Regional neurovascular coupling and cognitive performance in those with low blood pressure secondary to high-level spinal cord injury: improved by alpha-1 agonist midodrine hydrochloride

Cerebrovascular Reactivity Following Spinal Cord Injury

Background

Spinal cord injuries (SCI) often result in cardiovascular issues, increasing the risk of stroke and cognitive deficits.

Objectives

This study assessed cerebrovascular reactivity (CVR) using functional magnetic resonance imaging (fMRI) during a hypercapnic challenge in SCI participants compared to noninjured controls.

Methods

Fourteen participants were analyzed (n = 8 with SCI [unless otherwise noted], median age = 44 years; n = 6 controls, median age = 33 years). CVR was calculated through fMRI signal changes.

Results

The results showed a longer CVR component (tau) in the grey matter of SCI participants (n = 7) compared to controls (median difference = 3.0 s; p < .05). Time since injury (TSI) correlated negatively with steady-state CVR in the grey matter and brainstem of SCI participants (RS = -0.81, p = .014; RS = -0.84, p = .009, respectively). Lower steady-state CVR in the brainstem of the SCI group (n = 7) correlated with lower diastolic blood pressure (RS = 0.76, p = .046). Higher frequency of hypotensive episodes (n = 7) was linked to lower CVR outcomes in the grey matter (RS = -0.86, p = .014) and brainstem (RS = -0.89, p = .007).

Conclusion

Preliminary findings suggest a difference in the dynamic CVR component, tau, between the SCI and noninjured control groups, potentially explaining the higher cerebrovascular health burden in SCI individuals. Exploratory associations indicate that longer TSI, lower diastolic blood pressure, and more hypotensive episodes may lead to poorer CVR outcomes. However, further research is necessary to establish causality and support these observations.

A multimodal meta-analysis of regional functional and structural brain abnormalities in obsessive-compulsive disorder

Numerous neuroimaging studies of resting-state functional imaging and voxel-based morphometry (VBM) have revealed abnormalities in specific brain regions in obsessive-compulsive disorder (OCD), but results have been inconsistent. We conducted a whole-brain voxel-wise meta-analysis on resting-state functional imaging and VBM studies that investigated differences of functional activity and gray matter volume (GMV) between patients with OCD and healthy controls (HCs) using seed-based d mapping (SDM) software. A total of 41 independent studies (51 datasets) for resting-state functional imaging and 42 studies (46 datasets) for VBM were included by a systematic literature search. Overall, patients with OCD displayed increased spontaneous functional activity in the bilateral inferior frontal gyrus (IFG) (extending to the bilateral insula) and bilateral medial prefrontal cortex/anterior cingulate cortex (mPFC/ACC), as well as decreased spontaneous functional activity in the bilateral paracentral lobule, bilateral cerebellum, left caudate nucleus, left inferior parietal gyri, and right precuneus cortex. For the VBM meta-analysis, patients with OCD displayed increased GMV in the bilateral thalamus (extending to the bilateral cerebellum), right striatum, and decreased GMV in the bilateral mPFC/ACC and left IFG (extending to the left insula). The conjunction analyses found that the bilateral mPFC/ACC, left IFG (extending to the left insula) showed decreased GMV with increased intrinsic function in OCD patients compared to HCs. This meta-analysis demonstrated that OCD exhibits abnormalities in both function and structure in the bilateral mPFC/ACC, insula, and IFG. A few regions exhibited only functional or only structural abnormalities in OCD, such as the default mode network, striatum, sensorimotor areas, and cerebellum. It may provide useful insights for understanding the underlying pathophysiology of OCD and developing more targeted and efficacious treatment and intervention strategies.

Comparable dynamic cerebral autoregulation and neurovascular coupling of the posterior cerebral artery between healthy men and women

AIMS

Most studies focus on dynamic cerebral autoregulation (dCA) in the middle cerebral artery (MCA), and few studies investigated neurovascular coupling (NVC) and dCA in the posterior cerebral artery (PCA). We investigated NVC and dCA of the PCA in healthy volunteers to identify sex differences.

METHODS

Thirty men and 30 age-matched women completed dCA and NCV assessments. The cerebral blood flow velocity (CBFV) and mean arterial pressure were evaluated using transcranial Doppler ultrasound and a servo-controlled plethysmograph, respectively. The dCA parameters were analyzed using transfer function analysis. The NCV was evaluated by eyes-open and eyes-closed (24 s each) periodically based on voice prompts. The eyes-open visual stimulation comprised silent reading of Beijing-related tourist information.

RESULTS

The PCA gain was lower than that of the MCA in all frequency ranges (all p < 0.05). Phase was consistent across the cerebrovascular territories. The cerebrovascular conductance index (CVCi) and mean CBFV (MV) of the PCA were significantly higher during the eyes-open than eyes-closed period (CVCi: 0.50 ± 0.12 vs. 0.38 ± 0.10; MV: 42.89 ± 8.49 vs. 32.98 ± 7.25, both p < 0.001). The PCA dCA and NVC were similar between the sexes.

CONCLUSION

We assessed two major mechanisms that maintain cerebral hemodynamic stability in healthy men and women. The visual stimulation-evoked CBFV of the PCA was significantly increased compared to that during rest, confirming the activation of NVC. Men and women have similar functions in PCA dCA and NCV.

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.

Autonomic Cardiovascular Control, Psychological Well-Being, and Cognitive Performance in People With Spinal Cord Injury

PURPOSE

To examine associations between parameters of psychological well-being, injury characteristics, cardiovascular autonomic nervous system (ANS) control, and cognitive performance in persons with spinal cord injury (SCI) compared with age-matched uninjured controls. This is an observational, cross-sectional study including a total of 94 participants (52 with SCI and 42 uninjured controls: UIC). Cardiovascular ANS responses were continuously monitored at rest and during administration of the Paced Auditory Serial Addition Test (PASAT). Self-report scores on the SCI-Quality of Life questionnaires are reported for depression, anxiety, fatigue, resilience, and positive affect. Participants with SCI performed significantly more poorly on the PASAT compared with the uninjured controls. Although not statistically significant, participants with SCI tended to report more psychological distress and less well-being than the uninjured controls. In addition, when compared with uninjured controls, the cardiovascular ANS responses to testing were significantly altered in participants with SCI; however, these responses to testing did not predict PASAT performance. Self-reported levels of anxiety were significantly related to PASAT score in the SCI group, but there was no significant relationship between PASAT and the other indices of SCI-Quality of Life. Future investigations should more closely examine the relationship among cardiovascular ANS impairments, psychological disorders, and cognitive dysfunction to better elucidate the underpinnings of these deficits and to guide interventions aimed at improving physiological, psychological, and cognitive health after SCI. Tetraplegia, paraplegia, blood pressure variability, cognitive, mood.

Massive body-brain disconnection consequent to spinal cord injuries drives profound changes in higher-order cognitive and emotional functions: A PRISMA scoping review

Spinal cord injury (SCI) leads to a massive disconnection between the brain and the body parts below the lesion level representing a unique opportunity to explore how the body influences a person's mental life. We performed a systematic scoping review of 59 studies on higher-order cognitive and emotional changes after SCI. The results suggest that fluid abilities (e.g. attention, executive functions) and emotional regulation (e.g. emotional reactivity and discrimination) are impaired in people with SCI, with progressive deterioration over time. Although not systematically explored, the factors that are directly (e.g. the severity and level of the lesion) and indirectly associated (e.g. blood pressure, sleeping disorders, medication) with the damage may play a role in these deficits. The inconsistency which was found in the results may derive from the various methods used and the heterogeneity of samples (i.e. the lesion completeness, the time interval since lesion onset). Future studies which are specifically controlled for methods, clinical and socio-cultural dimensions are needed to better understand the role of the body in cognition.

