Diaphragmatic Activity Research Articles

Oxidants Regulated Diaphragm Proteolysis during Mechanical Ventilation in Rats.

Diaphragm dysfunction and atrophy develop during controlled mechanical ventilation. Although oxidative stress injures muscle during controlled mechanical ventilation, it is unclear whether it causes autophagy or fiber atrophy. Pretreatment of rats undergoing 24 h of mechanical ventilation with N-acetylcysteine prevents decreases in diaphragm contractility, inhibits the autophagy and proteasome pathways, but has no influence on the development of diaphragm fiber atrophy. Diaphragm dysfunction and atrophy develop during prolonged controlled mechanical ventilation. Fiber atrophy has been attributed to activation of the proteasome and autophagy proteolytic pathways. Oxidative stress activates the proteasome during controlled mechanical ventilation, but it is unclear whether it also activates autophagy. This study investigated whether pretreatment with the antioxidant N-acetylcysteine affects controlled mechanical ventilation-induced diaphragm contractile dysfunction, fiber atrophy, and proteasomal and autophagic pathway activation. The study also explored whether proteolytic pathway activity during controlled mechanical ventilation is mediated by microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes. Three groups of adult male rats were studied (n = 10 per group). The animals in the first group were anesthetized and allowed to spontaneously breathe. Animals in the second group were pretreated with saline before undergoing controlled mechanical ventilation for 24 h. The animals in the third group were pretreated with N-acetylcysteine (150 mg/kg) before undergoing controlled mechanical ventilation for 24 h. Diaphragm contractility and activation of the proteasome and autophagy pathways were measured. Expressions of microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes were measured with quantitative polymerase chain reaction. Controlled mechanical ventilation decreased diaphragm twitch force from 428 ± 104 g/cm (mean ± SD) to 313 ± 50 g/cm and tetanic force from 2,491 ± 411 g/cm to 1,618 ± 177 g/cm. Controlled mechanical ventilation also decreased diaphragm fiber size, increased expression of several autophagy genes, and augmented Atrogin-1, MuRF1, and Nedd4 expressions by 36-, 41-, and 8-fold, respectively. Controlled mechanical ventilation decreased the expressions of six microRNAs (miR-20a, miR-106b, miR-376, miR-101a, miR-204, and miR-93) that regulate autophagy genes. Pretreatment with N-acetylcysteine prevented diaphragm contractile dysfunction, attenuated protein ubiquitination, and downregulated E3 ligase and autophagy gene expression. It also reversed controlled mechanical ventilation-induced microRNA expression decreases. N-Acetylcysteine pretreatment had no affect on fiber atrophy. Prolonged controlled mechanical ventilation activates the proteasome and autophagy pathways in the diaphragm through oxidative stress. Pathway activation is accomplished, in part, through inhibition of microRNAs that negatively regulate autophagy-related genes.

Deep Learning for Prediction of Diaphragm Activity from the Surface Electromyogram

Abstract The electrical activity of the diaphragm (EAdi) is a novel monitoring parameter for patients under assisted ventilation and is used for assessing the patient’s neural respiratory drive. It is recorded by an array of electrodes placed inside the esophagus at the level of the diaphragm. A noninvasive alternative is the measurement of the electromyogram by means of skin surface electrodes (sEMG). The respiratory sEMG signal, however, is subject to electrocardiographic interference and crosstalk from other muscles and may also pick up a different part of the muscular activity. In this work, we propose to use a deep neural network to predict the electrical activity of the diaphragm as measured by a nasogastric catheter from sEMG measurements. We use a ResNet based architecture and train the network to directly regress the EAdi as a supervised learning task - we further investigate a heatmap based regression approach. The proposed methods are evaluated on a clinical dataset consisting of 77 recordings from mechanically ventilated patients. For the direct regression task, the network’s predictions reach a Pearson correlation coefficient (PCC) of 0.818 with EAdi on the hold-out set. The heatmap regression increases the PCC to 0.830 while at the same time achieving a lower mean absolute error, indicating a superior performance. From our results we conclude that sEMG measurements may be used to predict the internal activity of the diaphragm as measured invasively using a nasogastric catheter.

Long-Distance Axon Regeneration Promotes Recovery of Diaphragmatic Respiratory Function after Spinal Cord Injury.

