International standards to document remaining autonomic function after spinal cord injury

This is the first guideline describing the International Standards to document remaining Autonomic Function after Spinal Cord Injury (ISAFSCI). This guideline should be used as an adjunct to the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) including the ASIA Impairment Scale (AIS), which documents the neurological examination of individuals with SCI. The Autonomic Standards Assessment Form is recommended to be completed during the evaluation of individuals with SCI, but is not a part of the ISNCSCI. A web-based training course (Autonomic Standards Training E Program (ASTeP)) is available to assist clinicians with understanding autonomic dysfunctions following SCI and with completion of the Autonomic Standards Assessment Form (www.ASIAlearningcenter.com).

Assessment of autonomic dysfunction following spinal cord injury: rationale for additions to International Standards for Neurological Assessment

We present a preliminary report of the discussion of the joint committee of the American Spinal Injury Association (ASIA) and the International Spinal Cord Society concerning the development of assessment criteria for general autonomic function testing following spinal cord injury (SCI). Elements of this report were presented at the 2005 annual meeting of the ASIA. To improve the evaluation of neurological function in individuals with SCI and therefore better assess the effects of therapeutic interventions in the future, we are proposing a comprehensive set of definitions of general autonomic nervous system dysfunction following SCI that should be assessed by clinicians. Presently the committee recommends the recognition and assessment of the following conditions: neurogenic shock, cardiac dysrhythmias, orthostatic hypotension, autonomic dysreflexia, temperature dysregulation, and hyperhidrosis.

Aerobic exercise increases hippocampal volume and improves memory in multiple sclerosis: preliminary findings

Multiple sclerosis leads to prominent hippocampal atrophy, which is linked to memory deficits. Indeed, 50% of multiple sclerosis patients suffer memory impairment, with negative consequences for quality of life. There are currently no effective memory treatments for multiple sclerosis either pharmacological or behavioral. Aerobic exercise improves memory and promotes hippocampal neurogenesis in nonhuman animals. Here, we investigate the benefits of aerobic exercise in memory-impaired multiple sclerosis patients. Pilot data were collected from two ambulatory, memory-impaired multiple sclerosis participants randomized to non-aerobic (stretching) and aerobic (stationary cycling) conditions. The following baseline/follow-up measurements were taken: high-resolution MRI (neuroanatomical volumes), fMRI (functional connectivity), and memory assessment. Intervention was 30-minute sessions 3 times per week for 3 months. Aerobic exercise resulted in 16.5% increase in hippocampal volume and 53.7% increase in memory, as well as increased hippocampal resting-state functional connectivity. Improvements were specific, with no comparable changes in overall cerebral gray matter (+2.4%), non-hippocampal deep gray matter structures (thalamus, caudate: -4.0%), or in non-memory cognitive functioning (executive functions, processing speed, working memory: changes ranged from -11% to +4%). Non-aerobic exercise resulted in relatively no change in hippocampal volume (2.8%) or memory (0.0%), and no changes in hippocampal functional connectivity. This is the first evidence for aerobic exercise to increase hippocampal volume and connectivity and improve memory in multiple sclerosis. Aerobic exercise represents a cost-effective, widely available, natural, and self-administered treatment with no adverse side effects that may be the first effective memory treatment for multiple sclerosis patients.

Reminder: RMSSD and SD1 are identical heart rate variability metrics

Assessment of heart rate variability (HRV) is a common approach to examine cardiac autonomic nervous system modulation that has been employed in a variety of settings. Frequently, both the root mean square of successive differences (RMSSD) and SD1, which is a Poincaré plot component, have been used to quantify short-term heart rate variability. It is not typically appreciated, however, that RMSSD and SD1 are identical metrics of HRV. As a reminder to clinicians and researchers who use and study HRV, we show both empirically and mathematically that RMSSD and SD1 are identical metrics. Because the homology between RMSSD and SD1 is not commonly known, the inclusion of both measures has been reported in many recent publications. The inappropriate use of such redundant data may affect the interpretation of HRV studies. Muscle Nerve 56: 674-678, 2017.

