Motor Speech Disorders 115patients can “mouth” words. An electrolarynx can also provide a sound source. Writing and
gestures are other ave nues of communication. Therapy for patients with reduced breath support
includes postural changes, the use of clavicular breathing, and exercises to maximize inhalation
and control exhalation. Air wastage is also a prob lem when patients release air before initiating
phonation. Therapy to maximize the use of breath support is necessary for these patients. In some
patients, a Velcro waistband (girdle) can be used around the abdomen to maximize breath sup-
port during speech. The waistband should be removed periodically to allow the necessary deep
breathing.
Phonation-Resonance Pathologies
As discussed in Chapter 4, the speech mechanism can be viewed as a sound- source resonator.
The vocal cords are the sound source, and the neck and head are the resonating chambers. The
frequency and amplitude of vocal cord vibrations interact with the resonance characteristics of the
neck a nd head resonat i ng cha mbers, creat i ng acoust ic energ y t hat rad iates out du ri ng speech. Some
bands of energy from the sound source are amplified, whereas others are damped. Alterations in
the size, shape, and length of the oral- nasal cavity create speech sounds by changing the acoustic
properties of the energy coming from the glottis. (Unvoiced sounds are also a result of acoustic
changes produced by the alterations of the sound source in the resonating chamber.) Although
phonation and resonance are interdependent systems, it is clinically impor tant to examine the
dysarthrias resulting from laryngeal paralysis and velopharyngeal incompetence separately.
Laryngeal paralysis frequently occurs in spastic and f laccid dysarthrias due to upper and lower
motor neuron impairments. Spastic laryngeal paralysis is due to bilateral upper motor neuron
damage. Clinically, spasticity likely results in a harsh voice quality due to the hyperadduction
of the vocal cords. However, Darley et al. (1975) found breathiness to be a voice characteristic in
many of these patients. Duffy (1995) proposed that the breathiness is a result of compensation:
“This breathiness could ref lect a degree of vocal cord weakness, but could also represent a com-
pensatory response rather than a primary prob lem” (p. 136). In some patients, breathiness rather
than harshness results from attempts to avoid laryngeal constriction. When upper motor neuron
damage affects phonation, it usually causes harshness and, infrequently, decreased loudness. The
neurological bases for these impairments are unknown (Duffy, 1995).
Flaccid dysphonia is found in lower motor neuron damage, particularly when the vagus nerve
(cranial nerve X) is damaged. The paralysis may involve adduction or abduction and may be
bilateral or unilateral. When one or both of the vocal cords are para lyzed, they are usually fixed
in the paramedian position, that is, near the midline of the glottis. However, this fixation does not
always occur; in some patients, it is found in a more abducted position. The relative abduction or
adduction fixation largely accounts for the perceptual feature of the voice. The more abducted the
vocal cords, the more likely the perceptual feature is to be breathy; the more adducted the vocal
cords, the more likely the feature is to be harsh and strained. In unilateral adductor paralysis, the
perceptual features depend on the ability of the unaffected vocal cord to cross the glottal midline
and contact the affected vocal cord. This princi ple is the basis for voice therapy in which straining
and forcing exercises cause the unaffected vocal cord to cross the midline.
Cerebellar and extrapyramidal ner vous system damage can also affect the laryngeal valve.
Cerebellar damage causes ataxic (coordination) phonatory disturbances, and extrapyramidal
damage results in kinetic (motion or movement) disorders. Although a harsh voice quality may
result from cerebellar and extrapyramidal damage, pitch and loudness instability are often the
most prominent phonatory deficits. Impaired respiratory- phonatory synergy likely causes ataxic
phonatory disturbances (Zwirner, Murry, & Woodson, 1991). Rapid and slow unwanted phona-
tory movements, as well as the voice tremor seen in Parkinson’s disease, are the most common