Expiratory Muscle Activity Research Articles

Gastric Pressure Monitoring Unveils Abnormal Patient-Ventilator Interaction Related to Active Expiration: A Retrospective Observational Study.

Patient-ventilator dyssynchrony is frequently observed during assisted mechanical ventilation. However, the effects of expiratory muscle contraction on patient-ventilator interaction are underexplored. The authors hypothesized that active expiration would affect patient-ventilator interaction and they tested their hypothesis in a mixed cohort of invasively ventilated patients with spontaneous breathing activity. This is a retrospective observational study involving patients on assisted mechanical ventilation who had their esophageal pressure (Peso) and gastric pressure monitored for clinical purposes. Active expiration was defined as gastric pressure rise (ΔPgas) greater than or equal to 1.0 cm H2O during expiratory flow without a corresponding change in diaphragmatic pressure. Waveforms of Peso, gastric pressure, diaphragmatic pressure, flow, and airway pressure (Paw) were analyzed to identify and characterize abnormal patient-ventilator interaction. 76 patients were identified with Peso and gastric pressure recordings, of whom 58 demonstrated active expiration with a median ΔPgas of 3.4 cm H2O (interquartile range = 2.4 to 5.3) observed in this subgroup. Among these 58 patients, 23 presented the following events associated with expiratory muscle activity: (1) distortions in Paw and flow that resembled ineffective efforts, (2) distortions similar to autotriggering, (3) multiple triggering, (4) prolonged ventilatory cycles with biphasic inspiratory flow, with a median percentage (interquartile range) increase in mechanical inflation time and tidal volume of 54% (44 to 70%) and 25% (8 to 35%), respectively and (5) breathing exclusively by expiratory muscle relaxation. Gastric pressure monitoring was required to identify the association of active expiration with these events. Respiratory drive, assessed by the rate of inspiratory Peso decrease, was significantly higher in patients with active expiration (median [interquartile range] dPeso/dt: 12.7 [9.0 to 18.5] vs 9.2 [6.8 to 14.2] cmH2O/sec; P < 0.05). Active expiration can impair patient-ventilator interaction in critically ill patients. Without documenting gastric pressure, abnormal patient-ventilator interaction associated with expiratory muscle contraction may be mistakenly attributed to a mismatch between the patient's inspiratory effort and mechanical inflation. This misinterpretation could potentially influence decisions regarding clinical management.

Driving pressure of respiratory system and lung stress in mechanically ventilated patients with active breathing

BackgroundDuring control mechanical ventilation (CMV), the driving pressure of the respiratory system (ΔPrs) serves as a surrogate of transpulmonary driving pressure (ΔPlung). Expiratory muscle activity that decreases end-expiratory lung volume may impair the validity of ΔPrs to reflect ΔPlung. This prospective observational study in patients with acute respiratory distress syndrome (ARDS) ventilated with proportional assist ventilation (PAV+), aimed to investigate: (1) the prevalence of elevated ΔPlung, (2) the ΔPrs-ΔPlung relationship, and (3) whether dynamic transpulmonary pressure (Plungsw) and effort indices (transdiaphragmatic and respiratory muscle pressure swings) remain within safe limits.MethodsThirty-one patients instrumented with esophageal and gastric catheters (n = 22) were switched from CMV to PAV+ and respiratory variables were recorded, over a maximum of 24 h. To decrease the contribution of random breaths with irregular characteristics, a 7-breath moving average technique was applied. In each patient, measurements were also analyzed per deciles of increasing lung elastance (Elung). Patients were divided into Group A, if end-inspiratory transpulmonary pressure (PLEI) increased as Elung increased, and Group B, which showed a decrease or no change in PLEI with Elung increase.ResultsIn 44,836 occluded breaths, ΔPlung ≥ 12 cmH2O was infrequently observed [0.0% (0.0–16.9%) of measurements]. End-expiratory lung volume decrease, due to active expiration, was associated with underestimation of ΔPlung by ΔPrs, as suggested by a negative linear relationship between transpulmonary pressure at end-expiration (PLEE) and ΔPlung/ΔPrs. Group A included 17 and Group B 14 patients. As Elung increased, ΔPlung increased mainly due to PLEI increase in Group A, and PLEE decrease in Group B. Although ΔPrs had an area receiver operating characteristic curve (AUC) of 0.87 (95% confidence intervals 0.82–0.92, P < 0.001) for ΔPlung ≥ 12 cmH2O, this was due exclusively to Group A [0.91 (0.86–0.95), P < 0.001]. In Group B, ΔPrs showed no predictive capacity for detecting ΔPlung ≥ 12 cmH2O [0.65 (0.52–0.78), P > 0.05]. Most of the time Plungsw and effort indices remained within safe range.ConclusionIn patients with ARDS ventilated with PAV+, injurious tidal lung stress and effort were infrequent. In the presence of expiratory muscle activity, ΔPrs underestimated ΔPlung. This phenomenon limits the usefulness of ΔPrs as a surrogate of tidal lung stress, regardless of the mode of support.

