Exploring daily blood pressure fluctuations and cardiovascular risk among individuals with motor complete spinal cord injury: a pilot study

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 (R 2 =0.008) or baroreflex sensitivity (R 2 =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.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Toward rebalancing blood pressure instability after spinal cord injury with spinal cord electrical stimulation: A mini review and critique of the evolving literature

High-level spinal cord injury commonly leads to blood pressure instability. This manifests clinically as orthostatic hypotension (OH), where blood pressure can drop to the point of loss of consciousness, and autonomic dysreflexia (AD), where systolic blood pressure can climb to over 300 mmHg in response to an unperceived noxious stimulus. These blood pressure fluctuations can occur multiple times a day, contributing to increased vessel shear stress and heightened risk of cardiovascular disease. The pathophysiology of both of these conditions is rooted in impairments in regulation of spinal cord sympathetic preganglionic neurons, which control blood pressure by mediating vascular resistance and catecholamine release. Recently, spinal cord electrical stimulation has provided evidence that it may modulate these blood pressure imbalances. Early proposed mechanisms suggest activation of spinal cord dorsal horn neurons that ultimately act upon the sympathetic preganglionic neuronal pathways. For OH, spinal cord stimulation likely induces local activation of these neurons to generate baseline sympathetic tone and accompanying vasoconstriction. The mechanisms for spinal stimulation regulating AD are less clear, though some suggest it activates inhibitory circuits to dampen the overactive sympathetic response. While questions remain, spinal cord electrical stimulation is an intriguing new modality that may restore blood pressure regulation following spinal cord injury.

Diastolic blood pressure changes during episodes of autonomic dysreflexia

Objective: The current diagnostic criteria of autonomic dysreflexia (AD) is based solely on systolic blood pressure (SBP) increases from baseline without regard to changes in diastolic blood pressure (DBP). During urodynamics in persons with SCI at or above the sixth thoracic level (T6), we evaluated diastolic blood pressure (DBP) changes related with AD episodes.Design: Retrospective review of blood pressures recorded during urodynamics.Setting: Outpatient SCI urology program in a free standing rehabilitation center.Participants: Persons with spinal cord injury at or above the T6 level.Interventions: Urodynamic procedures performed between August 2018 to January 2019, as well as their prior testing for up to 10 years.Outcome Measures: Systolic and diastolic blood pressures were recorded during the procedure and episodes of AD defined as SBP >20 mmHg above baseline.Results: Seventy individuals accounting for 282 urodynamic tests were reviewed. AD occurred in 43.3% (122/282) of all urodynamics tests. The mean maximum SBP and DBP increase from baseline for those with AD were 35.5 ± 10.9 mmHg and 19.0±9.4 mmHg, respectively. There was a concomitant rise of DBP >10 mmHg with a SBP rise of >20 mmHg in 76.2% (93/122) of urodynamic tests. An elevation of DBP >10 mmHg was recorded in 23.8% (38/160) of urodynamics that did not have AD by the SBP definition.Conclusion: DBP increments of >10 mmHg with concurrent SBP increases of >20 mmHg occurs in the majority of AD episodes. Given the significance of cardiovascular complications in chronic SCI, further work is warranted to determine the significance of DBP elevations for defining AD.

Blood Pressure Instability in Persons With SCI: Evidence From a 30-Day Home Monitoring Observation

BACKGROUND

To determine the degree of blood pressure instability over a 30-day home observation in participants with spinal cord injury grouped by level of injury pertaining to cardiovascular autonomic regulation.

METHODS

This is an observational study completed at the Kessler Foundation and James J. Peters Veterans Medical Center. Seventy-two participants with tetraplegia (C1-T1), 13 with high thoracic (T2-T4), and 28 with low thoracic (T5-T12) injury participated in this study. Participants were asked to record their blood pressure using an ambulatory blood pressure monitor three times a day for 30 days.

RESULTS

The number of blood pressure fluctuations was significantly increased in the tetraplegia group compared with the paraplegia groups. Age and duration of injury contributed to an increase in the observation of 30-day blood pressure instability; however, completeness of injury did not.

CONCLUSION

The data indicate significant blood pressure instability that may not be exclusive to persons with tetraplegia; in fact, individuals with low thoracic injuries demonstrated severe blood pressure fluctuations. The use of a monitor at home for an extended period may help document dangerous and extreme fluctuations in blood pressure and should be considered an important adjunctive clinical practice for tracking of the secondary consequences in the spinal cord injury population.

Intravesical lidocaine decreases autonomic dysreflexia when administered prior to catheter change

OBJECTIVE

To evaluate the role of intravesical lidocaine in preventing autonomic dysreflexia (AD) during routine catheter changes in individuals with spinal cord injury (SCI) at T6 or above.

DESIGN

Prospective observational cohort study.

SETTING

Outpatient urology clinic.

PARTICIPANTS

Fifty consecutive individuals with SCI at or above T6 and a history of AD having a routine indwelling catheter change.

INTERVENTIONS

A treatment group of individuals received 10 ml of 2% lidocaine administered into the existing catheter 4-6 minutes prior to catheter change. The control group had the same amount of lidocaine administered into the urethra or suprapubic tract after removing the old catheter and immediately prior to inserting the new catheter (due to the delayed onset of action of the anesthetic, this was assumed to have no initial effect). Systolic blood pressures (SBP) were measured immediately after catheter insertion and then every 30-45 seconds for 5 minutes.

OUTCOME MEASURES

Incidence and magnitude of AD as determined by SBP following catheter change.

RESULTS

The incidence of AD in the lidocaine treatment group was 14.8% vs 47.8% in the control group (P = .011). Pretreatment with lidocaine also demonstrated a significantly attenuated rise in SBP immediately after the catheter change (9.5 mmHg vs 26.9 mmHg for post-treatment, P = .014) relative to baseline SBP.

CONCLUSION

In individuals with SCI at risk of AD, pretreatment with intravesical lidocaine prior to catheter change significantly decreased both the incidence and magnitude of AD. This suggests that pretreatment with intravesical lidocaine is helpful in individuals with SCI who are prone to AD.

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.