Impaired Dynamic Cerebral Autoregulation in Patients With Cerebral Venous Sinus Thrombosis: Evaluation Using Transcranial Doppler and Silent Reading Stimulation

OBJECTIVE

Cerebral venous sinus thrombosis (CVST) may impair dynamic cerebral autoregulation (dCA) of the middle cerebral artery (MCA). However, most studies have focused on dCA of the MCA; a few studies are based on the posterior cerebral artery (PCA) during silent reading and neurovascular coupling (NVC). This study explored the effects of CVST on dCA of the MCA and PCA during silent reading and NVC.

METHODS

From January 2021 to August 2022, 60 CVST patients and 30 controls were enrolled in this study. Non-invasive continuous beat-to-beat blood pressure, cerebral blood flow velocity and other associated information on the MCA and PCA during silent reading were collected using a transcranial Doppler. NVC assessment was performed by opening and closing the eyes periodically based on voice prompts, and eye-opening visual stimulation was achieved by silently reading Chinese tourism materials. Visual stimulation signals can selectively activate Brodmann's areas 17, 18, and 19 of the occipital when reading silently with open eyes, prompting them to release neurotransmitters and dilate PCA. dCA was determined by transfer function analysis.

RESULTS

In dCA of the PCA during silent reading, the CVST group's very low frequency phase was lower than that of the control group (p = 0.047). In NVC, the difference in the indexes of the cerebrovascular conductance and visually evoked flow response of the CVST group were lower than those of the control group (p = 0.017 and p = 0.019, respectively).

CONCLUSION

Compared with the control group, dCA and NVC of the PCA during silent reading were impaired in CVST patients.

The neurovascular unit in healthy and injured spinal cord

The neurovascular unit (NVU) reflects the close temporal and spatial link between neurons and blood vessels. However, the understanding of the NVU in the spinal cord is far from clear and largely based on generalized knowledge obtained from the brain. Herein, we review the present knowledge of the NVU and highlight candidate approaches to investigate the NVU, particularly focusing on the spinal cord. Several unique features maintain the highly regulated microenvironment in the NVU. Autoregulation and neurovascular coupling ensure regional blood flow meets the metabolic demand according to the blood supply or local neural activation. The blood-central nervous system barrier partitions the circulating blood from neural parenchyma and facilitates the selective exchange of substances. Furthermore, we discuss spinal cord injury (SCI) as a common injury from the perspective of NVU dysfunction. Hopefully, this review will help expand the understanding of the NVU in the spinal cord and inspire new insights into SCI.

Clinical trial of home blood pressure monitoring following midodrine administration in hypotensive individuals with spinal cord injury

BACKGROUND

Individuals with spinal cord injury (SCI) above thoracic level-6 (T6) experience impaired descending cortical control of the autonomic nervous system which predisposes them to blood pressure (BP) instability, including includes hypotension, orthostatic hypotension (OH), and autonomic dysreflexia (AD). However, many individuals do not report symptoms of these BP disorders, and because there are few treatment options that have been proven safe and effective for use in the SCI population, most individuals remain untreated.

OBJECTIVE

The primary aim of this investigation was to determine the effects of midodrine (10 mg) prescribed TID or BID in the home environment, compared to placebo, on 30-day BP, study withdrawals, and symptom reporting associated with OH and AD in hypotensive individuals with SCI.

DESIGN/METHODS

Participants were randomly assigned to received midodrine/placebo or placebo/midodrine, with a 2-weeks washout period in between, and both the participants and investigators were blinded to randomization order. Study medication was taken 2 or 3 times/day, depending on their sleep/wake schedule, BP, and any related symptoms were recorded before and 1 h after each dosage and periodically throughout the day.

RESULTS

Nineteen individuals with SCI were recruited; however, 9 withdrew prior to completion of the full protocol. A total of 1892 BP recordings (75 ± 48 recordings/participant/30-day period) were collected in the 19 participants over the two 30-day monitoring periods. Average 30-day systolic BP was significantly increased with midodrine compared to placebo (114 ± 14 vs. 96 ± 11 mmHg, respectively; P = 0.004), and midodrine significantly reduced the number of hypotensive BP recordings compared to placebo (38.7 ± 41.9 vs. 73.3 ± 40.6, respectively; P = 0.01). However, compared to placebo, midodrine increased fluctuations in BP, did not improve symptoms of OH, but did significantly worsen the intensity of symptoms associated with AD (P = 0.03).

CONCLUSION

Midodrine (10 mg) administered in the home environment effectively increases BP and reduces the incidence of hypotension; however these beneficial effects come at the expense of worsened BP instability and AD symptom intensity.

The Effect of a Neuronal Nitric Oxide Synthase Inhibitor on Neurovascular Regulation in Humans

BACKGROUND

Neurovascular coupling (NVC) is a key process in cerebral blood flow regulation. NVC ensures adequate brain perfusion to changes in local metabolic demands. Neuronal nitric oxide synthase (nNOS) is suspected to be involved in NVC; however, this has not been tested in humans. Our objective was to investigate the effects of nNOS inhibition on NVC in humans.

METHODS

We performed a 3-visit partially randomized, double-blinded, placebo-controlled, crossover study in 12 healthy subjects. On each visit, subjects received an intravenous infusion of either S-methyl-L-thiocitrulline (a selective nNOS-inhibitor), 0.9% saline (placebo control), or phenylephrine (pressor control). The NVC assessment involved eliciting posterior circulation hyperemia through visual stimulation while measuring posterior and middle cerebral arteries blood velocity.

RESULTS

nNOS inhibition blunted the rapidity of the NVC response versus pressor control, evidenced by a reduced initial rise in mean posterior cerebral artery velocity (-3.3% [-6.5, -0.01], P=0.049), and a reduced rate of increase (ie, acceleration) in posterior cerebral artery velocity (slope reduced -4.3% [-8.5, -0.1], P=0.045). The overall magnitude of posterior cerebral artery response relative to placebo control or pressor control was not affected. Changes in BP parameters were well-matched between the S-methyl-L-thiocitrulline and pressor control arms.

CONCLUSIONS

Neuronal NOS plays a role in dynamic cerebral blood flow control in healthy adults, particularly the rapidity of the NVC response to visual stimulation. This work opens the way to further investigation of the role of nNOS in conditions of impaired NVC, potentially revealing a therapeutic target.

