Comparison of direct and indirect calculations of laryngeal airway resistance in various voicing conditions.

Calculation of laryngeal airway resistance using intraoral pressure divided by airflow has become a widely accepted clinical tool. The estimation is based largely on theoretical assumptions, particularly regarding the relationship between intraoral and subglottal pressure. To determine the estimate's validity, direct measures of airflow and subglottal, intraoral and pharyngeal pressures were obtained for four men and four women. Subjects produced normal, loud, soft and simulated breathy and strained syllable trains. Comparison of direct and indirect calculations of laryngeal airway resistance revealed generally good correspondence, particularly for [pi] syllables, although the estimate's accuracy varied among individual subjects. Some interpretive caution is warranted for the extremes of laryngeal airway resistance, with resistance likely to be underestimated in the strained condition, and overestimated in the breathy condition.