Impact of passive heat stress on persons with spinal cord injury: Implications for Olympic spectators

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.

Heat in Germany: Health risks and preventive measures

Background

Climate change has already led to a significant temperature increase in Germany. The average temperature in the past decade was approximately 2°C above the pre-industrial level and eight of the ten hottest summers since the beginning of systematic weather records in 1881 were recorded in the last 30 years.

Methods

Based on a selective literature search and authors' own results, the article summarises the current state of knowledge on heat and its health impacts for Germany, addresses adaptation measures, and gives an outlook on implementation and research questions.

Results

Heat can aggravate pre-existing conditions such as diseases of the cardiovascular system, the respiratory tract, or the kidneys and trigger potentially harmful side effects for numerous medications. A significant increase in mortality is regularly observed during heat events. Previous approaches to mitigate the health impact of high temperatures include, for example, the heat alerts of the German Meteorological Service and recommendations for the preparation of heat-health action plans.

Conclusions

Evidence on health impacts of heat and awareness of the need for heat-related health protection have grown in recent years, but there is still a need for further action and research.

Thermophysiological aspects of wearable robotics: Challenges and opportunities

Technological advancements in the last two decades have enabled development of a variety of mechanically supporting wearable robots (i.e. exoskeletons) that are transitioning to practice in medical and industrial settings. The feedback from industry and recent controlled studies is highlighting thermal discomfort as a major reason for the disuse of the devices and a substantial barrier to their long-term adoption. Furthermore, a brief overview of the devices and their intended applications reveals that many of the potential users are likely to face thermal comfort issues because of either high exertion or medically related high heat sensitivity. The aim of this review is to discuss these emerging thermal challenges and opportunities surrounding wearable robots. This review discusses mechanisms, potential solutions, and a platform for systematically measuring heat transfer inhibition caused by wearing of an exoskeleton. Lastly, the potential for substantial metabolic rate reduction provided by exoskeletons to reduce worker thermal strain in warm-to-hot conditions is also considered.

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.