Human performance at environmental extremes Flashcards
What are the components of thermoregulation
Behaviour!
Cold Shivering Non shivering thermo BAT (increased metab) Pilo erection (minor) Vasoconstriction
Hot
Vasodilation
sweat
Metabolic rate can decrease here
What is meant by the ‘environment driven zone’ and the ‘prescriptive zone’ and what factor can change this?
EDZ = Temperatures at which the core temperature is raised after exercising above the typical amount for lower temperatures e.g. normally 10-25 deg it will always be raised to x and above 25 it will be >x.
Prescriptive zone = ambient temperatures at which the body raises the core temperatures to a consistent set level.
Potential effects of cold temperature on HR?
Shivering so increased HR
Gold standard of temperature measuring?
Oesophageal
Describe what happens if core temperature rises
39 normal in exercise (possibly 40)
41 ok - used in fever therapy
44 - heat stroke, death, brain damage
What happens if core temperature falls?
35 - reduced consciousness
31-33 VF
31 Death
Depending on speed people have survived as low as 14 degree core temp.
Describe the unified controller model of thermoregulation?
Sesory detect temperatures in core and shell - feel into single controller with a temperature set point. Mismatch in sensor temperature and set point causes effector stimulation.
Inibitory connectsions between ant and post so that there is only hot or cold response.
Describe the unified controller with individual effector loops model and describe the effector responses.
Set point in the brain individually triggers effectors/ These systems then cause a rise or fall in temperatre which is sensed and feedsback into the effector activity. Work towards same set point but effectors are activated in different amount.
Proportionality differs for each response based on rise/ fall in temperature and difference between shell and core temperature. Larger =sweating/shivering. smaller = vasocon/dilation.
Roles of anterior and posterior hypothalamus.
Anterior - vasodilation and sweating
Posterior - vasoconstriction and shivering
Describe the independent control loops for different effectors model.
The activity of each effector is dependent on an independent threshold value.
For example shivering and sweating need a start when the temperature deviates from the
Where is the central control point in the brain?
nucleus pre opticus - anterior hypothalamus
Describe the perception of temperature and factors that effect this.
Perception depends on sensation, sensitisation and rate of temperature change.
Sensors consist of free nerve endings.
Sense via TRP receptors which are independently triggered by different temperature range (peak activity varies for each one)
Extreme temperature TRP channels cause pain.
Can be triggered by menthol/ capacian.
Activity increased with sudden temperature change and decrease by prolonged stimulation (sensitisation)
How is metabolic rate at certain temperatures linked to age?
As a baby - higher SA:body so need more heat production as proportionally more heat loss. Metabolism increases faster as ambient lowers and starts increasing at higher temperatures
How significant is the role of BAT and where is it found
Neck and shoulders (perirenal in babies).
Only produces 8/10Ws
Describe apocrine sweat
Found on hair follicles Mixes with sebaceous glands to produce odour (proteins broken down). Located circum oral, eyelids, nipples, axillae, outer ear.
Not much role in temp reg
Describe eccrine sweat glands
Located all over body.
Can only become active in first 2 years of life (hot countries have more) however have capacity to grow. More dense (more sweat) on back than trunc, around spine, forehead, upper leg.
What is sweat capacity effected by?
Fitness, training, age, sex (males sweat more and have a higher capacity?), acclimatisation
How is blood follow affected by temperature? (distribution) effect of exericse?
Vasoconstriction and dilation.
Keeps blood to core structure to prevent heat loss.
Arteriovenous anastomoses prevent blood travelling through more superficial capillaries (preventing heat loss) and also shunts blood to deeper veins (preventing them going to superficial ones) means blood can get warmed by accompanying artery.
25-30c variation in arm blood flow.
In heat everything wants blood, vasdilation often is more important than maintaining BP in extremes of temp.
How is blood follow affected by temperature? (distribution) effect of exericse?
Vasoconstriction and dilation.
Keeps blood to core structure to prevent heat loss -blood to superficial veins closed off so has to go deep. shunts blood to deeper veins (preventing them going to superficial ones) means blood can get warmed by accompanying artery. (countercurrent heat exchange via venae comitans).
If too hot.
Arteriovenous anastomoses prevent blood travelling through capillaries meaning resistance is reduced and more blood travels to arm. Causes arm to get warmer, more blood in superficial veins and more heat loss.
25-30c variation in arm blood flow.
In heat everything wants blood, vasdilation often is more important than maintaining BP in extremes of temp.
Describe the various ways to measure temperature
Thermistors - adds resistance with heat
Thermocouples - 2 wires of different material that produce volage dependent on temperature difference
Radio pill - expensive, swallow with transmittor
Infrared thermometer e.g. tympanic membrane
heat flux disc - transducer than gives electric signal based on heat rate applied.
Many areas e.g. orifice, intra abdominal, su lingual, axillary.
Aural-Hearing defenders
Urine temp
Rectal good but slow to pick up changes.
Describe the various ways to measure temperature
Thermistors - adds resistance with heat
Thermocouples - 2 wires of different material that produce volage dependent on temperature difference
Radio pill - expensive, swallow with transmittor
Infrared thermometer e.g. tympanic membrane
heat flux disc - transducer than gives electric signal based on heat rate applied.
