Jonathan P. Williamson

Elastic properties of the central airways in obstructive lung diseases measured using anatomical optical coherence tomography

RATIONALE Our understanding of how airway remodeling affects regional airway elastic properties is limited due to technical difficulties in quantitatively measuring dynamic, in vivo airway dimensions. Such knowledge could help elucidate mechanisms of excessive airway narrowing. OBJECTIVES To use anatomical optical coherence tomography (aOCT) to compare central airway elastic properties in control subjects and those with obstructive lung diseases. METHODS After bronchodilation, airway lumen area (Ai) was measured using aOCT during bronchoscopy in control subjects (n = 10) and those with asthma (n = 16), chronic obstructive pulmonary disease (COPD) (n = 9), and bronchiectasis (n = 8). Ai was measured in each of generations 0 to 5 while airway pressure was increased from -10 to 20 cm H(2)O. Airway compliance (Caw) and specific compliance (sCaw) were derived from the transpulmonary pressure (Pl) versus Ai curves. MEASUREMENTS AND MAIN RESULTS Caw decreased progressively as airway generation increased, but sCaw did not differ appreciably across the generations. In subjects with asthma and bronchiectasis, Caw and sCaw were similar to control subjects and the Pl-Ai curves were left-shifted. No significant differences were observed between control and COPD groups. CONCLUSIONS Proximal airway elastic properties are altered in obstructive lung diseases. Although central airway compliance does not differ from control subjects in asthma, bronchiectasis, or COPD, Ai is lower in asthma and the Pl-Ai relationship is left-shifted in both asthma and bronchiectasis, suggesting that airways are maximally distended at lower inflating pressures. Such changes reflect alteration in the balance between airway wall distensibility and radial traction exerted on airways by surrounding lung parenchyma favoring airway narrowing. Clinical trial registered with Australian New Zealand Clinical Trials Registry (ACTRN12607000624482).

Measuring airway dimensions during bronchoscopy using anatomical optical coherence tomography

Airway dimensions are difficult to quantify bronchoscopically because of optical distortion and a limited ability to gauge depth. Anatomical optical coherence tomography (aOCT), a novel imaging technique, may overcome these limitations. This study evaluated the accuracy of aOCT against existing techniques in phantom, excised pig and in vivo human airways. Three comparative studies were performed: 1) micrometer-derived area measurements in 10 plastic tubes were compared with aOCT-derived area; 2) aOCT-derived airway compliance curves from excised pig airways were compared with curves derived using an endoscopic technique; and 3) airway dimensions from the trachea to subsegmental bronchi were measured using aOCT in four anaesthetised patients during bronchoscopy and compared with computed tomography (CT) measurements. Measurements in plastic tubes revealed aOCT to be accurate and reliable. In pig airways, aOCT-derived compliance measurements compared closely with endoscopic data. In human airways, dimensions measured with aOCT and CT correlated closely. Bland–Altman plots showed that aOCT diameter and area measurements were higher than CT measurements by 7.6% and 15.1%, respectively. Airway measurements using aOCT are accurate, reliable and compare favourably with existing imaging techniques. Using aOCT with conventional bronchoscopy allows real-time measurement of airway dimensions and could be useful clinically in settings where knowledge of airway calibre is required.

Using Optical Coherence Tomography To Improve Diagnostic and Therapeutic Bronchoscopy

Flexible bronchoscopy is a common procedure that is used in both diagnostic and therapeutic settings but does not readily permit measurement of central airway dimensions. Anatomic optical coherence tomography (a OCT), a modification of conventional optical coherence tomography (OCT), is a novel light-based imaging tool with the capacity to measure the diameter and lumen area of the central airways accurately during bronchoscopy. This study describes the first clinical use of aOCT imaging in the lower airways in three individuals with common endobronchial pathologies. During bronchoscopy, a specialized fiberoptic probe was passed through the biopsy channel of a standard flexible bronchoscope to the site of airway pathology. Airway dimensions were measured from the generated cross-sectional images in three subjects, one with subglottic tracheal stenosis (subject 1), one with malignant left main bronchus (LMB) obstruction (subject 2), and another with severe tracheomalacia (subject 3). Measured dimensions included internal airway diameter, cross-sectional area, and, in subject 1, stenosis length. Tracheal stenosis dimensions, measured using aOCT imaging, correlated with chest CT scan findings and guided the choice of airway stent (subject 1). The airway beyond a malignant obstruction of the LMB, and beyond bronchoscopic view, could be imaged using aOCT, and the distal extent of obstructing tumor identified (subject 2). The severity of newly diagnosed tracheomalacia was able to be quantified using aOCT imaging (subject 3). aOCT imaging during bronchoscopy allows accurate real-time airway measurements and may assist bronchoscopic assessment.

