Bergdahl- Chapter 26 and 27

Question 1

How does Boyle’s law relate to diving ?

Answer 1

P1V1= P2V2
therefore, in diving, when the pressure increases, the lung volume is severely reduced. Also, when the diver returns to the surface, the air volume re-expands to its original volume, which will make lung tissues rupture if the extra air cannot escape through the nose or mouth

Question 2

is water compressible ? what are the implications of this ?

Answer 2

water is noncompressible. this means that its pressure against a diver’s body increases directly with the depth of the dive

Question 3

what is hyperbaria ?

Answer 3

increased external pressure

Question 4

what are the two forces that produce hyperbaria ?

Answer 4

1) weight of the column of water directly above the diver

2) weight of the atmosphere at the water’s surface

Question 5

what in our body makes us less prone to increased external pressure in diving ?

Answer 5

the fact that water is a large portion of our body

Question 6

what happens after about 30 seconds of snorkelling ?

Answer 6

the carbon dioxide level in arterial blood increases causing the diver to sense the need to breathe and surface quickly

Question 7

what are the limits to snorkel size ? (2)

Answer 7

snorkelling adds to the volume of the anatomical dead space. it shouldn’t be too big therefore or it’ll enroach on alveolar ventilation

increased hydrostatic pressure as one descends beneath the water

Question 8

the duration and depth of a breath-hold dive depends on two things :

Answer 8

1) until arterial carbon dioxide pressure reaches the breakpoint (about 50 mmHg)
2) the relationship between a diver’s TLC and RV

Question 9

how does exercise reduce breath holding time ?

Answer 9

more carbon dioxide is being produced with exercise intensity

Question 10

what happens if you hyperventilate before a breath-hold dive ?

Answer 10

blackout

Question 11

what are the physiological reasons behind blacking out

Answer 11

hyperventilation preceding breath-hold, which means that PCO2 decreases to 15 mmHg. this extends the breath hold duration until the PCO2 increases to a level that stimulates ventilation

Question 12

what determines the critical diving depth before lung squeeze

Answer 12

the TLC/ RV ratio
should be 4 at the surface
basically if TLC> RV all is cool
if not, pulmonary pressure becomes less than the external water pressure, and blood goes into the alveoli

Question 13

what is the diving reflex ? what are the 4 physiological responses that it consists of ?

Answer 13

permits diving mammals to stay underwater for a while

1) bradycardia -the colder the water, the faster the reaction
2) decreased CO (CO= HR x SV so if HR smaller, CO is smaller- SV doesnt change)
3) increased peripheral vasoconstriction causes reduced blood flow to the limbs ensuring that oxygen sensitive organs like the brain and heart receive oxygen.
4) lactate accumulation in underperfused muscle (because the blood is going to the brain and heart)

Question 14

what is Henry’s Law ?

Answer 14

the quantity of gas dissolved in a liquid at a given temperature varies directly with the pressure differential between the liquid and gas solubility in the liquid

basically more molecules are soluble at a higher pressure

Question 15

as the diver ascends to the surface, how will the air volume breathed underwater expand ? what are the implications of this ?

Answer 15

in direct proportion to the reduction in external pressure.
therefore, if a diver takes a full breath and then fails to exhale while ascending, the rapidly expanding gas eventually ruptures the lungs. emboli (air bubbles) enter the pulmonary venous system, flow to the heart, block the blood supply
EMBOLISM

Question 16

what is pneumothorax caused by ?

Answer 16

air forced through the alveoli when lung tissue ruptures migrates laterally to burst through the pleura that covers the lungs. this means an air pocket forms in the chest cavity outside the lungs, and the continued expansion of trapped air during ascent collapses the ruptured lung

Question 17

what is mask squeeze ? how to avoid it ?

Answer 17

air in a facemask before a dive equals ambient air pressure, but then when you go deeper, the pressue differential develops between the inside and outside of the mask which creates a relative vacuum within the mask

you can avoid this by periodically exhaling through the nose in the mask to balance the pressures

Question 18

aerotitis- what is it ?

Answer 18

problem equalizing pressure within the air space of the Eustachian tubes which generally resist airflow
can cause middle ear hemorrhage and eardrum rupture

Question 19

what is aerosinusitis ?

Answer 19

congested sinuses prevent air pressure in these cavities from equalizing in diving
sinus air pressure that doesnt equalize during descent remains at atmospheric pressure while external pressure increases
this means that there can be a sinus squeeze due to the pressure differential, and sinus can bleed as blood occupies the space to equalize the pressure differential.

Question 20

what is nitrogen narcosis ?

