James F. Hogan

Ventilatory Support by Pacing of the Conditioned Diaphragm in Quadriplegia

Abstract We provided full-time ventilatory support In five patients with respiratory paralysis accompanying quadriplegia by continuous electrical pacing of both hemidia-phragms simultaneously for 11 to 33 months through the application to the phrenic nerves of a low-frequency stimulus. The strength and endurance of the diaphragm muscle increased with pacing. Biopsy specimens taken from two patients who had uninterrupted stimulation for 6 and 16 weeks showed changes suggestive of the development of fatigue-resistant muscle fibers. When we compared these results with those of our earlier experience with intermittent unilateral stimulation of the diaphragm in 17 patients with respiratory paralysis, we found that continuous bilateral pacing using low-frequency stimulation appeared to be superior because of more efficient ventilation of both lungs, fewer total coulombs required to effect the same ventilation, and absence of myopathic changes in the diaphragm muscle. For patients with respiratory paralysis and ...

Total Ventilatory Support in a Quadriplegic Patient with Radiofrequency Electrophrenic Respiration

Abstract A patient with respiratory paralysis from injury of the cervical cord was freed from dependence upon a mechanical respirator through the use of electrical stimulation of both phrenic nerves. This was accomplished with radiofrequency transmission to two radio receiver electrode assemblies implanted subcutaneously 14 months ago. By forceful contractions of his unparalyzed neck muscles the patient is able to assist ventilation voluntarily but is unable to support adequate ventilation by voluntary effort alone for more than a few minutes. Total ventilatory support by radiofrequency electrophrenic respiration has been maintained for more than 11 months. The two sides of the diaphragm are stimulated alternately for periods of 12 hours. Normal tidal volume and blood gas concentration with the patient in the recumbent position have been demonstrated. The tracheostomy tube has been removed; the patient can speak, and he has resumed some normal activities.

Long-term ventilatory support by diaphragm pacing in quadriplegia.

Thirty-seven quadriplegic patients with respiratory paralysis were treated by electrical stimulation of the phrenic nerves to pace the diaphragm. Full-time ventilatory support by diaphragm pacing was accomplished in 13 patients. At least half-time support was achieved in 10 others. There were two deaths unrelated to pacing in these two groups. Fourteen patients could not be paced satisfactorily, and 8 of these patients died, most of them from respiratory infections. The average time the 13 patients on total ventilatory support have had bilateral diaphragm pacemakers is 26 months. The longest is 60 months. Many of these patients are out of the hospital and several are in school or working. Injury to the phrenic nerves either by the initial trauma to the cervical cord or during operation for implantation of the nerve cuff was the most significant complication. Nerve damage from prolonged electrical stimulation has not been a problem thus far. A description of the pacemaker, the technique of its implantation, and the pacing schedule are reported.

Long‐Term Follow‐Up of Pacing of the Conditioned Diaphragm in Quadriplegia

ELEFTERIADES, J.A., et al.: Long‐Term Follow‐Up of Pacing of the Conditioned Diaphragm in Quadriplegia. The authors have previously shown that conditioning of the diaphragm for continuous bilateral pacing is a feasible and effective means of ventilation in patients with complete respiratory paralysis from high cervical (above C3) quadriplegia. The present study reports the long‐term results of continuous diaphragmatic pacing. Twelve quadriplegia patients underwent bilateral phrenic nerve pacemaker placement and diaphragm conditioning from 1981 to 1987. Pacing was initiated at 11 Hz and progressively decreased to 7.1 Hz. A pulse train duration of 1.3 seconds for adults and 0.9 seconds for children was used. Long‐term follow‐up information obtained included pacing status (full‐time, part‐time, or mechanical ventilation), ventilation parameters, and social circumstances. Of the 12 patients, 6 continued to pace full time (mean 14.8 years); all were living at home. Three patients paced for an average of 1.8 years before stopping; two were institutionalized. One patient who paced full time for 6.5 years before lapsing to part time, lived at home. Two patients were deceased; one paced continuously for 10 years before his demise, the other stopped pacing after 1 year. Patients who stopped full‐time pacing did so mainly for reasons of inadequate social or financial support or associated medical problems. All patients demonstrated normal tidal volumes and arterial blood gases while pacing full time. Despite theoretical concerns about long‐term nerve damage, no patient lost the ability to pace the phrenic nerve. Threshold currents did not increase over time (original/follow‐up: 0.46/0.47 for right, 0.45/0.46 for left), nor did maximal currents (original/follow‐up: 1.16/1.14 for right, 1.37/1.26 for left). This follow‐up confirms that quadriplegic patients are able to meet long‐term, full‐time ventilation requirements using phrenic nerve stimulation of the conditioned diaphragm. Careful review of diaphragmatic pacing candidates with respect to associated medical conditions, social support, and motivation is essential for appropriate patient selection and successful long‐term results.

