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6—THE LUNGS
TABLE 30.2 ■ Characteristics of Crackles in Various Disorders*
Diagnosis
Pulmonary fibrosis 6–14 Late inspiratory Fine
Congestive heart failure 4–9 Late or paninspiratory Coarse or fine
Pneumonia 3–7 Paninspiratory Coarse
Chronic airflow
obstruction
*Number of crackles is mean number of crackles ± 1 standard deviation, after the patient first coughs to
clear airway secretions. The descriptors early inspiratory, late inspiratory, paninspiratory, coarse, and fine
are observations made by clinicians listening with the stethoscope; the numbers under timing refer to when
crackles begin and end during a full inspiration (e.g., 0.5 à 0.9 means that crackles first appear at midinspiration
[0.5] and end when the patient has reached 90% of full inspiration [0.9]). Based on references 68,93,97.
Number of Crackles per
Inspiration Timing of Crackle
(0.5 → 0.9)
(0.4 → 0.8)
(0.3 → 0.7)
1–4 Early inspiratory Coarse or fine
(0.3 → 0.5)
Type of
Crackle
failure, pneumonia, and chronic obstructive lung disease. e crackles of interstitial brosis are
characteristically ne, have a large number of individual crackling sounds each inspiration, and
persist to the end of inspiration (i.e., they are late inspiratory crackles). Crackles of chronic airow
obstruction are coarse or ne, have the smallest number of crackling sounds, and are conned to
the rst half of inspiration (early inspiratory crackles). e crackles of heart failure and pneumonia
lie between these extremes; with treatment, the crackles of pneumonia become ner and move
toward the end of inspiration.
98,99
EBM Box 30.2 indicates the nding of early inspiratory crackles greatly increases the prob-
ability of chronic obstructive lung disease (LR = 14.6). Most patients with these crackles have
severe obstruction (LR = 20.8).
2. Wheezes
a. Presence of Wheezes
EBM Box 30.3 indicates that the nding of unforced wheezing increases the probability of
chronic obstructive lung disease a small amount (LR = 2.6) and decreases slightly the probability
of pulmonary embolism (LR = 0.4). If wheezing appears during methacholine challenge testing,
asthma is likely (LR = 6). e absence of wheezing in any of these settings is unhelpful.
In contrast, the nding of forced wheezing lacks diagnostic value, since it can be produced by
most healthy persons if they exhale forcibly enough.
b. Characteristics of Wheezing
e characteristics of wheezes are their length, pitch, and amplitude. Of these, only length and pitch
vary with severity of obstruction. e longer the wheeze, the more severe the obstruction (r = −0.89
between the proportion of the respiratory cycle occupied by wheezing and the patient’s FEV1,‡
p < 0.001).
63,110,111
Higher-pitched wheezes indicate worse obstruction than lower-pitched ones, and
eective bronchodilator therapy reduces the pitch of the patient’s wheeze.
Even so, the amplitude of the wheeze does not reect the severity of obstruction, principally
because many patients with severe obstruction have faint or no wheezes.
ports the old adage that, in a patient with asthma, the quiet chest is not necessarily a favorable sign but
may instead indicate a tiring patient who is unable to push air across the obstructed airways.
‡
See Chapter 28 for denition of FEV1.
100,109
63,110
63,100,110,111
is nding sup-
30—AUSCULTATION OF THE LUNGS
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EBM BOX 30.3 Wheezes, Rubs, and Squawks*
267
Likelihood Ratio† if Finding Is
Present Absent
Finding (Reference)
Sensitivity
(%)
Specificity
(%)
Unforced wheezing
Detecting chronic airflow
obstruction
21,23,25,100–103
Detecting pneumonia in
patients with cough
30–34,36,39,91,92
and fever
Detecting pulmonary
embolism
Wheezing during methacholine challenge testing
Detecting asthma
104–106
29
13–56 86–99 2.6 0.8
4–36 50–96 0.8 NS
3–31 68–91 0.4 NS
44 93 6.0 0.6
Pleural rub
Detecting pulmonary
embolism
Detecting pleural
effusion
106,107
26
1–14 91–99 NS NS
5 99 NS NS
Inspiratory Squawk
Hypersensitivity
11 97 3.2 NS
pneumonitis in patients
with interstitial lung
108
disease
21
*
Diagnostic standard: for chronic airflow obstruction, FEV1/FVC <0.6,
95% confidence interval for age, gender, and height;
101–103
for pulmonary embolism, see Chapter 34;
<0.7,
23,25,100
or less than lower
for asthma, FEV1 decrease ≥20% during methacholine challenge;29 for pleural effusion, chest
radiograph; and for hypersensitivity pneumonitis, clinical consensus using standard criteria.
†
Likelihood ratio (LR) if finding present = positive LR; LR if finding absent = negative LR.
COPD, Chronic obstructive pulmonary disease; NS, not significant.
LRs
0.1 0.2 0.5 12510
e slide whistle sound, a unique wheezing sound whose pitch rises during inspiration and
falls during expiration, has been described in a patient with a spherical tumor arising from the
carina that nearly completely obstructed the trachea.
