Pressure And The Lungs
Figure 1. Effects on lungs with glottis open and closed.
WHAT IS BAROTRAUMA?
'Baro' refers to pressure (e.g., a barometer is an instrument for
measuring pressure). Barotrauma is physical damage to any part of
the body as a result of unequal air pressures; it is from either
compression or expansion of a body part. The tissues may rupture,
blood supply may be compromised, or swelling may occur. All
conditions discussed in this chapter are forms of barotrauma.
In the case of diving, the unequal pressures are between some
cavity
of the body (the middle ear, the sinuses, the lungs, etc.) and the
ambient air pressure. The consequences of barotrauma may range
from mild discomfort in the affected area (e.g., ears or sinuses),
to
various levels of pain, to rupture of an organ, such as the ear's
tympanic membrane or a part of the lung. Rupture of an organ
while diving is particularly hazardous because of the risk of
drowning.
Barotrauma is one of three pressure-related problems encountered
in scuba diving; the other two are decompression sickness and
nitrogen narcosis (Table 2). Barotrauma problems (including the
most severe, arterial gas embolism), are physiologically
explainable
by Boyle's. Non-barotrauma, pressure-related problems are
physiologically explainable by the laws of Dalton and Henry, as
will
be discussed later.
WHAT BAROTRAUMA PROBLEMS CAN OCCUR ON DESCENT?
Most problems on descent relate to inadequate communication
between the upper airway and the middle ears and sinuses. The
most frequently en-countered problem on descent is middle ear
"squeeze," an ear discomfort or pain from shrinkage of the middle
ear space (Figure 2). This problem may begin at only a few feet
depth. The earliest symptoms are similar to the "ear stuffiness" we
sometimes feel when a plane rapidly descends. Unchecked during a
dive, the feeling can rapidly progress to actual pain and ear
damage.
The pathologic result of continued squeeze in any space is
engorgement of the mucosal lining, swelling, fluid buildup and
finally hemorrhage into the space. In unchecked middle ear
squeeze, the tympanic membrane or round window can collapse
inward and burst, leading to extreme dizziness (vertigo) and an
emergency situation. In a compilation of 1001 disorders referred
to
an otolaryngology (ear, nose, throat) diving specialist, the middle
ear accounted for 399 (40%); 314 of the total (31%) were
manifested by pain on descent (Roydhouse 1985).
WHAT IS THE CAUSE OF MIDDLE-EAR SQUEEZE AND HOW
CAN IT BE PREVENTED?
Squeeze on the middle ear is prevented by making sure inhaled
compressed air travels from the back of the nose (nasopharynx)
into the middle ear spaces. The only route of passage into the
middle ear is through a tiny, compressible canal called the
eustachian tube (after its discoverer, the Italian Bartolommeo
Eustachi, 1524-74). Anatomically, this is a soft and flexible canal
that functions as a one-way flutter valve; it easily opens up when
pressure in the middle ear is higher than in the nasopharynx, but
tends to close shut when pressure in the nasopharynx is higher
than in the middle ear. As a result, gas flow is passive from the
middle ear to the nasopharynx on ascent (you don't have to think
about it), but "active" on descent (you have to make it happen).
Figure 1. Effects on lungs with glottis open and closed.
WHAT IS BAROTRAUMA?
'Baro' refers to pressure (e.g., a barometer is an instrument for
measuring pressure). Barotrauma is physical damage to any part of
the body as a result of unequal air pressures; it is from either
compression or expansion of a body part. The tissues may rupture,
blood supply may be compromised, or swelling may occur. All
conditions discussed in this chapter are forms of barotrauma.
In the case of diving, the unequal pressures are between some
cavity
of the body (the middle ear, the sinuses, the lungs, etc.) and the
ambient air pressure. The consequences of barotrauma may range
from mild discomfort in the affected area (e.g., ears or sinuses),
to
various levels of pain, to rupture of an organ, such as the ear's
tympanic membrane or a part of the lung. Rupture of an organ
while diving is particularly hazardous because of the risk of
drowning.
Barotrauma is one of three pressure-related problems encountered
in scuba diving; the other two are decompression sickness and
nitrogen narcosis (Table 2). Barotrauma problems (including the
most severe, arterial gas embolism), are physiologically
explainable
by Boyle's. Non-barotrauma, pressure-related problems are
physiologically explainable by the laws of Dalton and Henry, as
will
be discussed later.
WHAT BAROTRAUMA PROBLEMS CAN OCCUR ON DESCENT?
Most problems on descent relate to inadequate communication
between the upper airway and the middle ears and sinuses. The
most frequently en-countered problem on descent is middle ear
"squeeze," an ear discomfort or pain from shrinkage of the middle
ear space (Figure 2). This problem may begin at only a few feet
depth. The earliest symptoms are similar to the "ear stuffiness" we
sometimes feel when a plane rapidly descends. Unchecked during a
dive, the feeling can rapidly progress to actual pain and ear
damage.
The pathologic result of continued squeeze in any space is
engorgement of the mucosal lining, swelling, fluid buildup and
finally hemorrhage into the space. In unchecked middle ear
squeeze, the tympanic membrane or round window can collapse
inward and burst, leading to extreme dizziness (vertigo) and an
emergency situation. In a compilation of 1001 disorders referred
to
an otolaryngology (ear, nose, throat) diving specialist, the middle
ear accounted for 399 (40%); 314 of the total (31%) were
manifested by pain on descent (Roydhouse 1985).
WHAT IS THE CAUSE OF MIDDLE-EAR SQUEEZE AND HOW
CAN IT BE PREVENTED?
Squeeze on the middle ear is prevented by making sure inhaled
compressed air travels from the back of the nose (nasopharynx)
into the middle ear spaces. The only route of passage into the
middle ear is through a tiny, compressible canal called the
eustachian tube (after its discoverer, the Italian Bartolommeo
Eustachi, 1524-74). Anatomically, this is a soft and flexible canal
that functions as a one-way flutter valve; it easily opens up when
pressure in the middle ear is higher than in the nasopharynx, but
tends to close shut when pressure in the nasopharynx is higher
than in the middle ear. As a result, gas flow is passive from the
middle ear to the nasopharynx on ascent (you don't have to think
about it), but "active" on descent (you have to make it happen).
Figure 1
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