Electrical nerve fatigue: Advantages of an alternating bidirectional waveform

Abstract 1. Four applications of stimulating waveforms, cathodal and anodal unidirectional current (UDC) and two types of alternating bidirectional current (ABDC-1 and -2), were evaluated for effectiveness for long-term stimulation. 2. The decrease in tidal volume was significantly greater with cathodal UDC and ABDC-2 stimulation than with ABDC-1 stimulation in both short- and long-term experiments with anesthetized dogs. 3. The decrease in tidal volume with cathodal UDC stimulation was only temporarily restored to control levels when the stimulation was changed to a new site lower on the nerve. 4. Phrenic nerve action potentials decreased significantly following cathodal UDC stimulation. However, this decrease was temporarily reversed by anodal UDC stimulation. ABDC-1 stimulation did not affect nerve action potentials during the stimulation period. 5. Over a 24-hr period there was no change in tidal volume using ABDC-1 stimulation, whereas using UDC cathodal stimulation there was marked decrease. 6. ABDC-1 stimulation required less electricity and energy developed at threshold than cathodal UDC stimulation. 7. We conclude that fatigue accompanying long-term electrophrenic respiration may be postponed by employing an alternating bidirectional symmetrical waveform.

Electrical Techniques for Stimulation of the Phrenic Nerve to Pace the Diaphragm: Inductive Coupling and Battery Powered Total Implant in Asynchronous and Demand Modes

A review of the electrical design of a rf inductively coupled phrenic nerve stimulator for the diaphragm developed in our laboratories will be discussed. Modifications of the original circuit are based on long‐term laboratory and clinical studies. A total implant battery powered stimulator was designed exclusively for animal studies to evaluate fhe effects of several stimulating parameters on diaphragm fatigue and neuromuscular structure. On the basis of these studies the optimum current level, stimulus frequency, respiratory rate, electrode configuration, and waveform were selected for clinical use to pace the diaphragm. A multiprogrammable dual output stimulator responsive to interrogation has been constructed and used in the experimental laboratory in anticipation of clinical application. There was an insignificant difference between the effect on neural structure or diaphragm function of stimulation with pulse width modulated constant voltage or with amplitude‐modulated constant current. Demand pacing: maintenance of normal PACO2 by monitoring ET PACO2 with feedback to the diaphragm pacemaker to adjust the pacing rate has been successful in the experimental animal.

Comparison of 180-degree and 360-degree skeletal muscle nerve cuff electrodes.

Use of skeletal muscle for cardiac augmentation is a promising technique for treatment of end-stage cardiac failure. An electrode woven through the latissimus dorsi that recruits nearby nerve fibers is commonly used to pace skeletal muscles both in clinical practice and in the laboratory. A proximally placed nerve cuff electrode offers potential advantages in improved recruitment of muscle fibers and low threshold for stimulation. We tested the effectiveness of a nerve cuff electrode passed directly about the proximal thoracodorsal nerve. Our report looks at the efficacy of nerve cuff electrode stimulation and compares electrical and histologic characteristics of a 180-degree wrap of the thoracodorsal nerve to a 360-degree wrap in dogs over 3 months. Threshold voltage at the commonly used pulse width of 200 microseconds was typically in the range of 400 to 600 mV for each electrode after 3 months. Statistical analysis revealed no significant difference (p < 0.05) in threshold voltage or current between the 180-degree and 360-degree nerve cuff electrode either at acute evaluation or after 3 months. Even contraction of latissimus dorsi was achieved with all implants. Adenosine triphosphatase staining revealed 100% conversion of type II to type I fibers in all stimulated muscles. Histologic examination of the thoracodorsal nerve and latissimus dorsi muscle revealed no abnormalities grossly or by light microscopy. Thus, a carefully applied nerve cuff electrode is an atraumatic, effective method for skeletal muscle stimulation. The 180-degree and 360-degree nerve cuff configurations are equally effective.

