Is cognitive function impaired while working in the heat and wearing Personal Protective Ensemble and Self-Contained Breathing Apparatus in fire fighters?

Michael Williams-Bell, M.Sc.

PhD Candidate – Applied Bioscience

University of Ontario Institute of Technology

Patrick J. DeFazio Health and Safety Seminar

Toronto, Ontario

February 3rd, 2015

Overview

• Previous Work• Why Study Fire Fighting?• Cognitive Function and Fire Fighting• Current Research• Future Research• Upcoming Studies

3

Why Study Fire Fighting?

On-Duty Fire Deaths 1977 - 2013

≈ 87 deaths per year

Fahy et al. (2014)

Physiological Demands

• Widely accepted that:• Fire fighting is physically demanding• Places significant demand on cardio-respiratory

system• Personal Protective Equipment (PPE):

• Weighs 10-15kg (23kg with SCBA)• Thick, multi-layered, limited water-vapour permeability

(Gledhill, 1992; Sothmann, 1992; Williams-Bell, 2009)

Personal Protective Equipment

SKIN SKIN

CLOTHING CLOTHING

Microenvironment

Liquid sweat saturates clothing

Heat dissipation from body to environment

Water vapour condenses and saturates clothing

↑ water vapour pressure in

microenvironment

Liquid sweat pools in

microenvironment

Results in continued storage of metabolic heat production and ↑ Tcore

(Adapted from Cheung, 2010)

Uncompensable Heat Stress

• Inability of the body to maintain a thermal steady state• Body continues to store heat and core temperature rises

– Can occur during periods of inactivity• Firefighter PPE may not allow for optimal evaporative

processes

Previous Literature:Core Temperature & Fire Fighting

• In the field, Tcore ↑ 1.3°C (≈ 39.0°C) in < 24-mins

• In the lab, intermittent physical work ≈ 38.9 – 39.0°C in <16-mins

• Continuous exercise ≈ 38.5 – 39.0°C over 41 to 196-mins at varying work intensities

(Romet & Frim, 1987; Van Gelder, 2008; Selkirk et al., 2004)

Cognitive Function & Fire Fighting

• Fire fighters are required to:– Maintain attention– Retain important details (e.g. points of egress)– Cognitive components related to decision making (e.g.

recognizing smoke patterns)– Air Management

(Morley et al., 2012; Williams-Bell et al., 2010)

Cognitive Function and Firefighting

• Under potentially life-threatening conditions, firefighters must make:– Important decisions– Remain vigilant– Recall various geographical landmarks within a

structural fire– Safe exit

Cognitive Function and Firefighting

• The few published studies have mostly examined simple reaction time– Major importance is correct decision, a few ms

unlikely to incur detrimental consequences– Tasks not challenging enough to detect differences

How does increasing core temperature affect cognitive function in fire fighters?

Previous Research:Cognitive Function in the Heat

• Limited data on cognitive changes following work in PPE– Most report no changes immediately following exertion

• Studies showing decrements typically report increased hypohydration or dehydration

• No decrement appears to be due to dissipation of thermal stress or simplicity of cognitive tasks

• Complex decision making processes (i.e. memory and learning) not typically assessed– Simple reaction time

(Morley et al., 2012; Rayson et al., 2005)

Objective

• Determine the effects of exertional heat stress resulting in core temperature increases on cognitive performance using complex tasks in a hot, humid environment (35°C and 50% humidity)

Methods

• Subjects: 19 male incumbent fire fighters

Age 35.6 ± 8.7 yearsYears of Service 9.0 ± 7.3 years

Body Mass 85.1 ± 12.6 kgHeight 176.3 ± 6.8 cm

Body Mass Index 27.3 ± 3.2 kg/m2

Body Fat 16.7 ± 5.8 %VO2MAX 45.2 ± 5.5 ml/kg/min

Values are mean ± S.D.

