Properties of the venous vascular system in the lower extremities of individuals with paraplegia

Incidence and risk factors of deep vein thrombosis in patients with spinal cord injury: a systematic review with meta-analysis

Background

Spinal cord injury (SCI) is a highly disabling disease with huge public health burden. The complications associated with it, especially deep vein thrombosis (DVT), further aggravate the disability.

Objective

To explore the incidence and risk factors of DVT after SCI, in order to provide guidance for disease prevention in the future.

Methods

A search was performed on PubMed, Web of Science, Embase, and Cochrane database up to November 9, 2022. Literature screening, information extraction and quality evaluation were performed by two researchers. The data was later combined by metaprop and metan commands in STATA 16.0.

Results

A total of 101 articles were included, including 223,221 patients. Meta-analysis showed that the overall incidence of DVT was 9.3% (95% CI: 8.2%-10.6%), and the incidence of DVT in patients with acute and chronic SCI was 10.9% (95% CI: 8.7%-13.2%) and 5.3% (95% CI: 2.2%-9.7%), respectively. The incidence of DVT decreased gradually with the accumulation of publication years and sample size. However, the annual incidence of DVT has increased since 2017. There are 24 kinds of risk factors that may contribute to the formation of DVT, involving multiple aspects of the baseline characteristics of the patient, biochemical indicators, severity of SCI, and comorbidities.

Conclusions

The incidence of DVT after SCI is high and has been gradually increasing in recent years. Moreover, there are numerous risk factors associated with DVT. Comprehensive preventive measures need to be taken as early as possible in the future.

Systematic Review Registration

www.crd.york.ac.uk/prospero, identifier CRD42022377466.

Secondary Acrocyanosis in a Paraplegic Patient With Spinal Cord Injury

Secondary acrocyanosis after spinal cord injury is extremely rare. We describe a case with secondary acrocyanosis in a complete T12 paraplegic patient. A 41-year-old man with complete T12 paraplegia after a gunshot wound to the thoracic spine 20 years prior presented with a four-month history of bilateral foot bluish discoloration precipitated when he sat with his legs down, improving rapidly after a few minutes of leg elevation. Changes in the skin color of the lower extremities were evaluated in the seated position for two hours. The skin color became darker, progressing to a bluish discoloration through the entire length of the legs. After two hours, the feet and most of the legs appeared deep purple. The color of the legs returned to their baseline three minutes later after the patient was placed supine in the bed. The diagnosis of secondary acrocyanosis due to the T12 spinal cord injury was established based on the physical examination and ancillary tests showing no peripheral ischemia. Other causes of secondary acrocyanosis were excluded during the work-up. This report presents the first case of a paraplegic patient with spinal cord injury presenting secondary acrocyanosis.

Development of a skin temperature map for dermatomes in individuals with spinal cord injury: a cross-sectional study

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

The aim of this study was to map the skin temperature (Tsk) of individuals with SCI and compare able-bodied individuals, and among the groups to demonstrate the effects of differences in the levels of injury (paraplegia and tetraplegia with high and low injuries).

SETTING

Outpatient clinic, Brazil.

METHODS

Individuals with tetraplegia (n = 20), paraplegia (n = 21), and able-bodied (n = 11) individuals were recruited. A noncontact infrared thermometer (IRT) was used to measure three times the Tsk at the forehead, and at the C2 to S2 dermatomes. Core body temperature was measured at the axilla using the IRT and three other clinical thermometers.

RESULTS

Autonomic regulation is impaired by the injury. A Tsk map was constructed for the three groups. Significant differences in the Tsk of dermatomes were observed when comparing individuals with SCI and the able-bodied at the following dermatomes: C3, C7, T2, T3, T8, T9, L1, L2, L4, and S2. When comparing individuals with tetraplegia and able-bodied individuals, the dermatomes that showed significant differences were C5, C6, C8, T1, T10, L3, and S1. Dermatomes C5-C7, and T5 showed significant differences between individuals with tetraplegia and those with paraplegia. For L5 and S1 in paraplegia significant differences were found when comparing high with low injury.

CONCLUSION

A Tsk map on dermatomes in individuals with SCI was implemented, and showed a significant difference between able-bodied. As temperature is a parameter for analyzing autonomic function, the study could benefit rehabilitation by providing baseline values when constructing clinical protocols.

Intermittent mild negative pressure applied to the lower limb in patients with spinal cord injury and chronic lower limb ulcers: a crossover pilot study

STUDY DESIGN

Randomized, assessor-blinded crossover pilot study.

OBJECTIVES

To explore the use of an intermittent negative pressure (INP) device for home use in addition to standard wound care (SWC) for patients with spinal cord injury (SCI) and chronic leg and foot ulcers before conducting a superiority trial.

SETTING

Patient homes and outpatient clinic.