Expiratory Muscle Activity Counteracts Positive End-Expiratory Pressure and Is Associated with Fentanyl Dose in Patients with Acute Respiratory Distress Syndrome.

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9-60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose-response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation.

The Relationship between Exercise Capacity and Muscle Strength, Physical Activity, Fatigue and Quality of Life in Patients with Cancer Cachexia

Background Exercise capacity is a significant determinant of mortality for cancer patients, so knowing the possible determinants of exercise capacity will produce physical and psychological benefits for individuals with cancer cachexia. Purpose To investigate the relationship between exercise capacity on peripheric and respiratory muscle strength, physical activity, fatigue and quality of life in subjects with cancer cachexia. Methods The study included 31 patients diagnosed with cancer cachexia. Functional capacity was assessed by 6-Minute Walk Test, hand grip strength and proximal muscle mass by hand dynamometer, respiratory muscle strength by the Maximum Expiratory Pressure and Maximum Inspiratory Pressure measurements, physical activity by International Physical Activity Questionnaire Short Form, fatigue by Brief Fatigue Inventory, and quality of life by EORT-QLQ-C30. The relationship between functional capacity and continuous independent variables was determined using Spearman’s or Pearson’s tests. Results A strong positive correlation was observed between exercise capacity and expiratory muscle strength (r = 0.75, p < 0.001), activity level (r = 0.68, p < 0.001), and quality of life global health status (r = 0.74, p < 0.001). Conversely, a strong negative correlation was found between exercise capacity and fatigue severity (r = −0.64, p < 0.001). Conclusion Higher exercise capacity in cancer cachexia patients is linked to reduced fatigue, improved respiratory muscle strength, increased physical activity levels, and enhanced quality of life. When designing rehabilitation programs or exercise interventions for individuals with cancer cachexia, it is crucial to assess their exercise capacity and tailor the programs accordingly.

Fentanyl induced disruption of the coordinated reciprocal activity of inspiratory and expiratory respiratory muscles

