Diaphragm pacing: the state of the art

Diaphragm pacing compared with mechanical ventilation in patients with chronic respiratory failure caused by diaphragmatic dysfunction: a systematic review and meta-analysis

BACKGROUND

The effectiveness of diaphragmatic electrical stimulation (DES) compared to mechanical ventilation (MV) in improving clinical outcomes such as quality-of-life (QOL) and hospital stay remains inconsistent.

METHODS

We conducted a systematic review and meta-analysis by searching PubMed, Scopus, Google Scholar, LILACS, and IEEE Xplore. We included comparative studies (randomized controlled trials and observational studies) of DES administered via the phrenic nerve or intramuscular electrodes, compared with MV in adults with diaphragmatic paralysis or paresis. Two authors independently extracted data and assessed bias, with discrepancies resolved by a senior author. Results were pooled using the inverse variance method.

RESULTS

Out of 1,290 articles, nine were included in the systematic review, totaling 852 subjects. In spinal cord injury (SCI), one study reported lower mortality with DES, while three found no difference compared to MV. In these patients, DES was associated with shorter hospital stay, similar QOL, and heterogeneous results on respiratory infections. In amyotrophic lateral sclerosis (ALS), DES was associated with higher mortality and similar QOL compared to MV. Most SCI studies had a serious risk of bias.

CONCLUSION

DES shows potential in reducing hospital stay and respiratory infections in SCI but is associated with higher mortality in ALS.

Lung and Diaphragm Protection During Mechanical Ventilation in Patients with Acute Respiratory Distress Syndrome

Patients with acute respiratory distress syndrome often require mechanical ventilation to maintain adequate gas exchange and to reduce the workload of the respiratory muscles. Although lifesaving, positive pressure mechanical ventilation can potentially injure the lungs and diaphragm, further worsening patient outcomes. While the effect of mechanical ventilation on the risk of developing lung injury is widely appreciated, its potentially deleterious effects on the diaphragm have only recently come to be considered by the broader intensive care unit community. Importantly, both ventilator-induced lung injury and ventilator-induced diaphragm dysfunction are associated with worse patient-centered outcomes.

Bilateral Diaphragmatic Paresis Due to an Iatrogenic Injury of the Phrenic Nerve: A Case Report

Bilateral diaphragmatic paresis is a rare entity with unknown incidence and is associated with severe respiratory dysfunction. In this case report we present a 69-year-old patient who sought emergency services due to dyspnea, orthopnea, and paroxysmal nocturnal dyspnea. The patient denied other complaints and mentioned that these symptoms began after being discharged from a hospitalisation for emphysematous acute cholecystitis, where he underwent laparoscopic cholecystectomy, which was complicated by extensive hemorrhage of the abdominal wall. On the physical examination, paradoxical breathing and peripheral oxygen saturation between 80-93% in supine and standing positions, respectively, were notable. The patient was admitted for further investigation, during which thoracic radiographs in inspiration and expiration showed no positional variation of the diaphragm, respiratory function tests revealed a restrictive pattern and electromyography demonstrated acute bilateral diaphragmatic neuropathic injury compatible with phrenic nerve injury. Therefore, by temporal correlation and exclusion of other apparent causes, an etiology in the context of the cholecystectomy was inferred. The patient was evaluated in a multidisciplinary manner and is currently undergoing a cardiopulmonary rehabilitation program in the Physical Medicine and Rehabilitation service, although with limited progress and still requiring non-invasive ventilation.

In a porcine model of implantable pacemakers for pediatric unilateral diaphragm paralysis, the phrenic nerve is the best target

BACKGROUND

A frequent complication of Fontan operations is unilateral diaphragmatic paresis, which leads to hemodynamic deterioration of the Fontan circulation. A potential new therapeutic option is the unilateral diaphragmatic pacemaker. In this study, we investigated the most effective stimulation location for a potential fully implantable system in a porcine model.

METHODS

Five pigs (20.8 ± 0.95 kg) underwent implantation of a customized cuff electrode placed around the right phrenic nerve. A bipolar myocardial pacing electrode was sutured adjacent to the motor point and peripherally at the costophrenic angle (peripheral diaphragmatic muscle). The electrodes were stimulated 30 times per minute with a pulse duration of 200 µs and a stimulation time of 300 ms. Current intensity was the only variable changed during the experiment.

RESULTS

Effective stimulation occurred at 0.26 ± 0.024 mA at the phrenic nerve and 7 ± 1.22 mA at the motor point, a significant difference in amperage (p = 0.005). Even with a maximum stimulation of 10 mA at the peripheral diaphragm muscle, however, no effective stimulation was observed.

CONCLUSION

The phrenic nerve seems to be the best location for direct stimulation by a unilateral thoracic diaphragm pacemaker in terms of the required amperage level in a porcine model.

Temporary diaphragm pacing for patients at risk of prolonged mechanical ventilation after extensive aortic repair

Objective

Prolonged mechanical ventilation (MV) after extensive aortic reconstructive surgery is common. Studies have demonstrated that diaphragm pacing (DP) improves lung function in patients with unilateral diaphragm paralysis. The goal of this study is to determine whether this technology can be applied to complex aortic repair to reduce prolonged MV and other respiratory sequelae.

Methods

A retrospective review was performed of patients who underwent temporary DP after extensive aortic reconstructive surgery between 2019 and 2022. The primary end point was prolonged MV incidence. Other measured end points included diaphragm electromyography improvement, length of hospitalization, duration of intensive care unit stay, and reintubation rates.

Results

Fourteen patients deemed at high risk of prolonged MV based on their smoking and respiratory history underwent DP after extensive aortic repair. The mean age was 70.2 years. The indications for aortic repair were a thoracoabdominal aortic aneurysm (n = 8, including 2 ruptured, 2 symptomatic, and 1 mycotic), a perivisceral aneurysm (n = 4), and a perivisceral coral reef aorta (n = 2). All patients had a significant smoking history (active or former) or other risk factors for ventilator-induced diaphragmatic dysfunction and prolonged MV. The mean total duration of MV postoperatively was 31.9 hours (range, 8.1-76.5 hours). The total average pacing duration was 4.4 days. Two patients required prolonged MV, with an average of 75.4 hours. Two patients required reintubation. No complications related to DP wire placement or removal occurred.