Many areas e.g. orifice, intra abdominal, su lingual, axillary.
Aural-Hearing defenders
Urine temp
Rectal good but slow to pick up changes.
What is a homeotherm?
An organism that maintains its temperature at a constant level via its metabolic activity
What is thermal conductance? How is relevant to the body?
Degree to which heat can be transferred to or from. different body parts have different conductances- a lot sue to blood supply. Conduction is due to gradients.
Also convection = ECF
Describe where thermoregulation fits in in the hierarchy of systems
Ranks highly
in heat - BP can drop (heatsyncope) and dehydration can occur
Location of heat sensors
Centrally - hypo, medulla oblongata, spinal cord
Peripherally free nerve endings via adelta or C fibres and spinothalamic tract.
Describe briefly the types of effectors of thermoregulation and their control
Shivering
Skeletal nervous supply
Sweating
Non medullated cholinergic symptathetic
Vasconstriction
Adrenergic Non medullated sympathetics
Vasodilation
Symp nerve or artine vasodilator nerves
Non shivering thermogenesis
Sympathetic adrenomedullary system
Catechoamine release (higher CO, vasoconstric, HR, non shvering thermo, glucose) Symp to adrenal medulla.
Endocrine control relating to seasons
How is the brain cooled? (possibly)
Cooler blood from mouth and nasal area is shunted towards brain known as selective brain cooling (SBC). Maybe only in animals/ dogs
Role of piloerection?
trap a layer of air - more sig with clothing?
What is hidromeiosis? Why has it developed?
Local phenomenon whereby sweat production is decreased by moisture on skin (only an effective heat loss mechanism if sweat actually evaporates).
Swelling of epidermis to block sweat glands
Reasons for reduction in sweating (x3)
Hydromeiosis, decrease in temperature (exponential decline)
Sweat gland fatigue (?)
Describe unconscious behavioural thermoreglation and technical regulation
Body postioning - towards fire, babies spread out, lizard off floor, clenched fists.
Technical = building shelter ect.
Also psychological changes e.g. mood and warmth/ cold.
How is mean body temperature calculated
Weighed averages
5 ways the body can gain or lose heat
Radiation Conduction Convection Respiration Evaporation
Describe conduction
Heat lost down temperature gradient from physical contact with solid materials in the environment
Minimal effect although more significant in extremes e.g. frost bite.
Depends on surface’s conductivity and specific heat capcity
Describe convection
Physical movement of air/water past the body which serves to carry heat.
Heat of body warms surrounding air that can be displaced by cold air due to a draught (forced) or natural buoyancy of warmer air.
70-80% of heat loss in cold
100% in water
Can cause heat gain if hot
Describe radiation
Can gain from envioronment too e.g infrared from a hot desert floor or working with fires ect.
Includes direct sun, reflected from sun and infrared (two way Infrared)
Describe the efficiency of the bodies metabolism to do work
Very inefficient. Not much energy actually lost in the form of mechanical work e.g. 0 in walking
What is the conceptual heat banalane equation?
Used to calculate rate of energy storage (M-W) = (K+C+R+Esk) + S M = metab produc W =Mechanical work K = Conduc loss C = Convec R = Resp Esk = Evap S = rate of energy storage
What parameters affect heat storage?
Energy production Energy loss Climate -Temp -Humidity -Air speed -Radiation temp - sunny or hot ground -Surface temp - determines conductive heat exchange
Personal
- clothing
- Metab rate
General formula to calculate heat loss from a speciefic mechanism?
Heat transfer = (SA x gradient difference)/resistance
How to calculate dry heat loss?
(temp of skin- ambient temp)/ Insulation from clothing and air layers
none at 35deg
Body maintains temp well in dry heat but still a relationship between skin temp and air temp
Describe evaporation
Heat transfer due to sweating
Liquid- vapour change requires heat (must evaporate so dripping doesnt count)
Describe respiration
Not much effect but large in dogs
How to calculate evaporative heat loss and trends with temp
(PH20 skin - PH20 ambient)/ (vapour resistance of clothing and air layers)
Depends on humidity
100% at 35 deg then no heat loss. and condensation/ heat gain above this.
At 50% (normal) can lose heat up to 50 deg
Describe heat balance in 100% humidity whilst exercising. What could limit maximal heat loss here?
No heat loss or gain at 35deg.
Increases/ decreases as you go up or donw in temp.
Resp heat loss max + dry heat loss max + wet heat loss max = limit to heat loss.
So if exercising at 1300 Ws to maintain heat balance the temp needs to be 25deg or lower and this is with maximal heat loss from all methods.
Often limited by sweat production.
Heat gained from radiation all affects this capcity to lsoe heat
Normal sweat production limit?
2/3l an hour max
Limited by dehydration
Describe repsiratory heat loss
Similar to evaporative.
More positive at lower and more neg at higher
Can lose up to 10% of total heat production
What does the comfort of clothing depend on?
Pressure sensors and temperature sensors (not wet sensors)
33dg skin temp = comfort
Skin wetness = % of skin considered to be fully wetted
How does clothing limit heat transfer?
Resistance in the form of thermal insulation from clothing layers and trapped air layers.
