The phonation quotient (PQ) is a measure of the upper airway aerodynamics. It is the ratio between the vital capacity and maximum phonation time. It can be used to monitor a variety of laryngeal diseases.
phonation quotient in mL per second =
= (vital capacity in mL) / (maximum phonation time in seconds)
maximum phonation time in seconds =
= (phonation volume in mL) / (mean flow rate in mL per second)
where:
• The phonation volume is the total air volume used during maximum sustained phonation.
• The mean flow rate (MFR) describes the velocity of a breath.
Interpretation:
• The average PQ for a normal population is between 120 and 190 mL per second. The upper limit ranges from 200 to 350 mL per second depending on the study.
• The phonation quotient is elevated in recurrent laryngeal nerve paralysis and with laryngeal lesions (polyps, nodules, neoplasma, etc.).
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