Conclusions

DP is safe and feasible for patients at high risk of pulmonary insufficiency after extensive aortic reconstructive surgery.

Phrenic Nerve Stimulation for Acute Respiratory Failure

Diaphragm inactivity during invasive mechanical ventilation leads to diaphragm atrophy and weakness, hemodynamic instability, and ventilatory heterogeneity. Absent respiratory drive and effort can, therefore, worsen injury to both lung and diaphragm and is a major cause of failure to wean. Phrenic nerve stimulation (PNS) can maintain controlled levels of diaphragm activity independent of intrinsic drive and as such may offer a promising approach to achieving lung and diaphragm protective ventilatory targets. Whereas PNS has an established role in the management of chronic respiratory failure, there is emerging interest in how its multisystem putative benefits may be temporarily harnessed in the management of invasively ventilated patients with acute respiratory failure.

Efficacy of aerobic training and resistance training combined with external diaphragm pacing in patients with chronic obstructive pulmonary disease: A randomized controlled study

OBJECTIVE

To evaluate the efficacy of aerobic training, resistance training combined with external diaphragm pacing in patients with chronic obstructive pulmonary disease.

DESIGN

Randomized controlled trial.

SETTING

The Fourth Rehabilitation Hospital of Shanghai, China.

PARTICIPANTS

82 (67.0  ±  6.5 years, 59.8% male) patients with stable chronic obstructive pulmonary disease were randomized to intervention group 1 (n  =  27), intervention group 2 (n  =  28), and control group (n  =  27).

INTERVENTION

Intervention group 1 received aerobic and resistance training, while intervention group 2 received additional external diaphragm pacing. Control group received aerobic training only.

MAIN MEASURES

1-year follow-up of physical activity, body composition, respiratory function and diaphragm function.

RESULTS

Intervention groups 1 and 2 showed statistically improvements in the difference value compared with control group in terms of 6-min walk distance (-95.28  ±  20.09 and -101.92  ±  34.91 vs -63.58  ±  23.38), forced expiratory volume in 1 s (-0.042  ±  0.027 and -0.130  ±  0.050 vs -0.005  ±  0.068), fat-free mass (-2.11  ±  3.74 and -3.82  ±  3.74vs 0.28  ±  1.49) and chronic obstructive pulmonary disease assessment test value (2.16  ±  0.85 and 2.38  ±  1.02 vs 1.50  ±  0.93). Intervention group 2 showed significant difference in arterial oxygen pressure (-4.46  ±  3.22 vs -1.92  ±  3.45), diaphragm excursion during deep breaths (-0.82  ±  0.74 vs -0.38  ±  0.29), and diaphragm thickness fraction (-8.77  ±  3.22 vs -4.88  ±  2.69) compared with control group.

CONCLUSION

The combination of aerobic training, resistance training, and external diaphragm pacing obtained significant improvements in physical activity, respiratory function, body composition, arterial oxygen pressure, and diaphragm function in patients with chronic obstructive pulmonary disease.

TRIAL REGISTRATION

ChiCTR1800020257, www.chictr.org.cn/index.aspx.

Neuroprosthesis for individuals with spinal cord injury

OBJECTIVE

Individuals who sustain a traumatic spinal cord injury (SCI) often have a loss of multiple body systems. Significant functional improvement can be gained by individual SCI through the use of neuroprostheses based on electrical stimulation. The most common actions produced are grasp, overhead reach, trunk posture, standing, stepping, bladder/bowel/sexual function, and respiratory functions.

METHODS

We review the fundamental principles of electrical stimulation, which are established, allowing stimulation to be safely delivered through implanted devices for many decades. We review four common clinical applications for SCI, including grasp/reach, standing/stepping, bladder/bowel function, and respiratory functions. Systems used to implement these functions have many common features, but are also customized based on the functional goals of each approach. Further, neuroprosthetic systems are customized based on the needs of each user.

RESULTS & CONCLUSION

The results to date show that implanted neuroprostheses can have a significant impact on the health, function, and quality of life for individuals with SCI. A key focus for the future is to make implanted neuroprostheses broadly available to the SCI population.

Proof of concept of an accelerometer as a trigger for unilateral diaphragmatic pacing: a porcine model

BACKGROUND

Unilateral diaphragmatic paralysis in patients with univentricular heart is a known complication after pediatric cardiac surgery. Because diaphragmatic excursion has a significant influence on perfusion of the pulmonary arteries and hemodynamics in these patients, unilateral loss of function leads to multiple complications. The current treatment of choice, diaphragmatic plication, does not lead to a full return of function. A unilateral diaphragmatic pacemaker has shown potential as a new treatment option. In this study, we investigated an accelerometer as a trigger for a unilateral diaphragm pacemaker (closed-loop system).

METHODS

Seven pigs (mean weight 20.7 ± 2.25 kg) each were implanted with a customized accelerometer on the right diaphragmatic dome. Accelerometer recordings (mV) of the diaphragmatic excursion of the right diaphragm were compared with findings using established methods (fluoroscopy [mm]; ultrasound, M-mode [cm]). For detection of the amplitude of diaphragmatic excursions, the diaphragm was stimulated with increasing amperage by a cuff electrode implanted around the right phrenic nerve.

RESULTS

Results with the different techniques for measuring diaphragmatic excursions showed correlations between accelerometer and fluoroscopy values (correlation coefficient 0.800, P < 0.001), accelerometer and ultrasound values (0.883, P < 0.001), and fluoroscopy and ultrasound values (0.816, P < 0.001).

CONCLUSION

The accelerometer is a valid method for detecting diaphragmatic excursion and can be used as a trigger for a unilateral diaphragmatic pacemaker.

Waiting to Inhale: Preventing Fatality From Seizure-Induced Apnea

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Feasibility of transesophageal phrenic nerve stimulation

BACKGROUND

Every year, more than 2.5 million critically ill patients in the ICU are dependent on mechanical ventilation. The positive pressure in the lungs generated by the ventilator keeps the diaphragm passive, which can lead to a loss of myofibers within a short time. To prevent ventilator-induced diaphragmatic dysfunction (VIDD), phrenic nerve stimulation may be used.

