Pulmonary secrets

Question 1

Review obstructive airway diseases and their pulmonary function test
abnormalities.

Answer 1

Obstructive airway diseases, including asthma, chronic bronchitis, emphysema, cystic fibrosis,
and bronchiolitis, exhibit diminished expiratory airflow and involve airways distal to the carina.
The FEV1, FEV1/FVC ratio, and the forced expiratory flow at 25% to 75% of FVC (FEF25-75)
are below predicted values. A decreased FEF25-75 reflects collapse of the small airways and is a
sensitive indicator of early airway obstruction. The FVC may be normal or decreased as a result
of respiratory muscle weakness or dynamic airway collapse with subsequent air trapping.
Table 9-1 compares the alterations in measures of lung function in various obstructive lung
diseases. Table 9-2 grades the severity of obstruction based on the FEV1/FVC ratio.

Question 2

Review restrictive lung disorders and their associated pulmonary function test
abnormalities.

Answer 2

Disorders that result in decreased lung volumes include abnormal chest cage configuration,
respiratory muscle weakness, loss of alveolar air space (e.g., pulmonary fibrosis, pneumonia),
and encroachment of the lung space by disorders of the pleural cavity (e.g., effusion, tumor).
The characteristic restrictive pattern is a reduction in lung volumes, particularly TLC and VC.
Airflow rates can be normal or increased.

Question 3

What is a flow-volume loop and what information does it provide?

Answer 3

Using routine spirometric values, flow-volume loops assist in identifying the anatomic location of
airway obstruction. Forced expiratory and inspiratory flow at 50% of FVC (FEF50 and FIF50) are
shown in Figure 9-3. Note that expiratory flow is represented above the x-axis, whereas inspiratory
flow is represented below the axis. In a normal flow-volume loop the FEF50/FIF50 ratio is 1.

Question 4

What are the characteristic patterns of the flow-volume loop in a fixed airway
obstruction, variable extrathoracic obstruction, and intrathoracic obstruction?

Answer 4

Upper airway lesions (e.g., tracheal stenosis) are fixed when there is a plateau during both inspiration
and expiration. The FEF50/FIF50 ratio remains unchanged. An extrathoracic obstruction occurs when
the lesion (e.g., tumor) is located above the sternal notch and is characterized by a flattening of the
flow-volume loop during inspiration. The flattening of the loop represents no further increase in
airflow because the mass causes airway collapse. The FEF50/FIF50 ratio is >1. An intrathoracic
obstruction is characterized by a flattening of the expiratory loop of a flow-volume loop, and the
FEF50/FIF50 ratio is

Question 5

What are the effects of surgery and anesthesia on pulmonary function?

Answer 5

All patients undergoing general anesthesia and surgical procedures (particularly in the thorax
and upper abdomen) exhibit changes in pulmonary function that promote postoperative
pulmonary complications. For instance, VC is reduced to approximately 40% of preoperative
values and remains depressed for at least 10 to 14 days after open cholecystectomy. Upper
abdominal procedures result in a decrease in FRC within 10 to 16 hours; FRC gradually returns
to normal by 7 to 10 days. The normal pattern of ventilation is also altered, with decreased sigh
breaths and decreased clearance of secretions.

Question 6

Describe standard lung volumes.

Answer 6

The tidal volume (TV) is the volume of air inhaled and exhaled with each normal breath.
Inspiratory reserve volume (IRV) is the volume of air that can be maximally inhaled beyond a
normal TV. Expiratory reserve volume (ERV) is the maximal volume of air that can be
exhaled beyond a normal TV. Residual volume (RV) is the volume of air that remains in the
lung after maximal expiration (Figure 9-1).