Compromise in inspiratory breathing following cervical spinal cord injury (SCI) is caused by damage to descending bulbospinal axons originating in the rostral ventral respiratory group (rVRG) and consequent denervation and silencing of phrenic motor neurons (PhMNs) that directly control diaphragm activation. In a rat model of high-cervical hemisection SCI, we performed systemic administration of an antagonist peptide directed against phosphatase and tensin homolog (PTEN), a central inhibitor of neuron-intrinsic axon growth potential. PTEN antagonist peptide (PAP4) robustly restored diaphragm function, as determined with electromyography (EMG) recordings in living SCI animals. PAP4 promoted substantial, long-distance regeneration of injured rVRG axons through the lesion and back toward PhMNs located throughout the C3–C5 spinal cord. These regrowing rVRG axons also formed putative excitatory synaptic connections with PhMNs, demonstrating reconnection of rVRG-PhMN-diaphragm circuitry. Lastly, re-lesion through the hemisection site completely ablated functional recovery induced by PAP4. Collectively, our findings demonstrate that axon regeneration in response to systemic PAP4 administration promoted recovery of diaphragmatic respiratory function after cervical SCI.

Information conveyed by electrical diaphragmatic activity during unstressed, stressed and assisted spontaneous breathing: a physiological study

BackgroundThe electrical activity of the crural diaphragm (Eadi), a surrogate of respiratory drive, can now be measured at the bedside in mechanically ventilated patients with a specific catheter. The expected range of Eadi values under stressed or assisted spontaneous breathing is unknown. This study explored Eadi values in healthy subjects during unstressed (baseline), stressed (with a resistance) and assisted spontaneous breathing. The relation between Eadi and inspiratory effort was analyzed.MethodsThirteen healthy male volunteers were included in this randomized crossover study. Eadi and esophageal pressure (Peso) were recorded during unstressed and stressed spontaneous breathing and under assisted ventilation delivered in pressure support (PS) at low and high assist levels and in neurally adjusted ventilatory assist (NAVA). Overall eight different situations were assessed in each participant (randomized order). Peak, mean and integral of Eadi, breathing pattern, esophageal pressure–time product (PTPeso) and work of breathing (WOB) were calculated offline.ResultsMedian [interquartile range] peak Eadi at baseline was 17 [13–22] μV and was above 10 μV in 92% of the cases. Eadimax defined as Eadi measured at maximal inspiratory capacity reached 90 [63 to 99] μV. Median peak Eadi/Eadimax ratio was 16.8 [15.6–27.9]%. Compared to baseline, respiratory rate and minute ventilation were decreased during stressed non-assisted breathing, whereas peak Eadi and PTPeso were increased. During unstressed assisted breathing, peak Eadi decreased during high-level PS compared to unstressed non-assisted breathing and to NAVA (p = 0.047). During stressed breathing, peak Eadi was lower during all assisted ventilation modalities compared to stressed non-assisted breathing. During assisted ventilation, across the different conditions, peak Eadi changed significantly, whereas PTPeso and WOB/min were not significantly modified. Finally, Eadi signal was still present even when Peso signal was suppressed due to high assist levels.ConclusionEadi analysis provides complementary information compared to respiratory pattern and to Peso monitoring, particularly in the presence of high assist levels.Trial registration The study was registered as NCT01818219 in clinicaltrial.gov. Registered 28 February 2013

Assessment of Central Drive to the Diaphragm by Twitch Interpolation: Normal Values, Theoretical Considerations, and Future Directions

Background: The twitch interpolation technique is a promising tool for assessing central drive to the diaphragm. It is used to quantify the degree of voluntary diaphragm activation during predefined breathing maneuvers. Objectives: This study was designed to (a) determine reference values for the level of voluntary activation of the diaphragm using the twitch occlusion technique in healthy adults and (b) explore the association between central drive to the diaphragm and volitional tests of respiratory muscle strength. Methods: Twenty-seven healthy volunteers aged 26 ± 14 years (18 male) were enrolled. Twitch transdiaphragmatic pressure (Pdi) was determined at relaxed functional residual capacity in response to cervical magnetic stimulation (CMS) of the phrenic nerves. The subjects were then instructed to gradually increase voluntary activation of the diaphragm, and the effects of superimposed magnetic stimuli on voluntary Pdi were assessed. Results: The twitch Pdi amplitude following CMS linearly decreased with increasing inspiratory effort. The resulting diaphragm voluntary activation index (DVAI) during maximal voluntary contraction was 75 ± 15% irrespective of gender or age. Twitch duration, half relaxation time, and area under the curve of superimposed Pdi deflections did not show a linear but an exponential association with increasing voluntary activation of the diaphragm. More than 2/3 of the decrease in the above values was evident after 1/3 of voluntary diaphragm contraction. Forced vital capacity (FVC) was inversely correlated with the DVAI. Conclusions: Twitch interpolation allows for assessment of central drive to the diaphragm. The maximum DVAI is independent of gender or age, and significantly related to FVC but not to maximum inspiratory pressure or Pdi as direct measures of diaphragm strength.

