Core Temperature Lability Predicts Sympathetic Interruption and Cognitive Performance during Heat Exposure in Persons with Spinal Cord Injuries.

Among persons with high spinal cord injury (Hi-SCI: > T5), changes in core body temperature (Tcore) and cognitive performance during heat exposure appear related to degree of sympathetic interruption. Twenty men with Hi-SCI (C4-T4, American Spinal Injury Association Impairment Scale [AIS] A-B) and 19 matched, able-bodied controls were acclimated to 27°C baseline (BL) before exposure to 35°C heat challenge (HC). Two groups, differentiated by increase in Tcore during HC, were identified: high responders (HR-SCI: ΔTcore ≥0.5°C; n = 13, C4-T2) and low responders (LR-SCI: ΔTcore <0.5°C; n = 7, C4-T4). Tcore, distal skin temperatures (Tskavg), and distal microvascular perfusion (LDFboth feet) were measured, as were indices of sympathetic integrity, mean arterial pressure (MAP), and extremity sweat rate (SRavg). Cognitive performance was assessed at BL and post-HC, using the Stroop Color and Word and Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) Digit Span tests. At BL, Tcore of the HR-SCI group (36.6 ± 0.4°C) was lower than that for the LR-SCI (37.1 ± 0.3°C; p = 0.011) and control groups (37.3 ± 0.3°C; p < 0.001). After HC, Tcore was not different among groups. MAP of the HR-SCI group (70.9 ± 9.8 mm Hg) was lower than that of the LR-SCI (81.8 ± 7.0 mm Hg; p = 0.048) and control groups (89.9 ± 9.9 mm Hg; p < 0.001). SRavg increased more in the control group (77.0 ± 52.5 nL/cm2/min) than in the HR-SCI group (15.5 ± 22.0 nL/cm2/min; p = 0.001). Only the HR-SCI group had significant increases in T-Scores of Stroop Word (7.5 ± 4.4; p < 0.001), WAIS-IV Digit Span Sequence (1.9 ± 1.8; p = 0.002), and WAIS-IV Digit Span Total (1.4 ± 1.6; p = 0.008). Persons with SCI who responded to HC with a greater change in Tcore demonstrated evidence of greater sympathetic interruption and had an associated improvement in cognitive performance.

Effect of Heat Exposure on Cognition in Persons with Tetraplegia.

Individuals with cervical spinal cord injury (SCI) have impaired thermoregulatory mechanisms attributed to interruption of motor, sensory, and autonomic neuropathways. To determine the effects of heat exposure on core body temperature (Tcore) and cognitive performance in persons with tetraplegia, 8 individuals with chronic tetraplegia (C3-C7, American Spinal Cord Injury Association Impairment Scale A-B) and 9 able-bodied controls were acclimated to 27°C at baseline (BL) before being exposed to 35°C for up to 120 min (Heat Challenge). Rectal temperature (Tcore), distal skin temperatures (Tskavg), sweat rate (QSavg), microvascular skin perfusion (LDFavg), and plasma norepinephrine (NE) were measured. Cognitive performance was assessed using Stroop Color and Word and Wechsler Adult Intelligence Scale-Fourth Edition Digit Span tests at BL and at the end of Heat Challenge. After Heat Challenge, Tcore increased 0.78 ± 0.18°C (p < 0.001) in tetraplegics after an average of 118 ± 5 min. Tcore did not change in controls after 120 min. The increase in QSavg was larger in controls than in tetraplegics (946 ± 672% vs. 51 ± 12%; p = 0.007, respectively). LDFavg increased only in controls (109 ± 93%; p = 0.008). Tskavg appeared to increase less in tetraplegics than in controls. Plasma NE levels remained lower in tetraplegics compared to controls after Heat Challenge (86 ± 64 vs. 297 ± 84 pg/mL, respectively; p < 0.001). Stroop Color, Interference, and WAIS-IV Sequence scores increased only in tetraplegics (19.4 ± 17.2%; p < 0.05, 8.3 ± 5.9%; p < 0.05, 29.1 ± 27.4%; p < 0.05, respectively). Dysfunctional thermoregulatory mechanisms in the tetraplegic group allowed Tcore to rise from subnormal levels to normothermia during heat exposure. Normothermia was associated with improvements in attention, working memory, and executive function.

