Evaluation of respiratory muscle activation in individuals with chronic spinal cord injury

Inspiratory Muscle Performance Is Related to Seated Balance Function in People With Spinal Cord Injury: An Observational Study

OBJECTIVE

To examine the relationship between inspiratory muscle performance (IMP) and functional sitting balance (FSB) in persons with chronic spinal cord injury (SCI). We hypothesized that a moderate correlation would be found between IMP and FSB and that individuals with better balance would have better IMP.

DESIGN

The SCI-specific modification of the Function in Sitting Test (FIST-SCI) measured FSB. The IMP measures included (1) maximal inspiratory pressure (MIP), (2) sustained MIP (SMIP), and (3) inspiratory duration. Upper extremity motor score (UEMS) and level of injury (LOI) were taken from International Standards for Neurological Classification of Spinal Cord Injury examinations. Spearman correlational analyses assessed relationships among these factors in the sample (N=37). Mann-Whitney U tests explored differences between 2 comparison group pairs (tetraplegia group [TG] vs paraplegia group [PG]; independent transfer group [ITG] vs assisted transfer group [ATG]). Regression analysis examined variables predictive of FSB in the TG.

SETTING

Research facility.

PARTICIPANTS

Volunteers with tetraplegia (n=21, American Spinal Injury Association Impairment Scale (AIS) A=8, B=7, C=6) and paraplegia (n=16, AIS A=9, B=4, C=3) (N=37).

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

IMP, LOI, UEMS, FIST-SCI.

RESULTS

UEMS, MIP, SMIP, and LOI had moderate to high correlations with FIST-SCI scores (ρ=0.720 (P<.001), 0.480 (P=.003), 0.467 (P=.004), 0.527 (P=.001), respectively). UEMS, MIP, and FIST-SCI scores were higher in the PG and ITG than the TG and ATG, respectively (PG vs. TG P values=<.001, .008, .002, respectively, and ITG vs. ATG P values=<.001, .032, <.001, respectively). Further, SMIP and UEMS predicted FIST-SCI balance scores in the TG, accounting for 55% of total variance (P<.001) (FIST-SCI=11.88+0.03 [SMIP]+0.425 [UEMS]).

CONCLUSIONS

The relationship between IMP and balance appears preserved after SCI. FSB was predicted, in part, via UEMS and SMIP in the TG. Future research should focus on the effect of SCI-based breathing interventions on FSB.

Acute intermittent hypoxia and respiratory muscle recruitment in people with amyotrophic lateral sclerosis: A preliminary study

Respiratory failure is the main cause of death in amyotrophic lateral sclerosis (ALS). Since no effective treatments to preserve independent breathing are available, there is a critical need for new therapies to preserve or restore breathing ability. Since acute intermittent hypoxia (AIH) elicits spinal respiratory motor plasticity in rodent ALS models, and may restore breathing ability in people with ALS, we performed a proof-of-principle study to investigate this possibility in ALS patients. Quiet breathing, sniff nasal inspiratory pressure (SNIP) and maximal inspiratory pressure (MIP) were tested in 13 persons with ALS and 10 age-matched controls, before and 60 min post-AIH (15, 1 min episodes of 10% O₂, 2 min normoxic intervals) or sham AIH (continuous normoxia). The root mean square (RMS) of the right and left diaphragm, 2nd parasternal, scalene and sternocleidomastoid muscles were monitored. A vector analysis was used to calculate summated vector magnitude (Mag) and similarity index (SI) of collective EMG activity during quiet breathing, SNIP and MIP maneuvers. AIH facilitated tidal volume and minute ventilation (treatment main effects: p < 0.05), and Mag (ie. collective respiratory muscle activity; p < 0.001) during quiet breathing in ALS and control subjects, but there was no effect on SI during quiet breathing. SNIP SI decreased in both groups post-AIH (p < 0.005), whereas Mag was unchanged (p = 0.09). No differences were observed in SNIP or MIP post AIH in either group. Discomfort was not reported during AIH by any subject, nor were adverse events observed. Thus, AIH may be a safe way to increase collective inspiratory muscle activity during quiet breathing in ALS patients, although a single AIH presentation was not sufficient to significantly increase peak inspiratory pressure generation. These preliminary results provide evidence that AIH may improve breathing function in people with ALS, and that future studies of prolonged, repetitive AIH protocols are warranted.

