compensatory response to hyperinflation-related diaphragmatic dysfunction. The persistence of this activity during sleep could attenuate sleep-related hypoventilation and also negatively impact sleep and clinical outcomes.Objectives: To assess the persistence of neck-muscle activity during sleep in patients with COPD recovering from severe exacerbations (i.e., requiring hospitalization) and its impact on sleep quality and recurrence of exacerbations.Methods: Video polysomnography with neck-muscle EMG was performed in patients with COPD who were recovering from a severe exacerbation. The follow-up period lasted 6 months to record the next severe exacerbation.Measurements and Main Results: Twenty-nine patients were included in the study (median [25th-75th percentile] age, 71 [64-72] yr; 55% male; body mass index, 24 [21-29]; FEV₁% predicted, 37 [29-45]; and BODE [body mass index, airflow obstruction, dyspnea, and exercise] index, 6 [5-7]). Twenty-six of these patients exhibited sleep-related neck-muscle activity, which was intermittent (limited to stage 3 sleep) in 17 and permanent throughout sleep in 9. α-Delta EEG activity during stage 3 sleep was observed in 87% of the patients. Compared with patients with no or intermittent neck-muscle activity, those with permanent neck-muscle activity showed more disrupted sleep, had experienced more exacerbations in the previous year, and suffered their next severe exacerbation earlier.Conclusions: Sleep-related neck-muscle activity occurs frequently in patients with COPD who are recovering from a severe exacerbation and seems to negatively affect sleep quality and prognosis; therefore, identification of this activity might improve COPD management after a severe exacerbation.

Surface respiratory electromyography and dyspnea in acute heart failure patients

Introduction and Objectives: 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. Methods: 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. Results: 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. Conclusion: 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.

The validity of surface EMG of extra-diaphragmatic muscles in assessing respiratory responses during mechanical ventilation: A systematic review

PURPOSE

Evidence supporting the utilization of surface EMG (sEMG) of extra-diaphragmatic muscles for monitoring of mechanical ventilation (MV) assistance is unclear. The purpose of this review was to assess the quality of literature available on using extra-diaphragmatic sEMG as an assessment technique of respiratory responses during MV.

METHODS

Studies using sEMG of extra-diaphragmatic respiratory muscles during MV were selected by two independent researchers after performing a database search of PubMed, CINAHL, GOOGLE SCHOLAR. Exclusion criteria were studies of patients with neuromuscular disorders, receiving neuromuscular blocking agents, receiving non-invasive MV, using needle EMG, and studies written in languages other than English. Quality of identified studies was assessed with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2). This study is registered with PROSPERO, number (CRD42018081341).

RESULTS

596 references were identified. Of the identified studies, 7 studies were included in the review. Findings demonstrate that sEMG of extra-diaphragmatic muscle activity is a valid and applicable tool to evaluate mechanical loading/unloading of respiratory muscles and respiratory drive or sensation. However, the quality of literature supporting sEMG as monitoring tool of respiratory responses were characterized by a high and unclear risk of bias.

CONCLUSIONS

Although it appears to be a valid and applicable tool, there is a scarcity of literature that directly demonstrates the diagnostic accuracy of sEMG of extra-diaphragmatic muscles in monitoring respiratory mechanics and respiratory drive or sensation during MV assistance across wide populations and conditions.

Muscles of Breathing: Development, Function, and Patterns of Activation

This review is a comprehensive description of all muscles that assist lung inflation or deflation in any way. The developmental origin, anatomical orientation, mechanical action, innervation, and pattern of activation are described for each respiratory muscle fulfilling this broad definition. In addition, the circumstances in which each muscle is called upon to assist ventilation are discussed. The number of "respiratory" muscles is large, and the coordination of respiratory muscles with "nonrespiratory" muscles and in nonrespiratory activities is complex-commensurate with the diversity of activities that humans pursue, including sleep (8.27). The capacity for speech and adoption of the bipedal posture in human evolution has resulted in patterns of respiratory muscle activation that differ significantly from most other animals. A disproportionate number of respiratory muscles affect the nose, mouth, pharynx, and larynx, reflecting the vital importance of coordinated muscle activity to control upper airway patency during both wakefulness and sleep. The upright posture has freed the hands from locomotor functions, but the evolutionary history and ontogeny of forelimb muscles pervades the patterns of activation and the forces generated by these muscles during breathing. The distinction between respiratory and nonrespiratory muscles is artificial, as many "nonrespiratory" muscles can augment breathing under conditions of high ventilator demand. Understanding the ontogeny, innervation, activation patterns, and functions of respiratory muscles is clinically useful, particularly in sleep medicine. Detailed explorations of how the nervous system controls the multiple muscles required for successful completion of respiratory behaviors will continue to be a fruitful area of investigation. © 2019 American Physiological Society. Compr Physiol 9:1025-1080, 2019.

