The Impact of Sleep Restriction and Simulated Physical Firefighting Work on Acute Inflammatory Stress Responses.

Alexander Wolkow,Brianna Larsen,Sally A. Ferguson,Luana C. Main,Brad Aisbett,Grace E. Vincent,Rene Lutter

doi:10.1371/journal.pone.0138128

Alexander Wolkow, Brianna Larsen + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0138128

Copy DOI

Abstract

ObjectivesThis study investigated the effect restricted sleep has on wildland firefighters’ acute cytokine levels during 3 days and 2 nights of simulated physical wildfire suppression work.MethodsFirefighters completed multiple days of physical firefighting work separated by either an 8-h (Control condition; n = 18) or 4-h (Sleep restriction condition; n = 17) sleep opportunity each night. Blood samples were collected 4 times a day (i.e., 06:15, 11:30, 18:15, 21:30) from which plasma cytokine levels (IL-6, IL-8, IL-1β, TNF-α, IL-4, IL-10) were measured.ResultsThe primary findings for cytokine levels revealed a fixed effect for condition that showed higher IL-8 levels among firefighters who received an 8-h sleep each night. An interaction effect demonstrated differing increases in IL-6 over successive days of work for the SR and CON conditions. Fixed effects for time indicated that IL-6 and IL-4 levels increased, while IL-1β, TNF-α and IL-8 levels decreased. There were no significant effects for IL-10 observed.ConclusionFindings demonstrate increased IL-8 levels among firefighters who received an 8-h sleep when compared to those who had a restricted 4-h sleep. Firefighters’ IL-6 levels increased in both conditions which may indicate that a 4-h sleep restriction duration and/or period (i.e., 2 nights) was not a significant enough stressor to affect this cytokine. Considering the immunomodulatory properties of IL-6 and IL-4 that inhibit pro-inflammatory cytokines, the rise in IL-6 and IL-4, independent of increases in IL-1β and TNF-α, could indicate a non-damaging response to the stress of simulated physical firefighting work. However, given the link between chronically elevated cytokine levels and several diseases, further research is needed to determine if firefighters’ IL-8 and IL-6 levels are elevated following repeated firefighting deployments across a fire season and over multiple fire seasons.

Highlights

Each year, firefighters are deployed to combat the threat of large wildfires to property and lives
The primary findings for cytokine levels revealed a fixed effect for condition that showed higher IL-8 levels among firefighters who received an 8-h sleep each night
Fixed effects for time indicated that IL-6 and IL-4 levels increased, while IL-1β, Tumour Necrosis Factor (TNF)-α and IL-8 levels decreased

Summary

Introduction

Firefighters are deployed to combat the threat of large wildfires to property and lives These deployments can last multiple days and require firefighters to perform extended hours (i.e., 12 to 15 h) of intense, intermittent, physical work with restricted sleep opportunities between shifts (i.e., 3 to 6 h) [1, 2, 3]. IL-6 and IL-4 cytokines display both pro- and anti-inflammatory activities that modulate inflammation [12,13,14,15]. Together, these processes coordinate the body's acute inflammatory response to a stressor to maintain homeostasis of the immune system. Severe or chronic stress exposure may exacerbate the immune response resulting in chronically elevated cytokine levels and associated adverse health outcomes [9, 16]

Objectives

Methods

Discussion

Conclusion