Single-session effects of acute intermittent hypoxia on breathing function after human spinal cord injury

After spinal cord injury (SCI) respiratory complications are a leading cause of morbidity and mortality. Acute intermittent hypoxia (AIH) triggers spinal respiratory motor plasticity in rodent models, and repetitive AIH may have the potential to restore breathing capacity in those with SCI. As an initial approach to provide proof of principle for such effects, we tested single-session AIH effects on breathing function in adults with chronic SCI. 17 adults (13 males; 34.1 ± 14.5 years old; 13 motor complete SCI; >6 months post injury) completed two randomly ordered sessions, AIH versus sham. AIH consisted of 15, 1-min episodes (hypoxia: 10.3% O2; sham: 21% O2) interspersed with room air breathing (1.5 min, 21% oxygen); no attempt was made to regulate arterial CO2 levels. Blood oxygen saturation (SpO2), maximal inspiratory and expiratory pressures (MIP; MEP), forced vital capacity (FVC), and mouth occlusion pressure within 0.1 s (P0.1) were assessed. Outcomes were compared using nonparametric Wilcoxon's tests, or a 2 × 2 ANOVA. Baseline SpO2 was 97.2 ± 1.3% and was unchanged during sham experiments. During hypoxic episodes, SpO2 decreased to 84.7 ± 0.9%, and returned to baseline levels during normoxic intervals. Outcomes were unchanged from baseline post-sham. Greater increases in MIP were evident post AIH vs. sham (median values; +10.8 cmH₂O vs. -2.6 cmH₂O respectively, 95% confidence interval (-18.7) - (-4.3), p = .006) with a moderate Cohen's effect size (0.68). P_0.1, MEP and FVC did not change post-AIH. A single AIH session increased maximal inspiratory pressure generation, but not other breathing functions in adults with SCI. Reasons may include greater spared innervation to inspiratory versus expiratory muscles or differences in the capacity for AIH-induced plasticity in inspiratory motor neuron pools. Based on our findings, the therapeutic potential of AIH on breathing capacity in people with SCI warrants further investigation.

Early Versus Late Tracheostomy in Patients With Acute Traumatic Spinal Cord Injury: A Systematic Review and Meta-analysis

BACKGROUND

Acute traumatic spinal cord injuries (SCIs) often result in impairments in respiration that may lead to a sequelae of pulmonary dysfunction, increased risk of infection, and death. The optimal timing for tracheostomy in patients with acute SCI is currently unknown. This systematic review and meta-analysis aims to assess the optimal timing of tracheostomy in SCI patients and evaluate the potential benefits of early versus late tracheostomy.

METHODS

We searched Medline, PubMed, Embase, Cochrane Central, Cochrane Database of Systematic Reviews, and PsycINFO for published studies. We included studies on adults with SCI who underwent early or late tracheostomy and compared outcomes. In addition, studies that reported a concomitant traumatic brain injury were excluded. Data were extracted independently by 2 reviewers and copied into R software for analysis. A random-effects meta-analysis was performed to estimate the pooled odds ratio (OR) or mean difference (MD).

RESULTS

Eight studies with a total of 1220 patients met our inclusion criteria. The mean age and gender between early and late tracheostomy groups were similar. The majority of the studies performed an early tracheostomy within 7 days from either time of injury or tracheal intubation. Patients with a cervical SCI were twice as likely to undergo an early tracheostomy (OR = 2.13; 95% confidence interval [CI], 1.24-3.64; P = .006) compared to patients with a thoracic SCI. Early tracheostomy reduced the mean intensive care unit (ICU) length of stay by 13 days (95% CI, -19.18 to -7.00; P = .001) and the mean duration of mechanical ventilation by 18.30 days (95% CI, -24.33 to -12.28; P = .001). Although the pooled risk of in-hospital mortality was lower with early tracheostomy compared to late tracheostomy, the results were not significant (OR = 0.56; 95% CI, 0.32-1.01; P = .054). In the subgroup analysis, mortality was significantly lower in the early tracheostomy group (OR = 0.27; P = .006). Finally, no differences in pneumonia between early and late tracheostomy groups were noted.

