Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

STUDY DESIGN

Longitudinal.

OBJECTIVES

The purpose of this study was to evaluate the effect of lower extremity resistance training on quadriceps fatigability, femoral artery diameter, and femoral artery blood flow.

SETTING

Academic Institution.

METHODS

Five male chronic spinal cord injury (SCI) individuals (American Spinal Injury Association (ASIA): A complete; C5-T10; 36+/-5 years old) completed 18 weeks of home-based neuromuscular electrical stimulation (NMES) resistance training. Subjects trained the quadriceps muscle group twice a week with four sets of 10 dynamic knee extensions against resistance while in a seated position. All measurements were made before training and after 8, 12, and 18 weeks of training. Ultrasound was used to measure femoral artery diameter and blood flow. Blood flow was measured before and after 5 and 10 min of distal cuff occlusion, and during a 4-min isometric electrical stimulation fatigue protocol.

RESULTS

Training resulted in significant increases in weight lifted and muscle mass, as well as a 60% reduction in muscle fatigue (P = 0.001). However, femoral arterial diameter did not increase. The range was 0.44+/-0.03 to 0.46+/-0.05 cm over the four time points (P = 0.70). Resting, reactive hyperemic, and exercise blood flow did not appear to change with training.

CONCLUSION

NMES resistance training improved muscle size and fatigue despite an absence of response in the supplying vasculature. These results suggest that the decreases in arterial caliber and blood flow seen with SCI are not tightly linked to muscle mass and fatigue resistance. In addition, muscle fatigue in SCI patients can be improved without increases in arterial diameter or blood flow capacity.

Rapid and extensive arterial adaptations after spinal cord injury

OBJECTIVE

To assess the time course of adaptations in leg vascular dimension and function within the first 6 weeks after a spinal cord injury (SCI).

DESIGN

Longitudinal study design.

SETTING

University medical center and rehabilitation clinic.

PARTICIPANTS

Six men were studied serially at 1, 2, 3, 4, and 6 weeks after SCI.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Diameter, blood flow, and shear rate levels of the common femoral artery (CFA), superficial femoral artery (SFA), brachial artery, and carotid artery were measured with echo Doppler ultrasound (diameter, blood flow, shear rate). Endothelial function in the SFA was measured with flow-mediated dilation (FMD). In addition, leg volume and blood pressure measurements were performed.

RESULTS

Femoral artery diameter (CFA, 25%; SFA, 16%; P<.01) and leg volume (22%, P<.01) decreased simultaneously, and these reductions were largely accomplished within 3 weeks postinjury. Significant increases were observed for basal shear rate levels (64% increase at week 3; 117% increase at week 6; P<.01), absolute FMD responses (8% increase at week 3, 23% increase at week 6; P<.05) and relative FMD responses (26% increase at week 3, 44% increase at week 6; P<.001).

CONCLUSIONS

Our findings show a rapid onset of adaptations in arterial dimension and function to extreme inactivity in humans. Vascular adaptations include extensive reductions in femoral diameter and leg volume, as well as increased basal shear rate levels and FMD responses, which all appear to be largely accomplished within 3 weeks after an SCI.

Rapid vascular adaptations to training and detraining in persons with spinal cord injury

OBJECTIVE

To assess the time course of arterial adaptations during 6 weeks of functional electric stimulation (FES) training and 6 weeks of detraining in subjects with spinal cord injury (SCI).

DESIGN

Intervention study (before-after trial).

SETTING

University medical center.

PARTICIPANTS

Volunteer sample of 9 subjects with SCI.

INTERVENTIONS

Six weeks of twice weekly FES cycling and 6 weeks of detraining.

MAIN OUTCOME MEASURES

Vascular characteristics were measured by plethysmography (baseline and peak blood flow of the thigh) and echo Doppler (diameter of the femoral artery and flow-mediated dilation [FMD]).

RESULTS

After 2 weeks of FES training, arterial characteristics changed significantly; there was an increase in baseline and peak blood flow, an increase in femoral artery diameter, and a decrease in FMD of the femoral artery. Detraining reversed baseline and peak thigh blood flow, vascular resistance, and femoral diameter toward pretraining values within 1 week. However, detraining did not restore the FMD of the femoral artery, even after 6 weeks.

