Reversal of adaptive left ventricular atrophy following electrically-stimulated exercise training in human tetraplegics

Temporal Changes of Cardiac Structure, Function, and Mechanics During Sub-acute Cervical and Thoracolumbar Spinal Cord Injury in Humans: A Case-Series

Individuals with cervical spinal cord injury (SCI) experience deleterious changes in cardiac structure and function. However, knowledge on when cardiac alterations occur and whether this is dependent upon neurological level of injury remains to be determined. Transthoracic echocardiography was used to assess left ventricular structure, function, and mechanics in 10 male individuals (median age 34 years, lower and upper quartiles 32–50) with cervical (n = 5, c-SCI) or thoracolumbar (n = 5, tl-SCI) motor-complete SCI at 3- and 6-months post-injury. Compared to the 3-month assessment, individuals with c-SCI displayed structural, functional, and mechanical changes during the 6-month assessment, including significant reductions in end diastolic volume [121 mL (104–139) vs. 101 mL (99–133), P = 0.043], stroke volume [75 mL (61–85) vs. 60 mL (58–80), P = 0.042], myocardial contractile velocity (S') [0.11 m/s (0.10–0.13) vs. 0.09 m/s (0.08–0.10), P = 0.043], and peak diastolic longitudinal strain rate [1.29°/s (1.23–1.34) vs. 1.07°/s (0.95–1.15), P = 0.043], and increased early diastolic filling over early myocardial relaxation velocity (E/E') ratio [5.64 (4.71–7.72) vs. 7.48 (6.42–8.42), P = 0.043]. These indices did not significantly change in individuals with tl-SCI between time points. Ejection fraction was different between individuals with c-SCI and tl-SCI at 3 [61% (57–63) vs. 54% (52–55), P < 0.01] and 6 months [58% (57–62) vs. 55% (52–56), P < 0.01], though values were considered normal. These results demonstrate that individuals with c-SCI exhibit significant reductions in cardiac function from 3 to 6 months post-injury, whereas individuals with tl-SCI do not, suggesting the need for early rehabilitation to minimize cardiac consequences in this specific population.

Phase 1 Safety Trial of Autologous Human Schwann Cell Transplantation in Chronic Spinal Cord Injury

A phase 1 open-label, non-randomized clinical trial was conducted to determine feasibility and safety of autologous human Schwann cell (ahSC) transplantation accompanied by rehabilitation in participants with chronic spinal cord injury (SCI). Magnetic resonance imaging (MRI) was used to screen eligible participants to estimate an individualized volume of cell suspension to be implanted. The trial incorporated standardized multi-modal rehabilitation before and after cell delivery. Participants underwent sural nerve harvest, and ahSCs were isolated and propagated in culture. The dose of culture-expanded ahSCs injected into the chronic spinal cord lesion of each individual followed a cavity-filling volume approach. Primary outcome measures for safety and trend-toward efficacy were assessed. Two participants with American Spinal Injury Association Impairment Scale (AIS) A and two participants with incomplete chronic SCI (AIS B, C) were each enrolled in cervical and thoracic SCI cohorts (n = 8 total). All participants completed the study per protocol, and no serious adverse events related to sural nerve harvest or ahSC transplantation were reported. Urinary tract infections and skin abrasions were the most common adverse events reported. One participant experienced a 4-point improvement in motor function, a 6-point improvement in sensory function, and a 1-level improvement in neurological level of injury. Follow-up MRI in the cervical (6 months) and thoracic (24 months) cohorts revealed a reduction in cyst volume after transplantation with reduced effect over time. This phase 1 trial demonstrated the feasibility and safety of ahSC transplantation combined with a multi-modal rehabilitation protocol for participants with chronic SCI.

Does aerobic exercise benefit persons with tetraplegia from spinal cord injury? A systematic review

CONTEXT

This review synthesizes the findings of previous research studies on the cardiovascular and metabolic benefits of aerobic exercise for individuals with tetraplegia secondary to spinal cord injury. They are often less active due to muscular paralysis, sensory loss, and sympathetic nervous system dysfunction that result from injury. Consequently, these persons are at higher risk for exercise intolerance and secondary health conditions.

OBJECTIVE

To evaluate the evidence concerning efficacy of aerobic exercise training for improving health and exercise performance in persons with tetraplegia from cervical injury.

METHODS

The search engines PubMed and Google Scholar were used to locate published research. The final 75 papers were selected on the basis of inclusion criteria. The studies were then rank-ordered using Physiotherapy Evidence Database.

RESULTS

Studies combining individuals with tetraplegia and paraplegia show that voluntary arm-crank training can increase mean peak power output by 33%. Functional electrical stimulation leg cycling was shown to induce higher peak cardiac output and stroke volume than arm-crank exercise. A range of peak oxygen uptake (VO_2peak) values have been reported (0.57-1.32 L/min). Both VO_2peak and cardiac output may be enhanced via increased muscle pump in the legs and venous return to the heart. Hybrid exercise (arm-crank and functional electrical stimulation leg cycling) can result in greater peak oxygen uptake and cardiovascular responses.

CONCLUSION

Evidence gathered from this systematic review of literature is inconclusive due to the lack of research focusing on those with tetraplegia. Higher power studies (level 1-3) are needed with the focus on those with tetraplegia.

Functional electrical stimulation cycling exercise after spinal cord injury: a systematic review of health and fitness-related outcomes

OBJECTIVES

The objective of this review was to summarize and appraise evidence on functional electrical stimulation (FES) cycling exercise after spinal cord injury (SCI), in order to inform the development of evidence-based clinical practice guidelines.

METHODS

PubMed, the Cochrane Central Register of Controlled Trials, EMBASE, SPORTDiscus, and CINAHL were searched up to April 2021 to identify FES cycling exercise intervention studies including adults with SCI. In order to capture the widest array of evidence available, any outcome measure employed in such studies was considered eligible. Two independent reviewers conducted study eligibility screening, data extraction, and quality appraisal using Cochranes' Risk of Bias or Downs and Black tools. Each study was designated as a Level 1, 2, 3 or 4 study, dependent on study design and quality appraisal scores. The certainty of the evidence for each outcome was assessed using GRADE ratings ('High', 'Moderate', 'Low', or 'Very low').

RESULTS

Ninety-two studies met the eligibility criteria, comprising 999 adults with SCI representing all age, sex, time since injury, lesion level and lesion completeness strata. For muscle health (e.g., muscle mass, fiber type composition), significant improvements were found in 3 out of 4 Level 1-2 studies, and 27 out of 32 Level 3-4 studies (GRADE rating: 'High'). Although lacking Level 1-2 studies, significant improvements were also found in nearly all of 35 Level 3-4 studies on power output and aerobic fitness (e.g., peak power and oxygen uptake during an FES cycling test) (GRADE ratings: 'Low').

CONCLUSION

Current evidence indicates that FES cycling exercise improves lower-body muscle health of adults with SCI, and may increase power output and aerobic fitness. The evidence summarized and appraised in this review can inform the development of the first international, evidence-based clinical practice guidelines for the use of FES cycling exercise in clinical and community settings of adults with SCI. Registration review protocol: CRD42018108940 (PROSPERO).

Reductions in Cardiac Structure and Function 24 Months After Spinal Cord Injury: A Cross-Sectional Study

OBJECTIVE

To determine the alterations in cardiac structure and function that occur in the months after spinal cord injury (SCI).