CONCLUSIONS

Based on the available data, patients with early tracheostomy within the first 7 days of injury or tracheal intubation had higher cervical SCI, shorter ICU length of stay, and shorter duration of mechanical ventilation compared to late tracheostomy. The risk of in-hospital mortality may be lower following an early tracheostomy. However, due to the quality of studies and insufficient clinical data available, it is challenging to make conclusive interpretations. Future prospective trials with a larger patient population are needed to fully assess short- and long-term outcomes of tracheostomy timing following acute SCI.

Respiratory muscle activation patterns during maximum airway pressure efforts are different in women and men

Maximum inspiratory and expiratory pressure values (PI_max and PE_max) are indirect measures of respiratory muscle strength that, in healthy adults, are known to be significantly lower in women compared to men. In part, sex differences in breathing kinematics, lung size, body composition, muscle mass, and muscle fiber composition are thought to be responsible for these effects. However, it is not known whether respiratory muscle activation during maximum respiratory efforts is also sex-specific. In this study, we addressed whether respiratory multi-muscle activation patterns during PI_max and PE_max efforts are different between healthy women and men. Forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), PI_max, PE_max, and surface electromyographic (sEMG) activity recorded from respiratory muscles during these maximum airway pressure efforts were obtained in 13 women and 11 men. Percent predicted values of FVC and FEV₁ were not significantly different in these two groups (women vs. men: 112 ± 14 vs. 105 ± 15%, p = 0.29; and 92 ± 12 vs. 93 ± 13, p = 0.82, Mean ± SD, respectively), while PI_max and PE_max measures were significantly lower in women compared to men (68 ± 16 vs. 88 ± 19 cmH₂O, p = 0.011; and 69 ± 13 vs. 94 ± 17, p = 0.0004, respectively). Using vector-based methodology, by calculating the Similarity Index (SI) as measure of the resemblance between two sEMG patterns and the Magnitude (Mag) representing the overall amount sEMG during motor task, we have found that although the Mag values for both PI_max and PE_max tasks were not significantly different in two groups, the SIs revealed significant sex-dependent differences in muscle activation patterns (0.89 ± 0.08 vs. 0.97 ± 0.02, p = 0.016; and 0.77 ± 0.11 vs. 0.92 ± 0.04, p = 0.0006, respectively). During the PI_max effort, presented as the percentage of total sEMG amplitude, activity of upper trapezius muscle was significantly larger (p = 0.001) while activation of rectus abdominus, oblique, and lower paraspinal muscles were significantly smaller (p = 0.002, p = 0.040, p = 0.005, respectively) in women when compared to the men (50 ± 21 vs. 22 ± 11%; 2 ± 2 vs. 8 ± 7; 4 ± 3 vs. 9 ± 7, 2 ± 3 vs. 7 ± 6, respectively). During PE_max effort, the percentage of sEMG activity were significantly larger in upper and lower trapezius, and intercostal muscles (p = 0.038, p = 0.049, p = 0.037, respectively) and were significantly smaller in pectoralis, rectus abdominus, and oblique muscles (p = 0.021, p < 0.0001, p = 0.048, respectively) in women compared to men (16 ± 10 vs. 9 ± 4%; 16 ± 9 vs. 8 ± 5; 36 ± 12 vs. 25 ± 9; 6 ± 3 vs. 15 ± 5; 14 ± 5 vs. 20 ± 7, respectively). These findings indicate that respiratory muscle activation patterns during maximum airway pressure efforts in healthy individuals are sex-specific. This information should be considered during respiratory motor control evaluation and treatment planning for people with compromised respiratory motor function.