METHODS

A 16-week crossover trial on 9 SCI patients (median age: 57 years, interquartile range [IQR] 52-66), with leg ulcers for 52 of weeks (IQR: 12-82) duration. At baseline, patients were allocated to treatment with INP + SWC or SWC alone. After 8 weeks, the ulcers were evaluated. To assess protocol adherence, the patients were then crossed over to the other group and were evaluated again after another 8 weeks. Lower limb INP treatment consisted of an airtight pressure chamber connected to an INP generator (alternating 10 s -40mmHg/7 s atmospheric pressure) used 2 h/day at home. Ulcer healing was assessed using a photographic wound assessment tool (PWAT) and by measuring changes in wound surface area (WSA).

RESULTS

Seven of nine recruited patients adhered to a median of 90% (IQR: 80-96) of the prescribed 8-week INP-protocol, and completed the study without side effects. PWAT improvement was observed in 4/4 patients for INP + SWC vs. 2/5 patients for SWC alone (P = 0.13). WSA improved in 3/4 patients allocated to INP + SWC vs. 3/5 patients in SWC alone (P = 0.72).

CONCLUSIONS

INP can be used as a home-based treatment for patients with SCI, and its efficacy should be tested in an adequately sized, preferably multicenter randomized trial.

Evidence for greater burden of peripheral arterial disease in lower extremity arteries of spinal cord-injured individuals

Spinal cord injury leads to increased risk for cardiovascular disease and results in greater risk of death. Subclinical markers of atherosclerosis have been reported in carotid arteries of spinal cord-injured individuals (SCI), but the development of lower extremity peripheral arterial disease (PAD) has not been investigated in this population. The purpose of this study was to determine the effect of spinal cord injury on ankle-brachial index (ABI) and intima-media thickness (IMT) of upper-body and lower-extremity arteries. We hypothesized that the aforementioned measures of lower-extremity PAD would be worsened in SCI compared with controls and that regular participation in endurance exercise would improve these in both groups. To test these hypotheses, ABI and IMT were determined in 105 SCI and compared with 156 able-bodied controls with groups further subdivided into physically active and sedentary. ABIs were significantly lower in SCI versus controls (0.96 ± 0.12 vs. 1.06 ± 0.07, P < 0.001), indicating a greater burden of lower-extremity PAD. Upper-body IMTs were similar for brachial and carotid arteries in controls versus SCI. Lower extremity IMTs revealed similar thicknesses for both superficial femoral and popliteal arteries, but when normalized for artery diameter, individuals with SCI had greater IMT than controls in the superficial femoral (0.094 ± 0.03 vs. 0.073 ± 0.02 mm/mm lumen diameter, P < 0.01) and popliteal (0.117 ± 0.04 vs. 0.091 ± 0.02 mm/mm lumen diameter, P < 0.01) arteries. The ABI and normalized IMT of SCI compared with controls indicate that subclinical measures of lower-extremity PAD are worsened in individuals with SCI. These findings should prompt physicians to consider using the ABI as a screening method to detect lower-extremity PAD in SCI.

Pressor response to passive walking-like exercise in spinal cord-injured humans

OBJECTIVE

To examine blood pressure responses during passive walking-like exercise in the standing posture (PWE) in spinal cord-injured (SCI) humans.

METHODS

Twelve motor-complete SCI individuals (cervical level 6 to thoracic level 12, ASIA grade: A or B) and twelve able-bodied controls (CON) participated in this study. SCI individuals were divided into a group with injury level at or above thoracic (T) 6 (HSCI, n = 7) and a group with injury level at or below T10 (LSCI, n = 5). Subjects carried out 6-minute quiet standing and then 12-minute PWE at 1 Hz using a gait training apparatus that enables subjects to stand and move their legs passively.

RESULTS

Mean arterial blood pressures (MAPs) at standing in HSCI, LSCI and CON were 69 +/- 5, 83 +/- 4 and 93 +/- 2 mmHg, respectively. MAP changed significantly during PWE only in HSCI and CON, increasing to 88 +/- 4 (P < 0.001) and 98 +/- 1 mmHg (P < 0.01), respectively. The former group showed a larger increase in MAP (P < 0.001).

INTERPRETATION

Spinal sympathetic reflexes can be induced in a region isolated from the brainstem in response to a stimulus originating below the level of the spinal cord injury, and the magnitude of increase in blood pressure is greater in SCI individuals with lesion level at or above T6 due to loss of supraspinal control of the major sympathetic outflow. This central mechanism may be one of the reasons why greater pressor response to PWE was observed in HSCI.