Alows effectors to stay in their utility range function
resistance against vapour (sweat transfer)
Why are humans considered tropic animals in terms of temperature regulation?
Maintain their temperature only above 20 deg when naked
How can cultural aspects to clothing affect temp reg?
Jobs e.g. chemical protection but overheating
Wearing clothes for fashion
How does core temp in humans vary? Fever vs exercise?
Increase to 39/40 possible in exercise
FEver = raised set point
Exercises = raised due to metabolim but body actively tries to decrease
What is postivie and negative error in terms of sensation?
Positive error = large positive difference in ambient - afferent ignals are above set point
Vice versa
What is energy efficiency
Energy consumed: External work performed
Describe the temperature ranges of comfort and how they are effected
33 degree skin temp in a 3.5 deg rang
0.2 clo increases 1 deg (jeans and tee is .6)
20W exercise decreases 1 deg
Increased air speed increases
At what skin temperatures cause skin wetness? Effects of local skin time?
34 = 6% wetness 35 = 20% wetness (slightly uncomfortable) ect. Burning above 45 Reduced dext under 20 Pain under 15 Numb under 7
How does clothing create a large still layer
Trapped air layers either side of clothing (6mm)
What type of heat transfer does fibre type primarily effect?
Primarily radiation e.g. reflective, re emit or absorptive clothing. (not to do with thickness)
What significance does clothing thickness have?
Increases vapour resistance - increases diffusion pathway - less on conductance/ convection
Weave of fibres also effects diffusion.
Also effect air permeability which is more significant in high winds.
Effect of clothing ensembles?
More layers of trapped air so incresed diffusion pathways. Each up to 6mm
How many units of equivalent still air thickeness does a 2mm clothing give? what does this depend on?
6 on body and also from layer + 2mm (size) +still layer of outside clothing (7mm) = 21
Loose fit- ight is less, location e.g. tight at shoulder and body shape.
How does air movement effect insulation?
Disturb air layers (typically outer layers), replace warm air with cold
How does garment movement effect insulation? effect of this?
Disturbed inner air layers. walking at 4m/h decreases vapour resis 80% and air resistance 60%
Other ways in which clothing effects heat balance besides providing insulation?
Weight and stiffness of the clothing require more energy to move.
Physiology - more fat in places with less insulation
Describe clothing comfort in more detail? How can it be improved through clothing qualities?
ALso depends on physical, physiological and psychological factors.
Temp sensation also depends on rate of change.
Increases feel of wetness as adds friction.
Looseness is also less comfortable particularly if wet as between toughing skin the clothing cools and then feels cold. If absorption also causes the skin to cool quicker as it gets wet.
Fibre weave and size affect the amount of direct contact with skin.
Why were nylon shirts uncomfortable? What would be a good design
Non permeable, flat weave structure that sticks to the skin.
2 layers, absorptive outside and permeable but low absorption inside (moisture condutive)
Why is buffering capacity to heat and moisture important for clothing? Gold standard?
Prevents clothing becoming wet and resulting in sharp decreases in temp after exercise (afterchill). Best in varying activity levels.
Phase change aterials where structure changes at certain temps
Describe evidence for acclimatization to cold
Not much - military for 4 weeks at - 20. only difference was they went to the toilet in the night less due to adaptations of kidney preventing hypertension.
Describe potential mechanisms for acclimatisation and differences in fitness
Hypothermic - allowing body temperature to fall to preserve energy
Insulative - Enhanced insulation hence preventing cooling **eskimos have lower sub-cut fat
metabolic - Increased production by non-shivering thermogenesis.
Fitness - tend to be metabolic
Low fitness - tend to be insulative (chicken vs egg)
Explain how champion channel swimmers deal with the cold
Used to be fatter
Now leaner but higher BMR due to nutrition and fitness
Relationship between skin fold and critical temperature
Higher skin fold then higher critical temperature (temp at which O2 uptake and metabolic rate start rising
How do eskimos adapt to cold climates?
behaviour - walrus skin
Higher hand blood flow at any temperature to maintain dexterity and prevent frostbite
Possible reasons for naked divers in Korea shivering the least?
Selection bias (people that have most fat are chosen to dive) vs developmental? (not genetic as now use wetsuits and effects have dissapeared)
Describe the balacne between function and safety of helicopter immenrsion suits and the types of clothing used
immersion suits can be wet or dry (water tight).
If impermeable then the wearer is subject to heat stress.
If permeable then cant survive in water as long if stranded
How does metabolic rate change with temperature?
Increases linearly
At what temperature will you see no ECG or not EEG
31 - but only pronounce dead when warm
What can survival data of shipwrecked people be used for?
Predicting chances of survival after abandonment in cold water. Planning rescue operations. Time decreases with age
Why do people die from the cold at different times?
stage 1 - Cold shock 3-5 minutes 2 - Swimming failure <30 minutes 3- Hypothermia >30 minutes 4- Post rescue collapse 50% stage 1 ad 2
What is cold shock?
Involuntary inhalation and hyperventilation - drowning.
Vasoconstriction - raised BP and more straign on heart - CVS event, Cerebrovasc event, inability to self rescue.
Reduces with repeated exposure
How is cognition effected by cold?
