Cardiovascular function in individuals with incomplete spinal cord injury: a systematic review

Assessment of Cardiac Autonomic Function by Short-Term Sensor-Based and Long-Term Heart Rate Variability Analyses in Individuals with Spinal Cord Injury After Long-Term Table Tennis Training

This study aimed to examine the acute and chronic effects of an exercising table tennis program on cardiac Autonomic Nervous System (ANS) and functional capacity in people with tetraplegia. Twenty males with tetraplegia (C6-C7), with a mean age of 38.50 ± 4.04 years old, were randomly assigned into two equal groups: A, who followed a 6-month exercise training program with table tennis 3 times per week, and B, who remained untrained. Additionally, 11 healthy sedentary men (group C) with a mean age of 39.71 ± 5.87 years old participated in the study as healthy controls. At baseline, all participants underwent a short-term (5 min) and a long-term (24 h ambulatory) ECG monitoring to evaluate the heart rate variability (HRV) indices and a maximal arm ergometric and dynamometric testing of the upper limbs. Moreover, the acute cardiac autonomic responses to maximal arm cycle exercise test were evaluated by Polar S810i sensor chest strap. At the end of the 6-month study, all parameters were revaluated only in groups A and B. At baseline, there was no statistically significant difference between the two patient groups. However, intra-group changes at the end of the 6-month study regarding the 24-h HRV monitoring indicated that group A statistically increased the standard deviation of R-R intervals (SDNN) by 13.9% (p = 0.007), the standard deviation of R-R intervals calculated every 5 min (SDANN) by 8.4% (p = 0.007), the very low frequency (VLF) by 7.1% (p = 0.042), and the low frequency [LF (ms2)] by 10.5% (p = 0.009), which almost reached the levels of group C. Favorable improvements were also noticed at the end of the study for group A in maximal exercise time of the upper limbs by 80.4% (p < 0.001) and maximal strength of the right hand by 27.8% (p < 0.001). Linear regression analysis after training showed that maximal exercise time was positively correlated with SDNN (r = 0.663, p = 0.036) and with LF (ms2) (r = 0.623, p = 0.045). Our results indicate that a 6-month table tennis training program is efficient and can improve cardiac ANS activity mainly by increasing sympathovagal balance.

Valsalva maneuver pressure recovery time is prolonged following spinal cord injury with correlations to autonomically-influenced secondary complications

PURPOSE

This work's purpose was to quantify rapid sympathetic activation in individuals with spinal cord injury (SCI), and to identify associated correlations with symptoms of orthostatic hypotension and common autonomically mediated secondary medical complications.

METHODS

This work was a cross-sectional study of individuals with SCI and uninjured individuals. Symptoms of orthostatic hypotension were recorded using the Composite Autonomic Symptom Score (COMPASS)-31 and Autonomic Dysfunction following SCI (ADFSCI) survey. Histories of secondary complications of SCI were gathered. Rapid sympathetic activation was assessed using pressure recovery time of Valsalva maneuver. Stepwise multiple linear regression models identified contributions to secondary medical complication burden.

RESULTS

In total, 48 individuals (24 with SCI, 24 uninjured) underwent testing, with symptoms of orthostatic hypotension higher in those with SCI (COMPASS-31, 3.3 versus 0.6, p < 0.01; ADFSCI, 21.2 versus. 3.2, p < 0.01). Pressure recovery time was prolonged after SCI (7.0 s versus. 1.7 s, p < 0.01), though poorly correlated with orthostatic symptom severity. Neurological level of injury after SCI influenced pressure recovery time, with higher injury levels associated with more prolonged time. Stepwise multiple linear regression models identified pressure recovery time as the primary explanation for variance in number of urinary tract infections (34%), histories of hospitalizations (12%), and cumulative secondary medical complication burden (24%). In all conditions except time for bowel program, pressure recovery time outperformed current clinical tools for assessing such risk.

CONCLUSIONS

SCI is associated with impaired rapid sympathetic activation, demonstrated here by prolonged pressure recovery time. Prolonged pressure recovery time after SCI predicts higher risk for autonomically mediated secondary complications, serving as a viable index for more "autonomically complete" injury.

Autonomic impairment is not explained by neurological level of injury or motor-sensory completeness

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

Determine how well common clinical assessments of level and completeness of injury are correlated with symptoms of autonomic blood pressure instability and secondary medical complications after spinal cord injury (SCI).

SETTING

Academic medical center, United States.

METHODS

Eighty-two individuals with (n = 48) and without (n = 34) SCI had symptoms of autonomic blood pressure instability quantified with the Autonomic Dysfunction Following SCI (ADFSCI) survey. Health histories quantified the secondary medical complications through number of urinary tract infections and hospitalizations in the past year, time to complete bowel program, and lifetime pressure injuries. Regression models were completed to identify strengths of associated correlations.

RESULTS

ADFSCI scores were significantly higher in individuals with SCI than controls. Neurological level of injury and ASIA impairment scale were both minimally correlated to symptoms of autonomic blood pressure instability, accounting for only 11.5% of variability in regression models. Secondary medical complications had similar, minimal correlations to level and motor/sensory completeness of SCI (R2 = 0.07 and R2 = 0.03 respectively). Contrasting this, symptoms of blood pressure instability on ADFSCI far outperformed the common clinical motor/sensory bedside exam, with moderately strong correlations to the ranked number of secondary medical complications after SCI (R2 = 0.31).

CONCLUSION

Neurological level of injury and motor/sensory completeness provided limited insights into which individuals with SCI would have blood pressure instability or secondary medical complications. Interestingly, symptoms of blood pressure instability outperform the clinical motor/sensory bedside exam, with higher correlations to secondary medical complications after SCI.

Delayed cerebrovascular reactivity in individuals with spinal cord injury in the right inferior parietal lobe: a breath-hold functional near-infrared spectroscopy study

Cerebrovascular reactivity (CVR) reflects the ability of blood vessels to dilate or constrict in response to a vasoactive stimulus, and allows researchers to assess the brain's vascular health. Individuals with spinal cord injury (SCI) are at an increased risk for autonomic dysfunction in addition to cognitive impairments, which have been linked to a decline in CVR; however, there is currently a lack of brain-imaging studies that investigate how CVR is altered after SCI. In this study, we used a breath-holding hypercapnic stimulus and functional near-infrared spectroscopy (fNIRS) to investigate CVR alterations in individuals with SCI (n = 20, 14M, 6F, mean age = 46.3 ± 10.2 years) as compared to age- and sex-matched able-bodied (AB) controls (n = 25, 19M, 6F, mean age = 43.2 ± 12.28 years). CVR was evaluated by its amplitude and delay components separately by using principal component analysis and cross-correlation analysis, respectively. We observed significantly delayed CVR in the right inferior parietal lobe in individuals with SCI compared to AB controls (linear mixed-effects model, fixed-effects estimate = 6.565, Satterthwaite's t-test, t = 2.663, p = 0.008), while the amplitude of CVR was not significantly different. The average CVR delay in the SCI group in the right inferior parietal lobe was 14.21 s (sd: 6.60 s), and for the AB group, the average delay in the right inferior parietal lobe was 7.08 s (sd: 7.39 s). CVR delays were also associated with the duration since injury in individuals with SCI, in which a longer duration since injury was associated with a shortened delay in CVR in the right inferior parietal region (Pearson's r-correlation, r = -0.59, p = 0.04). This study shows that fNIRS can be used to quantify changes in CVR in individuals with SCI, and may be further used in rehabilitative settings to monitor the cerebrovascular health of individuals with SCI.