Common carotid artery responses to the cold-pressor test are impaired in individuals with cervical spinal cord injury

Cervical spinal cord injury (SCI) leads to autonomic cardiovascular dysfunction that underlies the three- to fourfold elevated risk of cardiovascular disease in this population. Reduced common carotid artery (CCA) dilatory responsiveness during the cold-pressor test (CPT) is associated with greater cardiovascular disease risk and progression. The cardiovascular and CCA responses to the CPT may provide insight into cardiovascular autonomic dysfunction and cardiovascular disease risk in individuals with cervical SCI. Here, we used CPT to perturb the autonomic nervous system in 14 individuals with cervical SCI and 12 uninjured controls, while measuring cardiovascular responses and CCA diameter. The CCA diameter responses were 55% impaired in those with SCI compared with uninjured controls (P = 0.019). The CCA flow, velocity, and shear response to CPT were reduced in SCI by 100% (P < 0.001), 113% (P = 0.001), and 125% (P = 0.002), respectively. The association between mean arterial pressure and CCA dilation observed in uninjured individuals (r = 0.54, P = 0.004) was absent in the SCI group (r = 0.22, P = 0.217). Steady-state systolic blood pressure (P = 0.020), heart rate (P = 0.003), and cardiac contractility (P < 0.001) were reduced in those with cervical SCI, whereas total peripheral resistance was increased compared with uninjured controls (P = 0.042). Relative cerebral blood velocity responses to CPT were increased in the SCI group and reduced in controls (middle cerebral artery, P = 0.010; posterior cerebral artery, P = 0.026). The CCA and cardiovascular responsiveness to CPT are impaired in those with cervical SCI.NEW & NOTEWORTHY This is the first study demonstrating that CCA responses during CPT are suppressed in SCI. Specifically, CCA diameter, flow, velocity, and shear rate were reduced. The relationship between changes in MAP and CCA dilatation in response to CPT was absent in individuals with SCI, despite similar cardiovascular activation between SCI and uninjured controls. These findings support the notion of elevated cardiovascular disease risk in SCI and that the cardiovascular responses to environmental stimuli are impaired.

Evaluation of Cardiovascular Autonomic Function during Inpatient Rehabilitation following Traumatic Spinal Cord Injury

Assessment of the degree of impaired autonomic nervous system (ANS) function is not part of routine clinical practice during inpatient rehabilitation following traumatic spinal cord injury (SCI). The goal of this investigation was to determine the utility of the International Standards for Neurologic Classification of SCI (ISNCSCI) and the recently revised International Standards to document remaining Autonomic Function after SCI (ISAFSCI) in documenting cardiovascular ANS impairment during inpatient rehabilitation following traumatic SCI. Beat-to-beat recording of supine heart rate (HR) and blood pressure (BP) were collected at the bedside for estimation of total cardiovascular ISAFSCI score, cardio-vagal modulation (i.e., high frequency HR variability [HFHRV]) and sympathetic vasomotor regulation (i.e., Mayer wave component of systolic BP [SBPmayer]). A total of 41 participants completed baseline testing, which was conducted 11 ± 5 days from the admission ISNCSCI examination. There were no differences in supine HR or BP based on the ISNCSCI or ISAFSCI assessments. The HFHRV was generally lower with more distal lesions (r2 = 0.15; p = 0.01), and SBPmayer was significantly lower in those with American Spinal Injury Association Impairment Scale (AIS) A compared with AIS B, C, D (Cohen's d = -1.4; p < 0.001). There were no significant differences in HFHRV or SBPmayer in patients with or without ISAFSCI evidence of cardiovascular ANS impairment. These preliminary data suggest that neither the ISNCSCI nor the ISAFSCI are sensitive to changes in ANS cardiovascular function following traumatic SCI. Bedside assessment of HR and BP variabilities may provide insight, but are not readily available in the clinical setting. Further research is required to evaluate methods that accurately assess the degree of ANS impairment following traumatic SCI.

Vital sign differences between septic patients with tetraplegia and paraplegia

STUDY DESIGN

Retrospective chart review.

OBJECTIVES

Sepsis is a leading preventable cause of death in patients with chronic spinal cord injury (SCI). Individuals with tetraplegia may exhibit different signs and symptoms of infection compared to those with paraplegia. In this study, we examine differences in vital signs (VS) and mental status between septic patients with tetraplegia and paraplegia with the goal of improving early identification of sepsis in this population.

SETTING

Veterans hospital in Washington, USA.

METHODS

Participants consisted of 19 patients with tetraplegia and 16 with paraplegia who were transferred from an SCI Service to a higher level of care with sepsis between June 1, 2010 and June 1, 2018 (n = 35). We compared VS between patients with tetraplegia and paraplegia at baseline and during sepsis including temperature, heart rate (HR), and blood pressure as well as presence/absence of altered mental status (AMS).

RESULTS

While there were no significant VS differences between groups at baseline, septic patients with tetraplegia had lower maximum temperature (38.2 °C versus 39.2 °C, p = 0.003), lower maximum HR (106 versus 124 beats/minute, p = 0.004), and more frequent AMS compared to septic patients with paraplegia (79% versus 31%, p = 0.007).

CONCLUSION

Patients with tetraplegia may not be able to mount fever and tachycardia to the same degree as patients with paraplegia and may be more prone to developing AMS during sepsis. These findings suggest that changes to VS parameter cut-offs may improve sensitivity and be useful in identifying sepsis earlier in the tetraplegic population.

Acute submaximal exercise does not impact aspects of cognition and BDNF in people with spinal cord injury: A pilot study

Objective

To investigate the effect of acute submaximal exercise, based on the spinal cord injury (SCI) Exercise Guidelines, on cognition and brain-derived neurotrophic factor (BDNF) in people with SCI.

Design

Eight adults (7 males) with traumatic SCI volunteered in this pre-registered pilot study. In randomized order, participants completed submaximal intensity arm cycling (60% of measured peak-power output at 55–60 rpm) for 30 min or time-matched quiet rest (control condition) on separate days. Blood-borne BDNF was measured in serum and plasma at pre-intervention, 0 min and 90 min post-intervention. Cognition was assessed using the Stroop Test and Task-Switching Test on an electronic tablet pre- and 10 min post-intervention.

Results

Submaximal exercise had no effect on plasma [F(2,12) = 1.09; P = 0.365; η² = 0.069] or serum BDNF [F(2,12) = 0.507; P = 0.614; η² = 0.024] at either 0 min or 90 min post-intervention. Similarly, there was no impact of exercise on either Stroop [F(1,7) = 2.05; P = 0.195; η² = 0.065] or Task-Switching performance [F(1,7) = 0.016; P = 0.903; η² &lt; 0.001] compared to the control condition. Interestingly, there was a positive correlation between years since injury and resting levels of both plasma (r = 0.831; P = 0.011) and serum BDNF (r = 0.799; P = 0.023). However, there was not relationship between years since injury and the BDNF response to exercise.

Conclusions

Acute guideline-based exercise did not increase BDNF or improve aspects of cognition in persons with SCI. This work establishes a foundation for continued investigations of exercise as a therapeutic approach to promoting brain health among persons with SCI.

Management of blood pressure disorders in individuals with spinal cord injury

Blood pressure regulation is impacted by a spinal cord injury (SCI) due to impaired descending sympathetic vascular control. Common blood pressure problems in the SCI population include persistently low blood pressure with bouts of orthostatic hypotension and autonomic dysreflexia, which are more prevalent in individuals with lesions above the sixth thoracic vertebral level; however, they may occur regardless of the neurological level of injury. Although blood pressure disorders adversely impact daily function and quality of life, most individuals with SCI do not acknowledge this association. Few pharmacological options have been rigorously tested for safety and efficacy to manage blood pressure disorders in the SCI population. Furthermore, clinical management of any one blood pressure disorder may adversely impact others, as such treatment is complicated and not often prioritized.

Does task complexity impact the neurovascular coupling response similarly between males and females?

BACKGROUND

While previous studies have demonstrated a complex visual scene search elicits a robust neurovascular coupling (NVC) response, it is unknown how the duration of visual stimuli presentation influences NVC metrics. This study examined how stimuli duration, in addition to biological sex and self-reported engagement impact NVC responses.