Decentralized cardiovascular autonomic control and cognitive deficits in persons with spinal cord injury

Spinal cord injury (SCI) results in motor and sensory impairments that can be identified with the American Spinal Injury Association (ASIA) Impairment Scale (AIS). Although, SCI may disrupt autonomic neural transmission, less is understood regarding the clinical impact of decentralized autonomic control. Cardiovascular regulation may be altered following SCI and the degree of impairment may or may not relate to the level of AIS injury classification. In general, persons with lesions above T1 present with bradycardia, hypotension, and orthostatic hypotension; functional changes which may interfere with rehabilitation efforts. Although many individuals with SCI above T1 remain overtly asymptomatic to hypotension, we have documented deficits in memory and attention processing speed in hypotensive individuals with SCI compared to a normotensive SCI cohort. Reduced resting cerebral blood flow (CBF) and diminished CBF responses to cognitive testing relate to test performance in hypotensive non-SCI, and preliminary evidence suggests a similar association in individuals with SCI. Persons with paraplegia below T7 generally present with a normal cardiovascular profile; however, our group and others have documented persistently elevated heart rate and increased arterial stiffness. In the non-SCI literature there is evidence supporting a link between increased arterial stiffness and cognitive deficits. Preliminary evidence suggests increased incidence of cognitive impairment in individuals with paraplegia, which we believe may relate to adverse cardiovascular changes. This report reviews relevant literature and discusses findings related to the possible association between decentralized cardiovascular autonomic control and cognitive dysfunction in persons with SCI.

Effects of autonomic disruption and inactivity on venous vascular function

The effects of autonomic disruption and inactivity were studied on the venous vascular system. Forty-eight subjects, 24 with spinal cord injury (SCI) and 12 sedentary and 12 active able-bodied controls, participated in this study. Peripheral autonomic data were obtained to estimate sympathetic vasomotor control [low-frequency component of systolic blood pressure (LF(SBP))]. Vascular parameters were determined using strain-gauge venous occlusion plethysmography: venous capacitance (VC), venous emptying rate (VER), and total venous outflow (VO(t)). An additional vascular parameter was calculated: venous compliance [(VC/occlusion pressure) x 100]. VC and VO(t) were significantly different (SCI < sedentary < active). VER adjusted for VC was not different for any group comparison, whereas venous compliance was significantly lower in the SCI group than in the able-bodied groups and in the sedentary group compared with the active group. Regression analysis for the total group revealed a significant relationship between LF(SBP) and venous compliance (r = 0.64, P < 0.0001). After controlling for LF(SBP) through analysis of covariance, we found that mean differences for all venous vascular parameters did not change from unadjusted mean values. Our findings suggest that in subjects with SCI, the loss of sympathetic vasomotor tone contributes more than inactivity to reductions in venous vascular function. Heightened VC, VO(t), vasomotor tone, and venous compliance in the active group compared with the sedentary group imply that regular endurance training contributes to optimal venous vascular function and peripheral autonomic integrity.

Effect of pamidronate administration on bone in patients with acute spinal cord injury

Eleven subjects participated in a prospective placebo-controlled trial to address the efficacy of pamidronate in reducing bone loss in persons with acute spinal cord injury (SCI). We administered pamidronate (treatment) or normal saline (placebo) intravenously at baseline (22 to 65 days after injury) and sequentially over 12 months, with follow-up at 18 and 24 months. Regional bone mineral density (BMD) was lost over time, regardless of group. In the treatment group compared with the placebo group, we noted a mild early reduction in loss of total leg BMD. Significant bone loss from baseline occurred earlier in the placebo group at the regional sites than in the treatment group. However, by the end of the treatment and follow-up phases, both groups demonstrated a similar percent bone loss from baseline. Despite an early reduction in bone loss, pamidronate failed to prevent major, long-term bone loss in persons with acute neurologically complete SCI.

Impact of blood pressure dysregulation on health-related quality of life in persons with spinal cord injury: development of a conceptual model

OBJECTIVES

To identify medically relevant aspects of blood pressure dysregulation (BPD) related to quality of life in individuals with spinal cord injury (SCI), and to propose an integrated conceptual framework based on input from both individuals with SCI and their clinical providers. This framework will serve as a guide for the development of a patient-reported outcome (PRO) measure specifically related to BPD.

