Supraglottal Pressure Research Articles

Varying Supraglottic Pressure Using Controlled Supraglottic Pressure Phonation with a Straw-Shaped Mouthpiece in Healthy Subjects

ObjectiveThe objective of this study is to expand on a novel method for semi-occluded vocal tract therapy (SOVT) called controlled supraglottic pressure phonation, and investigate the mechanism that introduced supraglottic pressure mediates a decrease in impedance during SOVT therapy. Instead of the previously used CPAP mask, this study analyzes controlled supraglottic pressure phonation by use of a straw mouthpiece to deliver supraglottic pressure. MethodsTwenty-six human subjects were randomly assigned to one of four supraglottic pressure levels: 0, 2, 4, 6 cm H2O, which were controlled through a continuous positive airway pressure device. Subjects were asked to phonate during a SOVT task for one round (referred to as the “short-duration” task) and eight rounds (referred to as the “long-duration” task), in which acoustic and aerodynamic properties were measured before and after. Subjects were surveyed for the levels of discomfort experienced during controlled supraglottic pressure phonation therapy and subjective levels of improvement of vocal economy. ResultsSignificant differences were observed between pre- and post-task measurement for phonation threshold pressure for the long-duration task for the 2 cmH2O group. Frequency measurement was not found to have statistically significant differences. The perceived phonatory effort was not significantly different at any pressure levels. ConclusionsLower supraglottic pressure levels will improve ease of phonation for longer durations, however, shorter duration tasks will not be effective. Controlled supraglottic pressure phonation coupled with straw phonation may produce an improved vocal economy for those who have access to an oppositional airflow setup.

Hypopharyngeal geometry impact on air-induced loads on the supraglottis

Exercise-induced laryngeal obstruction (EILO) describes paradoxical laryngeal closure during inspiration at high-intensity exercise. It is hypothesised that during intense activity, the air-induced loads on supraglottic walls overcome their internal stiffness, leading to the obstruction. Recent investigations have revealed that the air-induced loads on the supraglottic walls vary nonlinearly with increasing flow rate. It is, however, unclear whether certain geometric configurations of the hypopharynx and larynx may contribute to the predisposition to EILO. This study investigates the influence of hypopharyngeal and laryngeal geometry on upper respiratory tract airflow and air-induced forces. A computational fluid dynamics model is developed to study airflow through larynx. Four real, adult upper respiratory tracts with variable configurations are considered. Two steady, uniform inspiratory flow rates of 60 L/min and 180 L/min are considered. The analysis shows that geometries with a space lateral to the epiglottis (EpiS) and piriform fossae (PF) directs the hypopharyngeal and supraglottic pressure field to remain positive and increase with the flow rate. In geometries with EpiS and PF, pressure differential occurs around the aryepiglottic fold producing a net inward force over the region. The three-fold increase in flow rate induces near ten-fold increases in force over the region which may facilitate the closure. It is concluded that hypopharyngeal anatomy, particularly the piriform fossae, play a significant role in the obstruction of the supraglottic airway and should be considered in research and clinical assessment of EILO.

Optimizing Aerodynamic Vocal Parameters by Varying Supraglottic Pressure Using “Controlled Supraglottic Pressure Phonation” in Healthy Subjects

The objective of this study is to introduce a novel method for semi-occluded vocal tract (SOVT) therapy called "controlled supraglottic pressure phonation," determine the mechanism by which supraglottic pressure contributes to lowering impedance during SOVT therapy, and provide the optimal supraglottic pressure range for SOVT exercises. Twenty-five human subjects were assigned to one of five supraglottic pressure levels, 0, 2, 4, 6, and 8 cmH2O, which were controlled through a continuous positive airway pressure device. Subjects were asked to phonate during both a short- and long-duration task, in which vocal properties were measured before and after. At the end of each task, the subjects reported the levels of discomfort and phonation difficulty on a 0-10 scale to assess the subjective improvement of vocal economy. Significant differences were observed between pre- and post-task measurements for phonation threshold pressure for both the short-duration and long-duration tasks. Phonation threshold flow and frequency measurements were found to have no statistically significant differences. The subjective measures showed elevated discomfort in the higher pressure inputs for both tasks relative to no air. Higher supraglottic pressure levels will improve ease of phonation, but the treatment discomfort needs to be considered as well, yielding an optimal supraglottic pressure range of 4-6 cmH2O. "Controlled supraglottic pressure phonation" serves as an alternative to straw phonation that may produce additional benefits.

