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INVESTIGATION OF LARYNGEAL DISEASE             153

patient has a picture taken while breathing quietly, during phonation, while
doing a Valsalva manoeuvre to outline the ventricles, and while doing forced
inspiration.

A laryngogram has the advantage over the tomogram that it can be
screened and the laryngeal movements better assessed.

SPECIAL INVESTIGATIONS. These tests are applied to voice problems rather
than to cases with organic disease processes.

1.  Tape Recordings. These are essential to record the progress of any case
having speech therapy.

2. Stroboscopy. This produces an optical illusion whereby an object moving
rapidly appears to move very slowly. The illusion is obtained by viewing the
larynx by indirect laryngoscopy using a stroboscope as the light source and
synchronizing the illumination with the frequency of the phonated 'ee\ This
arrests or slows down the rapid movement of the vibrating vocal cords and
allows of their inspection in any desired position by changing the phase of the
light.

3.  Pitch and Frequency Measurements. These measurements should be
performed on all patients with voice problems. The ideal speaking pitch
should be one third of the way up the patient's range. To measure this the
patient should sing his lowest note and then sing a scale so that his highest
frequency can be measured. The pitch frequency of his speaking voice should
then be measured and the speech therapist will then be able to adjust this to his
ideal conversational pitch one-third of the way up the range.

4.  Respiratory Function Tests. These tests are occasionally useful because
altered breathing patterns can cause vocal abnormalities.

5.  Fibreoptic Laryngoscopy. This is a new addition to the investigative
armoury resulting from the technological advances in fibreoptic instrumenta-
tion. It is possible to pass a small fibreoptic bundle through the nose and into
the larynx to examine certain areas very closely and also to avoid the need for
direct laryngoscopy in some cases with an overhanging epiglottis. It may also
be combined with Stroboscopy for laryngeal examination.

DIRECT LARYNGOSCOPY. A fuller description of the technique of this will be
given in Chapter 41. Suffice it to say at this point that it is the most important
laryngeal investigation. It permits a close examination of the laryngeal and
pharyngeal structures, it allows the extent of tumours to be assessed and
biopsied, and it is a route for minor laryngeal surgery such as vocal cord
stripping or removal of polyps and other benign tumours.

In recent years use has been made of the Zeiss operating microscope with a
400-mm lens for microlaryngoscopy. With this innovation many new instru-
ments have been developed to allow for fine microscopic work to be performed
on the laryngeal structures with a high degree of accuracy and thoroughness.
A stroboscopic light source may also be used with the microscope as an
additional help in micro-examination of the larynx.