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BPK 142 Lecture Flashcards > Lecture 12 - Cold and Underwater > Flashcards

Lecture 12 - Cold and Underwater Flashcards

1
Q

Humans are described as homeotherms.

  • Why?
  • What is our resting core temp?
  • Where is our core?
  • During exercise, how much can core temp increase?
A
  • we use behavioural and physiological mechanisms to regulate our core temperature
  • ~37 degrees celcius
  • hypothalamus, which is also site of temp regulation
  • can rise above 40degC, its increase is proportional to exercise intensity.
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2
Q

How do we measure our core temperature? (3)

A
  • rectal probes
  • esophageal probes,
  • Ingested pills that send a temperature signal from the Gastrointestinal system
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3
Q

How is skin temperature measured? What influences skin temperature (4)?

A
  • dermal patches

- influenced by the environment, metabolic rate, clothing and hydration state.

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4
Q

What are the 4 mechanisms of heat loss?

A
  • radiation
  • conduction
  • convection
  • evaporation
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5
Q

Define: radiation

A
  • the exchange of electromagnetic energy waves emitted from one object and absorbed by another
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6
Q

Define: conduction

  • Define: insulator

- Explain the relationship between conductive heat exchange and thickness of insulating substance

A
  • occurs whenever two surfaces with differing temperatures are in direct contact.
  • Insulator: do not conduct heat readily
  • The rate of conductive heat exchange is inversely related to the thickness of the insulating substance
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7
Q

Explain the difference between air and water in terms of conduction vs insulation

A

Still air is an excellent insulator, while water is an excellent conductor. Heat conduction in water is about 25 times greater than in air.

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8
Q

Define: convection

A
  • requires that one of the media be moving as occurs with a fluid or gaseous medium.
  • For example, heat transfer from skin to moving air or water
  • Convective heat loss during swimming is more than twice that during rest in still water.
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9
Q

Define: wind chill index

A
  • gives the equivalent still air temperature for a particular ambient temperature at different wind velocities
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10
Q

Define: evaporation

A
  • the transfer of heat from the body surface through the change of liquid water on the skin to a gaseous water vapour in the environment
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11
Q

What are the 2 primary physiological responses used by humans to defend against a cold environment?

A
  1. increase in metabolic rate

2. increased tissue insulation

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12
Q

Explain how we increase our metabolic rate to defend against a cold environment (2)

A
  • voluntary: exercise; can increase heat production 10-20 times the basal rate
  • involuntary: shivering; can increase basal rate 3-4 times basal rate
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13
Q

Explain how we increase our tissue insulation to defend against a cold environment

A
  • vasoconstriction of peripheral blood vessels and shunting of blood flow into deeper vessels
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14
Q

What are some behavioural responses to the cold?

A
  • wearing clothing, seeking shelter, starting a fire, etc.
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15
Q

List 3 factors that impact our response to cold

A
  • skinfold thickness (thicker the fat layer, greater the insulation
  • gender (women have greater insulation but more surface area, meaning they lose heat more rapidly than men)
  • clothing
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16
Q

What are some tips on how to dress for the cold?

A
  • layers!
  • you need more clothing insulation during rest than during exercise
  • getting your clothes wet = BAD; wear a water repellent and wind resistant outer layer
  • innermost layer should provide insulation and wick moisture away (polyester/polypropylene thermal underwear)
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17
Q

Explain hypothermia

  • define body core
  • where are the critical areas for heat loss?
A
  • medical emergency: body core temp below 35 degC
  • body core: refers to brain, heart, lungs, blood, liver, kidneys
  • head and neck, sides of chest, groin
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18
Q

What happens when core temperature drops below:

  • 32-34degC
  • 24-28degC
A
  • shivering ceases

- death

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19
Q

What factors are associated with hypothermia(7)?

A
  • Immersion in cold water or wet clothing
  • Wind
  • Physical exhaustion
  • Inadequate clothing for conditions
  • Low percent body fat
  • Hypoglycemia
  • Alcohol consumption (causes a decrease in shivering, increased blood flow to skin, impairs judgment)
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20
Q

How does hypothermia cause death?