METHODS

Participants (n = 20, female = 10) completed four visual paradigms. Three involved simple visual shapes presented at 0.5-, 2-, and 4-s intervals in randomized orders. The fourth paradigm was a complex visual scene search ("Where's Waldo?"). Participants completed eight cycles of 20-s eyes-closed followed by 40-s eyes-open. Transcranial Doppler ultrasound indexed posterior and middle cerebral artery velocities (PCA and MCA). Participants self-reported their engagement following each task (1 [minimal] to 10 [maximal]).

RESULTS

The "Where's Waldo?" task evoked greater PCA percent increase (all p < 0.001) and area under the curve during the first 30-s of the task (all p < 0.001) compared to simple shapes. Females displayed greater absolute baseline and peak PCA and MCA velocities across all tasks (all p < 0.002). Subjective engagement displayed moderate correlation levels with PCA percent increase (Spearman ρ = 0.58) and area under the curve (Spearman ρ = 0.60) metrics in males, whereas these were weak for females (Spearman ρ = 0.43 and ρ = 0.38, respectively).

CONCLUSIONS

The complex visual paradigm "Where's Waldo?" greatly augmented the signal-to-noise ratio within the PCA aspects of the NVC response compared to simple shapes. While both sexes had similar NVC responses, task engagement was more related to NVC metrics in males compared to females. Therefore, future NVC investigations should consider task engagement when designing studies.

Autonomic cardiovascular dysfunction during simple arithmetic test in a patient with cervical spinal cord injury-a case report

INTRODUCTION

Spinal cord injury (SCI) disrupts autonomic control of the cardiovascular system, which may lead to autonomic dysfunction. Growing amounts of evidence support the possibility that systemic and cerebral hemodynamic dysfunctions may contribute to cognitive deficits in patients with SCI.

CASE PRESENTATION

We present a case of autonomic cardiovascular dysfunction in a 55-year old female patient following non-traumatic cervical SCI. This case illustrates how a simple arithmetic test may elicit fluctuations in blood pressure causing cognitive disturbances.

DISCUSSION

Clinical awareness of autonomic dysfunction and cognitive deficits is relevant in neurorehabilitation of patients with SCI. Assessment of autonomic function should be evaluated according to recommendation from International Standards to document remaining Autonomic Function after Spinal Cord Injury (ISAFSCI) [1].

Autonomic dysreflexia associated with cervical spinal cord gliofibroma: case report

BACKGROUND

Autonomic dysreflexia (AD) is an abnormal reflex of the autonomic nervous system normally observed in patients with spinal cord injury from the sixth thoracic vertebra and above. AD causes various symptoms including paroxysmal hypertension due to stimulus. Here, we report a case of recurrent AD associated with cervical spinal cord tumor.

CASE PRESENTATION

The patient was a 57-year-old man. Magnetic resonance imaging revealed an intramedullary lesion in the C2, C6, and high Th12 levels. During the course of treatment, sudden loss of consciousness occurred together with abnormal paroxysmal hypertension, marked facial sweating, left upward conjugate gaze deviation, ankylosis of both upper and lower extremities, and mydriasis. Seizures repeatedly occurred, with symptoms disappearing after approximately 30 min. AD associated with cervical spinal cord tumor was diagnosed. Histological examination by tumor biopsy confirmed the diagnosis of gliofibroma. Radiotherapy was performed targeting the entire brain and spinal cord. The patient died approximately 3 months after treatment was started.

CONCLUSIONS

AD is rarely associated with spinal cord tumor, and this is the first case associated with cervical spinal cord gliofibroma. AD is important to recognize, since immediate and appropriate response is required.

Neuroprosthetic baroreflex controls haemodynamics after spinal cord injury

Spinal cord injury (SCI) induces haemodynamic instability that threatens survival^1-3, impairs neurological recovery^4,5, increases the risk of cardiovascular disease^6,7, and reduces quality of life^8,9. Haemodynamic instability in this context is due to the interruption of supraspinal efferent commands to sympathetic circuits located in the spinal cord¹⁰, which prevents the natural baroreflex from controlling these circuits to adjust peripheral vascular resistance. Epidural electrical stimulation (EES) of the spinal cord has been shown to compensate for interrupted supraspinal commands to motor circuits below the injury¹¹, and restored walking after paralysis¹². Here, we leveraged these concepts to develop EES protocols that restored haemodynamic stability after SCI. We established a preclinical model that enabled us to dissect the topology and dynamics of the sympathetic circuits, and to understand how EES can engage these circuits. We incorporated these spatial and temporal features into stimulation protocols to conceive a clinical-grade biomimetic haemodynamic regulator that operates in a closed loop. This 'neuroprosthetic baroreflex' controlled haemodynamics for extended periods of time in rodents, non-human primates and humans, after both acute and chronic SCI. We will now conduct clinical trials to turn the neuroprosthetic baroreflex into a commonly available therapy for people with SCI.

Multidimensional review of cognitive impairment after spinal cord injury

Cognitive impairment is highly prevalent in the population with spinal cord injury (SCI) and exerts a significant impact on functional independence and quality of life in this population. A number of neuroscientists have conducted preliminary investigations of cognitive deficits after SCI, but achieved marginally contradictory results due to some limitations such as the heterogeneity in the sample population, sample size, types of tests utilized, study design, and time since SCI. Therefore, this review mainly focuses on the characteristics, assessments, potential causality and treatment of cognitive impairment for better understanding such deficits in the SCI population.

Temporal evolution of neurovascular coupling recovery following moderate- and high-intensity exercise

PURPOSE

Studies examining neurovascular coupling (NVC) require participants to refrain from exercise for 12-24 hours. However, there is a paucity of empirical evidence for this restriction. The objectives for this study were to delineate the time-course recovery of NVC metrics following exercise and establish the NVC within- and between-day reliability.

METHODS

Nine participants completed a complex visual search paradigm to assess NVC via transcranial Doppler ultrasound of the posterior cerebral artery blood velocity (PCA). Measurements were performed prior to and throughout the 8-hour recovery period following three randomized conditions: 45 minutes of moderate-intensity exercise (at 50% heart-rate reserve), 30 minutes high-intensity intervals (10, 1-minute intervals at 85% heart-rate reserve), and control (30 minutes quiet rest). In each condition, baseline measures were collected at 8:00am with serial follow-ups at hours zero, one, two, four, six, and eight.

RESULTS

Area-under-the-curve and time-to-peak PCA velocity during the visual search were attenuated at hour zero following high-intensity intervals (all p < 0.05); however, these NVC metrics recovered at hour one (all p > 0.13). Conversely, baseline PCA velocity, peak PCA velocity, and the relative percent increase were not different following high-intensity intervals compared to baseline (all p > 0.26). No NVC metrics differed from baseline following both moderate exercise and control conditions (all p > 0.24). The majority of the NVC parameters demonstrated high levels of reliability (intraclass correlation coefficient: >0.90).

CONCLUSION

Future NVC assessments can take place a minimum of one hour following exercise. Moreover, all metrics did not change across the control condition, therefore future studies using this methodology can reliably quantify NVC between 8:00am and 7:00 pm.

Effect of 6-Month Exercise Training on Neurovascular Function in Spinal Cord Injury

INTRODUCTION

Although previous data show exacerbated incidence of cognitive impairment after spinal cord injury (SCI), the physiology that underlies this postinjury cognitive decline is unknown. One potential culprit is impairment in the ability of cerebral vasculature to alter regional flow to sustain neural metabolism (i.e., "neurovascular coupling"). We hypothesized that cerebrovascular responses to a working memory task are impaired in individuals with SCI and can be improved by aerobic exercise training.

