THE INFLUENCE OF SUDDEN VIGOROUS PHYSICAL EXERTION ON CARDIAC DEMAND UNDER AMBULATORY CONDITIONS AMONG FIREFIGHTERS

Abstract

Firefighters have a high prevalence of cardiovascular disease and its risk factors compared to the general population. The poor heart health of firefighters is implicated in their increased risk of sudden cardiac death (SCD) accounting for nearly 50% of all on-duty fatalities. Exercise may confer protective benefits against SCD in part due to the immediate blood pressure (BP) reductions of 5-8 mmHg following exercise, termed postexercise hypotension (PEH). PURPOSE: To examine the time course of PEH under ambulatory conditions after a maximal cardiopulmonary graded exercise stress test (GEST) among career firefighters. METHODS: Firefighters (n = 19) completed a maximal GEST and a non-exercise control (CONTROL) in random order on separate nonwork days and left the laboratory attached to an ambulatory BP (ABP) monitor for 19 hr. Ambulatory systolic BP (ASBP), diastolic BP (ADBP), and heart rate (AHR) were recorded at hourly intervals over 19 hr. The ambulatory rate pressure product (ARPP), an indicator of cardiac demand, was calculated as ASBPxAHRx10-3 at each hourly interval over 19 hr. Repeated measures ANCOVA tested if the ABP, AHR, and ARPP responses differed after GEST vs CONTROL over 19 hr. RESULTS: Firefighters were middle-aged (39.5 ± 8.9 yr), overweight (29.2 ± 4.0 kg/m2) men with elevated resting BP (123.1 ± 9.6/79.8 ± 10.4 mmHg), while resting HR (67.7 ± 11.3 bpm) and RPP (8.4 ± 1.7 mmHg*bpm*10-3) were in normal ranges. ASBP (16.6 ± 5.7 mmHg) and ADBP (3.1 ± 4.6 mmHg) increased after the GEST vs CONTROL over 19 hr (ps < 0.01), as did AHR (9.4 ± 7.9 bpm, p = 0.02) and ARPP (2.5 ± 1.1 mmHg*bpm*10-3, p < 0.01). CONCLUSION: Unexpectedly, the firefighters exhibited postexercise hypertension rather than PEH. The increases in ABP and AHR we observed resulted in a sustained increase in cardiac demand. Further investigation is needed to confirm our findings and determine whether the adverse hemodynamic responses we observed contribute to the high prevalence of SCD that firefighters experience on the job.