A
  • increased hemoglobin affinity for O2 → less O2 is released to the tissues
  • body tissues lack critical O2 needed for function → hypoxia of heart and brain plus metabolic acidosis
  • reduced brain function and cardiac output → ventricular fibrillation and death
21
Q

Explain: frostbite; How is it dangerous?

A
  • Freezing of superficial tissues which occurs when skin temperature reaches between minus 2 to minus 6 degrees C.
  • Many people are unaware of frostbite because the sensory nerves are blocked and the skin is numb
22
Q

Explain how cold exposure impacts your respiratory tract and the mechanisms that reduce it

A
  • Inhaled air is conditioned as it enters the upper respiratory passageways; its warmed to 37 degrees C and saturated with water vapor.
  • Since cold air is very dry the cells lining the respiratory passageways become dry and cause a possibility of throat irritation.
23
Q

What are the 5 things you can see decrease when muscle temperature decreases?

A
  • strength and power
  • nerve conduction velocity
  • reaction time
  • manual dexterity
  • flexibility
24
Q

What is the optimal marathon performance temperature? Why is this optimal?

A
  • 14 degC

- the most optimal because heat dissipation is minimized but performance of muscles is not hindered by cool weather

25
Q

Due to the increased metabolism associated with exercise on land, a drop in Tc during exercise is rare, but still possible. List an example.

A
  • very low intensity long duration walking or trekking
26
Q

Why do you lose heat more dramatically and rapidly in water?

A

water is 25 times more conductive than air

27
Q

What are the signs of hypothermia (5)?

A
  • confusion
  • shivering
  • difficulty speaking
  • sleepiness
  • stiff muscles
28
Q

What is the relationship between water pressure and depth?

A
  • The weight of a column of water directly above a diver’s body (hydrostatic pressure) increases directly with increasing depth. The pressure increases by one atmosphere for each additional 10 m (33 ft.) of depth.
  • 10m (33 ft.) = 2.0atmosphere
  • 20m (66 ft.) = 3.0 atmosphere
29
Q

State Boyle’s law

A
  • the volume of any gas varies inversely with the pressure on it
  • (ie) if the pressure is doubled, volume is halved
30
Q

There are limits to how long you can snorkel for. Why(2)?

A
  • Pressure effects: inspiratory muscles are unable to overcome external pressure (caused by compressive force of water) and expand thoracic cavity because you are breathing air at atmospheric pressure
  • Increase in pulmonary dead space(VD):
    Normal anatomical dead space +
    Dead space of regular snorkel = 150 ml + 150 ml= 300ml;

You will need to work harder, at a higher VT(more breaths), in order to maintain VA (volume of air that participates in gas exchange).

31
Q

What happens to your lungs, respiratory passages, sinus, and middle ear spaces as you go deeper into water?

A
  • volume will decrease and pressure will increase as you dive deeper
32
Q

Breath hold diving is dangerous and can cause lung damage; how?

A

As the diver descends, the air in the lungs is compressed → lung squeeze. When lung volume is compressed below residual volume → lung damage occurs as blood is sucked from the pulmonary capillaries into the alveoli

33
Q

Fill in the blankL “Normal” maximal breath holding time after a maximal inspiration of ambient air is ____ seconds.

A
  • 50-60s
34
Q

How do breath hold divers extend their breath hold time? Why is this dangerous?

A
  • Hyperventilation prior to breath-hold diving can significantly extend the breath-hold time. This is very dangerous due to the risk of blackout – loss of consciousness in the water.
  • Hyperventilating forcefully for one minute - can decrease PaCO2 from normal value of 40 mm Hg down to 15-20 mm Hg.
35
Q

Explain ascent induced hypoxia.

A

Diver hyperventilates, holds breath, and dives down to a certain depth.

  • gases in lung are compressed and partial pressures are increased
  • diver holds breath as long as possible and then starts to ascend
  • partial pressure of gases in lung decrease on ascent due to expansion of lungs
  • PaO2 decreases below critical point
  • diver loses consciousness and drowns
36
Q

define: scuba

- list the equipment for scuba diving (7)

A 
- self contained underwater breathing apparatus
equipment:
-mask and snorkel 
- clothing (wetsuit or drysuit, gloves, hood, fins, boots) 
- weight belt 
- buoyancy compensator 
- tank and backpack 
- depth gauge and pressure gauge 
- single hose, two-stage regulator
37
Q

What role do the 2 regulators you use when scuba diving play?

