Comparative study of electrophrenic nerve stimulation and mechanical ventilatory support in traumatic spinal cord injury

Closed-Loop, Cervical, Epidural Stimulation Elicits Respiratory Neuroplasticity after Spinal Cord Injury in Freely Behaving Rats

Over half of all spinal cord injuries (SCIs) are cervical, which can lead to paralysis and respiratory compromise, causing significant morbidity and mortality. Effective treatments to restore breathing after severe upper cervical injury are lacking; thus, it is imperative to develop therapies to address this. Epidural stimulation has successfully restored motor function after SCI for stepping, standing, reaching, grasping, and postural control. We hypothesized that closed-loop stimulation triggered via healthy hemidiaphragm EMG activity has the potential to elicit functional neuroplasticity in spinal respiratory pathways after cervical SCI (cSCI). To test this, we delivered closed-loop, electrical, epidural stimulation (CLES) at the level of the phrenic motor nucleus (C4) for 3 d after C2 hemisection (C2HS) in freely behaving rats. A 2 × 2 Latin Square experimental design incorporated two treatments, C2HS injury and CLES therapy resulting in four groups of adult, female Sprague Dawley rats: C2HS + CLES (n = 8), C2HS (n = 6), intact + CLES (n = 6), intact (n = 6). In stimulated groups, CLES was delivered for 12-20 h/d for 3 d. After C2HS, 3 d of CLES robustly facilitated the slope of stimulus-response curves of ipsilesional spinal motor evoked potentials (sMEPs) versus nonstimulated controls. To our knowledge, this is the first demonstration of CLES eliciting respiratory neuroplasticity after C2HS in freely behaving animals. These findings suggest CLES as a promising future therapy to address respiratory deficiency associated with cSCI.

Electrical epidural stimulation of the cervical spinal cord: implications for spinal respiratory neuroplasticity after spinal cord injury

Traumatic cervical spinal cord injury (cSCI) can lead to damage of bulbospinal pathways to the respiratory motor nuclei and consequent life-threatening respiratory insufficiency due to respiratory muscle paralysis/paresis. Reports of electrical epidural stimulation (EES) of the lumbosacral spinal cord to enable locomotor function after SCI are encouraging, with some evidence of facilitating neural plasticity. Here, we detail the development and success of EES in recovering locomotor function, with consideration of stimulation parameters and safety measures to develop effective EES protocols. EES is just beginning to be applied in other motor, sensory, and autonomic systems; however, there has only been moderate success in preclinical studies aimed at improving breathing function after cSCI. Thus, we explore the rationale for applying EES to the cervical spinal cord, targeting the phrenic motor nucleus for the restoration of breathing. We also suggest cellular/molecular mechanisms by which EES may induce respiratory plasticity, including a brief examination of sex-related differences in these mechanisms. Finally, we suggest that more attention be paid to the effects of specific electrical parameters that have been used in the development of EES protocols and how that can impact the safety and efficacy for those receiving this therapy. Ultimately, we aim to inform readers about the potential benefits of EES in the phrenic motor system and encourage future studies in this area.

Enabling respiratory control after severe chronic tetraplegia: an exploratory case study

Respiratory dysfunction is one of the most debilitating effects of spinal cord injury (SCI) impacting the quality of life of patients and caregivers. In addition, breathing difficulties impact the rehabilitation routine a patient may potentially undergo. Transcutaneous electrical spinal cord neuromodulation (TESCoN) is a novel approach to reactivate and retrain spinal circuits after paralysis. We demonstrate that acute and chronic TESCoN therapy over the cervical spinal cord positively impacts the breathing and coughing ability in a patient with chronic tetraplegia. ln addition, we show that the improved breathing and coughing ability are not only observed in the presence of TESCoN but persisted for a few days after TESCoN was stopped.NEW & NOTEWORTHY Noninvasive spinal neuromodulation improves breathing and coughing in a patient with severe and complete tetraplegia.

