Catecholamines, heart rate, and oxygen uptake during exercise in persons with spinal cord injury

Preliminary feasibility and acute physiological effects of a single session of upper limb vibration training for persons with spinal cord injury

CONTEXT

Strong upper limb musculature is essential for persons with spinal cord injury (SCI) to operate a manual wheelchair and live independently. Targeted upper limb vibration may be a viable exercise modality to build muscle efficiently while eliminating some of the barriers associated with exercise for persons with SCI.

OBJECTIVE

The purpose of this study was to assess preliminary feasibility of completing a single exercise session of upper limb vibration and compare the acute physiological effects to a single session of standard dumbbell resistance exercise.

METHODS

Individuals with SCI performed seven upper limb exercises (1) isometrically using a vibrating dumbbell at 30 Hz for 60 s (n = 22) and (2) using a standard isotonic resistance protocol (n = 15).

RESULTS

Nineteen (86.4%) of 22 participants were able to perform all vibration exercises at 30 Hz but hold time success rates varied from 33% (side flies and front raises) to 95% (internal rotation). No significant differences were found between vibration exercise and standard resistance protocol for blood lactate, power output, and heart rate (P > 0.05). Perceptions of the training were positive, with most participants (>70%) expressing interest to train with vibration in the future.

CONCLUSIONS

Vibration training was not feasible for all participants, suggesting an individualized approach to starting weight and progression may be necessary. Similar acute physiological changes were seen between vibration exercise and standard resistance protocol, suggesting they could have similar benefits. Additional research is needed to determine if vibration exercise is feasible and beneficial to incorporate into a long-term training program.

Mechanistic involvement of noradrenergic neuronal neurotransmitter release in cutaneous vasoconstriction during autonomic dysreflexia in persons with spinal cord injury

INTRODUCTION

Autonomic dysreflexia (AD) is a potentially life-threatening consequence in high (above T6) spinal cord injury that involves multiple incompletely understood mechanisms. While peripheral arteriolar vasoconstriction, which controls systemic vascular resistance, is documented to be pronounced during AD, the pathophysiological neurovascular junction mechanisms of this vasoconstriction are undefined. One hypothesized mechanism is increased neuronal release of norepinephrine and co-transmitters. We tested this by examining the effects of blockade of pre-synaptic neural release of norepinephrine and co-transmitters on cutaneous vasoconstriction during AD, using a novel non-invasive technique; bretylium (BT) iontophoresis followed by skin blood flow measurements via laser doppler flowmetry (LDF).

METHODS

Bretylium, a sympathetic neuronal blocking agent (blocks release of norepinephrine and co-transmitters) was applied iontophoretically to the skin of a sensate (arm) and insensate (leg) area in 8 males with motor complete tetraplegia. An nearby untreated site served as control (CON). Cutaneous vascular conductance (CVC) was measured (CVC = LDF/mean arterial pressure) at normotension before AD was elicited by bladder stimulation. The percent drop in CVC values from pre-AD vs. AD was compared among BT and CON sites in sensate and insensate areas.

RESULTS

There was a significant effect of treatment but no significant effect of limb/sensation or interaction of limb x treatment on CVC. The percent drop in CVC between BT and CON treated sites was 25.7±1.75 vs. 39.4±0.87, respectively (P = 0.004).

CONCLUSION

Bretylium attenuates, but does not fully abolish vasoconstriction during AD. This suggests release of norepinephrine and cotransmitters from cutaneous sympathetic nerves is involved in cutaneous vasoconstriction during AD.

Accidental boosting in an individual with tetraplegia - considerations for the interpretation of cardiopulmonary exercise testing

CONTEXT

Autonomic dysreflexia (AD), characterized by a transient increase in systolic blood pressure (BP), is experienced by individuals with spinal cord injury (SCI) and can be purposefully induced ('boosting') to counteract autonomic dysfunction that impairs cardiovascular responses to exercise. Herein, we demonstrate the impact of unintentional boosting observed during cardiopulmonary exercise testing (CPET) in an inactive male with SCI (C5, motor-complete).

FINDINGS

On two separate occasions the individual performed a standard arm-crank CPET (1-min stages, 7W increase in resistance) following by a longer CPET (4-min stages, 12W increase in resistance), both to volitional exhaustion. The second CPET was performed to confirm the accuracy of exercise intensity prescription and verify peak exercise parameters. Immediately following the second CPET on the initial visit, the individual reported symptoms of AD, verified as a 58mmHg increase in systolic BP from baseline. Relative to the first CPET, performed only 35 min earlier, there were pronounced differences in peak exercise responses. In comparison to the longer CPET performed on the second visit without a concomitant episode of AD (thereby controlling for the type of CPET protocol administered), peak exercise outcomes were considerably elevated: power output (Δ19W), oxygen uptake (Δ3.61 ml·kg·^-1min^-1), ventilation (Δ11.4 L ·min^-1) and heart rate (Δ9 b·min^-1).

CONCLUSION/CLINICAL RELEVANCE

This case raises important considerations around the nuances of CPET in this population. In individuals susceptible to BP instability, the physiologically boosted state may explain a significant proportion of the variance in peak aerobic capacity and should be closely monitored before and after clinical CPET.

Handcycling Training in Men with Spinal Cord Injury Increases Tolerance to High Intensity Exercise

Individuals with spinal cord injury are characterised by reduced physical capacity as compared to able-bodied persons, and are at risk of developing cardiovascular disease. The study aimed to evaluate the differences in physiological responses to an exercise test in handcycling-trained vs. able-bodied-trained and non-trained men. Eight males with spinal cord injury who were trained in handcycling, eighteen able-bodied males who were trained in powerlifting, and fourteen physically active non-athletes performed a graded arm crank ergometer test. The following physiological indices were measured before and during the test: heart rate, oxygen uptake, and blood lactate concentrations. Aerobic capacity was significantly higher in athletes with spinal cord injury compared to able-bodied athletes (p<0.01) and the control group (p<0.01). The heart rate achieved by handcycling-trained athletes was significantly lower as compared to powerlifters (p<0.01), however, the oxygen pulse was significantly higher (p<0.05). Handcycling-trained athletes reached significantly higher peak power (P_max) during the graded arm exercise in comparison with powerlifters, and significantly higher post exercise blood lactate concentration (p<0.05). The lactate threshold was observed at a significantly higher P in individuals with spinal cord injury compared to able-bodied-trained (p<0.05) and non-trained men (p<0.001). Athletes with spinal cord injury were found to have excellent aerobic capacity and better physiological adaptation to the maximal graded exercise test as compared to able-bodied-trained men. These findings emphasize the importance of regular physical exercise and its potential therapeutic role in the prevention of cardiovascular disease in patients with spinal cord injury.