OBJECTIVE

The goal of this study is to show the feasibility of transesophageal phrenic nerve stimulation (TEPNS). We hypothesize that selective phrenic nerve stimulation can efficiently activate the diaphragm with reduced co-stimulations.

METHODS

An in vitro study in saline solution combined with anatomical findings was performed to investigate relevant stimulation parameters such as inter-electrode spacing, range to target site, or omnidirectional vs. sectioned electrodes. Subsequently, dedicated esophageal electrodes were inserted into a pig and single stimulation pulses were delivered simultaneously with mechanical ventilation. Various stimulation sites and response parameters such as transdiaphragmatic pressure or airway flow were analyzed to establish an appropriate stimulation setting.

RESULTS

Phrenic nerve stimulation with esophageal electrodes has been demonstrated. With a current amplitude of 40 mA, similar response figures of the diaphragm activation as compared to conventional stimulation with needle electrodes at 10mA were observed. Directed electrodes best aligned with the phrenic nerve resulted in up to 16.9 % higher amplitude at the target site in vitro and up to 6 cmH20 higher transdiaphragmatic pressure in vivo as compared to omnidirectional electrodes. The activation efficiency was more sensitive to the stimulation level inside the esophagus than to the inter-electrode spacing. Most effective and selective stimulation was achieved at the level of rib 1 using sectioned electrodes 40 mm apart.

CONCLUSION

Directed transesophageal phrenic nerve stimulation with single stimuli enabled diaphragm activation. In the future, this method might keep the diaphragm active during, and even support, artificial ventilation. Meanwhile, dedicated sectioned electrodes could be integrated into gastric feeding tubes.

Cervical Epidural Electrical Stimulation Increases Respiratory Activity through Somatostatin-Expressing Neurons in the Dorsal Cervical Spinal Cord in Rats

We tested the hypothesis that dorsal cervical epidural electrical stimulation (CEES) increases respiratory activity in male and female anesthetized rats. Respiratory frequency and minute ventilation were significantly increased when CEES was applied dorsally to the C2-C6 region of the cervical spinal cord. By injecting pseudorabies virus into the diaphragm and using c-Fos activity to identify neurons activated during CEES, we found neurons in the dorsal horn of the cervical spinal cord in which c-Fos and pseudorabies were co-localized, and these neurons expressed somatostatin (SST). Using dual viral infection to express the inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADD), hM4D(Gi), selectively in SST-positive cells, we inhibited SST-expressing neurons by administering Clozapine N-oxide (CNO). During CNO-mediated inhibition of SST-expressing cervical spinal neurons, the respiratory excitation elicited by CEES was diminished. Thus, dorsal cervical epidural stimulation activated SST-expressing neurons in the cervical spinal cord, likely interneurons, that communicated with the respiratory pattern generating network to effect changes in ventilation.SIGNIFICANCE STATEMENT A network of pontomedullary neurons within the brainstem generates respiratory behaviors that are susceptible to modulation by a variety of inputs; spinal sensory and motor circuits modulate and adapt this output to meet the demands placed on the respiratory system. We explored dorsal cervical epidural electrical stimulation (CEES) excitation of spinal circuits to increase ventilation in rats. We identified dorsal somatostatin (SST)-expressing neurons in the cervical spinal cord that were activated (c-Fos-positive) by CEES. CEES no longer stimulated ventilation during inhibition of SST-expressing spinal neuronal activity, thereby demonstrating that spinal SST neurons participate in the activation of respiratory circuits affected by CEES. This work establishes a mechanistic foundation to repurpose a clinically accessible neuromodulatory therapy to activate respiratory circuits and stimulate ventilation.

Diaphragm Pacing: A Safety, Appropriateness, Financial Neutrality, and Efficacy Analysis of Treating Chronic Respiratory Insufficiency

OBJECTIVES

This study aimed to evaluate the safety and applicability of treating chronic respiratory insufficiency with diaphragm pacing relative to mechanical ventilation.

MATERIALS AND METHODS

A literature review and analysis were conducted using the safety, appropriateness, financial neutrality, and efficacy principles.

RESULTS

Although mechanical ventilation is clearly indicated in acute respiratory failure, diaphragm pacing improves life expectancy, increases quality of life, and reduces complications in patients with chronic respiratory insufficiency.

CONCLUSION

Diaphragm pacing should be given more consideration in appropriately selected patients with chronic respiratory insufficiency.

Diaphragm pacing using the minimally invasive cervical approach

CONTEXT

The implantation of commercially available phrenic nerve/diaphragm pacers has been available for more than 40 years and has enabled thousands of patients in over 40 countries to achieve freedom from invasive mechanical ventilation.

OBJECTIVE

The cervical approach to implantation of these pacers is described, as are the pros and cons of using this technique compared to intrathoracic and sub-diaphragmatic.

METHODS

Study design was a retrospective review of 1,522 subjects from the Avery Biomedical Devices (ABD) database who were implanted with the Avery diaphragm pacer. Long term statistics from patients implanted with diaphragm pacers are presented as well.

RESULTS

17% of cervically placed electrodes required at least one replacement compared to 18% of electrodes placed thoracically. Devices implanted cervically show no significant difference in their longevity than those implanted using the thoracic approach (P value of 0.9382 using Two-Sample t-Test). The mean longevity for both approaches was found to be 6.4 years. The majority of electrodes implanted have never required replacement. A majority of CCHS patients were implanted using the thoracic approach and only find it necessary to use the device during sleeping hours. Most of the cervically implanted patients are found to be older at the time of implantation and implanted for diagnoses that require longer daily use of the device.

CONCLUSION

The cervical approach for the implantation of phrenic nerve/diaphragm pacers is the most minimally invasive, but underutilized, technique that allows for the use of local or monitored anesthesia, does not require entering any body cavities, and keeps incision size small.

