Biomedical Engineering Reference
In-Depth Information
must be 50 to 60 dB SPL before one can
detect the sound. As a general guide, the
frequency ranges for various auscultation
sounds are as follows: cardiovascular, 20
to 1000 Hz; pulmonary, 150 to 1000 Hz;
gastrointestinal, 100 to 1000 Hz; and cer-
vical, 75 to 1200 Hz.
To hear sounds from the surface of
the body (e.g., chest wall, abdomen, or
neck), a conventional acoustic stetho-
scope can help. However, extra fat or
muscle, as well as background noise in
the environment, can reduce the overall
intensity, even for normal hearing listen-
ers. It is for this reason that some clever
advances have been made with stetho-
scopes by adding electronic amplifiers
and/or noise reduction circuits. These
electronic stethoscopes make it easier
for both normal hearing listeners and
some listeners with hearing loss. In some
cases, listeners with hearing loss may be
able to take their own hearing aids out
and perform auscultation with an ampli-
fied stethoscope. For many, however, this
is not always a desirable solution due to
lack of convenience and the need to mini-
mize the spread of infection. The incon-
venience comes from having to take the
hearing aids out, using the stethoscope,
and then putting the hearing aids back in.
For some, this creates a communication
barrier between the health professional
and the patient. Borrowing from a trick
that some health professionals use with
patients who have no more than a moder-
ate hearing loss, it may be possible to use
the conventional stethoscope as a tempo-
rary hearing aid. For example, the health
professional will place the stethoscope ear
tips into their patients' ears and then talk
to them through the bell and diaphragm.
This very act promotes understand-
ing, which could increase consent and
compliance. Likewise, the health profes-
sional with hearing loss could use the
stethoscope in this way so as not to lose
communicative contact with the patient
during auscultation. Spread of infection
could occur through poor infection con-
trol practices between physical contact
with the patient during auscultation and
handling one's hearing aids. To avoid
removing one's hearing aids (or implant
device) one or more alternative solutions
may be available, but there is no one-size-
fits-all approach. Table 14-1 lists some
alternative approaches to consider involv-
ing the stethoscope ear tips, stethoscope
ear tubes, or amplified stethoscope. For
those interested in an amplified stetho-
scope, Table 14-2 lists a number of prod-
ucts currently on the market or being sold
second-hand.
Potential consumers (and readers)
should have a basic understanding of the
decibel (dB) and amplification claims
made by stethoscope manufacturers.
Decibels are logarithmic numbers based
on a reference point that represents the
softest physical sound pressure that can
be detected by normal hearing individu-
als. Any amount above that reference
point is a ratio that reflects a change in
loudness, sound pressure, or power, each
of which yields very different values from
a mathematical standpoint. Audio prod-
ucts are often reported in sound pres-
sure level (SPL), not loudness or power.
For example, if a manufacturer reports
that their amplified stethoscope is
“50 times louder” than a conventional,
