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Original Research: Pulmonary Procedures |

Glottal Aperture and Buccal Airflow Leaks Critically Affect Forced Oscillometry MeasurementsArtifacts and Impulse Oscillometry FREE TO VIEW

Andras Bikov, MD, PhD; Neil B. Pride, MD, PhD; Michael D. Goldman, MD, PhD; James H. Hull, MD, PhD; Ildiko Horvath, MD, PhD; Peter J. Barnes, DM, DSc, Master FCCP; Omar S. Usmani, MBBS, PhD; Paolo Paredi, MD, PhD
Author and Funding Information

From the Airway Disease Section (Drs Bikov, Hull, Usmani, and Paredi and Profs Pride, Goldman, and Barnes), National Heart and Lung Institute, Imperial College London and Royal Brompton Hospital, London, England; and Department of Pulmonology (Dr Bikov and Prof Horvath), Semmelweis University, Budapest, Hungary.

CORRESPONDENCE TO: Paolo Paredi, MD, PhD, Airway Disease Section, National Heart and Lung Institute, Imperial College, Dovehouse St, London, SW3 6LY, England; e-mail: p.paredi@imperial.ac.uk


†Deceased.

Drs Usmani and Paredi contributed equally to this manuscript.

FUNDING/SUPPORT: Dr Bikov was supported by a European Respiratory Society Long-Term Fellowship. Dr Usmani is a recipient of a National Institutes of Health Research (NIHR) UK Career Development Fellowship. The study was supported by the NIHR Respiratory Disease Biomedical Research Unit at the Royal Brompton and Harefield NHS Foundation Trust and Imperial College London.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;148(3):731-738. doi:10.1378/chest.14-2644
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BACKGROUND:  The forced oscillation technique (FOT) measures respiratory resistance and reactance; however, the upper airways may affect the results. We quantified the impact of glottal aperture and buccal air leaks.

METHODS:  In the glottal aperture study (1) 10 healthy subjects (aged 34 ± 2 years) performed a total lung capacity maneuver followed by 10-s breath-hold with and without total glottal closure and (2) the effects of humming (incomplete glottal narrowing) on FOT measurements were studied in six healthy subjects. Glottal narrowing was confirmed by direct rhinolaryngoscopy. In the air leak study, holes of increasing diameter (3.5, 6.0, and 8.5 mm) were made to the breathing filters. Eleven healthy subjects (aged 33 ± 2 years) and five patients with COPD (aged 69 ± 3 years) performed baseline FOT measurements with the three modified filters.

RESULTS:  Narrow glottal apertures and humming generated whole-breath resistance at 5 Hz (R5) peaks, increased R5 (1.49 ± 0.37 kPa/L/s vs 0.34 ± 0.01 kPa/L/s, P < .001), and decreased whole-breath reactance at 5 Hz (X5) values (−2.10 ± 0.51 kPa/L/s vs −0.09 ± 0.01 kPa/L/s, P < .001). The frequency dependency of resistance was increased. Holes in the breathing filters produced indentations on the breathing trace. Even the smaller holes reduced R5 in healthy subjects (0.33 ± 0.02 to 0.24 ± 0.02 kPa/L/s, P < .01) and patients with COPD (0.50 ± 0.04 to 0.41 ± 0.04 kPa/L/s, P < .05), whereas X5 became less negative (from −0.09 ± 0.01 to −0.05 ± 0.01 in healthy subjects, P < .01; from −0.22 ± 0.06 to −0.11 ± 0.03 kPa/L/s in patients with COPD, P < .05).

CONCLUSIONS:  Visual inspection of the data is required to exclude glottal narrowing and buccal air leaks identified as R5 peaks and volume indentations, respectively, because these significantly affect FOT measurements.

Figures in this Article

Spirometry measures airflow obstruction but provides no information on underlying pathophysiologic mechanisms. In contrast, airflow resistance measured by body plethysmography1 provides a more physiologic assessment of airflow obstruction, but it is limited by cumbersome equipment and requires an experienced operator.

