Piokilotherms vs HomeothermsPiokilotherms vs Homeotherms

Piokilotherms: at mercy of the elementsPiokilotherms: at mercy of the elements Homeotherms: can function independent Homeotherms: can function independent

of the environmentof the environment Ability to maintain constant temperatureAbility to maintain constant temperature

Normal body temperature: 36.5-Normal body temperature: 36.5-37.537.5°C°C

During exercise can increase to 40°C with no ill During exercise can increase to 40°C with no ill effectseffects

Core temp: temperature of the hypothalamus, Core temp: temperature of the hypothalamus, temperature regulator of the bodytemperature regulator of the body

Thermal gradients: temperature differences from Thermal gradients: temperature differences from one point to another the lead to movement of one point to another the lead to movement of heatheat

Temperature always equilibrates from hot to coldTemperature always equilibrates from hot to cold

Temperature RegulationTemperature Regulation

MetabolismMetabolism ShiveringShivering Nonshivering thermogenesisNonshivering thermogenesis Metabolic RateMetabolic Rate Heat lossHeat loss

MetabolismMetabolism

Heat is produced naturally during normal Heat is produced naturally during normal metabolic reactionsmetabolic reactions

Most reactions lose ~75% of energy as Most reactions lose ~75% of energy as heatheat

At BMR heat loss is ~100 kcal/hrAt BMR heat loss is ~100 kcal/hr BMR is porportional to ¾ power of body BMR is porportional to ¾ power of body

weight (surface rule)weight (surface rule)

ShiveringShivering

Main mechanism for increasing heat Main mechanism for increasing heat during negative heat balanceduring negative heat balance

Involuntary muscle contractionInvoluntary muscle contraction Maximum shivering can increase body’s Maximum shivering can increase body’s

heat production 5Xheat production 5X

Preshivering tone can increase heat production Preshivering tone can increase heat production 50-100%50-100% An effective way to increase body temperature b/c no An effective way to increase body temperature b/c no

work is done by the muscles and most of the energy work is done by the muscles and most of the energy is expended is heatis expended is heat

Increases Q by increasing SV via increased Increases Q by increasing SV via increased venous returnvenous return

Limits: glycogen depletion, hypoglycemia, Limits: glycogen depletion, hypoglycemia, fatigue, ex., hypoxia, drugs (alcohol and fatigue, ex., hypoxia, drugs (alcohol and barbiturates) barbiturates)

Nonshivering thermogenesisNonshivering thermogenesis

Increased thyroxin secretion (thyroid) and Increased thyroxin secretion (thyroid) and catecholamine secretion (adrenals) catecholamine secretion (adrenals) increase metabolic rateincrease metabolic rate

Thyroxin increases the rate of all cellsThyroxin increases the rate of all cells Cats., esp norepi. release FFA, increasing Cats., esp norepi. release FFA, increasing

metabolic ratemetabolic rate

Metabolic Rate (Q10 and food)Metabolic Rate (Q10 and food)

Q10 is rate of a physiologic process at a Q10 is rate of a physiologic process at a particular temperature to the rate at a particular temperature to the rate at a temperature 10°C lowertemperature 10°C lower

Increased metabolic rate can be self-Increased metabolic rate can be self-perpetuating (dangerous)perpetuating (dangerous)

At high temperatures, hypothalamus loses At high temperatures, hypothalamus loses ability to cool the bodyability to cool the body

Rate of temperature increases faster at Rate of temperature increases faster at higher temperatureshigher temperatures

Metabolic rate temporarily increases Metabolic rate temporarily increases following food intake, esp. proteinsfollowing food intake, esp. proteins

Heat Loss Heat Loss

RadiationRadiation ConductionConduction ConvectionConvection EvaporationEvaporation

RadiationRadiation

Loss or gain in the form of electromagnetic Loss or gain in the form of electromagnetic waveswaves

At rest, in a comfortable environment, radiation At rest, in a comfortable environment, radiation accounts for 60% of total heat loss accounts for 60% of total heat loss

Varies with body position and clothesVaries with body position and clothes Human skin, regardless of color, absorbs ~97% Human skin, regardless of color, absorbs ~97%

of radiant energy that strikes itof radiant energy that strikes it

ConductionConduction

Transfer of heat from a body to an objectTransfer of heat from a body to an object Or, heat transfer within an organism down Or, heat transfer within an organism down

a thermal gradienta thermal gradient ~3% of total heat loss at room temperature ~3% of total heat loss at room temperature

occurs this wayoccurs this way

ConvectionConvection

Conduction of heat to air or waterConduction of heat to air or water Amounts to ~12% of all heat lost at room Amounts to ~12% of all heat lost at room

temperaturetemperature Heat is conducted to water or air, moves Heat is conducted to water or air, moves

so that other molecules can be heatedso that other molecules can be heated Faster in water or air?Faster in water or air?

