Forced oscillation technique to evaluate tracheostenosis in patients with neurologic injury

Differences Between Central Airway Obstruction and Chronic Obstructive Pulmonary Disease Detected with the Forced Oscillation Technique

Background

Obstructive ventilatory disturbances occur in both chronic obstructive pulmonary disease (COPD), a typical disease representative of peripheral airway obstruction, and central airway obstruction (CAO). Pulmonary function tests (PFTs), which depend on patient effort, are traditionally used to evaluate lung function. The forced oscillation technique (FOT) is an effort-independent method for examining lung function during tidal breathing. The FOT is used universally to assess respiratory function in patients with COPD. Several studies have measured FOT to assess ventilatory disturbances in CAO. The results showed that FOT measurements in patients with CAO were similar to those reported in patients with COPD. However, no studies have compared FOT measurements directly between CAO and COPD. The aim of this study was to identify differences in ventilatory disturbances between peripheral and central airway obstructions in COPD and CAO, before patients received pharmacological therapy or bronchoscopic interventions, respectively.

Patients and Methods

We retrospectively included 16 patients with CAO (10 cases of tracheal obstruction and 6 cases of bronchial obstruction) and 75 treatment-naïve patients with COPD (60 cases in Global Initiative for Chronic Obstructive Lung Disease [GOLD] stage II and 15 cases in GOLD stage III) that were admitted from December 2013 to May 2017. Prior to treatment, patients were examined with the FOT and PFTs.

Results

All parameters measured with the FOT in the inspiratory phase were significantly worse in patients with CAO than in patients with COPD. The PFTs showed that the CAO group had a significantly lower peak expiratory flow rate. In the airway wall thickening phenotype of COPD, a difference between the inspiratory and expiratory phases of the resonance frequency (ΔFres) was the best indicator for distinguishing between peripheral and central airway obstructions.

Conclusion

This study compared differences between CAO and COPD (mainly GOLD stage II). We found that the FOT measurement, ΔFres, was the optimal indicator of the difference between the airway wall thickening COPD phenotype and CAO. Thus, the difference might be due to mechanical changes that occur in COPD with airway wall thickening.

Expiratory reactance abnormalities in patients with expiratory dynamic airway collapse: a new application of impulse oscillometry

Expiratory dynamic airways collapse (EDAC) is a condition that affects the central airways; it is not well characterised physiologically, with relatively few studies. We sought to characterise impulse oscillometry (IOS) features of EDAC in patients with normal spirometry. Expiratory data were hypothesised to be the most revealing. In addition, we compared IOS findings in chronic obstructive pulmonary disease (COPD) patients with and without EDAC.

EDAC was identified at bronchoscopy as 75–100% expiratory closure at the carina or bilateral main bronchi. Four patient groups were compared: controls with no EDAC and normal lung function; lone EDAC with normal lung function; COPD-only patients; and COPD patients with EDAC.

38 patients were studied. Mean IOS data z-scores for EDAC compared to controls showed significantly higher reactance (X) values including X at 5 Hz, resonance frequency and area under the reactance curve (A_X). EDAC showed significantly greater expiratory/inspiratory differences in all IOS data compared to controls. Stepwise logistic regression showed that resonant frequency best discriminated between EDAC and normal control, whereas classification and regression tree analysis found A_X ≥3.523 to be highly predictive for EDAC in cases with normal lung function (14 out of 15 cases, and none out of eight controls).

These data show a new utility of IOS: detecting EDAC in patients with normal lung function.

Central airway expiratory dynamic airway collapse can be “silent” on breathing tests, but impulse oscillometry can reveal ithttp://ow.ly/9oIb30lIOka

Role of the impulse oscillometry in the evaluation of tracheal stenosis

INTRODUCTION AND OBJECTIVES

Tracheal stenosis is a rare and challenging disease. Bronchoscopy is the gold standard for diagnosis and assessment but brings inherent risks. Spirometry is commonly used to access obstructions but is not always feasible due to patient related factors. We therefore considered impulse oscillometry (IOS) as a non-invasive method to quantify airway obstruction and its potential use for diagnosis and follow-up of tracheal stenosis.

MATERIALS AND METHODS

Patients with confirmed tracheal stenosis were recruited between January 1st, 2015 and December 31st, 2016. Before bronchoscopy, all subjects underwent IOS and spirometry; for patients submitted to interventional bronchoscopy the same techniques were also performed after the procedure. We assessed the correlation between IOS measurements and airway narrowing as well as between IOS and spirometry values.

