Transcript Wheeze Patterns In Patients With Asthma and COPD ATS, 2009

Wheeze Patterns In Patients With Asthma and COPD
Raymond Murphy and Bryan Flietstra, Brigham and Women’s / Faulkner Hospitals, Boston MA
Materials and Methods
Patients: We studied 66 asthma patients and 109 COPD patients
using a multichannel lung sound analyzer (STG16). Fourteen
microphones were placed on the back and one microphone over the
trachea (1). Wheezes were characterized by rate, pitch, wheeze
transmission coefficient (WTC), tracheal transmission coefficient
(TTC), and left to right symmetry.
A 16-channel lung sound analyzer (shown below) was used to collect
20 seconds samples of sound during deeper than normal breathing.
channels are called daughter
wheezes. These definitions are
consistent with the theory that the
event, which generated a wheezing
or crackling sound, had occurred
closer to the mother channel
microphone than to the other
microphones. Indeed evidence
supporting this theory can be found
by examination of the stack plots of
the wheeze and crackles family
waveforms (2, 3).
Wheeze Transmission Coefficient (WTC)
A wheeze transmission coefficient
(WTC) characterizes the degree of
wheeze transmission to all
ipsilateral microphones.
Local Wheeze (WTC=32%)
Significant Wheeze Transmission (WTC=59%)
WTC of 100% corresponds to equal
wheeze transmission to all
ipsilateral microphones.
Trivial Transmission to Trachea (TTC=5%)
Significant Transmission to Trachea (TTC=261%)
TTC of 100% corresponds to equal
wheeze transmission to the mother
wheeze site over the chest and to
the trachea. TTC of 0% corresponds
to no transmission to the trachea.
TTC greater than 100%
corresponds to greater transmission
to the trachea than to the mother
chest site.
Acoustic Symmetry Coefficient (ASC)
Data Analysis: Multiple wheeze characteristics were analyzed. In
addition the data were analyzed using an algorithm derived from
analysis of multiple features of the lung sounds including amplitude
variation, crackle features, as well as wheezing.
ASC=100% when sounds in the left
and right lungs are identical.
ASC=0% when sounds are
completely different between left
and right lungs.
Wheeze Rate (%)
Pitch (Hz)
WTC (%)
TTC (%)
ASC (%)
48±25
248±80
43±9
113±95
31±8
46±24
215±94
45±8
121±208
34±8
No significant differences were seen in the features of wheezing
(WTC, TTC, and ASC) of patients with asthma and COPD. However,
the specialized algorithm developed from a broader range of acoustic
characteristics of the sounds in these patients yielded the following:
Sensitivity
0.657
Tracheal Transmission Coefficient (TTC)
An acoustic symmetry coefficient
(ASC) was calculated using a
technique that crosscorrelated the
signal between all symmetrical
channels.
COPD (n=101)
22±18
191±77
42±8
52±47
29±9
Specialized Acoustic Algorithm (Asthma vs COPD)
WTC of 0% corresponds to no
transmission (the wheeze is only
detected in one microphone).
A tracheal transmission coefficient
(TTC) characterizes the degree of
wheeze transmission to the trachea.
Wheeze Rate (%)
Pitch (Hz)
WTC (%)
TTC (%)
ASC (%)
Asthma (n=58)
27±18
256±100
37±9
71±66
27±11
Expiration
The concept of a abnormal sound
family was introduced and validated
in Vyshedskiy et al (2, 3). In short,
wheezes and crackles can be
detected by multiple microphones
located on the chest surface. The
group of waveforms corresponding to
the same event and recorded by
multiple microphones is referred to as
a wheeze family or crackle family.
The channel with highest amplitude is
called the mother wheeze and the
corresponding deflections at other
Results
Inspiration
It is sometimes a problem to determine if a patient should be
diagnosed as having bronchial asthma or COPD. As the pathology of
the two conditions is different we wondered if the wheeze patterns
differed in these diseases. Specifically we asked (1) if the acoustic
features of wheezing differed in the two conditions and (2) if an
algorithm that included an analysis of multiple features of the lung
sounds would be able to distinguish patients with COPD from those
with asthma.
A wheeze as it appears at multiple microphones
Wheeze
family
Purpose
Low Left to Right Symmetry (ASC=18%)
High Left to Right Symmetry (ASC=55%)
Specificity
0.736
Accuracy
0.715
Discussion
It is not surprising that the wheeze patterns in COPD patients do not
differ from those in patients with asthma as the mechanism of
production of the wheezing is likely similar (airway narrowing,
secretions). Likewise it is not surprising that when other features of the
lung sound patterns such as sound amplitude measurements and the
presence of crackles that the pattern differ in the two conditions. A
limitation of the study is that patients were categorized as having
asthma or COPD by the clinicians caring for them. While this was at a
teaching hospital there may be some errors in classification. A study of
a more strictly diagnosed group of patients is indicated as the test can
be done readily at the bedside and could help avoid the not
uncommon misdiagnosis of these conditions.
Conclusions
While wheeze patterns are similar in COPD and asthma, a specialized
algorithm based on multiple acoustic parameters shows a promise of
separating these conditions.
References
o Murphy R. In Defense of the Stethoscope. Respiratory Care 2008
Mar;53(3):355-69
o Vyshedskiy A, Bezares F, Paciej R, Ebril M, Shane J, Murphy R.
Transmission of Crackles in Patients with Interstitial Pulmonary Fibrosis,
Congestive Heart Failure, and Pneumonia. Chest 2005; 128:1468-1474;
o Vyshedskiy A, Alhashem RM, Paciej R, Ebril M, Rudman I, Fredberg JJ,
Murphy R. Mechanism of Inspiratory and Expiratory Crackles. CHEST
2009 January 135(1): 156-164