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.