METHODS

We assessed the effect of injury and 6-month full-body aerobic exercise training on the cerebral blood flow response to cognitive demand (i.e., neurovascular coupling) in 24 individuals with SCI and 16 controls. Cognitive demand was introduced in a graded fashion using a working memory task.

RESULTS

Reaction time tended to be higher in individuals with SCI, especially those with high-level (≥T4) injuries, possibly due to upper motor impairments. Neurovascular coupling was graded across task difficulty (P < 0.01) and followed cognitive demand, and injury itself did not have a significant effect (group effect P = 0.99, interaction P = 0.70). Individuals with low-level injuries (

CONCLUSION

Previously reported cognitive impairment after SCI may reflect a decline in neurovascular coupling primarily due to physical deconditioning rather than injury itself. The latter can be mitigated by aerobic exercise training.

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Key Words Collapse

MESH Headings

• Adult
• Cardiorespiratory Fitness
• Cognitive Dysfunction/etiology
• Cognitive Dysfunction/physiopathology
• Cognitive Dysfunction/therapy
• Exercise Therapy
• Female
• Humans
• Male
• Neurovascular Coupling
• Spinal Cord Injuries/physiopathology
• Spinal Cord Injuries/rehabilitation
• Young Adult

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Grants

• 15SDG23290000 American Heart Association-American Stroke Association

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Affiliation(s) Collapse

Duration and magnitude of bidirectional fluctuation in blood pressure: the link between cerebrovascular dysfunction and cognitive impairment following spinal cord injury

Individuals with spinal cord injury (SCI) have a significantly increased risk for cognitive impairment that is associated with cerebrovascular remodeling and endothelial dysfunction. The sub-acute stage following high thoracic SCI is characterized by increased fibrosis and stiffness of cerebral arteries. However, a more prolonged duration after SCI exacerbates cerebrovascular injury by damaging endothelium. Endothelial dysfunction is associated with reduced expression of transient receptor potential cation channel 4 that mediates the production of nitric oxide and epoxyeicosatrienoic acids following shear stress and the response to carbachol and other endothelium-dependent vasodilators. Reduced expression of CD31 in cerebral arteries also suggests the loss of endothelial cell integrity following chronic SCI. Repetitively transient hypertension and intermittent hypotension contribute to cerebrovascular endothelial dysfunction in the animals with a sub-acute stage of high thoracic SCI. The increase in vascular remodeling and endothelial dysfunction ultimately reduce cerebral blood flow, which promotes cerebral hypoperfusion and cognitive dysfunction in the chronic phase of SCI. In conclusion, the duration and magnitude of fluctuations in blood pressure after SCI play a vital role in the onset and progress of cerebrovascular dysfunction, which promotes the development of cognitive impairment.

A Primary Care Provider's Guide to Preventive Health After Spinal Cord Injury

Objective: Provide guidance for preventive health and health maintenance after spinal cord injury (SCI) for primary care providers (PCPs). Main message: Individuals with SCI may not receive the same preventive health care as the general population. Additionally, SCI-related secondary conditions may put their health at risk. SCI is considered a complex condition associated with many barriers to receiving quality primary care. Attention to routine preventive care and the unique health considerations of persons with SCI can improve health and quality of life and may prevent unnecessary health care utilization. Conclusion: PCPs are experts in preventive care and continuity of care, however individuals with SCI may not receive the same preventive care due to numerous barriers. This article serves as a quick reference for PCPs.

Beneficial Cardiac Structural and Functional Adaptations After Lumbosacral Spinal Cord Epidural Stimulation and Task-Specific Interventions: A Pilot Study

Cardiac myocyte atrophy and the resulting decreases to the left ventricular mass and dimensions are well documented in spinal cord injury. Therapeutic interventions that increase preload can increase the chamber size and improve the diastolic filling ratios; however, there are no data describing cardiac adaptation to chronic afterload increases. Research from our center has demonstrated that spinal cord epidural stimulation (scES) can normalize arterial blood pressure, so we decided to investigate the effects of scES on cardiac function using echocardiography. Four individuals with chronic, motor-complete cervical spinal cord injury were implanted with a stimulator over the lumbosacral enlargement. We assessed the cardiac structure and function at the following time points: (a) prior to implantation; (b) after scES targeted to increase systolic blood pressure; (c) after the addition of scES targeted to facilitate voluntary (i.e., with intent) movement of the trunk and lower extremities; and (d) after the addition of scES targeted to facilitate independent, overground standing. We found significant improvements to the cardiac structure (left ventricular mass = 10 ± 2 g, p < 0.001; internal dimension during diastole = 0.1 ± 0.04 cm, p < 0.05; internal dimension during systole = 0.06 ± 0.03 cm, p < 0.05; interventricular septum dimension = 0.04 ± 0.02 cm, p < 0.05), systolic function (ejection fraction = 1 ± 0.4%, p < 0.05; velocity time integral = 2 ± 0.4 cm, p < 0.001; stroke volume = 4.4 ± 1.5 ml, p < 0.01), and diastolic function (mitral valve deceleration time = -32 ± 11 ms, p < 0.05; mitral valve deceleration slope = 50 ± 25 cm s-1, p < 0.05; isovolumic relaxation time = -6 ± 1.9 ms, p < 0.05) with each subsequent scES intervention. Despite the pilot nature of this study, statistically significant improvements to the cardiac structure, systolic function, and diastolic function demonstrate that scES combined with task-specific interventions led to beneficial cardiac remodeling, which can reverse atrophic changes that result from spinal cord injury. Long-term improvements to cardiac function have implications for increased quality of life and improved cardiovascular health in individuals with spinal cord injury, decreasing the risk of cardiovascular morbidity and mortality.

Prolonged Targeted Cardiovascular Epidural Stimulation Improves Immunological Molecular Profile: A Case Report in Chronic Severe Spinal Cord Injury

In individuals with severe spinal cord injury (SCI), the autonomic nervous system (ANS) is affected leading to cardiovascular deficits, which include significant blood pressure instability, with the prevalence of systemic hypotension and orthostatic intolerance resulting in an increased risk of stroke. Additionally, persons with SCI rostral to thoracic vertebral level 5 (T5), where sympathetic nervous system fibers exit the spinal cord and innervate the immune system, have clinically significant systemic inflammation and increased infection risk. Our recent studies show that lumbosacral spinal cord epidural stimulation (scES), applied at the lumbosacral level using targeted configurations that promote cardiovascular stability (CV-scES), can safely and effectively normalize blood pressure in persons with chronic SCI. Herein we present a case report in a female (age 27 years) with chronic clinically motor complete cervical SCI demonstrating that 97-sessions of CV-scES, which increased systemic blood pressure, improved orthostatic tolerance in association with increased cerebral blood flow velocity in the middle cerebral artery, also promoted positive immunological changes in whole-blood gene expression. Specifically, there was evidence of the down-regulation of inflammatory pathways and the up-regulation of adaptative immune pathways. The findings of this case report suggest that the autonomic effects of epidural stimulation, targeted to promote cardiovascular homeostasis, also improves immune system function, which has a significant benefit to long-term cardiovascular and immunologic health in individuals with long-standing SCI.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier NCT02307565.