Electrical Neuromodulation of the Respiratory System After Spinal Cord Injury

Spinal cord injury (SCI) is a complex and devastating condition characterized by disruption of descending, ascending, and intrinsic spinal circuitry resulting in chronic neurologic deficits. In addition to limb and trunk sensorimotor deficits, SCI can impair autonomic neurocircuitry such as the motor networks that support respiration and cough. High cervical SCI can cause complete respiratory paralysis, and even lower cervical or thoracic lesions commonly result in partial respiratory impairment. Although electrophrenic respiration can restore ventilator-independent breathing in select candidates, only a small subset of affected individuals can benefit from this technology at this moment. Over the past decades, spinal cord stimulation has shown promise for augmentation and recovery of neurologic function including motor control, cough, and breathing. The present review discusses the challenges and potentials of spinal cord stimulation for restoring respiratory function by overcoming some of the limitations of conventional respiratory functional electrical stimulation systems.

Phrenic pacing compared with mechanical ventilation

STUDY DESIGN

Comparable case series.

OBJECTIVES

High-cervical spinal cord injury (SCI) may disrupt the ability to breathe sufficiently. To restore respiration a phrenic nerve pacer can be implanted. The aims of this study were to describe the use of phrenic nerve pacing in tetraplegics in Denmark and compare the users with a population of ventilator dependent tetraplegics.

SETTING

Clinics for Spinal Cord Injuries, and Respiratory Centre East, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.

METHODS

Nine tetraplegic individuals who had implantation of a phrenic nerve pacer and 16 home mechanical ventilator dependent tetraplegics met the inclusion criteria. Data were retrieved from medical records and a structured follow-up interview with seven individuals from each group.

RESULTS

No significant differences were found when comparing age at injury, time since injury, length of hospitalization, incidence of pneumonia, number of pneumonia hospitalizations, number of tracheal suctions, speech quality and activities of daily living or quality of life. On the Short Form Health Survey (SF36) mental health summary the median for both users of phrenic nerve pacing and users of mechanical ventilation was one s.d. above the mean of a standard population.

CONCLUSIONS

Nine people have had a phrenic nerve pacer implanted. They do not significantly differ from a group of home mechanical ventilator dependent tetraplegics on a number of performance measures, but both groups seem to have better quality of life than a standard population.

Spontaneous Functional Recovery in a Paralyzed Hemidiaphragm Following Upper Cervical Spinal Cord Injury in Adult Rats

Previous studies have shown that latent respiratory pathways can be activated by as phyxia or systemic theophylline administration to restore function to a hemidiaphragm paralyzed by C2 spinal cord hemisection in adult female rats. Based on this premise, electrophysiologic recording techniques were employed in the present investigation to first determine qualitatively whether latent respiratory pathways are activated spon taneously following prolonged post hemisection periods (4-16 weeks) without any therapeutic intervention. Our second objective in a separate group of hemisected an imals was to quantitate any documented functional recovery under the following stan dardized recording conditions: bilateral vagotomy, paralysis with pancuronium bro mide, artificial ventilation, and constant PCO2(maintained at 25 mmHg).

Activation of inspiratory muscles via spinal cord stimulation

Diaphragm pacing is a clinically useful modality providing artificial ventilatory support in patients with ventilator dependent spinal cord injury. Since this technique is successful in providing full-time ventilatory support in only ~50% of patients, better methods are needed. In this paper, we review a novel method of inspiratory muscle activation involving the application of electrical stimulation applied to the ventral surface of the upper thoracic spinal cord at high stimulus frequencies (300 Hz). In an animal model, high frequency spinal cord stimulation (HF-SCS) results in synchronous activation of both the diaphragm and inspiratory intercostal muscles. Since this method results in an asynchronous pattern of EMG activity and mean peak firing frequencies similar to those observed during spontaneous breathing, HF-SCS is a more physiologic form of inspiratory muscle activation. Further, ventilation can be maintained on a long-term basis with repetitive stimulation at low stimulus amplitudes (<1 mA). These preliminary results suggest that HF-SCS holds promise as a more successful method of inspiratory muscle pacing.

Specialized respiratory management for acute cervical spinal cord injury:: a retrospective analysis

BACKGROUND

In individuals with cervical spinal cord injury (SCI), respiratory complications arise within hours to days of injury. Paralysis of the respiratory muscles predisposes the patient toward respiratory failure. Respiratory complications after cervical SCI include hypoventilation, hypercapnea, reduction in surfactant production, mucus plugging, atelectasis, and pneumonia. Ultimately, the patient must use increased work to breathe, which results in respiratory fatigue and may eventually require intubation for mechanical ventilation. Without specialized respiratory management for individuals with tetraplegia, recurrent pneumonias, bronchoscopies, and difficulty in maintaining a stable respiratory status will persist.

