Effects of Varying Lengths and Diameters During Straw Phonation on an Excised Canine Model

Abstract

Objective/background: Straw phonation, a well-established method of vocal exercise, started over 100 years ago. However, some of the most basic questions about best practices remain including the ideal extension length and the ideal restriction (semiocclusion) diameter. This study aims to help answer these questions by looking at both separately, with all other variables controlled.

Methods: Four (4) straws with lengths of 5, 25, 50, and 75 centimeters and 4 restrictions with diameters of 3, 9, 15, and 21 mm were tested, separately. They were attached to the end of a simulated vocal tract which was then affixed to an excised canine larynx. Airflow was increased until the larynges achieved self-sustained phonation then aerodynamic, acoustic, and electroglottographic data were collected.

Results: There was a significant decrease in the phonation threshold pressure using the 5 and 25 cm straw lengths and the 9 and 15 mm restrictions. The phonation threshold flow and contact quotient saw insignificant changes, except in the case of the 3 mm restriction.

Discussion: It is theorized that the increased inertive reactance helps to decrease phonation threshold pressure. By controlling for all other variables, the effects of the length or diameter of the straw can be analyzed in isolation. These results narrow the significant range of lengths and diameters used in straw phonation.

Keywords: Excised larynges; Phonation threshold pressure; Semi-occluded vocal tract; Straw phonation.

Figure 1

Schematic of the excised bench setup. The electroglottograph electrodes sat on the posterior cricoarytenoid muscle and could be retracted when not in use as shown in the figure. Figure 2 shows a more detailed schematic of the simulated vocal tract.

Figure 2

Schematic of the simulated vocal tract as well as schematics for the length and restriction straw inserts. There is an inlet on the vocal tract where it is possible to attach an oppositional supraglottal airflow, although for this experiment this was not used. The inner diameter of the straw length was 20.5 mm and was variable for the straw restrictions.

Figure 3

Example of visual output for acoustic waveform (top) and the frequency spectrum (bottom) on the custom LabVIEW program used for data collection. This would be considered phonation and data would be collected.

Figure 4

Graph of the PTP means for the straw lengths on the left and the restrictions on the right. Note that the sample size for the 3 mm restriction was n=12, whereas all other conditions had sample size n=29.