Neurovascular Coupling Impairment in Heart Failure with Reduction Ejection Fraction

The hemodynamic consequences of a persistent reduced ejection fraction and unknown cardiac output on the brain have not been thoroughly studied. We sought to explore the status of the mechanisms of cerebrovascular regulation in patients with heart failure with reduced (HFrEF) and recovered (HFrecEF) ejection fraction. We monitored cerebral blood flow velocity (CBFV) with transcranial Doppler and blood pressure. Cerebral autoregulation, assessed by transfer function from the spontaneous oscillations of blood pressure to CBFV and neurovascular coupling (NVC) with visual stimulation were compared between groups of HFrEF, HFrecEF and healthy controls. NVC was significantly impaired in HFrEF patients with reduced augmentation of CBFV during stimulation (overshoot systolic CBFV 19.11 ± 6.92 vs. 22.61 ± 7.78 vs. 27.92 ± 6.84, p = 0.04), slower upright of CBFV (rate time to overshoot: 1.19 ± 3.0 vs. 3.06 (4.30) vs. 2.90 ± 3.84, p = 0.02); p = 0.023) and reduced arterial oscillatory properties (natural frequency 0.17 ± 0.06 vs. 0.20 ± 0.09 vs. 0.24 ± 0.07, p = 0.03; attenuation 0.34 ± 0.24 vs. 0.48 ± 0.35 vs. 0.50 ± 0.23, p = 0.05). Cerebral autoregulation was preserved. The neurovascular unit of subjects with chronically reduced heart pumping capability is severely dysfunctional. Dynamic testing with transcranial Doppler could be useful in these patients, but whether it helps in predicting cognitive impairment must be addressed in future prospective studies.

A prospective cohort study investigating contributors to mild cognitive impairment in adults with spinal cord injury: study protocol

BACKGROUND

Studies report rates of mild cognitive impairment (MCI) in spinal cord injury (SCI) range between 10 and 60%. This broad estimate of MCI in SCI is most likely a result of: (i) inconsistent operationalization of MCI; (ii) heterogeneity among individuals with SCI; (iii) failure to account for MCI subtypes, thereby adding to the heterogeneity of samples; and, (iv) poor control for traumatic brain injury (TBI) that obscures differentiation of MCI attributable to TBI versus other factors. There is a paucity of longitudinal studies following the course of MCI in SCI, and none that account for multiple predictors of MCI, including interactions among predictors.

METHODS

An inception cohort longitudinal study will assess approximately 100 individuals aged 17-80 years with acute SCI, with measures taken at three timepoints (baseline, 3 months post-baseline, and 12 months post-injury). Data relevant to medical care received within the first 24-48 h of presentation to the emergency department will be analysed, as will measures of cognition, injury characteristics, medical history, personal factors, psychological status, psychosocial functioning, and quality of life. Latent class mixture modelling will determine trajectories for the primary outcome of interest, cognitive functioning and its subtypes, and secondary outcomes of interest such as depression. Multiple regression analyses will identify predictors of MCI and its subtypes.

DISCUSSION

The prospective design will reveal change in cognitive functioning across time and unveil different outcome trajectories; thus addressing the lack of knowledge on trajectories of MCI and MCI subtypes in SCI. Through subtyping MCI, we hope to yield groups of cognitively impaired individuals with SCI that are potentially more homogenous and thereby stable and predictable. This is the first study to capture emergency department and acute care diagnostic evidence of mild TBI, which has been poorly controlled in previous studies. Our study will also be the first to distinguish the contribution of TBI from other factors to the development of MCI in individuals with SCI.

TRIAL REGISTRATION

The study was prospectively registered with the Australian and New Zealand Clinical Trial Registry ( ACTRN12619001702101 ) on 3rd December 2019.

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

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

Orthostatic Hypotension Is Associated With Cognitive Decline in Parkinson Disease

Introduction: Cognitive impairment and orthostatic hypotension (OH) are common, disabling Parkinson disease (PD) symptoms that are strongly correlated. Whether the relationship is causative or associative remains unknown. OH may occur without classic orthostatic symptoms of cerebral hypoperfusion (i.e., lightheadedness or dizziness). Whether longitudinal differences in cognition occur between symptomatic and asymptomatic OH patients has not been explored.

Objectives: We characterized the prevalence of OH, orthostatic symptoms, and cognitive impairment among PD patients and compared cognition between patients with and without OH, and between patients with symptomatic and asymptomatic OH.

Methods: Our cross-sectional, retrospective, observational study included 226 clinically diagnosed PD patients who underwent repeated standardized evaluations. Among these, 62 had longitudinal follow-up of > 3.5 years. We compared longitudinal Montreal Cognitive Assessment (MoCA) scores between patients remaining OH-free (n = 14) and those without baseline OH that developed OH (n = 28), matched for age, sex, education, and PD duration. We also compared MoCA scores between groups with asymptomatic OH (n = 13) and symptomatic OH (n = 13) matched for the same factors.

Results: In the cross-sectional analysis, OH patients had worse cognition. In the longitudinal analysis (mean follow-up = 5.3 years), OH patients had worse cognitive decline (p = 0.027). Cognitive impairment was similar between asymptomatic and symptomatic OH patients in the cross-sectional and longitudinal analyses.

Conclusions: OH is associated with cognitive impairment in PD. Further studies are needed in larger cohorts to expand our findings and to determine whether treating OH can prevent or delay cognitive dysfunction.

A Primary Care Provider's Guide to Autonomic Dysfunction Following Spinal Cord Injury

Spinal cord injury (SCI) disrupts the crucial "crosstalk" between the spinal autonomic nervous system and supraspinal control centers. Therefore, SCI may result not only in motor paralysis but also in potentially life-threatening impairments of many autonomic functions including, but not limited to, blood pressure regulation. Despite the detrimental consequences of autonomic dysregulation, management and recovery of autonomic functions after SCI is greatly underexplored. Although impaired autonomic function may impact several organ systems, this overview will focus primarily on disruptions of cardiovascular and thermoregulation and will offer suggestions for management of these secondary effects of SCI.

An Acute Bout of Soccer Heading Subtly Alters Neurovascular Coupling Metrics

Objective: The current investigation examined how a bout of soccer heading may impact brain function.

Design: Semi-randomized crossover cohort.

Setting: Controlled soccer heading.

Participants: Seven male soccer players (24.1 ± 1.5 years).

Intervention: 40 successful soccer headers were performed in 20 min (25 m, launch velocity ~80 km/h). X2 xPatch recorded linear and rotational head accelerations during each impact. A contact control “sham” condition – ball made body contact, but not by the head; and a no activity time “control” condition were also completed.

Main Outcome Measures: Posterior and middle cerebral artery (PCA and MCA, respectively), cerebral blood velocity (CBV) was recorded during a visual task (neurovascular coupling: NVC) alongside SCAT3 symptoms scores pre/post a controlled bout of soccer heading.

Results: Cumulative linear and rotational accelerations were 1,574 ± 97.9 g and 313,761 ± 23,966 rads/s², respectively, during heading and changes in SCAT3 symptom number (pre: 2.6 ± 3.0; post: 6.7 ± 6.2, p = 0.13) and severity (pre: 3.7 ± 3.6, post: 9.4 ± 7.6, p = 0.11) were unchanged. In the PCA, no NVC differences were observed, including: relative CBV increase (28.0 ± 7.6%, p = 0.71) and total activation (188.7 ± 68.1 cm, p = 0.93). However, MCA-derived NVC metrics were blunted following heading, demonstrating decreased relative CBV increase (7.8 ± 3.1%, p = 0.03) and decreased total activation (26.7 ± 45.3 cm, p = 0.04).