Greater in the wind (air movement)Greater in the wind (air movement) Wind chill effectWind chill effect Can also occur in the circulatory systemCan also occur in the circulatory system Heat moves with the blood from the Heat moves with the blood from the

core to the peripherycore to the periphery As skin temp. incr., heat loss to As skin temp. incr., heat loss to

environment increasesenvironment increases Rate is affected by blood flow and Rate is affected by blood flow and

temperature gradient (core/periphery)temperature gradient (core/periphery)

EvaporationEvaporation ~25% of heat is lost this way in a ~25% of heat is lost this way in a

comfortable environmentcomfortable environment Quantity of heat absorbed by sweat as it Quantity of heat absorbed by sweat as it

evaporates: latent heat of vaporizationevaporates: latent heat of vaporization Body loses 0.58 kcal/gm HBody loses 0.58 kcal/gm H22O O

evaporates evaporates Only means of cooling at high Only means of cooling at high

environmental temperatures, Critical for environmental temperatures, Critical for exerciseexercise

If body cannot lose heat this way, body If body cannot lose heat this way, body temp. increases rapidlytemp. increases rapidly

Sweat is only effective if it evaporatesSweat is only effective if it evaporates High humidity: evaporation reduced or High humidity: evaporation reduced or

preventedprevented Effective evaporation also hampered by Effective evaporation also hampered by

little air movementlittle air movement

Women have a lower sweating capacity Women have a lower sweating capacity than men dothan men do

Process occurs by sweating and Process occurs by sweating and insensible water loss: ventilation, diffusion insensible water loss: ventilation, diffusion through skin, does not include sweat, through skin, does not include sweat, urine, and fecesurine, and feces

Sweat rates are at 0 when temperature is Sweat rates are at 0 when temperature is lowlow

Hypothalamus and temperature Hypothalamus and temperature regulationregulation

Temperature regulatory centerTemperature regulatory center Responds to heat primarily through Responds to heat primarily through

heat-sensitive neurons in the preoptic heat-sensitive neurons in the preoptic area of anterior portionarea of anterior portion

More cold than heat receptors in the More cold than heat receptors in the skinskin

Thermoregulators transmit impulses to Thermoregulators transmit impulses to the spinal cord, to hypothalamus, the spinal cord, to hypothalamus, initiates responseinitiates response

Ant. Hypothalamus stimulates the sweat Ant. Hypothalamus stimulates the sweat glands, evaporative heat lossglands, evaporative heat loss

““Hunting Reflex” primarily in hands and Hunting Reflex” primarily in hands and feetfeet

Hypothalamus is the body’s thermostatHypothalamus is the body’s thermostat Set-point it tries to keepSet-point it tries to keep Sweating normally occurs at 37°CSweating normally occurs at 37°C Set-point can change in response to Set-point can change in response to

dehydration, starvation, and feverdehydration, starvation, and fever

Exercise in the ColdExercise in the Cold

ClothingClothing Oxygen ConsumptionOxygen Consumption VentilationVentilation HeartHeart Muscle StrengthMuscle Strength Metabolic ChangesMetabolic Changes

ClothingClothing

Insulation value of clothing must be Insulation value of clothing must be balanced with increased metabolic balanced with increased metabolic production of the exerciseproduction of the exercise

Traps warm air next to the skin an Traps warm air next to the skin an decreases heat loss by conduction and decreases heat loss by conduction and convectionconvection

Should be worn in layersShould be worn in layers

Oxygen ConsumptionOxygen Consumption

Maximum uptake is unaffected by the coldMaximum uptake is unaffected by the cold Submax. VOSubmax. VO22 increases in the cold increases in the cold Why?Why? Shivering can persist during exercise, Shivering can persist during exercise,

which also can increase VOwhich also can increase VO22

VentilationVentilation

Increases in the cold, particularly if Increases in the cold, particularly if exposure is suddenexposure is sudden

Abrupt exposure can lead to gasping Abrupt exposure can lead to gasping reflexreflex

HeartHeart Cold exposure causes peripheral Cold exposure causes peripheral

vasoconstriction, increase central BVvasoconstriction, increase central BV BP increase due to increased afterload BP increase due to increased afterload

and sometimes increased preload tooand sometimes increased preload too SV may increase, inc. EDVSV may increase, inc. EDV Changes in cardiac performance more Changes in cardiac performance more

common in mencommon in men Incidence of arrhythmias increase in Incidence of arrhythmias increase in

coldcold

Muscle StrengthMuscle Strength

Strength decreases with lower muscle Strength decreases with lower muscle temp.temp.

