Laparoscopic placement of electrodes for diaphragm pacing using stimulation to locate the phrenic nerve motor points

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.

Technique for implanting intramuscular electrodes in the diaphragm by videolaparoscopy in pigs

PURPOSE

To describe a novel approach for implanting intramuscular electrodes in the diaphragm through videolaparoscopy.

METHODS

We used twelve pigs for this videolaparoscopic technique, which permits at the same time to explore the diaphragm, to locate its motor points and to fix the electrodes in the diaphragm bilaterally. In this technique we used three trocars: one portal for a 10-mm 0° viewing angle laparoscope, one portal for the manipulation of structures and another for electrode implantation.

RESULTS

All animals survived the procedure without pneumothorax/capnothorax or other complication. Implanted electrodes provided an appropriate interface between the muscle and the electrical current generator, and electroventilation was satisfactorily generated in all animals.

CONCLUSION

This videolaparoscopic technique with three trocars enables the exploration and identification of motor points and an efficient fixation of one or two electrodes in each hemidiaphragm.

Effectiveness of diaphragmatic stimulation with single-channel electrodes in rabbits

Every year, a large number of individuals become dependent on mechanical ventilation because of a loss of diaphragm function. The most common causes are cervical spinal trauma and neuromuscular diseases. We have developed an experimental model to evaluate the performance of electrical stimulation of the diaphragm in rabbits using single-channel electrodes implanted directly into the muscle. Various current intensities (10, 16, 20, and 26 mA) produced tidal volumes above the baseline value, showing that this model is effective for the study of diaphragm performance at different levels of electrical stimulation

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.

Complete worldwide operative experience in laparoscopic diaphragm pacing: results and differences in spinal cord injured patients and amyotrophic lateral sclerosis patients

BACKGROUND

Diaphragm movement is essential for adequate ventilation, and when the diaphragm is adversely affected patients face lifelong positive-pressure mechanical ventilation or death. This report summarizes the complete worldwide multicenter experience with diaphragm pacing stimulation (DPS) to maintain and provide diaphragm function in ventilator-dependent spinal cord injury (SCI) patients and respiratory-compromised patients with amyotrophic lateral sclerosis (ALS). It will highlight the surgical experiences and the differences in diaphragm function in these two groups of patients.

METHODS

In prospective Food and Drug Administration (FDA) trials, patients underwent laparoscopic diaphragm motor point mapping with intramuscular electrode implantation. Stimulation of the electrodes ensued to condition and strengthen the diaphragm.

RESULTS

From March of 2000 to September of 2007, a total of 88 patients (50 SCI and 38 ALS) were implanted with DPS at five sites. Patient age ranged from 18 to 74 years. Time from SCI to implantation ranged from 3 months to 27 years. In 87 patients the diaphragm motor point was mapped with successful implantation of electrodes with the only failure the second SCI patient who had a false-positive phrenic nerve study. Patients with ALS had much weaker diaphragms identified surgically, requiring trains of stimulation during mapping to identify the motor point at times. There was no perioperative mortality even in ALS patients with forced vital capacity (FVC) below 50% predicted. There was no cardiac involvement from diaphragm pacing even when analyzed in ten patients who had pre-existing cardiac pacemakers. No infections occurred even with simultaneous gastrostomy tube placements for ALS patients. In the SCI patients 96% were able to use DPS to provide ventilation replacing their mechanical ventilators and in the ALS studies patients have been able to delay the need for mechanical ventilation up to 24 months.

CONCLUSION

This multicenter experience has shown that laparoscopic diaphragm motor point mapping, electrode implantation, and pacing can be safely performed both in SCI and in ALS. In SCI patients it allows freedom from ventilator and in ALS patients it delays the need for ventilators, increasing survival.

Minimally-invasive electrical stimulation of the pudendal nerve: a pre-clinical study for neural control of the lower urinary tract

AIMS

Electrical stimulation of afferent pudendal nerve fibers can evoke sustained bladder contractions (SBC) in cats, yet evidence of therapeutic efficacy in human subjects is lacking. This pre-clinical study was undertaken to test the hypothesis that robust bladder contractions can be generated with a minimally-invasive needle electrode.

MATERIALS AND METHODS

In seven adult cats, triggered electromyographic (EMG) signals from the external anal sphincter (EAS) were used to minimize the needle-to-nerve distance; while reflex bladder contractions were recorded as 20-sec trains of current pulses of varying amplitude (threshold to 10 mA) and frequency (1-100 Hz) were applied to the nerve. This stimulation paradigm was repeated at successively greater needle-to-nerve distances (0.5 cm intervals) and also at different electrode positions along the nerve.

RESULTS

Electrophysiological access to the pudendal nerve was consistently achieved, as indicated by the average threshold for EAS activation (0.31+/-0.19 mA). Using different combinations of stimulus amplitude and frequency, robust SBCs were evoked in every experiment. More rostral electrode positions exhibited stimulation amplitudes and corresponding maximum bladder pressures (0.68+/-0.36 mA and 25.3+/-3.5 cmH2O, respectively) that were comparable to those of more invasive stimulation methods.

