| The purpose of this study was to explore the nature of actively versus passively mediated changes in velopharyngeal closure force (VPCF) in response to intraoral air pressure (IOAP) perturbations. It was hypothesized that both passive and active responses of velopharyngeal closure force would be associated with modulations of intraoral air pressure. Two main questions were addressed; (1) Are changes in intraoral air pressure recorded during static speech tasks systematically associated with variations in velopharyngeal closure force? If so, how might those force changes be mediated? (2) Do short latency velopharyngeal closure force responses occur following unanticipated intraoral air pressure perturbations during sustained speech tasks? If so, what is the nature of the response, with respect to its direction, and latency?; Eleven adults, with a mean age of 36 (+/-14.04) years participated in the study. Medical histories were not significant. Participants produced vowel /u/ prolongations through a tube during two IOAP perturbation conditions, one static and one dynamic. For both tasks, measures of IOAP, VPCF and levator veli palatini (LEV) muscle activity were collected.; In general, VPCF variations were observed during modulations of IOAP across all subjects and tasks. Further, data indicated both active and passive VPCF responses. Active VPCF regulation was indicated by (1) statistically significant LEV muscle activity partial coefficients associated with the multiple linear regression model in 7/11 subjects, (2) short latency changes in the level of LEV muscle activity post versus pre IOAP perturbation and/or (3) the sequence and pattern of LEV muscle activity and VPCF levels post perturbation. Evidence of passive velopharyngeal closure responses were indicated with (1) a statistically significant IOAP partial coefficient associated with the multiple linear regression model in 9/11 subjects, (2) high cross correlation coefficients between VPCF and IOAP, and/or (3) a change of VPCF level post IOAP perturbation in the absence of change of muscle activity.; Thus, it was suggested that velopharyngeal closure force is accomplished via an interaction between the relative contributions of various velopharyngeal musculature (reported in previous studies), active VPCF regulation (via an IOAP feedback loop), and passive VPCF responses (via IOAP modulations) (Kuehn, Folkins & Cutting, 1982). |