The forced oscillation technique (FOT) is a more user- and patient-friendly method that has been used for one-half a century.2 FOT analyzes the pressure/flow responses of the airways to small forced oscillations delivered at the mouth and has noticeable advantages over spirometry and plethysmography because it is effort independent, requires only tidal breathing, and, therefore, can be carried out in children,3 during sleep,4 and during general anesthesia.5 Furthermore, FOT requires shorter operator training time. FOT also measures respiratory reactance (Xrs), which in patients with COPD6 is a surrogate marker of expiratory flow limitation.6,7 For these reasons, there has been recent interest in the use of FOT in various lung diseases.8,9 Indeed, some FOT parameters are useful measurements of small airways dysfunction.10

Recognizing the value of FOT, the European Respiratory Society11 published the standardization of this technique. Unfortunately, even though tongue position, cheek movement, and swallowing were acknowledged,12 the impact of upper airways, including glottis aperture and buccal air leaks, were not fully discussed.

Glottal aperture is a major determinant of airway resistance, and because of its variability,13,14 particularly in patients with airway obstruction,15,16 it may significantly affect respiratory impedance.17 Therefore, a sensitive FOT marker for this phenomenon is required. Buccal air leaks arise from the lips not being tightly sealed around the mouthpiece or from loose parts of the equipment, preventing airflow generated by the FOT loudspeaker from reaching the lungs, affecting FOT parameters. In this study, we developed a practical method to identify and quantify the impact of the glottal aperture and buccal air leaks on FOT measurements.

Subjects

Healthy volunteers had no history of chronic respiratory disease and normal spirometry. Patients with COPD were given the diagnosis based on the GOLD (Global Initiative for Chronic Obstructive Lung Disease) strategy18 and had a mean postbronchodilator FEV1 of 67.0% ± 4.0% predicted. All patients with COPD used inhaled corticosteroids in combination with a long-acting β-agonist and were instructed not to take their respiratory medications for at least 12 h prior to measurements. None of the participating subjects had a respiratory tract infection in the 4 weeks preceding the study, and all were current nonsmokers. The studies were approved by the National Research Ethics Committee (reference 08/H0709), and subjects gave written informed consent before enrollment.

Glottal Aperture Study

The effects of the glottal aperture on FOT parameters were investigated using two experimental approaches. In the first approach, we studied the effect of total glottal occlusion in 10 healthy volunteers (aged 34 ± 2 years; six men). Subjects performed a standardized breathing cycle divided into three phases: tidal breathing for 20 s, followed by inhalation to total lung capacity (TLC) and then breath-holding for 10 s to induce glottal closure, followed by normal breathing for 10 s. The same cycle was repeated after instructing the subjects to relax, thereby preventing glottal closure.19 Direct visualization using rhinolaryngoscopy (ENF-VQ; Olympus Medical Systems) was applied to ascertain the positioning of the glottal aperture in four of the subjects.

In the second approach, we assessed the effects of incomplete glottal occlusion in six healthy subjects (aged 34 ± 2 years; four men) who were instructed to inhale to end-inspiration volume (0.5-1 L) and then to hum for 10 s, thus producing incomplete glottal narrowing. The effects of humming on FOT measurements were compared with the measurements undertaken during tidal breathing. The glottal aperture was visualized directly as previously described in two subjects during humming.

Buccal Air Leak Study

In this study, we simulated an air leak from the lips of the volunteers, where the lips did not have a tight seal around the mouthpiece. Eleven healthy subjects (aged 33 ± 2 years; seven men) and five patients with COPD (aged 69 ± 3 years; one man) participated. Subjects performed FOT measurements in the following sequence: (1) normal breathing through the commonly used MicroGard disposable barrier breathing filters (CareFusion Corporation) and (2) repeated measurements (three times) using the same type of filters but with holes of increasing diameter (3.5, 6.0, and 8.5 mm) drilled in the upper aspect of the filter at 1 cm from the edge.