RESULTS

Twenty-one patients were included. Tracheal narrowing was inversely correlated with X5% (r -0.442, p 0.045) and positively correlated with FEV1/PEF (r 0.467, p 0.033). The stenosis length was inversely correlated with PEF and PEF% (r -0.729, p=0.001 and r -0.707, p=0.002, respectively). There was a strong correlation between spirometric and IOS values. We did not find any significant differences between pre- and post-intervention IOS values for patients assessed after interventional bronchoscopy.

CONCLUSIONS

Our study showed a weak correlation between X5% and tracheal narrowing making it unclear whether IOS can be used for physiological assessment of patients with tracheal stenosis. Stenosis length correlated with PEF making it a potential predictor of successful surgical approach. The correlation between IOS and spirometric values makes IOS a potential alternative in patients with suspected tracheal stenosis who are not able to perform spirometry. Larger scale studies should clarify the role of IOS in this pathology.

Usefulness of the forced oscillation technique in assessing the therapeutic result of tracheobronchial central airway obstruction

BACKGROUND

Pulmonary function tests (PFTs) comprise the traditional method for detecting central airway obstruction (CAO) and evaluating therapeutic effects, but are effort-dependent. By contrast, the forced oscillation technique (FOT) is performed during tidal breathing in an effort-independent mode and is universally used to assess respiratory function in patients with chronic obstructive pulmonary disease (COPD) and asthma. We used the FOT to measure airway resistance and reactance in patients with CAO before and after interventional bronchoscopy and compared the results to data obtained using PFTs.

METHODS

Twelve patients with CAO were recruited from December 2013 to July 2016. The FOT, PFTs, chest computed tomography (CT), COPD Assessment Test (CAT), and the modified Medical Research Council (mMRC) dyspnea scale were employed before and after interventional bronchoscopy. The minimum airway cross-sectional area (MACSA) was calculated using a CT image calculator.

RESULTS

Of the 12 patients, 6 had tracheal obstruction and 6 had bronchial obstruction. All FOT measurements, except ΔX5, were significantly improved after interventional bronchoscopy in all cases. The significance of the improvement was greater with the FOT than PFTs. The MACSA, CAT, and mMRC dyspnea scale scores also significantly improved in all cases. Furthermore, only alteration of resistance at 20 Hz (R20) significantly correlated with the alteration of the MACSA after intervention. No significant correlations were found for PFTs.

CONCLUSIONS

The FOT is suitable and convenient for assessing therapeutic results in patients with tracheobronchial CAO. The alteration of R20 is useful for estimating the airway dilation of CAO after interventional bronchoscopy.

Functional changes are associated with tracheal structural abnormalities in patients with acromegaly

INTRODUCTION

Although impaired pulmonary function and respiratory sleep disorders are described as responsible for increased mortality in acromegalic patients, little is known about the tracheal abnormalities in this group of patients. Thus, the objectives of this study were to describe the tracheal structural abnormalities and correlate these changes with the respiratory function and clinical data of acromegalic patients.

MATERIAL AND METHODS

This is a cross-sectional study that was carried out at two university hospitals. Twenty acromegalic patients underwent spirometry, forced oscillation technique, and computed tomography (CT) assessments. Dyspnea and daytime sleepiness were assessed using the Modified Medical Research Council (MMRC) scale and the Epworth Sleepiness Scale (ESS), respectively. Forty matched subjects served as controls.

RESULTS

The acromegalic patients exhibited larger median ratios between forced expiratory flow and forced inspiratory flow at 50% of the forced vital capacity (FEF50%/FIF50%) (2.05 vs. 1.06, p = 0.0001) compared with healthy volunteers. In the CT analysis, acromegalic patients exhibited larger median differences between their cervical and thoracic tracheal diameters (Δ tracheal diameters) (3 vs. 1 mm; p = 0.003). An association was found between FEF50%/FIF50% and the following variables: mean resistance (Rm), cervical tracheal diameter, and Δ tracheal diameters. Rm also exhibited a negative correlation with cervical tracheal diameter. Neither the MMRC scale nor the ESS exhibited any significant correlation with large airway obstruction (LAO) indices or with the measured tracheal diameters.

CONCLUSIONS

Acromegalic patients have tracheal structural abnormalities which are associated with functional indicators of LAO but not with clinical data.

[Treatment of malignant central airways obstruction by rigid bronchoscopy]

INTRODUCTION

Endobronchial resection is now the standard treatment for tracheobronchial narrowing due to malignancy. The clinical and functional respiratory improvement has been evaluated previously but only in heterogeneous population.