Opioid induced respiratory depression (OIRD) occurs when respiratory pump and/or airway muscle activity are reduced ostensibly due to reduced output from the brainstem respiratory control system, resulting in central (CA) and/or obstructive apnea (OA) and reduced breathing frequency. Although less commonly reported in the literature, ORID may also result from an inappropriate activation of accessory muscles leading to the “Wooden Chest Syndrome” (WCS) -when airflow is limited due to simultaneous activation of inspiratory and expiratory pump and/or airway respiratory muscles to decrease chest wall compliance and inappropriately increase airway resistance. This phenomenon is difficult to directly study in humans, but here we present data from our large animal model (adult female goats). We tested the hypothesis that IV fentanyl would lead to transient dysfunction in respiratory accessory muscles indicative of WCS. We surgically instrumented goats (n=7) with electromyographic (EMG) wires in inspiratory (diaphragm; DIA) and expiratory (Transversus Abdominus; TA) pump muscles, as well as airway dilator (Thyropharyngeus; Thy) and constrictor (Genioglossus; GG) muscles. After &gt;2 weeks of surgical recovery, responses to saline or various doses of fentanyl citrate (25-125 mcg/kg; IV) were tested for 30 min before and up to 90 min after injection. As described in an adjacent poster, particularly over the first several minutes after fentanyl injection, CA and OA were observed in some goats. However, disruption of airflow was primarily associated with increased simultaneous activation of pump and airway inspiratory and expiratory muscles resembling WCS. For most muscles, the rate of rise in muscle activity (an index of firing intensity) increased within 2 minutes following fentanyl injection and remained significantly (P&lt;0.05) elevated up to 90 minutes. During WCS periods, airflow was oscillatory or interrupted suggesting transient closure of the airway. In addition, there were time- and dose-dependent effects on frequency, duration, and total activity of the pump and airway muscles. By 60 minutes post-injection, there were periods of transient return of muscle activity and airflow to at or below baseline values. There was no significant effect of saline on muscle activity. Overall, these data suggest that following fentanyl injection in awake goats, there was an increase in firing of pump and airway muscles which ultimately disrupts the coordinated reciprocal activity of inspiratory and expiratory muscles and contributes to OIRD. Supported by NIH DA050571 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Immediate Effects of the Manual Therapy Traction Manipulations on Parameters of Cardiorespiratory System Functioning

The aim of this study was to determine the changes in the cardiorespiratory system activity under the influence of traction manipulations in the thoracic spine. The study involved 26 adults, including 18 women aged 39.6 ± 12.1 years and 8 men aged 36.3 ± 8.3 years. The mean age of patients was 38.6 ± 11.2 years. The work used an integral method of studying the cardiorespiratory system - spiroarteriocardiorhythmography (SAKR). SACR registration was performed before and after traction manipulations in the thoracic spine directly in the procedure of manual therapy. The study of the immediate effect of traction manipulations of SMT in the thoracic spine on the cardiorespiratory system allowed establishing the main significant effects: decrease in HR (min^-1) from 85.1 (77.1; 94.2) to 79.5 (69.8; 87.6), p=0.000, decrease in duration of QTC (s) from 0.419 (0.404; 0.434) to 0.413 (0.401; 0.427), p=0.012, decrease in CO (dm³) from 5.2 (4.6; 5.8) to 4.9 (4.4; 5.6), p=0.000, SI (dm³/m²) from 3.05 (2.75; 3.30) to 2.90 (2.62; 3.20), p=0.000, increase in Vexp (L/s) from 0.28 (0.22; 0.34) to 0.31 (0.25; 0.39), p=0.030. The obtained data suggest that the main effects of traction manipulations on the thoracic spine are associated more with the changes in hemodynamic parameters of blood circulation due to activation of expiratory muscles and chest mobility, when the suction mechanisms of the chest and cardiovascular function of diaphragm are activated.

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

BackgroundThe 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.PurposeTo 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.MethodsIntubated 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.ResultsOf 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 (EAdisurf) and of accessory muscles (ACCsurf) was higher in failure patients compared with success (group-by-time interaction p = 0.0174 and p < 0.001, respectively). EA of expiratory muscles (ESPsurf) during SBT increased more in failure than in weaned patients (group-by-time interaction p < 0.0001).ConclusionNon-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.

