Increased Central Arterial Stiffness after Spinal Cord Injury: Contributing Factors, Implications, and Possible Interventions

Why do different people with Spinal Cord Injury have differing severity of symptoms with Autonomic Dysreflexia? Exploring relationships of vascular alpha-1 adrenoreceptor and baroreflex sensitivity after SCI

Introduction

Individuals with spinal cord injury (SCI) commonly have autonomic dysreflexia (AD) with increased sympathetic activity. After SCI, individuals have decreased baroreflex sensitivity and increased vascular responsiveness.

Objective

To evalate relationship between baroreflex and blood vessel sensitivity with autonomic dysreflexia symptoms.

Design

Case control.

Setting

Tertiary academic center.

Patients

14 individuals with SCI, 17 matched uninjured controls.

Interventions

All participants quantified AD symptoms using the Autonomic Dysfunction Following SCI (ADFSCI)-AD survey. Participants received three intravenous phenylephrine boluses, reproducibly increasing systolic blood pressure (SBP) 15-40 mmHg. Continuous heart rate (R-R interval, ECG), beat-to-beat blood pressures (finapres), and popliteal artery flow velocity were recorded. Vascular responsiveness (α1 adrenoreceptor sensitivity) and heart rate responsiveness to increased SBP (baroreflex sensitivity) were calculated.

Main outcome measures

Baroreflex sensitivity after increased SBP; Vascular responsiveness through quantified mean arterial pressure (MAP) 2-minute area under the curve and change in vascular resistance.

Results

SCI and control cohorts were well-matched with mean age 31.9 and 29.6 years (p=0.41), 21.4% and 17.6% female respectively. Baseline MAP (p=0.83) and R-R interval (p=0.39) were similar. ADFSCI-AD scores were higher following SCI (27.9+/-22.9 vs 4.2+/-2.9 in controls, p=0.002).To quantify SBP response, MAP area under the curve was normalized to dose/bodyweight. Individuals with SCI had significantly larger responses (0.26+/-0.19 mmHg*s/kg*ug) than controls (0.06+/-0.06 mmHg*s/kg*ug, p=0.002). Similarly, leg vascular resistance increased after SCI (24% vs 6% to a normalized dose, p=0.007). Baroreflex sensitivity was significantly lower after SCI (15.0+/-8.3 vs 23.7+/-9.3 ms/mmHg, p=0.01). ADFSCI-AD subscore had no meaningful correlation with vascular responsiveness (R2=0.008) or baroreflex sensitivity (R2=0.092) after SCI.

Conclusions

While this confirms smaller previous studies suggesting increased α1 adrenoreceptor sensitivity and lower baroreflex sensitivity in individuals with SCI, these differences lacked correlation to increased symptoms of AD. Further research into physiologic mechanisms to explain why some individuals with SCI develop symptoms is needed.

Altered heart rate variability and pulse-wave velocity after spinal cord injury

BACKGROUND

Heart rate variability (HRV) and pulse-wave velocity (PWV), indicators of cardiac function, are altered in patients with spinal cord injury (SCI), suggesting that autonomic cardiac function and arterial stiffness may underlie the high risk of cardiovascular complications in these patients. No study has simultaneously investigated HRV and PWV in the same patients.

AIM

To evaluate cardiovascular complications in SCI patients by comparing HRV and PWV between patients with and without SCI.

METHODS

In this cross-sectional pilot study, patients with (n = 60) and without SCI (n = 60) were recruited from December 7, 2019 to January 21, 2020. Each participant received a five-minute assessment of HRV and the cardiovascular system using the Medicore HRV Analyzer SA-3000P. Differences in HRV and PWV parameters between participants with and without SCI were statistically examined.

RESULTS

We observed a significant difference between participants with and without SCI with respect to the standard deviation of all normal-to-normal intervals, square root of the mean sum of squared successive risk ratio interval differences, physical stress index, total power, very-low frequency, low frequency, high frequency, and arterial elasticity.

CONCLUSION

Patients with SCI have weaker sympathetic and parasympathetic activity as well as lower arterial elasticity compared to those without, suggesting that SCI may increase cardiac function loading.

Spinal cord injury impairs cardiac function due to impaired bulbospinal sympathetic control

Spinal cord injury chronically alters cardiac structure and function and is associated with increased odds for cardiovascular disease. Here, we investigate the cardiac consequences of spinal cord injury on the acute-to-chronic continuum, and the contribution of altered bulbospinal sympathetic control to the decline in cardiac function following spinal cord injury. By combining experimental rat models of spinal cord injury with prospective clinical studies, we demonstrate that spinal cord injury causes a rapid and sustained reduction in left ventricular contractile function that precedes structural changes. In rodents, we experimentally demonstrate that this decline in left ventricular contractile function following spinal cord injury is underpinned by interrupted bulbospinal sympathetic control. In humans, we find that activation of the sympathetic circuitry below the level of spinal cord injury causes an immediate increase in systolic function. Our findings highlight the importance for early interventions to mitigate the cardiac functional decline following spinal cord injury.