Surface electromyography in inspiratory muscles in adults and elderly individuals: A systematic review

INTRODUCTION

Electromyography (EMG) helps to evaluate disorders and pulmonary behavior, as impairments in respiratory muscle function are associated with the development of diseases. There is a wide range of methods and protocols used to record and analyze EMG obtained from respiratory muscles, demonstrating a lack of standardization.

OBJECTIVE

To identify the most common procedures used to record surface EMG (sEMG) of inspiratory muscles in adults and elderly individuals through a systematic review (primary), and to evaluate the quality of the report presented by the studies (secondary).

METHOD

Studies published from January 1995 until June 2018 were searched for in the Web of Science, PubMed, LILACS, EBSCO and Embase databases. Only studies evaluating sEMG of inspiratory muscles were included.

RESULTS

The electronic search retrieved a total of 6697 titles and 92 of them were included. A great variability on the methods applied to both recording and processing/analyzing data was found. Therefore, the synthesis of practical/clinical evidence to support immediate recommendations was impaired. In general, the descriptions presented by the studies are poor.

CONCLUSION

The most common procedures used for sEMG were identified. Methodological studies with objective comparisons were fundamental for improving standardization, given the impossibility of recommendations from this review.

Surface electromyographic evaluation of the neuromuscular activation of the inspiratory muscles during progressively increased inspiratory flow under inspiratory-resistive loading

This study aimed to evaluate neuromuscular activation in the scalene and sternocleidomastoid muscles using surface electromyography (EMG) during progressively increased inspiratory flow, produced by increasing the respiratory rate under inspiratory-resistive loading using a mask ventilator. Moreover, we attempted to identify the EMG inflection point (EMG^IP) on the graph, at which the root mean square (RMS) of the EMG signal values of the inspiratory muscles against the inspiratory flow velocity acceleration abruptly increases, similarly to the EMG anaerobic threshold (EMG^AT) reported during incremental-resistive loading in other skeletal muscles. We measured neuromuscular activation of healthy male subjects and found that the inspiratory flow velocity increased by approximately 1.6-fold. We successfully observed an increase in RMS that corresponded to inspiratory flow acceleration with ρ ≥ 0.7 (Spearman's rank correlation) in 17 of 27 subjects who completed the experimental protocol. To identify EMG^IP, we analyzed the fitting to either a straight or non-straight line related to the increasing inspiratory flow and RMS using piecewise linear spline functions. As a result, EMG^IP was identified in the scalene and sternocleidomastoid muscles of 17 subjects. We believe that the identification of EMG^IP in this study infers the existence of EMG^AT in inspiratory muscles. Application of surface EMG, followed by identification of EMG^IP, for evaluating the neuromuscular activation of respiratory muscles may be allowed to estimate the signs of the respiratory failure, including labored respiration, objectively and non-invasively accompanied using accessory muscles in clinical respiratory care.

Surface electromyography (sEMG) of extradiaphragm respiratory muscles in healthy subjects: A systematic review

The aim of this systematic review was to examine procedures used and outcome measures reported from surface EMG (sEMG) of extradiaphragm inspiratory muscles in healthy people. Relevant articles were searched using the concepts "electromyography (EMG)", "respiratory muscles (sternocleidomastoid [SM], scalene, intercostal [IC] and parasternal)" and "healthy" in the electronic databases: MEDLINE, PubMed, EMBASE, Cochrane CENTRAL and Database of Systematic Reviews, CINAHL, SPORTDiscus, LILACS, and PEDro. Twenty-five papers were included and quality assessment was performed using an adapted Downs and Black checklist. Twenty-eight percent of included papers were classified as moderate quality and the rest were low quality. The SM was the muscle most often investigated. Description of EMG techniques were often incomplete for features such as the procedure before electrode placement, description of the surface electrodes, the EMG detection mode and amplification. Of note, descriptions of the IC muscle electrode positioning varied widely. Comparison of outcomes among studies was challenging because of the very diverse EMG outcomes reported. There are many controversies regarding methods and technique used to assess sEMG of extradiaphragm inspiratory muscles. Therefore, studies with higher methodological quality utilizing standardized EMG procedures including electrode positioning will enable accurate and reliable comparison among studies of the extradiaphragm inspiratory muscles.