Venous response to orthostatic stress

Head-up tilt (HUT) induces a reduction in preload, which is thought to be restored through sympathetic venoconstriction, reducing unstressed volume (V(u)) and venous compliance (VeC). In this study, we assessed venous inflow and outflow responses and their reproducibility and determined the relation with autonomic function during HUT. Eight healthy non-pregnant women were subjected to 20 degrees head-down tilt to 60 degrees HUT at 20 degrees intervals. At each rotational step, we randomly assessed forearm pressure-volume (P-V) curves (venous occlusion plethysmography) during inflow (VeC(IN)) and outflow [venous emptying rate (VER(OUT))]. VeC(IN) was defined as the ratio of the slope of the volume-time curve and pressure-time curve, with direct intravenous pressure measurement. VER(OUT) was determined using the derivate of a quadratic regression model using cuff pressure. We defined V(u) as the y-intercept of the P-V curve. We calculated, for both methods, the coefficients of reproducibility (CR) and variation (CV). Vascular sympathetic activity was determined by spectral analysis. VeC(IN) decreased at each rotational step compared with the supine position (P<0.05), whereas VER(OUT) increased. CR of VeC(IN) was higher in the supine position than VER(OUT) but lower during HUT. CV varied between 19% and 25% (VeC(IN)) and between 12% and 21% (VER(OUT)). HUT decreased V(u). The change in VeC(IN) and VER(OUT) correlated with the change in vascular sympathetic activity (r= -0.36, P<0.01, and r=0.48, P<0.01). This is the first study in which a reproducible reduction in VeC(IN) and V(u) and a rise in VER(OUT) during HUT are documented. The alterations in venous characteristics relate to changes in vascular sympathetic activity.

Ultrasound assessment of popliteal vein compliance during a short deflation protocol

The purpose of the present study was to determine whether ultrasound is a useful tool to measure the venous characteristics of the lower extremity during a standard venous collecting cuff deflation protocol. To accomplish this, lower extremity pressure-cross-sectional area (CSA) and pressure-volume relationships were measured in eight (25 ± 1 yr) supine subjects. Popliteal vein CSA was assessed by using high-resolution ultrasound, while calf volume changes were simultaneously assessed by using venous occlusion plethysmography (VOP). Pressure-CSA and pressure-volume relationships were assessed at baseline, during the cold pressor (CP) test, and following sublingual nitroglycerin (NTG) administration. Relationships were modeled with a quadratic regression equation, and β1 and β2 were used as indexes of venous compliance. Popliteal vein regression parameters β1 (8.485 ± 2.616 vs. 7.638 ± 2.664, baseline vs. CP; 8.485 ± 2.616 vs. 7.734 ± 3.076, baseline vs. NTG; both P > 0.05) and β2 (−0.0841 ± 0.0241 vs. −0.0793 ± 0.0242, baseline vs. CP; −0.0841 ± 0.0241 vs. −0.0771 ± 0.0280, baseline vs. NTG; both P > 0.05) were not affected by CP or NTG. Similarly, calf regression parameters β1 and β2, obtained with VOP, were not altered during either trial. Intraclass correlations for venous compliance assessed with ultrasound and VOP were 0.92 and 0.97, respectively, indicating acceptable reproducibility. These data suggest that ultrasound is a functional and reproducible tool to assess the venous characteristics of the lower extremity, in addition to VOP. Additionally, popliteal vein and calf compliance were not affected by the CP test or NTG.

Evaluation of the effects of compression stockings using venous plethysmography in persons with spinal cord injury

BACKGROUND/OBJECTIVE

To examine the effect of graduated compression stockings (GCS) on the properties of the venous vascular system, as characterized by venous capacitance (VC) and venous outflow (VO), in the lower extremities of individuals with spinal cord injury (SCI), according to injury level.

METHODS

Nine male subjects with SCI (5 with low paraplegia [LP], 4 with high paraplegia [HP]) performed 2 plethysmography tests: with and without graduated compression knee-length stockings (pressure of 21 mm/Hg). The VC, VO, and cardiovascular parameters (heart rate and blood pressure) were evaluated with and without GCS.

RESULTS

The VC and VO were lower in patients with HP than in those with LP. For all subjects, VC was significantly lower (-14%) with GCS than without (1.77 +/- 1.18 vs 1.53 +/- 1.09 vol%, P < 0.01). On the contrary, VO did not differ significantly when wearing or not wearing GCS.

CONCLUSIONS

This study demonstrated that 21-mm/Hg knee-length GCS are sufficient to prevent venous distension in individuals with SCI, even those with longstanding paraplegia, by significantly decreasing venous capacitance. This intervention may help to prevent deep vein thrombosis.

Effects of Graduated Compression Stockings on Cardiovascular and Metabolic Responses to Exercise and Exercise Recovery in Persons With Spinal Cord Injury

OBJECTIVE

To investigate whether reporting blood redistribution by means of graduated elastic stockings affects exercise and postexercise responses in people with spinal cord injury (SCI).

DESIGN

Crossover trial.

SETTING

Physical medicine and rehabilitation department in France.

PARTICIPANTS

Fourteen men with traumatic SCI, grouped according to their level of injury.

INTERVENTIONS

Subjects performed 2 maximal wheelchair exercise tests 1 week apart, in random order and under a counter-balanced design. One test was done with and the other without graduated elastic stockings (21 mmHg).

MAIN OUTCOME MEASURES

Blood lactate, blood pressure, heart rate, maximal power output, and oxygen consumption (Vo2).

RESULTS

Postexercise venous lactate concentration was reduced in SCI subjects with lesion levels below T6 while wearing graduated elastic stockings during both exercise and recovery (10.9+/-3.9 mmol/L vs 12.5+/-4.6 mmol/L, P<.05). There were no significant differences in submaximal and maximal values (heart rate, Vo2, power output) between subjects tested with and without graduated elastic stockings.