Also lower enzyme activityAlso lower enzyme activity Increased MU recruitment may be Increased MU recruitment may be

necessary to compensatenecessary to compensate Other factors: increased muscle viscosity, Other factors: increased muscle viscosity,

decreased ATP metabolism and decreased ATP metabolism and contractilitycontractility

Metabolic ChangesMetabolic Changes Increase use of CHO as substrateIncrease use of CHO as substrate Light ex: glycogen depletes fasterLight ex: glycogen depletes faster Max ex: depletion is independent of Max ex: depletion is independent of

temp.temp. Prolonged exposure to cold: Prolonged exposure to cold:

hypoglycemia, suppresses shivering, hypoglycemia, suppresses shivering, core temp drops, lactate highercore temp drops, lactate higher

Fat metabolism suppressed, even Fat metabolism suppressed, even though cat. response is higherthough cat. response is higher

Acclimatization and Habituation to Acclimatization and Habituation to ColdCold

Acclimatize: physiologic compensation Acclimatize: physiologic compensation to environmental stress over timeto environmental stress over time

Habituation: lessening of the sensation Habituation: lessening of the sensation associated with an environmentassociated with an environment

Shivering thresholdShivering threshold First test of acclimatizationFirst test of acclimatization Cold-acclimatized people maintain heat Cold-acclimatized people maintain heat

production with less shivering, more production with less shivering, more nonshivering thermogenesisnonshivering thermogenesis

Hand and Feet temperatureHand and Feet temperature Second test for acclimatizationSecond test for acclimatization Acclimatized: maintain almost normal Acclimatized: maintain almost normal

temperaturetemperature Habituation also plays a roleHabituation also plays a role

Ability to sleep in the coldAbility to sleep in the cold Third and final testThird and final test Seems to depend on extent of Seems to depend on extent of

nonshivering thermogenesis induced by nonshivering thermogenesis induced by increased secretion of norepiincreased secretion of norepi

HypothermiaHypothermia

Depresses the CNS, lose ability to shiver, Depresses the CNS, lose ability to shiver, sleepiness, coma, deathsleepiness, coma, death

Lower temp: lower cellular met. rate, Lower temp: lower cellular met. rate, further lowering temp.further lowering temp.

Profound effects on the CV systemProfound effects on the CV system Central BV decreases; plasma Central BV decreases; plasma

sequestration, inadequate fluid intake, cold sequestration, inadequate fluid intake, cold diuresisdiuresis

Risk factorsRisk factors cold exposurecold exposure Lack of protective clothingLack of protective clothing LeannessLeanness Inadequate fluid intakeInadequate fluid intake High wind chillHigh wind chill Use of alcohol &/or drugsUse of alcohol &/or drugs Use of snow to relieve thirstUse of snow to relieve thirst Glycogen depletionGlycogen depletion

FrostbiteFrostbite

Caused by ice crystal formation within the Caused by ice crystal formation within the tissuetissue

Occurs in exposed skinOccurs in exposed skin Can lead to tissue deathCan lead to tissue death

Exercise in the HeatExercise in the Heat

Cardiovascular EffectsCardiovascular Effects

Plasma volume decreases Plasma volume decreases during exercise in the heatduring exercise in the heat

becomes acute at intensity increasesbecomes acute at intensity increases decrease of plasma volume is made worse decrease of plasma volume is made worse

by loss of body fluids through sweatingby loss of body fluids through sweating may not be enough blood to adequately may not be enough blood to adequately

perfuse all areas during exercise in the perfuse all areas during exercise in the heatheat

central blood volume may decrease and central blood volume may decrease and cause a decrease in cardiac filling cause a decrease in cardiac filling pressurepressure

results in increased HR in attempt to results in increased HR in attempt to compensate for lower SVcompensate for lower SV

submax. HR increases alsosubmax. HR increases also @ max levels, skin vessels @ max levels, skin vessels

vasoconstrict to help maintain blood vasoconstrict to help maintain blood pressure and Qpressure and Q

negative response on heat transfernegative response on heat transfer circulatory regulation takes precedence circulatory regulation takes precedence

over temperature regulation in this caseover temperature regulation in this case VO2 max is not impaired in the heat VO2 max is not impaired in the heat

unless the person was experiencing unless the person was experiencing thermal imbalance before beginning the thermal imbalance before beginning the exerciseexercise