Methods

Cognitive Function Testing• Clothing:

– Full Personal Protective Ensemble (PPE):• Flash hood, helmet, gloves, jacket, pants• SCBA - Harness, 30-minute 2200 psi cylinder

– Pre and Post test nude and dressed weight– Hydration: 5 mL/kg of body weight

• Pre, during, and post exercise

Methods

• Conducted in UOIT’s ACE Climate Chamber– Counter-balanced for circadian rhythm

• 10 subjects at 0800 & 9 subjects at 1300

• Core temperature pill ingested at least 8 hours prior to arriving at the laboratory

• Exertional heat stress protocol on treadmill:– Moderate workload: 4.5 km/h at 2.5% grade

Cognitive Testing

• CANTABeclipse (Cambridge Cognition, UK)• Tests used:

– Spatial Working Memory (SWM): retention of spatial information

– Rapid Visual Information Processing (RVP): sustained attention and processing speed

– Simple and 5-Choice Reaction Time (RTI)– Spatial Memory Span (SSP): working memory capacity– Paired Associates Learning (PAL): visual memory and new

learning

Recovery to 37.8°C

4.5 km/h, 2.5% grade

37.8 ◦CRest

38.5 ◦C

4.5 km/h, 2.5% grade

Rest39.0 ◦C

Nude Weight

Dressed Weight

4.5 km/h, 2.5% grade

CANTAB Tests = PAL, SSP 10-min

Fluid Replacement

CANTAB Tests = SWM, RVP, RTI 20-min

Forearm Immersion Active Cooling Recovery

Recovery

10 mins 10 mins

Experimental Protocol*Note: N = 11

at 39.0°C

Physiological Measurements

– Tcore measured every 20 seconds,

– Tskin measured every 20 seconds at 4 sites • Chest, arm, back, thigh

– Heart rate measured every 20 seconds– Thermal Sensation (TS), Thermal Comfort (TC), and

RPE measured following cognitive assessments

How Can We Measure Core Temperature???

End-Point Criteria

1. 4 hours of continuous work

2. core temperature reaching 39.5 °C

3. heart rate (HR) at or above 95% of maximal HR for 3 consecutive minutes

4. subject volitional termination due to dizziness, nausea, exhaustion or discomfort from the exercise protocol or the PPE and SCBA

5. termination by the researcher

Results

• Total Time: 85.2 ± 16.7 min

• Work (Exercise) Time: 62.0 ± 14.4 min

• Tcore ↑ from 37.1 ± 0.4 to 39.1 ± 0.4°C – Dynamic ∆ of 1.4 ± 0.3°C/hr

• ∆ in body mass of -1.1 ± 1.1%

Results: SWM - Retention of Spatial Information

Pre = 37.1°C Post = 39.1°C Recovery = 37.8°C700

750

800

850

900

950

1000

Sear

ch T

ime

(ms)

*

Search time

*Indicates different from Pre (p < 0.05).Data are mean ± S.E.M.

Results: Simple Reaction Time

Pre = 37.1°C Post = 39.1°C Recovery = 37.8°C250255260265270275280285290295300

Tim

e (

ms

)

*reaction

time

*Indicates different from Pre (p < 0.05).Data are mean ± S.E.M.

Results: PAL - Visual Memory and New Learning

Pre = 37.1°C 37.8°C 38.5°C 39.0°C Recovery = 37.8°C

0

2

4

6

8

10

12

Tota

l Err

ors

Fina

l Lev

el (#

) *total

errors

*Indicates different from Pre (p < 0.05).Data are mean ± S.E.M.

Results: SSP - Working Memory Capacity

Baseline = 37.1°C

37.8°C 38.5°C 39.0°C Recovery = 37.8°C

5.0

6.0

7.0

8.0

9.0

Sp

ati

al

Sp

an

Le

ng

th

* *

*Indicates different from Pre (p < 0.05).Data are mean ± S.E.M.

spatial span

length

Summary of Findings

• Retention of spatial information (SWM) search time was prolonged immediately following exercise (Tcore

of 39.1 ± 0.4°C)• Faster simple reaction time immediately following

exercise (Tcore of 39.1 ± 0.4°C)

• Working memory capacity declined at Tcore of 38.5 ± 0.2°C and 39.0 ± 0.1°C

• Visual memory and new learning was impaired at Tcore of 38.5 ± 0.2°C

Conclusion

• Once Tcore of 38.5°C is attained during exercise in PPE at a ∆ Tcore of 1.4°C/hr, higher-order cognitive function may be impaired

• Current results may be different than previous data due to implementation of cognitive testing familiarization

• Tests assessed immediately post exercise may have also shown differences at lower core temperatures if they had been measured during the test protocol as well

• Changes in reaction time or latency may not necessarily operationally relevant; correct decision most important factor

Conclusion

• May be due to a reduction in cognitive resources unable to combat heat stress and cognitive load

• First study to show restoration of cognitive function following active cooling with hand and forearm immersion in fire fighters

• Restoration may be due to the direction of core temperature movement; however, cognitive function at the same tcore of 37.8°C was not different

