Components of Dysarthria Defects
Dysarthria results from defects in five core physiological components of the motor speech system: respiration, phonation, resonance, articulation, and prosody, with overall speech intelligibility serving as the functional outcome measure. 1, 2
The Five Core Defective Components
1. Respiration (Breath Support and Control)
- Impaired breath support for speech production 1
- Reduced ability to sustain phonation due to inadequate respiratory control 1
- Audible inspiration may be present in acute stroke patients 3
- Maximum phonation time frequently deviates from normal values 3
2. Phonation (Voice Production)
- Harsh or breathy voice quality is characteristic 1, 3
- Monotonous pitch and reduced loudness variation 4, 5
- Maximum loudness often significantly impaired 3
- Voice may sound thickened or hoarse 2, 5
3. Resonance (Nasal Airflow)
- Hypernasality occurs when velopharyngeal closure is inadequate 1
- Degree of hypernasality varies based on lesion location and severity 1
- Affects overall speech quality and intelligibility 6
4. Articulation (Sound Production)
- Imprecise consonant articulation is the most frequently observed deficit 3
- Slow speech rate with reduced articulatory precision 1
- Slurred speech that may remain intelligible in mild-moderate cases 2
- Results from muscle weakness, abnormal tone, or incoordination 1, 6
5. Prosody (Speech Rhythm and Intonation)
- Monopitch and monoloudness patterns 1, 4
- Reduced emphatic stress and abnormal intonation contours 1
- Variable speech rate with possible rapid phoneme repetition 4, 5
- Decreased accentuation affecting natural speech melody 4
Overall Functional Impact
Speech Intelligibility
- Represents the cumulative effect of all component defects 1
- Measured by how well familiar and unfamiliar listeners understand speech 1
- Can range from mildly impaired (91% intelligibility) to completely unintelligible 3
- Disproportionately affects quality of life relative to physiological impairment severity 1, 7
Assessment Framework
Comprehensive evaluation must assess each component systematically using auditory-perceptual, acoustic, and physiological measures in contexts ranging from isolated sounds to conversational speech. 1
Evaluation Methods
- Quantitative tasks and rating scales for each subsystem 1
- Simple contexts: isolated sounds and consonant-vowel syllables 1
- Complex contexts: conversational speech and reading passages 1, 5
- Objective acoustic parameters including fundamental frequency and airway resistance 1, 3
Clinical Pitfall
Do not rely solely on perceptual assessment—dysarthria tests using only auditory-perceptual methods have weak psychometric qualities and should be supplemented with acoustic and physiological measurements. 1