Week 12 Flashcards
core
defined as the temperature of the hypothalamus, site of temp regulation
how is the temperature of the core measured
rectal and esophageal probes
- pills that are swallowed and send a temp signal from the gastrointestinal system
skin temperature
measured with dermal patches
influenced by the environment, metabolic rate, clothing and hydration state
radiation
the exchange of electromagnetic energy waves emitted from one object and absorbed by another
conduction
occurs whenever two surfaces with differing temperatures are in direct contact
- insulators do not conduct heat readily
the rate of conductive heat exchange is inversely related to the thickness of the insulating substance
- body fat, air trapped in goose down clothing, multiple layers
convection
requires that one of the media be moving as occurs with a fluid or gaseous medium
- heat transfer from skin to moving air or water
wind chill index
gives the equivalent still air temperature for a particular ambient temperature at different wind velocities
convection-dry suit
the temp gradient between skin and air and the air/water velocity are important factors in determining connective heat loss
evaporation
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
two primary physiological responses used by humans to defend against a cold enviorment
increase in metabolic rate
increased tissue insulation
non physiological responses to cold
proper clothing, seeking shelter, starting a fire
skin fold thickness affecting response to cold
the thicker the fat layer, the greater the insulation
gender affecting responses to cold
average female has more fat than average male
but women generally have larger surface area-mass ratios than men
which equals more rapid heat loss with larger ratio
women and men with similar skin fold thickness, women are found to lose heat more rapidly
clothing affecting responses to cold
function of the air layer next to the skin, the thickness of the clothing and the air trapped between layers of clothing
base layer, mid layer then outer layer
hypothermia
tc <35 degrees
body core: brain, heart, lungs, blood, liver, kidneys
critical areas for heat loss: head and neck, sides of chest, groin
shivering will cease when core temp falls below 32-34 degrees
death occurs around 24-28 degrees C
factors associated with hypothermia
- Immersion in cold water or wet clothing
- Wind
- Physical exhaustion
- Inadequate clothing for conditions 5. Low percent body fat
- Hypoglycemia
- Alcohol consumption
- causes a decrease in shivering, increased blood flow to skin, imapires judgment
hypothermia oxyhemoglobin curve
increased hemoglobin affinity for 02
less O2 is released to tissues
body tissues shift to anaerobic metabolism
hypoxia of heart and brain plus metabolic acidosis
depressed brain function and cardiac output
ventricular fibrillation and death
frostbite
freezing of superficial tissue that occurs when skin temp reaches between -2- -6
sensory nerves are blocked and skin is numb
cold exposure to respiratory tract
Inhaled air is conditioned as it enters the upper respiratory passageways - warmed to 37oC and saturated with water vapor.
* Therefore you can’t “freeze” your lungs when exercising in very cold weather.
since cold air is very dry, cells lining the respiratory passageways become dry and possibility of throat irriation
effects of cold on performance
All of the following are decreased when muscle and nerve temperature decrease:
– strength and power
– nerve conduction velocity – reaction time
– manual dexterity
– flexibility
cold on cardiovascular endurance
Optimal marathon race performance at an ambient temperature 14 degrees Celsius.
* more of the circulation can be directed to working muscle, as less is required for heat dissipation.
* Due to the increased metabolism, and heat production, associated with exercise, a drop in Tc during exercise is rare
* May occur with very low intensity, long duration walking or trekking.
* If Tc does drop, there will be a reduction in aerobic performance
underwater pressure affects
Pressure of air at sea level = 1.0 atmosphere or 760 mm Hg
* 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 33 feet, or 10 meters, of depth.
10m= 2.0 atmosphere
20m= 3.0 atmosphere
pressure effects
Body tissues are largely water, they are non -compressible.
* However, the body contains air cavities, which are compressible – lungs, respiratory passages, sinus and middle ear spaces
volume and pressure will change with diving depth.
boyles law on pressure
the volume of any gas varies inversely with the pressure on it
if pressure is doubled means volume is halved
limits to snorkel size because of pressure effects
when breathing through a snorkel, the diver must inspire air at atmospheric pressure.
– At a depth of only 3 ft., the compressive force of water against the chest cavity is so large that the inspiratory muscles are usually
unable to overcome external pressure to expand the thoracic cavity.
limits to snorkelling because of increase in pulmonary dead space
Normal anatomical dead space = 150 ml.
* Dead space of regular snorkel = 150 ml.
VA (mL)=VT –VD
No Snorkel: 350 ml = 500 ml - 150 ml
With snorkel: 350 ml = 650 ml - 300 ml
As snorkel size increases, VD increases. You will need to work harder, at a higher VT, in order to maintain VA.
VA = Alveolar ventilation (volume of air participate in gas exchange) VT = Tidal volume (volume/breath)
VD = Dead Space (air entrapped in airway)
breath hold diving
kin diver descends, the air in the lungs is compressedàlung squeeze.
* lung volume is compressed below residual volumeàlung damage d/t
blood sucked from the pulmonary capillaries into the alveoli
* “Normal” maximal breath holding time after a maximal inspiration of ambient air is approximately 50 - 60 seconds.
paradoxical drowning
Diver hyperventilates - holds breath- dives down to a certain depth- gases in lung are compressed and partial pressures are increased
* diver (still holding breath) starts to ascend- partial pressure of gases in lung decrease on ascent- PaO2 decreases below critical point à diver loses consciousness à drowns.
scuba diving
The two regulators 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.
open circuit scuba
as diver starts to inspire, slight negative pressure causes inspiratory valve on demand regulator to open- air enters diver’s lungs.
– On exhalation, the exhaled air is discharged into the water.
air embolism- problem with scuba
Diver inflates lungs- Diver ascends from depth- diver doesn’t exhale- VA
pressure decreases as he ascends- alveolar air volume increases- expands
alveoli- ruptures alveoli- air bubbles enter blood vessels- block an
artery in heart (heart attack) or brain (stroke) or other areaàpossibility of death
* Even with rapid, expert treatment, 16% of air embolism victims die.
* Never hold your breath scuba diving
pneumothorax- problem with scuba
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
treatment for the bends
recompression in hyperbaric chamber to force the nitrogen gas back into solution and then slow decompression
nitrogen narcosis- problem with scuba
At depths over 100 ft. (30m) the increased partial pressure and quantity of dissolved nitrogen produces an anesthetic effect on the central nervous system - effects similar to alcohol intoxication
- decreased attentiveness, awareness of cold hallucinations, and reckless behaviour
the bends- problem with scuba
Also called “decompression sickness”
* If the diver ascends to the surface too rapidly after a deep, prolonged dive, dissolved nitrogen moves out of lungs then travels in blood- N2 to tissues then forms bubbles in body tissues and fluids.
oxygen poisoning
ccurs when the inspired PO2 exceeds 1520 mm Hg for longer than 30-60 minutes
* Effects: - irritation of respiratory passages which progresses to pneumonia if exposure continues
- muscle twitching
- confusion, nausea - convulsions
mask squeeze
The term “squeeze” can be applied to 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
* 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
middle ear squeeze
Eustachian tube - a small membrane lined passage connecting the middle ear cavity and the back of the throat
* Purpose - equilibrate the pressure within the ear cavity with the outside by transferring air to or from the lungs