STUDY DESIGN

Cross-sectional SETTING: Rehabilitation Hospital PARTICIPANTS: Volunteers (N=29; 4 women, 25 men) between 3 and 24 months after SCI.

MAIN OUTCOME MEASURES

Transthoracic echocardiography was performed on each volunteer. The relationships between time since injury and neurologic and sensory levels of injury to cardiac structure and function were assessed via multiple linear regression.

RESULTS

Time since injury was most strongly associated with reductions in left ventricular end diastolic volume (r²=0.156; P=.034), end systolic volume (r²=0.141; P=.045), and mass (r²=0.138; P=.047). These structural changes were paralleled by reduced stroke volume (r²=0.143; P=.043) and cardiac output (r²=0.317; P=<.001). The reductions in left ventricular structure and systolic function were not differentially affected by neurologic or sensory levels of injury (P=.084-.921).

CONCLUSIONS

These results suggest progressive reductions in left ventricular structure and systolic function between 3 and 24 months after SCI that occur independent of neurologic and sensory levels of injury.

Influence of mid and low paraplegia on cardiorespiratory fitness and energy expenditure

STUDY DESIGN

Observational, Cross-sectional.

OBJECTIVE

Examine the influence of mid (MP) and low (LP) paraplegia on cardiorespiratory fitness (CRF), energy expenditure (EE), and physical activity levels (PAL), and compare these data to able-bodied (AB) individuals.

SETTING

Academic medical center.

METHODS

Persons with MP (n = 6, T6-T8, 83% male, age: 31 ± 11 y, BMI: 24 ± 7 kg/m²) and LP (n = 5; T10-L1, 100% male, age: 39 ± 11 y, BMI: 26 ± 5 kg/m²) and AB controls (n = 6; 67% male, age: 29 ± 12 y, BMI: 26 ± 5 kg/m²) participated. All participants underwent 45-min of arm-crank exercise where CRF and exercise EE were measured. Basal metabolic rate (BMR) was measured, and total daily EE (TDEE) and PAL were estimated.

RESULTS

Absolute VO_2Peak (MP: 1.6 ± 0.2, LP: 1.9 ± 0.1, AB: 2.5 ± 0.7 l/min), peak metabolic equivalents (MP: 6.8 ± 1.3, LP: 5.7 ± 0.7, AB: 8.8 ± 0.8 METs), peak power output (MP: 72.9 ± 11.5, LP: 86.8 ± 6.1, AB: 121.0 ± 34.8 Watts), and maximal heart rate (MP: 177.7 ± 9.8, LP: 157 ± 13.6, AB: 185.2 ± 8.5 bpm) were significantly different between the three groups (p < 0.05). BMR and TDEE did not significantly differ between the three groups (p > 0.05), whereas exercise EE (MP: 7.8 ± 1.2, LP: 9.5 ± 0.7, AB: 12.4 ± 3.5 kcal/min) and PAL (MP: 1.30 ± 0.04, LP: 1.32 ± 0.04, AB: 1.43 ± 0.06) significantly differed (p < 0.05). In the AB group, 33.3% and 66.7% were classified as sedentary or having low activity levels, respectively, while all persons with paraplegia were classified as sedentary according to PAL classifications.

CONCLUSION

Individuals with MP and LP have lower CRF, exercise EE, and PALs compared to AB individuals.

Beneficial Cardiac Structural and Functional Adaptations After Lumbosacral Spinal Cord Epidural Stimulation and Task-Specific Interventions: A Pilot Study

Cardiac myocyte atrophy and the resulting decreases to the left ventricular mass and dimensions are well documented in spinal cord injury. Therapeutic interventions that increase preload can increase the chamber size and improve the diastolic filling ratios; however, there are no data describing cardiac adaptation to chronic afterload increases. Research from our center has demonstrated that spinal cord epidural stimulation (scES) can normalize arterial blood pressure, so we decided to investigate the effects of scES on cardiac function using echocardiography. Four individuals with chronic, motor-complete cervical spinal cord injury were implanted with a stimulator over the lumbosacral enlargement. We assessed the cardiac structure and function at the following time points: (a) prior to implantation; (b) after scES targeted to increase systolic blood pressure; (c) after the addition of scES targeted to facilitate voluntary (i.e., with intent) movement of the trunk and lower extremities; and (d) after the addition of scES targeted to facilitate independent, overground standing. We found significant improvements to the cardiac structure (left ventricular mass = 10 ± 2 g, p < 0.001; internal dimension during diastole = 0.1 ± 0.04 cm, p < 0.05; internal dimension during systole = 0.06 ± 0.03 cm, p < 0.05; interventricular septum dimension = 0.04 ± 0.02 cm, p < 0.05), systolic function (ejection fraction = 1 ± 0.4%, p < 0.05; velocity time integral = 2 ± 0.4 cm, p < 0.001; stroke volume = 4.4 ± 1.5 ml, p < 0.01), and diastolic function (mitral valve deceleration time = -32 ± 11 ms, p < 0.05; mitral valve deceleration slope = 50 ± 25 cm s-1, p < 0.05; isovolumic relaxation time = -6 ± 1.9 ms, p < 0.05) with each subsequent scES intervention. Despite the pilot nature of this study, statistically significant improvements to the cardiac structure, systolic function, and diastolic function demonstrate that scES combined with task-specific interventions led to beneficial cardiac remodeling, which can reverse atrophic changes that result from spinal cord injury. Long-term improvements to cardiac function have implications for increased quality of life and improved cardiovascular health in individuals with spinal cord injury, decreasing the risk of cardiovascular morbidity and mortality.

Systolic and diastolic function in chronic spinal cord injury

Individuals with spinal cord injury develop cardiovascular disease more than age-matched, non-injured cohorts. However, progression of systolic and diastolic dysfunction into cardiovascular disease after spinal cord injury is not well described. We sought to investigate the relationship between systolic and diastolic function in chronic spinal cord injury to describe how biological sex, level, severity, and duration of injury correlate with structural changes in the left ventricle. Individuals with chronic spinal cord injury participated in this study (n = 70). Registered diagnostic cardiac sonographers used cardiac ultrasound to measure dimensions, mass, and systolic and diastolic function of the left ventricle. We found no significant relationship to severity or duration of injury with left ventricle measurements, systolic function outcome, or diastolic function outcome. Moreover, nearly all outcomes measured were within the American Society of Echocardiography-defined healthy range. Similar to non-injured individuals, when indexed by body surface area (BSA) left ventricle mass [-14 (5) g/m2, p < .01], end diastolic volume [-6 (3) mL/m², p < .05], and end systolic volume [-4 (1) mL/m², p < .01] were significantly decreased in women compared with men. Likewise, diastolic function outcomes significantly worsened with age: E-wave velocity [-5 (2), p < .01], E/A ratio [-0.23 (0.08), p < .01], and e’ velocity [lateral: -1.5 (0.3) cm/s, p < .001; septal: -0.9 (0.2), p < .001] decreased with age while A-wave velocity [5 (1) cm/s, p < .001] and isovolumic relaxation time [6 (3) ms, p < .05] increased with age. Women demonstrated significantly decreased cardiac size and volumes compared with men, but there was no biological relationship to dysfunction. Moreover, individuals were within the range of ASE-defined healthy values with no evidence of systolic or diastolic function and no meaningful relationship to level, severity, or duration of injury. Decreases to left ventricular dimensions and mass seen in spinal cord injury may result from adaptation rather than maladaptive myocardial remodeling, and increased incidence of cardiovascular disease may be related to modifiable risk factors.