The Clinical Relevance of Autonomic Dysfunction, Cerebral Hemodynamics, and Sleep Interactions in Individuals Living With SCI

A myriad of physiological impairments is seen in individuals after a spinal cord injury (SCI). These include altered autonomic function, cerebral hemodynamics, and sleep. These physiological systems are interconnected and likely insidiously interact leading to secondary complications. These impairments negatively influence quality of life. A comprehensive review of these systems, and their interplay, may improve clinical treatment and the rehabilitation plan of individuals living with SCI. Thus, these physiological measures should receive more clinical consideration. This special communication introduces the under investigated autonomic dysfunction, cerebral hemodynamics, and sleep disorders in people with SCI to stakeholders involved in SCI rehabilitation. We also discuss the linkage between autonomic dysfunction, cerebral hemodynamics, and sleep disorders and some secondary outcomes are discussed. Recent evidence is synthesized to make clinical recommendations on the assessment and potential management of important autonomic, cerebral hemodynamics, and sleep-related dysfunction in people with SCI. Finally, a few recommendations for clinicians and researchers are provided.

Construct validity of the international standards to document remaining autonomic function after spinal cord injury (ISAFSCI) (1st edition)

STUDY DESIGN

Observational study.

OBJECTIVES

To assess the construct validity of the International Standards to Document Remaining Autonomic Function after Spinal Cord Injury (ISAFSCI) (2012 1st Edition).

SETTING

Two Canadian spinal cord injury (SCI) centers.

METHODS

Data were collected between 2011-2014. Assessments included the ISAFSCI, standardized measures of autonomic function and a clinical examination. Construct validity of ISAFSCI was assessed by testing a priori hypotheses on expected ISAFSCI responses to standard measures (convergent hypotheses) and clinical variables (clinical hypotheses).

RESULTS

Forty-nine participants with an average age of 45 ± 12 years were included, of which 42 (85.7%) were males, 37 (77.6%) had a neurological level of injury at or above T6, and 23 (46.9%) were assessed as having motor and sensory complete SCI. For the six General Autonomic Function component hypotheses, two hypotheses (1 clinical, 1 convergent) related to autonomic control of blood pressure and one clinical hypothesis for temperature regulation were statistically significant. In terms of the Lower Urinary Tract, Bowel and Sexual Function component of the ISAFSCI, all the hypotheses (5 convergent, 3 clinical) were statistically significant except for the hypotheses on female sexual items (2 convergent, 2 clinical), likely due to small sample size.

CONCLUSION

The construct validity of ISAFSCI (2012 1st Edition) for the General Autonomic Function component was considered to be weak while it was much stronger for the Lower Urinary Tract, Bowel and Sexual Function component based on a priori hypotheses. These results can inform future psychometric studies of the ISAFSCI (2021 2nd Edition).

Differentiating essential hypertension from autonomic dysreflexia: a case report

INTRODUCTION

Autonomic dysreflexia (AD), a condition of critically raised blood pressure, is a severe complication of spinal cord injury. Primary (essential) hypertension may present with similar blood pressure levels to AD, though the causes, pathophysiology, presentation and treatment will differ.

CASE PRESENTATION

We report a case of a 74-year-old patient with a C1 spinal injury, who developed primary (essential) hypertension during her rehabilitation phase of care, requiring extensive investigations for autonomic dysreflexia. Despite this, no underlying cause was found; essential hypertension was subsequently confirmed with 24-hour ambulatory blood pressure monitoring. Treatment with an ACE inhibitor was introduced to good effect.

DISCUSSION

Essential hypertension can affect patients with spinal injury, even though most patients with higher level injuries (particularly cervical spinal cord injuries) are expected to have low resting baseline hypotension. Relevant features of this are presented within this case; a set of criteria to differentiate essential hypertension from autonomic dysreflexia are also proposed.

Systemic and Pulmonary Inflammation/Oxidative Damage: Implications of General and Respiratory Muscle Training in Chronic Spinal-Cord-Injured Patients

Chronic spinal cord injury affects several respiratory-function-related parameters, such as a decrease in respiratory volumes associated with weakness and a tendency to fibrosis of the perithoracic muscles, a predominance of vagal over sympathetic action inducing airway obstructions, and a difficulty in mobilizing secretions. Altogether, these changes result in both restrictive and obstructive patterns. Moreover, low pulmonary ventilation and reduced cardiovascular system functionality (low venous return and right stroke volume) will hinder adequate alveolar recruitment and low O₂ diffusion, leading to a drop in peak physical performance. In addition to the functional effects described above, systemic and localized effects on this organ chronically increase oxidative damage and tissue inflammation. This narrative review describes both the deleterious effects of chronic spinal cord injury on the functional effects of the respiratory system as well as the role of oxidative damage/inflammation in this clinical context. In addition, the evidence for the effect of general and respiratory muscular training on the skeletal muscle as a possible preventive and treatment strategy for both functional effects and underlying tissue mechanisms is summarized.

Characterization of heart rate changes associated with autonomic dysreflexia during penile vibrostimulation and urodynamics

STUDY DESIGN

Secondary data analysis.

OBJECTIVES

To characterize autonomic dysreflexia (AD) associated heart rate (HR) changes during penile vibrostimulation (PVS) and urodynamic studies (UDS).

SETTING

University-based laboratory.

METHODS

We analyzed blood pressure (BP) and HR data, recorded continuously, from 21 individuals (4 females; median age 41 years [lower and upper quartile, 37; 47]; median time post-injury 18 years [7; 27]; all motor-complete spinal cord injury (SCI) except one; cervical SCI = 15, thoracic [T1-T6] SCI = 6), who underwent PVS (11/21) or UDS (10/21).

RESULTS

Overall, 47 AD episodes were recorded (i.e. PVS = 37, UDS = 10), with at least one AD episode in each participant. At AD threshold, bradycardia was observed during PVS and UDS in 43% and 30%, respectively. At AD peak (i.e., maximum increase in systolic BP from baseline), bradycardia was observed during PVS and UDS in 65% and 50%, respectively. Tachycardia was detected at AD peak only once during UDS. Our study was limited by a small cohort of participants and the distribution of sex and injury characteristics.

CONCLUSIONS

Our findings reveal that AD-associated HR changes during PVS and UDS appear to be related to the magnitude of systolic BP increases. Highly elevated systolic BP associated with bradycardia suggests the presence of severe AD. Therefore, we recommend cardiovascular monitoring (preferably with continuous beat-to-beat recordings) during PVS and UDS to detect AD early. Stopping assessments before systolic BP reaches dangerously elevated levels, could reduce the risk of life-threatening complications in this cohort.

A Pilot Study of Intensive Locomotor-Related Skill Training and Transcranial Direct Current Stimulation in Chronic Spinal Cord Injury

BACKGROUND AND PURPOSE

Improved walking function is a priority among persons with motor-incomplete spinal cord injury (PwMISCI). Accessibility and cost limit long-term participation in locomotor training offered in specialized centers. Intensive motor training that facilitates neuroplastic mechanisms that support skill learning and can be implemented in the home/community may be advantageous for promoting long-term restoration of walking function. Additionally, increasing corticospinal drive via transcranial direct current stimulation (tDCS) may enhance training effects. In this pilot study, we investigated whether a moderate-intensity motor skill training (MST) circuit improved walking function in PwMISCI and whether augmenting training with tDCS influenced outcomes.