Sweating ResponseSweating Response

primary means of heat dissipation during primary means of heat dissipation during exercise (evaporation)exercise (evaporation)

in heat, sweating is very important b/c in heat, sweating is very important b/c body tends to gain rather than lose heat by body tends to gain rather than lose heat by radiation, conduction, and convectionradiation, conduction, and convection

during exercise, sweating is related more during exercise, sweating is related more to intensity than environmental to intensity than environmental temperaturetemperature

Acclimatization to heatAcclimatization to heat first two weeks of heat exposure results in first two weeks of heat exposure results in

lower heart rate, core temperature, RPE, lower heart rate, core temperature, RPE, and skin temperature at rest and during and skin temperature at rest and during exerciseexercise

primary physiological adjustments are primary physiological adjustments are increased peripheral heat conductance, increased peripheral heat conductance, plasma volume, and sweating, decreased plasma volume, and sweating, decreased core temperature at onset of sweating, and core temperature at onset of sweating, and improved distribution of sweat over the skinimproved distribution of sweat over the skin

CV AdaptationsCV Adaptations

acclimatization induces a 3-27% increase acclimatization induces a 3-27% increase in plasma volume, if acclimatization is in plasma volume, if acclimatization is done with exercise trainingdone with exercise training

increased plasma volume helps to increased plasma volume helps to maintain SV, central blood volume, and maintain SV, central blood volume, and sweating capacitysweating capacity

also increases in vasopressin, renin, and also increases in vasopressin, renin, and aldosterone in early daysaldosterone in early days

blood flow to the skin decreasesblood flow to the skin decreases decreased skin blood flow helps to decreased skin blood flow helps to

maintain central blood volume, which is maintain central blood volume, which is vital for maintaining BP, SV, and muscle vital for maintaining BP, SV, and muscle blood flow during exerciseblood flow during exercise

core temperature is lower during core temperature is lower during exerciseexercise

decrease in skin blood flow is decrease in skin blood flow is accompanied by a large increase in accompanied by a large increase in sweating and evaporative cooling sweating and evaporative cooling capacitycapacity

Sweating ResponseSweating Response

acclimatization increases this response acclimatization increases this response almost 3X, from ~1.5 l/hr to 4 l/hralmost 3X, from ~1.5 l/hr to 4 l/hr

accompanied by a more even distribution accompanied by a more even distribution of sweatingof sweating

sweat losses of sodium chloride decrease sweat losses of sodium chloride decrease b/c of increased secretion of aldosteroneb/c of increased secretion of aldosterone

Thermal DistressThermal Distress

includes dehydration, heat cramps, heat includes dehydration, heat cramps, heat exhaustion, heat syncope, and heat strokeexhaustion, heat syncope, and heat stroke

hyperthermia is caused by an imbalance hyperthermia is caused by an imbalance between heat gain and heat lossbetween heat gain and heat loss

DehydrationDehydration

loss of fluid from the bodyloss of fluid from the body can decrease sweat rate, plasma volume, can decrease sweat rate, plasma volume,

Q, VO2 max, work capacity, muscle Q, VO2 max, work capacity, muscle strength, and liver glycogenstrength, and liver glycogen

at fluid deficit of 5% of BW, symptoms at fluid deficit of 5% of BW, symptoms include discomfort, and alternating states of include discomfort, and alternating states of lethargy and nervousnesslethargy and nervousness

level >7% is extremely dangerouslevel >7% is extremely dangerous

at levels >10%, ability to walk is at levels >10%, ability to walk is impaired, and is accompanied by impaired, and is accompanied by discoordination and spasticitydiscoordination and spasticity

as 15% is neared, the person as 15% is neared, the person experiences delirium, shriveled skin, experiences delirium, shriveled skin, along with decreased urine volume, loss along with decreased urine volume, loss of ability to swallow food, and difficulty of ability to swallow food, and difficulty swallowing waterswallowing water

>20% the skin bleeds and cracks>20% the skin bleeds and cracks

thirst does not keep up with fluid thirst does not keep up with fluid requirementsrequirements

physical fitness helps prevent thisphysical fitness helps prevent this during prolonged exercise, can develop during prolonged exercise, can develop

hyponatremia, caused by excessive hyponatremia, caused by excessive sodium loss in the sweat without adequate sodium loss in the sweat without adequate replacementreplacement