Relationship Between Diaphragmatic Electrical Activity and Esophageal Pressure Monitoring in Children.

Mechanical ventilation is an essential life support technology, but it is associated with side effects in case of over or under-assistance. The monitoring of respiratory effort may facilitate titration of the support. The gold standard for respiratory effort measurement is based on esophageal pressure monitoring, a technology not commonly available at bedside. Diaphragmatic electrical activity can be routinely monitored in clinical practice and reflects the output of the respiratory centers. We hypothesized that diaphragmatic electrical activity changes accurately reflect changes in mechanical efforts. The objectives of this study were to characterize the relationship between diaphragmatic electrical activity and esophageal pressure. Prospective crossover study. Esophageal pressure and diaphragmatic electrical activity were simultaneously recorded using a specific nasogastric tube in three conditions: in pressure support ventilation and in neurally adjusted ventilatory support in a random order, and then after extubation. Children in the weaning phase of mechanical ventilation. The maximal swing in esophageal pressure and esophageal pressure-time product, maximum diaphragmatic electrical activity, and inspiratory diaphragmatic electrical activity integral were calculated from 100 consecutive breaths. Neuroventilatory efficiency was estimated using the ratio of tidal volume/maximum diaphragmatic electrical activity. Sixteen patients, with a median age of 4 months (interquartile range, 0.5-13 mo), and weight 5.8 kg (interquartile range, 4.1-8 kg) were included. A strong linear correlation between maximum diaphragmatic electrical activity and maximal swing in esophageal pressure (r > 0.95), and inspiratory diaphragmatic electrical activity integral and esophageal pressure-time product (r > 0.71) was observed in all ventilatory conditions. This correlation was not modified by the type of ventilatory support. On a short-term basis, diaphragmatic electrical activity changes are strongly correlated with esophageal pressure changes. In clinical practice, diaphragmatic electrical activity monitoring may help to inform on changes in respiratory efforts.

V2a Neurons Constrain Extradiaphragmatic Respiratory Muscle Activity at Rest.

Breathing requires precise control of respiratory muscles to ensure adequate ventilation. Neurons within discrete regions of the brainstem produce oscillatory activity to control the frequency of breathing. Less is understood about how spinal and pontomedullary networks modulate the activity of respiratory motor neurons to produce different patterns of activity during different behaviors (i.e., during exercise, coughing, swallowing, vocalizing, or at rest) or following disease or injury. Here, we use a chemogenetic approach to inhibit the activity of glutamatergic V2a neurons in the brainstem and spinal cord of neonatal and adult mice to assess their potential roles in respiratory rhythm generation and patterning respiratory muscle activity. Using whole-body plethysmography (WBP), we show that V2a neuron function is required in neonatal mice to maintain the frequency and regularity of respiratory rhythm. However, silencing V2a neurons in adult mice increases respiratory frequency and ventilation, without affecting regularity. Thus, the excitatory drive provided by V2a neurons is less critical for respiratory rhythm generation in adult compared to neonatal mice. In addition, we used simultaneous EMG recordings of the diaphragm and extradiaphragmatic respiratory muscles in conscious adult mice to examine the role of V2a neurons in patterning respiratory muscle activity. We find that silencing V2a neurons activates extradiaphragmatic respiratory muscles at rest, when they are normally inactive, with little impact on diaphragm activity. Thus, our results indicate that V2a neurons participate in a circuit that serves to constrain the activity of extradiaphragmatic respiratory muscles so that they are active only when needed.

Characterization of Esophageal Motility in Infants With Congenital Diaphragmatic Hernia Using High‐resolution Manometry

The aim of the study was to characterize esophageal motility and esophagogastric junction (EGJ) function in infants who underwent repair of an isolated congenital diaphragmatic hernia (iCDH). High-resolution manometry with impedance was used to investigate esophageal motility and EGJ function after diaphragmatic repair in 12 infants with iCDH (11 left-sided; 9 patch repair). They had esophageal motility studies during neonatal admission (n = 12), at 6 months (n = 10) and at 12 months of life (n = 7). Swallows were analyzed using conventional esophageal pressure topography and pressure flow analysis and were compared with 11 healthy preterm born infants at near-term age. Esophageal peristaltic motor patterns in patients with iCDH were comparable to controls. EGJ end-expiratory pressure was higher in patients with patch repair compared with controls (P = 0.050) and those without patch (P = 0.009). The difference between inspiratory and expiratory pressures at the EGJ was lower in patients with iCDH with patch (P = 0.045) compared to patients without. Patients with iCDH with patch showed increased Pressure Flow Index, resistance of bolus flow at the EGJ, compared with controls (P = 0.043). Normal esophageal wave patterns are present in the investigated patients with iCDH. EGJ end-expiratory pressure seems lower in patients with iCDH without patch suggesting a decreased EGJ barrier function hence increased vulnerability to gastroesophageal reflux. Patch repair appears to increase end-expiratory pressure at the EGJ above that of controls suggesting that patch surgery tightens the EGJ, thereby increasing flow resistance. This is in line with the increased Pressure Flow Index. In infants with a patch, the inspiration-expiration pressure difference is lower, reflecting diminished activity of the crural diaphragm.