Electrical activity of expiratory muscles in type 2 diabetes mellitus

Aim. To study the functional state of the expiratory muscles in patients with type 2 diabetes mellitus on the basis of changes in their electrical activity when using a functional test with a static expiratory effort. Materials and methods. 47 patients with type 2 diabetes mellitus and 40 patients without disorders of carbohydrate metabolism were examined. To study the electrical activity of the expiratory muscles, surface electromyography (EMG) of the external oblique abdominal muscle (OAM), rectus abdominis muscle (RAM), and internal intercostal muscles (IIM) was performed using a functional test with a static expiratory effort. Results. When performing a functional test with a static expiratory effort in both groups, a decrease in the frequency and an increase in the amplitude of EMG was observed, however, in patients with type 2 diabetes mellitus, these changes were less pronounced. There were also differences in the dynamics of changes in EMG indicators. In patients with type 2 diabetes mellitus, the decrease in the frequency of EMG OAM began from 10 seconds of the test, IIM – from 15 seconds, in the comparison group – from 5 and 10 seconds, respectively. The OAM EMG amplitude in the main group did not change significantly, in the comparison group it increased from 5 seconds of expiratory effort. At the 10th second of the test, the amplitude index of the EMG OAM in patients with type 2 diabetes mellitus was 10.4% lower (p=0.027) than in the comparison group, and at the 15th second – by 10.5% (p=0.033). Conclusion: The change in the electrical activity of the expiratory muscles in patients with type 2 diabetes mellitus is due to the slowed down dynamics of the frequency-amplitude characteristics of the EMG OAM, uncompensated IIM fatigue, as well as lower values of the OAM EMG amplitude when performing a functional exercise test with a static expiratory effort.

Expiratory activity during sleep in children.

Sleep irregularities and respiratory events (apnea, O2 desaturation or a combination thereof) are often present in the infant population. While inspiration is the main active process in the act of breathing, expiration is generally thought to occur passively. Although commonly considered as quiet during sleep, expiratory abdominal muscles have been proposed to be recruited to promote ventilation, facilitate gas exchange, and reduce the work of breathing during conditions of increased respiratory drive, exercise, or airway obstruction. In this study, we investigated the occurrence of expiratory abdominal muscle activity in polysomnographic studies of subjects (aged 0-2years) suspected of sleep disordered breathing. Our results indicate that abdominal muscle activation occurs during sleep, most frequently during non-rapid eye movement and rapid-eye movement states compared to slow-wave sleep. Furthermore, abdominal muscle activity was present during regular breathing or associated with respiratory events (apneas or O2 desaturation). In the latter case, abdominal muscle recruitment more frequently followed the onset of respiratory events and terminated with recovery from blood O2 desaturation events. We conclude that expiratory abdominal muscle activity contributes to the pattern of respiratory muscle recruitment during sleep in infants and given its temporal relationship with respiratory events, we propose that its recruitment could facilitate proper ventilation by counteracting airway resistance and O2 desaturation in infancy across different stages of sleep.

Comparison of disc and wire electrodes to restore cough via lower thoracic spinal cord stimulation

Objective To compare the safety and effectiveness of wire (WE) vs. disc (DE) electrodes to restore cough in subjects with spinal cord injury (SCI). Design Clinical trials assessing the effectiveness and clinical outcomes associated with two electrode systems to activate the expiratory muscles. Setting Inpatient hospital setting for DE or WE electrode insertion; outpatient evaluation of cough efficacy and instructions for home use. Participants Twenty-nine subjects with SCI; 17 participants with DE and 12 with WE implants. Intervention Surgical implantation of WE or DE to restore cough. Daily application of spinal cord stimulation (SCS) at home. Main outcome measure(s) Airway pressure (P) and peak airflow (F) generation achieved with SCS; clinical parameters including ease in raising secretions, incidence of acute respiratory tract infections (RTI) and side effects. Results P and F achieved with DE and WE were not significantly different. For example, at total lung capacity (TLC) with participant effort, P was 128 ± 12 cmH2O and 118 ± 14 cmH2O, with DE and WE, respectively. The degree of difficulty in raising secretions improved markedly in both groups. The incidence of RTI per year fell from 1.3 ± 0.3 and 1.3 ± 0.5–0.3 ± 0.1 and 0.1 ± 0.1 for DE and WE groups, respectively (P < 0.01 for both when compared to pre-implant values and NS between DE and WE groups). The only significant side effect i.e. short-term autonomic dysreflexia was also similar between groups. Conclusions The results of this investigation indicate that both DE and WE result in comparable degrees of expiratory muscle activation, clinical benefits and side effects. Importantly, SCS to restore cough can be achieved with use of WE which can be placed using minimally invasive techniques and associated reduction in cost, surgical time and overall risk. Trial registration: ClinicalTrials.gov identifier: NCT00116337., NCT01659541, FDA IDE: G980267

