Heat Stress, Dehydration and Cardiovascular Responses in Sugar Cane Cutters in Brazil

Abstract

Current evidence demonstrates that the planet’s climate is warming and that extreme heat waves are occurring more frequently. Outdoor workers are vulnerable to climate changes and are subject to risk of heat-related illness. Sugar cane cutters represent a labor force that is at high risk of heat-related illness due to high physical demands, long labor hours, and use of uniforms that dissipate heat poorly. PURPOSE: To investigate heat stress, dehydration and cardiovascular responses of sugar cane cutters during a typica work shift. METHODS: Eight male sugar cane workers (27 ± 7 years) volunteered for the study. Data collection occurred on a sugar cane plantation during the spring season. An ingestible telemetric temperature sensor and a heart rate monitor were used for measuring core temperature (Tcore) and heart rate (HR), respectively, continuously. Oxygen consumption (VO2) was measured using a portable metabolic cart during the first and second half of the work shift. Urine samples were collected pre- and post-work shift. Total sweat loss was calculated using body weight change and adjusting for water ingestion and urine output. A wet-bulb globe temperature (WBGT) station was used to monitor environmental heat stress. RESULTS: Total work shift time was 6:55 ± 0:18 hr with physical work duration of 5:28 ± 0:21 hr and rest time of 1:27 ± 0:09 hr. Mean and peak Tcore during the work shift were 37.82 ± 0.31 and 38.60 ± 0.41°C, respectively. All subjects achieved Tcore above 38°C. Mean and peak HR during the work shift were 137 ± 18 and 165 ± 11 bpm, respectively. VO2 was, on average, 21.2 ± 5.4 mL·kg-1·min-1 and was not different (p=0.296) between the first (22.6 ± 3.4 mL·kg-1·min-1) and second half (21.2 ± 5.4 mL·kg-1·min-1) of the work shifts. Volunteers ingested 6.0 ± 1.0 L of fluid and experienced a total sweat loss of 7.6 ± 2.3 L. WBGT index was on average 26.8 ± 2.3°C and above the permissible heat exposure threshold of 25°C for 1 hour of heavy work. CONCLUSIONS: Sugar cane cutting is a physically demanding occupation performed in a hot environment and associated with high Tcore and fluid loss. Preventative actions such as water ingestion, adequate rest, access to shade, and physiological monitoring should be implemented to reduce the risk of heat illness, particularly with the warming global climate. Supported by CNPq (404201/2013-0).