Alexander Wolkow

Sleep restriction during simulated wildfire suppression: Effect on physical task performance

Objectives To examine the effects of sleep restriction on firefighters’ physical task performance during simulated wildfire suppression. Methods Thirty-five firefighters were matched and randomly allocated to either a control condition (8-hour sleep opportunity, n = 18) or a sleep restricted condition (4-hour sleep opportunity, n = 17). Performance on physical work tasks was evaluated across three days. In addition, heart rate, core temperature, and worker activity were measured continuously. Rate of perceived and exertion and effort sensation were evaluated during the physical work periods. Results There were no differences between the sleep-restricted and control groups in firefighters’ task performance, heart rate, core temperature, or perceptual responses during self-paced simulated firefighting work tasks. However, the sleep-restricted group were less active during periods of non-physical work compared to the control group. Conclusions Under self-paced work conditions, 4 h of sleep restriction did not adversely affect firefighters’ performance on physical work tasks. However, the sleep-restricted group were less physically active throughout the simulation. This may indicate that sleep-restricted participants adapted their behaviour to conserve effort during rest periods, to subsequently ensure they were able to maintain performance during the firefighter work tasks. This work contributes new knowledge to inform fire agencies of firefighters’ operational capabilities when their sleep is restricted during multi-day wildfire events. The work also highlights the need for further research to explore how sleep restriction affects physical performance during tasks of varying duration, intensity, and complexity.

The impact of sleep restriction and simulated physical firefighting work on acute inflammatory stress responses

Objectives This 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. Methods Firefighters 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. Results 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. 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. Conclusion Findings 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.

Effects of work-related sleep restriction on acute physiological and psychological stress responses and their interactions: A review among emergency service personnel.

Emergency work can expose personnel to sleep restriction. Inadequate amounts of sleep can negatively affect physiological and psychological stress responses. This review critiqued the emergency service literature (e.g., firefighting, police/law enforcement, defense forces, ambulance/paramedic personnel) that has investigated the effect of sleep restriction on hormonal, inflammatory and psychological responses. Furthermore, it investigated if a psycho-physiological approach can help contextualize the significance of such responses to assist emergency service agencies monitor the health of their personnel. The available literature suggests that sleep restriction across multiple work days can disrupt cytokine and cortisol levels, deteriorate mood and elicit simultaneous physiological and psychological responses. However, research concerning the interaction between such responses is limited and inconclusive. Therefore, it is unknown if a psycho-physiological relationship exists and as a result, it is currently not feasible for agencies to monitor sleep restriction related stress based on psycho- physiological interactions. Sleep restriction does however, appear to be a major stressor contributing to physiological and psychological responses and thus, warrants further investigation.

Multiple Days of Heat Exposure on Firefighters’ Work Performance and Physiology

This study assessed the accumulated effect of ambient heat on the performance of, and physiological and perceptual responses to, intermittent, simulated wildfire fighting tasks over three consecutive days. Firefighters (n = 36) were matched and allocated to either the CON (19°C) or HOT (33°C) condition. They performed three days of intermittent, self-paced simulated firefighting work, interspersed with physiological testing. Task repetitions were counted (and converted to distance or area) to determine work performance. Participants were asked to rate their perceived exertion and thermal sensation after each task. Heart rate, core temperature (Tc), and skin temperature (Tsk) were recorded continuously throughout the simulation. Fluids were consumed ad libitum. Urine volume was measured throughout, and urine specific gravity (USG) analysed, to estimate hydration. All food and fluid consumption was recorded. There was no difference in work output between experimental conditions. However, significant variation in performance responses between individuals was observed. All measures of thermal stress were elevated in the HOT, with core and skin temperature reaching, on average, 0.24 ± 0.08°C and 2.81 ± 0.20°C higher than the CON group. Participants’ doubled their fluid intake in the HOT condition, and this was reflected in the USG scores, where the HOT participants reported significantly lower values. Heart rate was comparable between conditions at nearly all time points, however the peak heart rate reached each circuit was 7 ± 3% higher in the CON trial. Likewise, RPE was slightly elevated in the CON trial for the majority of tasks. Participants’ work output was comparable between the CON and HOT conditions, however the performance change over time varied significantly between individuals. It is likely that the increased fluid replacement in the heat, in concert with frequent rest breaks and task rotation, assisted with the regulation of physiological responses (e.g., heart rate, core temperature).

Relationships between inflammatory cytokine and cortisol responses in firefighters exposed to simulated wildfire suppression work and sleep restriction

The interplay between inflammatory and cortisol responses modulates an appropriate response to a stressor. Exposure to severe stressors, however, may alter the actions and relationships of these responses and contribute to negative health outcomes. Physical work and sleep restriction are two stressors faced by wildland firefighters, yet their influence on the relationship between inflammatory and cortisol responses is unknown. The aim of the present study was to quantify the relationship between the cytokine and cortisol responses to sleep restriction while performing simulated physical wildfire suppression work. Firefighters completed 3 days of simulated physical firefighting work separated by either an 8‐h (Control condition; n = 18) or 4‐h sleep (Sleep restriction condition; n = 17) opportunity on each of the two nights. Salivary cortisol and inflammatory cytokines (IL‐6, IL‐8, IL‐1β, TNF‐α, IL‐4, and IL‐10) were measured throughout each day. An increase in morning IL‐6 was related to a rise (6.2%, P = 0.043) in evening cortisol among firefighters in the sleep restriction condition. Higher morning IL‐6 levels were related to increased (5.3%, P = 0.048) daily cortisol levels, but this relationship was not different between conditions. Less pronounced relationships were demonstrated between TNF‐α, IL‐10, IL‐4, and cortisol independent of the sleep opportunity, but relationships did not persist after adjusting for demographic factors and other cytokines. These findings quantify the relationship between cytokine and cortisol responses among wildland firefighters exposed to simulated occupational stressors. Potential disturbances to the IL‐6 and cortisol relationship among sleep‐restricted firefighters’ supports further investigations into the negative health effects related to possible imbalances between these systems.