Cardiovascular and respiratory profiles during the sleep-wake cycle of rats previously submitted to chronic intermittent hypoxia.

What is the central question of this study? Chronic intermittent hypoxia (CIH) causes increased arterial pressure (AP), sympathetic overactivity and changes in expiratory modulation of sympathetic activity. However, changes in the short-term sleep-wake cycle pattern after CIH and their potential impact on cardiorespiratory parameters have not been reported previously. What is the main finding and its importance? Exposure to CIH for 10 days elevates AP in wakefulness and sleep but does not cause major changes in short-term sleep-wake cycle pattern. A higher incidence of muscular expiratory activity was observed in rats exposed to CIH only during wakefulness, indicating that active expiration is not required for the increase in AP in rats submitted to CIH. Chronic intermittent hypoxia (CIH) increases arterial pressure (AP) and changes sympathetic-respiratory coupling. However, the alterations in the sleep-wake cycle after CIH and their potential impact on cardiorespiratory parameters remain unknown. Here, we evaluated whether CIH-exposed rats present changes in their short-term sleep-wake cycle pattern and in cardiorespiratory parameters. Male Wistar rats (∼250g) were divided into CIH and control groups. The CIH rats were exposed to 8hday-1 of cycles of normoxia (fraction of inspired O2 =0.208, 5min) followed by hypoxia (fraction of inspired O2 =0.06, 30-40 s) for 10 days. One day after CIH, electrocorticographic activity, cervical EMG, AP and heart rate were recorded for 3h. Plethysmographic recordings were collected for 2h. A subgroup of control and CIH rats also had the diaphragm and oblique abdominal muscle activities recorded. Chronic intermittent hypoxia did not alter the time for sleep onset, total time awake, durations of rapid eye movement (REM) and non-REM (NREM) sleep and number of REM episodes in the 3h recordings. However, a significant increase in the duration of REM episodes was observed. The AP and heart rate were increased in all phases of the cycle in rats exposed to CIH. Respiratory frequency and ventilation were similar between groups in all phases, but tidal volume was increased during NREM and REM sleep in rats exposed to CIH. An increase in the incidence of active expiration during wakefulness was observed in rats exposed to CIH. The data show that CIH-related hypertension is not caused by changes in the sleep-wake cycle and suggest that active expiration is not required for the increase in AP in freely moving rats exposed to CIH.

Severe diaphragmatic dysfunction with preserved activity of accessory respiratory muscles in a critically ill child: a case report of failure of neurally adjusted ventilatory assist (NAVA) and successful support with pressure support ventilation (PSV)

BackgroundNeurally adjusted ventilatory assist (NAVA) is an alternative to pressure support ventilation (PSV) potentially improving patient-ventilator interaction. During NAVA, diaphragmatic electrical activity (EAdi) is used to trigger the ventilator and perform a proportional respiratory assistance. We present a case in which the presence of severe bilateral diaphragmatic dysfunction led to a failure of NAVA. On the contrary, the preserved activity of the accessory inspiratory muscles allowed a successful respiratory assistance using PSV.Case presentationA 10-year-old girl developed quadriplegia after neurological surgery. Initially, no spontaneous breathing activity was present and volume controlled ventilation was necessary. Two months later spontaneous inspiratory efforts were observed and a maximal negative inspiratory force of − 20 cmH2O was recorded. In addition, a NAVA nasogastric tube was placed. The recorded EAdi signal, despite showing a phasic activity, had a very low amplitude (1–2 μV). Two brief (15 min) breathing trials to compare PSV (pressure support = 8 cmH2O) with NAVA (Gain = 5 cmH2O/μV, inspiratory trigger = 0.3 μV) were performed. On PSV, the patient was well adapted with stable tidal volumes, respiratory rates, minute ventilation, end-tidal and venous carbon dioxide levels. When switched to NAVA, her breathing pattern became irregular and she showed clear sign of increased work of breathing and distress: tidal volume dropped and respiratory rate rose, leading to an increase in total minute ventilation. Nevertheless, end-tidal and venous carbon dioxide rapidly increased (from 49 to 55 mmHg and from 52 to 57 mmHg, respectively). An electromyographic study documented an impairment of the diaphragm with preserved activity of the accessory inspiratory muscles.ConclusionsWe document the failure of mechanical assistance performed with NAVA due to bilateral diaphragmatic dysfunction in a critically ill child. The preserved activity of some accessory respiratory muscles allowed to support the patient effectively with pressure support ventilation, i.e. by applying a pneumatic trigger. The present case underlines (i) the importance of the integrity of the respiratory centers, phrenic nerves and diaphragm in order to perform NAVA and (ii) the possible diagnostic role of EAdi monitoring in complex cases of weaning failure.

