Wade G. Holcomb

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.

Preliminary observations on magnetic resonance imaging in refractory epilepsy

We are studying the use of magnetic resonance (MR) imaging in localization of epileptogenic foci in patients with medically refractory partial epilepsy. Imaging is performed using a prototype resistive unit operating at 0.15 T. All studies include 7 mm axial sections obtained with a partial saturation sequence (TR = 200 msec) in which signals are recovered with a spin echo (TE = 11 msec) and images reconstructed using a modified 2D Fourier transform technique. Since the temporal lobe and limbic system are the commonest site of seizure foci in this group of patients, examinations were performed with the plane of section parallel to the temporal horns of the lateral ventricles. Consensus interpretations by a radiologist, neurologist and neurosurgeon have recognized findings considered possibly abnormal in six of 11 epilepsy patients and none of six normal volunteers. These preliminary results indicate that further study is warranted in this group of patients. Critical evaluation of such findings must be carried out in a larger group including normals and patients with a variety of neurologic disorders.

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.

The detection of pulmonary emboli by magnetic resonance imaging. Evaluation of imaging parameters.

The authors studied the influence of gating, cardiac cycle, and timing of rephasing gradients upon the detection of pulmonary emboli by MRI. Serial single-section MR images were obtained in normal dogs and dogs with experimental pulmonary emboli. Images with cardiac gating, respiratory gating, and ungated images were obtained. Cardiac gating in systole and late magnetization rephasing had the best diagnostic accuracy. Gated images were clearly superior to ungated; with combined cardiac and respiratory gating, sensitivity was 82% and specificity 88%. These results are sufficiently promising to warrant further studies.

Cardiac pacemakers: Principles and practices☆

Abstract The fact that prolonged electrical treatment for complete heart block and other arrhythmias is possible cannot be disputed. There is, however, a continuing need to define the parameters of long-term stimulation in precise terms which include current, voltage, stimulus duration, electrode surface area, and a specific need to relate these to the levels and conditions where pacing can be hazardous. The electrodes for permanent pacing may, at the discretion of the surgeon, be placed at thoracotomy or passed transvenously. In the case of the latter a unipolar system utilizing a stainless steel or Elgiloy cathode and a monophasic wave form are preferred. Synchronous pacing, although it is based on an impressive body of experimental evidence and numerous clinical studies, has not yet been proved clearly beneficial. Demand or standby pacing is probably the most significant and promising of recent modifications. Paired and coupled pacing, although hazardous, may have increasing usefulness in certain acute situations. Future development may lead to refinements in hardware or possibly to a completely new approach to the treatment of ventricular arrhythmias.

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.

A FOUR-CHANNEL CARDIAC DIMENSION GAUGE USING INDUCTIVELY COUPLED COILS

Publisher Summary Measurements of regional and global cardiac dimensions are useful in studying both the hemodynamic and mechanical function of the heart. These dimensions may be difficult to obtain; cineradiography using radiopaque markers involves expensive and complex equipment for obtaining and interpreting the data. Strain gauges introduce a variable degree of mechanical loading which may be undesirable. Currently, the transit time of an ultrasonic pulse transmitted between pairs of small crystals implanted in the myocardium is considered one of the more useful techniques available. However, the equipment is complex and requires electronically sophisticated personnel to operate; additionally, the need to implant the crystals in the myocardium risks impairment of regional muscle function. The mutual inductance between two coils varies proportionately, although in a nonlinear fashion, with the separation between them. This principle has been used successfully to measure ventricular diameters and length. However, the approach has not been as versatile as the ultrasonic technique. Interference between nearby pairs of coils has limited this technique to the monitoring of only one or two areas at a time. This chapter describes the development of a simple device using the mutual inductance principle that allows continuous monitoring of up to four cardiac dimensions simultaneously. The simplicity of calibration and use of this instrument has made it a valuable tool in the studies of left ventricular pathophysiology.