Conclusion: Although an acute bout of soccer heading did not result in an increase of concussion-like symptoms, there were alterations in NVC responses within the MCA during a visual task. This suggests an acute bout of repetitive soccer heading can alter CBV regulation within the region of the brain associated with the header impacts.

Cognitive Dysfunction in Persons with Chronic Spinal Cord Injuries

Cognitive dysfunction (CD) is pervasive in individuals who have chronic spinal cord injuries (SCI). Although classically associated with concomitant traumatic brain injuries, many other causes have been proposed, including premorbid neuropsychological conditions, mood disorders, substance abuse, polypharmacy, chronic pain and fatigue, sleep apnea, autonomic dysregulation, post-intensive care unit syndrome, cortical reorganizations, and neuroinflammation. The consequences of CD are likely widespread, affecting rehabilitation and function. CD in those with SCI should be recognized, and potentially treated, in order to provide the best patient care.

Vascular-Cognitive Impairment following High-Thoracic Spinal Cord Injury Is Associated with Structural and Functional Maladaptations in Cerebrovasculature

Individuals living with chronic spinal cord injury (SCI) often exhibit impairments in cognitive function, which impede their rehabilitation and transition into the community. Although a number of clinical studies have demonstrated the impact of impaired cardiovascular control on cognitive impairment, the mechanistic understanding of this deleterious relationship is still lacking. The present study investigates whether chronic disruption of cardiovascular control following experimental SCI results in cerebrovascular decline and vascular cognitive impairment. Fourteen weeks following a high thoracic SCI (at the third thoracic segment), rats were subjected to a battery of in vivo and in vitro physiological assessments, cognitive-behavioral tests, and immunohistochemical approaches to investigate changes in cerebrovascular structure and function in the middle cerebral artery (MCA). We show that in the MCA of rats with SCI, there is a 55% (SCI vs. control: 13.4 ± 1.9% vs. 29.63 ± 2.8%, respectively) reduction in the maximal vasodilator response to carbachol, which is associated with reduced expression of endothelial marker cluster of differentiation 31 (CD31) and transient receptor potential cation channel 4 (TRPV 4) channels. Compared with controls, MCAs in rats with SCI were found to have 50% (SCI vs. control: 1.5 ± 0.2 vs. 1 ± 0.1 a.u., respectively) more collagen 1 in the media of vascular wall and 37% (SCI vs. control: 30.5 ± 2.9% vs. 42.0 ± 4.0%, respectively) less distensibility at physiological intraluminal pressure. Further, the cerebral blood flow (CBF) in the hippocampus was reduced by 32% in the SCI group (SCI vs. control: 44.3 ± 4.5 mL/100 g/min vs. 65.0 ± 7.2 mL/100 g/min, respectively) in association with impairment of short-term memory based on a novel object recognition test. There were no changes in the sympathetic innervation of the vasculature and passive structure in the SCI group. Chronic experimental SCI is associated with structural alterations and endothelial dysfunction in cerebral arteries that likely contribute to significantly reduced CBF and vascular cognitive impairment.

Double-blinded, placebo-controlled crossover trial to determine the effects of midodrine on blood pressure during cognitive testing in persons with SCI

Study Design:

Clinical trial.

Objectives:

Individuals with spinal cord injury (SCI) above T6 experience impaired descending cortical control of the autonomic nervous system which predisposes them to hypotension. However, treatment of hypotension is uncommon in the SCI population because there are few safe and effective pharmacological options available. The primary aim of this investigation was to test the efficacy of a single dose of midodrine (10 mg), compared to placebo, to increase and normalize systolic blood pressure (SBP) between 110–120 mmHg during cognitive testing in hypotensive individuals with SCI. Secondary aims were to determine the effects of midodrine on cerebral blood flow velocity (CBFv) and global cognitive function.

Setting:

United States clinical research laboratory.

Methods:

Forty-one healthy hypotensive individuals with chronic (≥ 1-year post-injury) SCI participated in this 2-day study.

Seated SBP, CBFv, cognitive performance were monitored before and after administration of identical encapsulated tablets, containing either midodrine or placebo.

Results:

Compared to placebo, midodrine increased SBP (4±13 vs. 18±24 mmHg, respectively; p<0.05); however, responses varied widely with midodrine (−15.7 to +68.6 mmHg). Further, the proportion of SBP recordings within the normotensive range did not improve during cognitive testing with midodrine compared to placebo. Although higher SBP was associated with higher CBFv (p=0.02), global cognitive function was not improved with midodrine.

Conclusions:

The findings indicate that midodrine increases SBP and may be beneficial in some hypotensive patients with SCI; however, large heterogeneity of responses to midodrine suggest careful monitoring of patients following administration.

Network analysis identifies consensus physiological measures of neurovascular coupling in humans

Intimate communication between neural and vascular structures is required to match neuronal metabolism to blood flow, a process termed neurovascular coupling. The number of laboratories assessing neurovascular coupling in humans is increasing due to clinical interest in disease states, and basic science interest in a non-anesthetized, non-craniotomized, unrestrained, in vivo model. However, there is a lack of knowledge regarding how best to characterize the neurovascular response. To address this knowledge gap, we have amassed a highly powered human neurovascular coupling dataset, and deployed a network-based approach to reveal the most powerful and consistent metrics for quantifying neurovascular coupling. Using dimensionality reduction, community-based clustering, and majority-voting of traditional metrics (e.g. peak response, time to peak) and non-traditional metrics (e.g. varying time windows, pulsatility), we have identified which of the existing metrics predominantly characterize the neurovascular coupling response, are stable within and across participants, and explain the vast majority of the variance within our dataset of over 300 trials. We then harnessed our empirical approach to generate powerful novel metrics of neurovascular coupling, termed iAmplitude, iRate, and iPulsatility, which increase sensitivity when capturing population differences. These metrics may be useful to optimally understand neurovascular coupling in health and disease.

A Prospective Transcranial Doppler Ultrasound-Based Evaluation of the Effects of Repetitive Subconcussive Head Trauma on Neurovascular Coupling Dynamics

OBJECTIVE

To determine the effects of repetitive subconcussive head trauma on neurovascular coupling (NVC) responses.

DESIGN

Prospective cohort study collected between September 2013 and December 2016.

SETTING

University laboratory.

PARTICIPANTS

One hundred seventy-nine elite, junior-level (age, 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes recruited for preseason testing. Fifty-two nonconcussed athletes returned for postseason testing. Fifteen noncontact sport athletes (age, 20.4 ± 2.2 years) also completed preseason and postseason testing.

EXPOSURE(S)

Subconcussive sport-related head trauma.

MAIN OUTCOME MEASURES

Dynamics of NVC were estimated during cycles of 20 seconds eyes closed and 40 seconds eyes open to a visual stimulus (reading) by measuring cerebral blood flow (CBF) velocity in the posterior (PCA) and middle (MCA) cerebral arteries via transcranial Doppler ultrasound.

RESULTS

Both athlete groups demonstrated no significant differences in PCA or MCA NVC dynamics between preseason and postseason, despite exposure to a median of 353.5 (range, 295.0-587.3) head impacts (>2g) over the course of the season for contact sport athletes.

CONCLUSIONS

Within the context of growing concern over detrimental effects of repetitive subconcussive trauma, the current results encouragingly suggest that the dynamics of NVC responses are not affected by 1 season of participation in junior-level ice hockey or American football. This is an important finding because it indicates an appropriate postseason CBF response to elevated metabolic demand with increases in neural activity.

