Warren D W, Dalston R M, Mayo R
University of North Carolina Craniofacial Center, Department of Dental Ecology, Chapel Hill.
Cleft Palate Craniofac J. 1993 Mar;30(2):150-4. doi: 10.1597/1545-1569_1993_030_0150_hitpoa_2.3.co_2.
In some instances, hypernasality occurs despite an instrumental assessment of "adequate" velopharyngeal closure. The pressure-flow technique was used to assess the timing characteristics associated with velopharyngeal closure in 11 such subjects. The group's performance was compared to the aerodynamic characteristics of two other subject groups. One was comprised of 13 cleft palate subjects with adequate closure and normal nasal resonance, while the second group consisted of 16 noncleft subjects who also manifested normal speech. The data indicate that there are several unique timing features that differentiate the hypernasal but "adequate" group from the two control groups. These include a delay of about 50 ms in achieving closure, a longer interval of nasal emission, and a shorter duration of actual closure. Hypernasality seems to be associated with the actual time the velopharyngeal mechanism is open, rather than the volume of air escaping from the nasal chamber.
