Expiratory muscle activation by functional magnetic stimulation of thoracic and lumbar spinal nerves

Functional Magnetic Stimulation of Inspiratory and Expiratory Muscles in Subjects With Tetraplegia

BACKGROUND

Respiratory complications are major causes of morbidity and mortality in persons with a spinal cord injury, partly because of respiratory muscle paralysis. Earlier investigation has demonstrated that functional magnetic stimulation (FMS) can be used as a noninvasive technology for activating expiratory muscles, thus producing useful expiratory functions (simulated cough) in subjects with spinal cord injury.

OBJECTIVE

To evaluate the effectiveness of FMS for conditioning inspiratory and expiratory muscles in persons with tetraplegia.

DESIGN

A prospective before and after trial.

SETTING

FMS Laboratory, Louis Stokes Cleveland VA Medical Center, Cleveland, OH.

PARTICIPANTS

Six persons with tetraplegia.

METHOD

Each subject participated in a 6-week FMS protocol for conditioning the inspiratory and expiratory muscles. A magnetic stimulator was used with the center of a magnetic coil placed at the C7-T1 and T9-T10 spinous processes, respectively. Pulmonary function tests were performed before, during, and after the protocol.

MAIN OUTCOME MEASUREMENTS

Respiratory variables included maximal inspiratory pressure (MIP), inspiratory reserve volume (IRV), peak inspiratory flow (PIF), maximal expiratory pressure (MEP), expiratory reserve volume (ERV), and peak expiratory flow (PEF).

RESULTS

After 6 weeks of conditioning, the main outcome measurements (mean ± standard error) were as follows: MIP, 89.6 ± 7.3 cm H2O; IRV, 1.90 ± 0.34 L; PIF, 302.4 ± 36.3 L/min; MEP, 67.4 ± 11.1 cm H2O; ERV, 0.40 ± 0.06 L; and PEF, 372.4 ± 31.9 L/min. These values corresponded to 117%, 107%, 136%, 109%, 130%, and 124% of pre-FMS conditioning values, respectively. Significant improvements were observed in MIP (P = .022), PIF (P = .0001), and PEF (P = .0006), respectively. When FMS was discontinued for 4 weeks, these values showed decreases from their values at the end of the conditioning protocol, which suggests that continual FMS may be necessary to maintain improved respiratory functions.

CONCLUSION

FMS conditioning of the inspiratory and expiratory muscles improved voluntary inspiratory and expiratory functions. FMS may be a noninvasive technology for respiratory muscle training in persons with tetraplegia.

Abdominal Muscle Training Can Enhance Cough After Spinal Cord Injury

Background. Respiratory complications in people with high-level spinal cord injury (SCI) are a major cause of morbidity and mortality, particularly because of a reduced ability to cough as a result of abdominal muscle paralysis. Objective. We investigated the effect of cough training combined with functional electrical stimulation (FES) over the abdominal muscles for 6 weeks to observe whether training could improve cough strength. Methods. Fifteen SCI subjects (C4-T5) trained for 6 weeks, 5 days per week (5 sets of 10 coughs per day) in a randomized crossover design study. Subjects coughed voluntarily at the same time as a train of electrical stimulation was delivered over the abdominal muscles via posterolaterally positioned electrodes (50 Hz, 3 seconds). Measurements were made of esophageal (Pes) and gastric (Pga) expiratory pressures and the peak expiratory flow (PEFcough) produced at the 3 time points of before, during, and after the training. Results. During voluntary coughs, FES cough stimulation improved Pga, Pes, and PEFcough acutely, 20-fold, 4-fold, and 50%, respectively. Six weeks of cough training significantly increased Pga (37.1 ± 2.0 to 46.5 ± 2.9 cm H2O), Pes (35.4 ± 2.7 to 48.1 ± 2.9 cm H2O), and PEFcough (3.1 ± 0.1 to 3.6 ± 0.1 L/s). Cough training also improved pressures and flow during voluntary unstimulated coughs. Conclusions. FES of abdominal muscles acutely increases mechanical output in coughing in high-level SCI subjects. Six weeks of cough training further increases gastric and esophageal cough pressures and expiratory cough flow during stimulated cough maneuvers.