Inhibition of cholinesterases following percutaneous intoxication with V agents in rats

Female Wistar rats were percutaneously (p.c.) intoxicated (1xLD50) with VX and its two derivatives differing in their substitution on nitrogen (diethyl- and dibutyl- derivatives). Blood cholinesterase activity was continuously monitored; 100 min after the intoxication (or after death), acetylcholinesterase (AChE) activity was determined in diaphragm and brain parts (pontomedullar area – PM, frontal cortex – FC, and basal ganglia – BG). Blood ChE activity remains unchanged at very short interval (5 min) after VX administration; this interval was prolonged for diethyl- and dibutyl derivatives. AChE activity was decreased to 20–30% of control values in diaphragm, then in FC (60–70%) and PM (54–74%). AChE activity in BG was relatively resistant (cca 80%). When the AChE activity was compared for all three agents in relationship to survival (11 animals) or death (7 animals), significant differences between the activities in survived (32%) and died (13%) rats were demonstrated in diaphragm but not in the blood. This tendency (higher AChE activity in survived animals) was also observed in PM and FC, however, not statistically significant. It is concluded that both parts of the molecule – substitution on nitrogen atom and the rest of agent molecule (phosphorus head) probably influence penetration through the skin and simultaneously AChE inhibition. As hypothesis, AChE activity in diaphragm could be important for survival or death in case of acute p.c. intoxication with these types of V agents.

Excitation-inhibition balance regulates the patterning of spinal and cranial inspiratory motor outputs in rats in situ

Spinal phrenic nerve activity (PNA) drives the diaphragm but cranial hypoglossal nerve activity (HNA) also expresses synchronous activity during inspiration. Here, we investigated the effects of local disinhibition (bilateral microinjections of bicuculline) of the nucleus tractus solitarius (NTS), the pre-Bötzinger complex and Bötzinger complex core circuit (pre-BötC/BötC) and the Kölliker-Fuse nuclei (KFn) on the synchronization of PNA and HNA in arterially-perfused brainstem preparations of rats. To quantitatively analyze the bicuculline effects on a putatively distributed inspiratory central pattern generator (i-CPG), we quantified the phase synchronization properties between PNA and HNA. The analysis revealed that bicuculline-evoked local disinhibition significantly reduced the strength of phase synchronization between PNA and HNA at any target site. However, the emergence of desynchronized HNA following disinhibition was more prevalent after NTS or pre-BötC/BötC microinjections compared to the KFn. We conclude that the primary i-CPG is located in a distributed medullary circuit whereas pontine contributions are restricted to synaptic gating of synchronous HNA and PNA.

A hydrogel engineered to deliver minocycline locally to the injured cervical spinal cord protects respiratory neural circuitry and preserves diaphragm function

We tested a biomaterial-based approach to preserve the critical phrenic motor circuitry that controls diaphragm function by locally delivering minocycline hydrochloride (MH) following cervical spinal cord injury (SCI). MH is a clinically-available antibiotic and anti-inflammatory drug that targets a broad range of secondary injury mechanisms via its anti-inflammatory, anti-oxidant and anti-apoptotic properties. However, MH is only neuroprotective at high concentrations that cannot be achieved by systemic administration, which limits its clinical efficacy. We have developed a hydrogel-based MH delivery system that can be injected into the intrathecal space for local delivery of high concentrations of MH, without damaging spinal cord tissue. Implantation of MH hydrogel after unilateral level-C4/5 contusion SCI robustly preserved diaphragm function, as assessed by in vivo recordings of compound muscle action potential (CMAP) and electromyography (EMG) amplitudes. MH hydrogel also decreased lesion size and degeneration of cervical motor neuron somata, demonstrating its central neuroprotective effects within the injured cervical spinal cord. Furthermore, MH hydrogel significantly preserved diaphragm innervation by the axons of phrenic motor neurons (PhMNs), as assessed by both detailed neuromuscular junction (NMJ) morphological analysis and retrograde PhMN labeling from the diaphragm using cholera toxin B (CTB). In conclusion, our findings demonstrate that local MH hydrogel delivery to the injured cervical spinal cord is effective in preserving respiratory function after SCI by protecting the important neural circuitry that controls diaphragm activation.