Blast Exposure, White Matter Integrity, and Cognitive Function in Iraq and Afghanistan Combat Veterans.

The long-term effects of blast exposure are a major health concern for combat veterans returning from the recent conflicts in Iraq and Afghanistan. We used an optimized diffusion tensor imaging tractography algorithm to assess white matter (WM) fractional anisotropy (FA) in blast-exposed Iraq and Afghanistan veterans (n = 40) scanned on average 3.7 years after deployment/trauma exposure. Veterans diagnosed with a blast-related mild traumatic brain injury (mTBI) were compared to combat veterans with blast exposure but no TBI diagnosis. Blast exposure was associated with decreased FA in several WM tracts. However, total blast exposure did not correlate well with neuropsychological testing performance and there were no differences in FA based on mTBI diagnosis. Yet, veterans with mTBI performed worse on every neurocognitive test administered. Multiple linear regression across all blast-exposed veterans using a six-factor prediction model indicated that the amount of blast exposure accounted for 11-15% of the variability in composite FA scores such that as blast exposure increased, FA decreased. Education accounted for 10% of the variability in composite FA scores and 25-32% of FA variability in the right cingulum, such that as level of education increased, FA increased. Total blast exposure, age, and education were significant predictors of FA in the left cingulum. We did not find any effect of post-traumatic stress disorder on cognition or composite FA. In summary, our findings suggest that greater total blast exposure is a contributing factor to poor WM integrity. While FA was not associated with neurocognitive performance, we hypothesize that FA changes in the cingulum in veterans with multiple combat exposures and no head trauma prior to deployment may represent a marker of vulnerability for future deficits. Future work needs to examine this longitudinally.

Effect of Mild Cold Exposure on Cognition in Persons with Tetraplegia.

UNLABELLED: Persons with a cervical spinal cord injury (SCI) have impaired thermoregulatory mechanisms secondary to interrupted of motor, sensory, and sympathetic pathways. In this study, our primary aim was to determine the effect of cool temperature exposure on core body temperature (Tcore) and cognitive performance in persons with tetraplegia. Seven men with chronic tetraplegia (C3-C7, American Spinal Injury Association Impairment Scale [AIS] A-C) and seven able-bodied controls were exposed to 27°C temperature at baseline (BL) before being exposed to 18°C for ≤120 min (Cool Challenge). Rectal temperature (Tcore), distal skin temperatures (Tskavg), microvascular skin perfusion (LDFavg), and systolic blood pressure (SBP) were measured. Cognitive performance was assessed using Delayed Recall, Stroop Interference tests at the end of BL and Cool Challenge. After Cool Challenge, Tcore decreased -1.2±0.12°C (p<0.0001) in tetraplegics after an average of 109±15.9 min with no change in controls after 120 min. Tskavg declined in both groups, but decline was less in tetraplegics than in controls (-8.6±5.8% vs. -31.6±7.9%, respectively; p<0.0001). LDFavg declined only in controls (-72±17.9%; p<0.001). Plasma norepinephrine levels differed after Cool Challenge (tetraplegics vs. CONTROLS: 86±62 pg/mL vs. 832±431 pg/mL, respectively; p<0.01). SBP increased from BL to Cool Challenge only in controls (123±16 mm Hg to 149±17 mm Hg, respectively; p<0.01). Delayed Recall and Stroop Interference scores both declined in tetraplegics (-55±47.4%; p<0.05 and -3.9±3.8%; p<0.05, respectively), but not in controls. We conclude that persons with tetraplegia lack adequate thermoregulatory mechanisms to prevent downward drift in Tcore on exposure to cool temperatures. This decline in Tcore was associated with deterioration of working memory and executive function.