Neil McKaig M.S. CCC/SLP
extremely useful tool for the evaluation and management of dysphagia is the
stethoscope. Since its invention
medical practitioners have been acculturating sounds associated with human
physiology and incorporating their findings into their diagnostic impressions.
Cervical Auscultation (CA) is listening to the sounds of a swallow using an
amplifying instrument. When this procedure is used to assist in the evaluation
of the pharyngeal phase of swallowing, the critical events listened for are: (1)
the determination of the integrity of the airways protective mechanism and (2)
the relative timing of those sounds associated with the swallow.
Failure of this protective mechanism to perform properly, or the
disruption of the proper timing of this process may result in aspiration and the
secondary medical complications associated there with.
The protection of the airway during the swallow is a complex
myo-mechanical response to a
sub-cortically mediated action. As
with the working mechanism of the internal combustion engine, the timing of the
opening and closing of the valves in the system is critical to efficient
The stethoscope was invented by R.T.H. Laennec (1781-1826) around the year 1817.
He published his findings initially in 1819 in Traité de
l'auscultation médiate' (Tract
on Indirect Auscultation). His
device was a simple wooden tube about 12 inches long with a bell like opening
for placing on the patient’s chest and a narrower opening at the opposite end
for the physician’s ear. This
physician, whom many consider the father of chest medicine, himself died of
tuberculosis at the age of 45.
The binaural stethoscope, similar to the one that is commonly used by clinicians
today, was invented around 1840 by George P. Cammonn (1804-1863).
It consisted of two rigid tubes fitted to the ears with spring tension
and flexible rubber tubing extending to the auscultating bell.
A catalogue from 1866 lists various models of the Cammonn Stethoscope
ranging in price from $3.00 (for the hardened rubber model) to the deluxe with
covered springs at $5.00. Where
this may seem inexpensive to us, it would represent an expenditure of a man’s
entire weekly wages.
The idea of listening to the various sounds of the human body, including
listening to the swallow at the level of the cervical vertebrae, is not new,
despite the current interest in the technique of cervical auscultation.
In the early part of the 20th century, Dr. A. F. Hertz was investigating
the sounds of food as it passed through the alimentary canal.
He observed that in the liquid swallow, the sound is sharp and short and
coincides with the contraction of the mylohyoid muscle and elevation of the
larynx (Hertz, 1906).
In the mid-fifty's physicians were encouraged to use the technique to assess
pharyngeal swallow in those patients with bulbar poliomyelitis.
Electronic monitoring of cervical level breath sounds was also suggested
during the polio epidemic to reduce the need for a tracheotomy (Scott, 1956).
This was perhaps one of the first attempts at remote patient monitoring.
Through the next three decades, interest in this technique has remained
greatly in the laboratory where researchers have attempted to define more
accurately the sounds of deglutition.
Recently there has been a resurgence of interest as clinicians again look to this noninvasive procedure to augment their clinical evaluation of patients with suspected oropharyngeal dysphagia. Experiments into computer analysis of these swallowing sounds have been performed by Vice et al., (1994) at the University of Maryland, Takahashi et al., (1994) at the Showa Dental School in Tokyo, McKaig and Stroud (1996) at Prince Charles Hospital in Wales. These studies have demonstrated the usefulness of digitizing swallow sounds for measurement of duration and amplitude.
It is only through a full understanding of al the acoustic properties along with the myomechanical actions thereto related that Cervical Auscultation can become an additional tool in the dysphagia clinician repertoire. As cuts in the medical system continue, we will all be forced to rely more heavily on our clinical skills thus verification of sensitivity and specificity of techniques such as Cervical Auscultation will necessarily be ongoing.