2. PRESSURE–VOLUME RELATIONSHIPS
AND DIVING DEPTH
• Water pressure against a diver’s body increases
directly with the depth of the dive.
Two forces produce hyperbaria in diving:
• Weight of the column of water directly above the
diver (hydrostatic pressure)
• Weight of the atmosphere at the water’s surface.
3. Diving Depth and Gas Volume
• Boyle’s law states that at constant temperature, the
volume of a given mass of gas varies inversely with
its pressure.
4.
5.
6. Inspiratory Capacity and Diving Depth
• When breathing through a snorkel, the diver inspires
air at atmospheric pressure.
• At a depth of about 3 ft (1 m), the compressive force
of water against the chest cavity becomes large that
the inspiratory muscles cannot overcome external
pressure and expand thoracic dimensions.
7. Breath-Hold Diving
The duration and depth of a breath-hold dive
depends on two factors:
• Breath-hold duration until arterial carbon dioxide
pressure reaches the breath-hold breakpoint
• Relationship between a diver’s total lung
capacity(TLC) and residual lung volume (RLV)
8. Hyperventilation and Breath-Hold Diving
(Blackout)
• Hyperventilation before breath-hold diving extends
the breath-hold period but at the same time, the risk to
the diver greatly increases.
• Blackout, a sudden loss of consciousness, poses a
serious danger in skin diving
• A critical reduction in arterial PO2 causes blackout, a
condition that contributes to a total relaxation of
respiratory muscles.
• The breakpoint for breath holding corresponds to an
increase in arterial PCO2 to 50 mm Hg.
9. Depths Limits with Breath-Hold Diving:
Thoracic Squeeze
• Progressing deeper beneath the water subjects the
body’s air cavities to tremendous compressive forces.
Generally, when the lung volume compresses below
1.5 to 1.0 L.
• Internal and external pressures fail to equalize and
lung squeeze occurs.
• Excessive hydrostatic pressure on pulmonary air
volume causes extensive damage to pulmonary
tissues.
10. Diving Reflex in Humans
• Physiologic responses to immersion,
collectively termed the diving reflex, enable
diving mammals to spend considerable time
underwater. These responses include
(1) bradycardia
(2) decreased cardiac output
(3) increased peripheral vasoconstriction
(4) lactate accumulation in under perfused
muscle.
11. SCUBA DIVING
• The self-contained underwater breathing apparatus
(scuba), is the most common apparatus to supply air
under pressure for complete independence from the
surface.
• Air under pressure from an external source to
promotes inspiratory action.
• As below 1m, inspiratory muscle power cannot
overcome the compressive force of water against the
thoracic cavity.
12. The scuba system, strapped to the diver’s chest
or back, includes
• a tank of compressed air
• a demand regulator valve that delivers air with hose
and mouthpiece.
Two basic scuba designs exist:
(1) the common open-circuit system and
(2) the closed-circuit system,
13.
14. Open-Circuit Scuba
• This is used for submerged swimming with neutral
buoyancy in relatively shallow water.
• For most diving purposes, the steel or aluminum
tanks contain 2000 L of air compressed to about 3000
psi;
• One tank supplies enough air for a 0.5- to 1-hour dive
to moderate depths.
15. • The start of inspiration creates a slight negative
pressure. This opens the demand valve and releases
air to the diver at a pressure nearly equal to the
water’s external pressure.
• The positive pressure created with exhalation closes
the inspiratory valves and discharges the exhaled air
into the water.
• The scuba gear contains gauges that continually
monitor tank pressure and diving depth.
16. Drawbacks
• The air exhaled into the water generally contains
approximately 17% oxygen, so the open-circuit
system “wastes” about 75% of the total oxygen in the
tank.
• In addition, the diver requires a considerable mass of
air at increased depths to provide tidal volume for
adequate pulmonary ventilation.
17. • Contains moisture-free compressed air, making each
breath produce heat and moisture loss as the inspired
air warms and humidifies on its passage down the
respiratory tract.
• This causes substantial body heat loss during
prolonged diving.
• To counter heat loss, the diver breathes a heated gas
mixture of compressed helium-oxygen to avoid
hypothermia during deep diving.
Diver tanks
18. • Most common protective garment it counters cold
stress during diving.
• This is constructed of air-impregnated rubber, traps
water against the diver’s skin, which warms to body
temperature to provide the insulatory boundary.
• It is filled with tiny gas bubbles, provides insulation.
They furnish sufficient thermal protection for
relatively short dives, even in ice water.
• For longer dives in moderately cold water 17–18.5°C
a full wet suit offers insufficient thermal protection.
The wet suit
19. The modern dry suit
• Made from foam neoprene, crushed neoprene,
vulcanized rubber, or heavy-duty nylon with laminated
waterproof materials, and often worn over insulating
garments—maximizes protection from cold stress.
• This protective clothing ensemble keeps the diver dry,
has seals at the neck, wrists, and ankles and a
waterproof zipper to prevent water from entering the
suit.
• Dry-suit underwear traps a layer of air between the
diver and the water for additional insulation. Layering
of underwear adjusts insulation to water temperature.
20. Closed-Circuit Scuba
• This is a new diving form that used rebreathing of
pure oxygen and absorption of carbon dioxide within
a closed system.
• A small cylinder feeds pure oxygen into a bag from
which the diver breathes. This bag acts as a pressure
regulator.
• Valves in the breathing mask direct the exhaled gas
through a carbon dioxide absorbing canister that
contains soda lime; the carbon dioxide–free gas, then
passes back to the diver.
• The oxygen cylinder replenishes the oxygen
consumed in energy metabolism.
21.
22. • First, a serious medical emergency occurs if carbon
dioxide output exceeds its rate of absorption or if
absorption fails altogether.
• High concentrations of inspired oxygen, particularly
when breathed under high pressures beneath the
water, produce a variety of adverse effects on
physiologic functions, particularly those related to the
central nervous system.
Problems
23. Special problem with breathing gases at high
pressures
Figure • Scuba diving hazards from
failure to equalize internal and external
gas pressures.
TLC- it is the volume of air present in the chest after full inspiration (4-6L)
RLV- It is the volume of air remaining in the lungs after a maximal exhalation
