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.

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

STUDY DESIGN: Cross-sectional study. OBJECTIVES: Determine how well common clinical assessments of level and completeness of injury are correlated with symptoms of autonomic blood pressure instability and secondary medical complications after spinal cord injury (SCI). SETTING: Academic medical center, United States. METHODS: Eighty-two individuals with (n = 48) and without (n = 34) SCI had symptoms of autonomic blood pressure instability quantified with the Autonomic Dysfunction Following SCI (ADFSCI) survey. Health histories quantified the secondary medical complications through number of urinary tract infections and hospitalizations in the past year, time to complete bowel program, and lifetime pressure injuries. Regression models were completed to identify strengths of associated correlations. RESULTS: ADFSCI scores were significantly higher in individuals with SCI than controls. Neurological level of injury and ASIA impairment scale were both minimally correlated to symptoms of autonomic blood pressure instability, accounting for only 11.5% of variability in regression models. Secondary medical complications had similar, minimal correlations to level and motor/sensory completeness of SCI (R2 = 0.07 and R2 = 0.03 respectively). Contrasting this, symptoms of blood pressure instability on ADFSCI far outperformed the common clinical motor/sensory bedside exam, with moderately strong correlations to the ranked number of secondary medical complications after SCI (R2 = 0.31). CONCLUSION: Neurological level of injury and motor/sensory completeness provided limited insights into which individuals with SCI would have blood pressure instability or secondary medical complications. Interestingly, symptoms of blood pressure instability outperform the clinical motor/sensory bedside exam, with higher correlations to secondary medical complications after SCI.

Transcutaneous spinal cord stimulation and its impact on cardiovascular autonomic regulation after spinal cord injury.

Individuals with spinal cord injury (SCI) have significant dysfunction in cardiovascular autonomic regulation. Although recent findings postulate that spinal cord stimulation improves autonomic regulation, limited scope of past methods have tested only above level sympathetic activation, leaving significant uncertainty. To identify whether transcutaneous spinal cord stimulation improves cardiovascular autonomic regulation, two pairs of well-matched individuals with and without high thoracic, complete SCI were recruited. Baseline autonomic regulation was characterized with multiple tests of sympathoinhibition and above/below injury level sympathoexcitation. At three subsequent visits, testing was repeated with the addition submotor threshold transcutaneous spinal cord stimulation at three previously advocated frequencies. Uninjured controls demonstrated no autonomic deficits at baseline and had no changes with any frequency of stimulation. As expected, individuals with SCI had baseline autonomic dysfunction. In a frequency-dependent manner, spinal cord stimulation enhanced sympathoexcitatory responses, normalizing previously impaired Valsalva's maneuvers. However, stimulation exacerbated already impaired sympathoinhibitory responses, resulting in significantly greater mean arterial pressure increases with the same phenylephrine doses compared with baseline. Impaired sympathoexcitatory response below the level of injury were also further exacerbated with spinal cord stimulation. At baseline, neither individual with SCI demonstrated autonomic dysreflexia with the noxious foot cold pressor test; the addition of stimulation led to a dysreflexic response in every trial, with greater relative hypertension and bradycardia indicating no improvement in cardiovascular autonomic regulation. Collectively, transcutaneous spinal cord stimulation demonstrates no improvements in autonomic regulation after SCI, and instead likely generates tonic sympathoexcitation which may lower the threshold for dangerous autonomic dysreflexia.NEW & NOTEWORTHY Spinal cord stimulation increases blood pressure after spinal cord injury, though it is unclear if this restores natural autonomic regulation or induces a potentially dangerous pathological reflex. We performed comprehensive autonomic testing batteries, with and without transcutaneous spinal cord stimulation at multiple frequencies. Across 96 independent tests, stimulation did not change uninjured control responses, though all frequencies facilitated pathological reflexes without improved autonomic regulation for those with spinal cord injuries.

Patient Perceptions and Clinical Assessments of Cardiometabolic Disease After Subacute Spinal Cord Injury.

