Biomedical subjects

Anthony F DiMarco

Publications and source records attributed to Anthony F DiMarco.

9 recordsLinked to original sources

PubMed2006

Changes in expiratory muscle function following spinal cord section.

Following spinal cord injury, muscles below the level of injury develop variable degrees of disuse atrophy. The present study assessed the physiological changes of the expiratory muscles in a cat model of spinal cord injury. Muscle fiber typing, cross-sectional area, muscle weight, and changes in pressure-generating capacity were assessed in five cats spinalized at the T(6) level. Airway pressure (P)-generating capacity was monitored during lower thoracic spinal cord stimulation before and 6 mo after spinalization. These parameters were also assessed in five acute animals, which served as controls. In spinalized animals, P fell from 41 +/- l to 28 +/- 3 cm H2O (means +/- SE; P < 0.001). Muscle weight of the external oblique, internal oblique, transversus abdominis, and internal intercostal muscles decreased significantly (P < 0.05 for each). Muscle weight of the external oblique, internal oblique, transversus abdominis, and internal intercostal, but not rectus abdominis (RA), correlated linearly with P (r > 0.7 for each; P < 0.05 for each). Mean muscle fiber cross-sectional area of these muscles was significantly smaller (P < 0.05 for each; except RA) and also correlated linearly with P (r > 0.55 for each; P < 0.05 for each, except RA). In spinalized animals, the expiratory muscles demonstrated a significant increase in the population of fast muscle fibers. These results indicate that, following spinalization, 1) the expiratory muscles undergo significant atrophy and fiber-type transformation and 2) the P-generating capacity of the expiratory muscles falls significantly secondary to reductions in muscle mass.

Abdominal Muscles↗

PubMed2006

Spinal cord stimulation: a new method to produce an effective cough in patients with spinal cord injury.

Patients with spinal cord injury have an increased risk of developing respiratory tract infections as the result of expiratory muscle paralysis and consequent inability to cough. We have developed a method by which the expiratory muscles can be activated via lower thoracic and upper lumbar spinal cord stimulation to produce an effective cough mechanism. In a tetraplegic patient who required frequent (8.57+/-2.3 times per week [mean+/-SEM]) caregiver assistance to facilitate airway clearance and expectoration of secretions, three epidural electrodes were applied in the T9, T11, and L1 spinal cord regions. During stimulation at the T9 and L1 levels, airway pressures were 90 and 82 cm H2O, respectively. Peak expiratory flow rates were 6.4 L/s and 5.0 L/s; respectively. During combined (T9+L1) stimulation, airway pressure and expiratory flow rate increased to 132 cm H2O and 7.4 L/s, respectively. Addition of the third lead did not result in further increases in pressure generation. These values are characteristic of those observed with a normal subject. Because the patient is able to trigger the device independently, he no longer requires caregiver support for airway management. If confirmed in additional patients, spinal cord stimulation may be a useful method to restore an effective cough mechanism in patients with spinal cord injury.

Cough↗

PubMed2006

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.

Diaphragm↗

PubMed2006

Respiratory dysfunction and management in spinal cord injury.

Respiratory dysfunction is a major cause of morbidity and mortality in spinal cord injury (SCI), which causes impairment of respiratory muscles, reduced vital capacity, ineffective cough, reduction in lung and chest wall compliance, and excess oxygen cost of breathing due to distortion of the respiratory system. Severely affected individuals may require assisted ventilation, which can cause problems with speech production. Appropriate candidates can sometimes be liberated from mechanical ventilation by phrenic-nerve pacing and pacing of the external intercostal muscles. Partial recovery of respiratory-muscle performance occurs spontaneously. The eventual vital capacity depends on the extent of spontaneous recovery, years since injury, smoking, a history of chest injury or surgery, and maximum inspiratory pressure. Also, respiratory-muscle training and abdominal binders improve performance of the respiratory muscles. For patients on long-term ventilation, speech production is difficult. Often, practitioners are reluctant to deflate the tracheostomy tube cuff to allow speech production. Yet cuff-deflation can be done safely. Standard ventilator settings produce poor speech quality. Recent studies demonstrated vast improvement with long inspiratory time and positive end-expiratory pressure. Abdominal binders improve speech quality in patients with phrenic-nerve pacers. Recent data show that the level and completeness of injury and older age at the time of injury may not be related directly to mortality in SCI, which suggests that the care of SCI has improved. The data indicate that independent predictors of all-cause mortality include diabetes mellitus, heart disease, cigarette smoking, and percent-of-predicted forced expiratory volume in the first second. An important clinical problem in SCI is weak cough, which causes retention of secretions during infections. Methods for secretion clearance include chest physical therapy, spontaneous cough, suctioning, cough assistance by forced compression of the abdomen ("quad cough"), and mechanical insufflation-exsufflation. Recently described but not yet available for general use is activation of the abdominal muscles via an epidural electrode placed at spinal cord level T9-L1.

Breathing Exercises↗

PubMed2005

Restoration of respiratory muscle function following spinal cord injury. Review of electrical and magnetic stimulation techniques.

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.