CONCLUSIONS

Two weeks of hybrid FES training (4 exercise bouts) is sufficient to improve peak leg blood flow and arterial diameter, and to normalize FMD. In addition, detraining results in rapidly reversed vascular characteristics within 1 week.

Electrical stimulation-evoked resistance exercise therapy improves arterial health after chronic spinal cord injury

STUDY DESIGN

Repeated measures training intervention.

OBJECTIVES

To evaluate the effects of neuromuscular electrical stimulation (NMES)-induced resistance exercise therapy on lower extremity arterial health in individuals with chronic, complete spinal cord injury (SCI). We define "arterial health" using three surrogate markers: (a) resting diameter, (b) flow-mediated dilation (FMD), and (c) arterial range.

SETTING

Department of Kinesiology, University of Georgia, USA.

METHODS

We assessed five 36+/-5-year-old male individuals with chronic, complete SCI before, during, and after 18 weeks of training. The quadriceps femoris muscle group of both legs were trained twice a week with 4 x 10 repetitions of unilateral, dynamic knee extensions. The health of the posterior tibial artery was assessed using a B-mode ultrasound unit equipped with a high-resolution video capture device. Proximal occlusion was used to evoke ischemia for 5 min and then for 10 min. FMD was calculated using the peak diameter change (above rest) following 5 min occlusion. Arterial range was calculated using minimum (during occlusion) and maximum diameters (post 10 min occlusion). Hierarchical linear modeling accounted for the nested (repeated measures) experimental design.

RESULTS

FMD improved from 0.08+/-0.11 mm (2.7%) to 0.18+/-0.15 mm (6.6%) (P=0.004), and arterial range improved from 0.36+/-0.28 to 0.94+/-0.40 mm (P=0.001), after 18 weeks of training. Resting diameter did not significantly change.

CONCLUSIONS

Home-based, self-administered NMES resistance exercise therapy consisting of 80 contractions/week improved FMD and arterial range. This provides evidence that resistance exercise therapy can improve arterial health after SCI, which may reduce the risk of future cardiovascular disease.

Electrical stimulation alters FMD and arterial compliance in extremely inactive legs

PURPOSE

The main aim of the study was to assess the effect and time course of 4 wk of electrically induced leg training on arterial compliance and endothelial function.

METHODS

Six spinal cord-injured (SCI) individuals participated in 4 wk of daily one-leg functional electrical stimulation (FES) training for 30 min per session. Eight able-bodied individuals served as a control group (C) and were tested on one occasion. Echo Doppler measurements were performed before the FES training and after 1, 2, and 4 wk of training to measure vascular characteristics of femoral artery (FA), brachial artery (BA), and carotid artery (CA).

RESULTS

Baseline arterial compliance of FA (SCI: 0.0185 +/- 0.063 mm2 x mm Hg(-1); C: 0.066 +/- 0.017 mm2 x mm Hg(-1), P = 0.001) and CA (SCI: 0.073 +/- 0.02 mm2 x mm Hg(-1); C: 0.102 +/- 0.02 mm2 x mm Hg(-1), P = 0.02) was significantly decreased in SCI. Baseline endothelial function in the leg was significantly enhanced in SCI compared with C (SCI: 11 +/- 1.3%; C: 7.9 +/- 0.9%, P = 0.001). No differences between the groups were found for arterial compliance and endothelial function in the arm. Vascular changes after FES training showed an increase in arterial compliance (significant at week 4, P < 0.05) and a decrease in FMD response (significant at weeks 2 and 4, P < 0.05) in the FA of the trained leg only, with no changes evident in the other arteries examined.

CONCLUSION

Daily electrically induced training of an extremely deconditioned leg appears to enhance arterial compliance in the femoral artery and may normalize endothelial function.

Changes in skeletal muscle size and glucose tolerance with electrically stimulated resistance training in subjects with chronic spinal cord injury

OBJECTIVE

To determine the effect of residence-based, resistance exercise training (RET) on affected skeletal muscle size and glucose tolerance after long-standing, complete spinal cord injury (SCI).

DESIGN

Before-after trial.

SETTING

University laboratory trial.

PARTICIPANTS

Five men with chronic, complete SCI (C5-T9).

