Enhanced Firefighter Rehab Trial: The Role of Aspirin in Preventing Heat Stress Induced Platelet Activation

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.

Inclusion criteria

• Apparently healthy males and females aged 18-49 years

Exclusion criteria

• History of heart disease, vascular disease, or sudden death including prior MI, coronary revascularization, congenital heart disease or history of stroke
• Hypertension during screening: SBP>139 or DBP>89
• Those who are taking medications that may be expected to blunt the physiologic response to a treadmill exercise test (e.g. beta blockers)
• Prescription medication with known side effect of impaired thermoregulation
• Positive pregnancy test at any time during the study
• Resting ECG with clinical presentation suggesting coronary heart disease (e.g. pathologic Q wave)
• Known history of gastrointestinal disease or disorder i.e. diverticulitis which creates a theoretical risk of the core temperature capsule becoming lodged in the digestive tract
• Medications and supplements known to alter endothelial function (e.g. arginine, omega 3 fatty acids, NSAIDS, tobacco products. This exclusion may be disregarded for subjects willing to stop taking the supplement for the duration of the study
• At the discretion of the study physician for any other medical condition or prescription medication
• Known history of platelet dysfunction
• Aspirin allergy or intolerance