Forced Oscillometry Measurements

FOT measurements were performed using an Jaeger Impulse Oscillometry System (IOS) (CareFusion Corporation) in accordance with European Respiratory Society guidelines.7,11 The pneumotachometer was calibrated daily using a 3-L syringe, and pressure calibration was checked weekly with a reference resistance (0.2 kPa/L/s). In all measurements, a free-flow mouthpiece was used with a built-in tongue depressor to stabilize the position of the tongue. Subjects firmly supported their cheeks and the floor of their mouth (with their hands or chin rest) while seated with their neck in a comfortable neutral posture. Subjects wore a nose clip.

FOT pressure impulses (with a peak-to-peak amplitude of 0.40-0.50 kPa) were applied to the airways five times per second for 60 s using a minute ventilation < 10 L/min. Mean values of respiratory resistance (Rrs) and Xrs were calculated between frequencies of 5 and 35 Hz. Peak-to-peak impulse pressures20 were estimated by analyzing the pressure curves on the IOS primary tracings.

Data Analysis

Primary data from the IOS tracings showing airway pressure, volume, and flow were assessed using IOS version 4.67 software. In the baseline analysis, artifacts such as coughing and swallowing were excluded by limiting the analysis to periods free of spikes in magnitudes of whole-breath resistance at 5 Hz (R5) and whole-breath reactance at 5 Hz (X5) as previously reported.12 In baseline measurements, airflow leaks were excluded by high-gain display of volume in time, analyzing only tidal breaths free of large impulse transients (Fig 1). We tabulated mean whole-breath values of resistance and reactance at 5 Hz (R5, X5, respectively), resistance at 15 Hz, resonant frequency, and low-frequency reactance area (which is the integrated Xrs from 5 Hz to resonant frequency). To avoid confusion in the description of Xrs values becoming more negative, we describe the absolute magnitude of airway reactance. In the individual inspiratory and expiratory within-breath analysis, we report the mean values of inspiratory and expiratory R5 (R5i and R5e, respectively) and X5 (X5i and X5e, respectively) as assessed using the IOS software.

Figure Jump LinkFigure 1 –  A, B, Volume/time tracings illustrating ΔV only visible as indentations synchronous with impulse pressure pulses (P), particularly on the expiratory limb during air leak (3.5-mm hole) (B) but not at baseline (A). ΔV = leakage volume on the expiratory phase of the volume curve.Grahic Jump Location
Statistical Analysis

Data were analyzed using GraphPad Prism 5.03 statistical software (GraphPad Software, Inc). The results of healthy subjects and patients with COPD were compared using Student t test. Two-way analysis of variance applied with the Bonferroni post hoc test was used to compare the effects of air leaks and glottal changes on R5 as well as X5 in healthy vs COPD groups. Repeated-measures analysis of variance was used to assess changes in air leak markers, peak impulse pressures, glottal aperture markers, R5, X5, R5i, R5e, X5i, X5e, and R5i−R5e and X5i−X5e values. Linear regression analysis was used to evaluate the relationships between air leak markers and FOT parameters. Data are presented as mean ± SEM.

Glottal Aperture Study

Glottal aperture was visualized directly using a rhinolaryngoscope in four healthy subjects (Fig 2). Total glottal closure at TLC was associated with characteristically tall R5 spikes (Fig 2A). These R5 fluctuations were not detected when breath-holding at TLC was repeated with a relaxed open glottis (Fig 2B). Compared with total glottal closure, smaller increases in R5 peaks were observed during humming, which recreated incomplete glottal closure (Fig 2C).

Figure Jump LinkFigure 2 –  A-C, Tracings of respiratory V and R5 during a simultaneous visualization of the glottis during tidal breathing followed by breath-holding at TLC with total occlusion of the glottis (A) and relaxed glottis at TLC (B) and during humming (C). R5 is increased only when the glottis area is reduced. R5 = whole-breath resistance at 5 Hz; TLC = total lung capacity; V = volume.Grahic Jump Location
Effect of Glottal Aperture on FOT Parameters

Breath-holding with the glottis closed at TLC greatly increased R5 (P < .001), and X5 became more negative (P < .001) (Table 1). Furthermore, a significant increase was observed in peak-to-peak impulse pressures during the TLC maneuver (P < .001). Similar to the breath-holding maneuver, humming also significantly increased R5 (1.27 ± 0.19 kPa/L/s, P < .05), and the absolute value of X5 (−1.75 ± 0.25 kPa/L/s, P < .05) became more negative.