DESIGN

Three focus groups with individuals with SCI and 3 groups with SCI providers were analyzed using grounded-theory based qualitative analysis to ascertain how blood pressure impacts health-related quality of life (HRQOL) in individuals with SCI.

SETTING

Focus groups were conducted at 2 Veterans Affairs medical centers and a research center.

PARTICIPANTS

Individuals with SCI (n=27) in 3 focus groups and clinical providers (n=25) in 3 focus groups.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Not applicable.

RESULTS

Qualitative analysis indicated that all focus groups spent the highest percentage of time discussing symptoms of BPD (39%), followed by precipitators/causes of BPD (16%), preventative actions (15%), corrective actions (12%), and the impact that BPD has on social or emotional functioning (8%). While patient/consumer focus groups and provider focus groups raised similar issues, providers spent more time discussing precipitators/causes of BPD and preventative actions (38%) than patient/consumer groups (24%).

CONCLUSIONS

These results suggest that BPD uniquely and adversely impacts HRQOL in persons with SCI. While both individuals with SCI and their providers highlighted the relevant symptoms of BPD, the SCI providers offered additional detailed information regarding the precipitators/causes and what can be done to prevent/treat BPD. Further, the results suggest that persons with SCI are aware of how BPD impacts their HRQOL and are able to distinguish between subtle signs and symptoms. These findings exemplify the need for a validated and sensitive clinical measurement tool that can assess the extent to which BPD impacts HRQOL in patients with SCI.

Patterns of cognitive deficits in persons with spinal cord injury as compared with both age-matched and older individuals without spinal cord injury

Context/Objective: Cognitive deficits can impact as many as 60% of individuals with spinal cord injury (SCI). In an effort to identify the nature of cognitive deficits in SCI, we examined neuropsychological test performance in individuals with SCI, age matched healthy controls and older healthy controls.Design: Participants completed a motor-free neuropsychological test battery assessing attention, working memory, information processing speed, new learning /memory and executive control.Setting: Outpatient rehabilitation research facility.Participants: Participants included 60 individuals with chronic spinal cord injury [SCI; 32 with paraplegia (T2-T12) and 28 with tetraplegia (C3-T1)], 30 age-matched healthy controls (AMHC; 30-40 years old) and 20 older healthy controls (OHC; 50-60 years old).Outcome Measures: Wechsler Intelligence Scale - 3^rd edition (WAIS-III) Digit Span and Letter-Number Sequencing; Symbol Digit Modalities Test (SDMT) - oral version; California Verbal Learning Test-II; Paced Auditory Serial Addition Test (PASAT); Wechsler Abbreviated Scale of Intelligence (WASI); Delis-Kaplan Executive Function System; Verbal Fluency subtest.Results: Significant differences were noted between the SCI and AMHC groups on measures of information processing speed, new learning and memory, and verbal fluency. No significant differences were noted between the groups on tests of attention or working memory.Conclusion: The current study documented differences in specific realms of cognitive functioning between a chronic SCI sample and AMHC. Implications for cognitive rehabilitation and overall quality of life are discussed. Additional research is needed utilizing a more comprehensive battery of motor-free neuropsychological tests that avoid the confound of upper limb motor limitations on cognitive performance.

A small-scale clinical trial to determine the safety and efficacy of testosterone replacement therapy in hypogonadal men with spinal cord injury