Animals↗

PubMed2005

Combined intercostal and diaphragm pacing to provide artificial ventilation in patients with tetraplegia.

OBJECTIVE: To evaluate the usefulness of combined intercostal and diaphragm pacing to maintain independence from mechanical ventilation. DESIGN: A prospective trial. SETTING: Clinical research center at a large tertiary hospital. PARTICIPANTS: Four ventilator-dependent subjects with spinal cord injury with only unilateral phrenic nerve function. INTERVENTION: During an initial surgical procedure, a multipolar epidural disk electrode was positioned on the ventral surface of the upper-thoracic spinal cord via a hemilaminectomy to activate the inspiratory intercostal muscles. A phrenic nerve electrode was implanted unilaterally via the thoracic approach. MAIN OUTCOME MEASURES: Inspired volume production and duration that subjects could be comfortably maintained when off mechanical ventilatory support. RESULTS: Initial maximum inspired volumes from combined intercostal and diaphragm stimulation ranged between .23 and .93L and significantly increased over the course of reconditioning period to between 0.55 and 1.31L; subjects could be maintained off mechanical ventilation between 16 and 24 hours a day. CONCLUSIONS: Combined intercostal and unilateral diaphragm pacing may be a useful therapeutic modality capable of maintaining long-term ventilatory support in patients with only unilateral phrenic nerve function.

Diaphragm↗

PubMed2005

Phrenic nerve pacing via intramuscular diaphragm electrodes in tetraplegic subjects.

CONTEXT: Diaphragm pacing in ventilator-dependent tetraplegic subjects is usually achieved by the placement of phrenic nerve electrodes via thoracotomy. However, this technique may be accomplished less invasively via laparoscopic placement of IM electrodes, at a lower cost and with less risk of injury to the phrenic nerve. OBJECTIVE: To assess the feasibility of laparascopic placement of IM diaphragm electrodes to achieve long-term ventilatory support in ventilator-dependent tetraplegic subjects. DESIGN, SETTING, AND PARTICIPANTS: Two IM diaphragm electrodes were placed laparoscopically in each hemidiaphragm in five subjects with ventilator-dependent tetraplegia. Studies were performed either on an outpatient basis or with a single overnight hospitalization. Ventilator-dependent tetraplegic subjects were identified in whom bilateral phrenic nerve function was present, as determined by phrenic nerve conduction studies. Following electrode placement, subjects participated in a conditioning program to improve the strength and endurance of the diaphragm over a period of 15 to 25 weeks. The duration of the study was variable depending on the time necessary to determine the maximum duration that individuals could be maintained without mechanical ventilation support. MAIN OUTCOME MEASURES: Magnitude of inspired volume generation and duration of ventilatory support with bilateral diaphragm pacing alone. RESULTS: In four of the five subjects studied, initial bilateral diaphragm stimulation resulted in inspired volumes between 430 and 1,060 mL. Reconditioning of the diaphragm over several weeks resulted in substantial increases in inspired volumes to 1,100 to 1,240 mL. These subjects were comfortably maintained without mechanical ventilatory support for prolonged time periods by diaphragm pacing, by full-time ventilatory support in three subjects, and 20 h per day, in the fourth subject. No response to stimulation was observed in one subject, most likely secondary to denervation atrophy. CONCLUSIONS: Diaphragm pacing in ventilator-dependent tetraplegic subjects can be successfully achieved via laparascopic placement of IM electrodes.

Adult↗

PubMed2004

Clinical applications of electrical stimulation after spinal cord injury.

During the last one-half century, electrical stimulation has become clinically significant for improving health and restoring useful function after spinal cord injury. Short-term stimulation can be provided by electrodes on the skin or percutaneous fine wires, but implanted systems are preferable for long-term use. Electrical stimulation of intact lower motor neurons can exercise paralyzed muscles and reverse wasting; improve strength, endurance, and cardiovascular fitness; and may reduce the progression of osteoporosis. Other potential therapeutic uses being investigated include reduction of spasticity, prevention of deep vein thrombosis, and improvement of tissue health. Pacing of intact phrenic nerves in high tetraplegia can produce effective respiration without mechanical ventilation, allowing improved speech, increased mobility, and increased sense of well-being. Improvement of cough has also been demonstrated. Stimulation of intact sacral nerves can produce effective micturition and reduce urinary tract infection; it can also improve bowel function and erection. It is usually combined with posterior sacral rhizotomy to improve continence and bladder capacity, and the combination has been shown to reduce costs of care. Electroejaculation can now produce semen in most men with spinal cord injury. Significant achievements have also been made in restoring limb function. Useful hand grasp can be provided in C5 and C6 tetraplegia, reducing dependence on adapted equipment and assistants. Standing, assistance with transfers, and walking for short distances can be provided to selected persons with paraplegia, improving their access to objects, places, and opportunities that are inaccessible from a wheelchair. This review summarizes the current state of therapeutic and neuroprosthetic applications of electrical stimulation after spinal cord injury and identifies some future directions of research and clinical and commercial development.

Electric Stimulation Therapy↗

PubMed2002

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.

Adult↗