Under 33 reduced consciousness
10-15 fine
75 stunned denial and low reasoning
10-15 inappropriate behaviour
Describe hypothermia types and treatments
Acute (immersion) - severe cold stress, rapid body cooling before energy reserve is used. Rewarm spontaneously when removed from the cold.
Subacute (exhaustion) hypothermia - less sebere cold stress, energy reserves depleted. Spontaneous rewarming is less certain.
subchronic (urban) - moderate cold of rlong Fluid balance changes due to changes in BP - needs gentle warming
Submersion - >60 minutes under water - need rewarming before pronounce dead
Different treatments and outcomes
Why can children survive very cold temperatures underwater? Risks?
Larger SA:weight ratio so faster cooling of brain- reduces O2 demand. May be brain damage
Describe different methods of rewarming
Passive external - blankeys, bubblewrap, give energy, avoid water evap (change clothing)
Active external - forced air warming, chemical packs (50) chemical blankets (TNO blanket) (40), water bath
Active internal - Inhalation warming (pretty crap), Drinks, IV fluids (40-42), rewarming circuit - cardiopulmonary bypass - fem to fem
What is afterdrop? How can it be prevented (best method)
Physical afterdrop - core temp continues to decrease as warming outside takes time to effect the core.
Physiological afterdrop - vasodilation due to external warming so warm blood from core is pumped outwarms and is replaced by cold blood.
Best is total submersion (not rewarming hands first ect.
Also reduce… no exercise? keep extremities cold?
When does lethal aspiration amount occur?
22ml/kg sea water and 44 fresh
Red cross swimming advice?
Dont but can be helpful
Describe signs and symptoms of mild, moderate and severe hypothermia
Mild - symp - shivering BP, increased urine, mental confusion, hepatuc dysfunction? hypoglycaemia?
Mod - violent shiv, muscle miscoordination, stimbling, mild confusion, pale, blue extremities
Sev - HR, RR, BP decrease - HR in 30s, difficulty speaking, amnesia, inability to use hands, legs, blue and pufy skin below 30, stupor, irrational behaviour, AF, VT, organ failure
Paradoxical undressing - occur in mod-sev.
Terminal burrowing - hide and die syndrome - assocaiated with paradoxical undressing. If temp drops slowly, find a hole - primative self-protective behaviour?
Why is cooling bad?
Cellular structures, enzyme systems and temp dependent chemical reactions are disrupted
What is physiological amputation?
AVAs close, vasoconstriction occurs. Reduced blood flow to arm drastically
What are the possible reasons for decreased dexiterity in the hands? What is each caused by physiologically?
Decreased sensibility (change in receptors) Descreased muscle function Increased reaction time (change in receptors, nerves, effectors) Decreased joint function Decrease in cognitive functions/ motivation (central effects)
How can risk of skin freezing and dexterity problems be describe in terms of risks posed by conduction
Can be described in terms of contact coefficient (specific heat capacity, density and conductance) and contact time
How is risk of frostbite modulated and what is a potential negative effect of this?
Increase in metabolism
Wearing gloves - decreases dexterity in itself
Why is reduced dexterity an issue?
Leads to accidents,
Progress to frostbite/ tissue damage
At what temperature is dexeterity sharply lost? How does this effect performance?
15 degrees
Depends on task - fine finger tasks the most
Describe receptor sensitivity in cold and its effects
Located in muscle - motion apparatus
-muscle spindles, joints, ligaments
- lead in statesthesia (postion) and kinesthesia (movement)
Also superficial, pain, tactile, thermal
Decrease from 25
Sharp 6-8
Nervous block around 6
Therefore unlikely cause of dext at 15
Describe nerve conduction with cold and its effects
Decrease in velocity below 36
sharp decrease below 20
No conduction below 10
Well insulated (deep endings) so decrease slower than skin temp so could be a factor
Describe the cold’s effect on muscles, potential mechanism?
Decrease in power (force and contraction velocity) and endurance below 28/27
Depends on muscle for example triceps surae is less powerful but endures longer in cold
Lower endurance possibly due to loss of peripheral fibres - so less fibres try to deliver same force but working at same proportion of max contraction endurance may still be the same
Describe the effect of cold on joints/tendons
synovium becomes more vicous. Become colder quicker than muscle
Linear decline below 20
Major effect on fingers.
Describe how to cold can could cause central effects on dexterity
psycho-physiological factors such and thermal sensation and pain sensation.
People perform more negatively on tests with pain, decreased arousal, attention and reaction time.
Less CIVD with lower core temp- Hunting response.
Arm still functions normally if kept warm and core is chilled.
What are the critical mechanisms for loss of dexterity in the cold?
Joints - due to fast cooling it’s likely that at 15C skin temp the sudden decrease in dexterity is linked with a sudden decrease in joint movement (as they reach 20).
Muscles too, even when and is kept warm, cooling arm has a large effect
How can performance loss (dexiterity) be calculated
Daanen (2009) collected data on hand dexterity at different WCETst (several scales including grip strength, fing dext and hand dext).
Wearing air force clothing 2.3-2.5clo.
WCET 2- -30C.