CONCLUSIONS

The needle electrode provides a minimally-invasive approach that will enable the study of reflexes mediated by pudendal afferents in humans, and allow pre-operative testing before implanting a permanent device.

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.

The learning curve for investigational surgery: lessons learned from laparoscopic diaphragm pacing for chronic ventilator dependence

BACKGROUND

Electrical stimulation of the phrenic nerve motor point of the diaphragm through laparoscopic implantation of a pacing system is an option for high spinal cord-injured patients with chronic respiratory insufficiency. This study assesses the operative learning curve for the initial series of patients.

METHOD

A series of six patients underwent laparoscopic placement of a diaphragm pacing system. The operative procedure was divided into the following four steps for analysis and rapid adjustment after each operation: exposure of the diaphragm, mapping of the phrenic nerve motor point, implantation of the pacing electrodes, and final routing of the wires to the external system.

RESULTS

The first case required two operations, and the second case was unsuccessful because of a nonfunctioning phrenic nerve that led to a change in the preoperative screening criteria. The operative time decreased from 469 min for the first operation to 165 min for the sixth operation. The significant time decrease can be attributed to changes in the mapping and routing aspects of the operation. Key changes during this series that helped to reduce the operative time include abandonment of a software-dependent mapping technique, development of a grid algorithm for mapping, software improvement to increase the speed of stimulation and mapping, refinement of the mapping probe to maintain adequate suction on the diaphragm, shortening of the electrode lengths, and experience with the implantation of connections to the external electrodes. Presently, all five of the successfully implanted patients can be maintained on prolonged ventilatory support with the device.

CONCLUSION

Analysis of every step of this investigational procedure enabled us to make rapid changes in surgical protocol, leading to decreases in operative times and expectant improvements in patient safety and efficacy. In this series, analysis was the key to developing a low-risk cost-effective outpatient diaphragm pacing system.

Combination of variable frequency train stimulation and K+ channel blockade to augment skeletal muscle force

Several innovative approaches are being used to optimize the input-output relationship of muscle, including nonlinear stimulation paradigms and altering muscle membrane ion channel conductances. We tested the hypothesis that the combination of the K+ channel blocker, 3,4-diaminopyridine (DAP), and variable frequency train (VFT) stimulation improves muscle force to a greater extent than either modality alone. Studies were done in vitro on rat diaphragm muscle and contractions were quantified with respect to peak force, mean force, and force area. DAP increased all three force parameters by >50% during conventional 10-20-Hz stimulation, whereas VFT stimulation improved contractile performance for peak force only. When combined, DAP and VFT stimulation augmented peak force to a significantly greater extent than either modality alone. However, this came at a cost of a moderate decline in force area relative to DAP alone, although mean force was preserved. These force increases were generally well-maintained over the course of short-term repetitive stimulation. Thus, VFT stimulation and K+ channel blockade interact in a complex manner to modulate skeletal muscle force. The utility of the combined intervention for functional electrical stimulation may be greatest for mechanical tasks requiring high force levels early during the contraction.

Phrenic nerve pacing in a tetraplegic patient via intramuscular diaphragm electrodes

In patients with ventilator-dependent tetraplegia, phrenic nerve pacing (PNP) provides significant clinical advantages compared with mechanical ventilation. This technique however generally requires a thoracotomy with its associated risks and in-patient hospital stay and carries some risk of phrenic nerve injury. We have developed a method by which the phrenic nerves can be activated via intramuscular diaphragm electrodes. In one patient with ventilator-dependent tetraplegia, two intramuscular diaphragm electrodes were implanted into each hemidiaphragm near the phrenic nerve motor points via laparoscopic surgery. The motor points were identified employing a previously devised mapping technique. Because inspired volumes were suboptimal on the right, a second laparoscopic procedure was necessary to position electrodes near the anterior and posterior branches of the right phrenic nerve. During bilateral stimulation, inspired volume was 580 ml. After a reconditioning program of progressively increasing diaphragm pacing, maximum inspired volumes on the left and right hemidiaphragms increased significantly. Maximum combined bilateral stimulation was 1120 ml. Importantly, the patient has been able to comfortably tolerate full-time pacing. If confirmed in additional patients, PNP with intramuscular diaphragm electrodes via laparoscopic surgery may provide a less invasive and less costly alternative to conventional PNP.

Thoracoscopic placement of phrenic nerve electrodes for diaphragmatic pacing in children

BACKGROUND/PURPOSE

Diaphragmatic pacing can provide chronic ventilatory support for children who suffer from congenital central hypoventilation syndrome (CCHS) or cervical spinal cord injury. The authors report a new thoracoscopic approach for establishing diaphragm pacing.