METHODS

Twenty-five adults (chronic, motor-incomplete spinal cord injury) were randomized to a 3-day intervention of a locomotor-related MST circuit and concurrent application of sham tDCS (MST+tDCS sham ) or active tDCS (MST+tDCS). The primary outcome was overground walking speed. Secondary outcomes included walking distance, cadence, stride length, and step symmetry index (SI).

RESULTS

Analyses revealed significant effects of the MST circuit on walking speed, walking distance, cadence, and bilateral stride length but no effect on interlimb SI. No significant between-groups differences were observed. Post hoc analyses revealed within-groups change in walking speed (ΔM = 0.13 m/s, SD = 0.13) that app-roached the minimally clinically important difference of 0.15 m/s.

DISCUSSION AND CONCLUSIONS

Brief, intensive MST involving locomotor-related activities significantly increased walking speed, walking distance, and spatiotemporal measures in PwMISCI. Significant additive effects of tDCS were not observed; however, participation in only 3 days of MST was associated with changes in walking speed that were comparable to longer locomotor training studies.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A386 ).

Rebuilding Body-Brain Interaction from the Vagal Network in Spinal Cord Injuries

Spinal cord injuries (SCIs) exert devastating effects on body awareness, leading to the disruption of the transmission of sensory and motor inputs. Researchers have attempted to improve perceived body awareness post-SCI by intervening at the multisensory level, with the integration of somatic sensory and motor signals. However, the contributions of interoceptive-visceral inputs, particularly the potential interaction of motor and interoceptive signals, remain largely unaddressed. The present perspective aims to shed light on the use of interoceptive signals as a significant resource for patients with SCI to experience a complete sense of body awareness. First, we describe interoceptive signals as a significant obstacle preventing such patients from experiencing body awareness. Second, we discuss the multi-level mechanisms associated with the homeostatic stability of the body, which creates a unified, coherent experience of one's self and one's body, including real-time updates. Body awareness can be enhanced by targeting the vagus nerve function by, for example, applying transcutaneous vagus nerve stimulation. This perspective offers a potentially useful insight for researchers and healthcare professionals, allowing them to be better equipped in SCI therapy. This will lead to improved sensory motor and interoceptive signals, a decreased likelihood of developing deafferentation pain, and the successful implementation of modern robotic technologies.

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

OBJECTIVE

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

STUDY DESIGN

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSIONS

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

Effects of early exercise training on the severity of autonomic dysreflexia following incomplete spinal cord injury in rodents

Hemodynamic instability and cardiovascular (CV) dysfunction are hallmarks of patients living with cervical and high thoracic spinal cord injuries (SCI). Individuals experience bouts of autonomic dysreflexia (AD) and persistent hypotension which hamper the activities of daily living. Despite the widespread use of exercise training to improve health and CV function after SCI, little is known about how different training modalities impact hemodynamic stability and severity of AD in a model of incomplete SCI. In this study, we used implantable telemetry devices to assess animals with T2 contusions following 3.5 weeks of exercise training initiated 8 days post-injury: passive hindlimb cycling (T2-CYC, n = 5) or active forelimb swimming (T2-SW, n = 6). Uninjured and non-exercised SCI control groups were also included (CON, n = 6; T2-CON, n = 7; T10-CON, n = 6). Five weeks post-injury, both T2-CON and T2-CYC presented with resting hypotension compared to uninjured CON and T10-CON groups; no differences were noted in resting blood pressure in T2-SW versus CON and T10-CON. Furthermore, pressor responses to colorectal distention (AD) were larger in all T2-injured groups compared to T10-CON, and were not attenuated by either form of exercise training. Interestingly, when T2-injured animals were re-stratified based on terminal BBB scores (regardless of training group), animals with limited hindlimb recovery (T2-LOW, n = 7) had more severe AD responses. Our results suggest that the spontaneous recovery of locomotor and autonomic function after severe but incomplete T2 SCI also influences the severity of AD, and that short periods (3.5 weeks) of passive hindlimb cycling or active forelimb swimming are ineffective in this model.

Carbohydrate Considerations for Athletes with a Spinal Cord Injury

The Paralympic movement is growing in popularity, resulting in increased numbers of athletes with a spinal cord injury (SCI) competing in various sport disciplines. Athletes with an SCI require specialized recommendations to promote health and to maximize performance, as evidenced by their metabolic and physiological adaptations. Nutrition is a key factor for optimal performance; however, scientifically supported nutritional recommendations are limited. This review summarizes the current knowledge regarding the importance of carbohydrates (CHO) for health and performance in athletes with an SCI. Factors possibly affecting CHO needs, such as muscle atrophy, reduced energy expenditure, and secondary complications are analyzed comprehensively. Furthermore, a model calculation for CHO requirements during an endurance event is provided. Along with assessing the effectiveness of CHO supplementation in the athletic population with SCI, the evaluation of their CHO intake from the available research supplies background to current practices. Finally, future directions are identified. In conclusion, the direct transfer of CHO guidelines from able-bodied (AB) athletes to athletes with an SCI does not seem to be reasonable. Based on the critical role of CHOs in exercise performance, establishing recommendations for athletes with an SCI should be the overall objective for prospective research.

Quantitative analysis of dysautonomia in patients with autonomic dysreflexia

Autonomic dysreflexia (AD) is a life-threatening condition for individuals with cervical or high-thoracic spinal cord injury (SCI). The profile of autonomic dysfunction in AD using validated clinical autonomic tests has not been described so far, although it could be useful to identify SCI patients at greater risk of developing AD non-invasively. With this objective, 37 SCI patients (27% female) were recruited, and hemodynamic and cardiac parameters were continuously monitored to determine the presence of AD, defined as an increase of systolic blood pressure of 20 mmHg or higher after bladder filling with saline. Then, standard autonomic function testing was performed, including Deep Breathing, Valsalva Manoeuvre and Tilt Table Test. Finally, baroreflex sensitivity (BRS), and spectral analysis of heart rate and blood pressure variability were measured at rest. Catecholamines and vasopressin levels were also measured at supine and upright positions. The severity of SCI was assessed through clinical and radiological examinations. AD was observed in 73.3% of SCI patients, being 63.6% of them asymptomatic during the dysreflexive episode. AD patients displayed a drop in sympathetic outflow, as determined by decreased noradrenalin plasma levels, reduced sympathovagal balance and increased BRS. In line with decreased sympathetic activity, the incidence of neurogenic orthostatic hypotension was higher in AD patients. Our results provide novel evidence regarding the autonomic dysfunction in SCI patients with AD compared to non-AD patients, posing non-invasively measured autonomic parameters as a powerful clinical tool to predict AD in SCI patients.

Cardiac, Autonomic, and Cardiometabolic Impact of Exercise Training in Spinal Cord Injury: A QUALITATIVE REVIEW

INTRODUCTION

Direct and indirect effects of spinal cord injury lead to important cardiovascular (CV) complications that are further increased by years of injury and the process of "accelerated aging." The present review examines the current evidence in the literature for the potential cardioprotective effect of exercise training in spinal cord injury.