Posterolateral Surface Electrical Stimulation of Abdominal Expiratory Muscles to Enhance Cough in Spinal Cord Injury

Background. Spinal cord injury (SCI) patients have respiratory complications because of abdominal muscle weakness and paralysis, which impair the ability to cough. Objective. This study aims to enhance cough in high-level SCI subjects (n = 11, SCI at or above T6) using surface electrical stimulation of the abdominal muscles via 2 pairs of posterolaterally placed electrodes. Methods. From total lung capacity, subjects performed maximum expiratory pressure (MEP) efforts against a closed airway and voluntary cough efforts. Both efforts were performed with and without superimposed trains of electrical stimulation (50 Hz, 1 second) at a submaximal intensity set to evoke a gastric pressure ( Pga) of 40 cm H2O at functional residual capacity. Results. In the MEP effort, stimulation increased the maximal Pga (from 21.4 ± 7.0 to 59.0 ± 5.7 cm H2O) and esophageal pressure ( Pes; 47.2 ± 11.7 to 65.6 ± 13.6 cm H2O). During the cough efforts, stimulation increased Pga (19.5 ± 6.0 to 57.9 ± 7.0 cm H2O) and Pes (31.2 ± 8.7 to 56.6 ± 10.5 cm H2O). The increased expiratory pressures during cough efforts with stimulation increased peak expiratory flow (PEF, by 36% ± 5%), mean expiratory flow (by 80% ± 8%), and expired lung volume (by 41% ± 16%). In every subject, superimposed electrical stimulation improved peak expiratory flow during cough efforts (by 0.99 ± 0.12 L/s; range, 0.41-1.80 L/s). Wearing an abdominal binder did not improve stimulated cough flows or pressures. Conclusions. The increases in Pga and PEF with electrical stimulation using the novel posterolateral electrode placement are 2 to 3 times greater than improvements reported in other studies. This suggests that posterolateral electrical stimulation of abdominal muscles is a simple noninvasive way to enhance cough in individuals with SCI.

Physiotherapy secretion removal techniques in people with spinal cord injury: a systematic review

OBJECTIVE

To address whether secretion removal techniques increase airway clearance in people with chronic spinal cord injury (SCI).

DATA SOURCES AND STUDY SELECTION

MEDLINE/PubMed, CINAHL, EMBASE, and PsycINFO were searched from inception to May 2009 for population keywords (spinal cord injury, paraplegia, tetraplegia, quadriplegia) paired with secretion removal-related interventions and outcomes. Inclusion criteria for articles were a research study, irrespective of design, that examined secretion removal in people with chronic SCI published in English.

REVIEW METHODS

Two reviewers determined whether articles met the inclusion criteria, abstracted information, and performed a quality assessment using PEDro or Downs and Black criteria. Studies were then given a level of evidence based on a modified Sackett scale.

RESULTS

Of 2416 abstracts and titles retrieved, 24 met the inclusion criteria. Subjects were young (mean, 31 years) and 84% were male. Most evidence was level 4 or 5 and only 2 studies were randomized controlled trials. Three reports described outcomes for secretion removal techniques in addition to cough, whereas most articles examined the immediate effects of various components of cough. Studies examining insufflation combined with manual assisted cough provided the most consistent, high-level evidence. Compelling recent evidence supports the use of respiratory muscle training or electrical stimulation of the expiratory muscles to facilitate airway clearance in people with SCI.

CONCLUSION

Evidence supporting the use of secretion removal techniques in SCI, while positive, is limited and mostly of low level. Treatments that increase respiratory muscle force show promise as effective airway clearance techniques.

Surface functional electrical stimulation of the abdominal muscles to enhance cough and assist tracheostomy decannulation after high-level spinal cord injury

OBJECTIVE

Evaluation of noninvasive stimulation modalities to augment cough and assist tracheostomy decannulation in high-level tetraplegia.

STUDY DESIGN

Single case study.

METHODS

A 65-year-old man with C4 ASIA C tetraplegia had delayed rehabilitation due to a tracheostomy and recurrent pneumonia primarily resulting from ineffective cough. Anterior surface electrical stimulation (SES) of the abdominal musculature was conducted to train an effective cough and enable decannulation. Training occurred daily for 4 weeks. The patient was tested 1 year later with posterolateral SES to determine the relative clinical effect of this delivery method.

RESULTS

At baseline, the addition of anterior SES increased maximal expiratory pressure (80%), maximal expiratory cough pressure (67%), and peak expiratory flow rate (11%). Three weeks after training began, the patient was decannulated following a program of SES and assisted and voluntary coughing. Upon testing 1 year later, SES with posterolaterally placed electrodes also produced an enhancement of voluntary cough attempts.

