Elucidating mechanisms of attenuated skin vasodilation during passive heat stress in persons with spinal cord injury

OBJECTIVE

Persons with spinal cord injury (SCI) are unable to efficiently dissipate heat via thermoregulatory vasodilation as efficiently as able-bodied persons during whole body passive heat stress (PHS). Skin blood flow (SkBF) is controlled by dual sympathetic vasomotor systems: noradrenergic vasoconstrictor (VC) nerves and cholinergic vasodilator (VD) nerves. Thus, impaired vasodilation could result from inappropriate increases in noradrenergic VC tone that compete with cholinergic vasodilation or diminished cholinergic tone. To address this issue, we used bretylium (BR) which selectively blocks neural release of norepinephrine, thereby reducing noradrenergic VC tone. If impaired vasodilation during PHS is due to inappropriate increase in VC tone, BR treatment will improve SkBF responses during PHS.

DESIGN

Prospective interventional trial.

SETTING

laboratory.

PARTICIPANTS

22 veterans with SCI.

INTERVENTIONS

Skin surface areas with previously defined intact vs. impaired thermoregulatory vasodilation were treated with BR iontophoresis with a nearby untreated site serving as control/CON. Participants underwent PHS until core temperature rose 1°C.

OUTCOME MEASURES

Laser doppler flowmeters measured SkBF over BR and CON sites in areas with impaired and intact thermoregulatory vasodilation. Cutaneous vascular conductance (CVC) was calculated for all sites. Peak-PHS CVC was normalized to baseline (BL): (CVC peak-PHS/CVC BL) to quantify SkBF change.

RESULTS

CVC rise in BR sites was significantly less than CON sites in areas with intact (P = 0.03) and impaired (P = 0.04) thermoregulatory vasodilation.

CONCLUSION

Cutaneous blockade of neural release of noradrenergic neurotransmitters affecting vasoconstriction did not enhance thermoregulatory vasodilation during PHS in persons with SCI; rather BR attenuated the response. Cutaneous blockade of neural release of noradrenergic neurotransmitters affecting vasoconstriction did not restore cutaneous active vasodilation during PHS in persons with SCI.

Are Thermoregulatory Sweating and Active Vasodilation in Skin Controlled by Separate Nerves During Passive Heat Stress in Persons With Spinal Cord Injury?

Background

Sudomotor responses (SR) and active vasodilation (AVD) are the primary means of heat dissipation during passive heat stress (PHS). It is unknown if they are controlled by a single or separate set of nerves. Older qualitative studies suggest that persons with spinal cord injury (SCI) have discordant areas of sweating and vasodilation.

Objectives

To test the hypothesis that neural control of SR and AVD is through separate nerves by measuring SR and vasodilation in persons with SCI to determine if these areas are concordant or discordant.

Methods

Nine persons with tetraplegia, 13 with paraplegia, and nine able-bodied controls underwent PHS (core temperature rise 1°C) twice. Initially, the starch iodine test measured SR post-PHS in skin surface areas surrounding the level of injury. Subsequently, laser Doppler imagery scans measured vasodilation pre- and post-PHS in areas with and without SR. Percent change in red blood cell (RBC) flux was compared in areas with and without SR.

Results

Persons with tetraplegia were anhidrotic on all areas; however, the same areas demonstrated minimal RBC flux change significantly less than equivalent able-bodied skin surface areas. In persons with paraplegia, areas of intact SR correlated with areas of RBC flux change quantitatively comparable to able-bodied persons. In anhidrotic areas, RBC flux change was significantly less than areas with SR and likely resulted from non-AVD mechanisms.

Conclusion

In persons with SCI under PHS, areas with intact SR and AVD are concordant, suggesting these two aspects of thermoregulation are controlled by a single set of nerves.

Correlation of neurological level and sweating level of injury in persons with spinal cord injury

Objective: Thermoregulatory dysfunction after spinal cord injury (SCI) impairs quality of life and predisposes persons to life-threatening sequela of heat-related illness (HRI) in conditions of high ambient temperature. SCI clinicians currently have no objective way to predict which persons are at greatest risk of HRI. Evaporative cooling via sweating is the body's most efficient mechanism of heat dissipation. The relationship between the neurological level of injury (NLOI) and the degree of sudomotor dysfunction is not well defined. This study examines the relationship between the NLOI and sweating level of injury (SwLOI). This information can assist SCI clinicians in identifying individuals with SCI who have most impaired sudomotor function and thus highest risk of HRI.Design: Observational.Setting: Human physiology laboratory.Participants: 10 persons with tetraplegia (TP), 14 with paraplegia (PP) and 10 able-bodied (AB).Intervention: Passive heat stress (1°C rise in core temperature) with sweat responses (SR) quantified with the starch iodine test.Outcome measures: The most caudal dermatomal level in which sweating was visualized was recorded as the SwLOI, which was compared to the NLOI. Minimum, maximum and median differences between NLOI and SwLOI were calculated.Results: Persons with tetraplegia demonstrated no SR. Persons with paraplegia demonstrated SR at a median of 1 level below NLOI. Able-bodied controls demonstrated sweating on all skin surface areas.Conclusions: Persons with motor complete tetraplegia lack evaporative cooling capacity through SR during passive heat stress predisposing them to HRI. Meanwhile, persons with paraplegia sweat on average 1 dermatomal level below their NLOI.

The preliminary effects of moderate aerobic training on cognitive function in people with TBI and significant memory impairment: a proof-of-concept randomized controlled trial

This single-blinded RCT investigated cognitive effects of aerobic exercise in persons with TBI-related memory impairment. Five participants . were randomly assigned to 12-weeks of either supervised moderate intensity aerobic cycling or an active control. Outcome measures included neuropsychological assessments and structural neuroimaging (MRI,). The exercise group demonstrated greater improvements on auditory verbal learning (RAVLT; d=1.54) and processing speed (SDMT; d=1.58). The exercise group showed larger increases in volume of the left hippocampus (d=1.49) and right thalamus (d=1.44). These pilot data suggest that 12-weeks of moderate intensity aerobic cycling may improve memory and processing speed in those with TBI-related memory impairments.

Pulse article: Survey on the current usage of the International Standards for the Assessment of Autonomic Function after Spinal Cord Injury (ISAFSCI)

Study design

Online questionnaire.

Objectives

To identify the awareness, and current use, of the International Standards for the Assessment of Autonomic Function after SCI (ISAFSCI) and suggest necessary revisions.

Setting

An international collaboration of committee members.

Methods

A survey was drafted and consensus achieved among members of the International Standards Committee of the ASIA. The questionnaire was posted on SurveyMonkey for 2 months. A survey link was posted on the ASIA and ISCoS websites, and committee members circulated the survey to colleagues with the goal of obtaining a wide-spread international response.

Results

A total of 173 providers responded. About half (n = 84) of the respondents used the standards in some form. Forty-four percent (n = 72) felt they knew the difference between the standards and the data sets. Among 135 responses on the usefulness of the ISAFSCI, the bladder, bowel, and sexual function sections, and the heart rate, respiratory rate, blood pressure, and sudomotor sections for use in patients with tetraplegia were reported as most useful. Comments revealed that respondents would like more explanation regarding specific definitions of components of the standards, how/when to use the ISAFSCI, and how the ISAFSCI may assist in clinical care.

Conclusion

The ISAFSCI is used by a subset of SCI clinicians. Some find the standards useful, while others are unaware of the utility of the ISAFSCI to prevent morbidity and assist in documentation of autonomic recovery post SCI. Further clarification regarding the definition of various disorders, and how and why to use the ISAFSCI in the SCI population, is needed.

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).

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.