Effects of protective clothing on cardiovascular and thermal responses to heat stress

Research into the physiological impact of thermal protective clothing is dominated by field studies, limiting the number of variables that could be measured. This project sought to investigate the underlying mechanisms of heat strain in firefighters. Thus, a laboratory-based examination was undertaken, where seven males completed two trials of semi-recumbent, intermittent cycling (39.6°C, 45% relative humidity), wearing either the NSW Fire Brigades\u27 thermal protective ensemble, or shorts (control). Mean core temperature (T̄c : oesophagus, auditory canal, rectum), mean skin temperature (T̄sk) cardiac frequency (ƒc), stroke volume (Q), cardiac output (Q̇), mean arterial pressure (MAP), forearm blood flow (Q̇f), change in plasma volume (ΔPV), chest mean sweat rate (ṁsw), and overall sweat loss were measured. In the uniform trials, subjects experienced significantly shorter times to fatigue (52.5 versus 58.9 min), which occurred at lower peak work rates (204.3 versus 277.4 watts). Furthermore, greater average T̄c (37.9 versus 37.5°C) and T̄sk (37.3 versus 36.9°C) (P \u3c 0.05) were observed. Despite a greater overall gross sweat loss (923.0 versus 547.1 g.m-1·hr-1 ) in the uniform trial (P \u3c 0.05), ΔPV remained equivalent. There was a significant interaction between time and clothing on ƒc indicating that as time progressed, the effect of the uniform on ƒc became more powerful. Clothing had a significant effect on average ƒc, (133.8 versus 120.5 b·min-1 ), and average Q̇ (14.3 versus 12.2 l·min-1 ). However, there was no main effect on Q (107.5 versus 100.2 ml), indicating that the higher Q̇ was chronotropically driven. Furthermore, there was no main effect on ṁsw, or averageQ̇f. During the uniform experiment, subjects experienced greater thermal and cardiovascular strain. However, while the uniform reduced exercise tolerance, it did not affect the exercise mode, posture, or climate-specific (temperature and humidity) cardiovascular responses observed at the point of volitional fatigue. These results indicated that, when performing work at high intensities in hot conditions, homeostasis is already significantly compromised and that the additional stress imposed by the thermal protective ensemble presents a negligible, further impact upon physiological control