Impact of cervical spinal cord injury on the relationship between the metabolism and ventilation in rats

Cervical spinal cord injury typically results in respiratory impairments. Clinical and animal studies have demonstrated that respiratory function can spontaneously and partially recover over time after injury. However, it remains unclear whether respiratory recovery is associated with alterations in metabolism. The present study was designed to comprehensively examine ventilation and metabolism in a rat model of spinal cord injury. Adult male rats received sham (i.e., laminectomy) or unilateral mid-cervical contusion injury (height of impact rod: 6.25 or 12.5 mm). Breathing patterns and whole body metabolism (O₂ consumption and CO₂ production) were measured using a whole body plethysmography system conjugated with flow controllers and gas analyzer at the acute (1 day postinjury), subchronic (2 wk postinjury), and chronic (8 wk postinjury) injury stages. The results demonstrated that mid-cervical contusion caused a significant reduction in the tidal volume. Although the tidal volume of contused animals can gradually recover, it remains lower than that of uninjured animals at the chronic injury stage. Although O₂ consumption and CO₂ production were similar between uninjured and contused animals at the acute injury stage, these two metabolic parameters were significantly reduced in contused animals at the subchronic to chronic injury stages. Additionally, the relationships between ventilation, metabolism, and body temperature were altered by cervical spinal cord injury. These results suggest that cervical spinal cord injury causes a complicated reconfiguration of ventilation and metabolism that may enable injured animals to maintain a suitable homeostasis for adapting to the pathophysiological consequences of injury.NEW & NOTEWORTHY Ventilation and metabolism are tightly coupled to maintain appropriate energy expenditure under physiological conditions. Our findings demonstrate that cervical spinal cord injury results in the differential reduction of ventilation and metabolism at the various injury stages and leads to alterations in the relationship between ventilation and metabolism. These results from an animal model provide fundamental knowledge for understanding how cervical spinal cord injury impacts energy homeostasis.

Physiological Considerations to Support Podium Performance in Para-Athletes

The twenty-first century has seen an increase in para-sport participation and the number of research publications on para-sport and the para-athlete. Unfortunately, the majority of publications are case reports/case series or study single impairment types in isolation. Indeed, an overview of how each International Paralympic Committee classifiable impairment type impact athlete physiology, health, and performance has not been forthcoming in the literature. This can make it challenging for practitioners to appropriately support para-athletes and implement evidence-based research in their daily practice. Moreover, the lack of a cohesive publication that reviews all classifiable impairment types through a physiological lens can make it challenging for researchers new to the field to gain an understanding of unique physiological challenges facing para-athletes and to appreciate the nuances of how various impairment types differentially impact para-athlete physiology. As such, the purpose of this review is to (1) summarize how International Paralympic Committee classifiable impairments alter the normal physiological responses to exercise; (2) provide an overview of "quick win" physiological interventions targeted toward specific para-athlete populations; (3) discuss unique practical considerations for the para-sport practitioner; (4) discuss research gaps and highlight areas for future research and innovation, and (5) provide suggestions for knowledge translation and knowledge sharing strategies to advance the field of para-sport research and its application by para-sport practitioners.

Nutritional Considerations for Para-Cycling Athletes: A Narrative Review

Para-cycling is a sport including athletes with different disabilities competing on the track and on the roads using bicycles, tandems, tricycles, and handbikes. Scientific literature in this special population is scarce, especially in the field of sports nutrition. This review summarizes the physiological aspects and demands of para-cycling. This information together with the existing literature on nutritional interventions in this population, helps to discuss the nutritional considerations. To date, only a limited amount of recommendations are available for this population. In most para-cycling athletes, a reduction in active muscle mass and consequently a reduction in resting energy expenditure occurs, except for visually impaired athletes. Furthermore, carbohydrate and protein intake and hydration, supplementation, heat, and weight loss need to be tailored to the disability-specific adaptations such as the reduced active muscle mass, neurogenic bladder, and bowel, a reduced metabolic cost during exercise, and a higher risk of micronutrient deficiency.

A new perspective on cardiovascular drift during prolonged exercise

Prolonged exercise induces cardiovascular drift, which is characterized by decreasing mean arterial pressure (MAP), stroke volume and heart rate increase. Cardiovascular drift has been debated for a long time. Although the exact mechanisms underlying cardiovascular drift are still unknown, two theories have been proposed. The first is that increased skin blood flow displaces blood volume from central circulation to the periphery, which reduces stroke volume. According to this theory, the rise in heart rate is presumably responding to the drop in stroke volume and MAP. The alternative theory is that an increase in heart rate is due to an increase in sympathetic nervous activity causing reducing time at diastole, and therefore stroke volume. It may be difficult to determine a single robust factor accounting for cardiovascular drift, due to the broad range of circumstances. The primary focus of this review is to elucidate our understanding of cardiovascular drift during prolonged exercise through nitric oxide and force-frequency relationship. We highlight for the very first time that cardiovascular drift (in some conditions and within a specific time period) may be considered as a protective strategy against potential damage that could be induced by the intense and prolonged contraction of the myocardium.

Peak Torque Prediction Using Handgrip and Strength Predictors in Men and Women With Motor Complete Spinal Cord Injury

OBJECTIVES

To establish predictive equations for peak torque of muscle groups with totally and partially preserved innervation in individuals with motor complete spinal cord injury (SCI), based on hand dynamometry and strength predictor variables.

METHODS

The cross-sectional study conducted at a rehabilitation hospital consecutively recruited 108 men and women with SCI. All participants performed maximum peak torque tests for shoulder abduction/adduction (isokinetic), trunk flexion/extension (isometric), and handgrip strength testing (hand dynamometer) to establish predictive peak torque equations. The primary outcomes were peak torque variables. Handgrip strength, age, injury level, time since injury, age at injury, body mass, height, body mass index, and physical activity level were the secondary outcomes used as strength predictor variables.

RESULTS

Handgrip strength was a predictor variable for shoulder abduction/adduction peak torque. The best predictive models for shoulder abduction/adduction peak torque exhibited R 2 = 0.57 and R 2 = 0.60, respectively (p ≤ .05). Injury level showed the highest significant predictive capacity for trunk flexion/extension peak torque models (R 2 = 0.38 and R 2 = 0.29; p ≤ .05).

CONCLUSION

Shoulder abduction/adduction peak torque predictive equations may be an alternative for use in an accessible strength tool (hand dynamometry) to evaluate training and rehabilitation programs. Trunk flexion/extension peak torque equations exhibited moderate correlations and high standard error of the estimates and should be used with caution.

Substrate metabolism during recovery from circuit resistance exercise in persons with spinal cord injury

INTRODUCTION

Whole body energy expenditure and lipid oxidation (Lox) are upregulated during and after exercise. Persons with spinal cord injury (SCI) generally have a blunted ability to utilize fat during exercise, but it is unknown if their substrate partitioning is affected during recovery from exercise.

PURPOSE

To determine the effect of a single session of upper body circuit resistance exercise (CRE) on energy expenditure and Lox during exercise recovery in persons with and without SCI.

METHODS

Twenty four persons (3 groups; 7 male and 1 female per group) without paralysis (neurologically intact; N) or with chronic (≥ 1 yr) paraplegia (P) or tetraplegia (T) participated. Energy expenditure and substrate partitioning were assessed via indirect calorimetry before, during, and three times after (up to 120 min after) a single session of CRE, or time-matched seated control (CON).

RESULTS

During CRE, all groups experienced a similar relative increase in oxygen consumption (49 ± 13, 55 ± 11, and 48 ± 15% VO_2peak for N, P, and T, respectively). The Post_0-120 energy expenditure was greater following CRE vs. CON (P < 0.01) and independent of injury characteristics (10.6, 22.6, and 14.3% higher than CON for N, P, and T; P = 0.21). The absolute increase in Lox above CON during recovery was similar for N, P, and T (5.74 ± 2.81, 6.62 ± 3.10, and 4.50 ± 3.91 g, respectively; P = 0.45).