Coronary heart disease risk in volunteer firefighters in Victoria, Australia

ABSTRACT Coronary heart disease (CHD) is a major problem for firefighters, even when considering the healthy worker effect (HWE). Although volunteer firefighters outnumber paid personnel, previous research has focused on paid US firefighters. By contrast, no CHD data for Australian firefighters exist. Risk factor data were collected from 2,943 Australian volunteer firefighters and CHD risk was compared with reference “low-risk” and Australian population data. Predicted CHD risk for male and female firefighter was 19.2% and 5.1%, respectively. Female firefighters high blood pressure and fasting glucose was significantly lower than the general population, whereas all other risk factors was similar to the general population. Firefighters’ CHD risk was greater than other volunteer and paid emergency services, but the prevalence for most risk factors was similar to the general population. Therefore, Australian volunteer firefighters may not benefit from the HWE.

The effectiveness of health interventions in cardiovascular risk reduction among emergency service personnel

PurposeThe physical demands and hazards associated with emergency service work place particular stress on responders’ cardiovascular systems. Indeed, cardiovascular disease (CVD) is a significant problem for emergency service personnel. Although it may be difficult to alter the cardiovascular health hazards associated with the work environment, it is possible for personnel to control their modifiable CVD risk factors, cardiovascular fitness levels and subsequently, reduce their CVD risk. This review aimed to determine the effectiveness and methodological quality of health interventions designed to mitigate CVD risk in emergency service personnel.MethodsA literature search of electronic journal databases was performed. Sixteen relevant studies were assessed for methodological quality using a standardised assessment tool. Data regarding the effectiveness of each intervention were extracted and synthesised in a narrative format.ResultsFifteen studies were rated ‘Weak’ and one study was rated ‘Strong’. Interventions which combined behavioural counselling, exercise and nutrition were more effective in improving cardiovascular health than nutrition, exercise or CVD risk factor assessment-based interventions alone. Further, CVD risk factor assessment in isolation proved to be an ineffective intervention type to reduce CVD risk.ConclusionCombined interventions appear most effective in improving the cardiovascular health of emergency service personnel. Accordingly, fire and emergency service agencies should consider trialling multifaceted interventions to improve the cardiovascular health of personnel and avoid interventions focused only on one of nutrition, exercise or CVD risk factor assessment. However, as most studies were methodologically weak, further studies of a higher methodological quality are needed.

Psychophysiological relationships between a multi-component self-report measure of mood, stress and behavioural signs and symptoms, and physiological stress responses during a simulated firefighting deployment.

Physical work and sleep loss are wildland firefighting demands that elicit psychological and physiological stress responses. Research shows that these responses are statistically related which presents an opportunity to use subjective psychological questionnaires to monitor physiological changes among firefighters; an approach used extensively in sport settings. The aim of the present study was to investigate if changes in self-reported psychological factors on the multi-component training distress scale (MTDS), relate to cytokines and cortisol levels among firefighters completing three days of simulated physical firefighting work separated by an 8-h or restricted 4-h sleep each night. Each day firefighters completed the MTDS in the morning and salivary cortisol and inflammatory cytokines were measured throughout the day. When sleep restricted, firefighters demonstrated increases in MTDS factors of general fatigue, perceived stress and depressed mood that were related to elevated cytokines (TNF-α, IL-8, IL-10). Conversely, firefighters who had an 8-h sleep demonstrated a positive relationship between physical signs and symptoms and elevated IL-6, while depressed mood was inversely related to decreasing cortisol and cytokines (IL-6, TNF-α, IL-10). Findings highlight the utility of the MTDS to detect psychological changes that reflect physiological responses among firefighters. Future research that establishes thresholds for specific factors which predict health-related physiological changes, will allow fire agencies implement multi-component measures to monitor and manage the health of personnel on the fire-ground.

Personal sleep debt and daytime sleepiness mediate the relationship between sleep and mental health outcomes in young adults

Sleep duration and chronotype (i.e., morningness–eveningness) are associated with increased depression and anxiety risk, but differences in individual sleep need and lifestyle may mean these sleep parameters do not present the same risk across all individuals. This study explored the mediating role of sleep debt and daytime sleepiness in the relationship between sleep and mental health symptoms in young adults, a particularly vulnerable population.

Sleep in wildland firefighters: what do we know and why does it matter?

Wildland firefighters perform physical work while being subjected to multiple stressors and adverse, volatile working environments for extended periods. Recent research has highlighted sleep as a significant and potentially modifiable factor impacting operational performance. The aim of this review was to (1) examine the existing literature on firefighters’ sleep quantity and quality during wildland firefighting operations; (2) synthesise the operational and environmental factors that impact on sleep during wildland firefighting; and (3) assess how sleep impacts aspects of firefighters’ health and safety, including mental and physical health, physical task performance, physical activity and cognitive performance. Firefighters’ sleep is restricted during wildfire deployments, particularly when shifts have early start times, are of long duration and when sleeping in temporary accommodation. Shortened sleep impairs cognitive but not physical performance under simulated wildfire conditions. The longer-term impacts of sleep restriction on physiological and mental health require further research. Work shifts should be structured, wherever possible, to provide regular and sufficient recovery opportunities (rest during and sleep between shifts), especially in dangerous working environments where fatigue-related errors have severe consequences. Fire agencies should implement strategies to improve and manage firefighters’ sleep and reduce any adverse impacts on firefighters’ work.