Diaphragmatic pacing for the prevention of sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy is the leading cause of epilepsy related death. Currently, there are no reliable methods for preventing sudden unexpected death in epilepsy. The precise pathophysiology of sudden unexpected death in epilepsy is unclear; however, convergent lines of evidence suggest that seizure-induced respiratory arrest plays a central role. It is generally agreed that sudden unexpected death in epilepsy could be averted if the patient could be rapidly ventilated following the seizure. The diaphragm is a muscle in the chest which contracts to draw air into the lungs. Diaphragmatic pacing is a surgical intervention which facilitates normal ventilation in situations, such as spinal cord injury and sleep apnoea, in which endogenous respiration would be inadequate or non-existent. In diaphragmatic pacing, electrodes are implanted directly onto diaphragm or adjacent to the phrenic nerves which innervate the diaphragm. These electrodes are then rhythmically stimulated, thereby eliciting contractions of the diaphragm which emulate endogenous breathing. The goal of this study was to test the hypothesis that seizure-induced respiratory arrest and death can be prevented with diaphragmatic pacing. Our approach was to induce respiratory arrest using maximal electroshock seizures in adult, male, C57BL6 mice outfitted with EEG and diaphragmatic electrodes (n = 8 mice). In the experimental group, the diaphragm was stimulated to exogenously induce breathing. In the control group, no stimulation was applied. Breathing and cortical electrographic activity were monitored using whole body plethysmography and EEG, respectively. A majority of the animals that did not receive the diaphragmatic pacing intervention died of seizure-induced respiratory arrest. Conversely, none of the animals that received the diaphragmatic pacing intervention died. Diaphragmatic pacing improved postictal respiratory outcomes (two-way ANOVA, P < 0.001) and reduced the likelyhood of seizure-induced death (Fisher's exact test, P = 0.026). Unexpectedly, diaphragmatic pacing did not instantly restore breathing during the postictal period, potentially indicating peripheral airway occlusion by laryngospasm. All diaphragmatically paced animals breathed at some point during the pacing stimulation. Two animals took their first breath prior to the onset of pacing and some animals had significant apnoeas after the pacing stimulation. Sudden unexpected death in epilepsy results in more years of potential life lost than any other neurological condition with the exception of stroke. By demonstrating that seizure-induced respiratory arrest can be prevented by transient diaphragmatic pacing in animal models we hope to inform the development of closed-loop systems capable of detecting and preventing sudden unexpected death in epilepsy.

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Diaphragm pacing implantation in Japan for a patient with cervical spinal cord injury: A case report

RATIONALE

Traumatic cervical spinal cord injury (SCI) is a devastating condition leading to respiratory failure that requires permanent mechanical ventilation, which is the main driver of increased medical costs. There is a great demand for establishing therapeutic interventions to treat respiratory dysfunction following severe cervical SCI.

PATIENT CONCERNS AND DIAGNOSIS

We present a 24-year-old man who sustained a cervical displaced C2-C3 fracture with SCI due to a traffic accident. As the patient presented with tetraplegia and difficulty in spontaneous breathing following injury, he was immediately intubated and placed on a ventilator with cervical external fixation by halo orthosis. The patient then underwent open reduction and posterior fusion of the cervical spine 3 weeks after injury. Although the patient showed significant motor recovery of the upper and lower limbs over time, only a slight improvement in lung capacity was observed.

INTERVENTIONS AND OUTCOMES

At 1.5 years after injury, a diaphragmatic pacing stimulator was surgically implanted to support the patient's respiratory function. The mechanical ventilator support was successfully withdrawn from the patient 14 weeks after implantation. We observed that both the vital capacity and tidal volume of the patient were significantly promoted following implantation. The patient finally returned to daily life without any mechanical support.

LESSONS

The findings of this report suggest that diaphragmatic pacing implantation could be a promising treatment for improving respiratory function after severe cervical SCI. To our knowledge, this is the first SCI patient treated with a diaphragm pacing implantation covered by official medical insurance in Japan.

Prospective analysis of a surgical algorithm to achieve ventilator weaning in cervical tetraplegia

Objectives: Chronic ventilator dependency in cervical tetraplegia is associated with substantial morbidity. When non-invasive weaning methods have failed the primary surgical treatment is diaphragm pacing. Phrenic nerve integrity and diaphragm motor units are requirements for effective pacing but may need to be restored for successful weaning. A surgical algorithm that includes: 1. Diaphragm pacing, 2. Phrenic nerve reconstruction, and 3. Diaphragm muscle replacement, may provide the capability of reducing or reversing ventilator dependency in virtually all cervical tetraplegics.Design: Prospective case series.Setting: A university-based hospital from 2015 to 2019.Participants: Ten patients with ventilator-dependent cervical tetraplegia.Interventions: I. Pacemaker alone, II. Pacemaker + phrenic nerve reconstruction, or III. Pacemaker + diaphragm muscle replacement.Outcome measures: Time from surgery to observed reduction in ventilator requirements (↓VR), ventilatory needs as of most recent follow-up [no change (NC), partial weaning (PW, 1-12 h/day), or complete weaning (CW, >12 h/day)], and complications.Results: Both patients in Group I achieved CW at 6-month follow-up. Two patients in Group II achieved CW, and in another two patients PW was achieved, at 1.5-2-year follow-up. The remaining two patients are NC at 6 and 8-month follow-up, respectively. In group III, both patients achieved PW at 2-year follow-up. Complications included mucous plugging (n = 1) and pacemaker malfunction requiring revision (n = 3).Conclusion: Although more investigation is necessary, phrenic nerve reconstruction or diaphragm muscle replacement performed (when indicated) with pacemaker implantation may allow virtually all ventilator-dependent cervical tetraplegics to partially or completely wean.