Experimental Spinal Cord Injury Causes Left-Ventricular Atrophy and Is Associated with an Upregulation of Proteolytic Pathways

Spinal cord injury (SCI) causes autonomic dysfunction, altered neurohumoral control, profound hemodynamic changes, and an increased risk of heart disease. In this prospective study, we investigated the cardiac consequences of chronic experimental SCI in rats by combining cutting edge in vivo techniques (magnetic resonance imaging [MRI] and left-ventricular [LV] pressure-volume catheterization) with histological and molecular assessments. Twelve weeks post-SCI, MRI-derived structural indices and in vivo LV catheterization-derived functional indices indicated the presence of LV atrophy (LV mass in Control vs. SCI = 525 ± 38.8 vs. 413 ± 28.6 mg, respectively; p = 0.0009), reduced ventricular volumes (left-ventricular end-diastolic volume in Control vs. SCI = 364 ± 44 vs. 221 ± 35 μL, respectively; p = 0.0004), and contractile dysfunction (end-systolic pressure-volume relationship in Control vs. SCI = 1.31 ± 0.31 vs. 0.76 ± 0.11 mm Hg/μL, respectively; p = 0.0045). Cardiac atrophy and contractile dysfunction in SCI were accompanied by significantly lower blood pressure, reduced circulatory norepinephrine, and increased angiotensin II. At the cellular level, we found the presence of reduced cardiomyocyte size and increased expression of angiotensin II type 1 receptors and transforming growth factor-beta receptors (TGF-β receptor 1 and 2) post-SCI. Importantly, we found more than a two-fold increase in muscle ring finger-1 and Beclin-1 protein level following SCI, indicating the upregulation of the ubiquitin-proteasome system and autophagy-lysosomal machinery. Our data provide novel evidence that SCI-induced cardiomyocyte atrophy and systolic cardiac dysfunction are accompanied by an upregulation of proteolytic pathways, the activation of which is likely due to loss of trophic support from the sympathetic nervous system, neuromechanical unloading, and altered neurohumoral pathways.

Exercise and Health-Related Risks of Physical Deconditioning After Spinal Cord Injury

A sedentary lifestyle occurring soon after spinal cord injury (SCI) may be in contrast to a preinjury history of active physical engagement and is thereafter associated with profound physical deconditioning sustained throughout the lifespan. This physical deconditioning contributes in varying degrees to lifelong medical complications, including accelerated cardiovascular disease, insulin resistance, osteopenia, and visceral obesity. Unlike persons without disability for whom exercise is readily available and easily accomplished, exercise options for persons with SCI are more limited. Depending on the level of injury, the metabolic responses to acute exercise may also be less robust than those accompanying exercise in persons without disability, the training benefits more difficult to achieve, and the risks of ill-considered exercise both greater and potentially irreversible. For exercise to ultimately promote benefit and not impose additional impairment, an understanding of exercise opportunities and risks if exercise is undertaken by those with SCI is important. The following monograph will thus address common medical challenges experienced by persons with SCI and typical modes and benefits of voluntary exercise conditioning.

A comparison of passive hindlimb cycling and active upper-limb exercise provides new insights into systolic dysfunction after spinal cord injury

Active upper-limb and passive lower-limb exercise are two interventions used in the spinal cord injury (SCI) population. Although the global cardiac responses have been previously studied, it is unclear how either exercise influences contractile cardiac function. Here, the cardiac contractile and volumetric responses to upper-limb (swim) and passive lower-limb exercise were investigated in rodents with a severe high-thoracic SCI. Animals were divided into control (CON), SCI no exercise (NO-EX), SCI passive hindlimb cycling (PHLC), or SCI swim (SWIM) groups. Severe contusion SCI was administered at the T2 level. PHLC and SWIM interventions began on day 8 postinjury and lasted 25 days. Echocardiography and dobutamine stress echocardiography were performed before and after injury. Cardiac contractile indexes were assessed in vivo at study termination via a left ventricular pressure-volume conductance catheter. Stroke volume was reduced after SCI (91 µl in the NO-EX group vs. 188 µl in the CON group, P < 0.05) and was reversed at study termination in the PHLC (167 µl) but not SWIM (90 µl) group. Rates of contraction were reduced in NO-EX versus CON groups (6,079 vs. 9,225 mmHg, respectively, P < 0.05) and were unchanged by PHLC and SWIM training. Similarly, end-systolic elastance was reduced in the NO-EX versus CON groups (0.67 vs. 1.37 mmHg/µl, respectively, P < 0.05) and was unchanged by PHLC or SWIM training. Dobutamine infusion normalized all pressure indexes in each SCI group (all P < 0.05). In conclusion, PHLC improves flow-derived cardiac indexes, whereas SWIM training displayed no cardiobeneficial effect. Pressure-derived deficits were corrected only with dobutamine, suggesting that reduced β-adrenergic stimulation is principally responsible for the impaired cardiac contractile function after SCI.NEW & NOTEWORTHY This is the first direct comparison between the cardiac changes elicited by active upper-limb or passive lower-limb exercise after spinal cord injury. Here, we demonstrate that lower-limb exercise positively influences flow-derived cardiac indexes, whereas upper-limb exercise does not. Furthermore, neither intervention corrects the cardiac contractile dysfunction associated with spinal cord injury.

Body System Effects of a Multi-Modal Training Program Targeting Chronic, Motor Complete Thoracic Spinal Cord Injury

The safety and efficacy of pharmacological and cellular transplantation strategies are currently being evaluated in people with spinal cord injury (SCI). In studies of people with chronic SCIs, it is thought that functional recovery will be best achieved when drug or cell therapies are combined with rehabilitation protocols. However, any functional recovery attributed to the therapy may be confounded by the conditioned state of the body and by training-induced effects on neuroplasticity. For this reason, we sought to investigate the effects of a multi-modal training program on several body systems. The training program included body-weight-supported treadmill training for locomotion, circuit resistance training for upper body conditioning, functional electrical stimulation for activation of sublesional muscles, and wheelchair skills training for overall mobility. Eight participants with chronic, thoracic-level, motor-complete SCI completed the 12-week training program. After 12 weeks, upper extremity muscular strength improved significantly for all participants, and some participants experienced improvements in function, which may be explained by increased strength. Neurological function did not change. Changes in pain and spasticity were highly variable between participants. This is the first demonstration of the effect of this combination of four training modalities. However, balancing participant and study-site burden with capturing meaningful outcome measures is also an important consideration.

Effects of overground locomotor training on the ventilatory response to volitional treadmill walking in individuals with incomplete spinal cord injury: a pilot study

INTRODUCTION

Although there has been substantial emphasis on the neuromuscular and cardiovascular adaptations following rehabilitation, pulmonary adaptations in individuals with incomplete SCI (iSCI) in response to locomotor training have been less frequently studied. In healthy individuals, effective transition from rest to work is accomplished by a hyperpneic response, which exhibits an exponential curve with three phases. However, the degree to which our current understanding of exercise hyperpnea can be applied to individuals with iSCI is unknown. The purpose of this case series was to characterize exercise hyperpnea during a rest to constant work rate (CWR) transition before and after 12-15 weeks of overground locomotor training (OLT).