OBJECTIVES: To investigate the effectiveness of health care team communication regarding cardiometabolic disease (CMD) risk factors with patients with subacute spinal cord injury (SCI). DESIGN: Multi-site prospective cross-sectional study. SETTING: Five National Institute on Disability, Independent Living, and Rehabilitation Research Model SCI Rehabilitation Centers. PARTICIPANTS: Ninety-six patients with subacute SCI, aged 18-70 years, with SCI (neurologic levels of injury C2-L2, American Spinal Injury Association Impairment Scale grades A-D), and enrolled within 2 months of initial rehabilitation discharge (N=96). INTERVENTIONS: None. MAIN OUTCOME MEASURE(S): Objective risk factors of CMD (body mass index, fasting glucose, insulin, high-density lipoprotein cholesterol, triglyceride levels, and resting blood pressure). Patient reported recall of these present risk factors being shared with them by their health care team. Medications prescribed to patients to address these present risk factors were checked against guideline- assessed risk factors. RESULTS: Objective evidence of 197 CMD risk factors was identified, with patients recalling less than 12% of these (P<.0001) being shared with them by their health care team. Thirty-one individuals (32%) met criteria for a diagnosis of CMD, with only 1 of these patients (3.2%) recalling that this was shared by their health care team (P<.0001). Pharmacologic management was prescribed to address these risk factors only 7.2% of the time. CONCLUSIONS: Despite high prevalence of CMD risk factors after acute SCI, patients routinely do not recall being told of their present risk factors. Multifaceted education and professionals' engagement efforts are needed to optimize treatment for these individuals.

Diagnosis and management of cardiometabolic disease after spinal cord injury: Identifying gaps in physician training and practices.

CONTEXT: Cardiometabolic disease (CMD) frequently occurs in individuals with spinal cord injury (SCI), with growing awareness surrounding the expansive scope of this problem. As CMD has significant morbidity and mortality, early guidelines-based screening and management have been established. However, the extent to which these guidelines have been adopted are unclear. OBJECTIVE: Describe physicians' screening and management pattern for CMD in patients with SCI, as compared to SCI-specific CMD screening guidelines, and elucidate variables linked to screening and management patterns. METHODS: SCI medicine-boarded physicians were surveyed on screening timing for CMD following acute SCI, along with their practice pattern and comfort level managing common CMD risk factors. RESULTS: Of the forty-seven SCI medicine physicians that responded, 62% felt the ideal timing for CMD screening is 6 months after the acute injury. Of these same physicians, few were screening for insulin resistance and lipid dysregulation prior to 6 months after injury. In addition, less than half felt comfortable writing new prescriptions for anti-glycemic and anti-lipid medications. Furthermore, no association was found between the amount of CMD education with screening or management patterns. Finally, VA-based providers were more likely to screen for CMD within 6 months of injury and were more comfortable managing/starting anti-glycemic medications and statins. CONCLUSIONS: Despite the presence of SCI-specific CMD guidelines, gaps in screening and management practices still exist, most notably with insulin resistance and lipid dysregulation. VA-based providers generally screen and manage CMD risk factors more effectively, and further CMD education could consider emulating VA training modules.

Autonomic dysreflexia: Current pharmacologic management.