CONCLUSIONS

Energy expenditure and lipid utilization was increased similarly following circuit exercise in persons without and with spinal cord injury in a manner independent of level of injury.

Cardiovascular Autonomic Dysfunction in Spinal Cord Injury: Epidemiology, Diagnosis, and Management

Spinal cord injury (SCI) disrupts autonomic circuits and impairs synchronistic functioning of the autonomic nervous system, leading to inadequate cardiovascular regulation. Individuals with SCI, particularly at or above the sixth thoracic vertebral level (T6), often have impaired regulation of sympathetic vasoconstriction of the peripheral vasculature and the splanchnic circulation, and diminished control of heart rate and cardiac output. In addition, impaired descending sympathetic control results in changes in circulating levels of plasma catecholamines, which can have a profound effect on cardiovascular function. Although individuals with lesions below T6 often have normal resting blood pressures, there is evidence of increases in resting heart rate and inadequate cardiovascular response to autonomic provocations such as the head-up tilt and cold face tests. This manuscript reviews the prevalence of cardiovascular disorders given the level, duration and severity of SCI, the clinical presentation, diagnostic workup, short- and long-term consequences, and empirical evidence supporting management strategies to treat cardiovascular dysfunction following a SCI.

Effect of Body Weight-Supported Treadmill Training on Cardiovascular and Pulmonary Function in People With Spinal Cord Injury: A Systematic Review

Objective: To assess the current evidence with regard to the effects of body weight-supported treadmill training (BWSTT) on cardiovascular and pulmonary function in people with spinal cord injury (SCI) with a focus on outcomes of heart rate (HR), blood pressure (BP), and respiratory parameters. Methods: A systematic literature search was conducted through MEDLINE/PubMed, the Cumulative Index to Nursing and Allied Health Literature, and Physiotherapy Evidence Database. Clinical trials involving adults with SCI and focusing on the effects of BWSTT on HR, BP, and respiratory measurements were included. The quality of included studies was assessed using the Downs and Black scale. The level of evidence of each study was identified using the Spinal Cord Injury Rehabilitation Evidence system. Results: Nine studies that met inclusion criteria were evaluated and included in this review. Overall, the quality index of all included studies was low. All studies scored less than 21 out of 28 on the Downs and Black scale. The level of evidence varied from level 2 to level 4. Level 4 evidence supports the use of BWSTT to decrease resting and exercise HR and improve heart rate variability. The use of BWSTT to improve respiratory parameters after SCI is supported by one study with level 2 evidence. The evidence that supports the use of BWSTT to improve resting BP is inconclusive. Conclusion: There has been low to moderate evidence to support the use of BWSTT in individuals with SCI to improve cardiovascular and pulmonary health. Future randomized controlled trials are needed to investigate the effect of BWSTT on cardiovascular and pulmonary function in people with SCI and compare BWSTT to other physical rehabilitation interventions.

Intensity of physical activity as a percentage of peak oxygen uptake, heart rate and Borg RPE in motor-complete para- and tetraplegia

Objective

The aims were to describe VO_2peak, explore the potential influence of anthropometrics, demographics and level of physical activity within each cohort; b) to define common, standardized activities as percentages of VO_2peak and categorize these as light, moderate and vigorous intensity levels according to present classification systems, and c) to explore how clinically accessible methods such as heart-rate monitoring and Borg rating of perceived exertion (RPE) correlate or can describe light, moderate and vigorous intensity levels.

Design

Cross sectional.

Setting

Rehabilitation facility and laboratory environment.

Subjects

Sixty-three individuals, thirty-seven (10 women) with motor-complete paraplegia (MCP), T7-T12, and twenty-six (7 women) with motor-complete tetraplegia (MCT), C5-C8.

Interventions

VO_2peak was obtained during a graded peak test until exhaustion, and oxygen uptake during eleven different activities was assessed and categorized using indirect calorimetry.

Main outcome measures

VO_2peak, Absolute and relative oxygen consumption, Borg RPE.

Results

Absolute VO_2peak was significantly higher in men than in women for both groups, with fairly small differences in relative VO_2peak. For MCP sex, weight and time spent in vigorous-intensity activity explained 63% of VO_2peak variance. For MCT sex and time in vigorous-intensity activity explained 55% of the variance. Moderate intensity corresponds to 61–72% HR_peak and RPE 10–13 for MCP vs. 71–79% HR_peak, RPE 13–14 for MCT.

Conclusion

Using current classification systems, eleven commonly performed activities were categorized in relative intensity terms, (light, moderate and vigorous) based on percent of VO_2peak, HR_peak and Borg RPE. This categorization enables clinicians to better guide persons with SCI to meet required physical activity levels.

Exercise-Induced Alterations in Sympathetic-Somatomotor Coupling in Incomplete Spinal Cord Injury

The aim of this study was to understand how high- and low-intensity locomotor training (LT) affects sympathetic-somatomotor (SS) coupling in people with incomplete spinal cord injury (SCI). Proper coupling between sympathetic and somatomotor systems allows controlled regulation of cardiovascular responses to exercise. In people with SCI, altered connectivity between descending pathways and spinal segments impairs sympathetic and somatomotor coordination, which may have deleterious effects during exercise and limit rehabilitation outcomes. We postulated that high-intensity LT, which repeatedly engages SS systems, would alter SS coupling. Thirteen individuals (50 ± 7.2 years) with motor incomplete spinal cord injuries (American Spinal Injury Association Impairment Scale C or D; injury level >T6) participated in a locomotor treadmill training program. Patients were randomized into either a high-intensity (high-LT; 70-85% of maximum predicted heart rate; n = 6) group or a low-intensity (low-LT; 50-65% of maximum predicted heart rate; n = 7) group and completed up to 20 LT training sessions over 4-6 weeks, 3-5 days/week. Before and after taining, we tested SS coupling by eliciting reflexive sympathetic activity through a cold stimulation, noxious stimulation, and a mental math task while we measured tendon reflexes, blood pressure, and heart rate. Participants who completed high- versus low-LT exhibited significant decreases in reflex torques during triggered sympathetic activity (cold: -83 vs. 13%, p < 0.01; pain: -65 vs. 54%, p < 0.05; mental math: -43 vs. 41%; p < 0.05). Mean arterial pressure responses to sympathetic stimuli were slightly higher following high- versus low-LT (cold: 30 vs. -1.5%; pain: 6 vs. -12%; mental math: 5 vs. 7%), although differences were not statistically significant. These results suggest that high-LT may be advantageous to low-LT to improve SS coupling in people with incomplete SCI.

A new conceptual framework for the integrated neural control of locomotor and sympathetic function: implications for exercise after spinal cord injury

All mammals, including humans, are designed to produce sustained locomotor movements. Many higher centres are involved in movement, but ultimately these centres act upon a core "rhythm-generating" network within the brainstem-spinal cord. In addition, endurance-based locomotor exercise requires sympathetic neural support to maintain homeostasis and to provide needed metabolic resources. This review focuses on the roles and integration of these 2 neural systems. Part I reviews the cardiovascular, thermoregulatory, and metabolic functions under spinal sympathetic control as revealed by spinal cord injury at different levels. Part II examines the integration between brainstem-spinal sympathetic pathways and the neural circuitry producing motor rhythms. In particular, the rostroventral medulla (RVM) contains the neural circuitry that (i) integrates heart rate, contractility, and blood flow in response to postural changes; (ii) initiates and maintains cardiovascular adaptations for exercise; (iii) provides direct descending innervation to preganglionic neurons innervating the adrenal glands, white adipose tissue, and tissues responsible for cooling the body; (iv) integrates descending sympathetic drive for energy substrate mobilization (lipolysis); and (v) is the relay for descending locomotor commands arising from higher brain centres. A unifying conceptual framework is presented, in which the RVM serves as the final descending supraspinal "exercise integration centre" linking the descending locomotor command signal with the metabolic and homeostatic support needed to produce prolonged rhythmic activities. The role and rationale for an ascending sympathetic and locomotor drive from the lower to upper limbs within this framework is presented. Examples of new research directions based on this unifying framework are discussed.