Airflow through the supraglottis during inspiration

Exercise-induced laryngeal obstruction is a paradoxical laryngeal closure during inspiration at high-intensity exercise, with supraglottic closure being most common. This study develops a model based on the computational fluid dynamics to investigate airflow velocity and pressure and the air-induced loads on the supraglottis at various inspiratory flow rates. It is found that at high flow rates, positive wall pressure is formed in the hypopharynx localise towards its lower region, while posterior supraglottic wall pressures shift from positive to negative. These findings suggest that high inspiratory flow rates may increase supraglottic pressure differentials, ultimately contributing in the collapse.

Immediate and Short-term Effects of Straw Phonation in Air or Water on Vocal Fold Vibration and Supraglottic Activity of Adult Patients with Voice Disorders Visualized with Strobovideolaryngoscopy: A Pilot Study

Purpose The first purpose of this study was to investigate and compare the short-term effects after a semi-occluded vocal tract (SOVT) therapy session consisting of straw phonation (SP) in air or water on vocal fold vibration and supraglottic activity of adult patients with voice disorders, visualized with strobovideolaryngoscopy (SVL). The second purpose of this study was to investigate and compare immediate changes in the patients' vocal fold vibration and supraglottic activity during SP in air or water, visualized with SVL. Methods Twelve adult patients with voice disorders (eight women and four men, mean age 52 years) were assigned randomly to one of two study groups: SP in air or SP in water. Immediately before and after a therapy session of 15 min, participants underwent a rigid SVL to determine the short-term effects of the SP session. At the posttherapy examination, flexible SVL while performing SP was added to determine the effects occurring during SP. The visual-perceptual ratings were performed blindly and in random order by three laryngologists, using the Voice-Vibratory Assessment with Laryngeal Imaging rating form for stroboscopy. ResultsShort-term effects after SP: After the SP-in-air session, the supraglottic mediolateral compression decreased significantly. The SP-in-water session led to significantly increased left vibrational amplitude. Immediate effects during SP: During SP in air, a significantly increased left amplitude and mucosal wave, and significantly decreased mediolateral supraglottic activity, were found. SP in water tended to decrease the vibrational amplitude during performance of the task. A trend toward higher anteroposterior supraglottic compression was observed during both SP in air and water, being more prominent in the latter. Conclusion SP in air led to less false vocal fold adduction and consequently less hyperfunction. The small increment in anteroposterior supraglottic activity during SP in air and water might be related to epilarynx narrowing, an economic phenomenon associated with SOVT exercises. The effects on vibrational amplitude were rather ambiguous. The small reduction in amplitude during SP in water is expected to diminish vocal fold impact stress and therefore creates an ideal basis for voice therapy. The increment in amplitude and mucosal wave during SP in air might indicate insufficient supraglottic pressure to obtain the favorable effects of semi-occlusion. Whether or not the rise in amplitude after the SP-in-water session is due to voice efficiency or voice fatigue remains unknown. Future larger-scale investigation in subgroups of voice patients is needed to explore these hypotheses.

Measurement reliability of phonation threshold pressure in pediatric subjects.

Phonation threshold pressure (PTP), the minimum subglottal pressure (Ps ) 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. Pilot study evaluating PTP and Ps measurement reliability in children using labial and mechanical interruption. 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 Ps and supraglottal pressure at phonation cessation (offset PTP). Mean PTP and Ps and intrasubject coefficients of variation were compared. Correlations with age were evaluated. Mean PTP (P < .001) and Ps (P = .005) were higher for labial interruption. Intrasubject coefficients of variation for PTP (P = .554) and Ps (P = .305) were similar across methods. Coefficient of variation was related to age for mechanical-mask trials only (r = -0.628, P = .00175). 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. 3b Laryngoscope, 129:1520-1526, 2019.