INTERVENTION

Magnetic resonance images of the thighs and an oral glucose tolerance test were performed before and after RET. Subjects performed RET with both thighs, 2 d/wk for 4 sets of 10 unilateral, dynamic knee extensions for 12 weeks. Neuromuscular electric stimulation induced RET by activating the knee extensors.

MAIN OUTCOME MEASURES

Quadriceps femoris muscle cross-sectional area (CSA), plasma glucose, and insulin concentrations were measured before and after RET. Results Skeletal muscle CSA increased by 35% in the right quadriceps femoris (from 32.6 cm2 to 44.0 cm2) and by 39% in the left quadriceps femoris (from 34.6 cm2 to 47.9 cm2) as a result of training (P < .05). There were no significant changes in blood glucose or insulin after training. However, a trend for a reduction in plasma glucose levels was observed (P = .074). Conclusions Affected skeletal muscle can achieve substantial hypertrophy years after SCI with resistance exercise. Furthermore, our results suggest that this type of training may enhance glucose disposal.

Local Vascular Adaptations after Hybrid Training in Spinal Cord–Injured Subjects

PURPOSE

Studies investigating vascular adaptations in non-exercised areas during whole body exercise training show conflicting results. Individuals with spinal cord injury (SCI) provide a unique model to examine vascular adaptations in active tissue vs adjacent inactive areas. The purpose of this study is to assess the effects of 4 wk of voluntary arm and electrically stimulated leg exercise (8-12 sessions) on vascular adaptations in active areas (thigh and arms) and inactive areas (calf).

METHODS

Vascular characteristics were measured by plethysmography (blood flow and vascular resistance) and echo Doppler (diameter and flow-mediated dilation (FMD) after 13 min of ischemia).

RESULTS

After training, increased thigh baseline and peak blood flow, decreased thigh baseline vascular resistance, and increased diameter of the common femoral artery were found in the stimulated thigh tissue. Forearm and calf arterial parameters and FMD, in both superficial femoral artery and brachial artery, did not change. The lack of activity in the calf and concomitant insufficient elevation of blood flow during training, and the high initial training status of the arms are suggested to explain the absence of vascular adaptations in these areas.

CONCLUSION

The presence of vascular adaptations after only 4 wk of FES cycling indicates that adaptations occur in an early phase. In addition, 4 wk of whole body exercise training in SCI individuals leads to vascular adaptations in the exercised tissues (thigh) but not in nonstimulated passive tissue (calf).

The effects of body-weight supported treadmill training on cardiovascular regulation in individuals with motor-complete SCI

STUDY DESIGN

Four-month longitudinal within-subject exercise training study.

OBJECTIVE

Although body-weight supported treadmill training (BWSTT) has not shown promise as a means of improving ambulation in individuals with motor-complete spinal cord injury (SCI), it may still improve cardiovascular health and function in this population. The purpose of this study was to (i) investigate the effects of BWSTT on peripheral muscular and elastic artery dimension and function and measures of heart rate variability (HRV) and blood pressure variability (BPV) in individuals with motor-complete SCI, and (ii) to make a preliminary examination of what factors may predict favourable cardiovascular outcomes following BWSTT in this population.

SETTING

Centre for Health Promotion and Rehabilitation, McMaster University, Hamilton, Ontario, Canada.

METHODS

Six individuals (four male, two female; age 37.7+/-15.4 years) with chronic SCI (C4-T12; ASIA A-B; 7.6+/-9.4 years post-injury) were included in the present investigation. Doppler ultrasound was used to determine femoral (exercising; muscular), carotid (elastic) and brachial (non-exercising control; muscular) artery dimension and function before and after 4 months of BWSTT. Continuous heart rate and blood pressure were also recorded before and after 4-months of BWSTT to determine frequency domain measures of HRV and BPV; clinically valuable indices of neurocardiac and neurovascular control, respectively.

RESULTS

Two-way ANOVA (vessel x time) revealed no exercise-induced change in femoral or carotid artery cross-sectional area, blood flow or resistance and no change in carotid artery compliance following the 4 months of BWSTT compared to the non-exercising control brachial artery. However, there was a significant exercise-induced increase in femoral artery compliance. There were no exercise-induced changes in HRV or BPV when all participants were considered together. However, the results suggest that the subgroup of individuals who had a substantial heart rate response to BWSTT (n=3), experienced exercise-training induced changes in HRV reflective of a relative shift toward cardiac vagal predominance and reductions in BPV.