Difference in Muscle Activity of Respiratory Muscle During Maximum Inspiration and Expiration Due to Position Change and Tool Use

Purpose : In this study, we aimed to measure how respiratory muscle activity changes as posture changes. We also aimed to measure the inspiratory sternocleidomastoid (SCM) and upper trapezius (UT) muscle activities as well as expiratory rectus abdominis (RA) and oblique abdominis (OA) muscle activities in healthy male and female university students in their twenties. Methods : Using the percentage of reference voluntary contraction (% RVC) with electromyography, we measured the SCM, UT, RA, and OA muscle activities in 16 healthy male and female university students in their 20s according to position change and breather tool use. Results : We found that the average value of inspiratory and expiratory muscle activities by posture was highest when using the breather tool. When using the tool with 10-mm and 2-mm straws for standard breathing at rest in the sitting position, a statistically significant increase in SCM, UT, and OA activities occurred (p < 0.05). For standard breathing at rest in the supine position, a statistically significant increase in SCM, RA, and OA activities occurred (p < 0.05). Conclusion : In clinical application, it may be better to use a respiratory muscle-strengthening tool to increase the activity of inspiratory and expiratory muscles.

The study of respiratory muscles activation during respiratory muscle strength effort in adult females with chronic neck pain.

[Purpose] This study aimed to compare maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP) values and muscle activity during MIP and MEP between chronic neck pain and healthy participants. [Participants and Methods] Twenty chronic neck pain and 20 non-symptomatic females participated in this study. Maximal airway pressure (MIP and MEP) and surface electromyography (sEMG) for both sides of the upper trapezius, anterior scalene, pectoralis major and 6th intercostal muscles were recorded simultaneously. [Results] Significant differences of MIP and MEP values were found between the groups. The muscle activities of both sides of upper trapezius and 6th intercostal muscles during MEP were significantly higher in the chronic neck pain group than the healthy group except both sides of anterior scalene and pectoralis major muscles. During MIP, the activities of upper trapezius, 6th intercostal muscles and anterior scalene were significantly different between the two studied groups. Higher activity of left pectoralis major was found in the chronic neck pain group. [Conclusion] Decreasing values of MEP and MIP as well as muscles activities elevation in chronic neck pain participants were clearly demonstrated. Besides the musculoskeletal treatment, we suggest breathing exercise training to be considered in treatment programs.

The condition of the respiratory muscles in obstructive sleep disordered breathing according to electromyographic data

Aim . To study functional state of respiratory muscles in patients with obstructive sleep-disordered breathing (oSDB) of varying severity based on changes in electrical activity when using a stepwise-increasing respiratory load. Materials and methods . According to results of cardiorespiratory monitoring, the examined patients were divided into 4 groups. Group 1 included 16 patients without oSDB, group 2 – 16 patients with mild oSDB, group 3 – 8 patients with moderate oSDB, group 4 – 8 patients with severe oSDB. The assessment of electrical activity of inspiratory muscles and expiratory muscles was carried out using electromyography (EMG) when performing tests with a stepwise-increasing inspiratory and expiratory load. Results . During inspiratory test, a decrease in EMG frequency was observed, indicating respiratory muscles fatigue development, with a simultaneous increase in EMG amplitude due to the involvement of additional motoneurons in muscle contraction. In all cases, degree of increase in EMG amplitude prevailed over degree of decrease in EMG frequency. In patients of groups 3 and 4, there were no signs of diaphragm fatigue. Results of expiratory test in group 1, degree of increase in EMG amplitude prevailed over degree of decrease in EMG frequency. In the groups of patients with oSDB, prevalence of decrease in the EMG frequency over increase in EMG amplitude was observed, which indicates development of neuromuscular fatigue of expiratory muscles. Conclusion . Changes in functional state of respiratory muscles are associated with severity of oSDB and are characterized by different dynamics of the electrical activity of inspiratory and expiratory muscles in response to a functional test.