OBJECTIVE

This retrospective analysis examined the effectiveness of specialized respiratory management utilized in a regional SCI center.

METHODS

Individuals with C1-C4 SCI (N = 24) were the focus of this study as these neurological levels present with the most complicated respiratory status.

RESULTS

All of the study patients' respiratory status improved with the specialized respiratory management administered in the SCI specialty unit. For a majority of these patients, respiratory improvements were noted within 1 week of admission to our SCI unit.

CONCLUSION

Utilization of high tidal volume ventilation, high frequency percussive ventilation, and mechanical insufflation- exsufflation have demonstrated efficacy in stabilizing the respiratory status of these individuals. Optimizing respiratory status enables the patients to participate in rehabilitation therapies, allows for the opportunity to vocalize, and results in fewer days on mechanical ventilation for patients who are weanable.

Functional electrical stimulation in spinal cord injury respiratory care

The management of chronic respiratory insufficiency and/or long-term inability to breathe independently has traditionally been via positive-pressure ventilation through a mechanical ventilator. Although life-sustaining, it is associated with limitations of function, lack of independence, decreased quality of life, sleep disturbance, and increased risk for infections. In addition, its mechanical and electronic complexity requires full understanding of the possible malfunctions by patients and caregivers. Ventilator-associated pneumonia, tracheal injury, and equipment malfunction account for common complications of prolonged ventilation, and respiratory infections are the most common cause of death in spinal cord-injured patients. The development of functional electric stimulation (FES) as an alternative to mechanical ventilation has been motivated by a goal to improve the quality of life of affected individuals. In this article, we will review the physiology, types, characteristics, risks and benefits, surgical techniques, and complications of the 2 commercially available FES strategies - phrenic nerve pacing (PNP) and diaphragm motor point pacing (DMPP).

Diaphragm pacing in amyotrophic lateral sclerosis: a literature review

Amyotrophic lateral sclerosis (ALS) remains a rapidly progressive fatal degenerative disease of motor neurons for which there are few interventions to slow disease progression or improve quality of life. A diaphragm pacing system was approved by the U.S. Food and Drug Administration in September 2011 for ALS under a Humanitarian Device Exemption. News of this approval has been met with a combination of excitement and uncertainty by members of the ALS community. We review the currently available data on the diaphragm pacing system and its use in ALS. Diaphragm pacing appears to be reasonably safe in carefully selected patients, but flaws in the reporting on it thus far preclude conclusions regarding efficacy. Further study is needed.

[Diaphragmatic pacemaker as an alternative to mechanical ventilation in patients with cervical spinal injury]

OBJECTIVE

To verify that the diaphragmatic pacemaker is a form of respiratory support that can be used to replace a volumetric respirator in cervical spinal injury patients with cervical spinal lesion and diaphragmatic paralysis by means of its comparison with the traditional volumetric respirator.

DESIGN

Retrospective study of a prospective database and age-matched case-control study.

SETTING

Intensive Care Unit and Intermediate Care Respiratory Unit, Paraplegics National Hospital, Toledo (Spain).

PATIENTS

We collected data on all patients discharged from the Hospital with permanent respiratory support by volumetric respirator or diaphragmatic pacemaker during a follow-up period of 25 years. Personal interviews were conducted to evaluate health-related quality of life. Comparison and survival tests were used for statistical comparisons.

INTERVENTIONS

Quality of life questionnaire.

MAIN VARIABLES

The main variables collected were demographic data, hospital stay, mortality, family reintegration and health-related quality of life.

RESULTS

We evaluated the clinical records of 101 patients, 37 in the pacemaker-group and 64 in the volumetric respirator-group. Our results show that ICU admission duration and hospitalization as well as family reintegration, without significant differences, with a tendency to greater survival in pacemaker patients (18.18 versus 9.67 years by the Kaplan-Meier method, p<0.001). However, this difference becomes non-significant (p=0.06) after adjustment of the groups by age. Furthermore, better quality of life was found in these same patients with pacemakers in terms of security, communication, sociability, comfort and mobility in the patients.