CONCLUSIONS

BWSTT may cause an increase in femoral artery compliance in individuals with motor-complete SCI and therefore, should be encouraged as a means of improving cardiovascular health in this population. BWSTT may also cause modest improvements in measures of HRV and BPV in a select subgroup of individuals who respond to ambulation with moderate to large increases in HR. In the present study, factors associated with a substantial HR response to BWSTT were a propensity to orthostatic intolerance and muscular spasticity.

Exercise as a Health-Promoting Activity Following Spinal Cord Injury

Spinal cord injury is a catastrophic event that immeasurably alters activity and health. Depending on the level and severity of injury, functional and homeostatic decline of many body systems can be anticipated in a large segment of the paralyzed population. The level of physical inactivity and deconditioning imposed by SCI profoundly contrasts the preinjury state in which most individuals are relatively young and physically active. Involvement in sports, recreation, and therapeutic exercise is commonly restricted after SCI by loss of voluntary motor control, as well as autonomic dysfunction, altered fuel homeostasis, inefficient temperature regulation, and early-onset muscle fatigue. Participation in exercise activities also may require special adaptive equipment and, in some instances, the use of electrical current either with or without computerized control. Notwithstanding these limitations, considerable evidence supports the belief that recreational and therapeutic exercise improves the physical and emotional well-being of participants with SCI. This article will examine multisystem decline and the need for exercise after SCI. It will further examine how exercise might be used as a tool to enhance health by slowing multisystem medical complications unique to those with SCI. As imprudent exercise recommendations may pose avoidable risks of incipient disability, orthopedic deterioration, or pain, the special risks of exercise misuse in those with SCI will be discussed.

Preserved contribution of nitric oxide to baseline vascular tone in deconditioned human skeletal muscle

Deconditioning is a risk factor for cardiovascular disease. Exercise reduces this risk, possibly by improving the vascular endothelial nitric oxide (NO) pathway. The effect of deconditioning on the NO pathway is largely unknown. This study was designed to assess baseline NO availability in the leg vascular bed after extreme, long-term deconditioning (spinal cord-injured individuals, SCI) as well as after moderate, short-term deconditioning (4 weeks of unilateral lower limb suspension, ULLS). For this purpose, seven SCI were compared with seven matched controls. Additionally, seven healthy subjects were studied pre- and post-ULLS. Leg blood flow was measured by venous occlusion plethysmography at baseline and during infusion of 5 incremental dosages of N(G)-monomethyl-L-arginine (L-NMMA) into the femoral artery. Sodium nitroprusside (SNP) was infused to test vascular responsiveness to NO. Baseline leg vascular resistance tended to be higher in SCI compared with controls (37+/-4 versus 31+/-2 arbitrary units (AU), P=0.06). Deconditioning altered neither the vasoconstrictor response to L-NMMA (increase in resistance in SCI versus controls: 102+/-33% versus 69+/-9%; pre- versus post-ULLS: 95+/-18% versus 119+/-15%), nor the vascular responsiveness to NO. In conclusion, two human in vivo models of deconditioning show a preserved baseline NO availability in the leg skeletal muscle vascular bed.

Preserved flow-mediated dilation in the inactive legs of spinal cord-injured individuals

The aim of the study was to assess endothelial function, measured by flow-mediated dilation (FMD), in an inactive extremity (leg) and chronically active extremity (arm) within one subject. Eleven male spinal cord-injured (SCI) individuals and eleven male controls (C) were included. Echo Doppler measurements were performed to measure FMD responses after 10 and 5 min of arterial occlusion of the leg (superficial femoral artery, SFA) and the arm (brachial artery, BA), respectively. A nitroglycerine spray was administered to determine the endothelium independent vasodilatation in the SFA. In the SFA, relative changes in FMD were significantly enhanced in SCI compared with C (SCI: 14.1 +/- 1.3%; C: 9.2 +/- 2.3%), whereas no differences were found in the BA (SCI: 12.5 +/- 2.9%; C: 14.2 +/- 3.3%). Because the FMD response is directly proportional to the magnitude of the stimulus, the FMD response was also expressed relative to the shear rate. No differences between the groups were found for the FMD-to-shear rate ratio in the SFA (SCI:0.061 +/- 0.023%/s(-1); C: 0.049 +/- 0.024%/s(-1)), whereas the FMD-to-shear rate ratio was significantly decreased in the BA of SCI individuals (SCI: 0.037 +/- 0.01%/s(-1); C: 0.061 +/- 0.027%/s(-1)). The relative dilatory response to nitroglycerine did not differ between the groups. (SCI: 15.6 +/- 2.0%; C: 13.4 +/- 2.3%). In conclusion, our results indicate that SCI individuals have a preserved endothelial function in the inactive legs and possibly an attenuated endothelial function in the active arms compared with controls.

