Conditions: Heat Stress Disorders
Keywords: firefighter heat stress platelet activation aspirin
Allocation: RANDOMIZED | Intervention model: PARALLEL
Enrollment: 124
Healthy volunteers: yes

Brief summary:
The purpose of this study is to determine if aspirin taken by firefighters prevents platelets from becoming sticky when body temperature rises during work in protective clothing.

Detailed description:
Firefighters have the highest rate of line-of duty death (LODD) in the United States. More than half of these LODD are cardiovascular related occurring disproportionately around fire suppression activities. In addition, shift work, lifestyle factors, and the exposures associated with fire suppression (e.g. smoke, chemicals) may predispose the firefighter to earlier onset of heart disease or cause a pro-inflammatory state leading to endothelial dysfunction.

Fire suppression activities exacerbate cardiovascular strain and endothelial dysfunction and provide potential triggers for ischemic events (e.g. myocardial infarction, stroke). There is a rapid rise in heart rate following the activation of a fire company which may persist for as long as 20 minutes. Even in cases where heavy work is not being performed, the repetitive upper body exercise associated with tool use raises heart rate disproportionately to oxygen consumption.

Finally, there is a rapid rise in core body temperature from increased physical activity, environmental heat and impaired thermoregulation that has been shown to cause vasoconstriction and activate coagulation during heat stress (12, 13). This has recently been demonstrated in firefighters working in thermal protective clothing. The combination of triggers created during fire suppression may result in heart attack or stroke, especially in firefighters with risk factors for cardiovascular disease.

Interventions beyond basic fireground rehab may be required to minimize the effect of these triggers and enhance a firefighter's health and wellness. Fireground rehab typically focuses on cooling and rehydration of the firefighter following fire suppression or training with the assumption that these interventions will correct the underlying pathophysiology. Effective fireground rehab must deliver appropriate interventions and monitor the progress of the firefighter. While correcting hyperthermia and hypohydration are essential for continued performance, it is not clear if these therapies correct alterations in platelet or endothelial function or if other interventions are necessary to correct these physiological disturbances. Furthermore, the options for monitoring the firefighter beyond simply measuring heart and respiratory rate are limited. In our FEMA-funded Fireground Rehab Evaluation (FIRE) Trial, we demonstrated that five commercially available thermometers did not reliably measure or estimate core temperature following uncompensable heat stress (UHS) making it impossible to gauge the effectiveness of rehab interventions.

Arms:
arm 1: Two weeks of daily aspirin therapy prior to exercise, active cooling following exercise, aspirin immediately post exercise arm 2: Two weeks of daily aspirin therapy prior to exercise, active cooling following exercise, placebo immediately post exercise arm 3: Two weeks of daily aspirin therapy prior to exercise, passive cooling following exercise, aspirin immediately post exercise arm 4: Two weeks of daily aspirin therapy prior to exercise, passive cooling following exercise, placebo immediately post exercise arm 5: Two weeks of daily placebo prior to exercise, active cooling following exercise, aspirin immediately post exercise arm 6: Two weeks of daily placebo prior to exercise, active cooling following exercise, placebo immediately post exercise arm 7: Two weeks of daily placebo prior to exercise, passive cooling following exercise, aspirin immediately post exercise arm 8: Two weeks of daily placebo prior to exercise, passive cooling following exercise, placebo immediately post exercise

Interventions: intervention 1: Daily aspirin (ASA) intervention 2: Active cooling intervention 3: Acute aspirin (ASA) intervention 4: Passive cooling intervention 5: Daily placebo intervention 6: Acute placebo
Intervention descriptions: intervention 1: Two weeks 82 mg aspirin taken orally prior to exercise protocol intervention 2: Active cooling to remediate heat stress following exercise by placing hands and forearms into cold water intervention 3: 325 mg chewable aspirin administered immediately following exercise intervention 4: Removing protective garments for passive cooling following exercise intervention 5: Placebo comparator for daily aspirin therapy intervention 6: Placebo comparator for acute aspirin therapy

Protocol document: