Assessing the Site of Maximal Obstruction in the Trachea Using Lateral Pressure Measurement during Bronchoscopy

Assessment of Extensive Airway Obstruction Using Point-by-Point Lateral Pressure Measurements during Bronchoscopy

BACKGROUND

The positioning of the stent at the flow-limiting segment is crucial for patients with extensive airway obstruction to relieve dyspnea. However, CT and flow-volume curves cannot detect the area of maximal obstruction.

OBJECTIVES

The aim of this study is to physiologically evaluate extensive airway obstruction during interventional bronchoscopy.

METHODS

We prospectively measured point-by-point lateral airway pressure (Plat) at multiple points from the lower lobe bronchus to the upper trachea using a double-lumen catheter in 5 patients. The site of maximal obstruction was evaluated continuously to measure point-by-point Plat at multiple points when the airway catheter was withdrawn from the lower lobe bronchus to the upper trachea.

RESULTS

Remarkable pressure differences occurred at the site of maximal obstruction assessed by point-by-point Plat measurements. After initial stenting in 1 case, migration of the maximal obstruction to a nonstented segment of the weakened airway was seen with extensive stenosis from the trachea to the bronchi. In the second case, in addition to radiological analysis, point-by-point Plat measurements could identify the location of the maximal obstruction which contributed to dyspnea.

CONCLUSIONS

Point-by-point Plat measurement could be used to detect the site of maximal obstruction physiologically. Furthermore, Plat measurement could assess the need for additional procedures in real time in patients with extensive airway obstruction.

Evaluating the biomechanical characteristics of cuffed-tracheostomy tubes using finite element analysis

The objective of this study was to perform finite element analysis (FEA) of cuff inflation within an anatomically accurate model of an adult trachea in four different cuffed-tracheostomy tube designs. The leakage quantified by the distance between the cuff and trachea was largest for the Tracoe cuff and smallest for the Portex cuff. The smooth muscle stresses were greatest for the Portex and least for the Distal cuff, respectively. The proposed FEA model offers a promising approach to virtually evaluate the sealing efficacy of cuffed-tracheostomy tubes and the tracheal wall stresses induced by cuff inflation, prior to application.

Pulmonary Perfusion Using Intrabronchial Capnography in Pulmonary Artery Stenosis

Stenting at the flow-limiting segment can improve the ventilation-perfusion ratio in patients with central airway stenosis. However, there is no quantitative examination for assessing the perfusion status during interventional bronchoscopy. Intrabronchial capnography can estimate regional gas exchange by measuring carbon dioxide concentration. We herein report a case of bilateral bronchial stenosis where stenting was able to improve ventilation-perfusion ratio using intrabronchial capnography. A 44-year-old man was admitted to our institution with orthopnea. Chest computed tomography showed an extrinsic compression at the bilateral main bronchus and right pulmonary artery due to a mediastinal mass. After introduction of general anesthesia, arterial oxygen tension suddenly decreased in the supine position. After initial stenting, an increase was seen in ventilation at the right lung; however, a ventilation-perfusion mismatch occurred due to an increase in dead-space ventilation at the right pulmonary artery stenosis. Intrabronchial capnography was an effective modality to confirm the regional perfusion status during interventional bronchoscopy in real time.

Assessment of Bronchial Obstruction Using Lateral Pressure Measurement during Bronchoscopy

BACKGROUND

In patients with bronchial obstruction estimating the location of the maximal obstruction is crucial for guiding interventional bronchoscopy. However, flow-volume curves cannot discriminate between the right and left lungs.

OBJECTIVES

The aim of this study was to physiologically evaluate bronchial obstruction during interventional bronchoscopy.

METHODS

We prospectively measured lateral airway pressure (Plat) at either side of the obstruction using a double-lumen catheter (pressure-pressure [P-P] curve) simultaneously to assess the degree of bronchial obstruction in 22 patients. The shape of the P-P curve was assessed to confirm the site of maximal obstruction.

RESULTS

In the experimental study, Plat was uniform between both bronchi in the normal model. For the unilateral and bilateral obstruction models, a phase shift was only seen for the more obstructed side. In healthy subjects, the angle of the P-P curve was close to 45° and linear in shape. In patients with bronchial obstruction, the angle was much smaller but approached 45° after the bronchoscopic procedure. The degree of bronchial obstruction was significantly correlated with the angle of the P-P curve (r = -0.51, p < 0.01). Dyspnea significantly increased when the airway lumen was obstructed by more than 60% (p < 0.0001), and when the P-P curve appeared loop-shaped (p < 0.01).

CONCLUSIONS

The shape of the P-P curve could be used to detect the site of maximal obstruction for the optimal positioning of the stent and assess the need for additional procedures in real time in patients with bronchial obstruction.