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.

Preserved alpha-adrenergic tone in the leg vascular bed of spinal cord-injured individuals

BACKGROUND

Supraspinal sympathetic control of leg vascular tone is lost in spinal cord-injured individuals, but this does not result in a reduced leg vascular tone: Leg vascular resistance is even increased. The aim of this study was to assess the alpha-adrenergic contribution to the increased vascular tone in the lower extremity in patients without central sympathetic control of leg circulation.

METHODS AND RESULTS

Upper-leg vascular resistance responses to local infusion of incremental doses of phentolamine (a competitive antagonist of the alpha-adrenoceptor) into the femoral artery were determined in 10 spinal cord-injured individuals (SCI) and 8 healthy age-matched control subjects during local beta-adrenergic receptor blockade with propranolol. Basal leg vascular resistance was higher in SCI than in control subjects (41+/-6 arbitrary units [AU] versus 24+/-4 AU; P=0.034). The same accounts for minimal leg vascular resistance, assessed during reactive hyperemia, which was higher in SCI compared with control subjects (6.9+/-1.0 AU versus 2.5+/-0.2 AU; P<0.01). The maximal phentolamine-induced reduction in leg vascular resistance normalized to each individual's minimal resistance did not differ between the groups (68+/-17% and 51+/-4% for SCI and control subjects, respectively; P>0.1). A decline in mean arterial pressure was observed in both groups with increasing dosage of phentolamine. In response, baroreceptor-mediated vasoconstriction was observed in the noninfused leg of the control subjects, whereas in SCI individuals this reaction was absent.

CONCLUSIONS

These results indicate that the alpha-adrenoceptor-mediated vascular tone in the leg is preserved in spinal cord-injured individuals without sympathetic supraspinal control.

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.

Vascular remodeling after spinal cord injury

PURPOSE

Our purpose was to determine whether spinal cord injured (SCI) subjects have decreased femoral artery diameter and maximal hyperemic blood flow when expressed per unit of muscle volume compared with able-bodied (AB) individuals. A secondary purpose was to determine whether blood flow recovery rates were similar between groups.

METHODS

Blood flow was measured in the femoral artery using Doppler ultrasound after distal thigh cuff occlusion of 4 and 10 min. Muscle mass of the lower leg was determined by magnetic resonance imaging (MRI).

RESULTS

SCI individuals had smaller muscle cross-sectional areas (37%, P = 0.001) and volumes (38%, P = 0.001) than AB individuals. Furthermore, femoral artery diameter (0.76 +/- 0.14 vs 0.48 +/- 0.06 cm, AB vs SCI, P < 0.001) and femoral artery maximal blood flow (2050 +/- 520 vs 1220 +/- 240 mL x min-1, AB vs SCI, P < 0.001) were lower in SCI than AB individuals. Femoral artery diameter and maximal blood flow per unit muscle volume did not differ between SCI and AB individuals (P = 0.418 and P = 0.891, respectively). Blood flow recovery after ischemia was prolonged in SCI compared with AB individuals for both cuff durations (P = 0.048).

CONCLUSIONS

In summary, femoral artery diameter and maximal hyperemic blood flow response per unit muscle volume are not different between SCI and AB individuals. Vascular atrophy after SCI appears to be closely linked to muscle atrophy. Furthermore, the SCI compared with AB individuals had a prolonged time to recovery, which may suggest decreased vessel reactivity.

Arterial vascular properties in individuals with spina bifida

STUDY DESIGN

Observational cross-sectional study.