CASE PRESENTATION

Six subjects with cervical motor incomplete spinal cord injury participated in 12-15 weeks of OLT. Subjects were trained in 90-min sessions twice a week. All training activities were weight-bearing and under volitional control without the assistance of body-weight support harnesses, robotic devices or electrical stimulation. Six minutes of CWR treadmill walking was performed at self-selected pace with cardiorespiratory analysis throughout the tests before and after OLT. Averaged group data for tidal volume, breathing frequency or V_E showed no difference before and after training. V_E variability was decreased by 46.7% after OLT.

DISCUSSION

CWR V_E from rest to work was linear throughout the transition. Following OLT, there was a substantial reduction in V_E variability. Future research should investigate the lack of a phasic ventilatory response to exercise, as well as potential mechanisms of ventilatory variability and its implications for functional performance.

Challenging cardiac function post-spinal cord injury with dobutamine

There is general consensus that spinal cord injuries (SCI) above T6 result in altered sympathetic control of the heart, which negatively influences cardiac structure and function. To by-pass disrupted circuitry and investigate cardiac responses under enhanced sympathetic activity we utilized dobutamine (DOB) stress echocardiography. Animals were divided into a T2, 25g-cm contusive SCI (SCI) or an uninjured control (CON) group. Echocardiography was performed pre-SCI and at 1, 2 and 6weeks post-SCI. Increasing doses of DOB (5, 10 & 20μg/min/kg) were infused intravenously pre-SCI and at 1 and 6weeks post-SCI. Parasternal-short axis images were used to compare group differences in systolic function and track changes in response to SCI and DOB over time. One week post-SCI, stroke volume (SV), end diastolic volume (EDV), cardiac output (CO) and ejection fraction (EF) were all reduced compared to CON and these deficits persisted to 6weeks. We also found an increase in collagen deposition at 6weeks post SCI. Pre-SCI, DOB elicited a decrease in EDV and increases in CO, EF and HR but not SV. At 6weeks following SCI, in addition to increases in CO, EF and HR, DOB also induced increases in SV. This is the first report, to our knowledge, of DOB responses in a contusive SCI model with persistent cardiac impairments. The return of CO to pre-SCI levels and the substantial increase in SV at low DOB dosages shows that impaired descending control of the heart is directly contributing to reduced resting SV after SCI.

Effects of a Functional Electrical Stimulation-Assisted Cycling Program on Immune and Cardiovascular Health in Persons with Spinal Cord Injury

Background: Spinal cord injury (SCI) is associated with both a state of chronic inflammation and an increased prevalence of cardiovascular disease (CVD). These disorders are closely linked and have been shown to negatively influence one another. Participation in regular exercise has been shown to be an effective intervention strategy in the treatment of each of these disorders. For individuals with SCI who may lack the lower limb motor capabilities to perform certain traditional exercise modalities, functional electrical stimulation (FES) cycling may provide an effective alternative. Objective: The purpose of this study was to examine the effects of 12 weeks of FES training performed 3 times per week on physiological indices of cardiovascular function as well as molecular indices of inflammation and cardiovascular health. Methods: Ten individuals with chronic SCI were included. Measures of central and peripheral cardiovascular function as well as hematological and immunological markers were assessed before and after the 12-week exercise program. Results: Enhancements in exercise performance as well as a corresponding increase in peripheral cardiovascular function were achieved, as shown by a significant 34% increase in pulse volume (P = .04) and trends toward increases in cross-sectional area (P = .09) and arterial inflow volume (P = .11) of the common femoral artery. Despite this, no change in any hematological or immunological markers was evident. Conclusion: Although the efficacy of FES exercise in enhancing exercise performance (time and distance to fatigue) and peripheral cardiovascular function has been reaffirmed, no alterations in any molecular indices of cardiovascular risk were achieved.

The effect of FES-rowing training on cardiac structure and function: pilot studies in people with spinal cord injury

STUDY DESIGN

Two studies were conducted: Study-1 was cross-sectional; and Study-2 a longitudinal repeated measures design.

OBJECTIVES

To examine the influence of functional electrical stimulation (FES) rowing training on cardiac structure and function in people with spinal cord injury (SCI).

SETTING

A university sports science department and home-based FES-training.

METHODS

Fourteen participants with C4-T10 SCI (American Spinal Injury Association Impairment Scale A or B) were recruited for the studies. Cardiac structure and function, and peak: oxygen uptake ([Vdot ]O_2peak), power output (PO_peak) and heart rate (HR_peak), were compared between two FES-untrained groups (male n=3, female n=3) and an FES-trained group (male n=3) in Study-1 and longitudinally assessed in an FES-naive group (male n=1, female n=4) in Study-2. Main outcome measures left ventricular-dimensions, volumes, mass, diastolic and systolic function, and [Vdot ]O_2peak, PO_peak and HR_peak. In Study-2, in addition to peak values, the [Vdot ]O₂ sustainable over 30 min and the related PO and HR were also assessed.

RESULTS

Sedentary participants with chronic SCI had cardiac structure and function at the lower limits of non-SCI normal ranges. Individuals with chronic SCI who habitually FES-row have cardiac structure and function that more closely resemble non-SCI populations. A programme of FES-rowing training improved cardiac structure and function in previously FES-naive people.

CONCLUSION

FES-rowing training appears to be an effective stimulus for positive cardiac remodelling in people with SCI. Further work, with greater participant numbers, should investigate the impact of FES-rowing training on cardiac health in SCI.

SPONSORSHIP

We thank the INSPIRE Foundation, UK, for funding these studies.

Activity-Based Restorative Therapies after Spinal Cord Injury: Inter-institutional conceptions and perceptions

This manuscript is a review of the theoretical and clinical concepts provided during an inter-institutional training program on Activity-Based Restorative Therapies (ABRT) and the perceptions of those in attendance. ABRT is a relatively recent high volume and intensity approach toward the restoration of neurological deficits and decreasing the risk of secondary conditions associated with paralysis after spinal cord injury (SCI). ABRT is guided by the principle of neuroplasticity and the belief that even those with chronic SCI can benefit from repeated activation of the spinal cord pathways located both above and below the level of injury. ABRT can be defined as repetitive-task specific training using weight-bearing and external facilitation of neuromuscular activation. The five key components of ABRT are weight-bearing activities, functional electrical stimulation, task-specific practice, massed practice and locomotor training which includes body weight supported treadmill walking and water treadmill training. The various components of ABRT have been shown to improve functional mobility, and reverse negative body composition changes after SCI leading to the reduction of cardiovascular and other metabolic disease risk factors. The consensus of those who received the ABRT training was that ABRT has much potential for enhancement of recovery of those with SCI. Although various institutions have their own strengths and challenges, each institution was able to initiate a modified ABRT program.

Improving the Efficiency of Electrical Stimulation Activities After Spinal Cord Injury

In order to enhance spinal cord injury (SCI) rehabilitation programs using neuromuscular electrical stimulation (NMES) and functional electrical stimulation (FES) it is important to examine the manner in which muscle fibers are recruited and the dose-response relationship. A review of the literature suggests that premature force decline and early fatigue with NMES and FES activities may be alleviated with decreased current frequency and increased current intensity. Dose-response relationships with NMES and FES are dependent on the goals of interest as reversing muscle atrophy can be achieved with activities 2-3 times per week for 6 or more weeks while increasing bone mass is more limited and requires more intense activity with greater exercise frequency and duration, e.g., 3-5 days per week for at least 6-12 months. The best known protocol to elicit neurological improvement is massed practice activities-based restorative therapies (ABRT) (3-5 h per day for several weeks).