BACKGROUND: Autonomic dysreflexia (AD) is a frequent complication of spinal cord injury (SCI), though current clinical practice patterns for medication management of this condition are unknown. Correspondingly, it is unclear if national differences in practice patterns exist. OBJECTIVE: To determine trends in current pharmacologic management of AD throughout the Americas. DESIGN: International survey of current physician practice patterns. SETTING: Academic medical center. PARTICIPANTS: Sixty physicians managing patients with SCI and prescribing medications to manage AD. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Presence of a formal pharmacologic AD management protocol, first- and second-line medications, patient characteristics influencing pharmacologic management. RESULTS: The majority of physicians (69%) had a formal AD management protocol for inpatient care, with nitroglycerin ointment (82%) being the most common first-line medication. Strong national differences existed regarding the use of nitroglycerin ointment, with 98% of U.S.-based physicians using this as first-line medication and 0% of physicians in Canada or Latin America using this due to recent lack of medication availability. Only 67% of physicians had a preferred second-line medication, with preferences split between hydralazine (48%) and nifedipine (28%). A systolic blood pressure threshold for pharmacologic management was used by 56% of physicians, wheres 26% considered neurological level of injury in decisions to use medications for AD. Heart rate was used by only 5% of physicians in their decision to manage AD with medications. CONCLUSIONS: As of 2023, U.S.-based physicians caring for individuals with SCI largely have formal inpatient protocols in place for medication management of AD, with nearly all relying on nitroglycerin ointment as their first-line medication. In areas outside of the United States where nitroglycerin ointment is unavailable, pharmacologic practice patterns significantly differ.

The Impact of Transcutaneous Spinal Cord Stimulation on Autonomic Regulation after Spinal Cord Injury: A randomized crossover trial.

Importance: Individuals with spinal cord injury (SCI) have significant autonomic nervous system dysfunction. However, despite recent findings postulated to support that spinal cord stimulation improves dynamic autonomic regulation, limited scope of previous testing means the true effects remain unknown. Objective: To determine whether transcutaneous spinal cord stimulation improves dynamic autonomic regulation after SCI. Design: Single-blinded, randomized crossover trial with matched cohorts. Setting: Academic autonomic physiology laboratory. Participants: Two pairs of well-matched individuals with and without high-thoracic, complete SCI. Interventions: Sub-motor threshold transcutaneous spinal cord stimulation delivered at T10-T11 using 120Hz, 30Hz, and 30Hz with 5kHz carrier frequency at separate autonomic testing sessions. Main Outcomes and Measures: Baseline autonomic regulation was characterized with tests of above injury level sympathoexcitation (Valsalva's maneuver), sympathoinhibition (progressive doses of bolus intravenous phenylephrine), and below level sympathoexcitation (foot cold pressor test). At three subsequent visits, this testing battery was repeated with the addition of spinal cord stimulation at each frequency. Changes in autonomic regulation for each frequency were then analyzed relative to baseline testing for each individual and within matched cohorts. Results: Uninjured controls demonstrated no autonomic deficits at baseline and had no changes with any frequency of stimulation. Contrasting this, and as expected, individuals with SCI had baseline autonomic dysfunction. In a frequency-dependent manner, spinal cord stimulation enhanced sympathoexcitatory responses, normalizing previously impaired Valsalva's maneuvers. However, stimulation exacerbated already impaired sympathoinhibitory responses, resulting in significantly greater mean arterial pressure increases with the same phenylephrine doses compared to baseline. Impaired sympathoexcitatory response below the level of injury were also further exacerbated with spinal cord stimulation. At baseline, neither individual with SCI demonstrated autonomic dysreflexia with the noxious foot cold pressor test; the addition of stimulation led to a dysreflexic response in every trial, with greater relative hypertension and bradycardia indicating no improvement in autonomic regulation. Conclusions and Relevance: Transcutaneous spinal cord stimulation does not improve autonomic regulation after SCI, and instead likely generates tonic, frequency-dependent sympathoexcitation which may lower the threshold for autonomic dysreflexia.

Comparing the role of renal ultrasound vs MAG3 renal scans for evaluation of neurogenic bladder after spinal cord injury.