The addition of three new items in the Adapted Manual Wheelchair Circuit improves the discrimination between different levels of spinal cord injury

Purpose: To determine whether the inclusion of three additional items improved the discriminative capacity of the Adapted Manual Wheelchair Circuit (AMWC). Design: Cross-sectional study. Methods: A total of 126 men (median age 28.9 years [percentiles 25 and 75: 23.7; 38.5 years]) with spinal cord injury were consecutively enrolled and divided into three subgroups: high paraplegia (HP), medium paraplegia (MP), and low paraplegia (LP). The participants performed the AMWC with three additional items. Ability score and total time of AMWC (AMWC_AS and AMWC_TT) and AMWC plus the three additional items (AMWC+3_AS and AMWC+3_TT), 3 min of overground wheeling test and performance score were evaluated. Results: AMWC was not able to discriminate HP from MP and LP (Wilks' lambda = 0.93; P= 0.07). In contrast, AMWC+3 was able to discriminate between the three subgroups (Wilks' lambda = 0.86; P≤ 0.05). AMWC+3_AS presented a better sensitivity compared to AMWC_AS (lower success rate for all subgroups, 38.5% vs. 82.1% for HP; 49.0% vs. 75.5% for MP; 78.9% vs. 94.7% for LP). The LP group presented a significant higher AMWC+3_AS compared to MP and HP (17.0 vs. 16.5 and 16.5, respectively, P≤ 0.05). AMWC+3_TT was significantly lower in LP compared to MP and HP (139.85 s vs. 242.52 s and 326.21 s, respectively, P≤ 0.05). Conclusion: The AMWC+3 outcomes were able to discriminate between HP, MP, and LP subgroups, and the addition of the three items enhanced the sensitivity of the wheelchair circuit. The performance of LP was more evident with significant differences compared to HP and MP for all AMWC+3 outcomes.

Preserved Adrenal Function After Lumbar Spinal Cord Transection Augments Low Pressure Bladder Activity in the Rat

Spinal cord injury (SCI) disconnects supraspinal micturition centers from the lower urinary tract resulting in immediate and long-term changes in bladder structure and function. While cervical and high thoracic SCI have a greater range of systemic effects, clinical data suggest that those with lower (suprasacral) injuries develop poorer bladder outcomes. Here we assess the impact of SCI level on acute changes in bladder activity. We used two SCI models, T3 and L2 complete transections in male Wistar rats, and compared bladder pressure fluctuations to those of naïve and bladder-denervated animals. By 2 days after L2 transection, but not T3 transection or bladder denervation, small amplitude rhythmic contractions (1 mmHg, 0.06 Hz) were present at low intravesical pressures (<6 mmHg); these were still present 1 month following injury, and at 3 months, bladders from L2 SCI animals were significantly larger than those from T3 SCI or naïve animals. Low-pressure contractions were unaffected by blocking ganglionic signaling or bladder denervation at the time of measurements. L2 (and sham surgery) but not T3 transection preserves supraspinal adrenal control, and by ELISA we show lower plasma adrenal catecholamine concentration in the latter. When an adrenalectomy preceded the L2 transection, the aberrant low-pressure contractions more closely resembled those after T3 transection, indicating that the increased bladder activity after lumbar SCI is mediated by preserved adrenal function. Since ongoing low-pressure contractions may condition the detrusor and exacerbate detrusor-sphincter dyssynergia, moderating bladder catecholamine signaling may be a clinically viable intervention strategy.

Autonomic Nervous System in Paralympic Athletes with Spinal Cord Injury

Individuals sustaining a spinal cord injury (SCI) frequently suffer from sensorimotor and autonomic impairment. Damage to the autonomic nervous system results in cardiovascular, respiratory, bladder, bowel, and sexual dysfunctions, as well as temperature dysregulation. These complications not only impede quality of life, but also affect athletic performance of individuals with SCI. This article summarizes existing evidence on how damage to the spinal cord affects the autonomic nervous system and impacts the performance in athletes with SCI. Also discussed are frequently used performance-enhancing strategies, with a special focus on their legal aspect and implication on the athletes' health.

Circulating Progenitor Cell Response to Exercise in Wheelchair Racing Athletes

INTRODUCTION

Circulating progenitor cells (CPC) are a heterogeneous population of stem/progenitor cells in peripheral blood that participate in tissue repair. CPC mobilization has been well characterized in able-bodied persons but has not been previously investigated in wheelchair racing athletes. The purpose of this study was to characterize CPC and CPC subpopulation mobilization in elite wheelchair racing athletes in response to acute, upper-extremity aerobic exercise to determine whether CPC responses are similar to ambulatory populations.

METHODS

Eight participants (three females; age = 27.5 ± 4.0 yr, supine height = 162.5 ± 18.6 cm, weight = 53.5 ± 10.9 kg, V˙O2peak = 2.4 ± 0.62 L·min, years postinjury = 21.5 ± 6.2 yr) completed a 25-km time trial on a road course. Blood sampling occurred before and immediately after exercise for quantification of CPC (CD34), hematopoietic stem and progenitor cells (HSPC) (CD34/CD45), hematopoietic stem cells (HSC) (CD34/CD45/CD38), CD34 adipose tissue (AT)-derived mesenchymal stromal cells (MSC) (CD45/CD34/CD105/CD31), CD34 bone marrow (BM)-derived MSC (CD45/CD34/CD105/CD31), and endothelial progenitor cells (EPC) (CD45/CD34/VEGFR2) via flow cytometry. Blood lactate was measured before and after trial as an indicator of exercise intensity.

RESULTS

CPC concentration increased 5.7-fold postexercise (P = 0.10). HSPC, HSC, EPC, and both MSC populations were not increased postexercise. Baseline HSPC populations were significantly positively correlated to absolute V˙O2peak (rho = 0.71, P < 0.05) with HSC trending to positively correlate to V˙O2peak (rho = 0.62, P = 0.10). AT-MSC populations were trending to be negatively correlated to baseline V˙O2peak (rho = -0.62, P = 0.058). The change in CPC, EPC, and AT-MSC pre- and postexercise significantly positively correlated to the change in lactate concentrations (rho = 0.91 P = 0.002, 0.71 P = 0.047, 0.81 P = 0.02, respectively, all P < 0.05).

CONCLUSION

These data suggest that CPC content in wheelchair racing athletes is related to cardiorespiratory fitness, and responses to exercise are positively related to exercise intensity.