Airway pressure morphology and respiratory muscle activity during end-inspiratory occlusions in pressure support ventilation

BackgroundThe driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined.MethodsRetrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a “passive-like” decrease followed by plateau, a pattern with “clear plateau,” and an “irregular rise” pattern, which included all cases of late or continuous increase, with or without plateau.ResultsData from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmH2O, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively.ConclusionsThe pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.

Model‐Based Analysis of Lower Thoracic High‐Frequency Spinal Cord Stimulation (HF‐SCS) to Restore Effective Cough

BackgroundSpinal cord stimulation (SCS, 50 Hz) is a useful method to restore an effective cough in persons with spinal cord injury (SCI). In animal models, dorsal HF‐SCS (~500 Hz) produces similar level of expiratory muscle activation with much lower stimulus amplitudes. Currently, the mechanism of this behavior is unknown.ObjectiveThe aim of the present study was to develop a computational model of lower thoracic SCS to investigate the mechanisms of the expiratory muscle activation via HF‐SCS.MethodsWe created a computer model of an anatomically‐accurate finite element model (FEM) of the lower thoracic (T9) canine spinal cord and surrounding anatomy with an implanted SCS electrode array. This model consisted of two main components: 1) multicompartment cable models of dorsal afferent fibers and 2) ventral motor axons. Model analysis allowed calculation of the extracellular voltages generated during SCS and the corresponding activation thresholds of each fiber type.ResultsIn our simulations, we calculated the activation thresholds for several electrode combinations and stimulation frequencies (50 Hz, 500 Hz). As expected, the activation thresholds of the ventral motor axons were significantly higher than the activation thresholds of dorsal root axons. Therefore, low‐frequency SCS likely functions through the direct activation of ventral motor axons, while high‐frequency SCS operates via recruitment of myelinated afferent fibers at significantly lower stimulation amplitudes. In our simulations, the stimulation frequency did not significantly alter activation thresholds in dorsal or ventral axons.ConclusionsOur results suggest that both high‐ and low‐frequency SCS directly activate dorsal rootlets at low amplitudes (~1 mA); however, the trans‐synaptic spinal circuits responsible for eliciting cough are only effective at higher stimulation frequencies. Consequently, low‐frequency stimulation results in effective cough by bypassing this circuitry entirely to directly activate the ventral motor axons at the cost of requiring higher stimulation amplitudes. In future work, we will perform simulations directly assessing the ability of SCS to engage these spinal circuits. We will compare our model results to experimental measurements in an animal model of SCS to produce cough.DisclosureDr. DiMarco holds two U.S. patents for technology related to the content of this abstract: Method and Apparatus for Electrical Activation of the Expiratory Muscles to Restore Cough (5,999,855) and Bipolar Spinal Cord Stimulation to Activate the Expiratory Muscles to Restore Cough (8,751,004).Support or Funding InformationMerit Review Award I01‐RX‐001488 from the U.S. Department of Veterans Affairs, Rehabilitation Research and Development Service.