Respiratory functional and motor control deficits in children with spinal cord injury

Children with spinal cord injury (SCI) are at high risk for developing complications due to respiratory motor control deficits. However, underlying mechanisms of these abnormalities with respect to age, development, and injury characteristics are unclear. To evaluate the effect of SCI and age on respiratory motor control in children with SCI, we compared pulmonary function and respiratory motor control outcome measures in healthy typically developing (TD) children to age-matched children with chronic SCI. We hypothesized that the deficits in respiratory functional performance in children with SCI are due to the abnormal and age-dependent respiratory muscle activation patterns. Fourteen TD (age 7±2 yrs., Mean±SD) and twelve children with SCI (age 6±1 yrs.) were evaluated by assessing Forced Vital Capacity (FVC); Forced Expiratory Volume in 1sec (FEV₁); and respiratory electromyographic activity during maximum inspiratory and maximum expiratory airway pressure measurements (PI_max and PE_max). The results indicate a significant reduction (p<.01) of FVC, FEV₁ and PE_max values in children with SCI compared to TD controls. During PE_max assessment, children with SCI produced significantly decreased (p<.01) activation of respiratory muscles below the neurological level of injury (rectus abdominous and external oblique muscles). In addition, children with SCI had significantly increased (p<.05) compensatory muscle activation above the level of injury (upper trapezius muscle). In the TD group, age, height, and weight significantly (p<.05) contributed towards increase in FVC and FEV₁. In children with SCI, only age was significantly (p<.05) correlated with FVC and FEV₁ values. These findings indicate the degree of SCI-induced respiratory functional and motor control deficits in children are age-dependent.

Effects of Respiratory Training on Heart Rate Variability and Baroreflex Sensitivity in Individuals With Chronic Spinal Cord Injury

OBJECTIVE

To evaluate the effects of pressure threshold respiratory training (RT) on heart rate variability and baroreflex sensitivity in persons with chronic spinal cord injury (SCI).

DESIGN

Before-after intervention case-controlled clinical study.

SETTING

SCI research center and outpatient rehabilitation unit.

PARTICIPANTS

Participants (N=44) consisted of persons with chronic SCI ranging from C2 to T11 who participated in RT (n=24), and untrained control subjects with chronic SCI ranging from C2 to T9 (n=20).

INTERVENTIONS

A total of 21±2 RT sessions performed 5 days a week during a 4-week period using a combination of pressure threshold inspiratory and expiratory devices.

MAIN OUTCOME MEASURES

Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and beat-to-beat arterial blood pressure and heart rate changes during the 5-second-long maximum expiratory pressure maneuver (5s MEP) and the sit-up orthostatic stress test, acquired before and after the RT program.

RESULTS

In contrast to the untrained controls, individuals in the RT group experienced significantly increased FVC and FEV₁ (both P<.01) in association with improved quality of sleep, cough, and speech. Sympathetically (phase II) and parasympathetically (phase IV) mediated baroreflex sensitivity both significantly (P<.05) increased during the 5s MEP. During the orthostatic stress test, improved autonomic control over heart rate was associated with significantly increased sympathetic and parasympathetic modulation (low- and high-frequency change: P<.01 and P<.05, respectively).

CONCLUSIONS

Inspiratory-expiratory pressure threshold RT is a promising technique to positively affect both respiratory and cardiovascular dysregulation observed in persons with chronic SCI.

Respiratory motor training and neuromuscular plasticity in patients with chronic obstructive pulmonary disease: A pilot study

The objective of this study was to examine the feasibility of a full-scale investigation of the neurophysiological mechanisms of COPD-induced respiratory neuromuscular control deficits. Characterization of respiratory single- and multi-muscle activation patterns using surface electromyography (sEMG) were assessed along with functional measures at baseline and following 21±2 (mean±SD) sessions of respiratory motor training (RMT) performed during a one-month period in four patients with GOLD stage II or III COPD. Pre-training, the individuals with COPD showed significantly increased (p<0.05) overall respiratory muscle activity and disorganized multi-muscle activation patterns in association with lowered spirometrical measures and decreased fast- and slow-twitch fiber activity as compared to healthy controls (N=4). Following RMT, functional and respiratory sEMG activation outcomes during quite breathing and forced expiratory efforts were improved suggesting that functional improvements, induced by task-specific RMT, are evidence respiratory neuromuscular networks re-organization.