Structural remodeling of the heart and its premotor cardioinhibitory vagal neurons following T(5) spinal cord transection

Midthoracic spinal cord injury (SCI) is associated with enhanced cardiac sympathetic activity and reduced cardiac parasympathetic activity. The enhanced cardiac sympathetic activity is associated with sympathetic structural plasticity within the stellate ganglia, spinal cord segments T1-T4, and heart. However, changes to cardiac parasympathetic centers rostral to an experimental SCI are relatively unknown. Importantly, reduced vagal activity is a predictor of high mortality. Furthermore, this autonomic dysregulation promotes progressive left ventricular (LV) structural remodeling. Accordingly, we hypothesized that midthoracic spinal cord injury is associated with structural plasticity in premotor (preganglionic parasympathetic neurons) cardioinhibitory vagal neurons located within the nucleus ambiguus as well as LV structural remodeling. To test this hypothesis, dendritic arborization and morphology (cholera toxin B immunohistochemistry and Sholl analysis) of cardiac projecting premotor cardioinhibitory vagal neurons located within the nucleus ambiguus were determined in intact (sham transected) and thoracic level 5 transected (T5X) rats. In addition, LV chamber size, wall thickness, and collagen content (Masson trichrome stain and structural analysis) were determined. Midthoracic SCI was associated with structural changes within the nucleus ambiguus and heart. Specifically, following T5 spinal cord transection, there was a significant increase in cardiac parasympathetic preganglionic neuron dendritic arborization, soma area, maximum dendritic length, and number of intersections/animal. This parasympathetic structural remodeling was associated with a profound LV structural remodeling. Specifically, T5 spinal cord transection increased LV chamber area, reduced LV wall thickness, and increased collagen content. Accordingly, results document a dynamic interaction between the heart and its parasympathetic innervation.

Passive hind-limb cycling improves cardiac function and reduces cardiovascular disease risk in experimental spinal cord injury

Spinal cord injury (SCI) causes altered autonomic control and severe physical deconditioning that converge to drive maladaptive cardiac remodelling. We used a clinically relevant experimental model to investigate the cardio-metabolic responses to SCI and to establish whether passive hind-limb cycling elicits a cardio-protective effect. Initially, 21 male Wistar rats were evenly assigned to three groups: uninjured control (CON), T3 complete SCI (SCI) or T3 complete SCI plus passive hind-limb cycling (SCI-EX; 2 × 30 min day(-1), 5 days week(-1) for 4 weeks beginning 6 days post-SCI). On day 32, cardio-metabolic function was assessed using in vivo echocardiography, ex vivo working heart assessments, cardiac histology/molecular biology and blood lipid profiles. Twelve additional rats (n = 6 SCI and n = 6 SCI-EX) underwent in vivo echocardiography and basal haemodynamic assessments pre-SCI and at days 7, 14 and 32 post-SCI to track temporal cardiovascular changes. Compared with CON, SCI exhibited a rapid and sustained reduction in left ventricular dimensions and function that ultimately manifested as reduced contractility, increased myocardial collagen deposition and an up-regulation of transforming growth factor beta-1 (TGFβ1) and mothers against decapentaplegic homolog 3 (Smad3) mRNA. For SCI-EX, the initial reduction in left ventricular dimensions and function at day 7 post-SCI was completely reversed by day 32 post-SCI, and there were no differences in myocardial contractility between SCI-EX and CON. Collagen deposition was similar between SCI-EX and CON. TGFβ1 and Smad3 were down-regulated in SCI-EX. Blood lipid profiles were improved in SCI-EX versus SCI. We provide compelling novel evidence that passive hind-limb cycling prevents cardiac dysfunction and reduces cardiovascular disease risk in experimental SCI.

Can the efficacy of electrically stimulated pedaling using a commercially available ergometer BE improved by minimizing the muscle stress-time integral?

INTRODUCTION

The cardiorespiratory and muscular strength benefits of functional electrical stimulation (FES) pedaling for spinal cord injury (SCI) subjects are limited because the endurance of electrically stimulated muscle is low.

METHODS

We tested new electrical stimulation timing patterns (Stim3, designed using a forward dynamic simulation to minimize the muscle stress-time integral) to determine whether SCI subjects could increase work and metabolic responses when pedaling a commercial FES ergometer. Work, rate of oxygen uptake (VO(2)), and blood lactate data were taken from 11 subjects (injury level T4-T12) on repeated trials.

RESULTS

Subjects performed 11% more work pedaling with Stim3 than with existing stimulation patterns (StimErg) (P = 0.043). Average (VO(2)) and blood lactate concentrations were not significantly different between Stim3 (442 ml/min, 5.9 mmol/L) and StimErg (417 ml/min, 5.9 mmol/L).

CONCLUSION

The increased mechanical work performed with Stim3 supports the use of patterns that minimize the muscle stress-time integral to prolong FES pedaling.

Recurrent autonomic dysreflexia exacerbates vascular dysfunction after spinal cord injury

BACKGROUND CONTEXT

Individuals with high spinal cord injury (SCI) are prone to significant fluctuation in blood pressure with episodes of very high and low blood pressure during autonomic dysreflexia (AD) and orthostatic hypotension, respectively. We do not know how such blood pressure lability affects the vasculature.

PURPOSE

We used a well-characterized animal model of AD to determine whether increasing the frequency of AD during recovery from SCI would exacerbate injury-induced dysfunction in resistance vessels.

STUDY DESIGN/SETTING

Experimental animal study. International Collaboration On Repair Discoveries (ICORD), University of British Columbia, Canada.

METHODS

Complete transection of the T3 spinal cord was performed in male Wistar rats. For 14 days after injury, AD was induced via colorectal distension (CRD; 30 minutes per day) in the experimental group (SCI-CRD). One month after SCI, baseline cardiovascular parameters and severity of CRD-induced AD were assessed in SCI-CRD animals and SCI-only controls. Mesenteric arteries were harvested for in vitro myography to characterize vasoactive responses to phenylephrine (PE) and acetylcholine (ACh).

RESULTS

Mesenteric arteries from SCI-CRD animals exhibited larger maximal responses to PE than arteries from SCI-only controls. Hyperresponsiveness to PE was not a product of endothelial dysfunction because mesenteric arteries from both groups had similar vasodilator responses to ACh. Both SCI-only controls and SCI-CRD animals exhibited CRD-evoked AD 1 month after SCI; however, CRD-induced hypertension was less pronounced in animals that were previously exposed to CRD.

CONCLUSIONS

Injury-induced changes within the vasculature may contribute to the development of AD after SCI. Here, we provide evidence that AD itself has significant and long-lasting effects on vascular function. This finding has implications for the medical management of AD and provides an impetus for maintaining stable blood pressure.