Table Graphic Jump Location
TABLE 1 ]  Changes in Forced Oscillometry Parameters During Various Breathing Phases (n = 10)

Data are presented as mean ± SEM. R5 = whole-breath resistance at 5 Hz; TLC = total lung capacity; X5 = whole-breath reactance at 5 Hz.

In contrast, when subjects relaxed their glottis during the TLC maneuver, R5 decreased (P < .001) and X5 became more negative (P < .001) compared with values during tidal breathing. Furthermore, impulse pressures also decreased significantly (P < .001). Notably, breath-holding with closed glottis significantly increased frequency dependency of resistance and reactance (Fig 3).

Figure Jump LinkFigure 3 –  Effect of breath-holding with a closed glottis compared with tidal breathing on frequency dependence of Rrs and Xrs. The gray continuous lines indicate normal resistance (top) and reactance (bottom) values. Rrs = respiratory resistance; Xrs = respiratory reactance. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location
Buccal Air Leak Study

In the absence of air leaks at baseline, patients with COPD had higher whole-breath R5 (0.50 ± 0.04 kPa/L/s) and more-negative X5 values (−0.22 ± 0.06 kPa/L/s) compared with healthy subjects (0.33 ± 0.02 and −0.09 ± 0.01 kPa/L/s for R5 and X5, respectively; P < .01) (Table 2).

Table Graphic Jump Location
TABLE 2 ]  Changes in Forced Oscillometry Parameters Using Various-Sized Breathing Filter Holes

Data are presented as mean ± SEM. ΔV = leakage volume on the expiratory phase of the volume curve; R5e = expiratory resistance at 5 Hz; R5i = inspiratory resistance at 5 Hz; X5e = expiratory reactance at 5 Hz; X5i = inspiratory reactance at 5 Hz. See Table 1 legend for expansion of other abbreviations.

a 

Analysis of variance results.

b 

P < .01 baseline vs 3.5 mm.

c 

P < .05 by t test.

Within-breath analysis showed that both R5i and R5e were higher in patients with COPD (0.39 ± 0.03 and 0.58 ± 0.06 kPa/L/s, respectively) compared with healthy subjects (0.31 ± 0.02 and 0.34 ± 0.02 kPa/L/s, respectively; P < .010). Similarly, in patients with COPD, both X5i (−0.15 ± 0.02 kPa/L/s) and X5e (−0.31 ± 0.12 kPa/L/s) were larger (absolute value) compared with healthy subjects (−0.11 ± 0.01 and −0.08 ± 0.01 kPa/L/s for X5i and X5e, respectively; P < .05). X5i-X5e was larger in patients with COPD (0.16 ± 0.09 kPa/L/s) compared with healthy subjects (−0.03 ± 0.01 kPa/L/s, P = .01).

Identification of an Air Leak Marker

In the presence of air leaks, we identified volume transients, which are defined as rapid volume changes (Fig 1B) and were synchronous with the pressure pulses. Leakage volumes on the expiratory phase of the volume curves (ΔVs) were more clearly visible by enlarging (high-gain display) the IOS volume/time tracings and resembled step-wise indentations that were particularly pronounced on the expiratory limb of the breathing volume. Larger holes resulted in bigger air leaks and produced a correspondingly larger ΔV, suggesting ΔV as a possible marker of this phenomenon. In the absence of an air leak, the volume tracing appears to be smooth, with only minor indentations that may be better described as a tremor. In the presence of an air leak, these indentations become very noticeable. ΔV was affected by air leaks to a similar extent in healthy subjects and patients with COPD (P > .05).