CONCLUSIONS

Wearing elastic stockings affects postexercise responses by decreasing lactate concentration in well-trained, low-level paraplegic patients after a maximal exercise. The relatively low pressure generated by the stockings may not, however, influence the venous system enough to produce improved performance and cardiovascular responses.

Acute peripheral blood flow response induced by passive leg cycle exercise in people with spinal cord injury

OBJECTIVE

To determine the acute femoral artery hemodynamic response in paraplegic subjects during a passive leg cycle exercise.

DESIGN

Case series.

SETTING

Department of physical medicine and rehabilitation in a university in France.

PARTICIPANTS

A volunteer sample of 15 people with traumatic spinal cord injury.

INTERVENTION

Subjects performed a 10-minute session of passive leg cycle exercise in the sitting position.

MAIN OUTCOME MEASURES

We measured heart rate, maximal (Vmax), and minimal femoral artery blood flow velocity at rest and immediately after the passive leg cycle exercise, using quantitative duplex Doppler ultrasound. We calculated mean blood flow velocity (Vmean) and velocity index, representing the peripheral resistance, for each condition.

RESULTS

Vmax and Vmean increased (from .80+/-.18 m/s to .96+/-.24 m/s, P<.01; and from .058+/-.02 m/s to .076+/-.03 m/s, P<.01; respectively) after 10 minutes of passive leg cycle exercise. Heart rate did not change. The velocity index decreased from 1.23+/-0.15 to 1.16+/-0.21 (P=.038).

CONCLUSIONS

The results of this study suggest that acute passive leg cycle exercise increases vascular blood flow velocity in paralyzed legs of people with paraplegia. This exercise could have clinical implications for immobilized persons.

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.

Muscle Oxygenation of the Paralyzed Lower Limb in Spinal Cord???Injured Persons

PURPOSE

Even in the paralyzed lower limb muscle, EMG activity can be induced by imposing passive leg movement in standing posture in persons with spinal cord injury (SCI). The purpose of the present study was to ascertain whether the oxygenation level of the paralyzed lower limb muscle covaried with the muscle EMG activity during imposed passive leg movement.

METHODS

Six motor-complete SCI subjects and four neurologically normal controls were placed on a gait-training apparatus that enabled the SCI subjects to stand and move their legs passively. After a 1-min resting stage, consecutive passive alternate leg movements were performed at different frequencies (0.8, 1, 1.2, and 1 Hz, for 3 min at each stage). To obtain postexercise data, subjects were kept in a standing posture for 5 min after passive movement ceased. The EMG activity and concentration changes in the oxygenated (oxy-) and deoxygenated hemoglobin (Hb) (deoxy-Hb) were continuously measured using near-infrared spectroscopy (NIRS) from the gastrocnemius muscle.

RESULTS

In all SCI subjects, muscle EMG activity was observed during passive leg movement. The oxy-Hb level gradually increased, whereas the deoxy-Hb decreased, and these changes were independent of the total Hb changes. In the recovery stage, the total Hb level was found to exceed the preexercise level. In contrast to the SCI patients, the normal subjects showed neither EMG activity nor changes in oxy- or deoxy-Hb.

CONCLUSION

The present results demonstrate that passive leg movement can induce not only muscular activity but also alteration of muscle oxygenation level in the paralyzed lower leg. Particularly, induced muscular activity seems to correlate with increased perfusion of the muscle.

Ultrasound: a reproducible method to measure conduit vein compliance

Classical venous occlusion plethysmography (VOP) of the leg, often used to assess venous compliance, measures properties of the whole calf, including volume changes at the arterial side and the interstitial fluid accumulation that occurs as a result of the enhanced capillary pressure during venous occlusion. We present an ultrasound technique to measure the compliance of one major conduit vein in the leg. Ultrasound measurements of the popliteal vein were compared with classical VOP measurements, which were performed simultaneously in one subject. Six healthy individuals were measured on three occasions to assess short- and long-term reproducibility of the measurements. Six motor complete spinal cord-injured (SCI) individuals were included to compare venous compliance in subjects with known pathological changes of the venous system with controls. The ultrasound and VOP measurements of venous compliance correlated significantly ( r2= 0.39, P = 0.001). Ultrasound provides reproducible measurements with short- and long-term coefficients of variation ranging from 10 to 15% for popliteal vein compliance and from 2 to 9% for absolute diameters at the different venous pressure steps. In addition, by using ultrasound, we were able to detect an 80% reduction in the compliance of the popliteal vein in SCI individuals compared with controls ( P < 0.01). In conclusion, ultrasound is a suitable and reproducible method to measure conduit vein compliance and provides the possibility to specifically assess compliance of one vein instead of the whole calf.