The effects of stimulating lower leg muscles on the mechanical work and metabolic response in functional electrically stimulated pedaling

Functional electrical stimulation (FES) pedaling with the muscles of the upper leg has been shown to provide benefit to spinal cord injured (SCI) individuals. FES pedaling with electrical stimulation timing patterns that minimize the stress-time integral of activated muscles has been shown to increase the work individuals can perform during the exercise compared to existing FES stimulation timing patterns. Activation of the lower leg muscles could further enhance the benefit of FES pedaling by increasing the metabolic response to the exercise. For SCI individuals, the objectives of this study were to experimentally determine whether FES pedaling with the upper and lower leg muscles would affect the work generated and increase the physiological responses compared to pedaling with the upper leg muscles alone. Work, rate of oxygen consumption ·VO₂, and blood lactate data were measured from nine SCI subjects (injury level T4-T12) as they pedaled using upper leg and upper and lower leg muscle groups on repeated trials. The subjects performed 6% more work with the upper and lower legs than with the upper legs alone, but the difference was not significant (p = 0.2433). The average rate of oxygen consumption associated with the upper leg muscles (441 ±231 mL/min) was not significantly different from the corresponding average for the upper and lower legs (473 ±213 mL/min) (p = 0.1176). The blood lactate concentration associated with the upper leg muscles (5.9 ±2.3 mmoles/L) was significantly lower than the corresponding average for the upper and lower legs (6.8 ±2.3 mmoles/L) (p = 0.0049). The results indicate that electrical stimulation timing patterns that incorporate the lower leg muscles do increase the blood lactate concentrations. However, there was not enough evidence to reject the null hypothesis that stimulating the lower leg muscles affected the work accomplished or increased the rate of oxygen consumption. In conclusion, incorporating the lower leg muscles in the exercise does not lead to negative effects and could result in enhanced exercise outcomes in the long term.

Lower-extremity functional electrical stimulation decreases platelet aggregation and blood coagulation in persons with chronic spinal cord injury: a pilot study

BACKGROUND

Individuals with spinal cord injury (SCI) develop premature cardiovascular disease. Regular exercise reduces the incidence and symptoms of cardiovascular disease in able-bodied individuals; these salutary effects of exercise have not been documented in persons with SCI.

OBJECTIVE

To evaluate the effects of functional electrical stimulation leg cycle ergometry (FES-LCE) exercise training on platelet aggregation and blood coagulation in persons with SCI.

PARTICIPANTS

Subjects (n=14) with stable chronic (>1 year) paraplegia (T1-T10) or tetraplegia (C4-C8).

METHODS

Blood samples were collected before and after the first and eighth sessions (2 sessions per week for 4 weeks) of FES exercise.

RESULTS

Platelet aggregation was inhibited by 20% after the first session and by 40% (P < 0.001) after the eighth session. Thrombin activity was unchanged after the first session (10.7 +/- 0.85 s to 10.43 +/- 0.56 s) and decreased after the eighth session (12.5 +/- 1.98 s to 11.1 +/- 1.7 s; P < 0.0003). Antithrombin III activity increased after the first (103.8% +/- 8.9% to 110% +/- 6.9%; P < 0.0008) and eighth sessions (107.8% +/- 12.1% to 120.4% +/- 13.1%; P < 0.0001). Cyclic adenosine monophosphate increased after the first (9.9% + 2.5% to 15.8% +/- 3%; P < 0.001) and eighth sessions (17.8% +/- 4.2% to 36.5% +/- 7.6%; P < 0.0001). After the eighth session, factors V and X increased significantly (88% +/- 27% to 103% +/- 23%, P < 0.0001; 100% +/- 40% to 105% +/- 7%, P < 0.01, respectively); factors VII and VIII and fibrinogen did not change significantly. A significant reduction in platelet activation/aggregation was demonstrated in response to FES-LCE. The decrease in thrombin level was caused by the simultaneous increase in antithrombin activity.

CONCLUSION

These findings provide new insight into the potential protective effects of FES-LCE against the risk of cardiovascular disease.

Muscle stimulation waveform timing patterns for upper and lower leg muscle groups to increase muscular endurance in functional electrical stimulation pedaling using a forward dynamic model

Functional electrical stimulation (FES) of pedaling provides a means by which individuals with spinal cord injury can obtain cardiorespiratory exercise. However, the early onset of muscle fatigue is a limiting factor in the cardiorespiratory exercise obtained while pedaling an FES ergometer. One objective of this study was to determine muscle excitation timing patterns to increase muscle endurance in FES pedaling for three upper leg muscle groups and to compare these timing patterns to those used in a commercially available FES ergometer. The second objective was to determine excitation timing patterns for a lower leg muscle group in conjunction with the three upper leg muscle groups. The final objective was to determine the mechanical energy contributions of each of the muscle groups to drive the crank. To fulfill these objectives, we developed a forward dynamic simulation of FES pedaling to determine electrical stimulation on and off times that minimize the muscle stress-time integral of the stimulated muscles. The computed electrical stimulation on and off times differed from those utilized by a commercially available FES ergometer and resulted in 17% and 11% decrease in the muscle stress-time integral for the three upper leg muscle groups and four upper and lower leg muscle groups, respectively. Also, the duration of muscle activation by the hamstrings increased by 5% over a crank cycle for the computed stimulation on and off times, and the mechanical energy generated by the hamstrings increased by 20%. The lower leg muscle group did not generate sufficient mechanical energy to reduce the energy contributions of the upper leg muscle groups. The computed stimulation on and off times could prolong FES pedaling, and thereby provide improved cardiorespiratory and muscle training outcomes for individuals with spinal cord injury. Including the lower leg muscle group in FES pedaling could increase cardiorespiratory demand while not affecting the endurance of the muscles involved in the pedaling task.

Total haemoglobin mass but not cardiac volume adapts to long-term endurance exercise in highly trained spinal cord injured athletes

The oxygen transport system is an important component in the limitation of endurance performance in able-bodied and paraplegic athletes. The aim of the present study was to investigate the total haemoglobin mass (tHb, carbon monoxide rebreathing method) and cardiac volume (HV, echocardiography) in 25 highly endurance trained male spinal cord injured (mainly paraplegic) athletes (SCI-TRAINED) and to compare the results with those of 10 untrained spinal cord injured controls (SCI-UNTRAINED) and in 25 able-bodied elite endurance athletes (TRAINED). tHb and tHb/kg were higher in SCI-TRAINED than in SCI-UNTRAINED (748 +/- 110 vs. 629 +/- 209 g (464 +/- 68 vs. 390 +/- 130 mmol) (mean +/- SD), P = 0.02 and 10.3 +/- 1.3 vs. 7.9 +/- 2.0 g/kg (6.4 +/- 0.8 vs. 4.9 +/- 1.2 mmol/kg), P < 0.0001), while HV and HV/kg showed no significant differences between the two groups (765 +/- 93 vs. 793 +/- 164 ml and 10.6 +/- 1.4 vs. 10.3 +/- 2.5 ml/kg). No difference between SCI-TRAINED and TRAINED was found for septal diameter (9.5 +/- 1.0 mm vs. 9.7 +/- 0.7 mm). However, tHb and tHb/kg in SCI-TRAINED was lower than in TRAINED [896 +/- 123 g (556 +/- 76 mmol), P = 0.0003 and 12.6 +/- 1.3 g/kg (7.8 +/- 0.8 mmol), P < 0.0001]. In spinal cord injured athletes, tHb but not HV adapts moderately to chronic endurance exercise, although tHb in spinal cord injured athletes does not reach the level of able-bodied-trained persons.

