Response to Zajac and Warren We are happy to have the opportunity to respond to the letter by Drs. Zajac and Warren regarding our recent publication, and further explain the reasoning behind our choice of the variables used to estimate oral pressure during venting. We realized from their comments that our original document could ... Letter to the Editor
Letter to the Editor  |   December 01, 2000
Response to Zajac and Warren
 
Author Affiliations & Notes
  • Eileen M. Finnegan
    University of Iowa Iowa City
  • Henry T. Hoffman
    University of Iowa Hospitals and Clinics Iowa City
Article Information
Speech, Voice & Prosody / Speech / Letters to the Editor
Letter to the Editor   |   December 01, 2000
Response to Zajac and Warren
Journal of Speech, Language, and Hearing Research, December 2000, Vol. 43, 1534. doi:10.1044/jslhr.4306.1534
History: Received March 23, 2000 , Accepted July 25, 2000
 
Journal of Speech, Language, and Hearing Research, December 2000, Vol. 43, 1534. doi:10.1044/jslhr.4306.1534
History: Received March 23, 2000; Accepted July 25, 2000
We are happy to have the opportunity to respond to the letter by Drs. Zajac and Warren regarding our recent publication, and further explain the reasoning behind our choice of the variables used to estimate oral pressure during venting. We realized from their comments that our original document could have benefited from clarification on some points.
The first point we would like to clarify is that in our discussion, we sought to predict oral pressure based on group (not individual subject) data. To do so, we used values for group mean Pa (i.e., the mean Po in the nonvented condition) from the Kim et al. study, group mean Rlaw from our study, and group mean Rlx during production of a plosive from unpublished data. However, an estimate of Rlips during perturbation was needed for us to solve our equation for vented oral pressure. This leads to a second point of clarification concerning our logic for obtaining a Rlips value. Assuming the subjects formed an adequate seal around the bleed tube, Rlips would be determined solely by the bleed tube resistance, which is primarily determined by the physical characteristics of the tube. We used the individual data (from Figure 3 of the Kim et al. study) only to derive the resistance offered by the bleed tube. Given that the characteristics of the tube were presumably the same across subjects, this provided us with a Rlips value that was also common to all subjects in the group. We applied this value, along with the other group data, to predict the group oral pressure during venting. However, because the resistance of the bleed tube would be affected by the flow rate, the tube resistance should have been determined based upon the pressure and flow values associated with the group mean Po, rather than the individual's maximum Po. These values could also be obtained from Figure 3 of the Kim et al. study. At the flow rate associated with a Po of 0.47 kPa, the resistance of the bleed tube was 0.70 kPa/(l/s), rather than 0.75 kPa/(l/s). Use of this value predicted a group mean Po of 0.41 kPa, which is slightly less than the 0.42 kPa value originally predicted, but still relatively close to the measured group mean of 0.47 kPa. The similarity between the predicted group mean oral pressure and the reported group mean led us to speculate that the pressure changes could be due to a passive response to alteration in the relative resistances of the vocal tract. In other words, during labial bleed studies, it could be that the bleed tube resistance was large enough that oral pressure was maintained without any increase in respiratory activity.
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