Neck inspiratory muscle activation patterns during well-controlled inspiration

PURPOSE

Surprisingly, the activation characteristics of the neck inspiratory muscles as a function of key inspiratory mechanical parameters have yet to be demonstrated experimentally under well-controlled conditions. This study aimed to elucidate the muscle activation patterns of the neck inspiratory muscles by strictly controlling flow rate and lung volume.

METHODS

Thirteen healthy subjects matched their inspiratory flow rate at approximately 20-100% of peak flow rate (PFR) as steady as possible during inspiration. Amplitude of surface electromyogram (EMG) of the sternocleidomastoid (SCM) and scalene were calculated for every increase in %PFR over a duration corresponding to an increase in lung volume by 10% of forced vital capacity (FVC), as well as for every 5% increment of FVC over a point corresponding to an increase in flow rate by 20%PFR to determine the %PFR-EMG and %FVC-EMG relations, respectively.

RESULTS

Regression analyses showed that EMGs of the neck inspiratory muscles exponentially increased with increase in %PFR and their associated variables which reflect recruitment onset when increasing flow rate increased with increasing %FVC. In %FVC-EMG relation, a linear regression analysis showed positive slope at all %PFR and positive y-intercept at 80% PFR.

CONCLUSIONS

The main new finding is that the neck inspiratory muscle activities increase with flow rate as well as lung volume. The positive y-intercept of the %FVC-EMG relation at higher %PFR indicates that the neck inspiratory muscles are always activated even when lung volume level is low, implying that SCM is not necessarily an "accessory" muscle as described in previous observations.

Cortical drive to breathe in amyotrophic lateral sclerosis: a dyspnoea-worsening defence?

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing diaphragm weakness that can be partially compensated by inspiratory neck muscle recruitment. This disappears during sleep, which is compatible with a cortical contribution to the drive to breathe. We hypothesised that ALS patients with respiratory failure exhibit respiratory-related cortical activity, relieved by noninvasive ventilation (NIV) and related to dyspnoea.

We studied 14 ALS patients with respiratory failure. Electroencephalographic recordings (EEGs) and electromyographic recordings of inspiratory neck muscles were performed during spontaneous breathing and NIV. Dyspnoea was evaluated using the Multidimensional Dyspnea Profile.

Eight patients exhibited slow EEG negativities preceding inspiration (pre-inspiratory potentials) during spontaneous breathing. Pre-inspiratory potentials were attenuated during NIV (p=0.04). Patients without pre-inspiratory potentials presented more advanced forms of ALS and more severe respiratory impairment, but less severe dyspnoea. Patients with pre-inspiratory potentials had stronger inspiratory neck muscle activation and more severe dyspnoea during spontaneous breathing.

ALS-related diaphragm weakness can engage cortical resources to augment the neural drive to breathe. This might reflect a compensatory mechanism, with the intensity of dyspnoea a negative consequence. Disease progression and the corresponding neural loss could abolish this phenomenon. A putative cognitive cost should be investigated.

The effects of breathing exercise types on respiratory muscle activity and body function in patients with mild chronic obstructive pulmonary disease

[Purpose] Fragmentary studies on characteristics of respiratory muscles are being done to increase respiratory capacity by classifying exercises into voluntary respiratory exercise which relieves symptoms and prevents COPD and exercise using breathing exercise equipment. But this study found changes on respiratory pattern through changes on the activity pattern of agonist and synergist respiratory muscles and studied what effect they can have on body function improvement. [Subjects and Methods] Fifteen subjects in experimental group I that respiratory exercise of diaphragm and 15 subjects in experimental group II that feedback respiratory exercise were randomly selected among COPD patients to find the effective intervention method for COPD patients. And intervention program was conducted for 5 weeks, three times a week, once a day and 30 minutes a session. They were measured with BODE index using respiratory muscle activity, pulmonary function, the six-minute walking test, dyspnea criteria and BMI Then the results obtained were compared and analyzed. [Results] There was a significant difference in sternocleidomastoid muscle and scalene muscle and in 6-minute walk and BODE index for body function. Thus the group performing feedback respiratory had more effective results for mild COPD patients. [Conclusion] Therefore, the improvement was significant regarding the activity of respiratory muscles synergists when breathing before doing breathing exercise. Although, it is valuable to reduce too much mobilization of respiratory muscles synergists through the proper intervention it is necessary to study body function regarding improvement of respiratory function for patients with COPD.

