Comparing Exertional Heat Illness Risk Factors Between Patients and Controls

Comparison of Novel Putative Risk Factors for Exertional Heat Illness Between a Military Patient Cohort and Matched Control Cohort During Exercise Heat Stress

The arduous nature of military training and operations require personnel to encounter high heat load, e.g., during intense physical exertion, particularly in the heat. These conditions reduce operational effectiveness and expose personnel to a risk of incapacitation and death from exertional heat illness (EHI). The primary aim of this study is to compare putative 'chronic' EHI risk factors between a cohort who have suffered a history of EHI and a control cohort with no EHI history. The secondary aim is to examine the influence of these EHI risk factors on thermoregulation during a standard heat tolerance assessment.

Study Overview

• Status: Completed
• Conditions: Exertional Heat Illness
• Intervention / Treatment: Other: Heat Tolerance Assessment

Detailed Description

Military training and operations present a risk of incapacitation and death from Exertional Heat Illness (EHI). However, widely accepted EHI risk factors are absent in almost half of all United Kingdom (UK) military EHI cases, indicating that a significant number of EHI cases in military personnel involve alternative risk factors. Risk factors for EHI can been classified along a spectrum ranging from acute (e.g. recent poor sleep) to chronic (e.g. low fitness), with the role of chronic risk factors supported by the observation that individuals who have suffered an EHI are at a substantially increased risk of subsequent EHI. The primary aim of this study is to compare putative 'chronic' EHI risk factors (e.g. composition of gastrointestinal (GI) microbiome, infection and inflammation, trait-like psychological factors) between a cohort who have suffered a history of EHI and a control cohort with no EHI history. The secondary aim is to examine the influence of these EHI risk factors on thermoregulation during a standard heat tolerance assessment.

• Study Type: Observational
• Enrollment (Actual): 95

Contacts and Locations

Study Locations

• United Kingdom
  • Hampshire
    • Portsmouth, Hampshire, United Kingdom, PO1 2UP
      • University of Portsmouth

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 40 years (Adult)
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Individuals who have experienced a recent exertional heat illness and matched controls with no previous history of exertional heat illness

Description

Inclusion Criteria:

Individuals with a history of EHI:

• Previous EHI episode
• Normal resting ECG
• Male or female
• 18 - 40 years

Control participants:

• No previous history of EHI
• Normal resting ECG
• Male or female
• 18 - 40 years

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Individuals with a history of EHI; Service personnel who have a history of EHI.	Other: Heat Tolerance Assessment; 60-90 minutes exercise in hot (34 °C; 45% R.H.) conditions at 60%VO2max
Control participants without a history of EHI; Matched control participants with no history of EHI. They will be matched to the experimental group for parameters that are known to influence thermoregulatory responses to exercise heat-stress.; Relative aerobic fitness (V̇O2max; ml∙kg-1∙min-1); Body mass (kg); Body surface area (m2); Age; Sex	Other: Heat Tolerance Assessment; 60-90 minutes exercise in hot (34 °C; 45% R.H.) conditions at 60%VO2max

