Influence of work intensity on acute kidney injury risk during simulated occupational heat stress

Violation of the National Institute of Occupational Safety and Health (NIOSH) heat stress recommendations by exceeding the allowable wet bulb globe temperature (WBGT) for a given work intensity and work-rest ratio augments acute kidney injury (AKI) risk. Here, we tested the hypothesis that exceeding the allowable work intensity at a given WBGT and work-rest ratio would also worsen AKI risk. Twelve healthy adults completed two NIOSH recommendation compliant trials and one noncompliant trial consisting of a 4 h (half workday) exposure. Work-rest ratio was fixed at 30 min of walking and 30 min of rest each hour. Work intensity (metabolic heat production) was prescribed as a function of WBGT—412 ± 51 W [27.3 ± 0.3^̊C; high-intensity compliant (C_high)], 290 ± 75 W [31.6 ± 0.2^̊C; low-intensity compliant (C_low)], and 410 ± 61 W [31.7 ± 0.2^̊C; high-intensity noncompliant (NC_high)]. AKI risk was quantified by the product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase 2 normalized to urine specific gravity ([IGFBP7·TIMP-2]_USG). Peak core temperature was higher in NC_high trial (38.3 ± 0.4^̊C) compared with the compliant trials (C_high: 38.0 ± 0.3^̊C; C_low: 37.8 ± 0.4^̊C; P ≤ 0.0095). [IGFBP7·TIMP-2]_USG increased from preto immediately postexposure in all trials (time effect: P = 0.0454) but the peak increase was not different between trials [C_high: 0.89 ± 1.7 (ng/mL)²/1,000; C_low: 0.78 ± 1.7 (ng/mL)²/1,000; NC_high: 1.0 ± 1.4 (ng/mL)²/1,000; P = 0.7811]. Violating the NIOSH recommendations by exceeding either the allowable work intensity (i.e., NC_high vs. C_low) or WBGT (i.e., NC_high vs. C_high) resulted in a modest elevation in peak core temperature but did not modify AKI risk.