Estimating subglottal pressure via airflow interruption with auditory masking

Measurement reliability of phonation threshold pressure in pediatric subjects

OBJECTIVES/HYPOTHESIS

Phonation threshold pressure (PTP), the minimum subglottal pressure (P_s ) required for phonation, is sensitive to changes in laryngeal biomechanics and is often elevated with pathology. Little is reported on PTP in children; challenges with task performance and measurement reliability represent barriers to routine clinical assessment.

STUDY DESIGN

Pilot study evaluating PTP and P_s measurement reliability in children using labial and mechanical interruption.

METHODS

Twenty-two subjects aged 4 to 17 years (10.7 ± 3.9 years) participated. Ten trials were performed for each method; task order was randomized. For labial interruption, subjects produced /pα/ five times at softest (onset PTP) and comfortable amplitude. For mechanical interruption, subjects produced a sustained /α/ while a balloon valve interrupted phonation five times for 250 ms each; mechanical interruption was performed with a mouthpiece and mask. PTP was recorded as the difference between P_s and supraglottal pressure at phonation cessation (offset PTP). Mean PTP and P_s and intrasubject coefficients of variation were compared. Correlations with age were evaluated.

RESULTS

Mean PTP (P < .001) and P_s (P = .005) were higher for labial interruption. Intrasubject coefficients of variation for PTP (P = .554) and P_s (P = .305) were similar across methods. Coefficient of variation was related to age for mechanical-mask trials only (r = -0.628, P = .00175).

CONCLUSIONS

Differences in means are likely related to differences in task and PTP hysteresis effect. Reliability is comparable with all methods; using a mouthpiece may be preferable to a mask for mechanical interruption. Measurement of PTP is noninvasive, reliable, and may be a useful adjunct in pediatric voice assessment.

LEVEL OF EVIDENCE

3b Laryngoscope, 129:1520-1526, 2019.

Evaluation of auditory and visual feedback for airflow interruption

INTRODUCTION

Clinical application of mechanical interruption methods for measuring aerodynamic parameters has been hindered by relatively high intrasubject variability. To improve the intrasubject reliability, we evaluated the effect of auditory and visual feedback on subject performance when measuring aerodynamic parameters with the airflow interrupter.

METHODS

Eleven subjects performed four sets of 10 trials with the airflow interrupter: no feedback (control); auditory feedback (tone matching subject's F0 played over headphones); visual feedback (real-time feedback of sound pressure level, frequency, and airflow); and combined auditory and visual feedback. Task order was varied across subjects. The effect of each feedback method on mean and coefficient of variation (CV) of subglottal pressure (Ps), mean flow rate (MFR), and laryngeal airway resistance (RL; Ps/MFR) compared with that of the control trials was determined using paired t tests. Feedback methods were compared against each other using one-way repeated measures analysis of variance.

RESULTS

Each feedback method significantly decreased CV of RL compared with that of the control trials (auditory feedback: P=0.005; visual feedback: P=0.008; and combined feedback: P<0.001). Auditory feedback (P=0.011) and combined feedback (P=0.026) also decreased CV of MFR. Mean MFR was significantly higher during trials with visual feedback compared with that of the auditory feedback.

CONCLUSIONS

Each feedback method improved the intrasubject consistency when measuring RL. Feedback appeared to have a greater effect on MFR than Ps. Although there is no clear optimal feedback method, each is preferable to not providing any feedback during trials. Evaluating new methods of visual feedback to further improve MFR and thus RL measurement would be valuable.

Comparison of labial and mechanical interruption for measurement of aerodynamic parameters

OBJECTIVES/HYPOTHESIS

To directly compare the mechanical and labial interruption techniques of measuring subglottal pressure (P(s)), mean flow rate (MFR), and laryngeal resistance (R(L)).

METHODS

Thirty-four subjects performed 10 trials with both mechanical and labial interruption. P(s) and MFR were recorded, whereas R(L) was calculated by dividing P(s) by MFR. Coefficients of variation were calculated to compare intrasubject precision. A subset of 10 subjects performed the tasks twice with 30 minutes between sessions. Bland-Altman plots were used to determine intrasubject repeatability for each of the methods.

RESULTS

Mechanical interruption produced coefficients of variation for P(s), MFR, and R(L) of 0.0995, 0.127, and 0.129, respectively. Labial interruption produced coefficients of variation of 0.102, 0.147, and 0.169, respectively. P values were 0.824 for P(s), 0.159 for MFR, and 0.043 for R(L). The Bland-Altman plots revealed comparable repeatability between the two methods. The 95% confidence intervals of the Bland-Altman plots for mechanical interruption were (-0.050, 0.072), (-0.543, 1.832), and (-2.498, 10.528) for MFR, P(s), and R(L). Confidence intervals for labial interruption were (-0.018, 0.031), (0.057, 2.442), and (-3.267, 10.595) for MFR, P(s,) and R(L).

CONCLUSIONS

Mechanical interruption produced higher precision when measuring R(L) because of more reliable airflow measurements. Mechanical and labial interruption showed comparable repeatability. Further research into using mechanical interruption clinically is warranted.

Indirect estimation of laryngeal resistance via airflow redirection

OBJECTIVES

Our aim was to estimate aerodynamic parameters of laryngeal resistance (RL) and aerodynamic power indirectly from a subglottal pressure (Ps) data trace obtained with the airflow redirection system.

METHODS

During airflow interruption, the airflow redirection tank fills capacitively with pressure until it reaches the subject's Ps. Therefore, a time constant, tau, can be extracted from the data trace and used to calculate RL. The validity of applying this method to the estimation of RL was demonstrated with a computer model. Estimations were made for values of 10, 20, 30, 40, and 50 cm H2O per liter per second (L/s). Twenty subjects performed 10 trials on the experimental system designed to measure Ps. The values of RL and aerodynamic power were then calculated.

RESULTS

The computer model simulation yielded a maximum measurement error of 3.00% and a mean error of 1.78%. In human subject testing, the mean +/- SD laryngeal resistance was 22.61 +/- 8.65 cm H2O per L/s, the mean Ps was 6.91 +/- 1.94 cm H2O, and the mean aerodynamic power was 0.247 +/- 0.170 kPa x (L/s).

CONCLUSIONS

The proposed method of data analysis enables a clinician to estimate RL and aerodynamic power from a single experimental trial designed to measure Ps. This technique provides the clinician with an aerodynamic function report that can be used to analyze patient health and treatment efficacy.