Thermoregulation in an encapsulated environment
: Reducing thermoregulatory strain Experienced by warfighters when wearing fully encapsulating protective clothing with additional investigations of thermoregulatory control

  • Christie Nicole Garson

Student thesis: Doctoral Thesis


Operating in a hot environment when wearing clothing that is moisture vapour restrictive and thermally insulative, such as chemical and biological (CB) protective equipment, places a thermal burden on the wearer. The first two experiments addressed the general aim of this thesis, which was to quantify the thermoregulatory strain associated with wearing chemical, biological, radiological and nuclear (CBRN) individual protective equipment (IPE). CBRN IPE comprises of a suit (material of a low air permeability) and moisture vapour impermeable (MVIP) ancillary items such as a respirator, gloves and overboots, which increase insulation and impede evaporative cooling. The thermal burden associated with wearing military body armour (BA) was also quantified. Subsequent aims to investigate thermoregulatory control were explored in the third and fourth experiments. This thesis tested the general hypothesis that: improving the moisture vapour permeability (MVP) of CBRN ancillary items would alleviate thermoregulatory strain when worn in a hot, desert-like environment, and assessed whether a reduced thermoregulatory strain would be equal between the improved items.

The aim of the first study was to quantify the thermal burden imposed by each MVIP ancillary IPE, and that of the MVIP BA during exercise and recovery in a hot and dry environment. The thermal burden of each item was quantified by the measured reduction to thermoregulatory strain (internal and surface body temperature, heart rate, whole body sudomotor response and perceptual measures) when the item was not worn, thereby simulating the idealistic situation of a 100 % MVP material. To isolate only the thermal burden of the items, and not the metabolic cost associated with wearing the items, when an item was not worn a weight equivalent to the mass of the item was secured to the area from where the item had been removed. During the first experiment, at the sponsor’s request, the thermal burden of items were assessed cumulatively such that items were progressively not worn and the thermal load on the wearer gradually lessened as fewer items were worn over the different conditions. It was found that not wearing any one of the MVIP ancillary items decreased thermoregulatory strain, perception of thermoregulatory strain or both. The BA, represented by a soft armour liner (BAL) with a mass of 170 g reflecting the shape and impermeability of BA but without the weight, alleviated the greatest thermoregulatory strain on participants when not worn. This was evident by a 16.1 % (p < 0.001) improvement to the rate of whole body sweat evaporation and an enhanced rate of cooling of rectal temperature (Tre) by 0.31 ° (p < 0.05) during the 20-minute recovery period at the end of the protocol compared to the adjacent condition when the BAL was worn. Participants also felt less hot and less uncomfortable at some points during the protocol when the BAL was not worn. The least improvement to thermoregulatory strain occurred when the overboots were not worn as the only measure to be improved was a 35.2 minute (14.8 %, p < 0.05) increase to the predicted tolerance time (TT) to a Tre of 40 °C, or 28.5 minute (13.7 %, p < 0.05) improvement to a Tre of 39.5 °C. Improving the MVP of the gloves or respirator also improved whole body physiological and perceptual thermoregulatory measures to a greater degree than improving the MVP of the overboots, but to a lesser degree than the BAL.

The aim of the second study was to again quantify the thermal burden associated with each item but individually, not in a cumulative order, to obtain the true thermal burden of the item that was unaffected by reducing the overall thermal load placed on the body during later conditions, as in the first study. It was found that not wearing the gloves best alleviated thermoregulatory strain on participants, attenuating the rate of rise of Tre during continuous work by 0.37 ° (20.3 %, p < 0.001) culminating in an extended TT during continuous work by 9.2 minutes (21.3 %) in a 60-minute period (p < 0.05) compared to when the gloves were worn during the fully encapsulated condition. Perceptually, participants also felt less uncomfortable at some time points when the hands were exposed. Again, not wearing the overboots minimally reduced thermoregulatory strain. Improving the MVP of the BAL or respirator also reduced whole body thermoregulatory strain to a greater degree than improving the MVP of the overboots, but to a lesser degree than the gloves. Compared to the second study, underestimations of the thermal burden of the last items not to be worn during the first study (gloves and overboots) occurred during exercise, most likely because these items had less of a thermal load over which to demonstrate an improvement in the first study.

The first two studies highlighted that whole body thermoregulatory strain could be reduced during exercise-induced hyperthermia when wearing CBRN IPE, when only small body surface areas, such as the hands or face, were exposed, and might have influenced whole body thermoregulatory responses such as sweat rate or skin blood flow (SkBF). Thus, the aim of the third study was to determine whether exposing either the hands or the head to a hot, desert-like environment would result in the greatest change to local sweat rate (LSR) and SkBF at the torso, forearm and thigh, as well as whole body thermal perception during exercise. To isolate the influence of temperature perturbations only at the treated sites (the head or hands) on thermoregulatory responses, measures were analysed at the same mean body temperature (T̅b) during each condition. Thus, the influence of skin temperature (Tsk) from the untreated tissues (i.e. not the head or hands) on the changes to LSR and SkBF was minimal between conditions, and any differences would then be attributable to the perturbed local Tsk at the treated sites. However, no significant differences in LSR or SkBF at the torso, forearm or thigh, or whole body perceptual measures when T̅b was 37.5 °C during exercise, were identified during exposure of either the head or hands. The lack of significant findings was attributed to either thermal sensitivity being altered with the introduction of exercise or the methodological shortcomings of the study such as: the magnitude of the stimulus not being sufficient to elicit a measurable response; the equipment not being sensitive to detect small differences; or the day-to-day variations in the thermoregulatory response outweighing any measurable differences. During the third study it was noted that post-exercise, SkBF declined at all sites and LSR declined at all sites except the chest, even though T̅b remained elevated and these areas covered.

Therefore, the aim of the fourth study was to determine the influence of non-thermal mechanisms on LSR and SkBF responses post-exercise, and whether any of these mechanisms could result in the regional variations seen in the third study. It was found that as there was a homogenous sweat pattern response at regional sites (chest, back, forearm and thigh), the mechanism governing the sudomotor response was most likely systemic and was influenced by oesophageal temperature (Toe), exercise and / or posture. The regional LSR responses identified in the third study might have been due to an artifact of the confounding effects of clothing and / or mechanical pressure imposed on the sweat capsules. Further research was necessary, that standardized the duration of exercise pre-posture and clamped Toe post-exercise, to investigate the finding that the greatest decrease to LSR was during standing and sitting with the magnitude of the response being less during lying (lateral, prone and supine).

In conclusion, efficient thermoregulation is compromised in the encapsulated environment but can be improved by reducing the thermal burden of any of the ancillary items but particularly the MVIP gloves. To the sponsor, this might pose an attractive avenue for future improvements as air permeable prototype gloves have already gone through the initial product development and human testing phase as annexed in this thesis.

Overall, the general null hypothesis was rejected and the experimental hypothesis was accepted that improving the MVP of CBRN ancillary items alleviated thermoregulatory strain when exercising in a hot, desert-like environment, and that the reduced thermoregulatory strain was not equal between items.

Date of AwardMay 2016
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorJames R. House (Supervisor)

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