Arm Cycling Combined with Passive Leg Cycling Enhances VO2peak in Persons with Spinal Cord Injury Above the Sixth Thoracic Vertebra

Objective: To test whether passive leg cycling (PLC) during arm cycling ergometry (ACE) affects peak oxygen uptake (VO2peak) differently in individuals with spinal cord injury (SCI) at/above the 6th thoracic vertebra (T6) and below T6. Methods: We conducted a cross-sectional study, analyzed by univariate and multivariate regression models. Between- and within-group differences were examined during (a) ACE only, (b) ACE combined with PLC (ACE-PLC), and (c) ACE combined with functional electrical stimulation cycling (FES hybrid). Fifteen SCI subjects were recruited and grouped according to injury level: at/above T6 (SCI-high, n = 8) or below T6 (SCI-low, n = 7). VO2peak tests during ACE only, ACE-PLC, and FES hybrid were performed in random order on separate days. Results: In the SCI-high group, mean (SD) VO2peak was 19% higher during ACE-PLC than during ACE only [21.0 (3.8) vs 17.7 (5.0) mL·kg-1·min-1; p = .002], while VO2peak during FES hybrid cycling was 16% higher than during ACE-PLC [24.4 (4.1) mL·kg-1·min-1; p = .001]. No significant differences among exercise modalities were found for the SCI-low group. Conclusion: Additional training modalities (eg, PLC) during ACE facilitate exercise in SCI-high individuals, but not to the level of the FES hybrid method. Conversely, additional training modalities may not increase training load in SCI-low individuals.

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.

Cardiac Structure and Function in Elite Para-cyclists with Spinal Cord Injury

PURPOSE

We sought to explore the association between the spinal cord injury (SCI) level on the cardiac structure and the function observed in elite para-cyclists.

METHODS

Cross-sectional echocardiographic data from 44 elite SCI hand cyclists (39.8 ± 9 yr, 68% male/32% female) stratified by the level of SCI (cervical, N = 9; T1-T5, N = 10; below T5, N = 25) and 19 non-SCI blind/visually impaired (BVI) tandem cyclists (32.4 ± 7 yr, 58% male/42% female) were analyzed before the initiation of international competition.

RESULTS

Compared with non-SCI BVI cyclists, cervical SCI para-cyclists were observed with lower indexed left ventricular (LV) mass (99.6 ± 12 vs 125 ± 20 g·m, P = 0.01), posterior wall thickness (4.5 ± 0.3 vs 5.8 ± 0.7 mm·m, P < 0.001), interventricular septal wall thickness (4.8 ± 0.5 vs 5.7 ± 0.7 mm·m; P = 0.03), and left atrial volume (21 ± 3.5 vs 28 ± 7 mL·m; P = 0.02). In multivariable analyses, cervical SCI was independently associated with decreased LV wall thickness [interventricular septum (β = -0.67, P = 0.01), posterior wall (β = -0.98, P = 0.001)], decreased LV mass (β = -21, P < 0.001), and decreased left atrial volume index (β = -6.9, P = 0.001) compared with other levels of SCI and non-SCI BVI cyclists. There were no differences in ventricular function among any of the athlete groups.

CONCLUSION

Compared with para-cyclists with lower levels of SCI, the athletes with cervical SCI demonstrate attenuated cardiac size and concentric LV hypertrophy.

Physiological and lipid profile response to acute exercise at different intensities in individuals with spinal cord injury

STUDY DESIGN

Experimental and cross-sectional study.

OBJECTIVE

To assess the immediate effect of exercise on heart rate (HR), oxygen uptake (VO₂), pulmonary ventilation (PV), oxygen pulse (OP), glucose and lipids of wheelchair basketball players with spinal cord injury (SCI).

SETTING

Center of Studies in Psychobiology and Exercise-São Paulo, Brazil.

METHODS

In all, nine wheelchair basketball players with SCI and nine able-bodied controls (C) performed three exercise sessions at different intensities: ventilatory threshold 1 (VT1), 15% below VT1 and 15% above VT1 with a duration of ~24-34 min. HR, VO₂, PV, OP, glucose and lipids were analyzed.

RESULTS

VO_2, PV and OP were significantly lower in the players with SCI compared to C during the same intensity exercise sessions. However, the individuals with SCIs demonstrated increases in HR, PV and OP at similar rates to C. Triglycerides of the SCI group were elevated 30 min after the exercise session at VT1 compared to values before the exercise session (P=0.017); this elevation was not observed in group C. For the exercise sessions 15% above VT1, only glucose (P=0.040) and low-density lipoprotein (P=0.012) 30 min after the exercise were elevated in the SCI group compared to group C.

CONCLUSION

We conclude that the SCI group demonstrated increases in HR, PV and OP but not VO₂ with increased intensity of exercise at similar rates as in group C.

Implications of altered autonomic control on sports performance in athletes with spinal cord injury

It is well known that athletes with spinal cord injury (SCI) may experience altered autonomic physiology that impacts their exercise capacity and sports performance. This is particularly relevant given the ever-increasing number of individuals with SCI who are actively engaged in sports at all levels, from community-based adaptive sports to elite Paralympic competitions. As such, the purpose of this article is to review the present literature regarding the implications of altered autonomic control on the safety and performance of athletes with SCI. A particular emphasis will be placed on the autonomic aspects of cardiovascular and thermoregulatory control in the athlete population, as well as the implications of autonomic dysreflexia in enhancing sports performance. Further research is needed to understand the autonomic factors that influence athletes with SCI in order to ensure optimal and safe sports competition. Additionally, this information is crucially relevant to the coaches, sports administrators, and team medical staff who work closely with athletes with SCI.

Hemodynamic Adaptations to Regular Exercise in People With Spinal Cord Injury

Objective

To investigate the real-time cardiovascular response to the progressive overload exercise in different levels of spinal cord injury (SCI), and to find out whether regular exercise has effect on these cardiovascular responses.

Methods

The study enrolled 8 able-bodied individuals in the control group plus 15 SCI subjects who were divided into two groups by their neurological level of injury: high-level SCI group (T6 or above) and low-level SCI group (T7 or below). Also, subjects were divided into exercise group and non-exercise group by usual exercise habits. We instructed the subjects to perform exercises using arm ergometer according to the protocol and checked plethysmograph for the real time assessment of blood pressure, heart rate, and cardiac output.

Results

Six subjects were included in high-level SCI group (3 cervical, 3 thoracic injuries), 9 subjects in low-level SCI group (9 thoracic injuries), and 8 able-bodied individuals in control group. During arm ergometer-graded exercise, mean arterial pressure (MAP) was significantly lower in high-level SCI subjects of non-exercise group, compared with high-level SCI subjects of exercise group. In addition, HR was significantly higher in low-level SCI group compared with control group.

Conclusion

There are significant differences in mean arterial pressure of high-level SCI group according to usual exercise habits. We discovered that even in non-athlete high-level SCI, regular exercise can bring cardiac modulation through blood pressure control.

Salivary alpha amylase not chromogranin A reflects sympathetic activity: exercise responses in elite male wheelchair athletes with or without cervical spinal cord injury

Background

Salivary alpha amylase (sAA) and chromogranin A (sCgA) have both been suggested as non-invasive markers for sympathetic nervous system (SNS) activity. A complete cervical spinal cord injury leading to tetraplegia is accompanied with sympathetic dysfunction; the aim of this study was to establish the exercise response of these markers in this in vivo model.

Methods

Twenty-six elite male wheelchair athletes (C6–C7 tetraplegia: N = 8, T6–L1 paraplegia: N = 10 and non-spinal cord injured controls: N = 8) performed treadmill exercise to exhaustion. Saliva and blood samples were taken pre, post and 30 min post exercise and analysed for sAA, sCgA and plasma adrenaline concentration, respectively.