REVIEW METHODS

PubMed and Web of Science databases were screened for original studies investigating the effect of exercise-based interventions on aerobic capacity, cardiac structure/function, autonomic function, CV function, and/or cardiometabolic markers. We compared the effects in individuals <40 yr with time since injury <10 yr with those in older individuals (≥40 yr) with longer time since injury (≥10 yr), reasoning that the two can be considered individuals with low versus high CV risk factors.

SUMMARY

Studies showed similar exercise effects in both groups (n = 31 in low CV risk factors vs n = 15 in high CV risk factors). The evidence does not support any effect of exercise training on autonomic function but does support an increased peripheral blood flow, improved left ventricular mass, higher peak cardiac output, greater lean body mass, better antioxidant capacity, and improved endothelial function. In addition, some evidence suggests that it can result in lower blood lipids, systemic inflammation (interleukin-6, tumor necrosis factor α, and C-reactive protein), and arterial stiffness. Training intensity, volume, and frequency were key factors determining CV gains. Future studies with larger sample sizes, well-matched groups of subjects, and randomized controlled designs will be needed to determine whether high-intensity hybrid forms of training result in greater CV gains.

Heart rate and blood pressure response improve the prediction of orthostatic cardiovascular dysregulation in persons with chronic spinal cord injury

Unstable blood pressure after spinal cord injury (SCI) is not routinely examined but rather predicted by level and completeness of injury (i.e., American Spinal Injury Association Impairment Scale AIS classification). Our aim was to investigate hemodynamic response to a sit-up test in a large cohort of individuals with chronic SCI to better understand cardiovascular function in this population. Continuous blood pressure and ECG were recorded from individuals with SCI (n = 159) and non-injured individuals (n = 48). We found orthostatic hypotension occurred within each level and AIS classification (n = 36). Moreover, 45 individuals with chronic SCI experienced a drop in blood pressure that did not meet the criteria for orthostatic hypotension, but was accompanied by dramatic increases in heart rate, reflecting orthostatic intolerance. A cluster analysis of hemodynamic response to a seated position identified eight distinct patterns of interaction between blood pressure and heart rate during orthostatic stress indicating varied autonomic responses. Algorithmic cluster analysis of heart rate and blood pressure is more sensitive to diagnosing orthostatic cardiovascular dysregulation. This indicates blood pressure instability cannot be predicted by level and completeness of SCI, and the consensus statement definition of orthostatic hypotension is insufficient to characterize the variability of blood pressure and heart rate responses during orthostatic stress. Both blood pressure and heart rate responses are needed to characterize autonomic function after SCI.

Modulation of left ventricular diastolic filling during exercise in persons with cervical motor incomplete spinal cord injury

PURPOSE

To characterize left ventricular diastolic function during an exertional challenge in adults with incomplete cervical spinal cord Injury (icSCI).

METHODS

In this cross-sectional study, a two-group convenience sample was used to compare left ventricular LV diastolic performance during a 5-10 W·min-1 incremental arm ergometer exercise protocol, using bioimpedance cardiography. Subjects were eight males with cervical incomplete spinal cord injury (icSCI; C5-C7: age 39 ± 14 years) versus eight able-bodied males (CON: age 38 ± 13 years). Left ventricular (LV) diastolic indices included end-diastolic volume (EDV) and early diastolic filling ratio (EDFR). LV ejection time (LVET), inotropic index (dZ/dT2) and stroke volume (SV) were compared between the groups at peak exercise, and maximum workload for the icSCI group (isomax).

RESULTS

EDV (at peak exercise:131.4 ± 7.3 vs 188.78 ± 9.4, p < 0.001; at isomax: 131.4 ± 7.3 vs 169 ± 23, p = 0.0009) and EDFR (at peak exercise 73 ± 14% vs 119 ± 11%, p = 0.006; at isomax 94 ± 10; p = 0.009) were significantly reduced in icSCI compared to CON, respectively. Significant differences in LVET (icSCI: 273 ± 48 vs CON: 305 ± 68; p = 0.1) and dZ/dT2 (icSCI: 0.64 ± 0.11 vs CON: 0.85 ± 0.31; p = 0.1) were not observed at isomax, despite a significant decrease in SV in the subjects with icSCI (77.1 ± 6.05 mL vs 105.8 ± 9.2 mL, p < 0.00) CONCLUSION: Left ventricular filling was impaired in the subjects with icSCI as evidenced at both peak exercise and isomax. It is likely that restrictions on the skeletal muscle pump mechanized the impairment but increased left ventricular wall stiffness could not be excluded as a mediator.

Development of Cardiometabolic Health indicators to advance the quality of spinal cord injury rehabilitation: SCI-High Project

Context: Spinal cord injury or disease (SCI/D) leads to unchanged low-density lipoprotein and cholesterol, very low high-density lipoprotein a form of dyslipidemia and physical inactivity which combine to increase risk of morbidity and mortality from cardiometabolic disease. Herein, we describe the selection of structure, process and outcome indicators for adults in the first 18 months post-SCI/D rehabilitation admission. Methods: A Pan-Canadian Cardiometabolic Health Working Group was formed to develop a construct definition. Cardiometabolic risk factors were summarized in a Driver diagram. Release of the Paralyzed Veterans of America "Identification and Management of Cardiometabolic Risk after Spinal Cord Injury" and the International Scientific Exercise Guidelines: "Evidence-based scientific exercise guidelines for adults with spinal cord injury", informed the group's focus on prevention strategies to advance this Domain of rehabilitation admission. Results: The structure indicator identifies during rehabilitation the presence of appropriate time and resources for physical exercise prescription. Process indicators are lipid profile assessment at rehabilitation admission and documented exercise prescriptions prior to discharge. The outcome indicators track patient's knowledge retention regarding exercise prescription at discharge, current exercise adherence and lipid status 18 months after rehabilitation discharge. Conclusion: Routine national implementation of these indicators at the specified time points will enhance efforts to detect dyslipidemia and assure routine participation in endurance exercise. These indicators align with international initiatives to improve cardiometabolic health through interventions targeting modifiable risk factors specifically endurance exercising and optimal lipid profiles, crucial to augmenting cardiometabolic health after SCI/D.

Temporal analysis of cardiovascular control and function following incomplete T3 and T10 spinal cord injury in rodents

Spinal cord injury (SCI) is a devastating condition that results in whole‐body dysfunction, notably cardiovascular (CV) disruption and disease. Injury‐induced destruction of autonomic pathways in conjunction with a progressive decline in physical fitness contribute to the poor CV status of SCI individuals. Despite the wide use of exercise training as a therapeutic option to reduce CV dysfunction, little is known about the acute hemodynamic responses to the exercise itself. We investigated CV responses to an exercise challenge (swimming) following both high and low thoracic contusion to determine if the CV system is able to respond appropriately to the challenge of swimming. Blood pressure (BP) telemetry and echocardiography were used to track the progression of dysfunction in rodents with T3 and T10 SCI (n = 8 each) for 10 weeks postcontusion. At 1 week postinjury, all animals displayed a drastic decline in heart rate (HR) during the exercise challenge, likely a consequence of neurogenic shock. Furthermore, over time, all groups developed a progressive inability to maintain BP within a narrow range during the exercise challenge despite displaying normal hemodynamic parameters at rest. Echocardiography of T10 animals revealed no persistent signs of cardiac dysfunction; T3 animals exhibited a transient decline in systolic function that returned to preinjury levels by 10 weeks postinjury. Novel evidence provided here illustrates that incomplete injuries produce hemodynamic instability that only becomes apparent during an exercise challenge. Further, this dysfunction lasts into the chronic phase of disease progression despite significant recovery of hindlimb locomotion and cardiac function.