A randomized blinded comparison of two methods used for venous antistasis in tetraplegia

OBJECTIVE

The hemodynamic effects of slow sequential compression (SCD) were compared with rapid intermittent pulsatile compression (IPC) in subjects with complete tetraplegia.

METHODS

Twenty subjects underwent Doppler examination of the bilateral popliteal and femoral veins. Resting volume flow per minute (VFM), average venous velocity (AVV), and maximal venous velocity (MVV) were measured in both veins. SCD and IPC were then randomly applied to one limb each, followed by repeat Doppler measurements under compression conditions. Doppler spectral recordings were stored for future analysis, and then measured by an investigator blinded to testing conditions (rest versus compression) and device (SCD versus IPC).

RESULTS

Sequential compression and IPC compression both increased popliteal and femoral vein VFM, AVV, and MVV above resting levels (all p's < 0.001). In the femoral vein VFM (p < 0.05) and MVV (p < 0.05) were augmented during IPC compared to SCD compression.

CONCLUSION

As MVV best reflects performance effectiveness of compression devices, these data find IPC more effective than SCD for stimulating venous blood flow in subjects with tetraplegia.

Cardiovascular Health and Fitness in Persons with Spinal Cord Injury

There are many issues after spinal cord injury that have an impact on cardiovascular health and fitness. This article discusses many of the secondary conditions and changes that occur and how they are affected by maintenance of an active lifestyle. It also discusses many of the benefits and difficulties individuals face in maintaining a regular exercise program after spinal cord injury.

Autonomic Nervous System Dysfunction After Spinal Cord Injury

The autonomic nervous system (ANS) plays a key role in the regulation of many physiologic processes, mediated by supraspinal control from centers in the central nervous system. The role of autonomic dysfunction in persons with spinal cord injuries is crucial to understand because many aspects of the altered physiology seen in these individuals are directly caused by ANS dysregulation.

Preserved cardiac function after chronic spinal cord injury

OBJECTIVE

To assess the effect of chronic deconditioning on cardiac dimensions and function in subjects with high-level spinal cord injury (SCI), who represent a human in-vivo model of extreme inactivity.

DESIGN

Cross-sectional study.

SETTING

University medical center.

PARTICIPANTS

Seven men with tetraplegia and 7 able-bodied controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Echocardiographic measurements of resting cardiac dimensions, systolic function, and global and long-axis diastolic function.

RESULTS

Left ventricular mass index was significantly lower in the subjects with SCI than in the controls (90.8+/-26 g/m(2) vs 122+/-28.9 g/m(2); P=.05). In addition, dimensions of left ventricle, left atrium, and vena cava inferior were all significantly reduced in the subjects with SCI compared with controls (P<.05). There were no differences between the groups for any of the parameters reflecting systolic and global and long-axis diastolic function.

CONCLUSIONS

Tetraplegia is associated with a reduction in cardiac mass and dimensions. Resting diastolic and systolic function is not altered with continued exposure to inactivity, however, which suggests a remodeling of the heart as a physiologic adaptive process.

Exercise Recommendations for Individuals with Spinal Cord Injury

Persons with spinal cord injury (SCI) exhibit deficits in volitional motor control and sensation that limit not only the performance of daily tasks but also the overall activity level of these persons. This population has been characterised as extremely sedentary with an increased incidence of secondary complications including diabetes mellitus, hypertension and atherogenic lipid profiles. As the daily lifestyle of the average person with SCI is without adequate stress for conditioning purposes, structured exercise activities must be added to the regular schedule if the individual is to reduce the likelihood of secondary complications and/or to enhance their physical capacity. The acute exercise responses and the capacity for exercise conditioning are directly related to the level and completeness of the spinal lesion. Appropriate exercise testing and training of persons with SCI should be based on the individual's exercise capacity as determined by accurate assessment of the spinal lesion. The standard means of classification of SCI is by application of the International Standards for Classification of Spinal Cord Injury, written by the Neurological Standards Committee of the American Spinal Injury Association. Individuals with complete spinal injuries at or above the fourth thoracic level generally exhibit dramatically diminished cardiac acceleration with maximal heart rates less than 130 beats/min. The work capacity of these persons will be limited by reductions in cardiac output and circulation to the exercising musculature. Persons with complete spinal lesions below the T(10) level will generally display injuries to the lower motor neurons within the lower extremities and, therefore, will not retain the capacity for neuromuscular activation by means of electrical stimulation. Persons with paraplegia also exhibit reduced exercise capacity and increased heart rate responses (compared with the non-disabled), which have been associated with circulatory limitations within the paralysed tissues. The recommendations for endurance and strength training in persons with SCI do not vary dramatically from the advice offered to the general population. Systems of functional electrical stimulation activate muscular contractions within the paralysed muscles of some persons with SCI. Coordinated patterns of stimulation allows purposeful exercise movements including recumbent cycling, rowing and upright ambulation. Exercise activity in persons with SCI is not without risks, with increased risks related to systemic dysfunction following the spinal injury. These individuals may exhibit an autonomic dysreflexia, significantly reduced bone density below the spinal lesion, joint contractures and/or thermal dysregulation. Persons with SCI can benefit greatly by participation in exercise activities, but those benefits can be enhanced and the relative risks may be reduced with accurate classification of the spinal injury.

Echocardiographic evaluation of wheelchair-bound basketball players

BACKGROUND

Cardiopulmonary function in sedentary men whose lower limbs have been immobilized for years has been shown to be markedly lower than normal. However, the cardiopulmonary function of paraplegics who regularly activate their upper limps and trunk has been suggested to be almost normal in a few studies. The purpose of the present study was to evaluate the left ventricular dimensions, left ventricular mass, systolic and diastolic function in adolescent wheelchair-bound basketball players using echocardio-graphy, and to compare the results with those of sedentary adolescents unable to use their lower extremities and the results of able bodied controls.

METHODS

The study group consisted of 22 male adolescent high school students who were unable to use their lower extremities: 11 were members of a high school basketball team who had been regularly playing basketball for at least 2 years, and 11 were sedentary adolescents none of whom was engaged in any kind of routine training program. The control group consisted of 11 healthy able-bodied male adolescents of similar age.

RESULTS

There were no significant differences in left ventricular dimensions and wall thickness, aortic root, left atrium diameters, or left ventricular filling characteristics between the three groups. Wheelchair-bound basketball players had increased left ventricular ejection fraction and shortening fraction compared with the sedentary unable-bodied individuals. Although left ventricular ejection fractions were significantly lower than in normal adolescents, all ejection fraction values except one were within the normal limits in the unable-bodied basketball players.

CONCLUSION

The results of the present study suggest that an upper extremity exercise program and sports such as basketball can improve the cardiac functions and additional echocardiographic functions of people unable to use their lower extremities, potentially to normal levels.

Cardiac atrophy after bed rest and spaceflight

Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 (n = 5) and 12 (n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 +/- 2.2% (P = 0.005) after 6 wk with an additional atrophy of 7.6 +/- 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 +/- 12.2 vs. 153.4 +/- 12.1 g, P = 0.81). Mean wall thickness decreased (4 +/- 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 +/- 1.7% (P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 +/- 2.7% (P = 0.06) and RV end-diastolic volume by 16 +/- 7.9% (P = 0.06). After spaceflight, LV mass decreased by 12 +/- 6.9% (P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.

Blood volume and hemoglobin after spinal cord injury

OBJECTIVE

The main purpose of this study was to investigate the difference in total blood volume and hemoglobin mass between spinal cord-injured and able-bodied individuals.