Results

In all three subgroups, sAA and sCgA were elevated post exercise (P < 0.05). Whilst sCgA was not different between subgroups, a group × time interaction for sAA explained the reduced post-exercise sAA activity in tetraplegia (162 ± 127 vs 313 ± 99 (paraplegia) and 328 ± 131 U mL⁻¹ (controls), P = 0.005). The post-exercise increase in adrenaline was not apparent in tetraplegia (P = 0.74). A significant correlation was found between adrenaline and sAA (r = 0.60, P = 0.01), but not between adrenaline and sCgA (r = 0.06, P = 0.79).

Conclusions

The blunted post-exercise rise in sAA and adrenaline in tetraplegia implies that both reflect SNS activity to some degree. It is questionable whether sCgA should be used as a marker for SNS activity, both due to the exercise response which is not different between the subgroups and its non-significant relationship with adrenaline.

Cardiovascular response to peak voluntary exercise in males with cervical spinal cord injury

CONTEXT/OBJECTIVE

Traumatic damage to the cervical spinal cord is usually associated with a disruption of the autonomic nervous system (ANS) and impaired cardiovascular control both during and following exercise. The magnitude of the cardiovascular dysfunction remains unclear. The aim of the current study was to compare cardiovascular responses to peak voluntary exercise in individuals with tetraplegia and able-bodied participants.

DESIGN

A case-control study.

SUBJECTS

Twenty males with cervical spinal cord injury (SCI) as the Tetra group and 27 able-bodied males as the Control group were included in the study.

OUTCOME MEASURES

Blood pressure (BP) response one minute after the peak exercise, peak heart rate (HRpeak), and peak oxygen consumption (VO2peak) on an arm crank ergometer were measured. In the second part of the study, 17 individuals of the Control group completed the Tetra group's workload protocol with the same parameters recorded.

RESULTS

There was no increase in BP in response to the exercise in the Tetra group. Able-bodied individuals exhibited significantly increased post-exercise systolic BP after the maximal graded exercise test (123±16%) and after completion of the Tetra group's workload protocol (114±11%) as compared to pre-exercise. The Tetra group VO2peak was 59% and the HRpeak was 73% of the Control group VO2peak and HRpeak, respectively.

CONCLUSIONS

BP did not increase following maximal arm crank exercise in males with a cervical SCI unlike the increases observed in the Control group. Some males in the Tetra group appeared to be at risk of severe hypotension following high intensity exercise, which can limit the ability to progressive increase and maintain high intensity exercise.

The thermic response to food intake in persons with thoracic spinal cord injury

[Purpose] To investigate the influence of the level of spinal cord injury on the thermic effect of food intake (TEF) in persons with thoracic spinal cord injury. [Subjects and Methods] Seven male subjects with spinal cord injury (SCI; age, 40 ± 6 years) and six able-bodied subjects (AB; age, 37 ± 8 years) volunteered to participate in the present study. The subjects consumed an identical test meal consisting of 7.9 kcal/kg of body weight. Energy expenditure and plasma norepinephrine concentrations were measured over a 3-hour period. [Results] The adjusted TEF at 60 min was almost the same among the three groups [AB, SCI with high thoracic cord (T5–6) injury (HSCI), and SCI with low thoracic cord (T9–12) injury (LSCI)]. Although the LSCI group had almost the same adjusted TEF at 120 min as the AB group, the adjusted TEF at 120 min of the HSCI group was significantly lower than that of the AB group. The changes in plasma norepinephrine concentration and heart rate in response to food intake were similar among the three groups. [Conclusion] SCI at the T5–6 level results in a lower TEF due to sympathetic decentralization.

Is There an Association Between Markers of Cardiovascular Autonomic Dysfunction at Discharge From Rehabilitation and Participation 1 and 5 Years Later in Individuals With Spinal Cord Injury?

OBJECTIVES

To determine whether physical activity and participation 1 and 5 years after discharge are associated with measures of cardiovascular autonomic function: prevalence of hypotension and reduced peak heart rate at discharge from initial inpatient spinal cord injury (SCI) rehabilitation.

DESIGN

Prospective cohort study.

SETTING

Rehabilitation centers.

PARTICIPANTS

Individuals with SCI (N=146).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

We recorded markers of cardiovascular autonomic dysfunction (resting blood pressure and peak heart rate) and personal and lesion characteristics at the time of discharge from rehabilitation. Parameters for participation (social health status dimension of the Sickness Impact Profile) and physical activity (Physical Activity Scale for Individuals with Physical Disabilities [PASIPD]) were measured 1 and 5 years after discharge. Effects of prevalence of cardiovascular autonomic dysfunction were analyzed using linear regression analysis while correcting for possible confounders.

RESULTS

We found no significant association between hypotension and social health status dimension of the Sickness Impact Profile or PASIPD, either at 1 or at 5 years after discharge. A significant association between peak heart rate and social health status dimension of the Sickness Impact Profile was found at 1 year after discharge, showing poorer participation in individuals with low peak heart rate (ie, cardiovascular autonomic dysfunction). The unadjusted relation between peak heart rate and the social health status dimension of the Sickness Impact Profile was significant at 5 years, but not when adjusted for confounders. We found associations between peak heart rate and PASIPD for both 1 and 5 years after discharge; however, these were not significant after correction for potential confounding factors.

CONCLUSIONS

Autonomic dysfunction after SCI is a crucial factor influencing quality of life. We found that cardiovascular autonomic impairment, assessed from low peak heart rate, was associated with reduced participation after 1 year. The results suggest that peak heart rate at discharge from rehabilitation after SCI should be used to identify those needing additional support to facilitate physical activity and participation after discharge.

Differences in Left Ventricular Global Function and Mechanics in Paralympic Athletes with Cervical and Thoracic Spinal Cord Injuries

Following a spinal cord injury, there are changes in resting stroke volume (SV) and its response to exercise. The purpose of the following study was to characterize resting left ventricular structure, function, and mechanics in Paralympic athletes with tetraplegia (TETRA) and paraplegia (PARA) in an attempt to understand whether the alterations in SV are attributable to inherent dysfunction in the left ventricle. This retrospective study compared Paralympic athletes with a traumatic, chronic (>1 year post-injury), motor-complete spinal cord injury (American Spinal Injury Association Impairment Scale A-B). Eight male TETRA wheelchair rugby players (34 ± 5 years, C5-C7) and eight male PARA alpine skiers (35 ± 5 years, T4-L3) were included in the study. Echocardiography was performed in the left lateral decubitus position and indices of left ventricular structure, global diastolic and systolic function, and mechanics were derived from the average across three cardiac cycles. Blood pressure was measured in the supine and seated positions. All results are presented as TETRA vs. PARA. There was no difference in left ventricular dimensions between TETRA and PARA. Additionally, indices of global diastolic function were similar between groups including isovolumetric relaxation time, early (E) and late (A) transmitral filling velocities and their ratio (E/A). While ejection fraction was similar between TETRA and PARA (59 ± 4 % vs. 61 ± 7 %, p = 0.394), there was evidence of reduced global systolic function in TETRA including lower SV (62 ± 9 ml vs. 71 ± 6 ml, p = 0.016) and cardiac output (3.5 ± 0.6 L/min vs. 5.0 ± 0.9 L/min, p = 0.002). Despite this observation, several indices of systolic and diastolic mechanics were maintained in TETRA but attenuted in PARA including circumferential strain at the level of the papillary muscle (−23 ± 4% vs. −15 ± 6%, p = 0.010) and apex (−36 ± 10% vs. −23 ± 5%, p = 0.010) and their corresponding diastolic strain rates (papillary: 1.90 ± 0.63 s⁻¹ vs. 1.20 ± 0.51 s⁻¹, p = 0.028; apex: 3.03 ± 0.71 s⁻¹ vs. 1.99 ± 0.69 s⁻¹, p = 0.009). All blood pressures were lower in TETRA. The absence of an association between reduced global systolic function and mechanical dysfunction in either TETRA or PARA suggests any reductions in SV are likely attributed to impaired loading rather than inherent left ventricular dysfunction.