Fatigability during volitional walking in incomplete spinal cord injury: cardiorespiratory and motor performance considerations

Fatigability describes the decline in force production (i.e., performance fatigability) and/or changes in sensations regulating performance (i.e., perceived fatigability) during whole-body activity and poses a major challenge to those living with spinal cord injuries (SCI). After SCI, the inability to overcome disruptions to metabolic homeostasis due to cardiorespiratory limitations and physical deconditioning may contribute to increased fatigability severity. The increased susceptibility to fatigability may have implications for motor control strategies and motor learning. Locomotor training approaches designed to reduce fatigability and enhance aerobic capacity in combination with motor learning may be advantageous for promoting functional recovery after SCI. Future research is required to advance the understanding of the relationship between fatigability, cardiorespiratory function and motor performance following SCI.

Prediction of autonomic dysreflexia during urodynamics: a prospective cohort study

BACKGROUND

Autonomic dysreflexia is a severe and potentially life-threatening condition in patients with spinal cord injury, as it can lead to myocardial ischemia, brain hemorrhage, or even death. Urodynamic investigation is the gold standard to assess neurogenic lower urinary tract dysfunction due to spinal cord injury and reveal crucial pathological findings, such as neurogenic detrusor overactivity. However, neurogenic detrusor overactivity and urodynamic investigation are known to be leading triggers of autonomic dysreflexia. Therefore, we aimed to determine predictors of autonomic dysreflexia in individuals with spinal cord injury during urodynamic investigation.

METHODS

This prospective cohort study included 300 patients with spinal cord injuries and complete datasets of continuous non-invasive cardiovascular monitoring, recorded during same session repeat urodynamic investigation. We used logistic regression to reveal predictors of autonomic dysreflexia during urodynamic investigation.

RESULTS

We found that level of injury and presence of neurogenic detrusor overactivity were the only two independent significant predictors for autonomic dysreflexia during urodynamic investigation. A lesion at spinal segment T6 or above (odds ratio (OR) 5.5, 95% CI 3.2-9.4) compared to one at T7 or below, and presence of neurogenic detrusor overactivity (OR 2.7, 95% confidence interval (CI) 1.4-4.9) were associated with a significant increased odds of autonomic dysreflexia during urodynamic investigation. Both odds persisted after adjustment for age, sex, and completeness and stage of injury (adjusted OR (AOR) 6.6, 95% CI 3.8-11.7, and AOR 2.2, 95% CI 1.1-4.5, respectively). Further stratification by lesion level showed level-dependent significantly increased adjusted odds of autonomic dysreflexia, i.e., from C1-C4 (AOR 16.2, 95% CI 5.9-57.9) to T4-T6 (AOR 2.6, 95% CI 1.3-5.2), compared to lesions at T7 or below.

CONCLUSIONS

In patients with neurogenic lower urinary tract dysfunction due to spinal cord injury, autonomic dysreflexia is independently predicted by lesion level and presence of neurogenic detrusor overactivity. Considering the health risks associated with autonomic dysreflexia, such as seizures, stroke, retinal bleeding, or even death, we recommend both continuous cardiovascular monitoring during urodynamic investigation in all spinal cord-injured patients with emphasis on those with cervical lesions, and appropriate neurogenic detrusor overactivity treatment to reduce the probability of potentially life-threatening complications.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01293110 .

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.

Soluble TNFα Signaling within the Spinal Cord Contributes to the Development of Autonomic Dysreflexia and Ensuing Vascular and Immune Dysfunction after Spinal Cord Injury

Cardiovascular disease and susceptibility to infection are leading causes of morbidity and mortality for individuals with spinal cord injury (SCI). A major contributor to these is autonomic dysreflexia (AD), an amplified reaction of the autonomic nervous system (hallmarked by severe hypertension) in response to sensory stimuli below the injury. Maladaptive plasticity of the spinal sympathetic reflex circuit below the SCI results in AD intensification over time. Mechanisms underlying this maladaptive plasticity are poorly understood, restricting the identification of treatments. Thus, no preventative treatments are currently available. Neuroinflammation has been implicated in other pathologies associated with hyperexcitable neural circuits. Specifically, the soluble form of TNFα (sTNFα) is known to play a role in neuroplasticity. We hypothesize that persistent expression of sTNFα in spinal cord underlies AD exacerbation. To test this, we intrathecally administered XPro1595, a biologic that renders sTNFα nonfunctional, after complete, high-level SCI in female rats. This dramatically attenuated the intensification of colorectal distension-induced and naturally occurring AD events. This improvement is mediated via decreased sprouting of nociceptive primary afferents and activation of the spinal sympathetic reflex circuit. We also examined peripheral vascular function using ex vivo pressurized arterial preparations and immune function via flow cytometric analysis of splenocytes. Diminishing AD via pharmacological inhibition of sTNFα mitigated ensuing vascular hypersensitivity and immune dysfunction. This is the first demonstration that neuroinflammation-induced sTNFα is critical for altering the spinal sympathetic reflex circuit, elucidating a novel mechanism for AD. Importantly, we identify the first potential pharmacological, prophylactic treatment for this life-threatening syndrome.SIGNIFICANCE STATEMENT Autonomic dysreflexia (AD), a disorder that develops after spinal cord injury (SCI) and is hallmarked by sudden, extreme hypertension, contributes to cardiovascular disease and susceptibility to infection, respectively, two leading causes of mortality and morbidity in SCI patients. We demonstrate that neuroinflammation-induced expression of soluble TNFα plays a critical role in AD, elucidating a novel underlying mechanism. We found that intrathecal administration after SCI of a biologic that inhibits soluble TNFα signaling dramatically attenuates AD and significantly reduces AD-associated peripheral vascular and immune dysfunction. We identified mechanisms behind diminished plasticity of neuronal populations within the spinal sympathetic reflex circuit. This study is the first to pinpoint a potential pharmacological, prophylactic strategy to attenuate AD and ensuing cardiovascular and immune dysfunction.

Assessing Heart Rate Variability As a Surrogate Measure of Cardiac Autonomic Function in Chronic Traumatic Spinal Cord Injury

Background: Although cardiac autonomic dysfunction is a contributing factor for cardiovascular disease development in individuals with a spinal cord injury (SCI), it remains poorly understood. Heart rate variability (HRV) analysis has the potential to non-invasively assess the cardiac autonomic nervous system. The study objectives are (a) to determine if there are differences in HRV measures across neurological level of impairment (NLI) and American Spinal Cord Injury Association Impairment Scale (AIS) subgroups, and (b) to determine if there is a relationship between HRV frequency measures (low frequency [LF] and high frequency [HF]) at rest. Methods: We conducted a secondary data analysis of a primary data set from a published cross-sectional study of electrocardiogram recordings of 56 subjects (44 men and 12 women, mean age ± SD = 46.75 ± 12.44 years) with a chronic traumatic SCI (C1-T12, AIS A-D, ≥2 years post injury). HRV was analyzed using time and frequency domain measures. Results: There were no significant HRV differences across NLI and AIS subgroups. The LF and HF indices were positively correlated in the entire sample (r = 0.708, p < .0001) and among impairment subgroups. Conclusion: No differences were observed in the HRV time and frequency measures when compared across NLI and AIS subgroups. The results were considered inconclusive, since possible explanations include inadequate sample size as well as other physiological considerations. A positive correlation was found between LF and HF when assessed at rest. The relationship between LF and HF may not necessarily represent a rebalanced autonomic nervous system, but it does question the utility of solely measuring LF:HF at rest in persons with chronic SCI.