Prevoicing and prenasalization in Russian initial plosives

This study investigated the production of prevoiced initial plosives in Russian, including examining (i) how closure voicing varies depending on consonantal place, vocal context and speaker gender and (ii) whether Russian speakers rely on prenasalization to produce vocal fold vibration in initial closures, which is one of the mechanisms of reducing supraglottal pressure during oral occlusion. The study analyzed acoustic and airflow data from large samples of speakers and stimulus items, which made it possible to examine group-level patterns. Results for prevoicing duration revealed an effect of consonantal posteriority and adjacent vowel height. Shorter durations were seen in velars than bilabials or dentals and in tokens with high vowels (especially in male speech). Prevoiced tokens also showed higher levels of nasal flow than voiceless plosives during the initial part of closure. Nasal flow levels were lower in bilabials than dentals or velars and were not affected by vowel context. Speaker gender influenced voiceless tokens only. Towards the end of closure, voiced and voiceless tokens demonstrated comparable nasal flow levels. These results provide new insights into prevoicing in Russian and the link between prevoicing and prenasalization.

Significance of sonority information for voiced/unvoiced decision in speech synthesis

The quality of synthesized speech obtained from statistical parametric speech synthesis (SPSS) significantly relies on excitation source generation. Voiced/unvoiced decision is an essential component for generation of excitation source. It is obtained from fundamental frequency and other excitation source evidence in the existing literature. The discontinuity at the point of contact in the vocal-folds excites energy into the vocal-tract resulting voicing effect in the produced speech signal. The perceptual reflection of voicing over the sound produced is correlated with the sonority information which is related to less vocal-tract constriction and significant glottal vibration. Therefore, the possible variation in voicing with the change in supraglottal pressure due to vocal-tract constriction, rate of closing of vocal folds and regularity in structure of the signal are intact in the sonority associated with a sound unit. Voicing and degree of opening of vocal-tract are the two most effective correlates of sonority, that potentially contribute to the sonority hierarchy for sonorants and obstruents uniformly. Therefore, the voicing effect can be captured by the sonority measurement derived from system, source and suprasegmental information in the speech signal. In this work, a novel voiced/unvoiced decision method using sonority information is proposed and integrated in the SPSS framework for generation of excitation source. It leads to better voicing decision compared to the existing methods resulting in synthesized speech of improved quality, which is assured from objective and subjective analysis.

Evidence for active cavity expansion through advanced lingual place of constriction in voiced geminates

Geminate voicing requires both active and passive cavity expansion in order to delay the equalization of subglottal and supraglottal pressure (Ohala 1983, Ham 2001). Studies report differences in stop closure duration (Lahiri & Hankamer 1988) and pre-geminate vowel duration as cues to the laryngeal contrast. Following Schroeder (1967), Mermelstein (1967), and Iskarous (2010), we present results from formant transitions in the VC:V context and the anti-symmetric Fourier component coefficient, an = -2 (Fn-fn)/fn, to partially recover the area function of the vocal tract behind the geminate constriction. Voiced geminates exhibit significantly higher and positive coefficient values than their voiceless counterparts which implies that measured Fn values for voiced geminates are lower than their neutral tract formant values. This finding indicates that voiced geminates have a more anterior constriction compared to their voiceless counterparts. Without ruling out the role of passive cavity expansion through the cheek muscles, we conclude that in order to delay the pressure equalization the lingual constriction in voiced geminates is maintained at an anterior location compared to voiceless geminates in Bangla. Results from the slopes of first order F2 locus-equations are also presented to measure the differences in coarticulatory resistance between the voiced and voiceless geminates.Geminate voicing requires both active and passive cavity expansion in order to delay the equalization of subglottal and supraglottal pressure (Ohala 1983, Ham 2001). Studies report differences in stop closure duration (Lahiri & Hankamer 1988) and pre-geminate vowel duration as cues to the laryngeal contrast. Following Schroeder (1967), Mermelstein (1967), and Iskarous (2010), we present results from formant transitions in the VC:V context and the anti-symmetric Fourier component coefficient, an = -2 (Fn-fn)/fn, to partially recover the area function of the vocal tract behind the geminate constriction. Voiced geminates exhibit significantly higher and positive coefficient values than their voiceless counterparts which implies that measured Fn values for voiced geminates are lower than their neutral tract formant values. This finding indicates that voiced geminates have a more anterior constriction compared to their voiceless counterparts. Without ruling out the role of passive cavity expansion through the ...

