Phonation threshold pressure estimation using electroglottography in an airflow redirection system

Abstract

Objectives/hypothesis: The present study proposed to estimate phonation threshold pressure (PTP) noninvasively using airflow redirection into a pneumatic capacitance system.

Study design: Prospective study.

Methods: Subjects phonated into the device, which interrupts airflow mechanically and redirects the flow into a pneumatic capacitor. Five interruptions were effected per trial. PTP was estimated as the difference between subglottal pressure (SGP) and transglottal pressure at phonation offset. The novel method was tested for consistency in 20 normal human subjects at low (75 dB) and high (85 dB) sound pressure levels. The device was tested for validity on a tracheotomy patient.

Results: Mean SGP was 9.02 +/- 3.27 cm H(2)O, and mean PTP was 3.68 +/- 1.41 cm H(2)O. Intrasubject coefficient of variation, a measure of intrasubject consistency, was 0.33 +/- 0.23. Statistically significant differences existed between the means of SGP but not PTP at 75 dB and 85 dB. The correlation coefficient between accepted and experimental SGP in a tracheotomy patient was 0.947 (P < .001).

Conclusions: Measurements corresponded well to previously reported values, and intrasubject variability was low, indicating the device was consistent. Testing on a tracheotomy patient demonstrated validity. More research is needed to determine the sensitivity and specificity of the device in differentiating between normal and pathological voices. This device may have clinical application as a noninvasive and reliable method of estimating PTP and indicating that laryngeal health is likely abnormal.

Figure 1

Diagram of the PTP interruption-redirection system. The central components are as follows: (A) EGG electrodes; (B) microphone for SPL meter; (C) mouthpiece; (D) inflatable balloon valve; (E) air tank (pneumatic capacitor); (F) one-way air valve; (G) plugged air escape gate; (H) intraoral pressure transducer; (I) tank pressure transducer; (J) EGG; (K) digital data acquisition board; (L) laptop computer. Pneumatic cables are thick and electrical cables are thin.

Figure 2

Phonation threshold pressures from 20 normal subjects at low and high SPLs. There were no statistically significant differences between the means of both groups (p=0.191, t₁₉=−1.355, paired two-tailed t-test). The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median PTP for the given elongation level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points.

Figure 3

A sample interruption from the middle of a trial using the airflow interruption-redirection system. The intraoral pressure at the time of phonation offset (dashed line) is interpreted to be the transglottal pressure, and the peak tank pressure is interpreted to be the SGP. For each trial, as many transglottal pressure measurements as there were interruptions and a single SGP measurement were recorded. The differential pressure at each instance of phonation offset is the estimated PTP. The delayed rise in tank pressure during the interruption illustrates the capacitance characteristics. A minimum of five interruptions occurred within each ten second trial.

Figure 4

Coefficient of variation (C_v) in PTP from 20 normal subjects at low and high SPLs. There were no statistically significant differences between the means of both groups (p=0.845, t₁₉=−0.199, paired two-tailed t-test). The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median PTP for the given elongation level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points.

Figure 5

Subglottal and transglottal pressure during speech task in 20 normal subjects at low and high SPLs. The differences between the means of SGP (p<0.001, t₁₉=−4.803, paired two-tailed t-test) and transglottal pressure (p<0.001, t₁₉=−4.477, paired two-tailed t-test) in both SGP groups were statistically significant.

Figure 6

Experimentally measured SGP using the incomplete airflow redirection device (P_SE) as a function of directly measured SGP in a tracheotomy patient (P_ST).