METHODS

Between February 2009 and February 2011, we conducted a prospective single centre study at the University Hospital of Lille. Twenty-five patients with malignant tracheobronchial stenosis received a clinical and functional respiratory evaluation before and after a rigid bronchoscopy procedure to reduce the obstruction followed where appropriate by placement of an endobronchial stent.

RESULTS

Thirteen patients (52%) had primary lung cancer and in 12 the tumor had another origin. Nineteen patients (76%) received a stent after bronchial unblocking. Clinically, all patients felt an improvement in their dyspnea estimated by the Borg score with a median improvement of -2 points [-1; -4] following the procedure (P<0.001). In 96% the dyspnea visual analogic scale improved by 40 mm [27; 67] (P<0.0001). The FEV1 increased significantly after unblocking by 9% [-3.5; 28.5] (P<0.05). The Rint decreased significantly by -0.19 kPa/L per second [-0.06; -0.023] (P=0.001). Correlations between scales of dyspnea and spirometric values were not significant (P>0.05). The survival rate at 1 year was 29%.

CONCLUSION

Interventional bronchoscopy decreases dyspnea. It modestly improves respiratory function and decreases the Rint. However, lung function and dyspnea scales are not correlated. No spirometry factor can predict clinical dyspnea response but an elevated Borg dyspnea scale might be a good indicator.

Asymptomatic tracheal MALT lymphoma discovered on spirometric findings presenting with elevated respiratory resistance

Background

Central airway obstruction (CAO) may be caused by various etiologies. However, conventional chest X-rays are rarely diagnostic for patients with CAO.

Case presentation

We here described a 64-year-old asymptomatic female with tracheal mucosa-associated lymphoid tissue lymphoma discovered on spirometric findings during a complete physical examination. The plateau of forced expiratory flow was consistent with CAO. A decreased peak expiratory flow rate was noted at least 3 years before the diagnosis, and was attributed to an insufficient effort by the patient. Impulse oscillometric measurements, which were taken during quiet breathing and were effort-independent, suggested elevated respiratory resistance. These abnormalities completely disappeared after radiation therapy.

Conclusion

The addition of impulse oscillometry to spirometry may be useful for screening CAO in routine health examinations.

Oscillation mechanics of the respiratory system

The mechanical impedance of the respiratory system defines the pressure profile required to drive a unit of oscillatory flow into the lungs. Impedance is a function of oscillation frequency, and is measured using the forced oscillation technique. Digital signal processing methods, most notably the Fourier transform, are used to calculate impedance from measured oscillatory pressures and flows. Impedance is a complex function of frequency, having both real and imaginary parts that vary with frequency in ways that can be used empirically to distinguish normal lung function from a variety of different pathologies. The most useful diagnostic information is gained when anatomically based mathematical models are fit to measurements of impedance. The simplest such model consists of a single flow-resistive conduit connecting to a single elastic compartment. Models of greater complexity may have two or more compartments, and provide more accurate fits to impedance measurements over a variety of different frequency ranges. The model that currently enjoys the widest application in studies of animal models of lung disease consists of a single airway serving an alveolar compartment comprising tissue with a constant-phase impedance. This model has been shown to fit very accurately to a wide range of impedance data, yet contains only four free parameters, and as such is highly parsimonious. The measurement of impedance in human patients is also now rapidly gaining acceptance, and promises to provide a more comprehensible assessment of lung function than parameters derived from conventional spirometry.

Wheelchair components and pulmonary function in children with cerebral palsy

OBJECTIVE

This study investigates the effects of four individual wheelchair components (upper extremity supports, lateral trunk supports, anterior pelvic belt, and 30 degree posterior seat tilt), on pulmonary function in prepubertal children with cerebral palsy (CP).

METHODS

Participants who range in age from 5-10 years were evaluated using four wheelchair components in six configurations (conditions 1-6) using a planar seating simulator. The Respironics Non Invasive Cardiac Output monitor (NICO) and MasterScreen Impulse Oscillometry System (IOS) measured pulmonary function parameters. Repeated measures ANOVA was used to analyze effect of wheelchair conditions on total airway resistance (R(AW)).

RESULTS

Eight participants completed the protocol. R(AW) and minute ventilation (MV) varied with wheelchair condition. Lowest R(AW) was seen with two upper extremity supports or two lateral trunk supports. Differences were not significant (p = 0.253).