Estimating Vocal Effort from the Aerodynamics of Labial Fricatives: A Feasibility Study

Vocal effort in loud voice is produced with increased subglottal pressure during vowels and increased supraglottal pressure during consonants. In the paper, our main objective is to check whether it was supported by a parallel increase in the airflow resistance of the laryngeal articulator and of the supralaryngeal articulator, here the lips. For this comparison, our choice fell on the fricative consonants, as their production allows perfectly synchronous air pressure and airflow measurements. Also, the calculation of the real instantaneous aerodynamic resistance is possible with fricatives-as it is with vowels-whereas it is not possible with plosives. The present feasibility study on a healthy subject is based on direct subglottal and intraoral pressures and airflow measured for /f/ or /v/ and from the contiguous vowel produced in VCVCV nonsense words at different levels of intensity. The results support that the airflow resistances at the lips and that at the larynx are quite parallel. The airflow resistance at the lips during labial fricative production could provide a good picture of the laryngeal resistance during the production of continuous speech. This suggests clinical applications using both noninvasive inferred measurements of subglottal pressure variation and direct noninferred airflow measurements from more natural speech production tasks.

Analysis of Measured and Simulated Supraglottal Acoustic Waves

To date, although much attention has been paid to the estimation and modeling of the voice source (ie, the glottal airflow volume velocity), the measurement and characterization of the supraglottal pressure wave have been much less studied. Some previous results have unveiled that the supraglottal pressure wave has some spectral resonances similar to those of the voice pressure wave. This makes the supraglottal wave partially intelligible. Although the explanation for such effect seems to be clearly related to the reflected pressure wave traveling upstream along the vocal tract, the influence that nonlinear source-filter interaction has on it is not as clear. This article provides an insight into this issue by comparing the acoustic analyses of measured and simulated supraglottal and voice waves. Simulations have been performed using a high-dimensional discrete vocal fold model. Results of such comparative analysis indicate that spectral resonances in the supraglottal wave are mainly caused by the regressive pressure wave that travels upstream along the vocal tract and not by source-tract interaction. On the contrary and according to simulation results, source-tract interaction has a role in the loss of intelligibility that happens in the supraglottal wave with respect to the voice wave. This loss of intelligibility mainly corresponds to spectral differences for frequencies above 1500Hz.

Phase-locked flow field analysis in a synthetic human larynx model

The fluid flow within a human larynx plays an essential role in the fluid–structure–acoustic interaction during voice production. This study addresses the flow field downstream of aerodynamically driven, synthetic vocal folds. In order to quantitatively investigate the supraglottal formation of the flow field within one oscillation cycle of the vocal folds, a phase-locked PIV technique is introduced. The pseudo-time-resolved measurement results were averaged for each phase angle. When including a supraglottal channel, the jet was deflected from the centerline of the supraglottal channel and changed the direction of deflection in different cycles. The result is a bistable flow field. Therefore, a sorting method based on the mean cyclic supraglottal pressure difference was introduced. For both states of the flow field, a recirculation area was detected, interacting with the arising glottal jet in every oscillation cycle. This interaction could be identified as the major cause for supraglottal jet deflection, and the sense of rotation of the recirculation area defined the direction of deflection. The asymmetric structure of the flow field was caused by the geometric boundary condition, i.e., due to the present supraglottal channel. An additional key factor was found to be the contact between the two vocal folds in each oscillation cycle which interrupted the jet flow periodically. Removing the supraglottal channel resulted in a symmetric jet location. When avoiding vocal fold contact, the bistable behavior vanished and the jet was steadily deflected to one lateral side. In the present study, it cannot be confirmed that the Coanda effect is responsible for the deflection.