OBJECTIVE: Compare ability of renal ultrasound and Tc-99m mercaptoacetyltriglycine (MAG3) renal scan to identify upper urinary tract stasis. DESIGN: Retrospective chart review. SETTING: Outpatient Neuro-urology clinic serving a large SCI population. PARTICIPANTS: One hundred and sixty-five individuals with spinal cord injury, presenting for annual evaluation. INTERVENTIONS: Renal ultrasound, MAG3 renal scan. OUTCOME MEASURES: Radiologic evidence of upper urinary tract stasis as reviewed by independent radiologist. For renal ultrasounds, this included: mild hydronephrosis, dilation of collecting systems, pelviectasis, or caliectasis. For MAG3 renal scans, this included evidence of slow drainage of radioisotope, dilation of collecting systems, or reverse peristalsis. RESULTS: Forty-five individuals with spinal cord injury demonstrated upper tract stasis, with 12 identified by renal ultrasound and 43 identified by MAG3 renal scan. There was a strong relative correlation between test results (Yule's Q = 0.90), though MAG3 renal scan identified a significantly higher rate of upper tract stasis within the same patients (P < 0.0001). The odds ratio of improved identification using MAG3 renal scan was 16.5 (95% CI 3.96-68.76). CONCLUSIONS: While renal ultrasound is more effective at evaluating renal anatomy, MAG3 renal scan identifies significantly more upper urinary tract stasis than renal ultrasound and should be considered for SCI individuals with risk factors of upper tract injury.

Relationship of cardiometabolic disease risk factors with age and spinal cord injury duration.

CONTEXT/OBJECTIVES: Cardiometabolic disease (CMD) is increased after spinal cord injury (SCI), with an increased number of CMD risk factors that relate to higher mortality. The study objective was to characterize the relationship of age and injury duration with CMD. DESIGN: Retrospective cohort assessment of CMD risks using unbiased recursive partitioning to divide for group comparison: (1) Lowest Risk, (2) Moderate Risk, and (3) Highest Risk based on classification and regression trees predicting CMD diagnosis by age and injury duration. SETTING: Academic rehabilitation center laboratory. PARTICIPANTS: Adults (N = 103; aged 18-75) with traumatic SCI (C4-L2) of 3 months to 42 years duration. INTERVENTIONS: NA. OUTCOME MEASURES: CMD risk factors (obesity, insulin resistance, dyslipidemia, and hypertension) using Paralyzed Veterans of America SCI-specific guidelines. RESULTS: Obesity was prevalent (82%) and co-occurred with most other risk factors present. Age increased odds for CMD diagnosis by 1.05 per year (P = 0.02) and was directly related to elevated body mass index (BMI, ß = 0.42, P < 0.05), fasting glucose (ß = 0.58, P < 0.01), and higher systolic blood pressure (ß = 0.31, P < 0.10). In contrast, time since injury contributed to lower risk factor count (ß = -0.29, P < 0.10) and higher HDL-C (ß = 0.50, P < 0.01), and was not related to odds of CMD diagnosis. CONCLUSION: While SCI is linked to an increased risk of CMD, age is associated with higher CMD risk. Increased SCI duration related to improvement in individual CMD risk factors but did not decrease overall risk for CMD diagnosis. SCI may not uniformly increase CMD risks and highlight a necessary focus on weight management for risk prevention.

Hybrid Functional Electrical Stimulation Improves Anaerobic Threshold in First Three Years after Spinal Cord Injury.

The purpose of the present investigation was to assess the effects of whole-body exercise on the anaerobic threshold in individuals with spinal cord injury (SCI). Maximal oxygen uptake (VO2max) and oxygen uptake at anaerobic threshold (AT) were measured before and after six months of hybrid functional electrical stimulation row training in 47 participants with SCI aged 19-63, neurological levels of injury C4-L1, American Spinal Injury Association Impairment Scale grades A-D, and time since injury at enrollment from three months to 40 years. Changes in VO2max differed with time since injury, with greater increases earlier post-injury. The early chronic group (<3 years since injury; n = 31) increased VO2max from 1.65 ± 0.54 L/min at baseline to 1.83 ± 0.66 L/min at six months (p < 0.05), while the late chronic group (>3 years since injury; n = 16) did not change (1.42 ± 0.44 at baseline to 1.47 ± 0.41 L/min at six months, p = 0.36). Consistent with VO2max changes, AT increased in the early chronic group (1.03 ± 0.31 to 1.20 ± 0.40 L/min, p < 0.05) and did not change in the late chronic group (0.99 ± 0.31 to 0.99 ± 0.26 L/min, p = 0.92). Cumulative duration of exercise training was positively correlated to change in VO2max (r = 0.475, p < 0.05) but not to change in AT. Hybrid functional electrical stimulation row training is effective for increasing aerobic capacity and anaerobic threshold in individuals with SCI; however, these fitness benefits are only significant in individuals initiating the exercise intervention within three years of injury.