Men with spinal cord injury are at an increased risk for secondary medical conditions, including metabolic disorders, accelerated musculoskeletal atrophy, and, for some, hypogonadism, a deficiency, which may further adversely affect metabolism and body composition. A prospective, open label, controlled drug intervention trial was performed to determine whether 12 months of testosterone replacement therapy increases lean tissue mass and resting energy expenditure in hypogonadal males with spinal cord injury. Healthy eugonadal (n = 11) and hypogonadal (n = 11) outpatients with chronic spinal cord injury were enrolled. Hypogonadal subjects received transdermal testosterone (5 or 10 mg) daily for 12 months. Measurements of body composition and resting energy expenditure were obtained at baseline and 12 months. The testosterone replacement therapy group increased lean tissue mass for total body (49.6 ± 7.6 vs. 53.1 ± 6.9 kg; p < 0.0005), trunk (24.1 ± 4.1 vs. 25.8 ± 3.8 kg; p < 0.005), leg (14.5 ± 2.7 vs. 15.8 ±2.6  kg; p = 0.005), and arm (7.6 ± 2.3 vs. 8.0 ± 2.2 kg; p < 0.005) from baseline to month 12. After testosterone replacement therapy, resting energy expenditure (1328 ± 262 vs. 1440 ± 262 kcal/d; p < 0.01) and percent predicted basal energy expenditure (73 ± 9 vs. 79 ± 10%; p < 0.05) were significantly increased. In conclusion, testosterone replacement therapy significantly improved lean tissue mass and energy expenditure in hypogonadal men with spinal cord injury, findings that would be expected to influence the practice of clinical care, if confirmed. Larger, randomized, controlled clinical trials should be performed to confirm and extend our preliminary findings.

Cardiac autonomic responses to progressive head-up tilt in individuals with paraplegia

Beat-to-beat fluctuations in heart rate are partially controlled by the autonomic nervous system and may be altered by a spinal cord injury. The purpose of the present investigation was to examine the role of the autonomic nervous system in modulating the heart rate response to head-up tilt (HUT) in subjects with low lesion paraplegia. Nineteen subjects with paraplegia and nine age-, height-, and weight-matched control subjects consented to participate. A three lead ECG was used to acquire heart rate (HR), cardiac sympathetic [low frequency component of R-R interval variability (LFRRI)], vagal [high frequency component of R-R interval variability (HFRRI)] and sympatho-vagal balance (LF/HF). A finger photoplethysmograph was used to assess beat-to-beat blood pressure for the estimation of sympathetic vasomotor tone [low frequency component of peak systolic blood pressure variability (LFSBP)]. The results showed a significant main effect for tilt angle for the HR response to HUT, which was comparable between the groups. LFRRI was significantly increased (P < 0.001) and HFRRI was significantly reduced (P < 0.001) across tilt angle in the control group, whereas subjects with paraplegia demonstrated no significant change in LFRRI, but significantly reduced HFRRI (P < 0.001) across tilt angle. There was a significant interaction effect for LF/HF (P < 0.05). LFSBP was significantly reduced in the group with paraplegia compared to controls (P < 0.05). These findings suggest that although cardiac autonomic control is intact, there is a blunted sympathetic response to HUT in subjects with low lesion paraplegia, which may implicate an altered baroreceptor response to acute orthostatic provocation.

Infusion of neostigmine-glycopyrrolate for bowel evacuation in persons with spinal cord injury

Defecatory complications are common after spinal cord injury (SCI) and have been attributed, in part, to an imbalance of the autonomic nervous system between parasympathetic and sympathetic effects on the colon. Because parasympathetic (i.e., cholinergic) input to the bowel may be downregulated after SCI, it was hypothesized that neostigmine, a medication that increases cholinergic tone by blocking the metabolism of acetylcholine, might promote bowel evacuation in these persons. Since neostigmine is known to cause bradycardia and bronchoconstriction, we also assessed whether these side-effects could be prevented by coadministration of neostigmine with glycopyrrolate, an anticholinergic agent that has limited activity on the muscarinic receptors of the colon. The hypothesis was tested in 13 persons with SCI in whom videofluoroscopy was carried out after instillation of a barium oatmeal paste into the rectum and descending colon. On separate days, subjects received, in a randomized, blinded design, one of three intravenous infusates (normal saline, 2 mg neostigmine, or 2 mg neostigmine + 0.4 mg glycopyrrolate). The effect of these infusates on bowel evacuation of the barium paste, heart rate, and airway resistance was determined. Both neostigmine and neostigmine + glycopyrrolate resulted in prompt bowel evacuation. The nadir heart rate was lower after neostigmine alone than with the combination. Neostigmine administration increased both total and central airway resistance, an effect that was not observed with the coadministration of glycopyrrolate. Other side-effects of neostigmine and the combination of drugs included muscle fasciculations and dry mouth, both of which were mild and short-lived. Abdominal cramping was noted in subjects with spinal cord lesions below thoracic level 10. These results indicated that neostigmine/glycopyrrolate administration is safe and well tolerated in persons with chronic SCI.