WHEEZES, RUBS, AND SQUAWKS
Probability
Decrease Increase
+45%+30%+15%–15%–30%–45%
LRs
Wheeze, detecting asthma, during
methacholine challenge
Squawk, detecting hypersensitivity
pneumonitis, if interstitial lung disease
Wheeze, detecting COPD, if unforced
wheezes
112
268
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6—THE LUNGS
3. Stridor
In patients with tracheal stenosis after tracheostomy, stridor is a late nding, usually appearing
after symptoms like dyspnea, irritative cough, or diculty clearing the throat.65 Stridor indicates
that the airway diameter is less than 5 mm.
65
4. Pleural Rub
EBM Box 30.3 indicates that the presence or absence of a pleural rub does not change the prob-
ability of pulmonary embolism or pleural eusion.
5. Inspiratory Squawk
In patients presenting to pulmonary specialists with a variety of interstitial lung diseases,
the presence of the inspiratory squawk increases the probability of hypersensitivity pneumonitis
(LR = 3.2).
References may be accessed online at Elsevier eBooks for Practicing Clinicians.
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268.e5
CHAPTER
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31
Ancillary Tests
KEY TEACHING POINTS
• In patients with chronic dyspnea, a forced expiratory time of 9 seconds or more increases
probability of chronic obstructive lung disease; a forced expiratory time less than
3 seconds decreases probability of obstructive disease.
• Forced expiratory time is not prolonged in restrictive lung disease.
• A positive Snider test (i.e., inability to extinguish a burning match) increases the probability
of reduced forced expiratory volume in 1 second, either from obstructive or restrictive
lung disease.
I. Forced Expiratory Time
A. TECHNIQUE
To measure the forced expiratory time, the clinician places the stethoscope bell over the trachea of
the patient in the suprasternal notch and asks the patient to take a deep breath and blow it all out
as fast as possible.1 Using a stopwatch, the duration of the audible expiratory sound is determined
to the nearest half second.
Rosenblatt introduced this test in 1962 as a test of obstructive lung disease.
B. PATHOGENESIS
e forced expiratory time should be prolonged in obstructive disease simply because, by definition, the ratio of FEV1 to FVC (i.e., forced expiratory volume in 1 second divided by forced vital
capacity, a measure of flow rate) is reduced in this disorder. Slower flow rates prolong expiratory
times.
C. CLINICAL SIGNIFICANCE
EBM Box 31.1 summarizes the accuracy of this finding, showing that a forced expiratory time of
9 seconds or more increases the probability of obstructive disease (likelihood ratio [LR] = 3.9) and
a time less than 3 seconds decreases probability (LR = 0.2).
e forced expiratory time is a specific test for obstructive lung disease. Patients with restrictive lung disease, despite having reductions in the FEV1 similar to those seen in obstructive lung
disease, usually have forced expiratory times of 4 seconds or less.
2
1,2
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EBM BOX 31.1 Ancillary Tests
6—THE LUNGS
Finding (Reference)*
Forced expiratory time
Detecting chronic airflow
obstruction
≥9 seconds 5–50 86–99 3.9 …
3–9 seconds 42–94 … NS …
<3 seconds 1–10 26–89 0.2 …
Unable to blow out the match (Snider test)
Detecting FEV1 of ≤1.6L
*Diagnostic standard: for chronic airflow obstruction, FEV1/FVC
predicted from equations based on the patient’s age and height.
†
Likelihood ratio (LR) if finding present = positive LR; LR if finding absent = negative LR.
COPD, Chronic obstructive pulmonary disease; FEV1, forced expiratory time in 1 second; FVC, forced vital
capacity; NS, not significant; s, seconds.
1,3–5
LRs
Able to blow out match,
arguing against FEV
Forced expiratory time <3 seconds,
arguing against COPD
Sensitivity
(%)
6,7
62–90 91–93 9.6 0.2
Decrease Increase
0.1 0.2 0.5 12510
≤1.6 L
1
Specificity
(%)
ANCILLARY TESTS
Probability
Likelihood Ratio† if Finding Is
Present Absent
1,3
<0.7 or FEV1/FVC below normal as
4,5
+45%+30%+15%–15%–30%–45%
Unable to blow out match,
detecting FEV ≤1.6L
Forced expiratory time ≥9
seconds, detecting COPD
LRs
II.
Blow-Out-The-Match Test
A.
TECHNIQUE
e clinician lights a match and holds it 10 to 15
attempts to extinguish it by blowing as forcibly as possible. It is important that the patient hold
the mouth open and not purse the lips. Inability to extinguish the burning match is the positive
finding.
e match test was introduced by Snider in 1959, who reasoned that the ability to extinguish a
match was related to the velocity of exhaled air.
B.
CLINICAL SIGNIFICANCE
EBM Box 31.1 indicates that a positive Snider test (i.e., inability to extinguish the match) greatly
increases the probability that the patient’s FEV
= 9.6). Being able to extinguish the match argues against an FEV
forced expiratory time, the Snider test is abnormal in both obstructive and restrictive lung disease,
which probably explains why the Snider test performs poorly in studies using it as a specific sign
of obstructive disease.
8
References may be accessed online at Elsevier eBooks for Practicing Clinicians.
cm in front of the seated patient, who then
6
e test is often called the Snider test.
is at least moderately reduced to 1.6 L or less (LR
1
this low (LR = 0.2). Unlike the
1
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