Chemical-biological protective clothing: effects of design and initial state on physiological strain.

PURPOSE This study examined whether heat strain during low states of chemical and biological protection (CB(low)) impacted tolerance time (TT) after transition to a high state of protection (CB(high)) and whether vents in the uniform reduced heat strain during CB(low) and increased TT. METHODS There were eight men who walked at 35 degrees C in CB(low), and then transitioned to CB(high). Subjects wore fatigues in CB(low) with an overgarment during CB(high) (F+OG) or a new 1-piece (1PC) or 2PC uniform throughout CB(low) and CB(high). One condition also tested opened vents in the torso, arms, and legs of the 2PC uniform (2PC(vent)) during CB(low); these vents were closed during CB(high). Also worn were fragmentation and tactical vests and helmet. RESULTS Heart rates were reduced significantly during CB(low) for F+OG and 2PC(vent) (114 +/- 13) vs. 1 PC and 2PC (122 +/- 18). Rectal temperature (T(re)) increased least in CB(low) for F+OG (0.86 +/- 0.23 degree C) and was significantly lower for 2PC(vent) (1.02 +/- 0.25 degree C) vs. 2PC (1.11 +/- 0.27 degree C). T(re) increased rapidly during CB(high) for F+OG, which had the shortest TT (40 +/- 9 min). Increased thermal strain during CB(low) for 1PC negated its advantage in CB(high) and TT (46 +/- 21 min) was similar to F+OG. Differences in T(re) between 2PC and 2PC(vent) remained during CB(high) whereTT was increased during 2PC(vent) (74 +/- 17 min) vs. 2PC (62 +/- 19 min). CONCLUSIONS It was concluded that heat strain during CB(low) impacted TT during CB(high), and use of vents reduced heat strain during CB(low), thereby increasing TT.