Respiration under hypo- & hyperbaric conditions

Question 1

Physiological stresses with immersion act primarily on the

Answer 1

respiratory,

cardiovascular, and renal systems.

Question 2

with immersion The body experiences:

Answer 2

• Increased pressure, or hyperbarism
1 atm (760 mm Hg) for every 10 m depth.
Effects air-filled cavities of the body.
(Boyle's Law)
• Reduced gravitational effects
Central shift in blood volume: ­diuresis, ­Na+ & ­K+ excretion.
• Reduced ambient temperature
Hypothermia.

Question 3

Immersion up to the Neck: Respiratory factors results in

Answer 3

Positive pressure exerted by surrounding water on
the chest wall >10 cm H2O:
• Decrease in FRC, ERV
• Slight decrease in VC, RV
• IRV increases
• Pressure gradient from top to lung base (25 mm Hg)

Question 4

Immersion up to the Neck:

Cardiovascular &

Answer 4

• Increased venous return, RA pressure, SV & CO.
• Increased abdominal pressure.
• Decreased peripheral pooling of blood due to
decreased gravitational effects.
• Vasconstriction due to reduced temperature.
• Increased intra-thoracic blood volume.

Question 5

Breath-hold diving (voluntary)
• Limited by?
• Changes associated with the?
• Changes in \_\_\_\_ \_\_\_\_\_ \_\_\_\_during the decent,
and ascent phases of a dive.

Answer 5

oxygen stores.
‘dive reflex’.
alveolar gas exchange

Question 6

For every 10 m below the surface ambient pressure

is increased by

Answer 6

~ 1 atm.

10 x 100 cm H2O, equivalent to 98kPa, 735 mm Hg,

Question 7

Breath-hold can be prolonged by prior ________,

but this is dangerous!

Answer 7

hyperventilation

Question 8

• Hypoxia alone does not trigger ?

Answer 8

ventilation

Question 9

• Most people can breath-hold?

Answer 9

~1 min with practice.

Question 10

Full inspiration yields ~ 1L O2 in lungs (i.e. VC ~ 5L).
\ 600 - 700 mL O2 available for consumption before
PaCO2 rises to ~ 50 mmHg, at this point….?

Answer 10

the urge to breathe

takes over.

Question 11

High PaCO2 (and low pH) causes the subject to

Answer 11

breathe sooner.

Question 12

• Breathing is also stimulated by low

Answer 12

PaO2 (“hypoxic drive”), but only

under extreme conditions.

Question 13

• During descent to 10m there will be

Answer 13

incr. ­compression of
the abdomen. PAO2 maintained, although VO2
continues & quantity O2 decr..

Question 14

Transfer of CO2 from the blood into the alveoli is

compromised during descent, resulting in

Answer 14

significant

retention of CO2 in the blood (respiratory acidosis).

Question 15

• During ascent there will be expansion of the
_______& reversal of _________. The transfer of O2 from the alveoli to the blood will then be compromised as PAO2 _________.

Answer 15

abdomen
pressure
decreased

Question 16

Adaptations with Free diving training:

Answer 16

• Bradycardia.
• Vasoconstriction of peripheral
vessels.
• Splenic contraction, ­RBCs.
• Plasma accumulates in pulmonary
circulation, reducing VR, &
preventing collapse of lungs at
depth >30m.

Question 17

Free-divers reduce ___to a
minimum: restrict effort &
wear wet suit for warmth.

Answer 17

VO2

Question 18

Shallow water blackout (SWB):

Latent Hypoxia

Answer 18

loss of

consciousness at shallow depths.

Question 19

Shallow water blackout (SWB): • Most commonly occurs

Answer 19

within 5m of the surface,
where expanding lungs literally suck oxygen
from the divers blood reducing PaO2.
Blackout occurs quickly, insidiously and without
warning. Victims die without any idea of their
impending death.

Question 20

• Pre-dive ________increases risk of SWB

by ¯PaCO2 level at the start of the dive

Answer 20

hyperventilation

Question 21

At sea level the FIO2 is 0.21. What is it

at the top of Mt Everest (8848 m)?

Answer 21

the same

Question 22

• As altitude increases, ___________
decreases.
• Consequently, fewer molecules of?
• A fall in PAO2 is predicted by the?

Answer 22

barometric pressure (PB)
 O2 per unit volume of inspired air.

alveolar gas
equation.

Question 23

Moderate or Intermediate Altitude:
1,500 - 2,440 m
High Altitude:
2,440 - 4,270 m
Mt Ruapehu (2,797 m); Mt Cook (3754 m)
Very High Altitude:
4,270 - 5,490 m
Extreme Altitude:
5,490 - 8,848 m

Answer 23

Significant altitude illness rare.

Very accessible, & therefore where most problems occur.

Typical for base camps.
Gradual acclimatization needed.

Short time only possible.
Slow ascent & light workloads only.

Question 24

hypoxemia gives rise to

Answer 24

compensatory responses at High Altitude

Question 25

• If PACO2 were to remain at the normal resting value of 40mm Hg, then PAO2 would be ~ (PIO2 - PACO2) = 54 mm Hg.
• But, ventilation is stimulated by _______ -_____________
in the carotid bodies sensitive to PO2. VA = fR(VT - VD).
• Result of ­VA is to ¯PACO2, allowing an _________in PAO2.
• However, the decline in PaCO2 ______stimulation of central chemoreceptors, counteracting the initial hypoxic response.

Answer 25

peripheral chemoreceptors
increase
reduces

Question 26

At high altitude ∆PO2 between alveolar and mixed venous is less, therefore reducing

Answer 26

the pressure gradient for diffusion.

Question 27

Altitude Hypoxia typically has 3 Forms:

Answer 27

• Sudden (acute) exposure
e.g. Aircraft decompression
• Exposure over several weeks
e.g. Low-lander acclimatization
• Lifelong exposure
e.g. Permanent residents at high altitude

Question 28

Acute Exposure to Very High Altitude

Physiological responses:

Answer 28

• Hyperventilation, and consequent lowering of
PaCO2 (hypocapnia & respiratory alkalosis).
• Increased heart rate (abolished by b-adrenergic
blockcade).
• Increased plasma and urinary catecholamines.
• Increased cardiac output.
• Effects on cerebral function (loss of consciousness
with severe hypoxia).
• Alterations to regional blood flow in lungs due to
selective hypoxic vasoconstriction.

Question 29

Time course of altitude effects:

• Initial

Answer 29

Initial
hyperventilation &
hypocapnia
followed by reflex
inhibition of
ventilation.

Question 30

• adaptations of altitude effects:

Answer 30

achieved through renal
reduced HCO3- reabsorption & conserving H+.

high cap and mito density

Question 31

Acclimatization is the process by

Answer 31

which tolerance
and performance are improved over a period of
hours to months at altitude.

Question 32

Adaptation refers to

Answer 32

physiological and genetic
changes that occurs over a period of years to
generations who live permanently at high altitude.

Question 33

• Overall increase in work of breathing ~___

Immersion up to the Neck:

Answer 33

60%

Question 34

Immersion up to the Neck:

Renal results in

Answer 34

• ADH suppression (­diuresis).

* Increased ANP release (­diuresis & NaCl excretion).

Question 35

two types of acute mountain sickness

Answer 35

benign acute- 6-12 hours in 40% of people in high altitude

malignant- odema rare life threatening

Question 36

the acclimatised person has

Answer 36

high haem count
incr. O2 transport
large blood volume
may grow RV from hypoxic pulmonary vasoconstrict.