31st g. Heiner sell lectureship: secondary medical consequences of spinal cord injury

Persons with spinal cord injury (SCI) have secondary medical consequences of paralysis and/or the consequences of extreme inactivity. The metabolic changes that result from reduced activity include insulin resistance with carbohydrate disorders and dyslipidemia. A higher prevalence of coronary artery calcification was found in persons with SCI than that in matched able-bodied controls. A depression in anabolic hormones, circulating testosterone and growth hormone, has been described. Adverse soft tissue body composition changes of increased adiposity and reduced skeletal muscle are appreciated. Immobilization is the cause for sublesional disuse osteoporosis with an associated increased risk of fragility fracture. Bowel dysmotility affects all segments of the gastrointestinal tract, with an interest in better defining and addressing gastroesophageal reflux disease and difficulty with evacuation. Developing and testing more effective approaches to cleanse the bowel for elective colonoscopy are being evaluated. The extent of respiratory dysfunction depends on the level and completeness of SCI. Individuals with higher spinal lesions have both restrictive and obstructive airway disease. Pharmacological approaches and expiratory muscle training are being studied as interventions to improve pulmonary function and cough strength with the objective of reducing pulmonary complications. Persons with spinal lesions above the 6th thoracic level lack both cardiac and peripheral vascular mechanisms to maintain blood pressure, and they are frequently hypotensive, with even worse hypotension with upright posture. Persistent and/or orthostatic hypotension may predispose those with SCI to cognitive impairments. The safety and efficacy of anti-hypotensive agents to normalize blood pressure in persons with higher level cord lesions is being investigated.

A retrospective chart review of heart rate and blood pressure abnormalities in veterans with spinal cord injury

OBJECTIVE

Autonomic impairment may lead to increased prevalence of heart rate (HR) and blood pressure (BP) abnormalities in veterans with spinal cord injury (SCI). In addition, comorbid medical conditions and prescription medication use may influence these abnormalities, including bradycardia, and tachycardia, hypotension, hypertension as well as autonomic dysreflexia (AD), and orthostatic hypotension (OH).

DESIGN

A retrospective review of clinical and administrative datasets in veterans with SCI and compared the prevalence rates between clinical values and ICD-9 diagnostic codes in individuals with tetraplegia (T: C1-C8), high paraplegia (HP: T1-T6), and low paraplegia (LP: T7 and below).

RESULTS

The prevalence of clinical values indicative of a HR ≥ 80 beats per minute was higher in the HP compared to the LP and T groups. A systolic BP (SBP) ≤ 110 mmHg was more common in the T compared to the HP and LP groups, whereas the prevalence of a SBP ≥ 140 mmHg was increased in the LP compared to the HP and T groups. Diagnosis of hypertension was 39-60% whereas the diagnosis of hypotension was less than 1%. Diagnosis of AD and OH was highest in the T group, but remained below 10%, regardless of categorical lesion level. Antihypertensive medications were commonly prescribed (55%), and patients on these medications were less likely to have high BP. The odds ratio of higher SBP and DBP increased with age and body mass index (BMI).

CONCLUSION

In veterans with SCI, the prevalence of HR and BP abnormalities varied depending on level of lesion, age, BMI, and prescription medication use.