Effects of Spinal Cord Injury in Heart Rate Variability After Acute and Chronic Exercise: A Systematic Review

Background: Spinal cord injury (SCI) above T6 is followed by a loss of sympathetic supraspinal control of the heart, disturbing the autonomic balance and increasing cardiovascular risk. Heart rate variability (HRV) is a widely used tool for assessing the cardiac autonomic nervous system and positive adaptations after regular exercise in able-bodied subjects. However, adaptations in SCI subjects are not well known. Objectives: To compare HRV between able-bodied and SCI subjects and analyze the effects of chronic and acute exercise on HRV in the SCI group. Methods: We searched MEDLINE, Embase, Web of Science, SciELO, and Google Scholar databases to July 2016. We selected English and Spanish observational or experimental studies reporting HRV after training or acute exercise in SCI patients. We also included studies comparing HRV in SCI individuals with able-bodied subjects. Animal studies and nontraumatic SCI studies were excluded. We screened 279 articles by title and abstract; of these, we fully reviewed 29 articles. Eighteen articles fulfilled criteria for inclusion in this study. Results: SCI individuals showed lower HRV values in the low frequency band compared to able-bodied subjects. Regular exercise improved HRV in SCI subjects, however time and intensity data were lacking. HRV decreases after an acute bout of exercise on SCI subjects, but recovery kinetics are unknown. Conclusion: HRV is affected following SCI. Able-bodied subjects and SCI individuals have different values of HRV. Acute bouts of exercise change HRV temporarily, and chronic exercise might improve autonomic balance in SCI.

Fatigability, oxygen uptake kinetics and muscle deoxygenation in incomplete spinal cord injury during treadmill walking

PURPOSE

The purpose of the present study was to characterize hypothesized relationships among fatigability and cardiorespiratory fitness in individuals with chronic motor-incomplete SCI (iSCI) during treadmill walking. The theoretical framework was that exacerbated fatigability would occur concomitantly with diminished cardiorespiratory fitness in people with iSCI.

METHODS

Subjects with iSCI (n = 8) and an able-bodied reference group (REF) (n = 8) completed a 6-min walking bout followed by a walking bout of 30-min or until volitional exhaustion, both at a self-selected walking speed. Fatigability was assessed using both perceived fatigability and performance fatigability measures. Pulmonary oxygen uptake kinetics (VO₂ on-kinetics) was measured breath-by-breath and changes in deoxygenated hemoglobin/myoglobin concentration (∆[HHb]) of the lateral gastrocnemius was measured by near-infrared spectroscopy. Adjustment of VO₂ and ∆[HHb] on-kinetics were modeled using a mono-exponential equation.

RESULTS

Perceived fatigability and performance fatigability were 52% and 44% greater in the iSCI group compared to the REF group (p = 0.003 and p = 0.004). Phase II time constant (τp) of VO₂ on-kinetics and ∆[HHb] ½ time during resting arterial occlusion were 55.4% and 16.3% slower in iSCI vs REF (p < 0.01 and p = 0.047, respectively).

CONCLUSIONS

The results of the present study may suggest that compromised O₂ delivery and/or utilization may have contributed to the severity of fatigability in these individuals with iSCI. The understanding of the extent to which fatigability and VO₂ and Δ[HHb] on-kinetics impacts locomotion after iSCI will assist in the future development of targeted interventions to enhance function.

Multi-Domain Assessment of Autonomic Function in Spinal Cord Injury Using a Modified Autonomic Reflex Screen

The aim of this study was to characterize autonomic lesions in participants with spinal cord injury (SCI; n = 10) using an autonomic reflex screen, incorporating sudomotor, cardiovagal, and sympathetic adrenergic tests, as well as hemodynamic responses to head-up tilt (HUT). Hemodynamic responses were compared to healthy controls (n = 20) and previously published normative cutoffs in order better identify autonomic impairments. Sympathetic skin responses (SSRs), heart rate response to deep breathing (HR_DB), and heart rate and beat-to-beat blood pressure responses to Valsalva maneuver (VM) and HUT were measured. SCI participants demonstrated impairment in at least one domain, with 7 of 10 demonstrating autonomic impairment across all domains. No single test was concordant with orthostatic hypotension on HUT, in all participants. Measures of cardiovagal function, including HR_DB (SCI = 7.7 ± 3.8 beats/min vs. controls = 17.6 ± 8.1 beats/min) and Valsalva ratio (SCI = 1.53 ± 0.29 vs. controls = 1.85 ± 0.37), were significantly reduced in SCI participants, compared to controls (p < 0.05). These findings suggest that an autonomic reflex screen, which includes standardized testing protocol and normative data for comparison, is useful for determining the autonomic domains affected by the neurological injury in SCI. We also demonstrated significant cardiovagal impairment in SCI participants compared to controls, which warrants further investigation to determine whether cardiovagal dysfunction is associated with the negative cardiovascular outcomes, which are known to occur in SCI.

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

INTRODUCTION

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

CASE PRESENTATION

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

DISCUSSION

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

The effect of pressure and shear on tissue viability of human skin in relation to the development of pressure ulcers: a systematic review

Pressure ulcers are a significant problem in health care, due to high costs and large impact on patients' life. In general, pressure ulcers develop as tissue viability decreases due to prolonged mechanical loading. The relation between load and tissue viability is highly influenced by individual characteristics. It is proposed that measurements of skin blood flow regulation could provide good assessment of the risk for pressure ulcer development, as skin blood flow is essential for tissue viability. . Therefore, the aim of this systematic review is to gain insight in the relation between mechanical load and the response of the skin and underlying tissue to this loading measured in-vivo with non-invasive techniques. A systematic literature search was performed to identify articles analysing the relation between mechanical load (pressure and/or shear) and tissue viability measured in-vivo. Two independent reviewers scored the methodological quality of the 22 included studies. Methodological information as well as tissue viability parameters during load application and after load removal were extracted from the included articles and used in a meta-analysis. Pressure results in a decrease in skin blood flow parameters, compared to baseline; showing a larger decrease with higher magnitudes of load. The steepness of the decrease is mostly dependent on the anatomical location. After load removal the magnitude of the post-reactive hyperaemic peak is related to the magnitude of pressure. Lastly, shear in addition to pressure, shows an additional negative effect, but the effect is less apparent than pressure on skin viability.