CONCLUSIONS

Noninvasive SES can potentially assist decannulation of tracheostomies.

Optimal electrode placement for noninvasive electrical stimulation of human abdominal muscles

Abdominal muscles are the most important expiratory muscles for coughing. Spinal cord-injured patients have respiratory complications because of abdominal muscle weakness and paralysis and impaired ability to cough. We aimed to determine the optimal positioning of stimulating electrodes on the trunk for the noninvasive electrical activation of the abdominal muscles. In six healthy subjects, we compared twitch pressures produced by a single electrical pulse through surface electrodes placed either posterolaterally or anteriorly on the trunk with twitch pressures produced by magnetic stimulation of nerve roots at the T10level. A gastroesophageal catheter measured gastric pressure (Pga) and esophageal pressure (Pes). Twitches were recorded at increasing stimulus intensities at functional residual capacity (FRC) in the seated posture. The maximal intensity used was also delivered at total lung capacity (TLC). At FRC, twitch pressures were greatest with electrical stimulation posterolaterally and magnetic stimulation at T10and smallest at the anterior site (Pga, 30 ± 3 and 33 ± 6 cmH2O vs. 12 ± 3 cmH2O; Pes 8 ± 2 and 11 ± 3 cmH2O vs. 5 ± 1 cmH2O; means ± SE). At TLC, twitch pressures were larger. The values for posterolateral electrical stimulation were comparable to those evoked by thoracic magnetic stimulation. The posterolateral stimulation site is the optimal site for generating gastric and esophageal twitch pressures with electrical stimulation.

Optimal arrangement of magnetic coils for functional magnetic stimulation of the inspiratory muscles in dogs

In an attempt to maximize inspiratory pressure and volume, the optimal position of a single or of dual magnetic coils during functional magnetic stimulation (FMS) of the inspiratory muscles was evaluated in twenty-three dogs. Unilateral phrenic magnetic stimulation (UPMS) or bilateral phrenic magnetic stimulation (BPMS), posterior cervical magnetic stimulation (PCMS), anterior cervical magnetic stimulation (ACMS) as well as a combination of PCMS and ACMS were performed. Trans-diaphragmatic pressure (Pdi), flow, and lung volume changes with an open airway were measured. Transdiaphragmatic pressure was also measured with an occluded airway. Changes in inspiratory parameters during FMS were compared with 1) electrical stimulation of surgically exposed bilateral phrenic nerves (BPES) and 2) ventral root electrical stimulation at C5-C7 (VRES C5-C7). Relative to the Pdi generated by BPES of 36.3 +/- 4.5 cm H2O (Mean +/- SEM), occluded Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and a combined PCMS + ACMS were 51.7%, 61.5%, 22.4%, 100.3%, and 104.5% of the maximal Pdi, respectively. Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and combined ACMS + PCMS were 38.0%, 45.2%, 16.5%, 73.8%, and 76.8%, respectively, of the Pdi induced by VRES (C5-C7) (48.0 +/- 3.9 cm H2O). The maximal Pdi(s) generated during ACMS and combined PCMS + ACMS were higher than the maximal Pdi(s) generated during UPMS, BPMS, or PCMS (p < 0.05). ACMS alone induced 129.8% of the inspiratory flow (73.0 +/- 9.4 L/ min) and 77.5% of the volume (626 +/- 556 ml) induced by BPES. ACMS and combined PCMS + ACMS produce a greater inspiratory pressure than UPMS, BPMS or PCMS. ACMS can be used to generate sufficient inspiratory pressure, flow, and volume for activation of the inspiratory muscles.

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.

Functional magnetic ventilation in dogs

OBJECTIVE

To investigate the efficacy of the magnetic stimulation of inspiratory muscles as an alternative to mechanical ventilation and functional electric stimulation.

DESIGN

A prospective before-after trial.

SETTING

Functional magnetic stimulation laboratory in a Veterans Administration health care system.

ANIMALS

Six male mongrel dogs, each weighing between 25 and 35 kg.

INTERVENTIONS

Commercially available magnetic stimulators with a round magnetic coil were used. The center of the magnetic coil was placed posteriorly over the C5-7 vertebrae of the spinal cord transected dogs. Magnetic stimulation parameters were set at 80% intensity, 20 Hz, and a 1.2-second on and 3.8-second off pulse train.