OBJECTIVE

To assess the vascular characteristics of the arterial circulation in individuals with spina bifida (SB) in comparison with individuals with spinal cord injury (SCI) and able-bodied controls (C).

SETTING

University Medical Centre, Nijmegen, The Netherlands.

METHODS

Six spina bifida (SB), 15 spinal cord injury (SCI) and 10 C were included. Red blood cell velocities and arterial diameter of the common carotid artery and common femoral artery were measured using echo-Doppler ultrasound in a supine position. A venous blood sample was withdrawn for determination of blood viscosity.

RESULTS

In the common carotid artery, blood flow and wall shear stress were not different between the three groups. The diameter was smaller in SB compared with SCI and C. In the common femoral artery, blood flow was smaller in SB than in SCI and C. Wall shear stress was significantly higher in SB and SCI compared with C. High wall shear stress may lead to endothelial dysfunction and related cardiovascular disease.

CONCLUSION

Deteriorating vascular properties are present in SB as well as in spinal-cord-injured individuals in comparison with C. These properties tend to be more pronounced in SB than in SCI.

Restoring function after spinal cord injury

BACKGROUND

By affecting young people during the most productive period of their lives, spinal cord injury is a devastating problem for modern society. A decade ago, treating SCI seemed frustrating and hopeless because of the tremendous morbidity and mortality, life-shattering impact, and limited therapeutic options associated with the condition. Today, however, an understanding of the underlying pathophysiological mechanisms, the development of neuroprotective interventions, and progress toward regenerative interventions are increasing hope for functional restoration.

REVIEW SUMMARY

This study addresses the present understanding of SCI, including the etiology, pathophysiology, treatment, and scientific advances. The discussion of treatment options includes a critical review of high-dose methylprednisolone and GM-1 ganglioside therapy. The concept that limited rebuilding can provide a disproportionate improvement in quality of life is emphasized throughout.

CONCLUSIONS

New surgical procedures, pharmacologic treatments, and functional neuromuscular stimulation methods have evolved over the last decades that can improve functional outcomes after spinal cord injury, but limiting secondary injury remains the primary goal. Tissue replacement strategies, including the use of embryonic stem cells, become an important tool and can restore function in animal models. Controlled clinical trials are now required to confirm these observations. The ultimate goal is to harness the body's own potential to replace lost central nervous system cells by activation of endogenous progenitor cell repair mechanisms.

New algorithm to control a cycle ergometer using electrical stimulation

Data were collected from four male subjects to determine the relationships between load, speed and muscle use during cycle ergometry. These data were then used to construct equations to govern the stimulation of muscle in paralysed individuals, during cycle ergometry induced by functional electrical stimulation (FES) of the quadriceps, gluteus maximus and hamstring muscles. The algorithm was tested on four subjects who were paralysed owing to a complete spinal cord injury between T4 and T11. Using the multivariate equation, the control of movement was improved, and work was accomplished that was double (2940 Nm min(-1) compared with 5880 Nm min(-1)) that of traditional FES cycle ergometry, when muscle stimulation was also controlled by electrical stimulation. Stress on the body, assessed by cardiac output, was increased almost two-fold during maximum work with the new algorithm (81 min(-1) compared with 15 l min(-1) with the new algorithm). These data support the concept that the limitation to workload that a person can achieve on FES cycle ergometry is in the control equations and not in the paralysed muscle.

The effects of aging and activity on muscle blood flow

BACKGROUND

Our purpose was to determine if aging had an influence on muscle blood flow independent of habitual physical activity levels.

METHODS

Blood flow was measured in the femoral artery by Doppler ultrasound after cuff occlusion of 10 minutes. Active and inactive older subjects (73 +/- 7 years) were compared to active and inactive young subjects (26 +/- 6 years).

RESULTS

Peak blood flow capacity when normalized to lean muscle mass was related to activity level (p < 0.001), but not to age. Specifically, the young active group had higher peak blood flows than the young inactive (p = 0.031) or older inactive (p = 0.005) groups. Resting blood flow and conductance were not significantly different between groups. Mean arterial pressure was significantly higher in the older compared to young group (p = 0.002). Conductance was related to both activity (p = 0.002) and age (p = 0.003). A prolonged time for blood flow to recover was found in the older compared to the young group (p = 0.038) independent of activity status.