Answer 20

when you dive too deep, the nitrogen basically acts as alcohol. the partial pressure of any gas increases in the tank as you go down, so the nitrogen will double value to 1200 mmHg
it dissolves in the myelin membranes

Question 21

what is the standard depth we go to maximally to avoid nitrogen narcosis ?

Answer 21

300 feet of sea water

Question 22

what is decompression sickness ?

Answer 22

when dissolved nitrogen moves out of solution and forms bubbles in body tissues and fluids
usually when ascending to surface too rapidly

Question 23

how to treat decompression sickness ?

Answer 23

lengthy recompression in hyperbaric chamber to force nitrogen gas back into solution
gradual decompression then to provide time for gas to leave body

Question 24

what is oxygen poisoning ?

Answer 24

breathing high pressures of O2

Question 25

what are the three ways oxygen poisoning acts ?

Answer 25

1) irritates respiratory passages and induces bronchopneumonia
2) constricts cerebral blood vessels and alters CNS function
3) depresses CO2 elimination (Hb is saturated with O2, which causes buildup of CO2 because usually Hb transports considerable amounts of CO2)

Question 26

what are the three mixes used in mixed-gas diving ?

Answer 26

1) nitrox- for relatively shallow recreational dives. it reduces O2 poisoning but still, the nitrogen amount can be dangerous
2) heliox- deep diving, reduces resistance imposed by nitrogen, however, can result in high pressure nervous syndrome
3) trimix - helium, nitrogen, oxygen: dives to depths that may produce high pressure nervous syndrome (nausea, tremors, other CNS effects)

Question 27

what are two negative effects of breathing helium?

Answer 27

1) voice change

2) heat loss from helium’s high thermal conductivity

Question 28

how does the energy cost of diving compare to normal exercise ?

Answer 28

can be 30% more at slow speeds

Question 29

what is microgravity ?

Answer 29

weightless feeling because the gravitational pull on a rocket decreases as it moves farther from the Earth

Question 30

what happens to bodily fluids in microgravity ?

Answer 30

blood and fluids shift upwards and move into thoracocephalic region
(puffy face, decrease in waist, eye redness, skinny legs, headache)

Question 31

how do kidneys respond to the fluid shift ?

Answer 31

they up urine production

Question 32

how does the decrease in total fluid volume in microgravity change the cardiovascular function ?

Answer 32

reduces heart’s total work

overall heart size decreases from reduced LV

Question 33

how does the heart change sizes in microgravity ?

Answer 33

first it becomes bigger due to UB fluid shift. then, there’s negative feedback to regulate fluid balance by decreasing thirst and augmenting urine output
then the heart shrinks below normal size

Question 34

how does CO, SV, HR change in space ?

Answer 34

CO decreases

HR remains the same, but SV decreases

Question 35

how does SV change in space ?

Answer 35

at first, it increases because venous return increases but then with the decrease in plasma volume it decreases.

Question 36

what is space anemia ?

Answer 36

decrease in O2 since there’s a decrease in RBC

either due to RBC destruction or decreased RBC production

Question 37

what is the most persistent short term problem in space ?

Answer 37

space motion sickness

Question 38

in flight lower body negative pressure. what are its two functions ?

Answer 38

1) assesses orthostatic deconditioning during space flight and post landing
2) countermeasure against changes

applies negative pressure to the lower limbs to force fluid in vascular system to migrate downward

Question 39

do people gain or lose weight in space ?

Answer 39

usually lose

Question 40

what supplements do astronauts take ?

Answer 40

protein, but doesn’t seem to help

Question 41

how does body composition change in space ?

Answer 41

no changes in body fat or extracellular water

decline in FFM and body mass

Question 42

what are the 2 main physical stressors in space travel ?

Answer 42

1) decreased hydrostatic pressure gradients within the cardiovascular system
2) decreased weight loading on muscles

increase physiologic strain

Question 43

how does VO2max change in space ?

Answer 43

it decreases

Question 44

how does MAP increase in the upper body ?

Answer 44

from 70 to 100 mmHg

Question 45

how many weeks do we need to see a 10% change in deconditioning response of the cardiovascular system ? 10% change in body fluid redistribution ? 5% decline in bone mass ?

Answer 45

a 10% change in deconditioning response of the cardiovascular system ? 3 weeks

10% change in body fluid redistribution ? 2 weeks

5% decline in bone mass ? 3 months

Question 46

in space, VO2 goes down. what are the implications of this ?

Answer 46

less oxidative enzymes, O2 utilization
more lactate accumulation
acidosis