Effect of Air Leak on FOT Parameters

With increasingly bigger holes in the filters, the magnitude of peak-to-peak impulse pressures decreased similarly in both subject groups (P < .001) (Table 2). Of note, both R5 (P < .001) and X5 (P < .001) values were decreased (larger magnitude for X5), even with the smallest air leak (3.5 mm) (Fig 4). These changes were more significant in the patients with COPD than in the healthy subjects (P < .01) (Fig 4). However, both the R5 and the X5 baseline differences between these groups were progressively attenuated with larger air leaks. ΔV correlated with changes in R5 and X5 in both healthy subjects and patients with COPD. Air leaks also significantly decreased within-breath R5i and R5e and increased R5i-R5e values in both subject groups (P < .01). The magnitude of X5i and X5e decreased (were less negative) in both healthy subjects and patients with COPD (P < .01), but X5i-X5e decreased in the COPD group (P = .07) and not in the healthy group (P = .26) (Table 1).

Figure Jump LinkFigure 4 –  Effect of various hole sizes produced in the breathing filters to simulate air leaks of increasing magnitude on R5 and X5 in healthy subjects and patients with COPD. The gray continuous lines indicate normal resistance (top) and reactance (bottom) values. *P < .05. X5 = whole-breath reactance at 5 Hz. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location

Using direct visualization of the glottal anatomy, we identified for the first time, to our knowledge, in vivo in humans, IOS markers that accurately detect and quantify the effects of changes in the glottal aperture. In addition, we have determined the importance of buccal airflow leaks on FOT measurements. We have shown that minor changes in glottal aperture and small buccal airflow leaks can significantly affect FOT.

European Respiratory Society guidelines have standardized the FOT,11 but the critical influence of changes in glottal aperture or the phenomenon of buccal airflow leaks were not fully addressed.21 Flow signal analysis was suggested as a possible method to identify artifacts; however, no studies have investigated the usefulness of this aspecific and only qualitative marker. Improving these limitations may increase the utility of FOT in the measurement of airway resistance, expiratory flow limitation,6 and small airway function22 while also considering that most FOT analyzers available on the market do not automatically reject measurements affected by artifacts.

During the normal respiratory cycle, the vocal cords physiologically partially abduct with inhalation and partially adduct with end exhalation, providing positive end-expiratory pressure. Therefore, airflows are largely affected by glottis aperture, which in turn can affect IOS measurements. Of note, involuntary glottal closure is more common in patients with airway disease and importantly contributes to the syndrome of laryngeal dysfunction in clinical practice.15 Indeed, subjects with severe airway obstruction tend to unintentionally adduct their vocal cords, even during restful tidal breathing. This results in a reduced or narrowed glottal aperture and increased positive end-expiratory pressure, a mechanism that like pursed-lip breathing results in keeping the airway open.15,16

The effect of glottal aperture on FOT parameters has been investigated in only a limited number of studies,2325 which were either undertaken in animals only, did not visualize glottal aperture, or simulated an unnatural adduction of the vocal cords. Klein and colleagues23 observed increased Rrs and Xrs in a swine model by altering the posture of the head of the animals to cause a decrease in the cross-section of the pharyngeal and laryngeal regions.24,25 We confirm these experimental findings for the first time in vivo in humans using direct visualization of the vocal cords. Consistent with the present results in adults, a study in children with asthma or chronic cough confirmed that a 1- to 2-s closure of the glottis causes a significant increase of total Rrs.17

Rigau and colleagues26 used a mechanical experimental model to prove that a change in R5 (ΔR5) could be used to detect glottal closure in vocal cord dysfunction (VCD), a condition characterized by airway obstruction due to paradoxical adduction of the vocal cords. We confirm this experimental finding in vivo in humans. Because ΔR5 is a marker of variation in glottal aperture, FOT may be of aid in the diagnosis of VCD. This may be of particular interest in the differential diagnosis of VCD and asthma.

The present study not only confirms that glottal aperture significantly affects Rrs and Xrs but also importantly identifies ΔR5 as a marker of glottal closure in humans. Analysis of the resistance tracing has identified ΔR5 spikes when the glottis is closed following an inhalation to TLC and breath-holding.19 However, such changes were not present when the same breathing maneuver was repeated with a relaxed glottis.27 Crucially, not only was the present experiment carried out in vivo but also, for the first time, the position of the vocal cords was confirmed endoscopically. Rhinolaryngoscopy allows complete and reproducible visualization of the glottal aperture, enhancing the reliability of the results and conclusions. Interestingly, ΔR5 spikes were also detected during more physiologically incomplete glottal closure during humming, indicating that ΔR5 may identify a partial reduction of the glottal area. Because these R5 spikes are sudden and rapidly reversible, they are unlikely to be affected by the baseline airway obstruction.