MAIN OUTCOME MEASURES

The major outcomes were changes in tidal volume (VT), tracheal pressure (Ptr), and arterial partial pressure of carbon dioxide (PaCO2) and oxygen sustained by magnetic stimulation over time.

RESULTS

The average Vt and Ptr produced during functional magnetic ventilation (FMV) were.47+/-.07 L and -4.7+/-.51 cmH2O, respectively. Blood gas data showed that PaCO2 increased from a baseline of 33 to 75 mmHg, whereas pH decreased from 7.33 to 6.99 at the end of the 1-hour FMV period.

CONCLUSIONS

FMV was achieved for 2 hours in dogs with C2 spinal cord transection. Additional refinements in magnetic stimulation are needed to improve ventilation in animals.

Functional magnetic stimulation facilitates gastric emptying

OBJECTIVE

To evaluate the effect of functional magnetic stimulation (FMS) on gastric emptying in able-bodied and spinal cord injury (SCI) subjects.

DESIGN

A prospective, nonrandomized clinical experiment.

SETTING

SCI and disorder center in a Veterans Affairs medical facility.

PARTICIPANTS

Five healthy, able-bodied subjects and 4 subjects with SCI.

INTERVENTION

A commercially available magnetic stimulator was used; a round magnetic coil was placed along the T9 spinous process. The intensity of the magnetic stimulation was 60%, with a frequency of 20 Hz, and a burst length of 2 seconds for the gastric emptying protocol. Man Outcome Measures: Rate of gastric emptying and time required to reach gastric emptying half-time (GE(t1/2)) with and without FMS. Data fit into linear regression curve.

RESULTS

Accelerated gastric emptying was achieved in both able-bodied and SCI subjects. The mean +/- standard error of mean of the GE(t1/2) at baseline and with FMS was 36+/-2.9 minutes and 33+/-3.1 minutes, respectively, for able-bodied subjects, and 84+/-11.1 minutes and 59+/-12.7 minutes, respectively, for SCI subjects.

CONCLUSION

Gastric emptying was enhanced by FMS in able-bodied subjects and was greatly enhanced in SCI subjects. FMS can be a useful noninvasive therapeutic tool to facilitate gastric emptying in humans.

Mechanism of expiratory muscle activation during lower thoracic spinal cord stimulation

Lower thoracic spinal cord stimulation (SCS) may be a useful method to restore an effective cough mechanism. In dogs, two groups of studies were performed to evaluate the mechanism of the expiratory muscle activation during stimulation at the T(9)-T(10) level, which results in the greatest changes in airway pressure. In one group, expiratory muscle activation was monitored by evoked muscle compound action potentials (CAPs) from the internal intercostal muscles in the 10th, 11th, and 12th interspaces and from portions of the external oblique innervated by the L(1) and L(2) motor roots. SCS, applied with single shocks, resulted in short-latency CAPs at T(10) but not at more caudal levels. SCS resulted in long-latency CAPs at each of the more caudal caudal recording sites. Bilateral dorsal column sectioning, just below the T(11) spinal cord level, did not affect the short-latency CAPs but abolished the long-latency CAPs and also resulted in a fall in airway pressure generation. In the second group, sequential spinal root sectioning was performed to assess their individual mechanical contribution to pressure generation. Section of the ventral roots from T(8) through T(10) resulted in negligible changes, whereas section of more caudal roots resulted in a progressive reduction in pressure generation. We conclude that 1) SCS at the T(9)-T(10) level results in direct activation of spinal cord roots within two to three segments of the stimulating electrode and activation of more distal roots via spinal cord pathways, and 2) pathway activation of motor roots makes a substantial contribution to pressure generation.