By combining experimental models with prospective clinical studies, the authors show that spinal cord injury causes a rapid reduction in cardiac function that precedes structural changes, and that the loss of descending sympathetic control is the major cause of reduced cardiac function following spinal cord injury.

A systematic review of cardiovascular risk factors in patients with traumatic spinal cord injury

Objective: The main risk factors for cardiac events, and particularly for the development of atherosclerosis, are diabetes mellitus, arterial hypertension, dyslipidemia and smoking. Patients with a traumatic spinal cord injury (SCI) may present with autonomic nervous system dysfunction depending on their level of spinal cord injury. Studies have found a rise in cardiovascular mortality. A systematic review was conducted that focused on this patient group's predisposition to vascular risk. Methods: We performed a PubMed and Cochrane database search. After applying specific search criteria, 42 articles were included in our analysis out of a total of 10,784 matches. The articles were selected with the aim of establishing cardiovascular risk factors in patients with traumatic spinal cord injury. Results: Patients with SCI are at an increased risk for peripheral artery disease even in the absence of cardiovascular risk factors. Major vascular changes to the arteries of patients with SCI include: a reduction in lumen size, increased vessel wall tension, higher vascular stiffness, an impaired reactive hyperemic response, and a lack of reduced vascular resistance. The findings for carotid atherosclerosis were inconclusive. This group of patients also has a higher disposition for diabetes mellitus, lipid metabolism disorders and coronary artery disease. Paraplegics are more likely to suffer from dyslipidemia, obesity and PAD, while tetraplegics are more likely to have diabetes mellitus. Conclusions: Patients with SCI are more likely to have cardiovascular risk factors and have cardiovascular disease compared to the normal population. Peripheral circulatory disorders are particularly common. Patients with SCI are now considered to be a new risk group for cardiovascular disease; however, large epidemiological studies are needed to verify in more detail the cardiovascular risk profile of this patient group.

Exercise Improves Cardiorespiratory Fitness, but Not Arterial Health, after Spinal Cord Injury: The CHOICES Trial

Arterial stiffness, as measured by carotid-femoral pulse wave velocity (cfPWV), is elevated after spinal cord injury (SCI). In the uninjured population, exercise training has been shown to reduce arterial stiffness. In a randomized, multi-center clinical trial, we evaluated the impact of two exercise interventions on cardiovascular disease risk factors in persons with chronic SCI. A total of 46 adults with motor-complete SCI with neurological levels of injury between the fourth cervical and sixth thoracic spinal cord segments (C4-T6) were randomly assigned to either body-weight-supported treadmill training (BWSTT) or arm-cycle ergometer training (ACET). Participants trained 3 days per week for 24 weeks. Exercise session duration progressed gradually to reach 30 and 60 min for ACET and BWSTT, respectively. The primary outcome was arterial stiffness, assessed by cfPWV, and was measured at baseline, 12 weeks of training, and at 24 weeks. Secondary outcomes included cardiorespiratory fitness (CRF) and cardiometabolic health measures and were measured before and after completion of training. Fourteen participants per intervention arm completed the exercise intervention. Our results show no effect of either exercise intervention on arterial stiffness (p = 0.07) and cardiometabolic health measures (p > 0.36). However, peak oxygen uptake increased with ACET compared with BWSTT (p = 0.04). The findings of this trial demonstrate that although 24 weeks of upper-body exercise improved CRF in persons with motor-complete SCI ≥T6, neither intervention resulted in improvements in arterial stiffness or cardiometabolic health measures. ClinicalTrials.gov identifier: NCT01718977.

Selective neural stimulation methods improve cycling exercise performance after spinal cord injury: a case series

BACKGROUND

Exercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control. Existing electrical stimulation-driven cycling systems involve the paralyzed musculature but result in rapid force decline and muscle fatigue, limiting their effectiveness. This study explores the effects of selective stimulation patterns delivered through multi-contact nerve cuff electrodes on functional exercise output, with the goal of increasing work performed and power maintained within each bout of exercise.

METHODS

Three people with spinal cord injury and implanted stimulation systems performed cycling trials using conventional (S-Max), low overlap (S-Low), low duty cycle (C-Max), and/or combined low overlap and low duty cycle (C-Low) stimulation patterns. Outcome measures include total work (W), end power (Pend), power fluctuation indices (PFI), charge accumulation (Q), and efficiency (η). Mann-Whitney tests were used for statistical comparisons of W and Pend between a selective pattern and S-Max. Welch's ANOVAs were used to evaluate differences in PFIs among all patterns tested within a participant (n ≥ 90 per stimulation condition).