Diaphragm Stimulation Enhances Respiratory Function After Cervical Spinal Cord Injury

Purpose/HypothesisCervical spinal cord injury (CSCI) causes severe respiratory impairment and respiratory complications are a leading cause of illness and death. Although mechanical ventilation (MV) is lifesaving, MV use is associated with diaphragm atrophy and high respiratory infection rates. Intramuscular diaphragm stimulation, or diaphragm pacing (DP), is now used acutely to promote MV weaning. Preliminary reports suggest that DP may improve diaphragm activation, respiratory function, and promote recovery of independent respiration. The effects of DP, however, have not been systematically evaluated. Our purpose was to test the hypothesis that DP leads to an increase in voluntary diaphragm activation and improvements in respiratory function.SubjectsEleven adults with acute, traumatic CSCIs (6 males, mean age 40.8±12 years) who underwent implantation of DP wires due to failure to wean from MV participated (mean time on MV until DP wire implantation 16±10 days). Injuries were classified as C1 to C4 based on the ASIA Impairment Scale A or B (motor complete, n=10) and C (motor incomplete, n=1).Materials/MethodsRespiratory function and diaphragm activation were assessed within 3 days post implantation of the DP wires and assessments were repeated at regular intervals up to four months post DP implantation. Respiratory function was assessed using standard measures of tidal volume (Vt), forced vital capacity (FVC), and maximal inspiratory and expiratory pressures (MIP, MEP). Diaphragm activation was assessed by recording electromyograms (EMGs) from the intramuscular DP wires during maximal inspiratory maneuvers. All tests were conducted without assistance from DP and with the lowest ventilator setting tolerated.ResultsFollowing onset of DP, 9 of 11 individuals weaned from MV (mean time 35±24 days) and 6 individuals resumed independent respiration without use of DP. All measures of respiratory function increased over time (p<0.05). Average gains in respiratory function were: Vt, +24±31% (range −31 – 77%); FVC, +37±16% (range 17 – 63%); MIP, +43±56% (range −45 – 124%); MEP +67±64% (range −31 – 176%). Mean peak EMG burst amplitude during maximal inspiratory maneuvers increased 20% (range 0 – 92%).ConclusionsDuring an extended period of DP, adults with severe CSCIs demonstrated gains in respiratory function and volitional diaphragm activation. Nearly all individuals weaned from MV and over half progressed to independent respiration following onset of DP. Stimulation of the diaphragm is likely to promote muscle health which would contribute to weaning. In addition, the increased diaphragm muscle activation in many subject raises the possibility that DP and associated activation of sensory afferents evokes beneficial plasticity in the respiratory neural control system.Support or Funding InformationCraig H. Neilsen Foundation (EJF); NIH/NICHD K12 HD055929 (EJF); T32‐HD043730 (MDS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inspiratory pressure‐generating capacity is preserved during ventilatory and non‐ventilatory behaviours despite profound diaphragm muscle weakness in young adult dystrophic (mdx) mice

Diaphragm dysfunction is recognized in the mdx mouse model of muscular dystrophy, however there is a paucity of information concerning the neural control of dystrophic respiratory muscles. In young adult (8 weeks of age) male wild‐type and mdx mice, we assessed ventilatory capacity, neural activation of the diaphragm and external intercostal (EIC) muscles and inspiratory pressure‐generating capacity during ventilatory and non‐ventilatory behaviours. We hypothesized that respiratory muscle weakness is associated with impaired peak inspiratory pressure‐generating capacity in mdx mice.Ventilatory responsiveness to hypercapnic hypoxia was determined in conscious mice by whole‐body plethysmography. Diaphragm isometric and isotonic contractile properties were determined ex vivo. In anaesthetized mice, thoracic oesophageal pressure, and diaphragm and EIC electromyogram (EMG) activities were recorded during baseline conditions and sustained tracheal occlusion for 30–40s.Despite substantial diaphragm weakness, mdx mice retain the capacity to enhance ventilation during hypercapnic hypoxia. Peak volume‐ and flow‐related measures were also maintained in anaesthetized, vagotomized mdx mice. Peak inspiratory pressure was remarkably well preserved during chemoactivated breathing, augmented breaths, and maximal sustained efforts during airway obstruction in mdx mice. Diaphragm and EIC EMG activities were lower during airway obstruction in mdx compared with wild‐type mice.We conclude that ventilatory capacity is preserved in young mdx mice. Despite profound respiratory muscle weakness and lower diaphragm and EIC EMG activities during high demand in mdx mice, peak inspiratory pressure is preserved, owing to sufficient compensatory recruitment of accessory muscles beyond the primary muscles of inspiration. We suggest that a loss of compensation during progressive disease, combined with diaphragm dysfunction, underpins the development of respiratory system morbidity in dystrophic diseases.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vagal and spinal pulmonary afferents contribute to respiratory variability and gender‐specific response to mechanical challenge