Methodologic implications for rehabilitation research: Differences in heart rate variability introduced by respiration.

BACKGROUND: Heart rate variability is a measure of autonomic activity that is growing in popularity as a research outcome. However, despite its increased use, the known effects of respiration on heart rate variability measures are rarely accounted for in rehabilitation medicine research, leading to potential misinterpretation. OBJECTIVE: To describe the effect that unpaced and paced breathing introduces to heart rate variability measures in a rehabilitation medicine relevant example of individuals with spinal cord injury. DESIGN: Cross-sectional comparison of heart rate variability during unpaced and paced breathing (0.25 Hz, 15 breaths per minute) within the same individuals during the same lab session. SETTING: Academic autonomic physiology laboratory. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Mean low frequency (LF) and high frequency (HF) heart rate variability power, percentage of total power derived from the LF spectrum, LF:HF ratio. RESULTS: Fifty-nine individuals with spinal cord injury completed laboratory assessments using standardized protocols (NCT02139436). In repeated measures within individuals, mean LF power was significantly higher in unpaced breathing compared to paced breathing (1292 vs. 573 ms2 , p < .001). A Bland-Altman plot demonstrated significant positive proportional bias for LF power when comparing unpaced and paced breathing conditions (R2  = 0.39). Mean HF power was similar between unpaced and paced breathing conditions, although there were wide positive and negative differences between measures, leading to notable uncertainty when respiratory confounders were not accounted for. The percentages of total power derived from the LF spectrum and the mean LF:HF ratio were both significantly higher for unpaced breathing compared to paced breathing (64 vs. 42%, p < .001; and 3.2 vs. 1.1, p < .001, respectively). CONCLUSION: Respiration has a significant effect on heart rate variability following spinal cord injury, and not accounting for this has serious consequences for accurate interpretation of unpaced data. Future studies of heart rate variability in rehabilitation medicine should accordingly consider paced breathing.

Acute Spinal Cord Injury Is Associated With Prevalent Cardiometabolic Risk Factors.

OBJECTIVES: To (1) describe the prevalence of cardiometabolic disease (CMD) at spinal cord injury (SCI) rehabilitation discharge; (2) compare this with controls without SCI; and (3) identify factors associated with increased CMD. DESIGN: Multicenter, prospective observational study. SETTING: Five National Institute on Disability, Independent Living, and Rehabilitation Research Model SCI Rehabilitation Centers. PARTICIPANTS: SCI (n=95): patients aged 18-70 years, with SCI (neurologic levels of injury C2-L2, American Spinal Injury Association Impairment Scale grades A-D), and enrolled within 2 months of initial rehabilitation discharge. Control group (n=1609): age/sex/body mass index-matched entries in the National Health and Nutrition Examination Education Survey (2016-2019) (N=1704). INTERVENTIONS: None MAIN OUTCOME MEASURES: Percentage of participants with SCI with CMD diagnosis, prevalence of CMD determinants within 2 months of rehabilitation discharge, and other significant early risk associations were analyzed using age, sex, body mass index, insulin resistance (IR) by fasting glucose and Homeostasis Model Assessment (v.2), fasting triglycerides, high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol, total cholesterol, and resting blood pressure (systolic and diastolic). RESULTS: Participants with SCI had significantly higher diastolic blood pressure and triglycerides than those without SCI, with lower fasting glucose and HDL-C. A total of 74.0% of participants with SCI vs 38.5% of those without SCI were obese when applying population-specific criteria (P<.05). Low HDL-C was measured in 54.2% of participants with SCI vs 15.4% of those without (P<.05). IR was not significantly different between groups. A total of 31.6% of participants with SCI had ≥3 CMD determinants, which was 40.7% higher than those without SCI (P<.05). Interplay of lipids and lipoproteins (ie, total cholesterol:HDL-C ratio and triglyceride:HDL-C ratio) were associated with elevated risk in participants with SCI for myocardial infarction and stroke. The only significant variable associated with CMD was age (P<.05). CONCLUSIONS: Individuals with SCI have an increased CMD risk compared with the general population; obesity, IR, and low HDL-C are the most common CMD risk determinants; age is significantly associated with early CMD.

