Federal agencies recommend graded exercise testing (GXT) to evaluate candidates for HAZMAT duty which involves heat stress. However, the usual Bruce Protocol (BGXT) does not create heat stress (J Invest Med 2003;51 Suppl 1:S142A) due to its brevity, and also yields many false-positive indications of coronary artery disease (CAD). We therefore devised and tested a form of thermal GXT (TGXT) in which 14 non-smoking men (age = 40 ± 11 SD, BMI = 27 ± 3, serum cholesterol = 197 ± 41, 10-yr Framingham Risk Score for CAD = 4.3% ± 2.6) walked on a treadmill for 40 ± 9 min at 3.7 mi/hr and 5-10% grade while wearing a vinyl “Sauna Suit” to limit evaporative heat loss, as do the protective suits worn in HAZMAT responses. They also wore 5 lb wrist and ankle weights to simulate field conditions (tool kits, boots). Ingested thermistors showed a rise in core temperature of 2.5 ±0.9°F (p<0.001). Ear canal temperature rose 2.2 ± 1.2°F. Sweating was profuse and heat discomfort was marked (Young Scale = 7.2 ± 0.9, vs. [4 = neutral, 8 = very hot]). Maximal blood pressure (BP), heart rate (HR and % of age-predicted maximum) and electrocardiographic (ST-seg) responses were as follows: (Table)
Conclusions This TGXT produced substantial cardiovascular and thermal stress in pilot tests whose duration matched that of the air supply provided by HAZMAT respirators. More experience is needed to assess the specificity of ST-segment changes during TGXT.
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