Age- and gender-related variation in voiced stop prenasalization in Japanese

Modern Japanese is generally described as having phonologically voiced (versus voiceless) word-initial stops. However, phonetic details vary across dialects and age groups; in Takada's (2011) measurements of recordings of 456 talkers from multiple generations of talkers across five dialects, Osaka-area speakers and older speakers in the Tokyo area (Tokyo, Chiba, Saitama, and Kanagawa prefectures) typically show pre-voicing (lead VOT), but younger speakers show many “devoiced” (short lag VOT) values, a tendency that is especially pronounced among younger Tokyo-area females. There is also variation in the duration of the voice bar, with very long values (up to -200 ms lead VOT) observed in the oldest female speakers. Spectrograms of such tokens show faint formants during the stop closure, suggesting a velum-lowering gesture to vent supra-glottal air pressure to sustain vocal fold vibration. Further evidence of pre-nasalization in older Tokyo-area females comes from comparing amplitude trajectories for the voice bar to amplitude trajectories during nasal consonants, adapting a method proposed by Burton, Blumstein, and Stevens (1972) for exploring phonemic pre-nasalization contrasts. Differences in trajectory shape patterns between the oldest males and females and between older and younger females are like the differences that Kong, Syrika, and Edwards (2012) observed across Greek dialects.

A comparison of inspiratory airflow dynamics during sleep between upper airway resistance syndrome patients and healthy controls

A test of the hypothesis that upper airway resistance syndrome (UARS) patients have an increased prevalence of inspiratory airflow limitation (IFL) during sleep compared to healthy controls. We compared inspiratory airflow dynamics during sleep between 12 UARS patients (nine females and three males) and 12 healthy controls matched for age, gender and obesity with maximal age limited at 45years. A standard clinical polysomnogram (airflow measured with a nasal/oral pressure catheter) was performed to assess the impact of SDB on the participants' natural sleep. A second full-night polysomnogram with a pneumotachograph and a supraglottic pressure catheter to measure airflow and effort was performed to compare the maximal inspiratory airflow and effort and the percentage of flow-limited breaths during supine, continuous stage 2 sleep between groups. During clinical polysomnography, UARS participants did not differ significantly from controls in sleep architecture or fragmentation. We observed a small difference in apnea hypopnea index between UARS participants and controls (1.6 ± 1.9 vs. 0.4 ± 0.3, respectively; p = 0.035). During supine, continuous stage 2 sleep, 64.2% (35.8; mean (SD)) of UARS participants' breaths were flow-limited compared with 34.0% (39.3) of controls' breaths (p = 0.06). The groups did not differ in maximal inspiratory airflow or inspiratory effort. Our findings indicate a less-than-robust difference in respiratory parameters during sleep between UARS patients and healthy controls and no difference in standard sleep parameters or sleep fragmentation. We consider a pathophysiology of UARS that incorporates these findings.

The Supraglottic Effect of a Reduction in Expiratory Mask Pressure During Continuous Positive Airway Pressure

Patients with obstructive sleep apnea may have difficulty exhaling against positive pressure, hence limiting their acceptance of continuous positive airway pressure (CPAP). C-Flex is designed to improve comfort by reducing pressure in the mask during expiration proportionally to expiratory airflow (3 settings correspond to increasing pressure changes). When patients use CPAP, nasal resistance determines how much higher supraglottic pressure is than mask pressure. We hypothesized that increased nasal resistance results in increased expiratory supraglottic pressure swings that could be mitigated by the effects of C-Flex on mask pressure. Cohort study. Sleep center. Seventeen patients with obstructive sleep apnea/hypopnea syndrome and a mechanical model of the upper airway. In patients on fixed CPAP, CPAP with different C-Flex levels was applied multiple times during the night. In the model, 2 different respiratory patterns and resistances were tested. Airflow, expiratory mask, and supraglottic pressures were measured on CPAP and on C-Flex. Swings in pressure during expiration were determined. On CPAP, higher nasal resistance produced greater expiratory pressure swings in the supraglottis in the patients and in the model, as expected. C-Flex 3 produced expiratory drops in mask pressure (range -0.03 to -2.49 cm H(2)O) but mitigated the expiratory pressure rise in the supraglottis only during a sinusoidal respiratory pattern in the model. Expiratory changes in mask pressure induced by C-Flex did not uniformly transmit to the supraglottis in either patients with obstructive sleep apnea on CPAP or in a mechanical model of the upper airway with fixed resistance. Data suggest that the observed lack of expiratory drop in supraglottic pressure swings is related to dynamics of the C-Flex algorithm.