METHODS

Between 1997 and 2000, 9 children ranging in age from 5 to 15 years and suffering from these disorders underwent thoracoscopic placement of bilateral phrenic nerve electrodes. A 3- or 4-trocar technique was used to dissect the phrenic nerve in the midchest and suture a phrenic nerve electrode (Avery Laboratories I-110A, Commack, NY) into place. The electrode was tunneled to a subcutaneous pocket in the upper abdomen and attached to an implanted pacing unit.

RESULTS

Bilateral electrodes were placed successfully into all patients. The average procedure time was 3.3 hours (range, 2.5 to 4.6), and average hospital stay was 4.2 days (range, 3 to 5). Four patients experienced postoperative complications (pneumonia, atelectasis, bradycardia, and pneumothorax). Average follow-up has been 30 months (range, 15 to 49). Eight patients have reached their long-term pacing goals.

CONCLUSIONS

Phrenic nerve electrodes can be implanted thoracoscopically and allow the successful use of diaphragmatic pacing therapy. Avoidance of thoracotomy with its associated perioperative morbidity and scarring may encourage wider utilization of diaphragmatic pacing in children.

Thoracoscopic electrode implantation for diaphragm pacing in dogs

BACKGROUND

Diaphragm pacing is an attractive method of ventilatory support; however, it requires electrode implantation to the phrenic nerve or diaphragm. The thoracic approach is favored for several reasons, and it usually accompanies invasive bilateral thoracotomy.

OBJECTIVES

This study was conducted to develop a new electrode suitable for video-assisted thoracoscopic implantation, which is less invasive than the conventional thoracic approach.

METHODS

The feasibility of video-assisted thoracoscopic implantation was tested with newly designed electrodes using 5 mongrel dogs. Furthermore, diaphragm pacing was performed for 60 min to test whether or not the implanted electrodes were functional.

RESULTS

Video-assisted electrode implantation was successful in all 5 cases. No complications occurred during the implantation procedure. In acute-phase pacing trials, the electrodes stimulated the phrenic nerves for 60 min without any pacing failures. The mean value of PaCO(2) increased gradually from 32.2 +/- (SEM) 1.52 to 54.6 +/- 4.58 mm Hg, and the value of tidal volume decreased gradually from 242.9 +/- 31.3 to 147.5 +/- 24.5 ml in 60 min pacing.

CONCLUSIONS

The thoracoscopic implantation of new electrodes was less invasive, and was a safe procedure for diaphragm pacing. Meticulous care should be taken to avoid muscle fatigue.

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.

The effects of epimysial electrode location on phrenic nerve recruitment and the relation between tidal volume and interpulse interval

Electrode location is of vital importance to diaphragm pacing devices using electrodes implanted on the diaphragm. Complete phrenic nerve recruitment with a single epimysial electrode implanted on the abdominal surface of the diaphragm required placement within 1 cm of the motor point. Recruitment could be increased further using multiple electrodes, provided the electrodes were implanted on opposite sides of the phrenic nerve motor point. The location of the implanted electrode relative to the phrenic nerve motor point also affected the relation between the stimulus interpulse interval (IPI) and the measured tidal volume. Specifically, we found that electrodes implanted lateral to the phrenic nerve motor point had different tidal volume--IPI relations than electrodes placed anterior or posterior to the motor point. We concluded that properly placed epimysial electrodes are required to obtain adequate phrenic nerve recruitment for full time ventilation and knowledge of the relative location of the electrode with respect to motor point is necessary to predict the tidal volume produced by a specific IPI.

An implantable impedance pneumograph monitor for detection of diaphragm contraction and airway obstruction during diaphragm pacing

Impedance pneumography signals were characterised during diaphragm pacing using stimulating and recording electrodes placed on the abdominal surface of the diaphragm. These measurements were useful for the detection of muscle contraction without confounding effects from stimulus artifacts. Impedance pneumography signals were measured using 23 epimysial electrodes implanted in seven dogs with 1-5 experiments on each electrode. The polarity of the change in impedance associated with diaphragm pacing differed for each recording electrode and its configuration. Thirty-four of 57 cases produced increased impedance, 11 produced decreased impedance and the remaining 12 depended on the level of diaphragm activation. Impedance pneumography signals were useful for detecting complete airway obstruction. The mean difference between the impedance measured during open and obstructed airway conditions was 80% of the open airway impedance signal. The difference between open and obstructed airway impedance measurements was a mean of 2.3 times larger with a recording electrode on the same hemidiaphragm as the stimulating electrode, compared to an electrode placed on the opposite hemidiaphragm (p < 0.05, paired t test, four dogs). In addition, the differences between open and completely obstructed airways were a mean of 2.8 times larger when the second recording electrode was placed on the thorax at the fifth intercostal space, compared to the ninth intercostal space (p < 0.05, two-factor ANOVA, one dog, two replicates). It was concluded that impedance pneumograph circuitry could be incorporated into an existing diaphragm pacer using electrodes placed on the diaphragm to provide valuable measurements of the function of the device.