Computational fluid dynamics evaluation of excessive dynamic airway collapse

BACKGROUND

Excessive dynamic airway collapse, which is often caused by the collapse of the posterior membrane wall during exhalation, is often misdiagnosed with other diseases; stents can provide support for the collapsing airways. The standard pulmonary function tests do not necessarily show change in functional breathing condition for evaluation of these type of diseases.

METHODS

Flow characteristics through a patient's airways with excessive dynamic airway collapse have been numerically investigated. A stent was placed to support the collapsing airway and to improve breathing conditions. Computed tomography images of the patient's pre- and post-stenting were used for generating 3-Dimensional models of the airways, and were imported into a computational fluid dynamics software for simulation of realistic air flow behavior. Unsteady simulations of the inspiratory phase and expiratory phase were performed with patient-specific boundary conditions for pre- and post-intervention cases to investigate the effect of stent placement on flow characteristic and possible improvements.

FINDINGS

Results of post-stent condition show reduced pressure, velocity magnitude and wall shear stress during expiration. The variation in wall shear stress, velocity magnitude and pressure drop is negligible during inspiration.

INTERPRETATION

Although Spirometry tests do not show significant improvements, computational fluid dynamics results show significant improvements in pre- and post-treatment results, suggesting improvement in breathing condition.

Comparison of Airway Measurements for Tracheobronchial Stenosis Between Stereoscopic Bronchoscope and MD-CT

BACKGROUND

Stereoscopic bronchoscopy is a new diagnostic tool to measure the diameter and cross-sectional area of the airway. The stereoscopic bronchoscope, which operates the same as a standard bronchoscope, utilizes 2 lenses to measure the airway using the principles of triangulation. Furthermore, the stereoscopic bronchoscope has the capability to measure the size of the airway during intervention in real-time, including variable stenosis.

MATERIALS AND METHODS

To prospectively compare preoperative stereoscopic and multidetector computed tomography (MD-CT) images to select the appropriate stent size for airway stenosis. Stereoscopic and MD-CT images were then measured to confirm the correct placement of the stent.

RESULTS

Airway stenting was performed on 21 consecutive patients of whom, 15 were diagnosed with malignant and 6 with benign diseases. In total, 165 measurements were taken (134 healthy; 31 affected). For the diameter, Bland-Altman plots were used to measure data from 165 matched stereoscopic and MD-CT measurement sites (bias, 0.40±2.86 mm SD; percentage error, 33%), 134 healthy sites (bias, 0.554±2.83 mm SD; percentage error, 34%), and 31 affected sites (bias, 1.20±2.67 mm SD; percentage error, 52%). For the cross-sectional area, matched stereoscopic and MD-CT measurements were analyzed for 65 sites (bias, -10.53±92.85 mm SD; percentage error, 89%), 49 healthy sites (bias, -9.88±39.00 mm SD; percentage error, 32%), and 16 affected sites (bias, -13.12±48.81 mm SD; percentage error, 92%).

CONCLUSION

Stereoscopic bronchoscopy was able to accurately measure the size of the airway during intervention, to assist in selecting the appropriate size of the stent.

Tracheobronchomalacia

The term tracheobronchomalacia refers to excessively compliant and collapsible central airways leading to symptoms. Although seen as a coexisting condition with various other pulmonary condition, it may cause symptoms by itself. The condition is often misdiagnosed as asthma, bronchitis or just chronic cough due to a lack of specific pathognomonic history and clinical findings. The investigation revolves around different modes of imaging, lung function testing and usually confirmed by flexible bronchoscopy. The treatment widely varies based on the cause, with most cases treated conservatively with non-invasive ventilation. Some may require surgery or stent placement. In this article, we aim to discuss the pathophysiology behind this condition and recognize the common symptoms and causes of tracheobronchomalacia. The article will highlight the diagnostic steps as well as therapeutic interventions based on the specific cause.

Choke point physiology in airway stenting: A case presentation and discussion

BACKGROUND

The point in the airway that allows the smallest maximal flow is known as the "choke point". The tube law describes the velocity of the expired air, which cannot exceed the wave-speed. Flow limitation during forced expiration is affected by the relationship between the transmural pressure (Ptm) and cross-sectional area (A) of the airway. Wave speed is dependent on the stiffness of the airway wall, as well as on the cross-section of the airway itself (dA/dPtm).

METHODS

Airway stenting at the wave-speed, flow-limiting segment (choke point) is assessed by using a catheter, via the working channel of a stereoscopic bronchoscope, to measure the difference between lateral pressure and pleural pressure.

RESULTS

Based on the wave-speed concept of maximal expiratory flow limitation, stenting at the choke point increased the cross-sectional area and supported the weakened airway wall, thus improving expiratory flow limitation and relieving dyspnea.