(Results would change at different M)
Measured every 10m mins for one hour)
His results can be used to predict loss of function at certain WCETst and exposure times
Factors that affect cold contact risk? What does K (cooling speed/ time constant) depend on (curve based on Newtonian cooling curve)
K depends on contact coefficient (density, specific heat caaity and conductance), area of contact, gloves - material tye and thickness, skin blood flow, physiological status,
Effects of gloves on cooling
thicker then more resistance.
Also reduce skin freezing risk.
If metab low then will not maintain temp, just slow decline.
Thicker the glove the more the loss to dexterity
What is the difference between frostnip and frostbite
Frostnip is the first signs of frostbite. Tissues are cooled but not cellular destruction. May get white/yellow/red spots on skin (reversible), may be itchy and painful followed by numbness.
Frostbite involves cellular death
Stage1 =frostnip
stage 2 = superficial structures (normally recoverable) but blisters, swelling
Stage 3 - deep tissues and gangrene - irreversible
Why is damage to cells different with slow freezing?
Less ice crystals that damage cell membranes.
Instead ICF gets concentrated triggering cell death as proteins and ice separate
Why is re freezing so dangerous?
Swelling proceeds thawing.
This can re freeze - take frostbite from stage 2 to 3
Treatment for frostbite
Warm body best by whirlpool thermal bath.
Dont if danger of refreeze.
Allow necrosed areas to drop off (tissue loss up to swelling)
Protection mechanism against frostbite
CIVD - cold induced vasodilation.
Below 10C skin temp, AVAs open and vasodilation occurs so that flow increases. One digit at a time. Dependent partly on core temperature
How were studies conducted into the effect of sticking of metals to the skin? Significance of this?
Finger to metal at set temperature on scale, degree of stickiness measured by change in weight.
Latex glove with whole hand also tester.
For workplace coolers e.c.t.
At what temperature do metals start to stick to the skin?
Aluminium -6
Steel -7 (more sticky overall though)
Describe non freezing cold injury
Trench foot
Low temp for an increased period of time (below 16) (as short as 13 hours)
Moisture and unsatitary conditions may also cause.
Blistering, pain (initially), numbess +/- infection, gangrene, swelling, erythemia or cyanosis
Describe the 2 cold exposure standards
Local - risk of freezing of exosed skin (WCI)
whole body - required clothing insulation (IREQ)
Describe the Wind chill index
Developed by Siple and Passel in 1945.
cylinders raised up flag pole and recorder how quickly they freeze dependent on temp and wind speed.
Doesnt account for clothing so exaggerated.
WCI equation dependent on ambient temp and wind speed.
Unit in Wm-2 - heat loss per square m of the body
Tch (wind chill equivalent temperature) = 33-WCI/25.5C
Describe the WCET - versions/ experiments to calculate
WCETst - Steadman - more complex as accounts for clothing factors and heat balance but thought by many to be too complicated
Meteo Canada ‘new’ WCI
People put in wind tunnel - look at effects on cheek.
Used range of 2 to -30 WCET
Came up with new standard and table
What constitutes RISK and EXTREMELY HIGH RISK with the Meteo WCET
- 28 to -39 exposed skin will freeze in 10-30 mins
- 55 and cooler, less than 2 mins
What is the IREQ?
Resultant clothing insulation required during actual environmental conditions and activity of the body to maintain physiological requirements.
A measure of whole body cold stress.
Measured in clo
What can the IREQ be used for?
1 - cold stress index integrating environmental values
2 - A method of analysis to identify the relative effect of parameters on cold stress and evaluate measures for improvement
3 - a method of specifying clothing insulation requirements and selection of clothing to be used
What is the IREQ neutral?
Thermal insulation required to provide thermal neutrality at normal mean temperature with little or no physiological straign
What is the IREQ min and why was it developed?
Minimal thermal insulation required to maintain body temperature equilibrium (heat balance) at a sub normal body temperature. The highest level of physological straign to which humans should be exposed to when performing occupation work
How can subjects work in conditions without IREQ min levels of insulation?
Their core temp will fall so rotate them (formula to see how long to warm before returning), calculate DLE. Re warming methods ect.
What factors are accounted for by IREQ?
Ambient temp, radient temp, wind speed, humidity, metabolism/ activity level
Limit to how many clo can be achieved?
4-5
What is it DLE and what is it based on?
Duration limited exposure.
= Heat storage/ heat storage limit (Qlim)
Qlim normally 40 so reduction of 40Wh m-2 is maximal reduction of body heat content allowed.
Only relevant when below IREQ (not in heat balance)
Heat storage rate can be calculated from a formula which looks at difference in clo
Describe clo
American unit
1 clo = american bussiness suit
What is operative temp?
Ambient temp plus radiative
Give some common workplace recommendations regarding air velocity
avoid >1m/s in refrigerated rooms, use googles and clothing
Give some common workplace recommendations regarding selection of workers
May need to be screened or have medical certification if working in extreme cold. -Disease that interferes with cold response
Give some common workplace recommendations for high wind speeds
use screens or wind break garments
Give some common workplace recommendations for wet clothing
If light work then use impermeable outsides If mod then change clothing regularly and avoid periods of rest. easy ventilation (prevent accumulation of sweat?)
Give some common workplace recommendations for handling liquids
Alcohol and gasoline make you cool faster
Describe properties of a good work-warming regime
Heated tents, warm sweet drinks, radiators.