CONCLUSIONS

The NICO and IOS, independent of participant effort, measured R(AW) and MV, which varied by wheelchair seating condition. More research is needed with a larger sample to determine seating components' impact on pulmonary function. These methods objectively measured pulmonary function of young children with CP in wheelchairs and could facilitate further research into benefits of wheelchair postural support components.

Electrical circuit models of the human respiratory system reflect small airway impairment measured by impulse oscillation (IOS)

The use of the forced oscillatory input impedance parameter, frequency-dependence of Resistance (fdR), to assess small airway impairment (SAI) has not been widely accepted due to concern about the effects of "upper airway shunt" on oscillometric resistance and low frequency reactance. On the other hand, recent medical studies suggest that low frequency reactance is a very sensitive index of treatment intervention directed at small airways. The present study was undertaken to analyze and compare Impulse Oscillometry (IOS) resistance and reactance data with model-derived indices of small airway function from two models of the respiratory impedance, one with, and the other without an element for upper airway shunt capacitance. Fifty six patients with stable chronic obstructive lung disease of varying severity due to Cystic Fibrosis (CF) and 21 patients with asthma were evaluated by IOS testing. IOS data were input into the augmented RIC (aRIC) model with an upper airway shunt capacitance, and the extended RIC (eRIC) model, without a shunt capacitance element. Model-derived indices were compared between the two models for CF patients separately from asthma patients. We conclude that IOS indices of SAI are modeled equally well with or without upper airway shunt capacitance, and do not seem to be dependent on upper airway shunt capacitance.

Detecting upper airway obstruction in patients with tracheal stenosis

We propose a forced oscillation test modality for detecting upper airway obstruction (UAO) as an alternative to spirometric UAO indices in patients with tracheal stenosis. From oscillometry performed at different breathing flow rates, airway resistance at 5 Hz was determined at 0.5 l/s ( R), and flow dependence of resistance was computed as the regression slope of resistance vs. flow up to 1 l/s (Δ R/Δ V̇). It was first verified by measurement in 10 normal subjects and 10 patients with chronic obstructive pulmonary disease that Δ R/Δ V̇ was unaffected by the presence of peripheral airway obstruction and that external orifices (with lumen area down to 28 mm2) induced marked increases in R and Δ R/Δ V̇. Ten patients eligible for tracheal dilatation underwent spirometry and impulse oscillometry before and after intervention. Considering the lumen area of tracheal stenosis in the patients (42 ± 28 mm2, represented as the mean ± SD), the R and Δ R/Δ V̇ increases were of similar magnitude to those predicted by the external orifices. In addition, R ( r = −0.68; P = 0.001) and Δ R/Δ V̇ ( r = −0.65; P = 0.001) showed better correlations with minimal tracheal lumen than any spirometric UAO index. Δ R/Δ V̇, but not R, showed a consistent return to normal after intervention in the stenosis patients. We conclude that the forced oscillation test at different breathing flow rates up to 1 l/s provides a measure of UAO, namely flow dependence of resistance Δ R/Δ V̇, which can signal a critical level of tracheal stenosis and is not confounded by the presence of concomitant peripheral airway obstruction.

Management of severe tracheal stenosis using flexible bronchoscopy and impulse oscillometry

Although rigid bronchoscopy is the procedure of choice for interventional procedures of the proximal airway, flexible bronchoscopy can be used when lesions are not accessible by rigid equipment. We present an adolescent patient with tracheal stenosis whose airway was inaccessible through rigid bronchoscopy and thus required flexible bronchoscopy for all therapeutic procedures, including a stent placement. In addition, we describe our use of impulse oscillometry to monitor stent patency.

Medialization of paralyzed vocal fold does not increase respiratory resistance measured by impulse oscillometry

Injection laryngoplasty restores voice in subjects with unilateral vocal fold paralysis, but knowledge of its effects on airflow dynamics is limited. Impulse oscillometry (IOS) is a non-invasive technique to investigate airway resistance. It is easily performed during normal breathing. A prospective study was conducted in order to investigate the effects of autologous fascia injection on airflow dynamics. IOS, flow-volume spirometry, acoustic analysis of voice, voice handicap index (VHI) questionnaire and subjective dyspnoea score were recorded before and 5-11 months after the operation. There was no significant change in respiratory resistance (Rres) or other variables of IOS. FEV1/FVC decreased from 0.80 to 0.77 (P = 0.02), but other variables of spirometry did not change significantly. Acoustic properties of voice (noise-to-harmonics ratio, shimmer, jitter, maximal phonation time) and VHI improved significantly. No change in dyspnoea occurred. In conclusion, medializing of a paralysed vocal fold improves voice, but does not have a clinically significant adverse effect on breathing. Flow-volume spirometry is more sensitive than IOS to changes in airflow dynamics after medialization.