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Core temperature	Measured using a rectal thermistor.	At 60 minutes (or test termination if earlier) of Heat Tolerance Assessment
Core temperature	Measured using a rectal thermistor.	Rate of rise from 30 to 60 minutes (or test termination if earlier) of Heat Tolerance Assessment
Diversity of gastrointestinal microbiota	Measured in stool sample. Assessed by alpha diversity score.	Baseline
Diversity of gastrointestinal microbiota	Measured in stool sample. Assessed by beta diversity score.	Baseline
Abundance of gastrointestinal microbiota	Measured in stool sample. Assessed at level of phylum.	Baseline
Detection of sexually transmitted pathogens	Assessed from urine sample. Measured using cobas CT/NG assays.	Baseline
Detection of respiratory pathogens	Assessed from throat swab. Measured using Allplex assays.	Baseline
Detection of gastrointestinal pathogens	Assessed from stool swab. Measured using Allplex.	Baseline
Circulating Interleukin 6	Measured using ELISA	Baseline
Circulating Interleukin 6	Measured using ELISA	Post Heat Tolerance Assessment (within 15 minutes of test end)
Circulating C-Reactive Protein	Measured using ELISA	Baseline
Circulating C-Reactive Protein	Measured using ELISA	Post Heat Tolerance Assessment (within 15 minutes of test end)
Circulating Claudin 3	Measured using ELISA	Baseline
Circulating Claudin 3	Measured using ELISA	Post Heat Tolerance Assessment (within 15 minutes of test end)
Circulating Zonulin	Measured using ELISA	Baseline
Circulating lipopolysaccharide binding protein	Measured using ELISA	Baseline
Circulating lipopolysaccharide binding protein	Measured using ELISA	Post Heat Tolerance Assessment (within 15 minutes of test end)
Circulating intestinal fatty acid binding protein	Measured using ELISA	Baseline
Circulating intestinal fatty acid binding protein	Measured using ELISA	Post Heat Tolerance Assessment (within 15 minutes of test end)
Gastrointestinal illness symptomology questionnaire	Visual analogue scale (0-10). Higher scores indicate worse symptomology	Baseline
Gastrointestinal illness symptomology questionnaire	Visual analogue scale (0-10). Higher scores indicate worse symptomology	Pre Heat Tolerance Assessment
Gastrointestinal illness symptomology questionnaire	Visual analogue scale (0-10). Higher scores indicate worse symptomology	Immediately post Heat Tolerance Assessment
Respiratory illness symptomology, measured by Jackson common cold questionnaire	Higher scores indicate worse symptomology	Baseline
Sleep quality and quantity, measured by Pittsburgh Sleep Quality Index	Higher scores indicate worse sleep	Baseline -3 days
Motivation, measured by Motivation scale		Baseline -3 days
State-trait anxiety, measured by state-trait anxiety inventory form Y-2		Baseline -3 days
Risk taking, measured by the risk-taking inventory		Baseline -3 days
Resilience, measured by the Connor-Davidson resilience scale		Baseline -3 days
Stress, measured by perceived stress scale		Baseline -3 days
Mental readiness	Visual analogue scale (0-100). Higher scores indicate a lower state of mental readiness.	Baseline
Stress	Visual analogue scale (0-100). Higher scores indicate a greater state of stress.	Baseline

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Heat rate		At 5 minute intervals during the Heat Tolerance Assessment
Thermal comfort	Modified 9 point Gagge scale. Higher scores indicate worse comfort.	At 15 minute intervals during Heat Tolerance Assessment
Thermal sensation	Modified 9 point Gagge scale. Higher scores indicate hotter sensation	At 15 minute intervals during Heat Tolerance Assessment
Rating of Perceived Exertion	6-20 Borg scale. Higher scores indicate higher perceived exertion	At 15 minute intervals during Heat Tolerance Assessment
Skin Temperature	Weighted mean skin temperature	During Heat Tolerance Assessment
Sweat rate	Determined from change in nude body mass during the heat tolerance assessment	During Heat Tolerance Assessment

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Body mass		Baseline
Relative maximal aerobic fitness	Highest value measured in ml.kg-1.min-1 during a treadmill graded exercise test.	Baseline
Urine osmolality	Measured using freezing point depression	Baseline

Collaborators and Investigators

• Sponsor: University of Portsmouth
• Collaborators: Liverpool John Moores University; Institute of Naval Medicine (UK); Public Health Wales (UK); Headquarters Army Recruiting and Initial Training Command (UK)

Study record dates

Study Major Dates

• Study Start (Actual): February 1, 2022
• Primary Completion (Actual): March 6, 2023
• Study Completion (Actual): March 6, 2023

Study Registration Dates

• First Submitted: February 3, 2022
• First Submitted That Met QC Criteria: March 21, 2022
• First Posted (Actual): March 31, 2022

Study Record Updates

• Last Update Posted (Actual): May 22, 2023
• Last Update Submitted That Met QC Criteria: May 19, 2023
• Last Verified: May 1, 2023

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Wounds and Injuries; Heat Stress Disorders
• Other Study ID Numbers: 209321

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No