Feedforward discharges couple the singing central pattern generator and ventilation central pattern generator in the cricket abdominal central nervous system

We investigated the central nervous coordination between singing motor activity and abdominal ventilatory pumping in crickets. Fictive singing, with sensory feedback removed, was elicited by eserine-microinjection into the brain, and the motor activity underlying singing and abdominal ventilation was recorded with extracellular electrodes. During singing, expiratory abdominal muscle activity is tightly phase coupled to the chirping pattern. Occasional temporary desynchronization of the two motor patterns indicate discrete central pattern generator (CPG) networks that can operate independently. Intracellular recordings revealed a sub-threshold depolarization in phase with the ventilatory cycle in a singing-CPG interneuron, and in a ventilation-CPG interneuron an excitatory input in phase with each syllable of the chirps. Inhibitory synaptic inputs coupled to the syllables of the singing motor pattern were present in another ventilatory interneuron, which is not part of the ventilation-CPG. Our recordings suggest that the two centrally generated motor patterns are coordinated by reciprocal feedforward discharges from the singing-CPG to the ventilation-CPG and vice versa. Consequently, expiratory contraction of the abdomen usually occurs in phase with the chirps and ventilation accelerates during singing due to entrainment by the faster chirp cycle.

The nocturnal-polysomnogram and “non-hypoxic sleep-disordered-breathing” in children

ObjectiveTo characterize sleep-disordered breathing patterns not related to hypoxia resulting in fragmented sleep in children. MethodsWe reviewed the polysomnogram (PSG) data of children with sleep complaints who were being evaluated for sleep-disordered breathing and had an apnea-hypopnea-index ≤ 3. These data were compared to the recordings of the same children with nasal CPAP administered for one night and to 60 control subjects (children without any sleep complaints). A subgroup of children was monitored with esophageal manometry, but nasal cannula flow data was recorded in all cases. ResultsAbnormal breathing patterns, particularly flow limitation, could be seen with more severity and frequency compared to apnea or hypopnea. The observed abnormal breathing patterns were associated with EEG disturbances. ConclusionsPatterns such as flow-limitation, mouth-breathing, changes in inspiratory and expiratory time, rib-cage and expiratory muscle activity, transcutaneous CO2 electrode changes and snoring noises are all variables that should be systematically reviewed when analyzing nocturnal PSG. Current scoring guidelines emphasizes apnea-hypopnea and hypoxic-sleep disordered breathing and therefore treatment is often much delayed in this population of children with evidence of abnormal breathing patterns. Analysis of the various patterns of abnormal breathing noted above allows recognition of “non-hypoxic” sleep-disordered-breathing (SDB).

Genioglossus muscle activity during sniff and reverse sniff in healthy men.

What is the central question of this study? Maximal sniff nasal inspiratory and reverse sniff nasal expiratory pressures are measured as inspiratory and expiratory muscle strength, respectively. Is the genioglossus muscle activated during short maximal inspiratory and expiratory efforts through the nose? What is the main finding and its importance? Genioglossus muscle activity occurred with inspiratory muscle activity during a maximal sniff and with expiratory muscle activity during a maximal reverse sniff. These results indicate that genioglossus muscle activity is closely related to the generation of maximal sniff nasal inspiratory and reverse sniff nasal expiratory pressures. Maximal sniff nasal inspiratory pressure (SNIPmax ) is widely used to assess inspiratory muscle strength. The sniff nasal inspiratory pressure (SNIP) is lower in patients with neuromuscular disease with bulbar involvement compared with those without, possibly owing to impaired upper airway muscle function. However, the degree to which the genioglossus (GG) muscle, one of the upper airway muscles, is activated during inspiratory and expiratory efforts through the nose remains unclear. Therefore, we examined GG activity during short and sharp inspiratory and expiratory efforts through the nose, i.e. sniff and reverse sniff manoeuvres. In eight normal young subjects, we inserted fine wire electrodes into the GG muscle, parasternal intercostal and scalene (inspiratory) muscles and transversus abdominis (expiratory) muscle. We assessed EMG activity of each muscle and measured SNIP and reverse sniff nasal expiratory pressure (RSNEP) during sniffs and reverse sniffs from low to high intensities in the sitting position. The highest SNIP and RSNEP were analysed as SNIPmax and maximal RSNEP (RSNEPmax ), respectively. In each subject, GG EMG activity increased linearly with increasing SNIP and RSNEP. The SNIPmax and RSNEPmax were -85.1±15.9 and 83.2±24.2cmH2 O, respectively. Genioglossus EMG activity varied with EMG activity of the parasternal intercostal and scalene muscles during generation of SNIPmax and with EMG activity of the transversus abdominis muscle during RSNEPmax . Genioglossus EMG activity during generation of SNIPmax was higher than during RSNEPmax (62.9±31.1% EMG of SNIPmax , P=0.012). These results suggested that GG activity was closely related to the generation of both SNIPmax and RSNEPmax .

