Renal Considerations in the Heat Stress Recommendations

Overview

An epidemic of chronic kidney disease is occurring in laborers who undertake physical work outdoors in hot conditions. The reason for this is unknown, but may be related to kidney dysfunction caused by increases in body temperature and dehydration. The current heat stress recommendations for workers were not developed with regards for kidney health. The purpose of this study is to determine if the current recommendations protect against kidney dysfunction.

Study Type

• Study Type: Interventional
• Study Design
  • Allocation: Randomized
  • Intervention Model: Crossover Assignment
  • Primary Purpose: Basic Science
  • Masking: Double (Participant, Outcomes Assessor)
• Study Primary Completion Date: December 31, 2022

Interventions

• Other: 23.0°C WBGT – Study 1
  • For four hours, participants will walk on a treadmill to elicit 430 W of metabolic heat production in the following conditions: 23.0°C WBGT (29°C, 46% relative humidity) @ 60 min exercise per hour
• Other: 25.5°C WBGT – Study 1
  • For four hours, participants will walk on a treadmill to elicit 430 W of metabolic heat production in the following conditions: 25.5°C WBGT (31°C, 52% relative humidity) @ 45 min exercise per hour
• Other: 27.5°C WBGT – Study 1
  • For four hours, participants will walk on a treadmill to elicit 430 W of metabolic heat production in the following conditions: 27.5°C WBGT (33°C, 53% relative humidity) @ 30 min exercise per hour
• Other: 28.5°C WBGT – Study 1
  • For four hours, participants will walk on a treadmill to elicit 430 W of metabolic heat production in the following conditions: 28.5°C WBGT (34°C, 54% relative humidity) @ 15 min exercise per hour
• Other: 35.5°C WBGT – Study 1
  • For four hours, participants will walk on a treadmill to elicit 430 W of metabolic heat production in the following conditions: 35.5°C WBGT (40°C, 65% relative humidity) @ 15 min exercise per hour
• Other: 26.0°C WBGT – Study 2
  • For four hours, participants will walk on a treadmill at differing levels of metabolic heat production and environmental conditions (noted below), but at a fixed work-rest ratio of 30 minutes per hour. 26.0°C WBGT (31°C, 55% relative humidity) @ 530 W metabolic heat production
• Other: 27.5°C WBGT – Study 2
  • For four hours, participants will walk on a treadmill at differing levels of metabolic heat production and environmental conditions (noted below), but at a fixed work-rest ratio of 30 minutes per hour. 27.5°C WBGT (33°C, 53% relative humidity) @ 430 W metabolic heat production
• Other: 28.5°C WBGT – Study 2
  • For four hours, participants will walk on a treadmill at differing levels of metabolic heat production and environmental conditions (noted below), but at a fixed work-rest ratio of 30 minutes per hour. 28.5°C WBGT (34°C, 54% relative humidity) @ 330 W metabolic heat production
• Other: 30.5°C WBGT – Study 2
  • For four hours, participants will walk on a treadmill at differing levels of metabolic heat production and environmental conditions (noted below), but at a fixed work-rest ratio of 30 minutes per hour. 30.5°C WBGT (36°C, 55% relative humidity) @ 230 W metabolic heat production
• Other: 35.5°C WBGT – Study 2
  • For four hours, participants will walk on a treadmill at differing levels of metabolic heat production and environmental conditions (noted below), but at a fixed work-rest ratio of 30 minutes per hour. 35.5°C WBGT (40°C, 65% relative humidity) @ 430 W metabolic heat production

Arms, Groups and Cohorts

• Experimental: Study 1
  • Participants will walk on a treadmill at 3 mph and the grade will be adjusted to elicit 430 W of metabolic heat production (the most common work intensity). This study will systematically examine the NIOSH recommendations for prescribing work-to-rest ratios with increasing environmental heat stress (defined as Wet Bulb Globe Temperature, WBGT) at this fixed rate of metabolic heat production on kidney function.
• Experimental: Study 2
  • This study will systematically examine the NIOSH recommendations on changes in kidney function when the work-to-rest ratio is fixed at 30 min per hour (the most commonly prescribed work-to-rest ratio), but the rate of metabolic heat production and environmental heat stress differs (Figure 2). As described in Study 1, the appropriate rate of metabolic heat production will be elicited by having participants walk on a treadmill at 3 mph and the grade will be adjusted accordingly.

Clinical Trial Outcome Measures

Primary Measures

• Peak urinary [IGFBP7•TIMP-2]
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker

Secondary Measures

• Urinary NGAL
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Plasma NGAL
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Urinary IGFBP7
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Urinary TIMP-2
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Urinary IL-18
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Urinary L-FABP
  • Time Frame: through study completion, up to 20 weeks
  • Kidney injury marker
• Renal artery blood velocity
  • Time Frame: through study completion, up to 20 weeks
  • Index of kidney blood flow
• Segmental artery blood velocity
  • Time Frame: through study completion, up to 20 weeks
  • Index of kidney blood flow

Participating in This Clinical Trial

Inclusion Criteria

• Men and women – 18-44 y old – Body mass index ≤35.0 kg/m2 – Self-reported to be healthy. Exclusion Criteria:

• Not within defined age range – Estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73m2 – Deemed highly active according to the physical activity questionnaire (i.e., >3500 MET*min/wk) – Body mass index >35.0 kg/m2 – Current or history of any renal disease, heart disease, stroke, immune or autoimmune disease, and/or gastrointestinal disease/surgery – Hypertension during screening (systolic blood pressure >139 or diastolic blood pressure >89) – Using medications that blunt the physiological response to exercise (e.g., beta blockers) – Prescription medication with a known side effect of impaired temperature regulation or fluid balance (e.g., diuretics) – Positive pregnancy test at any time during the study or breast feeding – Current tobacco or electronic cigarette use or consistent use within the last 2 years – Inability to safely complete the peak oxygen uptake test

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 44 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

• Lead Sponsor
  • Indiana University
• Collaborator
  • State University of New York at Buffalo
• Provider of Information About this Clinical Study
  • Principal Investigator: Zachary J. Schlader, Associate Professor of Kinesiology – Indiana University
• Overall Contact(s)
  • Zachary J Schlader, PhD, 8128556953, zschlade@indiana.edu