Leg vascular resistance increases during head-up tilt in paraplegics

Despite loss of centrally mediated sympathetic vasoconstriction to the legs, spinal cord-injured individuals cope surprisingly well with an orthostatic challenge. This study assessed changes in leg vascular resistance following head-up tilt in healthy (C) and in paraplegic (P) individuals. After 10 min of supine rest, subjects were tilted 30 degrees head-up. Mean arterial pressure (MAP) and total peripheral resistance (TPR) increased in C (MAP from 76.7 +/ -6.6 mmHg to 80.6 +/- 8.2 mmHg; TPR from 1.12 +/- 0.26 AU to 1.19 +/ -0.31 AU) while both remained unchanged in P. Echo Doppler ultrasound determined red blood cell velocity in the femoral artery, which decreased (P from 18.9+/-6.2 cm/s to 12.5 +/- 4.5 cm/s, P = 0.001; C from 16.3 +/- 6.2 cm/s to 10.8 +/- 5.0 cm/s, P = 0.001) and leg vascular resistance, which increased (P from 402 +/- 137 AU to 643 +/- 274 AU, P = 0.001; C from 238 +/- 68 AU to 400 +/- 122 AU, P = 0.003) from supine to upright. The present study shows that independent of supraspinal sympathetic control, humans are able to increase leg vascular resistance and maintain blood pressure during head-up tilt.

Vascular adaptation to 4 wk of deconditioning by unilateral lower limb suspension

Physical inactivity or deconditioning is an independent risk factor for atherosclerosis and cardiovascular disease. In contrast to exercise, the vascular changes that occur as a result of deconditioning have not been characterized. We used 4 wk of unilateral lower limb suspension (ULLS) to study arterial and venous adaptations to deconditioning. In contrast to previous studies, this model is not confounded by denervation or microgravity. Seven healthy subjects participated in the study. Arterial and venous characteristics of the legs were assessed by echo Doppler ultrasound and venous occlusion plethysmography. The diameter of the common and superficial femoral artery decreased by 12% after 4 wk of ULLS. Baseline calf blood flow, as measured by plethysmography, decreased from 2.1 ± 0.2 to 1.6 ± 0.2 ml·min−1·dl tissue−1. Both arterial diameter and calf blood flow returned to baseline values after 4 wk of recovery. There was no indication of a decrease in flow-mediated dilation of the superficial femoral artery after ULLS deconditioning. This means that functional adaptations to inactivity are not simply the inverse of adaptations to exercise. The venous pressure-volume curve is shifted downward after ULLS, without any effect on compliance. In conclusion, deconditioning by 4 wk of ULLS causes significant changes in both the arterial and the venous system.

Significant reduction of the risk of venous thromboembolism in all long term immobile patients a few months after the onset of immobility

Prophylactic anticoagulation is a standard practice in patients with sudden lower limbs paralysis. Thromboprophylaxis is usually continued until the patient regains independent mobility. The duration of anticoagulation in long-term immobile patients is unknown. Spinal cord injury patients are the only population that was comprehensively studied and prophylactic anticoagulation is discontinued after 4 months as the risk of venous thromboembolism drops dramatically after 3-4 months. Development of muscle spasticity has been traditionally considered to be the reason for this low risk as lower limbs spasticity/spasms might be able to improve the calf muscle pump action. We are presenting the evidence from physiological studies of the lower limbs vascular system that cast doubt over this explanation and present an alternative hypothesis backed by several clinical circumstantial evidence suggesting that the vascular changes following long term lower limbs inactivity which are universal to all immobile patients is probably the main protecting factor. We suggest that prophylactic anticoagulation is necessary only on the first 4 months following the acute onset of immobility in all neurologically impaired immobile patients regardless of their muscle tone state.

Relationship between the duration of paralysis and bone structure: a pQCT study of spinal cord injured individuals

The aim of the present study was to describe bone loss of the separate compartments of trabecular and cortical bone, as well as changes in bone geometry of a large number of spinal cord injured (SCI) individuals. Eighty-nine motor complete spinal cord injured men (24 tetraplegics and 65 paraplegics) with a duration of paralysis of between 2 months and 50 years were included in the study. Distal epiphyses and midshafts of the femur, tibia, and radius were measured by peripheral quantitative computed tomography. The same measurements were performed in a reference group of 21 healthy able-bodied men of the same age range. In the femur and tibia, bone mass, total and trabecular bone mineral density (BMDtot and BMDtrab, respectively) of the epiphyses, as well as bone mass and cortical cross-sectional area of the diaphyses, showed an exponential decrease with time after injury in the spinal cord injured subjects. The decreasing bone parameters reached new steady states after 3-8 years, depending on the parameter. Bone mass loss in the epiphyses was approximately 50% in the femur and 60% in the tibia, while the shafts lost only approximately 35% in the femur and 25% in the tibia. In the epiphyses, bone mass was lost by reducing BMD, while in the shaft bone mass was lost by reducing cortical wall thickness, a process achieved by endosteal resorption advancing at a rate of about 0.25 mm/year within the first 5-7 years after injury. Except for a slight transient decrease in cortical BMD of the femoral and tibial shaft during the first 5 years after the spinal cord lesion, cortical BMD of the spinal cord injured subjects was found to be at reference values. Bone parameters of the radial epiphysis in paraplegic subjects showed no deficits compared to the reference group. Furthermore, a trend for an increased radial shaft diameter suggests periosteal apposition as a consequence of increased loading of the arms.