High-fat diet increases respiratory frequency and abdominal expiratory motor activity during hypercapnia

Breathing disorders are commonly observed in association with obesity. Here we tested whether high-fat diet (HFD) impairs the chemoreflex ventilatory response. Male Holtzman rats (300–320 g) were fed with standard chow diet (SD) or HFD for 12 weeks. Then, tidal volume (VT), respiratory frequency (fR) and pulmonary ventilation (VE) were determined in conscious rats during basal condition, hypercapnia (7% or 10% CO2) or hypoxia (7% O2). The mean arterial pressure (MAP), heart rate (HR) and baroreflex sensitivity were also evaluated in conscious rats. A group of anesthetized rats was used for the measurements of the activity of inspiratory (diaphragm) and expiratory (abdominal) muscles under the same gas conditions. Baseline fR, VT and VE were similar between SD and HFD rats. During hypercapnia, the increase of fR was exacerbated in conscious HFD rats (60 ± 3, vs. SD: 47 ± 3 Δ breaths.min−1, P < 0.05). In anesthetized rats, hypercapnia strongly increased abdominal muscle activity in HFD group (238 ± 27, vs. basal condition: 100 ± 0.3%; P < 0.05), without significant change in SD group (129 ± 2.1, vs. basal condition: 100 ± 0.8%; P = 0.34). The ventilatory responses to hypoxia were similar between groups. In conscious HFD rats, MAP and HR were elevated and the baroreflex function was impaired (P < 0.05). These data demonstrated that 12 weeks of HFD exaggerate the ventilatory response activated by hypercapnia. The mechanisms involved in these responses need more investigation in future studies.

Respiratory Muscle Effort during Expiration in Successful and Failed Weaning from Mechanical Ventilation.

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Respiratory muscle weakness in critically ill patients is associated with difficulty in weaning from mechanical ventilation. Previous studies have mainly focused on inspiratory muscle activity during weaning; expiratory muscle activity is less well understood. The current study describes expiratory muscle activity during weaning, including tonic diaphragm activity. The authors hypothesized that expiratory muscle effort is greater in patients who fail to wean compared to those who wean successfully. Twenty adult patients receiving mechanical ventilation (more than 72 h) performed a spontaneous breathing trial. Tidal volume, transdiaphragmatic pressure, diaphragm electrical activity, and diaphragm neuromechanical efficiency were calculated on a breath-by-breath basis. Inspiratory (and expiratory) muscle efforts were calculated as the inspiratory esophageal (and expiratory gastric) pressure-time products, respectively. Nine patients failed weaning. The contribution of the expiratory muscles to total respiratory muscle effort increased in the "failure" group from 13 ± 9% at onset to 24 ± 10% at the end of the breathing trial (P = 0.047); there was no increase in the "success" group. Diaphragm electrical activity (expressed as the percentage of inspiratory peak) was low at end expiration (failure, 3 ± 2%; success, 4 ± 6%) and equal between groups during the entire expiratory phase (P = 0.407). Diaphragm neuromechanical efficiency was lower in the failure versus success groups (0.38 ± 0.16 vs. 0.71 ± 0.36 cm H2O/μV; P = 0.054). Weaning failure (vs. success) is associated with increased effort of the expiratory muscles and impaired neuromechanical efficiency of the diaphragm but no difference in tonic activity of the diaphragm.