A
  • reduce the air pressure in the tank from approx. 2500 psi (when tank is full) to exactly the ambient water pressure at the diver’s mouth, allowing ease of breathing.
  • Underwater breathing systems must supply air at sufficient pressure to overcome the force of water against the diver’s chest.
38
Q

explain how an open circuit scuba differs from a closed circuit scuba

A
  • expired air is discharged into sea water and not back into tank unlike a closed circuit scuba
39
Q

Explain air embolism

A
  • Diver inflates lungs and begins ascent from depth → diver doesn’t exhale → pressure decreases as he ascends → air in alveoli expands (Boyle’s Law) to the point where alveoli rupture –> air bubbles enter blood vessels → block an artery in the heart (heart attack) or brain (stroke) or other area → possibility of death
  • so: NEVER hold your breath when scuba diving
  • even with rapid treatment, 16% of air embolism victims die
40
Q

define: embolus

A
  • any material that enters and obstructs a blood vessel
41
Q

explain: pneumothorax

A
  • aka: lung collapse
  • Rupture of alveoli
  • air pocket forms outside the lungs between the chest wall and lung tissue → continued expansion of this trapped air during ascent causes the ruptured lung to collapse
42
Q

explain: nitrogen narcosis

A

At depths over 100 ft., the increased partial pressure and quantity of dissolved nitrogen produces an anesthetic effect on the central nervous system - effects similar to alcohol intoxication → decreased awareness of cold, hallucinations, decreased attentiveness, reckless behavior. Dependent primarily on the depth of the dive and secondarily on the length of time at that depth.

43
Q

explain: decompression sickness

A
  • aka the bends
  • If the diver ascends to the surface too rapidly after a deep, prolonged dive, dissolved nitrogen moves out of solution and forms bubbles in body tissues and fluids.
  • within 4-6 hours after ascent, divers feel pain usually first around joints. If bubbles lodge in an artery it can cause permanent damage or death.
  • Treatment: recompression in a hyperbaric chamber forces N2 gas back into solution and then slow decompression
  • Prevention: - ascend to the surface in stages (follow standard decompression tables) to allow sufficient time for nitrogen to diffuse from the tissues to the blood without bubbles forming.
44
Q

explain: oxygen poisioning and the symptoms

A
  • Occurs when the inspired PO2 exceeds higher than normal pressure
    symptoms:
  • irritation of respiratory passages which progresses to pneumonia if exposure continues
  • muscle twitching
  • confusion, nausea
  • convulsions
45
Q

explain: mask squeeze

A
  • all the troubles that pressure can cause during descent, as a result of pressure differentials between two structures or spaces.
  • Mask should cover eyes and nose so that pressure inside the mask can be equalized with the outside ambient pressure during descent by occasionally blowing air out the nose.
  • If pressure is not equalized, a relative vacuum is created within the mask and blood vessels in and around the eyes rupture as the eyes bulge out of their sockets.
  • Don’t dive below 8 feet when wearing goggles
46
Q

explain: middle ear squeeze

- define: eustachian tube and state its purpose

A
  • Eustachian tube - a small membrane lined passage connecting the middle ear cavity and the back of the throat that equilibrates the pressure within the ear cavity with the outside by transferring air to or from the lungs
  • If the eustachian tube is either partially or totally blocked (anatomical problem or respiratory infection), increasing pressure against the eardrum during descent is not met by an equal force from the interior → a relative vacuum is created in the middle ear → hemorrhage of tissues in the middle ear (equalization of pressure by bleeding) and possible rupture of the eardrum
  • Symptoms - pain in the ears after descending only a few feet. Pain rapidly becomes severe as the descent continues
47
Q

A drop in Tc during exercise is rare. Why?

A
  • Exercise increases your metabolism, increasing your Tc.
48
Q

What is the normal and dangerous levels (risk of fainting) for PaO2?

A

Unconsciousness occurs when PaO2 decreases to 30 mm Hg. Normal PaO2=100 mm Hg.

BPK 142 Lecture Flashcards (13 decks)

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