Rrs decreased during the TLC maneuver with relaxed glottis. This may have been related to increased lung volumes28 or opening of the glottis.29

Of note, we observed that glottis aperture not only affects IOS parameters but also interferes significantly with the frequency dependency of resistance. This FOT parameter, defined as the progressive decreases of resistances from lower to higher frequencies, has been advocated as a marker of small airways dysfunction.11,30 Further studies are now required to verify the influence of upper airway physiology on the frequency dependency of resistance in patients with airway obstruction.

Some individuals find it difficult to seal their lips tightly around the mouthpiece because of anatomic reasons or poor oropharyngeal muscle strength. This may lead to loss of FOT pressure and impaired test results.31,32 We simulated these airflow leaks by producing holes of increasing diameter in the breathing filters attached to our FOT machine. Of note, the presence of holes in the breathing filters resulted in indentations, particularly on the expiratory limb, on the breathing volume tracings (volume transients, ΔV) (Fig 1), which were synchronous with the pressure pulses generated by the FOT machine. Larger filter holes resulted in bigger airflow leaks and correspondingly larger ΔV compared with smaller filter holes, suggesting ΔV as a possible airflow leak marker. This was further confirmed by the strong correlation between ΔV and R5 in both healthy subjects and patients with COPD. Remarkably, even the smallest hole (3.5-mm diameter) significantly decreased airway resistance and affected reactance values (Fig 4), indicating that a quality control of the tracing should always be carried out. Interestingly, airflow leaks significantly impaired FOT parameters, even in healthy subjects, and larger airflow leaks eliminated differences in R5 and X5 between patients with COPD and normal subjects, reducing the sensitivity and usefulness of this technique. Within-breath FOT analysis was also significantly affected, which may have significant clinical implications because it will reduce the ability of this technique to identify expiratory flow limitation. Therefore, we suggest that all FOT tracings be inspected for the presence of volume transients. When these are detected, subjects should be encouraged to wrap their lips tighter around the mouthpiece.

We used an IOS device in this study, which applies stronger peak-to-peak impulse pressures than pseudorandom noise instruments.20 Progressively greater air leaks decreased the size of the impulse pressures. These results are in concordance with the reduction of Rrs. Similarly, glottal closure increased and glottal abduction decreased impulse pressure sizes in parallel with alterations in Rrs.

In summary, glottal aperture and even small air leaks significantly affect FOT parameters. To correct these errors, we have identified ΔR5 and ΔV as markers of glottal occlusion and air leaks, respectively. We suggest that the tracings with primary data of every measurement be carefully checked before accepting the results. Further studies are required to investigate the use of FOT in the diagnosis of VCD.

Author contributions: P. P. had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. A. B. contributed to carrying out most of the measurements and to the first data analysis and writing of the first draft of the manuscript; N. B. P. contributed to the study design, support and feedback during study execution, and editing of the final manuscript; M. D. G. contributed the original idea and to the study design; J. H. H. contributed to the rhinolaryngoscopy and writing and final approval of the manuscript; I. H. contributed to the study concept and design, writing of the manuscript, and editing and final approval of the manuscript; P. J. B. contributed to the study concept and design, writing of the manuscript, and editing and final approval of the manuscript; and O. S. U. and P. P. contributed equally to the study design, data analysis, writing of the manuscript, and editing and final approval of the manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Usmani reports grants and honoraria in the past 3 years from Aerocrine, AstraZeneca, Boehringer Ingelheim GmbH, Chiesi Ltd, Edmond Pharma Srl, GlaxoSmithKline plc, Napp Pharmaceuticals Limited, Mundipharma International, Sandoz, Prosonix Ltd, Takeda Pharmaceutical Company Limited, and Zentiva Group outside of the submitted work. Drs Bikov, Hull, and Paredi and Profs Pride, Goldman, Horvath, and Barnes have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Role of sponsors: The sponsors had no role in the design of the study, the collection and analysis of the data, or the preparation of the manuscript.

