The speech regulating system: temporal and aerodynamic responses to velopharyngeal inadequacy.

Temporal and respiratory responses to a loss of velar resistance were measured in 107 subjects demonstrating varying degrees of velopharyngeal inadequacy. The subject data were compared to data generated by a mechanical model representing a passive system. The pressure-flow technique was used to estimate velopharyngeal orifice size and measure respiratory and temporal characteristics of aerodynamic events associated with the production of the nasal-plosive blend /mp/ in the word "hamper". Subjects were categorized as having adequate closure (less than 0.05 cm2), adequate/borderline closure (0.05-0.09 cm2), borderline/inadequate closure (0.10-0.19 cm2) and inadequate closure (greater than or equal to 0.20 cm2). The data revealed that intraoral pressure fell 10-fold in the model as velopharyngeal orifice area changed from adequate closure to inadequate. The subject data demonstrated only a 1.4-fold drop in pressure. Airflow data indicated that there was a 10-fold increase in respiratory volume in the subject data corresponding to the change from adequacy to inadequacy. When respiratory and temporal responses were assessed together, the findings revealed that airflow and temporal changes minimized the fall of pressure as velar resistance declined across groups.