CONCLUSIONS

Diaphragmatic pacemaker ventilation is an effective alternative to mechanical ventilation with similar efficacy that improve quality of life in patients with severe respiratory failure due to cervical spinal cord injury.

Neuromuscular electrical stimulation in neurorehabilitation

This review provides a comprehensive overview of the clinical uses of neuromuscular electrical stimulation (NMES) for functional and therapeutic applications in subjects with spinal cord injury or stroke. Functional applications refer to the use of NMES to activate paralyzed muscles in precise sequence and magnitude to directly accomplish functional tasks. In therapeutic applications, NMES may lead to a specific effect that enhances function, but does not directly provide function. The specific neuroprosthetic or "functional" applications reviewed in this article include upper- and lower-limb motor movement for self-care tasks and mobility, respectively, bladder function, and respiratory control. Specific therapeutic applications include motor relearning, reduction of hemiplegic shoulder pain, muscle strengthening, prevention of muscle atrophy, prophylaxis of deep venous thrombosis, improvement of tissue oxygenation and peripheral hemodynamic functioning, and cardiopulmonary conditioning. Perspectives on future developments and clinical applications of NMES are presented.

Inspiratory muscle pacing in spinal cord injury: case report and clinical commentary

BACKGROUND/OBJECTIVE

A significant fraction of patients with cervical spinal cord injury suffer from respiratory muscle paralysis and dependence on chronic mechanical ventilation. In selected patients, diaphragm pacing (DP) through electrical stimulation of the phrenic nerves provides an alternative to mechanical ventilation with significant advantages in life quality.

METHODS

A case report of an individual who successfully underwent DP using intramuscular diaphragm electrodes. A brief review of the state of the art of DP including the clinical benefits of DP, patient selection and evaluation, description of equipment, methods of transition from mechanical ventilation to DP, potential complications and side effects, long-term outcome, and potential future developments in this field is included.

RESULTS

Several available DP systems are available, including conventional ones in which electrodes are positioned directly on the phrenic nerves through thoracotomy and less invasive systems in which electrodes are placed within the diaphragm through laparoscopy. For patients with only unilateral phrenic nerve function, a combined intercostal and unilateral diaphragm pacing system is under development.

CONCLUSIONS

In patients with ventilator-dependent tetraplegia, there are alternative methods of ventilatory support, which offer substantial benefits compared to mechanical ventilation.

Functional Electrical Stimulation for Neuromuscular Applications

Paralyzed or paretic muscles can be made to contract by applying electrical currents to the intact peripheral motor nerves innervating them. When electrically elicited muscle contractions are coordinated in a manner that provides function, the technique is termed functional electrical stimulation (FES). In more than 40 years of FES research, principles for safe stimulation of neuromuscular tissue have been established, and methods for modulating the strength of electrically induced muscle contractions have been discovered. FES systems have been developed for restoring function in the upper extremity, lower extremity, bladder and bowel, and respiratory system. Some of these neuroprostheses have become commercialized products, and others are available in clinical research settings. Technological developments are expected to produce new systems that have no external components, are expandable to multiple applications, are upgradable to new advances, and are controlled by a combination of signals, including biopotential signals from nerve, muscle, and the brain.

Restoration of respiratory muscle function following spinal cord injury

Respiratory complications are a leading cause of morbidity and mortality in patients with spinal cord injury. Several techniques, currently available or in development, have the capacity to restore respiratory muscle function allowing these patients to live more normal lives and hopefully reduce the incidence of respiratory complications. Bilateral phrenic nerve pacing, a clinically accepted technique to restore inspiratory muscle function, allows patients with ventilator dependent tetraplegia complete freedom from mechanical ventilation. Compared to mechanical ventilation, phrenic nerve pacing provides patients with increased mobility, improved speech, improved comfort level and reduction in health care costs. The results of clinical trials of laparoscopically placed intramuscular diaphragm electrodes suggest that diaphragm pacing can also be achieved without the need for a thoracotomy and associated long hospital stay, and without manipulation of the phrenic nerve which carries a risk of phrenic nerve injury. Other clinical trials are being performed to restore inspiratory intercostal function. In patients with only unilateral phrenic nerve function who are not candidates for phrenic nerve pacing, combined intercostal and unilateral diaphragm pacing appears to provide benefits similar to that of bilateral diaphragm pacing. Clinical trials are also underway to restore expiratory muscle function. Magnetic stimulation, surface stimulation and spinal cord stimulation of the expiratory muscles are promising techniques to restore an effective cough mechanism in this patient population. These techniques hold promise to reduce the incidence of respiratory tract infections, atelectasis and respiratory failure in patients with spinal cord injury and reduce the morbidity and mortality associated with these complications.