Blunted heart rate response to vagal withdrawal in persons with tetraplegia

Cardiovascular autonomic mechanisms control heart rate (HR) and determination of heart rate variability (HRV) permits the quantitative assessment of relative shifts in autonomic cardiac control during head-up tilt (HUT). The study herein used HRV techniques to determine the vagal and sympathetic contribution to the change in HR during HUT in persons with tetraplegia (T; n = 7) paraplegia (P; n = 7) and a non-spinal cord injured (non-SCI; n = 8) control group. Heart rate (HR) was continuously monitored and cardiovascular autonomic responses were assessed for 5-minutes at supine and at 45 degrees HUT. Change associated with tilt from supine to 45 degrees HUT was calculated for HR (deltaHR), high & low frequency HRV (HF & LF) and the LF/HF ratio. HR and LF power were lower in the T compared to the P and non-SCI groups at 45 degrees HUT, whereas there were no group differences for HF at 45 degrees HUT. The LF/HF ratio was lower in the T compared to the non-SCI group at 45 degrees HUT. The relationship between delta HR and delta HF response differed between groups (significant group x delta HF interaction) such that the slope of this relationship was reduced in the T (-1.026: 95% CI: -2.623 to 0.571) compared with the non-SCI (-6.985: 95% CI: -11.25 to 2.72) and P (-5.218: 95% CI: -8.197 to -2.239) groups. There was no significant interaction effect for the relationships between deltaHR and deltaLF or deltaLF/HF. In summary, although the magnitude of vagal withdrawal was comparable among the groups, the increase in HR was attenuated in the group with tetraplegia, which may reflect reduced sympathetic cardiac modulation or altered SA node responsiveness to vagal withdrawal.

Systemic and cerebral hemodynamics during cognitive testing

OBJECTIVE

Cognitive deficits are reported in 10-60% of individuals with SCI, the primary etiology of these deficits is believed to be concomitant traumatic brain injury (TBI). We recently documented diminished memory and marginally deficient attention and processing speed in individuals with SCI discordant for hypotension but matched for TBI.

METHODS

Twenty-nine individuals participated: 16 non-SCI controls, 6 paraplegic (T2-T10) and 7 tetraplegic (C4-C8). The Stroop test was used to measure cognitive function and transcranial Doppler ultrasound was used to measure cerebral blood flow (CBF) while resting (5 min) and continuously during cognitive testing. Mean arterial pressure (MAP) was calculated from three brachial blood pressures and cerebral vascular resistance index was calculated as: CVRi = MAP/CBF.

RESULTS

The paraplegia group (54 ± 6) was marginally older than the non-SCI (42 ± 15; p = 0.06) and tetraplegic (42 ± 11; p = 0.09) groups. Compared to non-SCI group, normalized t-score on the Stroop Color (SC) task was significantly lower in the paraplegic group (p < 0.05). In the tetraplegic group, MAP was significantly lower (p < 0.05) than the non-SCI and paraplegic groups, and related to SC t-score (r (2) = 0.873; p < 0.01). In the paraplegic group, CBF was reduced (p < 0.05) and CVRi increased (p < 0.05) compared to the non-SCI group, and CVRi was increased compared to the tetraplegic group (p < 0.05). A significant inverse relationship was noted between change in CVRi and SC t-score in the non-SCI group.

CONCLUSION

Asymptomatic hypotension relates to cognitive performance in persons with tetraplegia; therefore, BP normalization should be considered. The inappropriate cerebral vascular response to cognitive testing and poor test performance should be investigated in persons with paraplegia.

Arterial stiffness in persons with paraplegia

BACKGROUND

Arterial stiffness recently has been identified as an independent risk factor for cardiovascular disease. An accurate and noninvasive estimate of arterial stiffness can be made through close examination of the pulse wave contour, and is expressed as the augmentation index (AI). Increased stiffness is associated with increased systolic blood pressure (SBP), pulse pressure, and reduced baroreceptor sensitivity. The purpose of this study was to compare the common carotid AI in participants with paraplegia vs able-bodied controls as well as compare group differences for blood pressure while supine and in response to gravitational stress.

PARTICIPANTS

Study participants were 19 healthy individuals with paraplegia (below T6) and 9 able-bodied controls matched for age, height, and weight.

METHODS

An electronic tilt table was used for testing responses to gravitational stress at 4 angles (-10 degrees, 10 degrees, 35 degrees, and 75 degrees). AI was assessed at each angle of tilt using an externally applied high-fidelity strain-gauge transducer placed over the right common carotid artery.

RESULTS

AI was augmented in the group with paraplegia compared with the able-bodied group (8.0 +/- 3.9 vs 6.7 +/- 2.8, respectively; P < 0.05). Supine blood pressure and the SBP response to tilt did not differ between the groups, and there were no tilt-angle effects on SBP.

