Physiological responses to heat stress in groundskeepers: an observational field study

The extent to which groundskeepers experience thermal and cardiovascular strain, dehydration, and accompanying declines in kidney function during work in hot-humid conditions is unknown. Demographics, thermal and cardiovascular strain, hydration, and kidney function were assessed in 20 groundskeepers (18 men; mean ± SD, age = 37.9 ± 8.4 years, body mass index = 31.5 ± 7.5 kg⋅m^-2) during work on two summer days. Before (AM) and after (PM) the work shift, resting blood pressure (BP) and heart rate (HR) were measured and urine and blood samples were collected. During the work shift, fluid intake was recorded, gastrointestinal temperature (T_GI) was recorded, and HR was recorded continuously. In 45% of participants, AM BP > 130/80 mm Hg on Day 1 and Day 2. Peak HR and T_GI achieved across both days were 143 ± 15 b·min^-1 and 37.7 ± 0.3 °C, respectively, and average peak wet bulb globe temperature was 39.1 ± 3.5 °C. On both days, urine specific gravity (U_SG = 1.021 ± 01) and urine color (U_COL = 6 ± 1) did not change across the work shift (all P > 0.28), but most subjects began with concentrated urine (62.5% U_SG ≥ 1.020 and 95% U_COL ≥ 4). Total fluid intake = 2.3 ± 1.6 L during work and consisted of 70% water, 25% sugar-sweetened beverages, 5% other. For six subjects, the average estimated glomerular filtration rate (eGFR) at AM was ≤ 60 mL·min^-1·1.73 m^-2. Five subjects had SCr increases from AM to PM ≥ 0.3 mg·dL^-1, signifying an acute kidney injury (AKI). While hyperthermia was not prevalent, subjects began and ended the workday with concentrated urine. Hypertension, obesity, and low water intake may have contributed to the overall low kidney function and AKIs observed.