Respiratory variability is important in order to respond to internal and external perturbations. While vagal afferents have been shown to be important for feedback during breathing, the influence of spinal afferents has not been as well described. We hypothesized that disruption of vagal and spinal afferents reduces respiratory variability during eupnea and alters respiratory response during thoracic mechanical restriction (banding). We measured costal diaphragm and thyroarytenoid electromyography (EMG) activity in sodium pentobarbital anesthetized spontaneously breathing male and female Sprague Dawley rats. We conducted three sets of experiments to elucidate contributions of vagal, and spinal afferents: A) inhalation of 10% nebulized lidocaine to attenuate pulmonary vagal afferents B) bilateral injections of 10% lidocaine into the pleural space to attenuate thoracic afferent feedback; C) bilateral tracheal vagotomy caudal to the larynx. Solutions of 10% lidocaine were mixed with saline and 2% Evans Blue dye to confirm the distribution of lidocaine following nebulization and injection. Additionally, banding was performed before and after each experimental protocol. Banding significantly increased costal diaphragm amplitude which was further increased with each intervention, however there was a gender specific increase in thyroarytenoid activity with only ~50% of males demonstrating this phenomenon. Both lidocaine protocols demonstrated features of vagotomy including reduction of each eupneic phase duration coefficient of variance as well as alterations in EMG amplitude. These results demonstrate gender‐specific effects of the respiratory system to challenges, and provide preliminary evidence of the importance of non‐vagal pulmonary feedback. Moreover, this present study could have broad clinical implications in disorders such as spinal cord injury.Support or Funding InformationThis work was supported by NIH grants HL 111215, HL 103415 and OT20D001983, the Craig F. Neilson Foundation Pilot Research Grant 546714, Kentucky Spinal Cord and Head Injury Research Trust, and the Commonwealth of Kentucky Challenge for Excellence.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Apolipoprotein E modulates respiratory motor plasticity following cervical spinal cord injury

Each year, 17,700 Americans suffer a spinal cord injury, over half of which occur at the cervical level. These high level injuries can interrupt bulbospinal neurons that innervate the phrenic motornucleus, the origin of the phrenic nerve. Loss of these descending inputs to the phrenic nerve paralyzes the ipsilateral diaphragm, leading to breathing impairments. One approach to promote recovery of breathing function is by enhancing plasticity through strengthening of synapses or activating spared but latent pathways in the spinal cord. Activation of the latent crossed phrenic pathway can lead to a form of respiratory motor plasticity known as long term facilitation (LTF), which is characterized by a prolonged increase in breathing motor output. LTF can be induced through exposure to intermittent hypoxia (IH) or by intermittently dosing the spinal cord with serotonin (5‐HT). While a portion of the spinal cord injured population responds to IH therapy with the expected increase in respiratory output, others remain non‐responders. This inconsistency indicates that variability in the human population may influence how individuals respond to treatments that aim to enhance plasticity. Therefore, we propose that genetic diversity among the SCI population could be a key factor in determining an individual's propensity for plasticity. Apolipoprotein E (apoE) is a promising candidate gene that could be responsible for this variability because one of the apoE alleles, E4, has previously been shown to reduce synaptic plasticity by decreasing expression of glutamate receptors when compared to the E2 or E3 alleles. The present study investigates the influence of human apoE4 on respiratory motor plasticity in rats following C2 hemisection. 20 weeks after injury, rats were dosed with one isoform of the human apoE protein, E3 or E4, prior to receiving intermittent 5‐HT to induce LTF. Diaphragmatic EMG recordings demonstrated that animals exposed to human apoE3 protein exhibited an increase in diaphragmatic activity ipsilateral to the injury, but this increase was abolished in E4 dosed animals. Analysis of tissue dosed with human apoE protein indicated that apoE also modulates synaptic expression of glutamate receptors, a crucial component of LTF induction. Collectively, these experiments demonstrate ApoE4's potential to inhibit plasticity following spinal cord injury, emphasizing the importance of considering genetic diversity while developing SCI therapeutics for the human population.Support or Funding InformationNational Science Foundation Graduate Research Fellowship, University of Kentucky College of Medicine Fellowship for Excellence in Graduate Research, University of Kentucky Startup FundsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Impact of spontaneous breathing during mechanical ventilation in acute respiratory distress syndrome.