Peak heart rates and sympathetic function in tetraplegic nonathletes and athletes

PURPOSE

To examine differences in peak heart rate (HR) and measures of sympathetic function between nonathletes and athletes with chronic, motor-complete, cervical spinal cord injury (SCI).

METHODS

Eight nonathletic men with SCI (C4-C7; age 47 ± 9 yr, with injury duration of 16 ± 9 yr) and 13 athletic men with SCI (C5-C8; age 37 ± 8 yr, with injury duration of 16 ± 6 yr) participated in the study. Measures of sympathetic function included palmar sympathetic skin responses (SSR) to median nerve stimulation, and systolic (SBP) and diastolic (DBP) blood pressure responses to a passive sit-up test. Peak HR responses were assessed during a maximal exercise test.

RESULTS

Compared to the athletic group, the nonathletic group exhibited lower peak HR (102 ± 34 vs 161 ± 20 bpm, P < 0.001) and average SSR scores (0.13 ± 0.35 vs 2.41 ± 1.97, P = 0.008), along with greater reductions in SBP and DBP in response to passive sit-up (SBP: -22 ± 10 vs -9 ± 12 mm Hg, P = 0.019; DBP: -18 ± 8 mm Hg vs -4 ± 9 mm Hg, P = 0.003). On the basis of the criteria for orthostatic hypotension (OH) (drop in SBP ≥ 20 mm Hg or DBP ≥ 10 mm Hg), 88% and 23% of nonathletes and athletes had OH.

CONCLUSIONS

Attenuated peak HR in nonathletic individuals with tetraplegia may be secondary to impairments in sympathetic function including absent SSR and OH. Furthermore, the degree of preserved sympathetic function documented in tetraplegic athletes may suggest a predisposition to engage in high-performance sports. Collectively, our findings provide novel insight into the importance of the sympathetic nervous system for exercise performance.

Perspective: Does Laboratory-Based Maximal Incremental Exercise Testing Elicit Maximum Physiological Responses in Highly-Trained Athletes with Cervical Spinal Cord Injury?

The physiological assessment of highly-trained athletes is a cornerstone of many scientific support programs. In the present article, we provide original data followed by our perspective on the topic of laboratory-based incremental exercise testing in elite athletes with cervical spinal cord injury. We retrospectively reviewed our data on Great Britain Wheelchair Rugby athletes collected during the last two Paralympic cycles. We extracted and compared peak cardiometabolic (heart rate and blood lactate) responses between a standard laboratory-based incremental exercise test on a treadmill and two different maximal field tests (4 min and 40 min maximal push). In the nine athletes studied, both field tests elicited higher peak responses than the laboratory-based test. The present data imply that laboratory-based incremental protocols preclude the attainment of true peak cardiometabolic responses. This may be due to the different locomotor patterns required to sustain wheelchair propulsion during treadmill exercise or that maximal incremental treadmill protocols only require individuals to exercise at or near maximal exhaustion for a relatively short period of time. We acknowledge that both field- and laboratory-based testing have respective merits and pitfalls and suggest that the choice of test be dictated by the question at hand: if true peak responses are required then field-based testing is warranted, whereas laboratory-based testing may be more appropriate for obtaining cardiometabolic responses across a range of standardized exercise intensities.

The role of autonomic function on sport performance in athletes with spinal cord injury

Devastating paralysis, autonomic dysfunction, and abnormal cardiovascular control present significant hemodynamic challenges to individuals with spinal cord injury (SCI), especially during exercise. In general, resting arterial pressure after SCI is lower than with able-bodied individuals and is commonly associated with persistent orthostatic intolerance along with transient episodes of life-threatening hypertension, known as "autonomic dysreflexia." During exercise, the loss of central and reflexive cardiovascular control attenuates maximal heart rate and impairs blood pressure regulation and blood redistribution, which ultimately reduces venous return, stroke volume, and cardiac output. Thermoregulation also is severely compromised in high-lesion SCI, a problem that is compounded when competing in hot and humid conditions. There is some evidence that enhancing venous return via lower body positive pressure or abdominal binding improves exercise performance, as do cooling strategies. Athletes with SCI also have been documented to self-induce autonomic dysreflexia before competition with a view of increasing blood pressure and improving their performance, a technique known as "boosting." For health safety reasons, boosting is officially banned by the International Paralympics Committee. This article addresses the complex issue of how the autonomic nervous system affects sports performance in athletes with SCI, with a specific focus on the potential debilitating effects of deranged cardiovascular control.

Serum lipid profile in subjects with traumatic spinal cord injury

Background and Aims

Few large studies have examined the relationship between spinal cord injury (SCI) and lipid profile. We studied serum lipid concentrations in subjects with traumatic SCI in relation to the degree of neurological involvement and time since injury, and compared them with values from a reference sample for the Spanish population (DRECE study).

Materials and Methods

A retrospective cohort was built from 177 consecutive cases with traumatic SCI admitted to the SCI unit of the Miguel Servet Hospital in Aragon (Spain). Outcome measures (cholesterol, triglycerides, HDL-c and LDL-c levels) were analyzed according to the ASIA Impairment Scale (AIS), neurological level of injury (involvement of all limbs vs. only lower limbs), and time since injury. All analyses were adjusted for age and sex.

Results

Cases without preserved motor function (AIS A or B) had lower total and HDL cholesterol than the others (-11.4 [-21.5, -1.4] mg/dL total cholesterol and -5.1 [-8.8, -1.4] mg/dL HDL-c), and cases with all-limb involvement had lower total, HDL, and LDL cholesterol than those with only lower-limb involvement (-14.0 [-24.6, -3.4] mg/dL total cholesterol, -4.1 [-8.0, -0.2] mg/dL HDL-c, and -10.0 [-19.7, -0.3] mg/dL LDL-c) (all p<0.05). No association was found between lipid concentrations and time since injury. Concentrations of lipid subfractions and triglycerides in SCI subjects were lower than in sex- and age-stratified values from the reference sample.

Conclusion

A high degree of neurological involvement in SCI (anatomically higher lesions and AIS A or B) is associated with lower total cholesterol and HDL-c.

Heart rate response during underwater treadmill training in adults with incomplete spinal cord injury

BACKGROUND

Walking on a submerged treadmill can improve mobility in persons displaying lower limb muscle weakness and balance deficits. Little is known, however, regarding the effect of water treadmill exercise on cardiac performance in persons with incomplete spinal cord injury (iSCI).

OBJECTIVE

To assess heart rate response during underwater treadmill training (UTT) in adults with iSCI.