Heat crampsHeat cramps

characterized by involuntary cramping and characterized by involuntary cramping and spasm in muscle groups used during exercisespasm in muscle groups used during exercise

it occurs in people who have exercised and it occurs in people who have exercised and sweated heavilysweated heavily

often the individual is conditioned and often the individual is conditioned and acclimatizedacclimatized

fluid and electrolyte replacement, rest, some fluid and electrolyte replacement, rest, some say magnesium helpssay magnesium helps

Heat exhaustionHeat exhaustion

rapid, weak pulse, hypotension, faintness, rapid, weak pulse, hypotension, faintness, profuse sweating and psychological profuse sweating and psychological disorientationdisorientation

results from acute plasma volume loss and results from acute plasma volume loss and inability of the circulation to compensate inability of the circulation to compensate for the concurrent vasodilation in the skin for the concurrent vasodilation in the skin and the active working musclesand the active working muscles

TreatmentTreatment

have person lie down in cool areahave person lie down in cool area administer fluidsadminister fluids rest and drink plenty of fluids for next 24 rest and drink plenty of fluids for next 24

hr.hr. not allowed to participate for rest of the not allowed to participate for rest of the

dayday

Heat syncopeHeat syncope

related to heat exhaustion, but can occur related to heat exhaustion, but can occur without major sweat losswithout major sweat loss

typically, it occurs after exercise when the typically, it occurs after exercise when the individual stops moving and blood poolsindividual stops moving and blood pools

can occur secondary to heat exhaustion or can occur secondary to heat exhaustion or independentlyindependently

Heat strokeHeat stroke

failure of hypothalamic temperature failure of hypothalamic temperature regulatory center; represents a major regulatory center; represents a major medical emergencymedical emergency

principally caused by failure of the principally caused by failure of the temperature regulatory center in temperature regulatory center in hypothalamus, which causes failure of the hypothalamus, which causes failure of the body’s heat loss mechanismsbody’s heat loss mechanisms

characterized by a high core temperature, hot, characterized by a high core temperature, hot, dry skin, and extreme CNS dysfunctiondry skin, and extreme CNS dysfunction

associated with increases in plasma associated with increases in plasma norepinehprine, epi, and endotoxin levels that norepinehprine, epi, and endotoxin levels that have been associated with vascular collapsehave been associated with vascular collapse

risk is greatest in high temperatures, humidity, risk is greatest in high temperatures, humidity, hottest time of the day, and on days with little hottest time of the day, and on days with little windwind

TreatmentTreatment

cool person with tepid watercool person with tepid water ice packs on the groin, neck, and axillaice packs on the groin, neck, and axilla send to hospital ASAPsend to hospital ASAP

PreventionPrevention

ensure athletes are well-conditionedensure athletes are well-conditioned avoid overheatingavoid overheating be aware of early symptoms of heat stress: be aware of early symptoms of heat stress:

thirst, fatigue, lethargy, and visual disturbancesthirst, fatigue, lethargy, and visual disturbances athletes should not train harder than normal athletes should not train harder than normal

intensityintensity should not compete if have an illness should not compete if have an illness

accompanied by a feveraccompanied by a fever

schedule practice during the cooler times schedule practice during the cooler times of the dayof the day

modify or cancel sessions when the wet modify or cancel sessions when the wet bulb temperature is 25.5°C or greaterbulb temperature is 25.5°C or greater

plan regular fluid breaksplan regular fluid breaks supply a drink that is cold and contains supply a drink that is cold and contains

some CHO and electrolytessome CHO and electrolytes

hyperhydrate before activityhyperhydrate before activity fluid replacement should be encouraged fluid replacement should be encouraged

during the early stages of practice and during the early stages of practice and competitioncompetition

athletes should be weighed every day athletes should be weighed every day before and after practice. If a 2-3% before and after practice. If a 2-3% decrease in weight, should consume decrease in weight, should consume more fluid, if 4-6%, should decrease more fluid, if 4-6%, should decrease activity levels, 7% loss, consult a activity levels, 7% loss, consult a physicianphysician

RhabdomyolysisRhabdomyolysis Myoglobin excretion is increasedMyoglobin excretion is increased Myoglobin is cleared by the kidneysMyoglobin is cleared by the kidneys Kidneys shut down, especially with heatKidneys shut down, especially with heat Can lead to deathCan lead to death Occurs with excessive exerciseOccurs with excessive exercise RareRare May be a predisposition, latent metabolic May be a predisposition, latent metabolic

disorderdisorder Diuretics contribute to thisDiuretics contribute to this CHO as well, but a rare possibilityCHO as well, but a rare possibility