Epicardiac Radiofrequency Cardiac Pacemaker Implant Preliminary Report

A newly designed epicardiac radiofrequency (RF) pacemaker implant is described. The technique allows for a possible two-month battery life and is more efficient and practical than previous RF epicardiac pacemakers. Preliminary studies on 20 animals show that stimulation with the conventional external RF unit, although difficult for prolonged periods in the canine (for anatomical reasons), is possible. Studies on electrode size and configuration were done, and the reasons for selecting a platinum peg electrode are discussed.

Physiologic characteristics of canine skeletal muscle: implications for timing skeletal muscle cardiac assist devices

BACKGROUND Optimal clinical stimulation for skeletal muscle cardiac assist systems (such as dynamic cardiomyoplasty) is not clearly defined. The pressure-generating capacity of canine skeletal muscle ventricles (SMVs) at a variety of preloads and stimulation frequencies was examined as was time for SMVs to develop peak pressure. METHODS SMVs were analyzed just after construction and after 3 months of electrical conditioning. Pressure generation and time to develop peak pressure were determined using a distensible mandrel. RESULTS Higher preloads resulted in increased pressure generation; conditioned SMVs generated significantly less pressure than unconditioned SMVs. Increasing stimulation frequency from 20 to 50 Hz increased pressure-generating capacity; increases beyond 50 Hz did not result in further increases. Time to 90% peak pressure was least at 10 HZ and 65 Hz. CONCLUSIONS Higher stimulation frequencies and preloads result in a more quickly contracting muscle, which generates more pressure. Midrange stimulation frequencies of 30 Hz provide optimal muscle strength and minimize time to develop peak pressure. Initiation of contraction should begin before the time maximal pressure is desired.

Skeletal muscle ventricles in continuity with the bloodstream.

Abstract Background and Aim of Study: The prevalence of end‐stage congestive heart failure and limitation of clinical alternative treatments present the need for creative new solutions. Formation of a ventricle from skeletal muscle (SMV) has shown promise in the animal laboratory. Two modes of the SMV for cardiac assistance, the counterpulsation (CP‐SMV) and the ventricular assist (VA‐SMV), using the latissimus dorsi muscle were applied in a canine model. Ability to augment arterial pressure was assessed. The effect of stimulation delay on the degree of augmentation was also evaluated. Methods and Results: Thirty‐five SMVs were connected in continuity with the bloodstream in the two modes: (1) CP‐SMV (aorta‐to‐aorta) (n =12); and (2) VA‐SMV (left ventricular [LV] apex‐to‐aorta) (n=23). In the CP‐SMV mode, designed to simulate the intra‐aortic balloon pump, the SMV was simply interposed into the path of the descending aorta (DAo) without prosthetic valves in either the inflow or the outflow conduit. In order to obligate blood flow through the SMV, the DAo was ligated between the two grafts. In the VA‐SMV mode, the connection was made with valved conduits from the LV apex (inflow) to the ascending aorta (outflow) (n = 11) or to the DAo (n = 12). The ascending aorta (AAo) was also ligated proximal to the outflow conduit for the same reason of obligating blood flow through the SMV. The SMV was timed to contract in diastole in both the CP‐SMV mode and the VA‐SMV mode. In the VA‐SMV mode, the average systolic pressure without stimulation was 101.6 ± 2.2 mmHg and with stimulation 118.21±4.78 mmHg (mean augmentation, 14.5±2.6 mmHg) (p < 0.01). In the CP‐SMV mode, the average systolic pressure without stimulation was 97±32 mmHg and with stimulation, 122±26 mmHg (mean augmentation, 25±8.6 mmHg) (p < 0.001). We also extended earlier work on timing of stimulation of isolated SMV by evaluating the effect of stimulation delay on the degree of augmentation in continuity with the bloodstream with the SMV in the VA‐SMV configuration. Delays of 50 msec to 225 msec were evaluated. SMV stimulation was via the thoracodorsal nerve at an amplitude of 1.5 V and a frequency of 25 Hz. The greatest augmentation occurred at a stimulation delay of 150 msec (p < 0.001). Conclusion: Both counterpulsation and assist configurations produced effective diastolic augmentation. Although diastolic augmentation occurred with all timing delays, the optimal delay was 150 msec. Complications in the survival animals include AAo problems, SMV rupture, respiratory insufficiency, intraoperative instability, and thrombosis (which occurred in 51% [18/35] of the animals). This high frequency of thrombosis in the canine model suggests the use of a less thrombogenic SMV lining, more aggressive or prolonged anticoagulation, or an alternative animal model.