Cardiovascular and respiratory control: acclimatisation and fever Flashcards
Acclimatisation
Individual response to environmental change
Adaptation
Traits heritable through generations
Peripheral cold injury
Trench food
Frost bite
Trench foot
When soldiers who fought in soggy trenches during WWI.
Caused by the cooling of peripheral nerve and muscle, which then caused sensory and motor malfunction
Frostbite
Results from freezing of tissue. Can lose finger tips and toes etc
You’re not dead until you’re warm - why and how
Immersion in cold water with high thermal conductivity can lead to hypothermia but subcutaneous fat will provide something insulation.
Woman trapped under ice I’m freezing water for 80 minutes
After 40 minutes: cardiopulmonary arrest
After 80 minutes was recused: treated with cardiopulmonary I pass amd axtracoeal blood warming
After 4 hours: heart started to beat again and made a nearly full recovery
Why? At freezing temperatures, cellular oxygen demand was reduced so much that cells could survive without effective circulation
Surgically induced hypothermia
May provide benefits that outweigh risks
- neurosurgery on inaccessible aneurysm: body can be cooled by extracorpeal circulation so that blood flow is stopped for ~15minutes
- cardiac surgery e.g valve replacement cold cardioplegia is used to stop heart for ~60 minutes
what groups of people show adaptations to prolonged cold exposure
aborigines and inuits
How did aborigines adapt to prolonged cold exposure
- nomads that lived outside and wore no clothing
- very cold temperatures at night
- normally, people shiver to maintain core temp
BUT shivering keeps you awake - aborigines have reduce shivering and their core temperature will drop, but they sleep well
pros and cons of vasoconstriction for thermoregulation
helps maintain core temp
but causes problems such as loss of manual dexterity and frostbit
how is manual dexterity improved and risk of frost bite reduced?
paradoxical vasodilation
- blood flow and skin temp show a hunting reaction
well developed in inuits
who has developed hunting reaction
inuits
what shows hunting reaction
subject finger immersed in ice water for prolonged time.
will vasocontrict to maintain core temp then paradoxically dilate to provide protective effects.
Finger temperature shows oscillations as changes from contraction to dilation
what causes adaptation to prolonged cold exposure
though to be combination of genetic adaptation and acclimatisation
pros and cons of involuntary muscle activity
can increase heat production x 5 briefly, but raises convective heat loss
when does vasoconstriction of skin vessels mostly occur
in the TZ
main response to cold exposure
increase heat production mechanisms
- voluntary muscle activity
- involuntary muscle activity
- brown fat metabolism
decreased heat loss mechanisms
- behavioural (heating, clothes)
- vasoconstriction of skin vessels
- horripilation
acclimatisation to prolonged heat exposure
within 7 days:
- sweat and evaporation capacity increased
- salt loss during sweating is reduced to 20% of initial value
physiological changes to continued heat exposure
- rectal temp increases initially, then after 9 days reduces close to normal
- HR increase initially, then after 9 days reduces close to normal
- sweating increases rapidly across 9 days
increased heat loss mechanisms
- behavioural
- vasodilation of skin vessels
- sweating
reduced heat producton
- inactivity, inertia
- anorexia - high water content foods are preferred
Fever
mild to modest elevation in body temp
37.5-40 degrees C
common sign of infection
what happens to set point during fever
- body tried to maintain original set point and so patient feels cold
- Body then achieves set point and so doesn’t feel cold
symptoms of hyperthermia
heat syncope
heat exhaustion
heat stroke
heat syncope
fainting due to vasodilation and fall in BP
heat exhaustion
water & salt deficiency due to prolonged sweating
heat stroke
loss of thermoregulatory control as brain temp rises and function fails - usually fatal
Malignant hypothermia
triggered by drugs
2,4DNP originally an explosive then reintroduces to stimulate metabolism and promote weightloss
DNP is now banned
thermoregulation in elderly
- physiologically less efficient
- mobility greatly reduced and so is shivering and vasoconstriction in response to cold
- heat-producing lean body mass diminishes
- financial difficulties keeping heating off in winter
- in the heat elderly show reduced sweating and vasodilation
thermoregulation in neonates
- linear VS area VS volume change
- heat loss is proportional to surface area
- heat production is proportional to volume
neonates have a greater surface area to volume ratio than adults =
produce relatively little heat but lose relatively more
- neonates are prone to drop in core temp in response to cold stimuli
- they can vasoconstrict and vosodilate skin blood vessels and they can sweat