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.

High-intensity, whole-body exercise improves blood pressure control in individuals with spinal cord injury: A prospective randomized controlled trial.

Blood pressure regulation following spinal cord injury (SCI) is often compromised due to impaired vascular sympathetic control, leading to increased reliance on cardiovagal baroreflex sensitivity to maintain pressure. Whole-body exercise improves cardiovagal baroreflex sensitivity in uninjured individuals, though has not been explored in those with SCI. Our objective was to determine changes in cardiovagal baroreflex sensitivity following 6 months of high-intensity, whole-body exercise in individuals with SCI compared to lower-intensity, arms only exercise, or waitlist. This randomized controlled trial recruited individuals with SCI aged 18-40 years old. Sixty-one individuals were randomized, with 38 completing at least one cardiovagal baroreflex sensitivity assessment. Whole-body exercise was performed with hybrid functional electrical stimulation rowing prescribed as two to three times per week, for 30-60 minutes with a target heart rate of >75% of maximum. The arms only exercise group performed upper body rowing exercise with the same prescription as whole-body exercise. Waitlist controls were not enrolled in any explicit training regimen. After 6 months, those in arms only exercise or waitlist crossed over to whole-body exercise. Cardiovagal baroreflex sensitivity was assessed via the neck suction technique at baseline and at three-month intervals thereafter. Intention to treat analysis with a structured equation model demonstrated no significant effect of waitlist control or arms only exercise on cardiovagal baroreflex sensitivity. Whole-body exercise significantly improved cardiovagal baroreflex sensitivity at 6 months for those initially randomized (p = 0.03), as well as those who crossed over from arms only exercise or waitlist control (p = 0.03 for each). However, amount of exercise performed and aerobic gains (VO2max) each poorly correlated with increases in cardiovagal baroreflex sensitivity (R2<0.15). In post-hoc analyses, individuals with paraplegia made significantly greater gains in baroreflex sensitivity compared to those with tetraplegia (p = 0.02), though gains within this group were again poorly correlated to gains in aerobic capacity. Clinicaltrials.gov number NCT02139436.

Improving hindlimb locomotor function by Non-invasive AAV-mediated manipulations of propriospinal neurons in mice with complete spinal cord injury.

After complete spinal cord injuries (SCI), spinal segments below the lesion maintain inter-segmental communication via the intraspinal propriospinal network. However, it is unknown whether selective manipulation of these circuits can restore locomotor function in the absence of brain-derived inputs. By taking advantage of the compromised blood-spinal cord barrier following SCI, we optimized a set of procedures in which AAV9 vectors administered via the tail vein efficiently transduce neurons in lesion-adjacent spinal segments after a thoracic crush injury in adult mice. With this method, we used chemogenetic actuators to alter the excitability of propriospinal neurons in the thoracic cord of the adult mice with a complete thoracic crush injury. We showed that activating these thoracic neurons enables consistent and significant hindlimb stepping improvement, whereas direct manipulations of the neurons in the lumbar spinal cord led to muscle spasms without meaningful locomotion. Strikingly, manipulating either excitatory or inhibitory propriospinal neurons in the thoracic levels leads to distinct behavioural outcomes, with preferential effects on standing or stepping, two key elements of the locomotor function. These results demonstrate a strategy of engaging thoracic propriospinal neurons to improve hindlimb function and provide insights into optimizing neuromodulation-based strategies for treating SCI.