Awake Measures of Nasal Resistance and Upper Airway Resistance on CPAP during Sleep

Since on CPAP, the nose is the primary determinant of upper airway resistance, we assess utility of noninvasive measures of nasal resistance during wakefulness as a predictor of directly assessed upper airway resistance on CPAP during sleep in patients with obstructive sleep apnea/hypopnea syndrome. Patients with complaints of snoring and excessive daytime sleepiness were recruited. 14 subjects underwent daytime evaluations including clinical assessment, subjective questionnaires to assess nasal symptoms and evaluation of nasal resistance with acoustic rhinometry (AR) and active anterior rhinomanometry (RM) in the sitting and supine positions. Patients underwent nocturnal polysomnography on optimal CPAP with measurements of supraglottic pressure to evaluate upper airway resistance. Comparisons were made between nasal resistance using AR and RM during wakefulness, and between AR and RM awake and upper airway resistance during sleep. Our study shows that measures of awake nasal resistance using AR and RM had little or no correlation to each other in the sitting position, whereas there was significant but weak correlation in the supine position. Upper airway resistance measured while on CPAP during sleep did not show significant relationships to any of the awake measures of nasal resistance (AR or RM). Awake measurements of nasal resistance do not seem to be predictive of upper airway resistance during sleep on CPAP.

Inspiratory airflow dynamics during sleep in veterans with Gulf War illness: a controlled study

To determine whether veterans with Gulf War Illness (GWI) are distinguished by sleep-disordered breathing, we compared inspiratory airflow dynamics during sleep between veterans with GWI and asymptomatic veterans of the first Gulf War. We recruited 18 male veterans with GWI and 11 asymptomatic male veterans of the first Gulf War by advertisement. The two samples were matched for age and body mass index. Each participant underwent a first full-night polysomnogram (PSG) while sleeping supine using standard clinical monitoring of sleep and breathing. A second PSG was performed measuring airflow with a pneumotachograph in series with a nasal mask and respiratory effort with a supraglottic pressure (Psg) catheter to assess the presence of inspiratory airflow limitation during supine N2 sleep. We determined the prevalence of flow-limited breaths by sampling continuous N2 sleep and plotting inspiratory flow against Psg for each breath in the sample. We expressed the prevalence of flow-limited breaths as their percentage in the sample. Compared to controls, veterans with GWI had an increased frequency of arousals related to apneas, hypopneas, and mild inspiratory airflow limitation. During supine N2 sleep, veterans with GWI had 96 ± 5% (mean ± SD) of their breaths flow-limited while controls had 36 ± 25% of their breaths flow limited (p < 0.0001). Veterans with GWI experience sleep-disordered breathing that may distinguish them from asymptomatic veterans of the first Gulf War.

Inspiratory airflow dynamics during sleep in irritable bowel syndrome: a pilot study

This study is a preliminary test of the hypothesis that the pathophysiology of irritable bowel syndrome (IBS) derives from pharyngeal collapse during sleep. We studied inspiratory airflow dynamics during sleep in 12 lean females with IBS and 12 healthy female controls matched for age and obesity. A standard clinical polysomnogram (airflow measured with a nasal/oral pressure catheter) was performed to assess the impact of pharyngeal collapse on the participants' natural sleep. A second polysomnogram with a pneumotachograph and a supraglottic pressure catheter to measure airflow and effort was performed to compare the maximal inspiratory airflow and effort and the prevalence of inspiratory airflow limitation (IFL) during supine stage 2 sleep between groups. During clinical polysomnography, IBS participants did not differ significantly from controls in sleep architecture or respiration. The difference in apnea-hypopnea index between IBS participants and controls, however, approached statistical significance (2.8 +/- 2.7 vs 1.1 +/- 1.5, respectively; p = 0.079). Although nine of the 12 IBS participants had a prevalence of IFL of at least 33% during supine stage 2 sleep, they did not differ from controls in maximal inspiratory airflow, inspiratory effort, or the prevalence of IFL. Controls, however, differed from IBS participants in having their prevalence of IFL during stage 2 sleep positively correlated with age (r = 0.86; p = 0.0003) while IBS participants demonstrated no relationship between the prevalence of IFL and age. Our findings, while less than definitive, suggest a prevalence pattern of pharyngeal collapse during sleep among females with IBS that differs from that of healthy females, providing necessary background to inform further work on the relationship of pharyngeal collapse during sleep to IBS.