Avoid caffeine due to diuretic and circulatory effects.
Give some common workplace recommendations for working in very cold environements
Buddy system, constantly monitor, education, avoid rest/ low work, avoid sweat
Give some common workplace recommendations for exposed skin temp limit and wet clothing temp limit and maintaining manual dex
Exposed skin
Give some common workplace recommendations on avoiding contact injury
How does a change in temperature affect acute injury and illness rates
Increaseing temp above 30 deg increases heat related injury but also acute injury in general - affects behaviour and alterness. INcrese in MSK disorders.
Increase in disorders in the cold too (more stead increase)
Trends with heat injury in the army and possible reasons
Decreases with age.
New recruits worked harder?
New recruits less experienced?
How does temperature affect humidity
Both increase
Larger possible variation in humidity with increasing temperature
Why are coal mines so dangerous? Why are salt mines not as bad?
decrease in 1 km = increase in temp by 30deg.
Spray rocks with water to prevent resp disease - increase in humidity
Salt mines are dry
what factors affect tolerance to heat?
1 Age - increase in CVS disease 2 Fitness -Lower metab rate at same VO2/ work rate SA:mass ratio Maximal sweat rate
What is the range of lethal core temperatures? (where data from)
40 deg - 10%
41 deg - 50%
Some ok at 43
From Mecca - may have been hotter in field
How does proportions of heat loss from different modalities change as temperature increases?
More evap
Less everything else
Describe Blagden experiment? What is the significance?
15 minutes in 120 deg dry heat
Steak and egg cooked
Shows efficacy of sweat rate
Why are heat waves so dangerous (in terms of normal distibution)
Shift normal distrib to right pushing more people into lethal core temps
Why are there more heat related deaths in the elderly?
Less fit (due to decline in activity and physiology) so lower CVS reserve
Lower sweat rate
Polypharmacy
Comorbidities
Describe ways of measuring sweat loss/ sweat rate
Inject metacholine (induces maximal sweat)
Use petroleum jelly to show sweat better (different colour with sweat).
Use a ventilated sweat capsule on skin (humid in vs out)
How does sweat rate decline in the elderly? By how much?
same no of active glands but lower rate per gland
What is CVS reserve and how does it affect heat tolerance?
The hearts capacity to increase its output from resting to maximal rate. (the difference between the two).
More able to increase CO to increase cutaneous perfusion and increase heat loss.
Describe salt loss in heat exposure vs intake in Western diet
Salt loss in heat exposure e.g. arathon may be 10-20g/day
Western diet = 10g
Define a light, moderate and serious salt deficiency
.75 g/kg sev
Symptoms of salt deficiency
light - dizziness and fatigue
mod - nausea, cramps (?) and vomiting
sev - heat inblance, shock
Describe the circle of salt loss
salt loss - anorexia - more salt loss - vomiting - more salt loss
Describe symptoms of dehydration in terms of %loss of body weight
2 - thirst 4 - dry mouth 6 - increase in HR and temp 8 - swollen tongue, difficulty with speech, reduced mental and physical performance (6.4l) 12 - need IV drip 14 - death, fast temp increase
Impact of dehydration on heat balance/ HR - 6% loss
Increase in HR and temp with work, may just keep increasing? Done at 49 deg
What does the CDC say intentional rapid weight loss is associated with what?
Dehydration and hyperthermia
Describe some mechanisms to prevent dehydration and experiments
hydromeiosis
less sweat in tropics than desert at same temp.
More when skin is dried
More when skin is shaved - swelling of the epidermis.
Why does heat and the human body pose a CVS challenge. How does the body compensate for this
Standing posture, cutaneous vasodlation, large SA:mass and sweat loss decreases BP, Co.
Lower splanchnic, renal and muscle flow
Why are chemical attacks in war so effective?
Need to wear impermeable CW protective clothing - can lose up to 10l of water in 24hours
How much water can humans absorb?
1-1.25l/hr
Why did heat illness in US army in 90s decrease? This resulted in water?
Education about hydration.
More hyponatraemia caused injury
Whats the difference between acclimatisation and acclimation? pros of acclimation?
NAtural vs artificial.
Can become acclimated quicker
What occurs in acclimatisation over how long?
5 days temp and HR decrease (170 vs 130). more than 7 then no real benefit
What is the constant stress model vs costant straign? pros and cons?
constant core temp or HR vs same circumstances.
People dont like working hard. Faster. May become dehydrated or hyponatraemia
What factors allows acclimatisation to occur
Sweat sodium conc is decreased
Start sweating earlier
Changed distribution of sweat
Increased sweating
Decreased HR and BMR and resting temp (and fitness?)
Increased aldosterone - increases sweat and salt absorption.
Increased sensitivity to aldosterone.
Lower CV strain (BP maintained
Improved skin BF
More effective distribution of CO - fluid shifts between ICF and ECF.
improved distribution of sweat over skin surface.
Lower core and skin temp for exercise
High work capcity
Improved comfort Reduced reliance on carb metab
Describe acclimation decay
1 week 40% gone
2 weeks 80%
3 weeks almost 100%
Faster decline in winter
Heat tolerance and water requirements
Increases - up to 1l/ hr in heavy work in 25deg in CW clothing
Describe the effect of temperature on fitness performance
Increases HR and decreases performance (dutch marathon).