CONCLUSION

In normotensive persons with paraplegia, AI was increased significantly compared with matched able-bodied controls, which may suggest the premature development of arterial disease in this population.

A prospective report on the prevalence of heart rate and blood pressure abnormalities in veterans with spinal cord injuries

OBJECTIVE

Decentralized autonomic cardiovascular regulation may lead to increased prevalence of heart rate (HR) and blood pressure (BP) abnormalities in veterans with SCI. In addition, comorbid medical conditions and prescription medication use may increase HR and BP abnormalities. These abnormalities include bradycardia, and tachycardia, hypotension, hypertension as well as autonomic dysreflexia and orthostatic hypotension; the prevalence of which is unknown.

DESIGN

HR and BP data were measured during a routine annual physical examination in 64 veterans with SCI. Measurements of HR and BP were recorded in the seated and supine positions to document the influence of body position and to document intra-subject variability in these assessments.

RESULTS

All subjects were chronically injured (20 ± 14 years), 33 subjects were tetraplegic (T: C3-C8), nine had high paraplegia (HP: T1-T6), and 22 had low paraplegia (LP: T7-L2). Regardless of position, the prevalence of bradycardia was increased in the T group, whereas prevalence of tachycardia was increased in the HP and LP groups. Systolic hypotension was more common in the T and HP groups than the LP group and positional effects were most evident in the T group. Systolic hypertension was comparable in the T and HP groups but was twice as prevalent in the LP group. Increased prevalence of individuals with three or more medical conditions and prescribed three or more medications which might influence HR and BP was observed.

CONCLUSION

Decentralized autonomic regulation, comorbid medical conditions, and prescription medication use in veterans with SCI result in HR and BP abnormalities; our data suggest that these abnormalities vary depending on the level of injury and orthostatic positioning.

Orthostatic hypotension and orthostatic hypertension in American veterans

PURPOSE

Abnormal blood pressure (BP) response to orthostatic maneuvers may predict adverse health outcomes. Orthostatic hypotension (OH) is defined as a fall in BP of ≥20/10 mmHg, and orthostatic hypertension (OHTN) is defined as an increase in systolic BP (SBP) of ≥20 mmHg, with standing. Herein, we document the prevalence of OH and OHTN in American veterans.

METHODS

The influence of demographic characteristics, life habits, co-incident medical conditions, and prescription medication use on these prevalence rates and associations between abnormal orthostatic BP responses and severity of self-reported symptoms of fatigue, dizziness, trouble concentrating, and head and neck discomfort were determined.

RESULTS

286 veterans participated; 14 % were classified with OH, 22 % with OHTN, and 64 % with normal BP responses to standing (reference group). An increased prevalence of the diagnosis of diabetes mellitus (27 %) and hypertension (63 %) was noted, which did not differ by orthostatic BP classification. Veterans with OH were older than the reference group and were prescribed more antihypertensive medications than the reference and OHTN groups. While the prevalence of OH increased with age, the prevalence of OHTN was comparable in young (20-30 years) and old (70+ years) veterans (17 vs. 19 %, respectively). The severity of fatigue and dizziness was increased in veterans with OH and OHTN compared to the reference group.

CONCLUSION

These data suggest a relatively high prevalence of OH and OHTN, which is associated with increased self-reported severity of fatigue and dizziness in American veterans, findings which may adversely impact long-term health outcomes.

Partial angiotensin-converting enzyme inhibition during acute orthostatic stress in persons with tetraplegia

INTRODUCTION

Individuals with tetraplegia rely on the renin-angiotensin system for orthostatic blood pressure control.

OBJECTIVES

To determine the effect of partial angiotensin-converting enzyme (ACE) inhibition on heart rate (HR), active plasma renin (PR), and mean arterial blood pressure (MAP) during acute orthostasis in subjects with tetraplegia (n = 7) and nondisabled persons (n = 8).

METHODS

Subjects were instructed to avoid caffeine and alcohol for 24 hours before testing and to report to the laboratory between 10 AM and 1 PM. Progressive head-up tilt (15 degrees, 25 degrees, 35 degrees, and 45 degrees) was performed on 2 separate days; Day 1: without ACE inhibition; Day 2: after intravenous (IV) infusion of enalaprilat (0.625 mg).