Diaphragmatic Activity and Respiratory Function Following C3 or C6 Unilateral Spinal Cord Contusion in Mice

The majority of spinal cord injuries (SCIs) are cervical (cSCI), leading to a marked reduction in respiratory capacity. We aimed to investigate the effect of hemicontusion models of cSCI on both diaphragm activity and respiratory function to serve as preclinical models of cervical SCI. Since phrenic motoneuron pools are located at the C3-C5 spinal level, we investigated two models of preclinical cSCI mimicking human forms of injury, namely, one above (C3 hemicontusion-C3HC) and one below phrenic motoneuron pools (C6HC) in wild-type swiss OF-1 mice, and we compared their effects on respiratory function using whole-body plethysmography and on diaphragm activity using electromyography (EMG). At 7 days post-surgery, both C3HC and C6HC damaged spinal cord integrity above the lesion level, suggesting that C6HC potentially alters C5 motoneurons. Although both models led to decreased diaphragmatic EMG activity in the injured hemidiaphragm compared to the intact one (-46% and -26% in C3HC and C6HC, respectively, both p = 0.02), only C3HC led to a significant reduction in tidal volume and minute ventilation compared to sham surgery (-25% and -20% vs. baseline). Moreover, changes in EMG amplitude between respiratory bursts were observed post-C3HC, reflecting a change in phrenic motoneuronal excitability. Hence, C3HC and C6HC models induced alteration in respiratory function proportionally to injury level, and the C3HC model is a more appropriate model for interventional studies aiming to restore respiratory function in cSCI.

Diaphragm Pacing in Spinal Cord Injury Can Significantly Decrease Mechanical Ventilation in Multicenter Prospective Evaluation

BACKGROUND

Cervical spinal cord injury (SCI) can lead to dependence on mechanical ventilation (MV) with significant morbidity and mortality. The diaphragm pacing system (DPS) was developed as an alternative to MV.

METHODS

We conducted a prospective single arm study of DPS in MV dependent patients with high SCI and intact phrenic nerves. Following device acclimation, pacing effectiveness to provide ventilation was evaluated. The primary endpoint was the number who could use DPS to breathe for four continuous hours without MV. Secondary endpoints included the number of patients that could use DPS 24 hours/day free of MV and the ability of DPS to maintain clinically acceptable tidal volume (Vt). In addition, we conducted a meta-analysis that included the prospective study along with data from four recently published studies to evaluate DPS hourly use.

RESULTS

Fifty-three patients were implanted in the prospective study. Most were male (77.4%) with a median time from injury to treatment of 28.3 (IQR 12.1, 83.3) months. Four- and 24-hour use occurred in 96.2% (95%CI - 87.0%, 99.5%) and 58.5% (95% CI - 44.1%, 74.9%), respectively. Four and 24-hour results in the meta-analysis cohort (n=196) exhibited similar results 92.2% (95% CI - 82.6%,96.7%) and 52.7% (95% CI - 36.2%,68.6%) using DPS for four and 24 hours, respectively. DPS use significantly exceeded the calculated basal tidal volume requirements by a mean of 48.4% (95% CI - 37.0, 59.9%; p<0.001).

CONCLUSIONS

This study demonstrates that in most ventilator-dependent patients, diaphragm pacing can effectively supplement or completely replace the need for MV and support basal metabolic requirements.

Development of closed-loop modelling framework for adaptive respiratory pacemakers

OBJECTIVE

Ventilatory pacing by electrical stimulation of the phrenic nerve has many advantages compared to mechanical ventilation. However, commercially available respiratory pacing devices operate in an open-loop fashion, which require manual adjustment of stimulation parameters for a given patient. Here, we report the model development of a closed-loop respiratory pacemaker, which can automatically adapt to various pathological ventilation conditions and metabolic demands.

METHODS

To assist the model design, we have personalized a computational lung model, which incorporates the mechanics of ventilation and gas exchange. The model can respond to the device stimulation where the gas exchange model provides biofeedback signals to the device. We use a pacing device model with a proportional integral (PI) controller to illustrate our approach.

RESULTS

The closed-loop adaptive pacing model can provide superior treatment compared to open-loop operation. The adaptive pacing stimuli can maintain physiological oxygen levels in the blood under various simulated breathing disorders and metabolic demands.

CONCLUSION

We demonstrate that the respiratory pacing devices with the biofeedback can adapt to individual needs, while the lung model can be used to validate and parametrize the device.

SIGNIFICANCE

The closed-loop model-based framework paves the way towards an individualized and autonomous respiratory pacing device development.

Phrenic nerve stimulation prevents diaphragm atrophy in patients with respiratory failure on mechanical ventilation

BACKGROUND

Diaphragm atrophy and dysfunction is a major problem among critically ill patients on mechanical ventilation. Ventilator-induced diaphragmatic dysfunction is thought to play a major role, resulting in a failure of weaning. Stimulation of the phrenic nerves and resulting diaphragm contraction could potentially prevent or treat this atrophy. The subject of this study is to determine the effectiveness of diaphragm stimulation in preventing atrophy by measuring changes in its thickness.

METHODS

A total of 12 patients in the intervention group and 10 patients in the control group were enrolled. Diaphragm thickness was measured by ultrasound in both groups at the beginning of study enrollment (hour 0), after 24 hours, and at study completion (hour 48). The obtained data were then statistically analyzed and both groups were compared.

RESULTS

The results showed that the baseline diaphragm thickness in the interventional group was (1.98 ± 0.52) mm and after 48 hours of phrenic nerve stimulation increased to (2.20 ± 0.45) mm (p=0.001). The baseline diaphragm thickness of (2.00 ± 0.33) mm decreased in the control group after 48 hours of mechanical ventilation to (1.72 ± 0.20) mm (p<0.001).

CONCLUSIONS

Our study demonstrates that induced contraction of the diaphragm by pacing the phrenic nerve not only reduces the rate of its atrophy during mechanical ventilation but also leads to an increase in its thickness - the main determinant of the muscle strength required for spontaneous ventilation and successful ventilator weaning.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov (18/06/2018, NCT03559933, https://clinicaltrials.gov/ct2/show/NCT03559933 ).

The terminal segment of the human phrenic nerve as a novel implantation site for diaphragm pacing electrodes: Anatomical and clinical description

BACKGROUND

Diaphragm pacing allows certain ventilator-dependent patients to achieve weaning from mechanical ventilation. The reference method consists in implanting intrathoracic contact electrodes around the phrenic nerve during video-assisted thoracic surgery, which involves time-consuming phrenic nerve dissection with a risk of nerve damage. Identifying a phrenic segment suitable for dissection-free implantation of electrodes would constitute progress.