Effects of 18 days of bed rest on leg and arm venous properties

Venous function may be altered by bed rest deconditioning. Yet the contribution of altered venous compliance to the orthostatic intolerance observed after bed rest is uncertain. The purpose of this study was to assess the effect of 18 days of bed rest on leg and arm (respectively large and small change in gravitational gradients and use patterns) venous properties. We hypothesized that the magnitude of these venous changes would be related to orthostatic intolerance. Eleven healthy subjects (10 men, 1 woman) participated in the study. Before (pre) and after (post) 18 days of 6° head-down tilt bed rest, strain gauge venous occlusion plethysmography was used to assess limb venous vascular characteristics. Leg venous compliance was significantly decreased after bed rest (pre: 0.048 ± 0.007 ml·100 ml-1·mmHg-1, post: 0.033 ± 0.007 ml·100 ml-1·mmHg-1; P < 0.01), whereas arm compliance did not change. Leg venous flow resistance increased significantly after bed rest (pre: 1.73 ± 1.08 mmHg·ml-1·100 ml·min, post: 3.10 ± 1.00 mmHg·ml-1·100 ml·min; P < 0.05). Maximal lower body negative pressure tolerance, which was expressed as cumulative stress index (pressure·time), decreased in all subjects after bed rest (pre: 932 mmHg·min, post: 747 mmHg·min). The decrease in orthostatic tolerance was not related to changes in leg venous compliance. In conclusion, this study demonstrates that after bed rest, leg venous compliance is reduced and leg venous outflow resistance is enhanced. However, these changes are not related to measures of orthostatic tolerance; therefore, alterations in venous compliance do not to play a major role in orthostatic intolerance after 18 days of head-down tilt bed rest.

Increasing blood flow before exercise in spinal cord-injured individuals does not alter muscle fatigue

Previous studies have shown increased fatigue in paralyzed muscle of spinal cord-injured (SCI) patients (Castro M, Apple D Jr, Hillegass E, and Dudley GA. Eur J Appl Physiol 80: 373-378, 1999; Gerrits H, Hopman MTE, Sargeant A, and de Haan A. Clin Physiol 21: 105-113, 2001). Our purpose was to determine whether the increased muscle fatigue could be due to a delayed rise in blood flow at the onset of exercise in SCI individuals. Isometric electrical stimulation was used to induce fatigue in the quadriceps femoris muscle of seven male, chronic (>1 yr postinjury), complete (American Spinal Injury Association, category A) SCI subjects. Cuff occlusion was used to elevate blood flow before electrical stimulation, and the magnitude of fatigue was compared with a control condition of electrical stimulation without prior cuff occlusion. Blood flow was measured in the femoral artery by Doppler ultrasound. Prior cuff occlusion increased blood flow in the first 30 s of stimulation compared with the No-Cuff condition (1,350 vs. 680 ml/min, respectively; P < 0.001), although blood flow at the end of stimulation was the same between conditions (1,260 ± 140 vs. 1,160 ± 370 ml/min, Cuff and No-Cuff condition, respectively; P = 0.511). Muscle fatigue was not significantly different between prior cuff occlusion and the control condition (32 ± 13 vs. 35 ± 10%; P = 0.670). In conclusion, increased muscle fatigue in SCI individuals is not associated with the prolonged time for blood flow to increase at the onset of exercise.

Spinal Cord Injury Risk Assessment for Thromboembolism (SPIRATE Study)

OBJECTIVE

To identify risk factors for venous thromboembolism (VTE) during the rehabilitation phase of spinal cord injury.

DESIGN

A comprehensive review of the charts of all patients admitted between 1992 and 1995 for rehabilitation after spinal cord injury. Only records including evidence for objective testing for thromboembolism were included. The analysis variables included type and location of spinal cord injury, American Spinal Injury Association classification, concomitant injuries, surgical procedures, complications, preexisting illnesses, and use of antithrombotic prophylaxis. Hierarchically optimal classification tree analysis was employed to develop a nonlinear model for predicting deep vein thrombosis.

RESULTS

The analysis sample consisted of these 243 persons with acute spinal cord injury, 51 of whom had venous thromboembolism, and eight of whom died. A three-variable model emerged that identified patient groups differing in relative likelihood of experiencing deep vein thrombosis. The highest likelihood group were patients with cancer over the age of 35 yrs. Women between the ages of 36 and 58 yrs without cancer were also at increased risk, as were cancer-free men with flaccid paralysis.

CONCLUSIONS

Venous thromboembolism is more likely to develop in spinal cord injury patients who are older, obese, and have flaccid paralysis or cancer. These patients should receive vigorous prophylaxis against venous thromboembolism.

