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In Depth Tutorials and Information
When performing follow-up testing on our example
individual, the comparison with previous testing is the
key. If FVC is declining, for example, this decline could
be significant or it could simply be the expected decline
in lung function associated with aging. One way to judge
a change's significance is to look at the percent predicted
value. If the FVC was 120% of the predicted normal 2
years ago and, in spite of a decreased absolute FVC value
in the current testing, the percent predicted remains at
120%, it can be assumed the drop was the expected drop
due to age-related loss of lung function. If, on the other
hand, the percent predicted is now 100%, this would be
of concern, suggesting that the loss in exhaled volume
was worse than could be accounted for by age.
Thus, in spite of the inaccuracies that calculated percent
of predicted normal can pose in the OI population and the
difficulties deciding which pulmonary function abnormal-
ities are real and which are miscalculations, it is the longi-
tudinal follow-up of these values that provides a way to
monitor the pulmonary function in the OI population.
We've used the FVC in the example above, but spi-
rometry provides another important measure, the forced
expiratory volume in 1 second or FEV1. This value rep-
resents the amount of air exhaled during the first second
of the FVC maneuver. Those with normal lung function
exhale about 80% of their breath during the first sec-
ond of a forced exhalation. Classically, individuals with
restrictive lung problems, whether due to intrinsic lung
disease or chest wall abnormalities, have a symmetric
reduction in their FVC and FEV1. If impairment of the
FEV1 is out of proportion to the impairment in FVC or
there is a low FEV1 with a normal FVC, this is suggestive
of airflow obstruction. Obstructive lung disease tends to
reduce the rate of exhalation, often with little or no effect
on the total volume of air exhaled, at least when obstruc-
tion is relatively mild.
When obstructive physiology is present in an OI
patient, and depending on the clinical setting, it is some-
times important to differentiate large airway obstruction,
such as from a tortuous or kinked trachea, tracheo- or
laryngomalacia, or an upper airway mass, from small air-
way obstruction as seen in chronic obstructive pulmonary
disease (COPD) and asthma. Several approaches can help
differentiate the location of obstruction, since treatment can
be different depending on the cause. Large airway obstruc-
tion tends to cause changes to the flow-volume graph with
low plateauing either during expiration or during both
expiration and inspiration ( Figure 35.1 ). Radiologic evalu-
ation can help differentiate the site of obstruction as well.
FIGURE 35.1 Examples of flow-volume relationships in individ-
uals with normal lows, reduced expiratory lows due to obstructive
lung disease, and reduced expiratory and inspiratory low due to a
fixed extrathoracic obstruction. In this type of graph, expiratory low
is positive and inspiratory low is negative. Each loop represents a
single cycle of inspiration and exhalation.
The chest X-ray is still the best and safest way to evalu-
ate the bony thorax and, as with pulmonary function
testing, comparisons with previous images help in the
diagnosis and follow-up of lung problems from pneu-
monias to pneumothorax and from airway distortion to
cardiac enlargement. Physical examination can point to
pectus deformities of the chest, but chest X-ray can help
the clinician appreciate the magnitude of compression
to the heart and lungs ( Figure 35.2 ).
Because plane films of the chest can be difficult to
evaluate when thoracic structures are distorted and
compressed, it is sometimes necessary to move to chest
CT. Risks of chest CT relate primarily to the increase in
radiation exposure that each evaluation provides com-
pared with the dose of a chest X-ray. Hopefully, this risk
will be reduced by future improvements in detector
sensitivity and software that allows for lower radiation
exposures. Risks from X-rays are increased in children
and young adults. 7 Therefore, careful consideration
of the need for frequent CT scans should be weighed
against this risk.
Evaluation for Sleep-Disordered Breathing
Sleep apnea, abnormalities of sleep architecture and
insomnias are growing issues in the general population.
The pulmonary issues of OI may magnify these sleep
problems because of distorted neck and tracheal anat-
omy, tracheo- and laryngomalacia and the potential for
impaired gas exchange. 8 While the actual evaluation of
sleep in a formal sleep laboratory is usually performed
by certified specialists, those caring for OI patients can
facilitate more accurate testing by helping sleep lab per-
sonnel understand the unique needs of patients with OI.
It is important that the patient's own usual sleep posi-
tion be mimicked in the sleep lab and this can be facili-
tated by having the patient bring their own pillows and
Pulmonary Radiology
Chest X-rays and chest CT scanning are central to
the evaluation of acute and chronic lung disease in OI.
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