Facilitating spontaneous breathing has been traditionally recommended during mechanical ventilation in acute respiratory distress syndrome (ARDS). However, early, short-term use of neuromuscular blockade appears to improve survival, and spontaneous effort has been shown to potentiate lung injury in animal and clinical studies. The purpose of this review is to describe the beneficial and deleterious effects of spontaneous breathing in ARDS, explain potential mechanisms for harm, and provide contemporary suggestions for clinical management. Gentle spontaneous effort can improve lung function and prevent diaphragm atrophy. However, accumulating evidence indicates that spontaneous effort may cause or worsen lung and diaphragm injury, especially if the ARDS is severe or spontaneous effort is vigorous. Recently, such effort-dependent lung injury has been termed patient self-inflicted lung injury (P-SILI). Finally, several approaches to minimize P-SILI while maintaining some diaphragm activity (e.g. partial neuromuscular blockade, high PEEP) appear promising. We update and summarize the role of spontaneous breathing during mechanical ventilation in ARDS, which can be beneficial or deleterious, depending on the strength of spontaneous activity and severity of lung injury. Future studies are needed to determine ventilator strategies that minimize injury but maintaining some diaphragm activity.

Differential effects of a 5‐HT1A receptor agonist on breathing and swallow motor patterns

Swallow disorder (dysphagia) can cause aspiration and lead to pneumonia in a number of patient populations, including individuals with cervical spinal cord injury. Dysphagia is characterized by dysfunction in the swallow motor pattern, which is a sequential activation of muscles that propels the bolus into the esophagus and prevents entry into the airway. Diaphragm activity contributes to effective swallow by generating negative pressure which draws the bolus into the esophagus. There currently are no effective pharmacological treatments for dysphagia, and we aim to explore the effects of a potential treatment agent by first assessing its effects on baseline breathing and swallow. We use EMG to record breathing patterns and water‐induced swallow in pentobarbital‐anesthetized spontaneously breathing cats. EMGs are recorded from the mylohyoid, thyrohyoid, thyroarytenoid, thyropharyngeus, cricopharyngeus (upper esophageal sphincter), and diaphragm muscles, and trans‐diaphragmatic pressure is measured by monitoring esophageal and stomach pressures. The serotonin 5‐HT1A receptor agonist 8‐OH‐DPAT is delivered via the vertebral artery in doses ranging from 1μg/kg – 50 μg/kg. We report here differential effects of low‐dose (3 μg/kg) and high dose (30 μg/kg) 8‐OH‐DPAT on swallow‐breathing coordination, behavior‐specific muscle recruitment patterns, and the sequential muscle activation necessary for proper movement of a bolus through the pharynx. This work will potentially inform treatment of patients with dysphagia, including those with cervical spinal cord injuries.Support or Funding InformationThis work was supported by NIH grants HL 111215, HL 103415 and OT20D001983, the Craig F. Neilson Foundation Pilot Research Grant 546714, Veterans Affairs Rehabilitation, Research and Development RCSB92495 (DRH), Kentucky Spinal Cord and Head Injury Research Trust, Rebecca F. Hammond Endowment (DRH), and the Commonwealth of Kentucky Challenge for Excellence.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ultrasonography comparison of diaphragm thickness and excursion between athletes with and without lumbopelvic pain

ObjectiveThe aim of this study was to compare diaphragm thickness and excursion between athletes with and without lumbopelvic pain (LPP) by trans-costal and trans-hepatic rehabilitative ultrasound imaging (RUSI), respectively. DesignA case-control study. SettingAmateur and semiprofessional athletes teams. ParticipantsForty matched-paired athletes with LPP (n = 20; LPP case group) and without LPP (n = 20; Healthy control group) were recruited. Main outcome measuresDiaphragm thickness and excursion (cm) were assessed during relaxed respiratory activity (maximum inspiration–Tins, expiration–Texp and difference–Tins-exp) by trans-costal and trans-hepatic rehabilitative ultrasound imaging (RUSI), respectively. ResultsStatistically significant differences (P < .05) with an effect size from moderate to large (d = 0.63–1.07) were shown for bilateral diaphragm thickness reductions at Tins and thickness difference at Tins-Texp of the right hemi-diaphragm for athletes with LPP compared to healthy athletes. ConclusionsAthletes who suffered from LPP presented a reduced diaphragm thickness compared to healthy matched-paired athletes. Therefore, these novel findings may suggest that diaphragm reeducation could be a main focus of intervention related to athletic performance, prevention and rehabilitation. Nevertheless, these findings should be considered with caution due to the possible influence of the RUSI measurement errors of the diaphragm activation during normal breathing.