Adenosinergic mechanisms underlying recovery of diaphragm motor function following upper cervical spinal cord injury: potential therapeutic implications

OBJECTIVES

In adult rats, a latent respiratory motor pathway can be pharmacologically activated with 1,3-dimethylxanthine (theophylline) to restore respiratory-related activity to a hemidiaphragm paralysed by an ipsilateral upper cervical (C2) spinal cord hemisection. The purpose of this review is to describe mechanisms that underlie theophylline-induced recovery of respiratory-related function following C2 hemisection and to underscore the therapeutic potential of theophylline therapy in spinal cord injured patients with respiratory deficits.

METHODS

Theophylline mediates recovery of respiratory-related activity via antagonism of central adenosine A(1) receptors. When administered chronically, the drug restores and maintains recovered function. Since theophylline is an adenosine receptor antagonist with affinity for both the adenosine A(1) and A(2) receptors, we assessed the relative contributions of each receptor to functional recovery. While A(1) receptor antagonism plays a predominant role, activation of the A(2) receptors by specific agonists subserves the A(1) receptor-mediated actions. That is, when an adenosine A(2) receptor agonist is administered first, it primes the system such that subsequent administration of the A(1) antagonist induces a greater degree of recovered respiratory activity than when the antagonist alone is administered.

RESULTS

Chronic oral administration of theophylline in C2 hemisected animals demonstrates that even when animals have been weaned from the drug, theophylline-induced recovered respiratory actions persist. This suggests that in clinical application, it may not be necessary to maintain patients on long-term theophylline. We have shown that recovery of respiratory-related activity in the ipsilateral phrenic nerve can occur spontaneously 3-4 months after C2 hemisection. Theophylline administration after this post-injury period obliterates/negates the recovery function. This indicates strongly that there is therapeutic window (more acutely after injury) for the initiation of theophylline therapy. We have also demonstrated that peripheral (carotid bodies) adenosine A(1) receptors can be selectively activated to modulate theophylline-induced CNS actions. Blocking central adenosine receptors while simultaneously activating peripheral adenosine receptors minimizes the potential of respiratory muscle fatigue with theophylline.

DISCUSSION

The significance of the current findings lies in the potential clinical application of theophylline therapy in spinal cord injured patients with respiratory deficits. The ultimate goal of theophylline therapy is to wean ventilator-dependent patients off ventilatory support. Thus far, our animal studies suggest that the onset of theophylline therapy must be soon after injury.

The crossed phrenic phenomenon: a model for plasticity in the respiratory pathways following spinal cord injury

Hemisection of the cervical spinal cord rostral to the level of the phrenic nucleus interrupts descending bulbospinal respiratory pathways, which results in a paralysis of the ipsilateral hemidiaphragm. In several mammalian species, functional recovery of the paretic hemidiaphragm can be achieved by transecting the contralateral phrenic nerve. The recovery of the paralyzed hemidiaphragm has been termed the "crossed phrenic phenomenon." The physiological basis for the crossed phrenic phenomenon is as follows: asphyxia induced by spinal hemisection and contralateral phrenicotomy increases central respiratory drive, which activates a latent crossed respiratory pathway. The uninjured, initially latent pathway mediates the hemidiaphragm recovery by descending into the spinal cord contralateral to the hemisection and then crossing the midline of the spinal cord before terminating on phrenic motoneurons ipsilateral and caudal to the hemisection. The purpose of this study is to review work conducted on the crossed phrenic phenomenon and to review closely related studies focusing particularly on the plasticity associated with the response. Because the review deals with recovery of respiratory muscles paralyzed by spinal cord injury, the clinical relevance of the reviewed studies is highlighted.