Baroreceptor reflex during forced expiratory maneuvers in individuals with chronic spinal cord injury

Pulmonary and cardiovascular dysfunctions are leading causes of morbidity and mortality in patients with chronic Spinal Cord Injury (SCI). Impaired respiratory motor function and decreased Baroreflex Sensitivity (BS) are predictors for the development of cardiopulmonary disease. This observational case-controlled clinical study was undertaken to investigate if respiratory motor control deficits in individuals with SCI affect their ability to perform the Valsalva maneuver, and to determine if a sustained Maximum Expiratory Pressure (MEP) effort can serve as an acceptable maneuver for determination of the BS in the event that the Valsalva maneuver cannot be performed. The BS outcomes (ms/mmHg) were obtained using continuous beat-to-beat arterial blood pressure (BP) and heart rate (HR) recordings during Valsalva or MEP maneuvers in thirty nine individuals with chronic C3-T12 SCI. Twenty one participants (54%) reported signs of intolerance during the Valsalva maneuver and only 15 individuals (39%) were able to complete this task. Cervical level of injury was a significant risk factor (p=0.001) for failing to complete the Valsalva maneuver, and motor-complete injury was a significant risk factor for symptoms of intolerance (p=0.04). Twenty eight participants (72%) were able to perform the MEP maneuver; the other 11 participants failed to exceed the standard airway pressure threshold of 27cm H2O. Neither level nor completeness of injury were significant risk factors for failure of MEP maneuver. When the required airway pressure was sustained, there were no significant differences between BS outcomes obtained during Valsalva and MEP maneuvers. The results of this study indicate that individuals with high-level and motor-complete SCI are at increased risk of not completing the Valsalva maneuver and that baroreflex-mediated responses can be evaluated by using sustained MEP maneuver when the Valsalva maneuver cannot be performed.

Respiratory Training Improves Blood Pressure Regulation in Individuals With Chronic Spinal Cord Injury

OBJECTIVE

To investigate the effects of respiratory motor training (RMT) on pulmonary function and orthostatic stress-mediated cardiovascular and autonomic responses in individuals with chronic spinal cord injury (SCI).

DESIGN

Before-after intervention case-controlled clinical study.

SETTING

SCI research center and outpatient rehabilitation unit.

PARTICIPANTS

A sample of (N=21) individuals with chronic SCI ranging from C3 to T2 diagnosed with orthostatic hypotension (OH) (n=11) and healthy, noninjured controls (n=10).

INTERVENTIONS

A total of 21±2 sessions of pressure threshold inspiratory-expiratory RMT performed 5d/wk during a 1-month period.

MAIN OUTCOME MEASURES

Standard pulmonary function test: forced vital capacity, forced expiratory volume in one second, maximal inspiratory pressure, maximal expiratory pressure, beat-to-beat arterial blood pressure, heart rate, and respiratory rate were acquired during the orthostatic sit-up stress test before and after the RMT program.

RESULTS

Completion of RMT intervention abolished OH in 7 of 11 individuals. Forced vital capacity, low-frequency component of power spectral density of blood pressure and heart rate oscillations, baroreflex effectiveness, and cross-correlations between blood pressure, heart rate, and respiratory rate during the orthostatic challenge were significantly improved, approaching levels observed in noninjured individuals. These findings indicate increased sympathetic activation and baroreflex effectiveness in association with improved respiratory-cardiovascular interactions in response to the sudden decrease in blood pressure.

CONCLUSIONS

Respiratory training increases respiratory capacity and improves orthostatic stress-mediated respiratory, cardiovascular, and autonomic responses, suggesting that this intervention can be an efficacious therapy for managing OH after SCI.

Respiratory motor function in seated and supine positions in individuals with chronic spinal cord injury

