Impact Of Simulated Shipboard Firefighting On Myocardial Function

Shipboard fires threaten crew safety and fleet readiness and require considerable physical exertion to contain. Sudden cardiac events are the top cause of on-duty deaths among structural firefighters and prior research indicates that firefighting can trigger these incidents. This has not been examined for shipboard firefighting. PURPOSE: Determine the effect of simulated shipboard firefighting on myocardial function. METHODS: Seventeen subjects (24 ± 5 y, 81.7 ± 14.1 kg, BMI 25.8 ± 3) were screened with the US Navy Physical Readiness Test. Subjects, in full firefighter gear and breathing apparatus, carried two 20 kg buckets down an 80 m hallway and up and down a staircase. They then performed lifting, striking, and pulling tasks in a 40 °C, 40% RH chamber until volitional fatigue, SCBA pressure ≤ 500 psi, core temperature ≥ 39.5 °C, HR reached age-predicted max twice, or continuous work was unsustainable. Left ventricular end-systolic diameter (LVESD) and end-diastolic diameter (LVEDD) were measured via ultrasound, and fractional shortening (FS) was calculated before testing (PRE), immediately post-exercise (IPE), and after a 60-minute recovery (60post). Heart rate (HR), core temperature (Tc), and blood pressure (BP) were monitored. Mean arterial pressure (MAP) was calculated. RESULTS: HR (p < 0.001), Tc (p < 0.001), and MAP (p < 0.001) increased during firefighting activities. Tc and MAP returned to PRE at 60post (p = 0.56), but HR remained elevated (p < 0.001). LVESD and FS differed between PRE and IPE (LVESD Δ = -0.56 ± .13 mm, p < 0.001; FS Δ = 12 ± 2 %, p < 0.001) and differed between IPE and 60post (LVESD Δ = 0.65 ± .11 mm, p < 0.001; FS Δ = -13 ± 2 %, p < 0.001) but did not differ between PRE and 60post. LVEDD fell between PRE and 60post (Δ = 1.17 ± 0.2 mm, p < 0.001) and IPE and 60post (Δ = 0.98 ± 0.14 mm, p < 0.001) but not differ between PRE and IPE. CONCLUSIONS: These results show that simulated shipboard firefighting imposes cardiovascular stresses similar to structural firefighting. Reduced FS IPE indicates a decrease in heart contractility. Increased LVESD and LVEDD show heightened left ventricular workload and risk of ischemia. Although these changes were transient, the findings highlight a potential increased cardiovascular risk for sailors, especially those less fit, during repeated or prolonged firefighting tasks. Supported by: Office of Naval Research N000142312829