Other contributions: This study is entirely based on projects that Prof Goldman was sadly unable to finish before his passing in 2010. His ideas have been instrumental to the study design and interpretation of the data. The authors hope that their conclusions and this article do justice to Prof Goldman’s passion for science and to his legacy.

ΔR5

change in whole-breath resistance at 5 Hz

ΔV

leakage volume on the expiratory phase of the volume curve

FOT

forced oscillation technique

IOS

Impulse Oscillometry System

R5

whole-breath resistance at 5 Hz

R5e

expiratory resistance at 5 Hz

R5i

inspiratory resistance at 5 Hz

Rrs

respiratory resistance

TLC

total lung capacity

VCD

vocal cord dysfunction

X5

whole-breath reactance at 5 Hz

X5e

expiratory reactance at 5 Hz

X5i

inspiratory reactance at 5 Hz

Xrs

respiratory reactance

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Klein C, Smith HJ, Reinhold P. Respiratory mechanics in conscious swine: effects of face mask, head position and bronchoconstriction evaluated by impulse oscillometry. Res Vet Sci. 2003;75(1):71-81. [CrossRef] [PubMed]
 
Reed WR, Roberts JL, Thach BT. Factors influencing regional patency and configuration of the human infant upper airway. J Appl Physiol (1985). 1985;58(2):635-644. [PubMed]
 
Liistro G, Stănescu D, Dooms G, Rodenstein D, Veriter C. Head position modifies upper airway resistance in men. J Appl Physiol (1985). 1988;64(3):1285-1288. [PubMed]
 
Rigau J, Farré R, Trepat X, Shusterman D, Navajas D. Oscillometric assessment of airway obstruction in a mechanical model of vocal cord dysfunction. J Biomech. 2004;37(1):37-43. [CrossRef] [PubMed]
 
Brancatisano TP, Dodd DS, Engel LA. Respiratory activity of posterior cricoarytenoid muscle and vocal cords in humans. J Appl Physiol. 1984;57(4):1143-1149. [PubMed]
 
Briscoe WA, Dubois AB. The relationship between airway resistance, airway conductance and lung volume in subjects of different age and body size. J Clin Invest. 1958;37(9):1279-1285. [CrossRef] [PubMed]
 
Stănescu DC, Clément J, Pattijn J, van de Woestijne KP. Glottis opening and airway resistance. J Appl Physiol. 1972;32(4):460-466. [PubMed]
 
Meraz EG, Nazeran H, Ramos CD, et al. Analysis of impulse oscillometric measures of lung function and respiratory system model parameters in small airway-impaired and healthy children over a 2-year period [published correction appears inBiomed Eng Online. 2011;10:43]. Biomed Eng Online. 2011;10:21. [CrossRef] [PubMed]
 
Marchal F, Mazurek H, Habib M, Duvivier C, Derelle J, Peslin R. Input respiratory impedance to estimate airway hyperreactivity in children: standard method versus head generator. Eur Respir J. 1994;7(3):601-607. [CrossRef] [PubMed]
 
Peslin R, Duvivier C, Gallina C, Cervantes P. Upper airway artifact in respiratory impedance measurements. Am Rev Respir Dis. 1985;132(3):712-714. [PubMed]
 