CONCLUSIONS

The prolonged recovery time in the older subjects may suggest a reduced vascular reactivity associated with increased cardiovascular disease risk. Peak blood flow capacity is maintained in older subjects by physical activity. In summary, maximal flow capacity and prolonged recovery of blood flow are influenced by different mechanisms in young and older active and inactive subjects.

Increased vascular resistance in paralyzed legs after spinal cord injury is reversible by training

The purpose of the present study was to determine the effect of a spinal cord injury (SCI) on resting vascular resistance in paralyzed legs in humans. To accomplish this goal, we measured blood pressure and resting flow above and below the lesion (by using venous occlusion plethysmography) in 11 patients with SCI and in 10 healthy controls (C). Relative vascular resistance was calculated as mean arterial pressure in millimeters of mercury divided by the arterial blood flow in milliliters per minute per 100 milliliters of tissue. Arterial blood flow in the sympathetically deprived and paralyzed legs of SCI was significantly lower than leg blood flow in C. Because mean arterial pressure showed no differences between both groups, leg vascular resistance in SCI was significantly higher than in C. Within the SCI group, arterial blood flow was significantly higher and vascular resistance significantly lower in the arms than in the legs. To distinguish between the effect of loss of central neural control vs. deconditioning, a group of nine SCI patients was trained for 6 wk and showed a 30% increase in leg blood flow with unchanged blood pressure levels, indicating a marked reduction in vascular resistance. In conclusion, vascular resistance is increased in the paralyzed legs of individuals with SCI and is reversible by training.

Peak exercise capacity of electrically induced ambulation in persons with paraplegia

INTRODUCTION

Persons with spinal cord injury (SCI) are generally limited to exercise activities using the relatively smaller, less productive upper extremities with limited benefits as compared with leg exercise training. Functional electrical stimulation (FES) assisted ambulation has previously been demonstrated to allow persons with paraplegia to stand and ambulate limited distances.

PURPOSE

This study compared the peak physiological responses of persons with paraplegia during FES ambulation and voluntary arm exercise.

METHODS

Fifteen subjects (T -T ) previously habituated to FES ambulation, completed peak testing of both arm cranking (AC) and FES walking to the point of exhaustion. The AC tests were performed using a graded incremental protocol to exhaustion in 3-min stages and 10-W power output increments. The FES walking test consisted of successive 10-m walking bouts, each trial progressively increased in pace. Metabolic activity was continuously monitored via open-circuit spirometry with heart rate (HR) determined by a 12-lead electrocardiograph for AC and by direct palpation during FES.

RESULTS

Peak VO(2) did not differ between AC (22.9 +/- 3.8 mL x kg x min(-1)) and FES (22.7 +/- 3.9 mL x kg x min(-1)). FES ambulation elicited significantly greater peak values of HR (191 beats x min(-1) versus 179 beats x min(-1)) and lower peak values of respiratory exchange ratio (1.06 vs 1.12) compared with AC. There were no significant differences in peak values of any other variables.

CONCLUSION

This study indicates that FES ambulation performance, in persons with paraplegia, elicits similar exercise capacity, as indicated by similar peak oxygen consumption, as voluntary arm exercise.

Shear stress levels in paralyzed legs of spinal cord-injured individuals with and without nerve degeneration

The purpose of this study was to assess the relationship between inactivity and shear stress, the frictional force of blood against the endothelium, in spinal cord injury (SCI) subjects. SCI group offers a unique "model of nature" to study the effects of inactivity. Nine SCI subjects with upper (SCI-U) and 5 with a lower (SCI-L) motoneuron lesion and 10 able-bodied controls (C) were included. A venous blood sample was withdrawn to determine blood viscosity. Red blood cell velocities and arterial diameters of the common carotid artery (CCA) and common femoral artery (CFA) were measured by using echo-Doppler ultrasound in a supine position. No differences were observed in wall shear stress in the CCA between groups. In the CFA, peak and mean wall shear stress were significantly increased in SCI (14.1 and 1.2 Pa, respectively) compared with C (10.2 and 0.9 Pa, respectively). Because SCI-U and SCI-L showed no differences in shear stress levels, inactivity and not nerve degeneration seems to cause the elevated shear stress levels in the CFA in SCI. However, the lack of central neural control as a causal factor cannot be ruled out.