Pleurisy (cont.)
How does the pleura work?
The pleura is composed of two layers
of thin lining tissue. The layer covering the lung (visceral pleura) and the
parietal pleura that covers the inner wall of the chest are lubricated by
pleural fluid. Normally, there is about 10-20 ml of clear liquid that acts as a
lubricant between these layers.
The fluid is continually absorbed and replaced, mainly through the outer lining
of the pleura. Pressure inside the pleura is negative (as in sucking) and
becomes even more negative during inspiration (breathing in). The pressure
becomes less negative during exhalation (breathing out). Therefore, the space
between the two layers of pleura always has a negative pressure. The
introduction of air (positive pressure) into the space (such as from a knife
wound) will result in a collapse of the lung.
What are the symptoms of pleurisy?
- Pain in the chest that is aggravated by breathing
- Shortness of breath
- "Stabbing" sensation
The most common symptom of pleurisy is pain that is
generally aggravated by inspiration (breathing in). Although the lungs
themselves do not contain any pain nerves, the pleura contains abundant nerve
endings. When extra fluid
accumulates in the space between the layers of pleura, the pain usually is a
less severe form of pleurisy. With very large amounts of fluid accumulation, the
expansion of the lungs can be limited, and shortness of breath can worsen.
How is pleurisy diagnosed?
The pain of pleurisy is very distinctive. The pain is in the chest and
is usually sharp and aggravated by breathing. However, the pain can be confused
with the pain of:
To make the diagnosis of pleurisy, the doctor examines
the chest in the area of pain and can often hear (with a stethoscope) the
friction that is generated by the rubbing of the two inflamed layers of pleura
with each breath. The noise generated by this sound is termed a pleural friction
rub. (In contrast, the friction of the rubbing that is heard with pericarditis
is synchronous with the heartbeat and does not vary with respiration.) With
large amounts of pleural fluid accumulation, there can be decreased breath
sounds (less audible respiratory sounds heard through a stethoscope) and the chest is dull sounding
when the doctor drums on it (dullness upon percussion).
A chest x-ray in the upright position and while lying on the side is an
accurate tool in diagnosing small amounts of fluid in the pleural space. It is
possible to estimate the amount of fluid collection by findings on the x-ray.
(Occasionally, as much as 4-5 liters of fluid can accumulate inside the pleural
space.)
Ultrasound is also a very sensitive method of detecting the presence of
pleural fluid.
A CT
scan can be very helpful in detecting trapped
pockets of pleural fluid as well as in determining the nature of the tissues surrounding the area.
Removal of pleural fluid with a needle and syringe (aspiration) is
essential in diagnosing the cause of pleurisy. The fluid's color, consistency,
and clarity are analyzed in the laboratory. The fluid analysis is defined as
either an "exudate" (high in protein, low in sugar, high in LDH enzyme, and high
white cell count; characteristic of an inflammatory process) or a "transudate"
(containing normal levels of these body chemicals). Causes of exudative fluid
include infections (such as pneumonia), cancer, tuberculosis,
and collagen diseases (such as rheumatoid arthritis and lupus). Causes of transudative fluid
are congestive heart failure and liver and kidney diseases. Pulmonary emboli can
cause either transudates or exudates in the pleural space.
The fluid can also be tested for the presence of
infectious organisms and cancer cells. In some cases, a small piece of pleura
may be removed for microscopic study (biopsied) if there is suspicion of tuberculosis (TB) or
cancer.
Next: How is pleurisy treated? »
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