Figures

Figure Jump LinkFigure 1 –  A, B, Volume/time tracings illustrating ΔV only visible as indentations synchronous with impulse pressure pulses (P), particularly on the expiratory limb during air leak (3.5-mm hole) (B) but not at baseline (A). ΔV = leakage volume on the expiratory phase of the volume curve.Grahic Jump Location
Figure Jump LinkFigure 2 –  A-C, Tracings of respiratory V and R5 during a simultaneous visualization of the glottis during tidal breathing followed by breath-holding at TLC with total occlusion of the glottis (A) and relaxed glottis at TLC (B) and during humming (C). R5 is increased only when the glottis area is reduced. R5 = whole-breath resistance at 5 Hz; TLC = total lung capacity; V = volume.Grahic Jump Location
Figure Jump LinkFigure 3 –  Effect of breath-holding with a closed glottis compared with tidal breathing on frequency dependence of Rrs and Xrs. The gray continuous lines indicate normal resistance (top) and reactance (bottom) values. Rrs = respiratory resistance; Xrs = respiratory reactance. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location
Figure Jump LinkFigure 4 –  Effect of various hole sizes produced in the breathing filters to simulate air leaks of increasing magnitude on R5 and X5 in healthy subjects and patients with COPD. The gray continuous lines indicate normal resistance (top) and reactance (bottom) values. *P < .05. X5 = whole-breath reactance at 5 Hz. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1 ]  Changes in Forced Oscillometry Parameters During Various Breathing Phases (n = 10)

Data are presented as mean ± SEM. R5 = whole-breath resistance at 5 Hz; TLC = total lung capacity; X5 = whole-breath reactance at 5 Hz.

Table Graphic Jump Location
TABLE 2 ]  Changes in Forced Oscillometry Parameters Using Various-Sized Breathing Filter Holes

Data are presented as mean ± SEM. ΔV = leakage volume on the expiratory phase of the volume curve; R5e = expiratory resistance at 5 Hz; R5i = inspiratory resistance at 5 Hz; X5e = expiratory reactance at 5 Hz; X5i = inspiratory reactance at 5 Hz. See Table 1 legend for expansion of other abbreviations.

a 

Analysis of variance results.

b 

P < .01 baseline vs 3.5 mm.

c 

P < .05 by t test.

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Klein C, Smith HJ, Reinhold P. Respiratory mechanics in conscious swine: effects of face mask, head position and bronchoconstriction evaluated by impulse oscillometry. Res Vet Sci. 2003;75(1):71-81. [CrossRef] [PubMed]
 
Reed WR, Roberts JL, Thach BT. Factors influencing regional patency and configuration of the human infant upper airway. J Appl Physiol (1985). 1985;58(2):635-644. [PubMed]
 
Liistro G, Stănescu D, Dooms G, Rodenstein D, Veriter C. Head position modifies upper airway resistance in men. J Appl Physiol (1985). 1988;64(3):1285-1288. [PubMed]
 
Rigau J, Farré R, Trepat X, Shusterman D, Navajas D. Oscillometric assessment of airway obstruction in a mechanical model of vocal cord dysfunction. J Biomech. 2004;37(1):37-43. [CrossRef] [PubMed]
 
Brancatisano TP, Dodd DS, Engel LA. Respiratory activity of posterior cricoarytenoid muscle and vocal cords in humans. J Appl Physiol. 1984;57(4):1143-1149. [PubMed]
 
Briscoe WA, Dubois AB. The relationship between airway resistance, airway conductance and lung volume in subjects of different age and body size. J Clin Invest. 1958;37(9):1279-1285. [CrossRef] [PubMed]
 
Stănescu DC, Clément J, Pattijn J, van de Woestijne KP. Glottis opening and airway resistance. J Appl Physiol. 1972;32(4):460-466. [PubMed]
 
Meraz EG, Nazeran H, Ramos CD, et al. Analysis of impulse oscillometric measures of lung function and respiratory system model parameters in small airway-impaired and healthy children over a 2-year period [published correction appears inBiomed Eng Online. 2011;10:43]. Biomed Eng Online. 2011;10:21. [CrossRef] [PubMed]
 
Marchal F, Mazurek H, Habib M, Duvivier C, Derelle J, Peslin R. Input respiratory impedance to estimate airway hyperreactivity in children: standard method versus head generator. Eur Respir J. 1994;7(3):601-607. [CrossRef] [PubMed]
 
Peslin R, Duvivier C, Gallina C, Cervantes P. Upper airway artifact in respiratory impedance measurements. Am Rev Respir Dis. 1985;132(3):712-714. [PubMed]
 
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