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 homeostasis is independent of calf venous compliance in subjects with paraplegia

The purpose of this study was to examine cardiac hemodynamics during acute head-up tilt (HUT) and calf venous function during acute head-down tilt (HDT) in subjects with paraplegia compared with sedentary nondisabled controls. Nineteen paraplegic males (below T6) and nine age-, height-, and weight-matched control subjects participated. Heart rate, stroke volume, and cardiac output were assessed using the noninvasive acetylene uptake method. Venous vascular function of the calf was assessed using venous occlusion plethysmography. After supine measurements were collected, the table was moved to 10 degrees HDT followed by the three levels of HUT (10, 35, and 75 degrees ) in random order. Cardiac hemodynamics were similar between the groups at all positions. Calf circumference was significantly reduced in the paraplegic group compared with the control group (P < 0.001). Venous capacitance and compliance were significantly reduced in the paraplegic compared with control group at supine and HDT. Neither venous capacitance (P = 0.37) nor compliance (P = 0.19) increased from supine with 10 degrees HDT in the paraplegic group. A significant linear relationship was established between supine venous compliance and supine cardiac output in the control group (r = 0.80, P < 0.02) but not in the paraplegic group. The findings of reduced calf circumference and similar venous capacitance at supine rest and 10 degrees HDT in the paraplegic group imply that structural changes may have limited venous dispensability in individuals with chronic paraplegia. Furthermore, the lack of a relationship between supine venous compliance and supine cardiac output suggests that cardiac homeostasis does not rely on venous compliance in subjects with paraplegia.

Blood flow and muscle fatigue in SCI individuals during electrical stimulation

Our purpose was to measure blood flow and muscle fatigue in chronic, complete, spinal cord-injured (SCI) and able-bodied (AB) individuals during electrical stimulation. Electrical stimulation of the quadriceps muscles was used to elicit similar activated muscle mass. Blood flow was measured in the femoral artery by Doppler ultrasound. Muscle fatigue was significantly greater (three- to eightfold, P < or = 0.001) in the SCI vs. the AB individuals. The magnitude of blood flow was not significantly different between groups. A prolonged half-time to peak blood flow at the beginning of exercise (fivefold, P = 0.001) and recovery of blood flow at the end of exercise (threefold, P = 0.009) was found in the SCI vs. the AB group. In conclusion, the magnitude of the muscle blood flow to electrical stimulation was not associated with increased muscle fatigue in SCI individuals. However, the prolonged time to peak blood flow may be an explanation for increased fatigue in SCI individuals.

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.

Sympathetic nervous system activity and cardiovascular homeostatis during head-up tilt in patients with spinal cord injuries

The relationship between sympathetic nervous system activity and cardiovascular responses to head-up tilt in patients with spinal cord injuries and in able-bodied subjects was studied. Twenty-seven adults, nine in each of the three groups (tetraplegia, paraplegia, and able-bodied subjects) were tilted 70 degrees, head up, for 12 minutes after 20 minutes supine rest. Differences between steady-state measurements of mean arterial pressure, stroke volume, and sympathetic nervous system activity were estimated in both positions. Sympathetic nervous system activity was reflected by the low-frequency peak of the blood pressure variability spectrum. From supine rest to head-up tilt, low-frequency power increased in able-bodied subjects (median, 0.42 mm Hg2, p = 0.003), which was different (p = 0.015) from patients with tetraplegia and paraplegia (-0.15 and -0.10 mm Hg2, respectively). Stroke volume and mean arterial pressure decreased in patients with tetraplegia (-40% and -9 mm Hg, respectively; p = 0.008, both variables) more than in able-bodied subjects (-33%, 11 mm Hg, respectively) or patients with paraplegia (-24%, 8 mm Hg, respectively). Results indicated increased sympathetic nervous system activity during head-up tilt in able-bodied subjects, but not in patients with paraplegia or tetraplegia, whereas patients with tetraplegia, but not paraplegia, showed poorer cardiovascular homeostasis than able-bodied subjects. This suggests that patients with paraplegia maintained cardiovascular homeostasis during head-up tilt without increased sympathetic nervous system activity.

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.

Mechanisms of thrombosis in spinal cord injury

Many studies failed to identify a hypercoagulable imbalance in the blood factors or decreased anticoagulant activity. On the other hand, fibrinolysis, a process unrelated to hypercoagulability but closely related to endothelial cell integrity, is predictably altered and contributes to the persistence of venous occlusion by thrombosis. There is considerable evidence that interruption of neurologic impulses and the ensuing paralysis cause metabolic changes in blood vessels and that blood vessel changes are accountable for venous thrombosis. Altered venous competence with complete spinal cord injury manifests by a decrease in venous distensibility and capacity and an increase in venous flow resistance. Vascular adaptations to inactivity and muscle atrophy, rather than the effect of a nonworking leg-muscle pump and sympathetic denervation, seem to lead to the thrombosis; indicating that thrombosis resulting from venous incompetence cannot be reversed by anticoagulation alone.

