1. Increased platelets may increase cardiac risk for up to 24-hours
Anthony Walker1,2, Toby Keene3, Ben Rattray PhD1
1Research Institute for Sport and Exercise, University of Canberra, Canberra, Australia;
2ACT Fire & Rescue Service, Canberra, Australia, 3ACT Ambulance Service, Canberra, Australia
INTRODUCTION
RESULTS
When firefighters work in the heat, they experience increases in platelet numbers (a clotting agent) which can be sustained for up to 90 minutes 1,2. The leading cause of firefighter mortality and morbidity is cardiovascular events, likely linked to this increase in platelets.
Australasian firefighters complete multi-day deployments during natural disasters and the timeline for platelet numbers to return to baseline is currently unknown in these settings. Thus the aim of this study was to assess changes 24-hrs post a simulated firefighting task in the heat.
Figure 1: Mean ± SD Tc (A) and % HR max (B) at 5-minute intervals during testing. * represents a significant difference to previous measure (p<0.05)3.
METHODS
Figure 2: Mean ± SD Platelets (A) and % leukocytes (B) pre-heat, post-heat, post+1hr and post+24hrs* represents a significant difference between time points (p<0.05) 3.
42 male urban firefighters (Table 1) completed two 20-min work tasks in the heat (100 ± 5°C) separated by a 10-min passive rest. Core temperatures (Tc) and heart rates (HR) along with platelet and leukocyte numbers were evaluated pre and directly following work and after 1 and 24 hrs of rest.
DISCUSSION
This study has shown that, when firefighters work in the heat, they sustain high Tc leading to elevated HR and changes to immune function. Increased platelet and leukocyte numbers, may lead to clotting in the blood, which combined with high heart rates is likely leading to an increased risk of a cardiac event or stroke during, and in the hours following work in the heat.
When Australasian firefighters work in multi-day deployments, the ongoing elevations in platelets in the blood shown in this study may be increasing the risk of a medical event on the fireground. Currently, only limited formal recovery protocols exist for firefighters following work in the heat which needs further study.
Table 1: Mean ± SD descriptive data of participants (n=42)
Age (yrs)
39.9 ± 8.5
Height (m)
1.8 ± 0.1
Weight (kg)
84.5 ± 8.3
Aerobic capacity (ml.kg-1.min-1)
57.3 ± 8.0
Body fat (%)
20.3 ± 7.2
References
1 Smith DL et al., (2014) Clotting and Fibrolytic changes after firefighting activities. MSSE. 46(3)
2 Hostler D et al., (2014) A Randomized controlled trial of Aspirin and Exertional Heat Stress Activation of
Platelets in Firefighters during exertion in Thermal Protective Clothing. Prehosp Emerg Care. 18(3)
3 Walker A et al., (2015) Immune and inflammatory responses of Australian firefighters after repeated exposures
to the heat. Ergonomics. In Press