Increased diaphragmatic contribution to inspiratory effort during neurally adjusted ventilatory assistance versus pressure support: an electromyographic study

BACKGROUND

Neurally adjusted ventilatory assist (NAVA), regulated exclusively by the electromyographic activity (EA) of the diaphragm (EAdi), could affect the distribution of neural drive to the various inspiratory muscles. The objective of this study was to compare EAdi, EA of the scalene (EAscal), and EA of the alae nasi (EAan), according to the ventilatory mode and assist level in 12 mechanically ventilated patients.

METHODS

Seven assist levels of pressure support ventilation (PSV) and NAVA were sequentially applied. EAdi, EAscal, and EAan were quantified and expressed as a percentage of their maximum values. The relative contributions of extradiaphragmatic muscles to inspiratory efforts were assessed by calculating EAscal/EAdi and EAan/EAdi ratios. Three assist levels for each of the two ventilatory modes that resulted in EAdi values of 80 to 100%, 60 to 80%, and 40 to 60% were assigned to three groups (N1, N2, and N3). Results are expressed as median and interquartile range.

RESULTS

EA of inspiratory muscles decreased during PSV and NAVA (P < 0.0001). Although EAdi remained constant within groups (P = 0.9), EAscal was reduced during NAVA compared with PSV in N1 and N3 (65% [62 to 64] and 27% [18 to 34] in NAVA vs. 90% [81 to 100] and 49% [40 to 55] in PSV, P = 0.007). Altogether, EAscal/EAdi and EAan/EAdi ratios were lower in NAVA than PSV (0.7 [0.6 to 0.7] and 0.7 [0.6 to 0.8] in NAVA vs. 0.9 [0.8 to 1.1] and 0.9 [0.7 to 1.1] in PSV, P < 0.05).

CONCLUSIONS

NAVA and PSV both reduced extradiaphragmatic inspiratory muscle activity, in proportion to the level of assistance. Compared with PSV, NAVA resulted in a predominant contribution of the diaphragm to inspiratory effort.

Unrecognized suffering in the ICU: addressing dyspnea in mechanically ventilated patients

BACKGROUND

Intensive care unit (ICU) patients are exposed to many sources of discomfort. Although increasing attention is being given to the detection and treatment of pain, very little is given to the detection and treatment of dyspnea (defined as "breathing discomfort").

METHODS

Published information on the prevalence, mechanisms, and potential negative impacts of dyspnea in mechanically ventilated patients are reviewed. The most appropriate tools to detect and quantify dyspnea in ICU patients are also assessed.

RESULTS/CONCLUSIONS

Growing evidence suggests that dyspnea is a frequent issue in mechanically ventilated ICU patients, is highly associated with anxiety and pain, and is improved in many patients by altering the ventilator settings.

CONCLUSIONS

Future studies are needed to better delineate the impact of dyspnea in the ICU and to define diagnostic, monitoring and therapeutic protocols.

Estimation of patient's inspiratory effort from the electrical activity of the diaphragm

OBJECTIVES

To calculate an index (termed Pmusc/Eadi index) relating the pressure generated by the respiratory muscles (Pmusc) to the electrical activity of the diaphragm (Eadi), during assisted mechanical ventilation and to assess if the Pmusc/Eadi index is affected by the type and level of ventilator assistance. The Pmusc/Eadi index was also used to measure the patient's inspiratory effort from Eadi without esophageal pressure.

DESIGN

Crossover study.

SETTING

One general ICU.

PATIENTS

Ten patients undergoing assisted ventilation.

INTERVENTION

Pressure support and neurally adjusted ventilator assist delivered, each, at three levels of ventilatory assistance.

MEASUREMENT AND MAIN RESULTS

Airways flow and pressure, esophageal pressure, and Eadi were continuously recorded. Sixty tidal volumes for each ventilator settings were analyzed off-line, at three time points during inspiration. For each time point, Pmusc/Eadi index was calculated. Pmusc/Eadi index was also calculated from airway pressure drop during end-expiratory occlusions. Pmusc/Eadi index was very variable among patients, but within one patient it was not affected by type and level of ventilator assistance. Pmusc/Eadi index decreased during the inspiration. Pmusc/Eadi index obtained during an occlusion from airway pressure swing was tightly correlated with that derived from esophageal pressure during tidal ventilation and allowed to estimate pressure time product.