This case-controlled clinical study was undertaken to investigate to what extent pulmonary function in individuals with chronic spinal cord injury (SCI) is affected by posture. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax) were obtained from 27 individuals with chronic motor-complete (n=13, complete group) and motor-incomplete (n=14, incomplete group) C2-T12 SCI in both seated and supine positions. Seated-to-supine changes in spirometrical (FVC and FEV1) and airway pressure (PImax and PEmax) outcome measures had different dynamics when compared in complete and incomplete groups. Patients with motor-complete SCI had tendency to increase spirometrical outcomes in supine position showing significant increase in FVC (p=.007), whereas patients in incomplete group exhibited decrease in these values with significant decreases in FEV1 (p=.002). At the same time, the airway pressure values were decreased in supine position in both groups with significant decrease in PEmax (p=.031) in complete group and significant decrease in PImax (p=.042) in incomplete group. In addition, seated-to-supine percent change of PImax was strongly correlated with neurological level of motor-complete SCI (ρ=-.77, p=.002). These results indicate that postural effects on respiratory performance in patients with SCI can depend on severity and neurological level of SCI, and that these effects differ depending on respiratory tasks. Further studies with adequate sample size are needed to investigate these effects in clinically specific groups and to study the mechanisms of such effects on specific respiratory outcome measures.

The Voluntary Response Index in Electromyographic Study During Landing Test of the Patients With ACL Deficiency: A New Study Protocol

BACKGROUND

Daily Increased rate of anterior cruciate ligament (ACL) injuries in athletes calls for more investigation in these patients to differentiate copers from noncoper ACL-deficient (ACLD) knees as soon as possible.

OBJECTIVES

The current study aims to introduce a new electromyographic protocol, named voluntary response index (VRI), that might help to categorize and differentiate patients with ACLD knee from others in the early stage.

MATERIALS AND METHODS

Thirty-four patients with ACLD knee were allocated into two equal groups, namely, coper and noncoper groups, based upon their ability to return to sport during the preceding six months. The patients with ACLD knee were asked to perform a jump on a force platform from a 75-cm distance.

RESULTS

The results were compared with 17 matched healthy participants. The electromyographic disposable electrodes were attached to the seven muscles of the lower extremity of the participants before performing the test. The outcome measures were the magnitude and similarity index of the VRI, time to stop, vertical ground reaction force, the displacement of the center of pressure's (COP) path line length, and the participants' Tegner, IKDC (International Knee Documentation Committee) as well as KOOS (Knee injury and Osteoarthritis Outcome Score) questionnaires scores. Using the appropriate statistical analysis, the electromyographic and force plate data were compared among the three groups. All efforts went into determining whether an association exists between the findings of each group and the participants' functional questionnaires scores.

CONCLUSIONS

The results of this study would be helpful in objectively differentiating the patients with ACLD knee into coper and noncoper groups to receive appropriate treatments before their return to the competitions.

Long-term facilitation of ventilation in humans with chronic spinal cord injury

RATIONALE

Intermittent stimulation of the respiratory system with hypoxia causes persistent increases in respiratory motor output (i.e., long-term facilitation) in animals with spinal cord injury. This paradigm, therefore, has been touted as a potential respiratory rehabilitation strategy.

OBJECTIVES

To determine whether acute (daily) exposure to intermittent hypoxia can also evoke long-term facilitation of ventilation after chronic spinal cord injury in humans, and whether repeated daily exposure to intermittent hypoxia enhances the magnitude of this response.

METHODS

Eight individuals with incomplete spinal cord injury (>1 yr; cervical [n = 6], thoracic [n = 2]) were exposed to intermittent hypoxia (eight 2-min intervals of 8% oxygen) for 10 days. During all exposures, end-tidal carbon dioxide levels were maintained, on average, 2 mm Hg above resting values. Minute ventilation, tidal volume, and breathing frequency were measured before (baseline), during, and 30 minutes after intermittent hypoxia. Sham protocols consisted of exposure to room air and were administered to a subset of the participants (n = 4).

MEASUREMENTS AND MAIN RESULTS

Minute ventilation increased significantly for 30 minutes after acute exposure to intermittent hypoxia (P < 0.001), but not after sham exposure. However, the magnitude of ventilatory long-term facilitation was not enhanced over 10 days of intermittent hypoxia exposures.

CONCLUSIONS

Ventilatory long-term facilitation can be evoked by brief periods of hypoxia in humans with chronic spinal cord injury. Thus, intermittent hypoxia may represent a strategy for inducing respiratory neuroplasticity after declines in respiratory function that are related to neurological impairment. Clinical trial registered with www.clinicaltrials.gov (NCT01272011).