STUDY DESIGN

This study characterizes a free terminal phrenic segment never fully described before. We conducted a cadaver study (n = 14) and a clinical observational study during thoracic procedures (n = 54).

RESULTS

A free terminal phrenic segment was observed on both sides in 100% of cases, "jumping" from the pericardium to the diaphragm and measuring 60 mm [95% confidence interval; 48-63] and 72.5 mm [65-82] (right left, respectively; p = 0.0038; cadaver study). This segment rolled up on itself at end-expiration and became unravelled and elongated with diaphragm descent (clinical study). Three categories of fat pads were defined (type 1: pericardiophrenic bundle free of surrounding fat; type 2: single fatty fringe leaving the phrenic nerve visible until diaphragmatic entry; type 3: multiple fatty fringes masking the site of penetration of the phrenic nerve) that depended on body mass index (p = 0.001, clinical study). Hematoxylin-eosin and toluidine blue staining (cadaver study) showed that all of the phrenic fibers in the distal, pre-branching part of the terminal segment were contained within a single epineurium containing a variable number of fascicles (right: 1 [95%CI 0.65-4.01]; left 5 [3.37-7.63]; p = 0.03).

CONCLUSION

Diaphragm pacing through periphrenic electrodes positioned on the terminal phrenic segment should be tested.

Diaphragm dysfunction: A comprehensive review from diagnosis to management

Although the diaphragm represents a critical component of the respiratory pump, the clinical presentations of diaphragm dysfunction are often non-specific and can be mistaken for other more common causes of dyspnoea. While acute bilateral diaphragm dysfunction typically presents dramatically, progressive diaphragm dysfunction associated with neuromuscular disorders and unilateral hemidiaphragm dysfunction may be identified incidentally or by recognising subtle associated symptoms. Diaphragm dysfunction should be considered in individuals with unexplained dyspnoea, restrictive respiratory function tests or abnormal diaphragm position on plain chest imaging. A higher index of suspicion should occur for individuals with profound orthopnoea, those who have undergone procedures in proximity to the phrenic nerve(s) or those with co-morbid conditions that are associated with diaphragm dysfunction, particularly neuromuscular disorders. A systematic approach to the evaluation of diaphragm function using non-invasive diagnostic techniques such as respiratory function testing and diaphragm imaging can often confirm a diagnosis. Neurophysiological assessment may confirm diaphragm dysfunction and assist in identifying an underlying cause. Identifying those with or at risk of respiratory failure can allow institution of respiratory support, while specific cases may also benefit from surgical plication or phrenic nerve pacing techniques. This article is protected by copyright. All rights reserved.

Phrenic Nerve Stimulator Placement via the Cervical Approach: Technique and Anatomic Considerations

BACKGROUND

Diaphragmatic pacing via phrenic nerve stimulation can help improve breathing and facilitate mechanical ventilation weaning in patients with respiratory failure secondary to brainstem injury, high cervical spinal cord injury, or congenital central hypoventilation. Devices can be placed utilizing several techniques; however, nuances regarding placement are not well published.

OBJECTIVE

To describe our experience with phrenic nerve stimulator placement via the cervical approach with a focus on surgical anatomy, variations, and technique.

METHODS

Placement of phrenic nerve stimulator via a cervical approach is described in detail.

RESULTS

Successful placement of phrenic nerve stimulator without complication.

CONCLUSION

The cervical approach for the placement of a phrenic nerve stimulator is a safe and effective option for patients. Detailed knowledge of anatomy and anatomic variations is required. Potential advantages and disadvantages are discussed.

Initial Assessment of the Percutaneous Electrical Phrenic Nerve Stimulation System in Patients on Mechanical Ventilation

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Maintaining diaphragm work using electrical stimulation during mechanical ventilation has been proposed to attenuate ventilator-induced diaphragm dysfunction. This study assessed the safety and feasibility of temporary percutaneous electrical phrenic nerve stimulation on user-specified inspiratory breaths while on mechanical ventilation.

Spinal cord injury: A multisystem physiological impairment/dysfunction

Spinal cord injury (SCI) is a complex disease that affects not only sensory and motor pathways below the neurological level of injury (NLI) but also all the organs and systems situated below this NLI. This multisystem impairment implies comprehensive management in dedicated SCI specialized centers, by interdisciplinary and multidisciplinary teams, able to treat not only the neurological impairment, but also all the systems and organs affected. After a brief history of the Spinal Cord Medicine, the author describes how to determine the level and severity of a SCI based on the International Standards for Neurological Classification of Spinal Cord Injury and the prognosis factors of recovery. This article provides also a review of the numerous SCI-related impairments (except for urinary, sexual problems and pain treated separately in this issue), their principles of management and related complications.

Impact of unilateral diaphragm elevation on postoperative outcomes in bilateral lung transplantation - a retrospective single-center study

This study evaluated the impact of unilateral diaphragm elevation following bilateral lung transplantation on postoperative course. Patient data for all lung transplantations performed at our institution between 01/2010 and 12/2019 were reviewed. Presence of right or left diaphragm elevation was retrospectively evaluated using serial chest X-rays performed while patients were standing and breathing spontaneously. Right elevation was defined by a > 40 mm difference between right and left diaphragmatic height. Left elevation was present if the left diaphragm was at the same height or higher than the right diaphragm. In total, 1093/1213 (90%) lung transplant recipients were included. Of these, 255 (23%) patients exhibited radiologic evidence of diaphragm elevation (right, 55%; left 45%; permanent, 62%). Postoperative course did not differ between groups. Forced expiratory volume in 1 second, forced vital capacity and total lung capacity were lower at 1-year follow-up in patients with permanent than in patients with transient or absent diaphragmatic elevation (P = 0.038, P < 0.001, P = 0.002, respectively). Graft survival did not differ between these groups (P = 0.597). Radiologic evidence of diaphragm elevation was found in 23% of our lung transplant recipients. While lung function tests were worse in patients with permanent elevation, diaphragm elevation did not have any relevant impact on outcomes.