CONCLUSION

To ensure correct stent positioning and thus optimal functional benefit, it is important to locate the exact position of tracheobronchial stenosis.

Left and right lung asynchrony as a physiological indicator for unilateral bronchial obstruction in interventional bronchoscopy

BACKGROUND

In patients with bronchial obstruction, pulmonary function tests may not change significantly after intervention. The airflow asynchrony in both lungs due to unilateral bronchial obstruction may be applicable as a physiological indicator. The airflow asynchrony is reflected by the difference in the left and right lung sound development at tidal breathing.

OBJECTIVES

To investigate the usefulness of left and right lung asynchrony due to unilateral bronchial obstruction as a physiological indicator for interventional bronchoscopy.

METHODS

Fifty cases with central airway obstruction were classified into three groups: tracheal, bronchial and extensive obstruction. The gap index was defined as the absolute value of the average of gaps between the left and right lung sound intensity peaks for a 12-second duration.

RESULTS

Before interventional bronchoscopy, the gap index was significantly higher in the bronchial (p<0.05) and extensive obstruction groups (p<0.05) than in the tracheal group. The gap index in cases with unilateral bronchial obstruction of at least 80% (0.18±0.04 seconds) was significantly higher than in cases with less than 80% obstruction (0.02±0.01 seconds, p<0.05). After intervention for bronchial obstruction, the dyspnea scale (p<0.001) and gap index significantly improved (p<0.05), although no significant improvements were found in spirometric assessments. The responder rates for dyspnea were 79.3% for gap indexes over 0.06 seconds and 55.6% for gap indexes of 0.06 seconds or under.

CONCLUSIONS

Assessment of left and right lung asynchrony in central airway obstruction with bronchial involvement may provide useful physiological information for interventional bronchoscopy.

Tracheobronchial stenosis: causes and advances in management

Tracheobronchial stenosis, narrowing of the airways by neoplastic or nonneoplastic processes, may be focal, as occurs with postintubation tracheal stenosis or a focal narrowing from a tumor, or more diffuse, such as those caused by inflammatory diseases. Symptoms develop when the narrowing impedes flow and increases resistance within the airways. Computed tomography defines the extent and severity of disease; endoscopy facilitates understanding of the cause so that an algorithm for treatment can be devised. Bronchoscopic interventions include balloons, ablative treatment, and stenting to provide symptomatic relief. Surgical resection may be curative and a multidisciplinary approach to tracheobronchial stenosis is required.

Subjective assessment using still bronchoscopic images misclassifies airway narrowing in laryngotracheal stenosis

OBJECTIVES

Severity of airway narrowing is relevant to management decision-making processes in patients with laryngotracheal stenosis. Airway lumen is frequently assessed subjectively based on still images obtained during airway examinations or objectively using image analysis software applied to radiological or bronchoscopic images. The purpose of this study was to determine whether strictures classified as mild, moderate or severe degrees of airway narrowing based on subjective assessments by a group of experienced bronchoscopists using still images, matched the classifications derived from morphometric bronchoscopy measurements and whether the results of subjective assessments correlated with the level of bronchoscopic experience.

METHODS

Thirty-five bronchoscopic doublet still images of benign causes of laryngotracheal stenosis containing normal and abnormal airway cross-sectional areas were objectively analysed using morphometric bronchoscopy and classified as mild (<50%), moderate (50-70%) or severe (>70%). These images were then subjectively assessed by 42 experienced bronchoscopists participating in an interventional bronchoscopy course. Descriptive statistics were used to explore the accuracy of the participants' classifications. Correlation coefficients were used to study the relationship between participants' subjective assessments and bronchoscopy experience.

RESULTS

Only 47% of strictures were correctly classified by study participants (mean 16.48 ± 2.8). Of the 1447 responses included in this analysis, 755 were incorrect: 71 (9%) were over-classifications of strictures' severity and 684 (91%) were under-classifications. There was no correlation between number of strictures correctly classified and number of lifetime bronchoscopies or number of strictures seen by bronchoscopists in an average month.

CONCLUSIONS

Experienced bronchoscopists often misclassify the degree of airway narrowing when using still bronchoscopic images to subjectively assess strictures of benign aetiology.

Respiratory Review of 2012: Bronchoscopic Innovations and Advances

Recent advances in bronchoscopy have led to changes in clinical diagnostics and therapeutics in pulmonary medicine. In diagnostic bronchoscopy, there have also been new developments in endobronchial ultrasound technology which may be incorporated into clinical practice in the near future. Functional bronchoscopy, which evaluates information such as airway pressure, airflow, or gas exchange, suggests promising clinical advances in the near future. In therapeutic bronchoscopy, bronchoscopic volume reduction is a novel approach for the treatment of severe emphysema. In this review, seven recently published articles representing current advances in bronchoscopy are summarized and discussed.