Effects of autonomic disruption and inactivity on venous vascular function

The effects of autonomic disruption and inactivity were studied on the venous vascular system. Forty-eight subjects, 24 with spinal cord injury (SCI) and 12 sedentary and 12 active able-bodied controls, participated in this study. Peripheral autonomic data were obtained to estimate sympathetic vasomotor control [low-frequency component of systolic blood pressure (LF(SBP))]. Vascular parameters were determined using strain-gauge venous occlusion plethysmography: venous capacitance (VC), venous emptying rate (VER), and total venous outflow (VO(t)). An additional vascular parameter was calculated: venous compliance [(VC/occlusion pressure) x 100]. VC and VO(t) were significantly different (SCI < sedentary < active). VER adjusted for VC was not different for any group comparison, whereas venous compliance was significantly lower in the SCI group than in the able-bodied groups and in the sedentary group compared with the active group. Regression analysis for the total group revealed a significant relationship between LF(SBP) and venous compliance (r = 0.64, P < 0.0001). After controlling for LF(SBP) through analysis of covariance, we found that mean differences for all venous vascular parameters did not change from unadjusted mean values. Our findings suggest that in subjects with SCI, the loss of sympathetic vasomotor tone contributes more than inactivity to reductions in venous vascular function. Heightened VC, VO(t), vasomotor tone, and venous compliance in the active group compared with the sedentary group imply that regular endurance training contributes to optimal venous vascular function and peripheral autonomic integrity.

Contractile properties of the quadriceps muscle in individuals with spinal cord injury

Selected contractile properties and fatigability of the quadriceps muscle were studied in seven spinal cord-injured (SCI) and 13 able-bodied control (control) individuals. The SCI muscles demonstrated faster rates of contraction and relaxation than did control muscles and extremely large force oscillation amplitudes in the 10-Hz signal (65 +/- 22% in SCI versus 23 +/- 8% in controls). In addition, force loss and slowing of relaxation following repeated fatiguing contractions were greater in SCI compared with controls. The faster contractile properties and greater fatigability of the SCI muscles are in agreement with a characteristic predominance of fast glycolytic muscle fibers. Unexpectedly, the SCI muscles exhibited a force-frequency relationship shifted to the left, most likely as the result of relatively large twitch amplitudes. The results indicate that the contractile properties of large human locomotory muscles can be characterized using the approach described and that the transformation to faster properties consequent upon changes in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles.

Baroreceptor sensitivity response to phase IV of the Valsalva maneuver in spinal cord injury

Due to the increased prevalence of ischemic heart disease and hypertension reported in individuals with chronic spinal cord injury (SCI), we investigated whether subjects with low level SCI (paraplegia), without apparent evidence of coronary artery disease, exhibit normal baroreceptor and autonomic function. Eighteen males participated in this study: seven normotensive with paraplegia, five hypertensive with paraplegia and six normotensive non-SCI controls. The Valsalva maneuver was performed by maintaining a pressure of 40 mmHg over 15 s and R-R intervals (RRI) and arterial blood pressure were measured continuously. Phase IV of the Valsalva maneuver was determined by linear regression analysis between RRI and systolic pressure, with a final slope calculated. The power spectra for RRI and blood pressure variability parameters were also analyzed, in addition to the index alpha, a frequency domain estimate of the overall gain in baroreceptor control of the RRI-arterial blood pressure. The normotensive subjects with paraplegia were found to have an impaired baroreceptor response when compared with age-matched, non-SCI controls. In addition, the levels of both the low frequency and high frequency spectral components of RRI and the index alpha were reduced in these individuals at rest. These cumulative findings strongly suggest that the integrity of the sinoaortic baroreceptors, as well as efferent parasympathetic function, may be compromised in otherwise apparently healthy individuals with chronic paraplegia.

Evaluation of a training program for persons with SCI paraplegia using the Parastep 1 ambulation system: part 2. Effects on physiological responses to peak arm ergometry

OBJECTIVE

To examine the task-nonspecific effects of functional neuromuscular stimulation (FNS)-assisted ambulation training on the physiological responses of persons with paraplegia to upper extremity exercise challenge.

DESIGN

Before-after trial.

SETTING

Human spinal cord injury (SCI) applied research laboratory.

PARTICIPANTS

Twelve men and three women with motor- and sensory-complete thoracic-level SCI (T4-T11), mean age 28.2 +/- 6.8yrs (range, 21.1 to 45.2yrs), mean injury duration 3.7 +/- 3.0yrs (range, 7 to 8.8yrs).

INTERVENTION

Thirty-two sessions of FNS ambulation training using a commercial six-channel system (Parastep 1). This system is composed of a microprocessor-controlled electrical stimulation unit and a walking frame outfitted with finger switches that allow the user to independently control the system and stimulation parameters.

OUTCOME MEASURES

Peak and subpeak physiological responses to arm ergometry testing and upper extremity strength measures, obtained before and after the FNS ambulation training.

RESULTS

Statistically significant increases in peak values for time to fatigue, peak power output, and peak VO2 (all p < .001). Heart rate was significantly lower throughout subpeak levels of arm ergometry after the ambulation training (p < .05). Values of upper extremity strength were not significantly altered after training.

CONCLUSIONS

FNS ambulation by persons with SCI paraplegia results in task-nonspecific training adaptations. Central cardiovascular adaptations were indicated as the primary source of these beneficial alterations in exercise responses.

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.