Thirty-Six-Month Follow-up of Diaphragm Pacing with Phrenic Nerve Stimulation for Ventilator Dependence in Traumatic Tetraplegia: The Way Forward for Spinal Cord Injury Rehabilitation in a Developing Country

Respiratory failure and chronic ventilator dependence in tetraplegics following cervical injuries located high on the spine (C1-C3) constitute significant challenges in the rehabilitation of patients given the occurrence of repeated hospitalizations and an ever-increasing financial burden. A 30-year-old man presented with posttraumatic tetraplegia following an unstable injury at the C1-C2 level with cord compression; he was managed by posterior stabilization and decompression followed by ventilator dependence and no rehabilitation until 6 months postinjury. We implanted phrenic nerve stimulator electrodes bilaterally for indirect diaphragm pacing by an implantable pulse generator that allowed for weaning from mechanical ventilation and spontaneous ventilator-free breathing at 20 weeks post-implantation and which facilitated post-tetraplegia rehabilitation. At 36 months after implantation, the patient is ventilator- free without any procedure-related complications or respiratory infections. Diaphragm pacing with phrenic nerve stimulation may be a way forward for ventilator-dependent tetraplegics in developing countries to pursue effective rehabilitation and improved quality of life.

PREVENTION OF RESPIRATORY MUSCLE DYSFUNCTION DUE TO DIAPHRAGM ATROPHY IN CHILDREN WITH RESPIRATORY FAILURE

The aim of the study was to determine whether diaphragm-protective mechanical ventilation can prevent diaphragm atrophy in children with respiratory failure. Materials and methods. We complete the prospective single-center cohort study. Data analysis included 82 patients 1 month - 18 years old, divided into I group (lung-protective MV) and II group (diaphragm-protective in addition to lung-protective MV). Patients were divided into age subgroups. Stages of the study: 1st day (d1), 3rd (d3), 5th (d5), 7th (d7), 9th (d9), 28th (d28). We studied changes in diaphragm thickness at the end of exhalation and compared them with these indicators at patient`s admission to the study (baseline). Primary endpoint was length of stay in ICU, secondary endpoints were complications (prolonged MV). Results are described as arithmetic mean (X) and standard deviation (σ) with level of significance p. Results. There were significant differences in length of stay in ICU among patients of the 1st and 5th age subgroups: in 1st age subgroup this data was in 1.3 times lower in II group, compared with I group (p <0,05); in 5th age subgroup the situation was the opposite - length of stay in ICU was in 1.4 times higher in II group, compared with I group (p<0.05). There were no patients who required lifelong mechanical ventilation in any of the groups. Changes in the thickness of the diaphragm, which indicate its atrophy, were the most significant among patients of the first, second, third and fourth age subgroups and the severity of atrophy was higher among patients of group I, compared with patients of group II. Conclusions. Diaphragm-protective mechanical ventilation significantly prevents diaphragm atrophy in children with respiratory failure in 2nd, 4th, and 5th age subgroups. Providing goal-directed diaphragm-protective MV might reduce the length of stay in ICU among patients of 1st and 5th age subgroups. There were no observed complications like lifelong mechanical ventilation in both patient`s group.

Clinical strategies for implementing lung and diaphragm-protective ventilation: avoiding insufficient and excessive effort

Mechanical ventilation may have adverse effects on both the lung and the diaphragm. Injury to the lung is mediated by excessive mechanical stress and strain, whereas the diaphragm develops atrophy as a consequence of low respiratory effort and injury in case of excessive effort. The lung and diaphragm-protective mechanical ventilation approach aims to protect both organs simultaneously whenever possible. This review summarizes practical strategies for achieving lung and diaphragm-protective targets at the bedside, focusing on inspiratory and expiratory ventilator settings, monitoring of inspiratory effort or respiratory drive, management of dyssynchrony, and sedation considerations. A number of potential future adjunctive strategies including extracorporeal CO₂ removal, partial neuromuscular blockade, and neuromuscular stimulation are also discussed. While clinical trials to confirm the benefit of these approaches are awaited, clinicians should become familiar with assessing and managing patients’ respiratory effort, based on existing physiological principles. To protect the lung and the diaphragm, ventilation and sedation might be applied to avoid excessively weak or very strong respiratory efforts and patient-ventilator dysynchrony.

Minimally Invasive Injection to the Phrenic Nerve in a Porcine Hemidiaphragmatic Paralysis Model: A Pilot Study

BACKGROUND

Neurodegenerative diseases and spinal cord injury can affect respiratory function often through motor neuron loss innervating the diaphragm. To reinnervate this muscle, new motor neurons could be transplanted into the phrenic nerve (PN), allowing them to extend axons to the diaphragm. These neurons could then be driven by an optogenetics approach to regulate breathing. This type of approach has already been demonstrated in the peripheral nerves of mice. However, there is no established thoracoscopic approach to PN injection. Also, there is currently a lack of preclinical large animal models of diaphragmatic dysfunction in order to evaluate the efficacy of potential treatments.

OBJECTIVE

To evaluate the feasibility of thoracoscopic drug delivery into the PN and to assess the viability of hemidiaphragmatic paralysis in a porcine model.

METHODS

Two Landrace farm pigs underwent a novel procedure for thoracoscopic PN injections, including 1 nonsurvival and 1 survival surgery. Nonsurvival surgery involved bilateral PN injections and ligation. Survival surgery included a right PN injection and transection proximal to the injection site to induce hemidiaphragmatic paralysis.

RESULTS

PN injections were successfully performed in both procedures. The animal that underwent survival surgery recovered postoperatively with an established right hemidiaphragmatic paralysis. Over the 5-d postoperative period, the animal displayed stable vital signs and oxygenation saturation on room air with voluntary breathing.

CONCLUSION

Thoracoscopic targeting of the porcine PN is a feasible approach to administer therapeutic agents. A swine model of hemidiaphragmatic paralysis induced by unilateral PN ligation or transection may be potentially used to study diaphragmatic reinnervation following delivery of therapeutics.