The utility of the forced oscillation technique in assessing bronchodilator responsiveness in patients with asthma

OBJECTIVE

To address the utility of the forced oscillation technique (FOT) in assessing bronchodilator responsiveness compared with forced expiratory volume in 1s (FEV(1)).

METHODS

This is a retrospective analysis of consecutive 126 patients with a clinical history of asthma without any other lung diseases at a pulmonary function testing laboratory. The following measurements were obtained three times each, before and after two doses of pirbuterol 0.2mg inhalation: the respiratory resistance at 5Hz (Rrs5), the mean respiratory resistance between 5 and 20Hz (Rrs5-20), and the mean respiratory conductance (Grs5-20) by FOT and the FEV(1) by spirometer. These measurements were transformed into dimensionless subject-specific effect-size "d-scores" by dividing them by the estimated pooled within-subject standard deviation.

RESULTS

Descriptive statistics for each value were the following [mean baseline value (+/-sd), Delta value (pre- minus post value), and d-score (P value compared to FEV(1))]: Grs5-20 (Ls(-1)kPa(-1)) [1.79+/-0.53, Delta=+0.39, d=2.64 (P<0.001)], Rrs5-20 (kPaL(-1)s) [0.60+/-0.16L, Delta=-0.10, d=2.56 (P=0.001)], Rrs5 (kPaL(-1)s) [0.78+/-0.25, Delta=-0.16, d=2.52 (P<0.001)], and FEV(1) (L) [1.90+/-0.64, Delta=-0.20, d=1.83]. The higher d-score of Grs5-20, Rrs5-20 and Rrs5 compared to FEV(1) indicates that these are better indicators for bronchodilator response than FEV(1). The percentages of subjects exhibiting change in the expected direction after bronchodilator were not significantly different between each value: Rrs5 (85.7%), Rrs5-20 (83.3%), Grs5-20 (83.3%), and FEV(1) (83.3%) [P>0.05].

CONCLUSIONS

Several forced oscillation measures, namely Grs5-20, Rrs5-20 and Rrs5, are more accurate and sensitive for detecting bronchodilator response than FEV(1) in patients with asthma.

Bronchodilator effect of infused B-type natriuretic peptide in asthma

STUDY OBJECTIVE

To determine the bronchodilator effect of recombinant human B-type natriuretic peptide (BNP; nesiritide) on patients with asthma.

DESIGN

A prospective, open-label study.

SETTING

Outpatient setting.

PATIENTS

Eight adult patients with asthma confirmed by > 12% and > 200 mL increase in FEV1 after bronchodilator inhalation.

INTERVENTIONS

An IV nesiritide bolus, 2 microg/kg, followed by continuous infusion for a total of 3 h at escalating doses of 0.01, 0.02, and 0.03 microg/kg/min for 1 h each as tolerated.

MEASUREMENTS

Spirometry and forced oscillation technique (FOT) measurements were both obtained at baseline and every 30 min during the infusion. Two doses of albuterol, 90 microg, inhalation via metered-dose inhaler were then administered at the end of nesiritide infusion, followed by repeat spirometry and FOT measurements after 30 min. Primary end points were FEV1 and FVC changes after the nesiritide infusion for 3 h. Wilcoxon signed-ranks tests were used to compare the effects of nesiritide and albuterol.

RESULTS

Baseline measurements (mean +/- SD) were as follows: FEV1, 1.89 +/- 0.87 L; FVC, 3.02 +/- 0.99 L; respiratory resistance at 5 Hz (Rrs5), 10.3 +/- 3.85 cm H2O . s/L; and mean respiratory resistance at 5 to 20 Hz, 7.56 +/- 1.92 cm H2O/L/s. Mean baseline serum BNP level was 27 +/- 27 pg/mL. After 180 min of nesiritide infusion, the following measurements showed significant changes: FEV1 increased to 2.41 +/- 0.78 L (mean increase, 520 mL), p = 0.012; FVC increased to 3.65 +/- 1.05 L (mean increase, 630 mL), p = 0.017; and Rrs5 decreased to 8.24 +/- 4.02 cm H2O/L/s, p = 0.017. After albuterol, there were no further significant changes in these measurements.

CONCLUSION

IV nesiritide is an effective bronchodilator in patients with asthma.