Predictors Of Microvascular Impairment After Simulated Shipboard Firefighting Tasks

Cardiac events are the leading cause of on-duty firefighter death. The reactive hyperemia index (RHI) is a metric of microvascular function and a predictor of future cardiovascular events. Inconsistent RHI responses have been reported after firefighting and may be attributed to protocols with varying exercise intensities. Systolic blood pressure response (SBPR) also predicts future cardiovascular disease but has not been studied in the context of firefighting. PURPOSE: To test the hypothesis that RHI after simulated shipboard firefighting is associated with SBPR and peak firefighting heart rate (HR). METHODS: Healthy adults (n = 17, age; 24 ± 5 y, VO2max; 44.4 ± 7.1 mL·kg-1·min-1) completed a VO2max protocol with SBPR measured at the end of the first stage (2.7 km·h-1, 10% grade). In a separate visit, the firefighting tasks were performed in protective garments and breathing apparatus and included an 80 m walk, carrying two 20 kg buckets up and down a flight of stairs (3.4 m), followed by circuits of simulated firefighting tasks (lifting, striking, and pulling) in a heated chamber (40 °C, 40 %RH). Circuits were repeated until volitional fatigue or safety stopping criteria were met. During firefighting work, peak HR was recorded. Before, immediately after, and 1 hour after firefighting work, RHI was measured. To assess the effect of SBPR and exercise intensity, participants were grouped post hoc into low, moderate, and high tertiles for SBPR and peak firefighting HR. Separate two-way RM ANOVA (tertile group by time) assessed differences in RHI responses between SBPR and peak HR groups. RESULTS: SBPR was 153 ± 21 mmHg. Peak HR during firefighting was 92 ± 4 % age-predicted max. Impaired RHI was observed in the groups with peak HR > 90 % age-predicted maximum during firefighting work (ΔRHI = -0.66 ± 0.55; p ≤ 0.03) and with SBP > 165 mmHg during the first stage of the VO2 max protocol (ΔRHI = -0.83 ± 0.64; p ≤ 0.02). Regardless of group, RHI was lower immediately after firefighting (1.41 ± 0.30) vs before and 1 h after (pre; 1.92 ± 0.49, 1 h after; 1.97 ± 0.51, p < 0.01). CONCLUSIONS: High intensity firefighting tasks which elicit HR > 90 % age-predicted HR max may lead to impaired microvascular function, even in healthy individuals. Those with higher exercise blood pressure responses may be predisposed to post-exercise microvascular impairment. Supported by: Office of Naval Research N000142312829