Practical Applications

• These data further compliment the safe work limits previously reported by Selkirk and McLellan (2004)

• Implementing hand and forearm immersion will ↓ Tcore & restore cognitive function to combat re-entry into an emergency scene

• Important information for Incident Commanders and emphasizes the importance of active cooling during rehabilitation periods

Fire Fighting Heat Stress Wheel

• Work Intensity: Moderate (primary search, overhaul, ladder setup, vehicle extrication)

• Temp: 31-35°C• Humidity: 21-40%• Time to Cognitive

Impairments (38.5°C): 53 mins

(Selkirk and McLellan, 2004)

Next Step…

VSStandardized Tests

Serious Games

Future Research

• Develop ecologically valid cognitive assessment tools related to fire fighting– e.g. using serious games

• Perform simulated fire fighting activities in a climate chamber at specific durations and intensities typical of fire scenes

• Determine if cognitive function can be trained to become more robust under stressful conditions

Upcoming Studies

• Determine if a serious game can be used to assess decision making (i.e. cognitive function) in fire fighters

• Determine if a serious game can be used as a training tool over the course of a 28 day work cycle to improve cognitive function in the heat

Upcoming Studies

• Implement Microsoft Kinect technology to develop a serious game to train safe lifting techniques

Acknowledgements

Grant Funding:

Graduate Funding:

Undergraduates:Trevor LapointeAshley TompsettShawna BurenPatrick CheongKyle SnowdyRyan GilleyA. VazhappillySinead O’Brien

Advisors:Dr. Steve PassmoreDr. Andrew HogueDr. Bill KapralosDr. Sil MiorCmdr. A. KostiukFF J. McGillFF G. BoisseauPartners:Toronto Fire ServicesWinnipeg Fire Paramedic Service

Advisors:Dr. Bernadette MurphyDr. Tom McLellan

References

• Barr, D., Gregson, W., & Reilly, T. (2010). The thermal ergonomics of firefighting reviewed. Applied ergonomics, 41(1), 161-172.

• Cheung, S. S. (2010). Advanced environmental exercise physiology: Human Kinetics.• Fahy, F. F., LeBlanc, P. R., & Molis, J. L. (2014). Firefighter Fatalities in the United

Staties - 2013. Quincy, MA: National Fire Protection Association.• Gledhill, N., & Jamnik, V. K. (1992). Characterization of the physical demands of

firefighting. Can J Sport Sci, 17(3), 207-213. • Morley, J., Beauchamp, G., Suyama, J., Guyette, F. X., Reis, S. E., Callaway, C. W.,

& Hostler, D. (2012). Cognitive function following treadmill exercise in thermal protective clothing. European journal of applied physiology, 112(5), 1733-1740.

• Rayson, M. P., Wilkinson, D. M., Carter, J. M., Richmond, V. L., Blacker, S. D., Bullock, N., . . . Jones, D. A. (2005). Physiological assessment of firefighting in the built up environment Fire Research Technical Report 2. Wetherby, UK.

• Romet, T. T., & Frim, J. (1987). Physiological responses to fire fighting activities. European journal of applied physiology and occupational physiology, 56(6), 633-638.

References

• Selkirk, G. A., & McLellan, T. M. (2004). Physical work limits for Toronto firefighters in warm environments. J Occup Environ Hyg, 1(4), 199-212. doi: 10.1080/15459620490432114

• Sothmann, M. S., Saupe, K., Jasenof, D., & Blaney, J. (1992). Heart rate response of firefighters to actual emergencies. Implications for cardiorespiratory fitness. J Occup Med, 34(8), 797-800.

• Van Gelder, C. M., Pranger, L. A., Wiesmann, W. P., Stachenfeld, N., & Bogucki, S. (2008). An experimental model of heat storage in working firefighters. Prehospital Emergency Care, 12(2), 225-235.

• Williams-Bell, F. M., Boisseau, G., McGill, J., Kostiuk, A., & Hughson, R. L. (2010). Air management and physiological responses during simulated firefighting tasks in a high-rise structure. Appl Ergon, 41(2), 251-259. doi: 10.1016/j.apergo.2009.07.009

• Williams-Bell, F. M., Boisseau, G., McGill, J., Kostiuk, A., & Hughson, R. L. (2010). Physiological responses and air consumption during simulated firefighting tasks in a subway system. Applied Physiology, Nutrition, and Metabolism, 35(5), 671-678.