CONCLUSIONS

Pmusc is tightly related to Eadi, by a proportionality coefficient that we termed Pmusc/Eadi index, stable within each patient under different conditions of ventilator assistance. The derivation of the Pmusc/Eadi index from Eadi and airway pressure during an expiratory occlusion enables a continuous estimate of patient's inspiratory effort.

Atividade mioelétrica dos músculos respiratórios em crianças asmáticas durante manobra inspiratória máxima

OBJETIVOS: avaliar a atividade dos músculos escalenos e esternocleidomastóideo (ETMD) no período basal e durante manobra de pressão inspiratória máxima (PImax) em crianças asmáticas. MÉTODOS: foram estudadas 15 crianças, divididas em grupo asma (n=8) e grupo controle (n=7). Foi realizada a análise da função pulmonar e da PImax através da espirometria e da manovacuometria, respectivamente. A atividade mioelétrica dos músculos escaleno e ETMD foram realizadas pela eletromiografia de superfície durante período basal e manobra de PImax. RESULTADOS: a eletromiografia de superfície (EMGs) basal do músculo escaleno é maior no grupo asma quando comparado ao grupo controle. Diferentemente, a EMGs basal do músculo ETMD não apresentou diferença significativa nos grupos estudados. O percentual da EMGs dos músculos escaleno e ETMD durante manobra de PImax foi maior no grupo asma quando comparado ao grupo controle. CONCLUSÕES: EMGs do escaleno durante o período basal está aumentada em crianças asmáticas. A atividade eletromiográfica do músculo ETMD no período basal é similar em ambos os grupos estudados. A EMGs dos músculos ETMD e escaleno na geração de pressão intratorácica, durante a manobra de PImax, está aumentada em crianças asmáticas.

Coordination of respiratory muscles assessed by means of nonlinear forecasting of demodulated myographic signals

Pulmonary diseases such as obstructive sleep apnea syndrome (OSAS) affect function of respiratory muscles. Individuals with OSAS suffer intermittent collapse of the upper airways during sleep due to unbalanced forces generated by the contraction of the diaphragm and upper airway dilator muscles. Respiratory rhythm and pattern generation can be described via nonlinear or coupled oscillators; therefore, the resulting activation of different respiratory muscles may be related to complex nonlinear interactions. The aims of this work were: to evaluate locally linear models for fitting and prediction of demodulated myographic signals from respiratory muscles; and to analyze quantitatively the influence of a pulmonary disease on this nonlinear forecasting related to low and moderate levels of respiratory effort. Electromyographic and mechanomyographic signals from three respiratory muscles (genioglossus, sternomastoid and diaphragm) were recorded in OSAS patients and controls while awake during an increased respiratory effort. Variables related to auto and cross prediction between muscles were calculated from the r(2) coefficient and the estimation of residuals, as functions of prediction horizon. In general, prediction improved linearly with higher levels of effort. A better prediction between muscle activities was obtained in OSAS patients when using genioglossus as the predictor signal. The prediction was significant for more than two respiratory cycles in OSAS patients compared to only a half cycle in controls. It could be concluded that nonlinear forecasting applied to genioglossus coupling with other muscles provides a promising assessment to monitor pulmonary diseases.

Surface EMG to assess and quantify upper airway dilators activity during non-invasive ventilation

This study tests the hypothesis that the surface electromyographic (EMG) activity of upper airway dilators would respond to inspiratory loading in a healthy humans model of ventilator trigger asynchrony. EMG activity was measured in levator alae-nasi, genioglossus, parasternal, scalene and diaphragm muscles in eight subjects. They breathed quietly through a face mask and then were connected to a mechanical ventilator. Recordings were performed during nasal breathing against negative pressure triggers (-2.5%, -5% and -10% of maximal inspiratory pressure) and during oro-nasal breathing with a "-10% trigger". Scalene, alae-nasi and genioglossus EMG activity level increased with the "-10% trigger". While no breathing route dependence was found in scalene, the significant increase was only found for nasal breathing in alae-nasi and for oro-nasal breathing in genioglossus. The dyspnea intensity was significantly correlated with the EMG activity level of these three muscles. Surface EMG of airway dilator muscles could be used as a complementary tool to assess inspiratory drive during mechanical ventilation.