Laparoscopic implant instrument for the placement of intramuscular electrodes in the diaphragm

We have developed an endoscopic instrument that will allow a surgeon to safely, dependably and accurately place intramuscular (IM) electrodes in the diaphragm. This instrument has been used to implant 28 IM electrodes in the diaphragms of eleven acute and four chronic dogs. All electrodes achieved full activation of the diaphragm muscle, producing tidal volumes up to 130% V(TCRIT), the critical volume necessary for basal ventilatory support, with unilateral stimulation. The surgeon is able to control the angle of the IM electrode insertion needle, which enables the needle to approach the diaphragm at an angle that is parallel to the surface of the muscle. This insures good control over the depth of needle penetration into the muscle, which greatly reduces the risk of accidentally passing the needle through the diaphragm and entering the thorax. Endoscopic placement of IM electrodes into the diaphragm opens opportunities to provide cost effective negative pressure ventilation to patients who are unable to effect sufficient ventilation by central nervous system (CNS) control of respiration.

Quantitative assessment of respiratory function following contusion injury of the cervical spinal cord

In this study, we describe a new method for quantitative assessment of phrenic inspiratory motor activity in two models of cervical spinal cord contusion injury. Anesthetized rats received contusion injury either to the descending bulbospinal respiratory pathway on one side of the spinal cord alone (C2 lateralized contusion) or to both the descending pathway, as well as the phrenic motoneuron pool bilaterally (C4/C5 midline contusion). Following injury, respiratory-associated phrenic nerve motor activity was recorded under standardized and then asphyxic conditions. Phrenic nerve efferent activity was rectified, integrated, and quantitated by determining the mean area under the integrated neurograms. The mean integrated area of the four inspiratory bursts recorded just before turning off the ventilator (to induce asphyxia) was determined and divided by the integrated area under the single largest respiratory burst recorded during asphyxia. This latter value was taken as the maximal inspiratory motor response that the rat was capable of generating during respiratory stress. Thus, a percentage of the maximal inspiratory motor drive was established for breathing in control and injured rats under standardized conditions. The results indicate that noninjured rats use 52 +/- 1.8% of maximal inspiratory motor drive under standardized conditions. In C2-contused rats, the results showed that while the percentage of maximal inspiratory motor drive on the noncontused side was similar to the control (55 +/- 4.1%), it was increased on the contused side (78 +/- 2.6%). In C4/5 lesions, the results indicate that this percentage was increased on both sides (77 +/- 4.4%). The results show the feasibility for performing quantitative evaluation of respiratory dysfunction in an animal model of cervical contusion injury. These findings lend to further development of this model for investigations of neuroplasticity and/or therapeutic interventions directed at ameliorating respiratory compromise following cervical spinal cord trauma.

Diaphragm pacing for respiratory insufficiency

Diaphragm pacing (DP) by electrical stimulation of the phrenic nerve offers important advantages to a highly select group of patients with respiratory paralysis. The patient wears an external radiofrequency (RF) transmitter over an implanted receiver, and a stimulating current is induced without the need for any transcutaneous wires. We review the conditions and requirements of patients who may benefit most from DP. We outline the preoperative evaluation and procedures for surgical implantation. We discuss the risk of diaphragmatic fatigue posed by initiation of DP and the use of gradual conditioning to limit this problem. Other problems encountered by patients in the course of DP can be minimized by well-instructed home caregivers and by systematic medical follow-up. Although a few patients derive considerable benefit from DP, many patients with respiratory paralysis are better treated by less invasive means such as nasal bilevel positive airway pressure or intermittent positive pressure ventilation, which we also review.

Alternative methods of ventilatory support for the patient with ventilatory failure due to spinal cord injury

Ventilatory insufficiency and impaired airway secretion clearance are common complications of spinal cord injury (SCI) and can lead to respiratory failure which is the leading cause of death in both the acute and chronic stages. Standard invasive management options such as intubation, tracheostomy and electrophrenic respiration have been reviewed. The review findings are consistent with our clinical experience in that these invasive options appear to entail unacceptably high morbidity and risks of mortality. A number of detailed parameters are suggested for evaluating the respiratory functioning of the individual in order to determine the most acceptable and successful noninvasive systems for both ventilatory support and evacuation of airway secretions. They are physiological substitutes for the action of the inspiratory and expiratory muscles. These techniques are described in detail. We conclude that noninvasive techniques can safely and effectively obviate the need for intubation, tracheostomy and electrophrenic pacemakers in appropriate individuals with SCI.