Expiratory pharyngeal narrowing during central hypocapnic hypopnea.

Ventilatory motor output is an important determinant of upper airway patency during sleep. We hypothesized that central hypocapnic hypopnea would lead to increased expiratory upper airway resistance and pharyngeal narrowing during non-REM sleep. Noninvasive positive pressure ventilation was used to induce hypocapnic hypopnea in 20 healthy subjects. Expiratory pressure was set at the lowest pressure (2 cm H(2)O), and inspiratory pressure was increased gradually during each 3-minute noninvasive positive pressure ventilation trial by increments of 2 cm H(2)O. Analysis 1 (n = 9) included measured retropalatal cross-sectional area (CSA) using nasopharyngoscope to compare CSA at five points of the respiratory cycle between control (eupneic) and hypopneic breaths. The pharyngeal pressure (P(ph)) was measured using a catheter positioned at the palatal rim. Analysis 2 (n = 11) included measured supraglottic pressure and airflow to compare inspiratory and expiratory upper airway resistance (R(UA)) at peak flow between eupneic and hypopneic breaths. Expiratory CSA during hypopneic breaths was decreased relative to eupnea (CSA at beginning of expiration [BI]: 101.5 +/- 6.3 vs. 121.6 +/- 8.9%; P < 0.05); P(ph)-BI was lower than that generated during eupnea (1.5 +/- 0.3 vs. 3.3 +/- 0.9 cm H(2)O; P < 0.05). Body mass index was an independent predictor of retropalatal narrowing during hypopnea. Hypopnea-R(UA) increased during expiration relative to eupnea (14.0 +/- 5.7 vs. 10.6 +/- 2.5 cm H(2)O/L/s; P = 0.01), with no change in inspiratory resistance. Expiratory pharyngeal narrowing occurs during central hypocapnic hypopnea. Reduced ventilatory drive leads to increased expiratory, but not inspiratory, upper airway resistance. Central hypopneas are obstructive events because they cause pharyngeal narrowing.

Reliable Time to Estimate Subglottal Pressure

Measuring subglottal pressure (P(s)) with complete interruption can be problematic due to unsteady plateaus in supraglottal pressure data traces during balloon valve interruption. Subjectively determining when the graph plateaus neglect the effects of laryngeal, auditory, and other physical reflexes may alter patient effort and glottal configuration. If the P(s) estimation was made at a consistent time before the onset of reflexes, the recorded pressure would not be dependent on subjective analysis by a clinician, and intrasubject data would be more precise. Previously collected data using the airflow interruption system have shown consistency at approximately 150 milliseconds after balloon valve inflation. To evaluate the validity of estimating P(s) at this point, a theoretical and a physical model were applied. A theoretical ideal gas model of capacitance calculated the time necessary for supraglottal pressure to equilibrate with P(s). Using a mechanical pseudolung which served as a constant pressure source, known subresistor pressures were compared to the pressure measured by the interruption device. Both models confirmed the validity of measuring P(s) consistently at 150 milliseconds into the 500-millisecond interruption. In human trials testing 25 subjects, mean intrasubject standard deviation using this optimal time constant was 0.66+/-0.37cm H(2)O, and 1.11+/-0.48cm H(2)O when performing plateau analysis (P<0.0005). This novel modification to the clinically feasible interruption model for P(s) estimation demonstrates a marked improvement in the reliability of balloon valve interruption while maintaining the validity demonstrated in previous studies.