Efeitos da pressão positiva expiratória nas vias aéreas sobre a atividade eletromiográfica da musculatura acessória da inspiração em portadores de DPOC

OBJETIVO: Avaliar a atividade eletromiográfica (AE) dos músculos esternocleidomastoideo (ECM) e escaleno durante e após a aplicação de expiratory positive airway pressure (EPAP, pressão positiva expiratória nas vias aéreas) em portadores de DPOC. MÉTODOS: Ensaio clínico simples cego com 13 indivíduos hígidos como controles e 12 pacientes com DPOC estável. No momento basal, foram determinados a AE em respiração espontânea, parâmetros da função pulmonar e a força muscular respiratória. Posteriormente, foi aplicada EPAP de 15 cmH2O com uma máscara facial durante 25 min, com o registro do sinal eletromiográfico dos músculos ECM e escaleno a cada 5 min. Um último registro foi obtido 10 min após a retirada da máscara. RESULTADOS: Observamos que o comportamento da AE dos músculos ECM e escaleno foi semelhante nos controles e pacientes com DPOC (p = 0,716 e p = 0,789, respectivamente). Porém, ao longo da aplicação de EPAP, ambos os músculos mostraram uma tendência ao aumento da AE. Além disso, houve uma redução significativa da AE do ECM entre o momento final e basal (p = 0,034). CONCLUSÕES: A aplicação de EPAP promoveu uma redução significativa da AE do músculo ECM tanto nos controles quanto nos portadores de DPOC estável. Porém, isso não ocorreu em relação à AE do músculo escaleno.

Respiratory muscle function and activation in chronic obstructive pulmonary disease

Inspiratory muscles are uniquely adapted for endurance, but their function is compromised in chronic obstructive pulmonary disease (COPD) due to increased loads, reduced mechanical advantage, and increased ventilatory requirements. The hyperinflation of COPD reduces the flow and pressure-generating capacity of the diaphragm. This is compensated by a threefold increase in neural drive, adaptations of the chest wall and diaphragm shape to accommodate the increased volume, and adaptations of muscle fibers to preserve strength and increase endurance. Paradoxical indrawing of the lower costal margin during inspiration in severe COPD (Hoover's sign) correlates with high inspiratory drive and severe airflow obstruction rather than contraction of radially oriented diaphragm fibers. The inspiratory muscles remain highly resistant to fatigue in patients with COPD, and the ultimate development of ventilatory failure is associated with insufficient central drive. Sleep is associated with reduced respiratory drive and impairments of lung and chest wall function, which are exaggerated in COPD patients. Profound hypoxemia and hypercapnia can occur in rapid eye movement sleep and contribute to the development of cor pulmonale. Inspiratory muscles adapt to chronic loading with an increased proportion of slow, fatigue-resistant fiber types, increased oxidative capacity, and reduced fiber cross-sectional area, but the capacity of the diaphragm to increase ventilation in exercise is compromised in COPD. In COPD, neural drive to the diaphragm increases to near maximal levels in exercise, but it does not develop peripheral muscle fatigue. The improvement in exercise capacity and dyspnea following lung volume reduction surgery is associated with a substantial reduction in neural drive to the inspiratory muscles.

Can the electromyographic fatigue threshold be determined from superficial elbow flexor muscles during an isometric single-joint task?

The purpose of this study was to compare the electromyographic fatigue threshold (EMG(FT)) values determined simultaneously from superficial elbow flexor muscles during an isometric single-joint task. Eight subjects performed isometric elbow flexions at randomly ordered percentages of maximal voluntary contraction (20, 30, 40, 50 and 60%). During these bouts, electromyographic (EMG) activity was measured in the anterior head of Deltoïd, lateral head of Triceps brachii, Brachioradialis and both short and long head of Biceps brachii. For each subject and each muscle, the EMG amplitude data were plotted as function of time for the five submaximal bouts. The slope coefficient of the EMG amplitude versus time linear relationships were plotted against force level. EMG(FT) was determined as the y-intercept of this relationship and considered as valid only if the following criteria were met: (1) significant positive linear regression (P < 0.05) between force and slope coefficient, (2) an adjusted coefficient of determination for force versus slope coefficient relationship greater than 0.85, and (3) a standard error for the EMG(FT) below 5% of maximal voluntary contraction. The EMG(FT) could only be determined for one muscle (the long head of Biceps brachii) and only in three out of the eight subjects (mean value = 24.9 +/- 1.1% of maximal voluntary contraction). The lack of EMG(FT) in most of the subjects (5/8) could be explained by putative compensations between elbow muscles which were indirectly observed in some subjects. In this way, EMG(FT) should be studied from a more simple movement i.e., ideally a movement implying mainly one muscle.