Buspirone for functional improvement after acute traumatic spinal cord injury: a propensity score-matched cohort study.

STUDY DESIGN: Retrospective analysis of treated inpatients compared to expected neurorecovery from a propensity score-matched national database cohort. OBJECTIVE: Evaluate the effectiveness of buspirone on clinical neurorecovery following traumatic SCI when started during acute inpatient rehabilitation. SETTING: University-based hospital in Boston, USA. METHODS: Chart review yielded thirty-one individuals with acute, traumatic SCI treated with buspirone during inpatient rehabilitation from 2011-2017. Propensity score matching to a cohort of individuals from the spinal cord injury model systems (SCIMS) national database was completed. Changes in upper extremity motor score (UEMS), lower extremity motor score (LEMS), American Spinal Injury Association Impairment Scale (AIS), neurological level of injury (NLI), and functional impairment measure (FIM) from admission to discharge and discharge to 1 year were computed and compared between matched pairs (buspirone and mean national SCIMs cohort). A local control cohort not treated with buspirone was similarly compared to a matched mean national SCIMs group to identify location-specific effects. RESULTS: From admission to discharge from inpatient rehabilitation, 95% confidence intervals of changes in UEMS (-2.43 to +2.78), LEMS (-1.02 to +6.02), AIS (-0.04 to +0.35), NLI (-0.42 to +1.08), and FIM (-4.42 to +6.40) were not significantly different between those individuals who received buspirone and their propensity-matched SCIMS cohort. Similarly, changes in these metrics were not significantly different at 1-year follow up. Buspirone group individuals with initial clinically complete SCI demonstrated a higher 1-year conversion rate to incomplete injury (6 out of 14; 42.9%) compared to the matched national SCIMS cohort (14 out of 70; 21.2%, p = 0.047) though this was not significantly different from non-buspirone local controls (p = 0.25). CONCLUSIONS: Retrospective analysis shows no statistically significant difference in gross markers of neurorecovery following acute traumatic SCI when buspirone is initiated indiscriminately during acute inpatient rehabilitation. In individuals with clinically complete SCI, findings suggest possible increased rates of 1-year conversion to incomplete injury.

The effect of heart rate variability on blood pressure is augmented in spinal cord injury and is unaltered by exercise training.

PURPOSE: To define differences in heart rate and blood pressure variability (HRV/BPV) after spinal cord injury (SCI) compared with uninjured controls, and to determine whether variabilities are impacted by whole-body exercise after SCI. METHODS: Individuals with SCI (n = 40), aged 18-40, and uninjured age/sex-matched controls (n = 22) had HRV and BPV determined during supine paced (0.25 Hz) breathing. Spectral and cross-spectral values were derived for fluctuations at low (LF 0.05-0.15 Hz) and high (HF 0.20-0.30 Hz) frequencies. Thirty-two individuals with SCI further underwent either 6 months of whole-body exercise training (n = 17) or a control intervention (n = 15). RESULTS: Individuals with SCI had injuries graded A-C in severity, neurological levels of injury C1-T10. LF and HF HRV and LF BPV were significantly lower in individuals with SCI (p = 0.008-0.002), though HF BPV was similar. The LF cross-spectrum demonstrated similar phase and gain relationships between groups. The HF phase relationship between pressure and heart rate differed markedly: individuals with SCI demonstrated a -11.7 ± 3.4° phase lag (241 ± 70 ms feedback mechanism of pressure into heart rate), whereas uninjured controls demonstrated a +21.5 ± 10.8° phase lead (443 ± 224 ms feedforward mechanism of heart rate into pressure, p = 0.007). Whole-body exercise increased mean VO2peak by 2.09 ml/kg, whereas HRV, BPV, and their cross-spectral relationships were not significantly altered relative to the control intervention after SCI. CONCLUSION: After SCI, marked frequency-specific differences exist in the relationship between heart rate and blood pressure variabilities. The high-frequency cross-spectral relationship indicates that a feedback mechanism of blood pressure into heart rate may predominate in this range.

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.