Affects people with slower times more.
Decrease the impact of climate and sports clothing in American foolball
Increase in humidity and temp may mean that heat storage rate is positive with kit on and are at risk.
Highest risk in pre seasons training when players are acclimated
What is the treatment for hyperthermia? Possible down side?
Ice bath - vasoconstriction? - at core temp over 40 does not occur.
Harder to ECG and defib if wet
Risk of mortality/ morbidity from hyperthermia is associated with what?
Time spent over 39.5 deg.
Treat immediately and transport later
Describe the effects of anthropometrics on heat tolerance
Body SA - more heat loss/gain
Adiposity - no effect on heat gain as vascular but helps prevent heat loss
Body mass - passive weight load (M), heat sink - more energy to heat up
Describe the symptoms of heat illness.
Heat cramps - musclar
N/V
Thirst, sweating
Heat syncope
Heat exhaustion - dehydration/hyponat
- pale cool skin
- weakness
- Dizziness
- Fatigue (can also get chronic fatigue
- Chills or goose bumps
Heat stroke
- Strong and rapid pulse
- Organ dysfunction
- Hot and dry skin
- Confusion
Predisposing factors to heat illness
Dehydration
- Alcohol
- Duiretics
- Intestinal problems
- reduced food and liquid
Low fitness Non-acclimated Adiposity Age Sleep deprivation Long term high level exercise Protective clothing Previous heat illness
Drugs
- Stimulants
- BBs
- Anticholinergics
- Digitalis
Also make worse
- fever
- hypertension
- infection
- burns
Describe predisposition, mechanism, treatment and prevention to heat exhaustion
sustained exertion in heat, lack of acclimation
or failure to replace water loss, salt deficiency
mech:
dehydration, depleted circulatory volume,
competing demands from muscle and skin
Treatment
move to cool environment rest recumbent, fluids
if mentally alert, stay alert for heat stroke development
Describe predisposition, mechanism, treatment and prevention to heat stroke
sustained exertion in heat, lack of acclimation
or failure to replace water loss.
mech:
failure of thermoregulatory system, leading to
loss of evaporative cooling by reduced sweating
treatment
move to cool environment, rapid cooling (avoid
overcooling)
Broadly describe the ways to assess heat stress and strain
Empirical
Single measuring device to determine climate. Compared with an index table to ascertain the stress added by metab rate and clothing.
Analytical
Each parameter measured individually to synthesise and final figure which is then compared with a reference value. May predict core temp increase or decrease
Parameters assessed in heat stress
Ambient temp Radiant Relative humidity Air speed Metab Clo
Empirical vs analytical pros and cons
Empiraical is more simple to administer
Analytical - can analyse the effect of parameters on heat stress individually.
Describe the botsball
Black ball (+/- water around gauge inside) dry air temp monitor
What is the WBGT? How can it be used to find thermal strain
Wet bulb globe temperature.
Several measurements - inputted into calc to generate result
What are the specific analytic methods of determining heat stress
Ereq (required sweat rate) = (C+M+R)
(includes clothing as it effects C and R)
PHS - Physiologiacal heat strain which is synthesed from Ereq to calculate
How are heat stress measures used in the workplace? Compared with effort and expertise
Simplest used first e.g. screening, checklist, WGBT then later comes analytical e.g. rational model but requires much more expertise
Simple - Diagnostic evaluation using ISO standard e.g. WBGT
Exceeding limit then go to complex
Complex
Analytic evalulation using ISO stnadard
Ereq or PHS
Exceeding then do individual
Individual
Individual monitoring of physiological reactions
Output
Results in risk assessment, workplace adjustment, work-rest cycles, limitation of working time
History of the WBGT
Fighting in Sahara in WWII, mines, boot camps in US. Only had Prescriptive zone and WHO technical report
What was the WHOs technical report on heat stress and what was wrong with it?
<38 core temp ok
<39 ok if closely monitored
Based on pop and core temp estimates - variation means 2% would be above 41 and at risk = generalisability
What does the WBGT consist of and what does each measure
Wet bulb - evap, air speed, ambient temp, radiation (small)
Globe - radiation and air temp and wind speed
Dry bulb
Calculations for WBGT
.7Tnwb(natural wb) + .3Tg when inside
.7Tnwb +..2Tg+ .1db when in sunlight
How are WBGT thresholds (WBGT TLV) calculated?
USing Lind’s prescriptive zone. Plot WGBT value at prescriptive zone threshold vs M
Describe the prescriptive zone experiment method and author.
People 60-90 mins of constant metabolic work - measure core temp.
Lind
What are the presriptive zone vs environmentally driven zone? Implications
Prescriptive zone core temperature in not effected by the environment and so raises to the same level at a set M.
Environemtnally driving zone - Environment contributes to a rise in body temp with work - loss of thermoregulation. -shouldnt work here
Caveats of the WBGT TLV/ flaws.
Doesnt account for clothing
8 hours of continual work.
Limites are lower if unacclimated and wind
Not good for extreme temps
How does clothing effect WBGT TLV? scale?
Pushes graph to the left (core temp vs WBGT)- WGBT TVL decreases at certain M. Parallel line below for WGBT vs M.