RESULTS

HR was reduced during orthostasis in the tetraplegia compared with the nondisabled group (P < 0.0001), and was unaffected by ACE inhibition in either group. PR was not increased with orthostasis in either group, but was increased after ACE inhibition in both groups (P < 0.001). MAP was not affected by orthostasis in either group, but was reduced with ACE inhibition in both groups (P < 0.01). In the tetraplegia group, MAP was initially reduced after ACE inhibition, but was maintained thereafter with increasing angles of tilt, and no subject complained of symptomatic orthostatic hypotension.

CONCLUSION

Subjects with tetraplegia were tolerant of an acute bout of orthostatic stress after partial ACE inhibition. This may have clinical relevance because of the increased prevalence of type 2 diabetes mellitus in this population and the use of ACE inhibitors for the treatment of progressive renal and cardiovascular disease.

Effect of hypotensive challenge on systemic hemodynamics and cerebral blood flow in persons with tetraplegia

INTRODUCTION

Individuals with tetraplegia have impaired central control of sympathetic vascular modulation and blood pressure (BP); how this impairment affects cerebral blood flow (CBF) is unclear.

OBJECTIVES

To determine if persons with tetraplegia maintain CBF similarly to able-bodied controls after a hypotensive challenge.

METHODS

Seven individuals with chronic tetraplegia and seven age-matched, non-SCI control subjects underwent a hypotensive challenge consisting of angiotensin-converting enzyme (ACE) inhibition (1.25 mg enalaprilat) and 45 degrees head-up tilt (HUT). Heart rate (HR), low frequency systolic BP variability (LFsbp), brachial mean arterial pressure (MAP) and middle cerebral artery CBF were measured before and after the challenge. Group differences for the baseline (BL) to post-challenge response were determined by repeated measures ANOVA.

RESULTS

HR did not differ between the groups in response to the hypotensive challenge. LFsbp response was significantly reduced in the tetra compared to the control group (-38 +/- 51 vs. 72 +/- 93%, respectively). MAP did not differ between the groups at BL but was significantly lower in the tetra compared to the control group post-challenge (55 +/- 13 vs. 71 +/- 9 mmHg, respectively); the percent change in MAP was significantly greater in the tetra than in the control group (-29 +/- 14.1 vs. -13 +/- 9%, respectively). However, CBF did not differ between the groups at baseline or post-challenge; the percent change in CBF post-challenge was not different between the tetra and control groups (-29 +/- 13.2 vs. -23 +/- 10.3%, respectively).

INTERPRETATION

Despite impaired sympathetic vasomotor and BP control, CBF in persons with tetraplegia was comparable to that of control subjects during a hypotensive challenge.

Direct and reflexive effects of nitric oxide synthase inhibition on blood pressure

Direct effects of vasoactive substances on blood pressure can be examined in individuals with tetraplegia due to disruption of descending spinal pathways to sympathetic preganglionic neurons, as cervical lesions interfere with baroreceptor reflex buffering of sympathetic outflow. In this study, we assessed effects of the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (L-NAME) on mean arterial pressure, heart rate, and plasma norepinephrine concentrations in individuals with tetraplegia vs. effects shown in a neurologically intact control group. Seven individuals with tetraplegia and seven age-matched controls received, on separate visits and in the following order, placebo (30 ml normal saline) and 0.5, 1, 2, and 4 mg/kg L-NAME intravenously over 60 min. Supine hemodynamic data were collected, and blood was sampled at the end of each infusion and at 120, 180, and 240 min thereafter. L-NAME increased mean arterial pressure, and the relative increase was greater in the tetraplegia group than in the control group. Heart rate was reduced after L-NAME administration in both groups. L-NAME decreased plasma norepinephrine in the control group but not in the group with tetraplegia. These findings suggest that reflexive sympathoinhibition normally buffers the pressor response to nitric oxide synthase inhibition, an effect that is not evident in individuals with tetraplegia as a result of decentralized sympathetic vasomotor control.