Respiratory motor control disrupted by spinal cord injury: mechanisms, evaluation, and restoration

Pulmonary complications associated with persistent respiratory muscle weakness, paralysis, and spasticity are among the most important problems faced by patients with spinal cord injury when lack of muscle strength and disorganization of reciprocal respiratory muscle control lead to breathing insufficiency. This review describes the mechanisms of the respiratory motor control and its change in individuals with spinal cord injury, methods by which respiratory function is measured, and rehabilitative treatment used to restore respiratory function in those who have experienced such injury.

Locomotor step training with body weight support improves respiratory motor function in individuals with chronic spinal cord injury

This prospective case-controlled clinical study was undertaken to investigate to what extent the manually assisted treadmill stepping locomotor training with body weight support (LT) can change respiratory function in individuals with chronic spinal cord injury (SCI). Pulmonary function outcomes (forced vital capacity /FVC/, forced expiratory volume one second /FEV1/, maximum inspiratory pressure /PImax/, maximum expiratory pressure /PEmax/) and surface electromyographic (sEMG) measures of respiratory muscles activity during respiratory tasks were obtained from eight individuals with chronic C3-T12 SCI before and after 62±10 (mean±SD) sessions of the LT. FVC, FEV1, PImax, PEmax, amount of overall sEMG activity and rate of motor unit recruitment were significantly increased after LT (p<0.05). These results suggest that these improvements induced by the LT are likely the result of neuroplastic changes in spinal neural circuitry responsible for the activation of respiratory muscles preserved after injury.

Respiration following spinal cord injury: evidence for human neuroplasticity

Respiratory dysfunction is one of the most devastating consequences of cervical spinal cord injury (SCI) with impaired breathing being a leading cause of morbidity and mortality in this population. However, there is mounting experimental and clinical evidence for moderate spontaneous respiratory recovery, or "plasticity", after some spinal cord injuries. Pre-clinical models of respiratory dysfunction following SCI have demonstrated plasticity at neural and behavioral levels that result in progressive recovery of function. Temporal changes in respiration after human SCI have revealed some functional improvements suggesting plasticity paralleling that seen in experimental models-a concept that has been previously under-appreciated. While the extent of spontaneous recovery remains limited, it is possible that enhancing or facilitating neuroplastic mechanisms may have significant therapeutic potential. The next generation of treatment strategies for SCI and related respiratory dysfunction should aim to optimize these recovery processes of the injured spinal cord for lasting functional restoration.

Evaluation of respiratory muscle activation using respiratory motor control assessment (RMCA) in individuals with chronic spinal cord injury

During breathing, activation of respiratory muscles is coordinated by integrated input from the brain, brainstem, and spinal cord. When this coordination is disrupted by spinal cord injury (SCI), control of respiratory muscles innervated below the injury level is compromised leading to respiratory muscle dysfunction and pulmonary complications. These conditions are among the leading causes of death in patients with SCI. Standard pulmonary function tests that assess respiratory motor function include spirometrical and maximum airway pressure outcomes: Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), Maximal Inspiratory Pressure (PImax) and Maximal Expiratory Pressure (PEmax). These values provide indirect measurements of respiratory muscle performance(6). In clinical practice and research, a surface electromyography (sEMG) recorded from respiratory muscles can be used to assess respiratory motor function and help to diagnose neuromuscular pathology. However, variability in the sEMG amplitude inhibits efforts to develop objective and direct measures of respiratory motor function. Based on a multi-muscle sEMG approach to characterize motor control of limb muscles, known as the voluntary response index (VRI), we developed an analytical tool to characterize respiratory motor control directly from sEMG data recorded from multiple respiratory muscles during the voluntary respiratory tasks. We have termed this the Respiratory Motor Control Assessment (RMCA). This vector analysis method quantifies the amount and distribution of activity across muscles and presents it in the form of an index that relates the degree to which sEMG output within a test-subject resembles that from a group of healthy (non-injured) controls. The resulting index value has been shown to have high face validity, sensitivity and specificity. We showed previously that the RMCA outcomes significantly correlate with levels of SCI and pulmonary function measures. We are presenting here the method to quantitatively compare post-spinal cord injury respiratory multi-muscle activation patterns to those of healthy individuals.