Acute cardiovascular changes following heat exposure during simulated shipboard firefighting

Like structural firefighting, shipboard firefighting requires extreme exertion. However, shipboard firefighting may be a unique cardiovascular stress as most sailors lack extensive firefighting experience and may complete significant work before reaching the fire scene. Several indices of acute cardiovascular impairment have been associated with the high prevalence of sudden cardiac death among structural firefighters. However, acute cardiovascular responses to shipboard firefighting have yet to be described. The aim of this study was to investigate cardiac, macrovascular and microvascular responses to simulated shipboard firefighting. Nineteen participants donned protective equipment before completing the simulated shipboard firefighting protocol (SBFFP), which included lifting, striking and pulling tasks repeated until a stopping criterion was met (maximum heart rate, volitional fatigue, breathing air supply depleted). Echocardiography, aortic and brachial blood pressure, subendocardial viability ratio (SEVR), and reactive hyperaemia index were measured before, after and 1 h after the protocol. Immediately after SBFFP, left ventricular end diastolic and systolic diameter, brachial systolic blood pressure, SEVR, and the reactive hyperaemia index decreased (P ≤ 0.0121), while ventricular fractional shortening increased (P < 0.0001). All of these metrics returned to baseline after 1 h (P ≥ 0.0699), except SEVR, which remained decreased (P = 0.0400). There were no changes in aortic blood pressures (P ≥ 0.0671). These data represent the cardiovascular strain and subsequent impairment expected after shipboard firefighting operations, and may be mechanisms contributing to acutely increased risk of cardiac events after firefighting.