Alterations in autonomic cerebrovascular control after spinal cord injury

Among chronic cardiovascular and metabolic sequelae of spinal cord injury (SCI) is an up-to four-fold increase in the risk of ischemic and hemorrhagic stroke, suggesting that individuals with SCI cannot maintain stable cerebral perfusion. In able-bodied individuals, the cerebral vasculature is able to regulate cerebral perfusion in response to swings in arterial pressure (cerebral autoregulation), blood gases (cerebral vasoreactivity), and neural metabolic demand (neurovascular coupling). This ability depends, at least partly, on intact autonomic function, but high thoracic and cervical spinal cord injuries result in disruption of sympathetic and parasympathetic cerebrovascular control. In addition, alterations in autonomic and/or vascular function secondary to paralysis and physical inactivity can impact cerebrovascular function independent of the disruption of autonomic control due to injury. Thus, it is conceivable that SCI results in cerebrovascular dysfunction that may underlie an elevated risk of stroke in this population, and that rehabilitation strategies targeting this dysfunction may alleviate the long-term risk of adverse cerebrovascular events. However, despite this potential direct link between SCI and the risk of stroke, studies exploring this relationship are surprisingly scarce, and the few available studies provide equivocal results. The focus of this review is to provide an integrated overview of the available data on alterations in cerebral vascular function after SCI in humans, and to provide suggestions for future research.

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.

Presentation of neurogenic shock within the emergency department

BACKGROUND

Injury to the spinal cord can result in loss of sympathetic innervation causing a drop in BP and HR, this condition is known as neurogenic shock. There is debate among the literature on how and when neurogenic shock presents and what values of HR and BP should be used to define it. Previous studies do not take into account multiple prehospital and emergency department recordings.

OBJECTIVE

To improve understanding of how neurogenic shock presents in humans, allowing better identification and treatment.

METHODS

The Trauma Audit and Research Network database for an adult major trauma centre was used to isolate patients with a spinal cord injury. Qualifying patients had all available BPs and HRs collated into a database. Patients with neurogenic shock were isolated, allowing data analysis.

RESULTS

Out of 3069 trauma patients, 33 met the inclusion criteria, of which 15 experienced neurogenic shock. 87% of the patients who had neurogenic shock experienced it within 2 hours of injury. Neurogenic shock below the T6 level was less common (p=0.009); however, there were still four cases in the cohort. More patients with complete spinal cord injury had neurogenic shock (p=0.039).

CONCLUSIONS

Neurogenic shock is variable and unpredictable. It can present in the prehospital environment and without warning in a patient with previously normal vital signs. The medical team should be aware of it in all patients with spinal cord injury regardless of injury level.

Comparison of Autonomic Reactions during Urodynamic Examination in Patients with Spinal Cord Injuries and Able-Bodied Subjects

BACKGROUND/PURPOSE

This study compares heart rate variability (HRV) and systolic blood pressure (SBP) changes of spinal cord injury (SCI) patients during urodynamic study (UDS) with able-bodied controls.

METHODS

Twenty four complete suprasacral SCI patients (12 tetraplegia and 12 paraplegia) and 12 age-matched able-bodied volunteers received BP and HRV evaluation throughout urodynamic examination. We chose seven time points during the examinations: resting, Foley catheter insertion, start of infusion, and infused volume reaching 1/4, 2/4, 3/4 and 4/4 of maximal capacity. At each time point, electrocardiogram with a duration of 5 min was used for power spectral density analysis of HRV.

RESULTS

Only control subjects displayed significant elevation of SBP during Foley catheter insertion compared to resting values. Both control and tetraplegic groups experienced significant elevation of SBP at maximal bladder capacity compared to resting values. Tetraplegic values were also significantly greater than the other two groups. Control subjects displayed significant elevation of low frequency/high frequency (LF/HF) ratios during Foley catheter insertion and when approaching maximum bladder capacity. These findings were not seen in the paraplegic and tetraplegic groups. However, subgroup analysis of tetraplegic subjects with SBP elevation >50 mmHg demonstrated a similar LF/HF response to the able-bodied controls.

CONCLUSION

Tetraplegic patients experienced BP elevation but did not experience significant changes in HRV during bladder distension. This finding may imply that different neurological pathways contribute to AD reaction and HRV changes during bladder distension. However, profound AD during UDS in tetraplegic patients was associated with corresponding changes in HRV. Whether HRV monitoring would be beneficial in SCI patients presenting with significant AD, it needs further studies to elucidate.

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.

Exercise and sports science Australia (ESSA) position statement on exercise and spinal cord injury

Traumatic spinal cord injury (SCI) may result in tetraplegia (motor and/or sensory nervous system impairment of the arms, trunk and legs) or paraplegia (motor and/or sensory impairment of the trunk and/or legs only). The adverse effects of SCI on health, fitness and functioning are frequently compounded by profoundly sedentary behaviour. People with paraplegia (PP) and tetraplegia (TP) have reduced exercise capacity due to paralysis/paresis and reduced exercising stroke volume. TP often further reduces exercise capacity due to lower maximum heart-rate and respiratory function. There is strong, consistent evidence that exercise can improve cardiorespiratory fitness and muscular strength in people with SCI. There is emerging evidence for a range of other exercise benefits, including reduced risk of cardio-metabolic disease, depression and shoulder pain, as well as improved respiratory function, quality-of-life and functional independence. Exercise recommendations for people with SCI are: ≥30min of moderate aerobic exercise on ≥5d/week or ≥20min of vigorous aerobic ≥3d/week; strength training on ≥2d/week, including scapula stabilisers and posterior shoulder girdle; and ≥2d/week flexibility training, including shoulder internal and external rotators. These recommendations may be aspirational for profoundly inactive clients and stratification into "beginning", "intermediate" and "advanced" will assist application of the recommendations in clinical practice. Flexibility exercise is recommended to preserve upper limb function but may not prevent contracture. For people with TP, Rating of Perceived Exertion may provide a more valid indication of exercise intensity than heart rate. The safety and effectiveness of exercise interventions can be enhanced by initial screening for autonomic dysreflexia, orthostatic hypotension, exercise-induced hypotension, thermoregulatory dysfunction, pressure sores, spasticity and pain.

Contemporary Cardiovascular Concerns after Spinal Cord Injury: Mechanisms, Maladaptations, and Management

Cardiovascular (CV) issues after spinal cord injury (SCI) are of paramount importance considering they are the leading cause of death in this population. Disruption of autonomic pathways leads to a highly unstable CV system, with impaired blood pressure (BP) and heart rate regulation. In addition to low resting BP, on a daily basis the majority of those with SCI suffer from transient episodes of aberrantly low and high BP (termed orthostatic hypotension and autonomic dysreflexia, respectively). In fact, autonomic issues, including resolution of autonomic dysreflexia, are frequently ranked by individuals with high-level SCI to be of greater priority than walking again. Owing to a combination of these autonomic disturbances and a myriad of lifestyle factors, the pernicious process of CV disease is accelerated post-SCI. Unfortunately, these secondary consequences of SCI are only beginning to receive appropriate clinical attention. Immediately after high-level SCI, major CV abnormalities present in the form of neurogenic shock. After subsiding, new issues related to BP instability arise, including orthostatic hypotension and autonomic dysreflexia. This review describes autonomic control over the CV system before injury and the mechanisms underlying CV abnormalities post-SCI, while also detailing the end-organ consequences, including those of the heart, as well as the systemic and cerebral vasculature. The tertiary impact of CV dysfunction will also be discussed, such as the potential impediment of rehabilitation, and impaired cognitive function. In the recent past, our understanding of autonomic dysfunctions post-SCI has been greatly enhanced; however, it is vital to further develop our understanding of the long-term consequences of these conditions, which will equip us to better manage CV disease morbidity and mortality in this population.