Diverse cognitive impairment after spinal cord injury is associated with orthostatic hypotension symptom burden

This study: 1) compared cognitive functioning between individuals with chronic (>1 year) spinal cord injury (SCI) and non-injured controls and, 2) assessed associations between symptoms of autonomic dysreflexia and orthostatic hypotension with cognitive functioning in SCI participants with a history of unstable blood pressure (BP). Thirty-two individuals with SCI (C4-L2, American Spinal Injury Association Impairment Scale A-D) and thirty age, sex-matched non-injured controls participated in this study. Participants completed a motor-free neuropsychological test battery assessing 1) memory, 2) attention/concentration/psychomotor speed and, 3) executive function. Nineteen participants with SCI who had injuries ≥T6 and a history of unstable BP also completed the Autonomic Dysfunction Following Spinal Cord Injury (ADFSCI) questionnaire. Cognitive function was significantly lower in people with SCI across measures of memory and executive function compared to non-injured controls. Significant, moderate-to-large associations were observed between cumulative (frequency x severity) orthostatic hypotension and total BP instability symptoms scores, with measures of attention/concentration/psychomotor speed and executive function. These data demonstrate a 10 - 65% reduced performance across specific realms of cognitive functioning in individuals with SCI relative to non-injured controls. Furthermore, cumulative subjective scores for symptoms of unstable BP were associated with diverse cognitive deficits. These findings, in individuals without co-occurring traumatic brain injury, imply cardiovascular dysregulation plays a role in cognitive deficits observed in this population.

Sleep-disordered breathing is associated with brain vascular reactivity in spinal cord injury

OBJECTIVE

To determine the population-level odds of individuals with spinal cord injury (SCI) experiencing fatigue and sleep apnea, to elucidate relationships with level and severity of injury, and to examine associations with abnormal cerebrovascular responsiveness.

METHODS

We used population-level data, meta-analyses, and primary physiologic assessments to provide a large-scale integrated assessment of sleep-related complications after SCI. Population-level and meta-analyses included more than 60,000 able-bodied individuals and more than 1,800 individuals with SCI. Physiologic assessments were completed on a homogenous sample of individuals with cervical SCI and matched controls. We examined the prevalence of (1) self-reported chronic fatigue, (2) clinically identified sleep apnea, and 3) cerebrovascular responsiveness to changing CO₂.

RESULTS

Logistic regression revealed a 7-fold elevated odds of chronic fatigue after SCI (odds ratio [OR] 7.9, 95% confidence interval [CI] 3.5-16.2), and that fatigue and trouble sleeping are correlated with the level and severity of injury. We further show that those with SCI experience elevated risk of clinically defined sleep-disordered breathing in more than 600 individuals with SCI (pooled OR 3.1, 95% CI 1.3-7.5). We confirmed that individuals with SCI experience a high rate of clinically defined sleep apnea using primary polysomnography assessments. We then provide evidence using syndromic analysis that sleep-disordered breathing is a factor strongly associated with impaired cerebrovascular responsiveness to CO₂ in patients with SCI.

CONCLUSIONS

Individuals with SCI have an increased prevalence of sleep-disordered breathing, which may partially underpin their increased risk of stroke. There is thus a need to integrate sleep-related breathing examinations into routine care for individuals with SCI.

The Blood Pressure Pendulum following Spinal Cord Injury: Implications for Vascular Cognitive Impairment

Cognitive impairment following spinal cord injury (SCI) has received considerable attention in recent years. Among the various systemic effects of SCI that contribute towards cognitive decline in this population, cardiovascular dysfunction is arguably one of the most significant. The majority of individuals with a cervical or upper-thoracic SCI commonly experience conditions called orthostatic hypotension and autonomic dysreflexia, which are characterized by dangerous fluctuations in systemic blood pressure (BP). Herein, we review the potential impact of extreme BP lability on vascular cognitive impairment (VCI) in individuals with SCI. Albeit preliminary in the SCI population, there is convincing evidence that chronic hypotension and hypertension in able-bodied individuals results in devastating impairments in cerebrovascular health, leading to VCI. We discuss the pertinent literature, and while drawing mechanistic comparisons between able-bodied cohorts and individuals with SCI, we emphasize the need for additional research to elucidate the mechanisms of cognitive impairment specific to the SCI population. Lastly, we highlight the current and potential future therapies to manage and treat BP instability, thereby possibly mitigating VCI in the SCI population.

Epidural Spinal Cord Stimulation Facilitates Immediate Restoration of Dormant Motor and Autonomic Supraspinal Pathways after Chronic Neurologically Complete Spinal Cord Injury

Epidural Spinal Cord Stimulation (eSCS) in combination with extensive rehabilitation has been reported to restore volitional movement in a select group of subjects after motor-complete spinal cord injury (SCI). Numerous questions about the generalizability of these findings to patients with longer term SCI have arisen, especially regarding the possibility of restoring autonomic function. To better understand the effect of eSCS on volitional movement and autonomic function, two female participants five and 10 years after injury at ages 48 and 52, respectively, with minimal spinal cord preservation on magnetic resonance imaging were implanted with an eSCS system at the vertebral T12 level. We demonstrated that eSCS can restore volitional movement immediately in two female participants in their fifth and sixth decade of life with motor and sensory-complete SCI, five and 10 years after sustaining severe radiographic injuries, and without prescribed or significant pre-habilitation. Both patients experienced significant improvements in surface electromyography power during a volitional control task with eSCS on. Cardiovascular function was also restored with eSCS in one participant with cardiovascular dysautonomia using specific eSCS settings during tilt challenge while not affecting function in a participant with normal cardiovascular function. Orgasm was achieved for the first time since injury in one participant with and immediately after eSCS. Bowel-bladder synergy improved in both participants while restoring volitional urination in one with eSCS. While numerous questions remain, the ability to restore some supraspinal control over motor function below the level of injury, cardiovascular function, sexual function, and bowel and bladder function should promote intense efforts to investigate and develop optimization strategies to maximize recovery in all participants with chronic SCI.

Measurement of Neurovascular Coupling in Neonates

Neurovascular coupling refers to the mechanism that links the transient neural activity to the subsequent change in cerebral blood flow, which is regulated by both chemical signals and mechanical effects. Recent studies suggest that neurovascular coupling in neonates and preterm born infants is different compared to adults. The hemodynamic response after a stimulus is later and less pronounced and the stimulus might even result in a negative (hypoxic) signal. In addition, studies both in animals and neonates confirm the presence of a short hypoxic period after a stimulus in preterm infants. In clinical practice, different methodologies exist to study neurovascular coupling. The combination of functional magnetic resonance imaging or functional near-infrared spectroscopy (brain hemodynamics) with EEG (brain function) is most commonly used in neonates. Especially near-infrared spectroscopy is of interest, since it is a non-invasive method that can be integrated easily in clinical care and is able to provide results concerning longer periods of time. Therefore, near-infrared spectroscopy can be used to develop a continuous non-invasive measurement system, that could be used to study neonates in different clinical settings, or neonates with different pathologies. The main challenge for the development of a continuous marker for neurovascular coupling is how the coupling between the signals can be described. In practice, a wide range of signal interaction measures exist. Moreover, biomedical signals often operate on different time scales. In a more general setting, other variables also have to be taken into account, such as oxygen saturation, carbon dioxide and blood pressure in order to describe neurovascular coupling in a concise manner. Recently, new mathematical techniques were developed to give an answer to these questions. This review discusses these recent developments.