RESULTS

At least one selective pattern significantly (p < 0.05) increased W and Pend over S-Max in each participant. All selective patterns also reduced Q and increased η compared with S-Max for all participants. C-Max significantly (p < 0.01) increased PFI, indicating a decrease in ride smoothness with low duty cycle patterns.

CONCLUSIONS

Selective stimulation patterns can increase work performed and power sustained by paralyzed muscles prior to fatigue with increased stimulation efficiency. While still effective, low duty cycle patterns can cause inconsistent power outputs each pedal stroke, but this can be managed by utilizing optimized stimulation levels. Increasing work and sustained power each exercise session has the potential to ultimately improve the physiological benefits of stimulation-driven exercise.

Effect of Exercise on Cardiovascular Function Following Spinal Cord Injury: A REVIEW

Spinal cord injury (SCI) is associated with a reduced level of physical activity, deterioration of patient body composition, metabolic profile, quality of life, and psychological functioning. As a result, risk of cardiovascular disease (CVD) increases and CVD-related death occurs at an earlier age than in individuals without SCI. Regular participation in exercise has been shown to exert beneficial effects also in patients with SCI. In this review, we analyze and discuss the effects of regular exercise training in SCI on cardiovascular function, autonomic function of the cardiovascular system, arterial stiffness, metabolism, inflammation, and gene expression.

Increased pulse wave velocity in persons with spinal cord injury: the effect of the renin-angiotensin-aldosterone system

Increased pulse wave velocity (PWV), a marker of cardiovascular disease (CVD), has been reported in otherwise healthy individuals with spinal cord injury (SCI) compared with age-matched uninjured controls. Due to decentralized descending sympathetic vascular control, individuals with injuries above T6 are prone to orthostatic hypotension and, as a result, depend on the renin-angiotensin-aldosterone system (RAAS) to maintain orthostatic blood pressure (BP). The purpose of this study was to determine resting PWV, a noninvasive surrogate of central arterial stiffness, in individuals with cervical (C4-T1; n = 11) and thoracic (T6-T12; n = 11) SCI, compared with age-matched controls (controls; n = 11). Next, our aim was to describe group differences in BP, plasma norepinephrine (NE), and renin response to head-up tilt (HUT). Finally, we sought to determine the relationship between PWV and the orthostatic change in BP, NE, and the plasma renin during HUT among the groups. PWV was significantly increased in both cervical (8.81 ± 1.91 m/s) and thoracic (7.36 ± 1.58 m/s) SCI compared with the controls (5.53 ± 0.95 m/s; P < 0.05). The change from supine to 60° HUT in BP and NE was significantly reduced and change in plasma renin was significantly increased in the cervical group compared with the thoracic and control groups. Group affiliation and change in plasma renin were significant predictors of PWV (R² = 0.63, P = 0.001). These data suggest that dependency on the RAAS for orthostatic BP maintenance may be associated with increased PWV and risk of CVD in the SCI population.NEW & NOTEWORTHY Our novel findings suggest that increased arterial stiffness in individuals with SCI may be due to greater dependency on the RAAS to maintain hemodynamic stability during an orthostatic challenge. Asymptomatic orthostatic hypotension can occur in persons with SCI during transition from the supine to the seated position and during other upright activities of daily living; however, it is seldom addressed by clinicians.

[Possibilities of application of cardio-ankle vascular index in patients with cerebrovascular diseases]

This publication focuses on the feasibility of using the cardio-ankle vascular index (CAVI) in patients with cerebrovascular diseases. The authors consider the pathological conditions and risk factors of stroke associated with increased arterial stiffness, methods for its assessment, the advantages of using CAVI, the experience of using CAVI in patients with cardiovascular diseases, in particular, in neurological patients. The complexity of the application of CAVI in the Russian population, promising directions for determining the index in neurology as well as the importance of CAVI borderline indicators are shown. It is emphasized that stroke patients should be screened with a mandatory study of CAVI.

Surgical Neurostimulation for Spinal Cord Injury

Traumatic spinal cord injury (SCI) is a devastating neurological condition characterized by a constellation of symptoms including paralysis, paraesthesia, pain, cardiovascular, bladder, bowel and sexual dysfunction. Current treatment for SCI involves acute resuscitation, aggressive rehabilitation and symptomatic treatment for complications. Despite the progress in scientific understanding, regenerative therapies are lacking. In this review, we outline the current state and future potential of invasive and non-invasive neuromodulation strategies including deep brain stimulation (DBS), spinal cord stimulation (SCS), motor cortex stimulation (MCS), transcutaneous direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) in the context of SCI. We consider the ability of these therapies to address pain, sensorimotor symptoms and autonomic dysregulation associated with SCI. In addition to the potential to make important contributions to SCI treatment, neuromodulation has the added ability to contribute to our understanding of spinal cord neurobiology and the pathophysiology of SCI.