METHODS

Seven males and 4 females with iSCI (age = 48 ± 13 years; 5 ± 8 years after injury) completed 8 weeks of UTT (3 sessions per week; 3 walks per session) incorporating individually determined walking speeds, personalized levels of body weight unloading, and gradual, alternating increases in speed and duration. Heart rate was monitored during the last 15 seconds of the final 2 minutes of each walk.

RESULTS

Over the course of 3 biweekly periods in which walking speed remained constant, heart rate fell by 7% (7 ± 1 b•min(-1); P < .001) in weeks 2 and 3, 14% (17 ± 6 b•min(-1); P < .001) in weeks 4 and 5, and 17% (21 ± 11 b•min(-1); P < .001) in weeks 6 and 7.

CONCLUSION

In adults with iSCI, progressively greater absolute and relative reductions in submaximal exercise heart rate occurred after 2 months of UTT featuring a systematic increase in training volume.

Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury

We asked whether elastic binding of the abdomen influences respiratory mechanics during wheelchair propulsion in athletes with cervical spinal cord injury (SCI). Eight Paralympic wheelchair rugby players with motor-complete SCI (C5-C7) performed submaximal and maximal incremental exercise tests on a treadmill, both with and without abdominal binding. Measurements included pulmonary function, pressure-derived indices of respiratory mechanics, operating lung volumes, tidal flow-volume data, gas exchange, blood lactate, and symptoms. Residual volume and functional residual capacity were reduced with binding (77 ± 18 and 81 ± 11% of unbound, P < 0.05), vital capacity was increased (114 ± 9%, P < 0.05), whereas total lung capacity was relatively well preserved (99 ± 5%). During exercise, binding introduced a passive increase in transdiaphragmatic pressure, due primarily to an increase in gastric pressure. Active pressures during inspiration were similar across conditions. A sudden, sustained rise in operating lung volumes was evident in the unbound condition, and these volumes were shifted downward with binding. Expiratory flow limitation did not occur in any subject and there was substantial reserve to increase flow and volume in both conditions. V̇o2 was elevated with binding during the final stages of exercise (8-12%, P < 0.05), whereas blood lactate concentration was reduced (16-19%, P < 0.05). V̇o2/heart rate slopes were less steep with binding (62 ± 35 vs. 47 ± 24 ml/beat, P < 0.05). Ventilation, symptoms, and work rates were similar across conditions. The results suggest that abdominal binding shifts tidal breathing to lower lung volumes without influencing flow limitation, symptoms, or exercise tolerance. Changes in respiratory mechanics with binding may benefit O2 transport capacity by an improvement in central circulatory function.

Circulating angiogenic biomolecules at rest and in response to upper-limb exercise in individuals with spinal cord injury

OBJECTIVE

Individuals with spinal cord injury (SCI) show structural and functional vascular maladaptations and muscle loss in their lower limbs. Angiogenic biomolecules play important roles in physiological and pathological angiogenesis, and are implicated in the maintenance of muscle mass. This study examined the responses of angiogenic molecules during upper-limb aerobic exercise in patients with SCI and in able-bodied (AB) individuals.

METHODS

Eight SCI patients with thoracic lesions (T6-T12, ASIA A) and eight AB individuals performed an arm-cranking exercise for 30 minutes at 60% of their VO2max. Plasma concentrations of vascular endothelial growth factor (VEGF-A165), VEGF receptor 1 (sVEGFr-1), VEGF receptor 2 (sVEGFr-2), metalloproteinase 2 (MMP-2), and endostatin were measured at rest, after exercise, and at 1.5 and 3.0 hours during recovery.

RESULTS

The two-way analysis of variance showed non-significant main effects of "group" and significant main effects of "time/exercise" for all angiogenic biomolecules examined (P < 0.01-0.001). The arm-cranking exercise significantly increased plasma concentrations of VEGF, sVEGFr-1, sVEGFr-2, MMP-2, and endostatin in both groups (P < 0.001-0.01). The magnitude of the increase was similar in both patients with SCI and AB individuals, as shown by the non-significant group × time interaction for all angiogenic parameters.

CONCLUSIONS

Upper-limb exercise (arm-cranking for 30 minutes at 60% of VO2max) is a sufficient stimulus to trigger a coordinated circulating angiogenic response in patients with SCI. The response of angiogenic molecules to upper-limb aerobic exercise in SCI appears relatively similar to that observed in AB individuals.

A retrospective chart review of heart rate and blood pressure abnormalities in veterans with spinal cord injury

OBJECTIVE

Autonomic impairment may lead to increased prevalence of heart rate (HR) and blood pressure (BP) abnormalities in veterans with spinal cord injury (SCI). In addition, comorbid medical conditions and prescription medication use may influence these abnormalities, including bradycardia, and tachycardia, hypotension, hypertension as well as autonomic dysreflexia (AD), and orthostatic hypotension (OH).

DESIGN

A retrospective review of clinical and administrative datasets in veterans with SCI and compared the prevalence rates between clinical values and ICD-9 diagnostic codes in individuals with tetraplegia (T: C1-C8), high paraplegia (HP: T1-T6), and low paraplegia (LP: T7 and below).

RESULTS

The prevalence of clinical values indicative of a HR ≥ 80 beats per minute was higher in the HP compared to the LP and T groups. A systolic BP (SBP) ≤ 110 mmHg was more common in the T compared to the HP and LP groups, whereas the prevalence of a SBP ≥ 140 mmHg was increased in the LP compared to the HP and T groups. Diagnosis of hypertension was 39-60% whereas the diagnosis of hypotension was less than 1%. Diagnosis of AD and OH was highest in the T group, but remained below 10%, regardless of categorical lesion level. Antihypertensive medications were commonly prescribed (55%), and patients on these medications were less likely to have high BP. The odds ratio of higher SBP and DBP increased with age and body mass index (BMI).

CONCLUSION

In veterans with SCI, the prevalence of HR and BP abnormalities varied depending on level of lesion, age, BMI, and prescription medication use.

Decentralized cardiovascular autonomic control and cognitive deficits in persons with spinal cord injury

Spinal cord injury (SCI) results in motor and sensory impairments that can be identified with the American Spinal Injury Association (ASIA) Impairment Scale (AIS). Although, SCI may disrupt autonomic neural transmission, less is understood regarding the clinical impact of decentralized autonomic control. Cardiovascular regulation may be altered following SCI and the degree of impairment may or may not relate to the level of AIS injury classification. In general, persons with lesions above T1 present with bradycardia, hypotension, and orthostatic hypotension; functional changes which may interfere with rehabilitation efforts. Although many individuals with SCI above T1 remain overtly asymptomatic to hypotension, we have documented deficits in memory and attention processing speed in hypotensive individuals with SCI compared to a normotensive SCI cohort. Reduced resting cerebral blood flow (CBF) and diminished CBF responses to cognitive testing relate to test performance in hypotensive non-SCI, and preliminary evidence suggests a similar association in individuals with SCI. Persons with paraplegia below T7 generally present with a normal cardiovascular profile; however, our group and others have documented persistently elevated heart rate and increased arterial stiffness. In the non-SCI literature there is evidence supporting a link between increased arterial stiffness and cognitive deficits. Preliminary evidence suggests increased incidence of cognitive impairment in individuals with paraplegia, which we believe may relate to adverse cardiovascular changes. This report reviews relevant literature and discusses findings related to the possible association between decentralized cardiovascular autonomic control and cognitive dysfunction in persons with SCI.