Occupational heat exposure is linked to the development of kidney injury and disease in individuals who frequently perform physically demanding work in the heat. For instance, in Central America, an epidemic of chronic kidney disease of non-traditional origin (CKDnt) is occurring among manual laborers, while potentially related epidemics have emerged in India and Sri Lanka. There is growing concern that workers in the United States suffer with CKDnt, but reports are limited. One of the leading hypotheses is that repetitive kidney injury caused by physical work in the heat can progress to CKDnt. Whether heat stress is the primary causal agent or accelerates existing underlying pathology remains contested. However, the current evidence supports that heat stress induces tubular kidney injury, which is worsened by higher core temperatures, dehydration, longer work durations, muscle damaging exercise, and consumption of beverages containing high levels of fructose. The purpose of this narrative mini review is to identify occupations that may place United States workers at greater risk of kidney injury and CKDnt. Specifically, we reviewed the scientific literature to characterize the demographics, environmental conditions, physiological strain (i.e., core temperature increase, dehydration, heart rate), and work durations in sectors typically experiencing occupational heat exposure, including farming, wildland firefighting, landscaping, and utilities. Overall, the surprisingly limited available evidence characterizing occupational heat exposure in United States workers supports the need for future investigations to understand this risk of CKDnt.
Background: Cold-water immersion impairs manual dexterity when finger temperature is below 15˚C. This exposes divers to increased risk of error. We hypothesized that whole-body active heating would maintain finger temperatures and dexterity during cold-water immersion. Methods: Twelve subjects (six males) (22±2 years old; BMI 23.9±2.5; body fat 16±6%) completed 60-minute head-out water immersion (HOWI) wearing a 7mm wetsuit and 3mm gloves in thermoneutral water (TN 25˚C) and cold water (CW 10˚C)while wearing a water-perfused suit (WP) with 37˚C water circulated over the torso, arms, and legs. Gross (Minnesota Manual Dexterity Test [MMDT]) and fine (modified Purdue Pegboard [PPT]) dexterity were assessed before, during and after immersion. Core body and skin temperatures were recorded every 10 minutes. Results: MMDT (TN -25±14%; CW -72±23%; WP -67±29%; p<0.05) and PPT (TN -16±9%; CW: -45±10%; WP: -38±13%; p<0.05) performance decreased during immersion. MMDT and PPT did not differ between CW and WP. Immediately following immersion gross dexterity was recovered in all conditions. Post-immersion fine dexterity was still impaired in CW (p<0.01), but not WP or TN. Core and skin temperatures decreased during immersion in CW and WP (p<0.05) but did not differ between CW and WP. Conclusions: Manual dexterity decreased during immersion. Dexterity was further impaired during cold-water immersion and was not maintained by water perfusion active heating. Warm water perfusion did not maintain finger temperature above 15˚C but hand temperature remained above these limits, suggesting a need to reassess thermal thresholds for working divers in cold-water conditions.
Wet bulb temperatures (Twet) during extreme heat events are commonly 31°C. Recent predictions indicate that Twet will approach or exceed 34°C. Epidemiological data indicate that exposure to extreme heat events increases kidney injury risk. We tested the hypothesis that kidney injury risk is elevated to a greater extent during prolonged exposure to Twet=34°C compared to Twet=31°C. Fifteen healthy men rested for eight hours in Twet=31 (0)°C and Twet=34 (0)°C. Insulin-like growth factor-binding protein 7 [IGFBP7], tissue inhibitor of metalloproteinase 2 [TIMP-2], and thioredoxin 1 (TRX-1) were measured from urine samples. The primary outcome was the product of IGFBP7 and TIMP-2 [IGFBP7·TIMP-2], which provided an index of kidney injury risk. Plasma interleukin-17a (IL-17a) was also measured. Data are presented at pre and after eight hours of exposure, and as mean (SD) change from preexposure. The increase in [IGFBP7·TIMP-2] was markedly greater at eight hours in the 34°C (+26.9 (27.1) [ng/mL]2/1000) compared to the 31°C (+6.2 (6.5) [ng/mL]2/1000) trial (p<0.01). Urine TRX-1, a marker of renal oxidative stress, was higher at eight hours in the 34°C (+77.6 (47.5) ng/min) compared to the 31°C (+16.2 (25.1) ng/min) trial (p<0.01). Plasma IL-17a, an inflammatory marker, was elevated at eight hours in the 34°C (+199.3 (90.0) fg/dL; p<0.01) compared to the 31°C (+9.0 (95.7) fg/dL) trial. Kidney injury risk is exacerbated during prolonged resting exposures to Twet experienced during future extreme heat events (34°C) compared to that experienced currently (31°C), likely due to oxidative stress and inflammatory processes.
Purpose: This study examined the independent effects of cold-water submersion and a rehydration strategy on an aerobic endurance performance and orthostatic tolerance following a four-hour dive in cold water (10°C). Methods: Nine male subjects completed a control (CON) performance and lower-body negative pressure test (LBNP) and two water immersion visits with either no rehydration (NR) or a post-immersion rehydration (RH) with 1 L of water. Following submersion, subjects ran to exhaustion and submitted to LBNP. Results: Core body temperature declined during submersion and remained reduced from baseline until the run (P <0.001) and was not different between NR and RH (P = 0.13). Total urine output during submersion was not different between groups (1.69 ± 0.49 (NR), 1.75 ± 0.52 (RH) L; P = 0.74) eliciting a body mass reduction of -2.2 ± 0.3 and -0.8 ± 0.3% (P < 0.01), respectively. Run duration was not different (547 ± 141 (NR), 566 ± 152 (RH) s; P = 0.79); however, both NR and RH run duration was shorter compared to CON (722 ± 170 s; P = 0.04). Cumulative stress index was suppressed in NR (534 ± 163 mmHg*min) and RH (591 ± 129 mmHg*min) compared to CON (707 ± 170 mmHg*min, P ≤ 0.03), with no differences between submersion trials (P = 0.23). Conclusions: Compared to a non-submersed state, run duration and orthostatic tolerance was reduced following a four-hour, cold-water submersion. Rehydration with 1 L of water following submersion did not offer a performance advantage over no rehydration.
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