Improved coil design for functional magnetic stimulation of expiratory muscles

Our studies have demonstrated effective stimulation of the expiratory muscles in patients with spinal cord injury (SCI) using functional magnetic stimulation (FMS). The observed contraction of the expiratory muscles and functional improvement of the pulmonary functions make functional magnetic stimulation an appropriate tool for expiratory muscle training. To fully capitalize on the benefits of FMS for expiratory muscle training, this study aimed to optimize the magnetic coils (MCs). The primary goal of this study was to investigate how two parameters of the MC size and winding structure, would affect expiratory muscle training. By varying these parameters, our approach was to conceptualize and evaluate the induced electric field and nerve activation function distributions of six coils, round 9.2, 13.7, and 20 cm, and spiral 9.2-, 13.7-, and 20-cm coils in the computer modeling phase. Round 9.2 cm, spiral 13.7 cm, and spiral 20-cm coils were also evaluated in experimental studies for induced electrical field and in clinical studies of expiratory muscles. Both the computer models and experimental measurements indicated that the spiral 20-cm coil can not only stimulate more expiratory spinal nerves but can also stimulate them more evenly. In addition, coils with larger diameters had better penetration than those with smaller diameters. The clinical results showed that the spiral 20-cm coil produced higher expiratory pressure, flow, and volume in five able-bodied subjects, and it was the coil of choice among the subjects when asked their preferences. In our attempt to optimize MC design for FMS of expiratory muscle training, we followed the designing guidelines set out in our previous study and arrived at a more effective tool.

Functional magnetic stimulation for conditioning of expiratory muscles in patients with spinal cord injury

OBJECTIVE

To evaluate the effectiveness of functional magnetic stimulation (FMS) in conditioning expiratory muscles patients with spinal cord injury (SCI).

DESIGN

A prospective before-after trial.

SETTING

The Functional Magnetic Stimulation Laboratory of the SCI Health Care Group, VA Long Beach Health Care System, and the Spinal Cord Injury Services, Department of Veterans Affairs, Palo Alto Health Care System.

PARTICIPANTS

Eight men with tetraplegia.

INTERVENTION

Expiratory muscle training was achieved by placing a magnetic stimulator with a round magnetic coil along subjects' lower thoracic spine.

MAIN OUTCOME MEASURES

Measures taken were the maximal expired pressure at total lung capacity (MEP-TLC) and at functional residual capacity (MEP-FRC), expiratory reserve volume (ERV), and the forced expiratory flow rate at TLC (FEF-TLC) and at FRC (FEF-FRC) by subjects' voluntary maximal efforts.

RESULTS

After 4 weeks of conditioning, the mean +/- standard error of the mean values were: MEP-TLC, 55.3 +/- 8.6cmH(2)O; MEP-FRC, 29.6 +/- 5.6cmH(2)O; ERV,.57 +/-.08L; FEF-TLC, 4.3 +/- 0.5L/s; and FEF-FRC, 1.9 +/- 0.2L/s. These values correspond to, respectively, 129%, 137%, 162%, 109%, and 127% of pre-FMS conditioning values. When FMS was discontinued for 2 weeks, the MEP-TLC returned to its pre-FMS training value.

CONCLUSION

A 4-week protocol of FMS of the expiratory muscles improves voluntary expiratory muscle strength significantly, indicating that FMS can be a noninvasive therapeutic technology in respiratory muscle training for persons with tetraplegia.

Functional magnetic stimulation of the colon in persons with spinal cord injury

OBJECTIVE

To evaluate the usefulness of functional magnetic stimulation (FMS) as a noninvasive method to stimulate the colon in individuals with spinal cord injury (SCI).

DESIGN

A prospective before-after trial consisting of 2 protocols.

SETTING

FMS laboratories of 2 SCI centers.

PARTICIPANTS

Two able-bodied men and 13 men with SCI levels ranging from C3 to L1. Protocol 1 consisted of 9 subjects, 2 of whom were excluded from the analysis. Protocol 2 consisted of 4 subjects.

INTERVENTION

Commercially available magnetic stimulators with round magnetic coils (MCs) were used. Protocol 1 measured the effects of FMS on rectal pressure by placing the MC on the transabdominal and lumbosacral regions. Protocol 2 consisted of a 5-week stimulation period to investigate the effects of FMS on total and segmental colonic transit times (CTTs).

MAIN OUTCOME MEASURE

An increase in rectal pressure and a decrease in CTT by magnetic stimulation.

RESULTS

Data were averaged and the standard error of the mean was calculated. Statistically significant changes in rectal pressure and CTT were also measured. Rectal pressures increased from 26.7 +/- 7.44cmH(2)O to 48.0 +/- 9.91cmH(2)O, p =.0037, with lumbosacral stimulation, and from 30.0 +/- 6.35cmH(2)O to 42.7 +/- 7.95cmH(2)O, p =.0015, with transabdominal stimulation. With FMS, the mean CTT decreased from 105.2 to 89.4 hours, p =.02.

CONCLUSION

FMS is able to stimulate the colon and reduce CTT. FMS is a noninvasive, technological advancement for managing neurogenic bowel in patients with SCI.