Using local scale exponent to characterize heart rate variability in response to postural changes in people with spinal cord injury

Heart rate variability (HRV) is a promising marker for evaluating the remaining autonomic function in people with spinal cord injury (SCI). HRV is commonly assessed by spectral analysis and detrended fluctuation analysis (DFA). This study aimed to investigate whether local scale exponent α(t) can reveal new features of HRV that cannot be reflected by spectral measures and DFA coefficients. We studied 12 participants with SCI and 15 healthy able-bodied controls. ECG signals were continually recorded during 10 min sitting and 10 min prone postures. α(t) was calculated for scales between 4 and 60 s. Because α(t) could be overestimated at small scales, we developed an approach for correcting α(t) based on previous studies. The simulation results on simulated monofractal time series with α between 0.5 and 1.3 showed that the proposed method can yield improved estimation of α(t). We applied the proposed method to raw RR interval series. The results showed that α(t) in healthy controls monotonically decreased with scale at scales between 4 and 12 s (0.083–0.25 Hz) in both the sitting and prone postures, whereas in participants with SCI, α(t) slowly decreased at almost all scales. The sharp decreasing trend in α(t) in controls suggests a more complex dynamics of HRV in controls. α(t) at scales between 4 (0.25 Hz) and around 7 s (0.143 Hz) was lower in subjects with SCI than in controls in the sitting posture; α(t) at a narrow range of scales around 12 s (0.083 Hz) was higher in participants with SCI than in controls in the prone posture. However, none of normalized low frequency (0.04–0.15 Hz) power, the ratio of low frequency power to high frequency (0.15–0.4 Hz) power and long-term (>11 beats) DFA coefficient showed significant difference between healthy controls and subjects with SCI in the prone posture. Our results suggest that α(t) can reveal more detailed information in comparison to spectral measures and the standard DFA parameters.

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.

Acute Cardiorespiratory and Metabolic Responses During Exoskeleton-Assisted Walking Overground Among Persons with Chronic Spinal Cord Injury

BACKGROUND

Lower extremity robotic exoskeleton technology is being developed with the promise of affording people with spinal cord injury (SCI) the opportunity to stand and walk. The mobility benefits of exoskeleton-assisted walking can be realized immediately, however the cardiorespiratory and metabolic benefits of this technology have not been thoroughly investigated.

OBJECTIVE

The purpose of this pilot study was to evaluate the acute cardiorespiratory and metabolic responses associated with exoskeleton-assisted walking overground and to determine the degree to which these responses change at differing walking speeds.

METHODS

Five subjects (4 male, 1 female) with chronic SCI (AIS A) volunteered for the study. Expired gases were collected during maximal graded exercise testing and two, 6-minute bouts of exoskeleton-assisted walking overground. Outcome measures included peak oxygen consumption (V̇O2peak), average oxygen consumption (V̇O2avg), peak heart rate (HRpeak), walking economy, metabolic equivalent of tasks for SCI (METssci), walk speed, and walk distance.

RESULTS

Significant differences were observed between walk-1 and walk-2 for walk speed, total walk distance, V̇O2avg, and METssci. Exoskeleton-assisted walking resulted in %V̇O2peak range of 51.5% to 63.2%. The metabolic cost of exoskeleton-assisted walking ranged from 3.5 to 4.3 METssci.

CONCLUSIONS

Persons with motor-complete SCI may be limited in their capacity to perform physical exercise to the extent needed to improve health and fitness. Based on preliminary data, cardiorespiratory and metabolic demands of exoskeleton-assisted walking are consistent with activities performed at a moderate intensity.

Neuroprotection, Plasticity Manipulation, and Regenerative Strategies to Improve Cardiovascular Function following Spinal Cord Injury

Damage to the central nervous system, as in the case of spinal cord injury (SCI), results in disrupted supraspinal sympathetic influence and subsequent cardiovascular control impairments. Consequently, people with SCI suffer from disordered basal hemodynamics and devastating fluctuations in blood pressure, as in the case of autonomic dysreflexia (AD), which likely contribute to this population's leading cause of mortality: cardiovascular disease. The development of AD is related, at least in part, to neuroanatomical changes that include disrupted descending supraspinal sympathetic control, changes in propriospinal circuitry, and inappropriate afferent sprouting in the dorsal horn. These anatomical mechanisms may thus be targeted by neural regenerative and protective therapies to improve cardiovascular control and reduce AD. Here, we discuss the relationship between abnormal cardiovascular control and its underlying neuroanatomy. We then review current studies investigating biochemical strategies to reduce the severity of AD through: 1) reducing aberrant calcitonin gene-related peptide immunoreactive afferent sprouting; 2) inhibiting inflammatory processes; and 3) re-establishing descending supraspinal sympathetic control. Finally, we discuss why additional biochemical agents and combinational approaches may be needed to completely ameliorate this condition.

Perioperative implications of the patient with autonomic dysfunction

PURPOSE OF REVIEW

The autonomic nervous system functions to control heart rate, blood pressure, respiratory rate, gastrointestinal motility, hormone release, and body temperature on a second-to-second basis. Here we summarize some of the latest literature on autonomic dysfunction, focusing primarily on the perioperative implications.

RECENT FINDINGS

The variety of autonomic dysfunction now extends to a large number of clinical conditions in which the cause or effect of the autonomic component is blurred. Methods for detecting dysautonomia can be as simple as performing a history and physical examination that includes orthostatic vital signs measured in both recumbent and vertical positions; however, specialized laboratories are required for definitive diagnosis. Heart rate variability monitoring is becoming more commonplace in the assessment and understanding of autonomic instability. Degenerative diseases of the autonomic nervous system include Parkinson's disease and multiple system atrophy, with the most serious manifestations being postural hypotension and paradoxical supine hypertension. Other conditions occur in which the autonomic dysfunction is only part of a larger disease process, such as diabetic autonomic neuropathy, traumatic brain injury, and spinal cord injury.

SUMMARY

Patients with dysautonomia often have unpredictable and paradoxical physiological responses to various perioperative stimuli. Knowledge of the underlying pathophysiology of their condition is required in order to reduce symptom exacerbation and limit morbidity and mortality during the perioperative period.

Sympathetic skin responses and autonomic dysfunction in spinal cord injury

Sympathetic skin responses (SSRs), a measure of sympathetic cholinergic sudomotor function, have been used in the assessment of autonomic dysfunction in patients with spinal cord injury (SCI). This review highlights the basic mechanisms underlying SSRs as well as their application to the SCI population. We address the utility of SSRs in assessing autonomic function, the relationship between autonomic and sensorimotor impairment, and the association between SSRs and the sequelae of autonomic dysfunction in SCI, particularly autonomic dysreflexia and orthostatic hypotension. Overall, SSRs are a rapid, convenient and non-invasive method illustrating that the severity of autonomic impairment can be independent from sensorimotor impairment. We suggest that SSRs be used in conjunction with other validated autonomic tests in order to predict or document autonomic dysfunction in SCI.