DESIGN

Total blood volumes of 13 able-bodied and 10 spinal cord-injured individuals (lesion >T4) were determined using the carbon monoxide method. The reproducibility of the total blood volume determination in our setting and the effect of increased physical activity were assessed.

RESULTS

Comparison of groups showed a significantly higher hemoglobin mass in able-bodied compared with spinal cord-injured individuals. The total blood volume expressed per kilogram of body mass in able-bodied individuals was significantly greater than in spinal cord-injured individuals.

CONCLUSIONS

These results suggest that total blood volume and hemoglobin mass are decreased in spinal cord-injured individuals with a lesion above T4, which may be related to their inactive lifestyle, because total blood volume increased with increased physical activity in these subjects.

Physical performance and cardiovascular and metabolic adaptation of elite female wheelchair basketball players in wheelchair ergometry and in competition

Spinal cord injury leads to a pronounced reduction of cardiovascular, pulmonary, and metabolic ability. Physical activity, up to and including high-performance sports, has obtained importance in the course of rehabilitation and the postclinical phase. Thirteen elite female wheelchair basketball players from the German National Basketball Team and 10 female sedentary spinal cord-injured persons were examined in the study. Heart volume was measured by an echocardiography. All subjects underwent a graded exercise test on a wheelchair ergometer. Additionally, heart rate, lactate, and player points were measured during a competitive basketball game in wheelchair basketball players. Cardiac dimensions were larger for spinal cord-injured wheelchair basketball players (620.3 ml; 9.6 ml x kg(-1)) in comparison with spinal cord-injured persons (477.4 ml; 8.2 ml x kg(-1)) but did not exceed the heart volume of untrained nonhandicapped persons. In contrast, athletes with amputations or those having had poliomyelitis reached training-induced cardiac hypertrophy in relation to body mass (713.7 ml; 13.2 ml x kg(-1)), as observed in nonhandicapped athletes. During graded wheelchair ergometry, wheelchair basketball players showed a higher maximal work rate (59.9 v 45.5 W), maximal oxygen consumption (33.7 v 18.3 ml x min(-1) x kg(-1)), and maximal lactate (9.1 v 5.47 mmol x l(-1)) without a difference in maximal heart rate and workload at AT4 than did spinal cord-injured persons. The average heart rate during the wheelchair basketball game was 151 x min(-1), and the lactate concentration was 1.92 mmol x l(-1). Female athletes with a less severe handicap and higher maximal oxygen consumption during the graded exercise test reached a higher game level in the evaluation. During the competitive basketball game, high cardiovascular stress was observed, indicating a fast aerobic metabolism; the anaerobic lactic acid capacity played a subordinate role. Wheelchair basketball is an effective and suitable sport to enhance physical performance and to induce positive physiological adaptations.

Peripheral nerve stimulation for restoration of motor function

This review paper discusses the use of electrical stimulation to restore function after upper motor neurone type of paralysis. It describes the basic physiology of electrical stimulation, the electrophysiology and biomaterials associated with using metal electrodes to deliver charge to living tissue, and also the adverse effects of stimulation. The central concepts of electrode applications, stimulus parameters, muscle fatigue, and stimulation control are covered. Next, a survey of clinical applications is made with focus on upper and lower limb applications. A concluding section mentions the current status of commercial products available for stimulation.

Evaluation of a training program for persons with SCI paraplegia using the Parastep 1 ambulation system: part 5. Lower extremity blood flow and hyperemic responses to occlusion are augmented by ambulation training

OBJECTIVE

To test whether 12 weeks of exercise conditioning using functional neuromuscular stimulation (FNS) ambulation alters the resting lower extremity blood flow and hyperemic responses to vascular occlusion in subjects with paraplegia, and to determine whether an association exists between limb flow and lower extremity fat-free mass.

DESIGN

Pretest, posttest.

SETTING

Academic medical center.

PARTICIPANTS

Subjects with chronic neurologically complete paraplegia.

INTERVENTION

Thirty-two sessions of microprocessor-controlled ambulation using electrically stimulated contractions of lower extremity muscles and a rolling walker.

OUTCOME MEASURES

Subjects underwent quantitative Doppler ultrasound examination of the common femoral artery (CFA) before and after training. End-diastolic arterial images and arterial flow-velocity profiles obtained at rest and after 5 minutes of suprasystolic thigh occlusion were computer-digitized for analysis of heart rate (HR), CFA peak systolic velocity (PSV), CFA cross-sectional area (CSA), flow velocity integral (FVI), pulse volume (PV), and CFA (arterial) inflow volume (AIV).

RESULTS

Significant effects of training on CSA (p < .0001), FVI (p < .05), computed PV (p < .001), and computed AIV (p < .01) were observed. Resting HR was lower following training (p < .05). The change for resting PSV approached but did not reach significance (p = .083). Analysis of postocclusion PV and AIV showed significant effects for conditioning status (p values < .01), postcompression time (p values < .0001), and their interaction (p values < .01). At 1 minute after occlusion, the posttraining AIV response was 78.2% greater in absolute magnitude and 17.4% more robust when expressed as a percentage change from its resting value than before training. Significant correlations were found between thigh fat free mass and both AIV and PV (p values < .05).

CONCLUSION

Exercise training using FNS ambulation increases the resting lower extremity AIV in individuals with paraplegia and augments the hyperemic response to vascular occlusion. Improved posttraining blood flow is attributable both to vascular structural changes and upregulation of vascular flow control mechanisms. Limb mass is associated with the volume of arterial blood flow.

Lower extremity blood flow and responses to occlusion ischemia differ in exercise-trained and sedentary tetraplegic persons

OBJECTIVE

To test whether lower extremity blood flow and hyperemic responses to vascular occlusion differ among electrically stimulated exercise trained and sedentary tetraplegic persons and subjects without tetraplegia (control).

DESIGN

Blinded cross-sectional comparison, control group.

SETTING

Academic medical center.

PARTICIPANTS

Ten sedentary tetraplegic men, 10 tetraplegic persons previously habituated to electrically stimulated cycling exercise for 0.4 to 7 years, and 10 nondisabled controls.

OUTCOME MEASURES

Subjects underwent quantitative Doppler ultrasound examination of the common femoral artery (CFA). End-diastolic arterial images and arterial flow-velocity profiles obtained at rest and following five minutes of suprasystolic thigh occlusion were computer digitized for analysis of heart rate (HR), CFA peak systolic velocity (PSV), CFA cross-sectional area (CSA), flow velocity integral (FVI), and computed CFA inflow volume (IV).

RESULTS

No group main effects were observed for resting HR or FVI. At rest, trained tetraplegic men had 14.9% greater PSV, 29.8% larger CSA, and 51.3% greater IV (p values < .05) than sedentary tetraplegic subjects. Resting PSV and IV of the trained subjects did not differ from controls, although CSA was smaller than controls (p < .05). Following occlusion, PSV, CSA, and IV averaged 16.5%, 33.4%, and 65.1% greater for trained tetraplegics persons, respectively, than sedentary tetraplegic subjects (p values < .05). Only CSA differed between the control and the trained groups (p < .05).

CONCLUSION

Tetraplegic persons conditioned by electrically stimulated cycling have greater lower extremity blood flow and hyperemic responses to occlusion than do their sedentary counterparts.