Intermittent abdominal pressure ventilator in a regimen of noninvasive ventilatory support

The purpose of this work is to present 640 patient-years of experience using the intermittent abdominal pressure ventilator (IAPV) in a regimen of noninvasive ventilatory support for patients with paralytic/restrictive respiratory insufficiency. Fifty-two of the 54 patients who used the IAPV used 24-hour noninvasive ventilatory support. Thirty-eight of the 52 patients could tolerate less than 15 minutes of free time off their ventilators except by the successful use of glossopharyngeal breathing (GPB). No patient, however, retained an indwelling tracheostomy and none required or used supplemental oxygen therapy. Forty-eight of the 54 patients used the IAPV for daytime support for a mean of 12.9 +/- 11.5 years (3 months to 39 years) while using other forms of noninvasive support overnight. All 48 patients maintained normal minute ventilation and end-tidal PCO2 on the IAPV. One patient used the IAPV only for nocturnal ventilatory support for six months. Five patients relied on the IAPV as their sole method of ventilatory support 24 hours a day for a mean of 13.4 +/- 11.2 years (range, 2 to 31 years). Three of these five patients had no free time and were studied by nocturnal SaO2 monitoring that demonstrated a mean SaO2 of 95 percent or greater and a minimum SaO2 of 86 percent. The maximum end-tidal PCO2 was 49 mm Hg during sleep on the IAPV. The 48 patients receiving daytime IAPV support reported few difficulties. However, two of the five patients using the IAPV 24 hours a day had development of sacral decubiti. The IAPV became ineffective for 12 patients after 12.3 +/- 9.5 years of use. These patients then switched to daytime mouth IPPV. We conclude that the IAPV is a safe and effective method of long-term daytime ventilatory support for patients with paralytic/restrictive respiratory insufficiency. Its use is optimized when employed in combination with other noninvasive methods of ventilatory support, thus eliminating the need for tracheostomy, and optimizing the use of GPB. Regular follow-up is important because the IAPV can become less effective with time.

Electrophrenic ventilation: a different perspective

Since 1972, radio-frequency electrophrenic nerve pacing (EPP) has been an option for assisting the ventilation of patients with chronic paralytic respiratory insufficiency. Most of the medical literature has been favorable regarding its continued application. We reviewed the literature to determine how "successful" application of EPP was defined. Our studies indicated that long-term follow-up of EPP patients has been generally inadequate with little emphasis placed on incidence and severity of complications. There was no standardization in defining successful experiences with EPP. Upper airway instability during pacing, lack of internal pacemaker alarms, and the risk of sudden pacemaker failure necessitate permanent tracheostomy in the great majority of patients but complications of the presence of a tracheostomy were not considered in evaluating the desirability of EPP. Some EPP patients became independent of any ventilatory support thus benefiting minimally from the time commitment, effort, and extreme expense needed for EPP placement and training. We conclude that EPP is a valid option for the properly screened patient but that expense, failure rate, morbidity and mortality remain excessive and that alternative methods of ventilatory support should be explored.

Noninvasive options for ventilatory support of the traumatic high level quadriplegic patient

The ventilation of 25 ventilator-dependent traumatic quadriplegic patients was supported by noninvasive means of ventilatory assistance. Twenty-four of the 25 were initially managed by endotracheal intubation, and 23 of these went on to tracheostomy intermittent positive pressure ventilation before being converted to NVA. Seventeen of the 23 patients had their tracheostomies closed. This included three patients with no significant free time except with the use of glossopharyngeal breathing. Seven of the 25 patients who used NVA for at least one year with no significant free time have employed NVA for a mean of 7.4 +/- 7.4 years (1 to 22 years). Mouth IPPV was the most common form of NVA used both during the daytime and overnight. The wrap ventilators, intermittent abdominal pressure ventilator, and GPB were also employed for long-term respiratory support. It was concluded that, in general, because of their youth, intact mental status and bulbar musculature, and absence of obstructive lung disease, patients with traumatic high level spinal cord injury are candidates to benefit from these techniques.