Ventilator-induced diaphragm dysfunction: translational mechanisms lead to therapeutical alternatives in the critically ill

Mechanical ventilation [MV] is a life-saving technique delivered to critically ill patients incapable of adequately ventilating and/or oxygenating due to respiratory or other disease processes. This necessarily invasive support however could potentially result in important iatrogenic complications. Even brief periods of MV may result in diaphragm weakness [i.e., ventilator-induced diaphragm dysfunction [VIDD]], which may be associated with difficulty weaning from the ventilator as well as mortality. This suggests that VIDD could potentially have a major impact on clinical practice through worse clinical outcomes and healthcare resource use. Recent translational investigations have identified that VIDD is mainly characterized by alterations resulting in a major decline of diaphragmatic contractile force together with atrophy of diaphragm muscle fibers. However, the signaling mechanisms responsible for VIDD have not been fully established. In this paper, we summarize the current understanding of the pathophysiological pathways underlying VIDD and highlight the diagnostic approach, as well as novel and experimental therapeutic options.

Temporary transvenous diaphragm pacing vs. standard of care for weaning from mechanical ventilation: study protocol for a randomized trial

BACKGROUND

Mechanical ventilation (MV) is a life-saving technology that restores or assists breathing. Like any treatment, MV has side effects. In some patients it can cause diaphragmatic atrophy, injury, and dysfunction (ventilator-induced diaphragmatic dysfunction, VIDD). Accumulating evidence suggests that VIDD makes weaning from MV difficult, which involves increased morbidity and mortality.

METHODS AND ANALYSIS

This paper describes the protocol of a randomized, controlled, open-label, multicenter trial that is designed to investigate the safety and effectiveness of a novel therapy, temporary transvenous diaphragm pacing (TTVDP), to improve weaning from MV in up to 88 mechanically ventilated adult patients who have failed at least two spontaneous breathing trials over at least 7 days. Patients will be randomized (1:1) to TTVDP (treatment) or standard of care (control) groups. The primary efficacy endpoint is time to successful extubation with no reintubation within 48 h. Secondary endpoints include maximal inspiratory pressure and ultrasound-measured changes in diaphragm thickness and diaphragm thickening fraction over time. In addition, observational data will be collected and analyzed, including 30-day mortality and time to discharge from the intensive care unit and from the hospital. The hypothesis to be tested postulates that more TTVDP patients than control patients will be successfully weaned from MV within the 30 days following randomization.

DISCUSSION

This study is the first large-scale clinical trial of a novel technology (TTVDP) aimed at accelerating difficult weaning from MV. The technology tested provides the first therapy directed specifically at VIDD, an important cause of delayed weaning from MV. Its results will help delineate the place of this therapeutic approach in clinical practice and help design future studies aimed at defining the indications and benefits of TTVDP.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03096639 . Registered on 30 March 2017.

Paced breathing and phrenic nerve responses evoked by epidural stimulation following complete high cervical spinal cord injury in rats

Spinal cord injury (SCI) at the level of cervical segments often results in life-threatening respiratory complications and requires long-term mechanical ventilator assistance. Thus restoring diaphragm activity and regaining voluntary control of breathing are the primary clinical goals for patients with respiratory dysfunction following cervical SCI. Epidural stimulation (EDS) is a promising strategy that has been explored extensively for nonrespiratory functions and to a limited extent within the respiratory system. The goal of the present study is to assess the potential for EDS at the location of the phrenic nucleus (C₃-C₅) innervating the diaphragm: the main inspiratory muscle following complete C₁ cervical transection. To avoid the suppressive effect of anesthesia, all experiments were performed in decerebrate, C₁ cervical transection, unanesthetized, nonparalyzed ( n = 13) and paralyzed ( n = 7) animals. Our results show that C₄ segment was the most responsive to EDS and required the lowest threshold of current intensity, affecting tracheal pressure and phrenic nerve responses. High-frequency (200-300 Hz) EDS applied over C₄ segment (C₄-EDS) was able to maintain breathing with normal end-tidal CO₂ level and raise blood pressure. In addition, 100-300 Hz of C₄-EDS showed time- and frequency-dependent changes (short-term facilitation) of evoked phrenic nerve responses that may serve as a target mechanism for pacing of phrenic motor circuits. The present work provides the first report of successful EDS at the level of phrenic nucleus in a complete SCI animal model and offers insight into the potential therapeutic application in patients with high cervical SCI. NEW & NOTEWORTHY The present work offers the first demonstration of successful life-supporting breathing paced by epidural stimulation (EDS) at the level of the phrenic nucleus, following a complete spinal cord injury in unanesthetized, decerebrate rats. Moreover, our experiments showed time- and frequency-dependent changes of evoked phrenic nerve activity during EDS that may serve as a target mechanism for pacing spinal phrenic motor networks.

Diaphragm Dysfunction in Critical Illness

The diaphragm is the major muscle of inspiration, and its function is critical for optimal respiration. Diaphragmatic failure has long been recognized as a major contributor to death in a variety of systemic neuromuscular disorders. More recently, it is increasingly apparent that diaphragm dysfunction is present in a high percentage of critically ill patients and is associated with increased morbidity and mortality. In these patients, diaphragm weakness is thought to develop from disuse secondary to ventilator-induced diaphragm inactivity and as a consequence of the effects of systemic inflammation, including sepsis. This form of critical illness-acquired diaphragm dysfunction impairs the ability of the respiratory pump to compensate for an increased respiratory workload due to lung injury and fluid overload, leading to sustained respiratory failure and death. This review examines the presentation, causes, consequences, diagnosis, and treatment of disorders that result in acquired diaphragm dysfunction during critical illness.

Diaphragm Dysfunction: Diagnostic Approaches and Management Strategies

The diaphragm is the main inspiratory muscle, and its dysfunction can lead to significant adverse clinical consequences. The aim of this review is to provide clinicians with an overview of the main causes of uni- and bi-lateral diaphragm dysfunction, explore the clinical and physiological consequences of the disease on lung function, exercise physiology and sleep and review the available diagnostic tools used in the evaluation of diaphragm function. A particular emphasis is placed on the clinical significance of diaphragm weakness in the intensive care unit setting and the use of ultrasound to evaluate diaphragmatic action.