Study of Thermoregulation in Exercise Heat Stroke in the Military Environment

Overview

The EXPLO-MITO study is an ancillary study from the main EXPLO-CCE study (NCT04593316; IDRCB: 2020-A01967-32). The Heat Tolerance Test (HTT) is a physiological exploration that has several advantages for use in research and clinical settings. Unlike the walk-run test, it is performed under controlled conditions, both environmentally (temperature control, humidity, etc.) and in terms of effort intensity. In addition, there are published interpretation criteria for this test allowing to characterize thermoregulation profiles and to distinguish between Heat Intolerant (HI) and Heat Tolerant (HT) patients. The reproducibility of this test and its performance in a climatic chamber allows a true comparison of thermophysiological responses (heart rate, rectal and skin temperatures, skin blood flow and sweat loss), which was not possible with the run-walk test, which was more a field test validating a physical aptitude for recovery (so-called "occupational" test) than a physiological exploration evaluating a response to stress by comparing it with the expected response in a population of young, healthy, properly trained subjects. Moreover, the HTT is a much less physiologically demanding test than the 8-km run. The HTT, which corresponds to a 2-hour walk at 5 km/h with a 2% slope at 40°C and 40% relative humidity, is a so-called "compensable" thermal stress; that is, under these conditions of exercise and environment, when the individual has normal thermoregulatory capacities, a thermal equilibrium plateau is reached during the second hour, when the individual's thermolysis capacities make it possible to compensate for the production of heat by the exercise and the gain of heat related to the environment. On average, this plateau is between 38° and 39°C. This is clearly not the case with our experience of physiological monitoring of the 8-km walk-run which rarely allows a temperature plateau to be reached and is accompanied by a temperature rise constantly above 39°C. In addition to being performed in the laboratory, this test is therefore completely safe. For all these reasons (reproducibility, relevance, predictive value of recurrence), this test has been used for more than 30 years by the Israeli army for the assessment of these cases of exercise heat stroke before their return to work. There is therefore a fair amount of published data and hindsight on the use and interest of this test. The Israeli test has the highest level of recommendation (Grade A) of all the other published heat tolerance tests. Also, the availability of a climatic chamber means that this test can now be proposed as one of the explorations available to clinicians who have to decide on the fitness of soldiers after exercise heat stroke.

Interventions

• Other Bike stress test
  This is an incremental exercise under maximal pedaling on an Excalibur® type bike with electromagnetic brake over 36 minutes during which gas exchanges are continuously measured through a face mask (Cosmed®).
• Other Heat Tolerance Test
  The test consists of a walk on a treadmill in shorts, bare chest or bra for women, at 5 km/h and 2% slope in an environment at 40°C, 40% relative humidity, without convection. During the test, rectal temperature, heart rate and skin temperature will be monitored continuously. The blood pressure will be measured manually every 30 minutes during the test.
• Other Heat nociception test
  This test consists in applying a thermal flux generated by an infrared light source on a beam of 1 cm diameter on 2 areas of the dominant lower limb (glabrous face of the forearm and thenar eminence). Participants will be instructed to remove their limb as soon as the sensation of heat begins to become uncomfortable. The time between the beginning of the stimulus and the moment of withdrawal will be recorded.

Primary outcome measures

• Percentage of heat intolerant individuals based on the Heat Tolerance Test [Time frame: Through study completion (48 months)]

Eligibility criteria

Inclusion criteria

• Be included in the main EXPLO-CCE study;
• Subject trained or re-trained at 2 aerobic sessions per week;
• At least 2 months from the exercise heat stroke experience

Exclusion criteria

• Subject with a current medication treatment (for the control group only),
• Subject with a contraindication to the ingestion of a thermal capsule, namely:

• Weight less than 37 kg
• Inflammatory, motor or obstructive disease of the digestive tract
• History of digestive surgery
• Participant requiring a CT or MRI scan prior to removal of the thermal capsule (scheduled scan)
• Presence of an implantable electronic device (e.g. pacemaker)

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Observational model

Case-control

Study locations

France · 1 center

• Institut de Recherche Biomédicale des Armées — Brétigny-sur-Orge

Identifiers

NCT: NCT05847465 · 2019PBMD03-1 · 2023-A00156-39

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