Known as WBGTadjusted
Describe work rest cycles ad caveats?
Based on 1 hour
Maximum of 6 per day
Describe the steps made if an environemnt exceeds the WGBT to be safe?
CAn modify environment/ M?
Can screen and ensure workers are healthy and monitor individually?
CAn use work rest cycles?
Can use clothing that creates a microclimate?
How would a smaller globe change the WBGT?
Increase the speed of temp change (need mathmatically comensating)
Less precise?
How much M if sitting quiety vs running 10km/hr
130 vs 850W (W.hr)
How can we measure inputs into heat balance equation precisely?
Sweat rate - weight
Resp - measure temp and humidity in and out
Radiation, convection control
How is most heat lost in cold and hot environemtns
cold - 75% convective, 10% resp, 5% evap
Hot - 75% evap
Describe the effects of solar radiation and factors that determine how much we absorb
up to 1000W.m2 in tropics
Depends on
Latitude
Cloud cover
skin and garment colour (only for visible range)
position in the sky and postion of individual (determines SA with exposure
Effects of clothing on heat balance factors
Decrease in convective heat loss, evaporative and radiative
Increase in work rate due to to weight and stifness
How do we prioritise clothing?
Fashion
Feel
Fit (pressure)
Function
Differences between clothing material properties and garment properties on heat balance
Material Insulation Air/ vapour resistance Radiation reflection/ asorption moisture Absorption
Garment Design Layers Fit Ventilation
Describe the relationship between heat resistance(or vapour resistance) and material thickness
Linear increase
Effects on insulation with water impermeability/ weave
Increasingly tight weave = less convective and vapour diffusion
Semi perm - vastly decreased evap e.g. goretex but does not allow droplets in.
Impermeable membrane - no vapour diffusion but condensation so increased convection
Wind and movement effect on clo?
Decrease clo as more ventilation and less resistance
Descibe behavioural adaptations to climate
Autonomic behavioural regulation e.g. clenching fists, orientating towards a heat source
Changes in mood.
Long term behavioural adaptation – acclimatisation to climate
technical regulation
Includes psychological changes e.g. changes in mood.
How far in rectal probe?
10cm
Tympanic temperature?
Not bad - brain tem
Aural temp?
Ear defenders - not that accurate
Radiopills measure what?
Itraabdominal temp
Risks of cold exposure
Hypothermia/insidious hypothermia • Cardiovascular stress • Freezing cold injury (frostbite/frostnip) cell damage • Non-freezing cold injury (trench foot) nerves/blood vessels • Dexterity loss • Discomfort
Symptoms of hypothermia
Mild - symp - shivering BP, increased urine, mental confusion, hepatuc dysfunction? hypoglycaemia?
Mod - violent shiv, muscle miscoordination, stimbling, mild confusion, pale, blue extremities
Sev - HR, RR, BP decrease - HR in 30s, difficulty speaking, amnesia, inability to use hands, legs, blue and pufy skin below 30, stupor, irrational behaviour, AF, VT, organ failure
At what temp is there multi organ failure and heat stroke
44C
Lind experiment when and how was temp measured?
1963 and rectal temp.
Describe HSI, Ereq, Swreq
HSI: Ereq = M- (C+R)
Ereq/Emax x 100%. >100 then cant thermoreg.
Not good enough as not sweat rate
Later SWreq = Ereq/ r (sweat efficiency)
Here Ereq calc is more comprehensive
Ereq = M- W- (C + R + Eres +Cres)
Risks of freezing at specific WCI
28-39 = mod freeze in 10-15 40-47 = high 5-10 48-54 = very high 2-5 <55 = extrememly high <2
Difference in DLE in cold vs hot
Too cold vs too hot or too dehydrated
Difference in Abos vs Inuit and cold adaptation
Abos - hypothermic- know that the temperature will increase so shivering doesnt occur and temperature falls.
Inuit - metabolic adaptation (role of diet0, behavioural mostly but also blood flow to hands
Safe maximal temperatyre for healthy fit subjects
Lab is 39.2 40C in mecca - 10% mort 42 - 60 43 - 80 80 at 42
Critical temp of nerve conduction
20 -
Decreases from 36
Sharper from 20-24
Block below 10
With what skin temp does temperature become uncomfortable
Slight at: 32 35 More at: 30 36
Skin wettedness and temp
34 = 6 35 = 20 26 = 40%
Condition and local skin temp
0.5 frostbite 7 numberness 15 pain 20 reduced dext 25 cool 45 pain >45 burns (time dependent)
Each additional layer of clothing adds up to how much air layer?
6mm
Walking reduces resistance by how much
4ms - 60% air res
80% vapour resis
Weight of clothing efffect on metab
Central is efficient
Hands and feet can increase 5x per kilo
Receptor critical temp
10
Minor 25-8
6-8 drops rapidly
<6 block
Joint critical temp
24
When does shivering occur
36
severe at 35
1 clo in equivalent unit
.7 too
- 155m2C/W
0. 1m2C/W
Water conducts heat how many times faster than ai?
2
Factors that interact to improve physiologic adjustments and exercise tolerance during heat stress?
SHAFTS Sensible Hydration Acclimatised Fitness Thin Sober All increase tolerance to heat