Quantifying tracheobronchial tree dimensions: methods, limitations and emerging techniques

The ability to measure airway dimensions is important for clinicians, interventional bronchoscopists and researchers in order to accurately quantify structural abnormalities and track their changes over time or in response to treatment. Most quantitative airway measurements are based on X-ray computed tomography and, more recently, on multidetector computed tomography. Quantitative bronchoscopic techniques have also been developed, although these are less widely employed. Emerging techniques, including magnetic resonance imaging, endoscopic optical coherence tomography, endobronchial ultrasound and confocal endomicroscopy, provide new research tools with potential clinical applications. An understanding of issues related to the acquisition, processing and analysis of images, and how such issues impact on imaging the tracheobronchial tree, is essential in order to assess measurement accuracy and to make effective use of the newer methods. This article contributes to this understanding by providing a comprehensive review of current and emerging techniques for quantifying airway dimensions.

Applying anatomical optical coherence tomography to quantitative 3D imaging of the lower airway

Endoscopic treatment of lower airway pathologies requires accurate quantification of airway dimensions. We demonstrate the application of a real-time endoscopic optical coherence tomography system that can image lower airway anatomy and quantify airway lumen dimensions intra-operatively. Results demonstrate the ability to acquire 3D scans of airway anatomy and include comparison against a pre-operative X-ray CT. The paper also illustrates the capability of the system to assess the real-time dynamic changes within the airway that occur during respiration.

Managing obstruction of the central airways

Lung cancer is the most common cause of cancer death in Australia, Europe and the USA. Up to 20–30% of these cancers eventually affect the central airways and result in reduced quality of life, dyspnoea, haemoptysis, post‐obstructive pneumonia and ultimately death. Non‐malignant processes may also lead to central airway obstruction and can have similar symptoms. With the development of newer technologies, the last 20 years have seen the emergence of the field of interventional pulmonology to deal specifically with the diagnosis and management of thoracic malignancy, including obstruction of the central airways. This review discusses the pathology, pre‐procedure work‐up and management options for obstructing central airway lesions. Several treatment modalities exist for dealing with endobronchial pathology with local availability and expertise guiding choice of treatment. While the literature lacks large, multicentre, randomized studies defining the optimal management strategy for a given problem, there is growing evidence from numerous case studies of improved physiology, of quality of life and possibly of survival with modern interventional techniques.

Phenotyping airway disease with optical coherence tomography

Airway diseases are a major concern around the world. However, the pace of new drug and biomarker discovery has lagged behind those of other common disorders such as cardiovascular diseases and diabetes. One major barrier in airway research has been the inability to accurately visualize large or small airway remodelling or dysplastic/neoplastic (either pre or early cancerous) changes using non‐ or minimally invasive instruments. The advent of optical coherence tomography (OCT) has the potential to revolutionize airway research and management by allowing investigators and clinicians to visualize the airway with resolution approaching histology and without exposing patients to harmful effects of ionizing radiation. Thus, with the aid of OCT, we may be able to accurately determine and quantify the extent of airway remodelling in asthma and chronic obstructive pulmonary disease, detect early pre‐cancerous lesions in smokers for chemoprevention, study the upper airway anatomy of patients with obstructive sleep apnea in real time while they are asleep and facilitate optimal selection of stents for those with tracheal obstruction. In this paper, we review the current state of knowledge of OCT and its possible application in airway diseases.

Feasibility of Applying Real-time Optical Imaging During Bronchoscopic Interventions for Central Airway Obstruction

BackgroundInterventional bronchoscopists manage central airway obstruction (CAO) through dilation, tumor ablation, and/or stent insertion. Anatomical optical coherence tomography (aOCT), a validated light-based imaging technique, has the unique capacity of providing bronchoscopists with intraprocedural central airway measurements. This study aims to describe the potential role of real-time aOCT in guiding interventions during CAO procedures. MethodsProspective case series were recruited from patients referred for bronchoscopic management of symptomatic CAO. Preprocedure chest computed tomography (CT) scans were analyzed for relevant airway dimensions, such as stenosis caliber and length, and aided procedure planning. During bronchoscopy, an aOCT fiberoptic probe was inserted through the working channel of the bronchoscope to image the airway stenosis. From these aOCT images, stenosis dimensions were measured and compared with the preprocedure CT measurements. Preprocedure and postprocedure spirometry, Medical Research Council dyspnea score, and Eastern Cooperative Oncology Group performance status were collected to assess intervention efficacy. ResultsFourteen patients were studied. CT and aOCT-based measurements of airway caliber and length correlated closely (r2=0.87, P<0.001). Bland-Altman analysis showed strong agreement between measurements (mean difference 0.4±8.6 mm). The real-time nature of aOCT imaging provided the advantage of more up-to-date measurements where a delay occurred between CT and bronchoscopy or where the quality of the CT image was suboptimal. After bronchoscopy, the predicted forced expiratory flow in 1 second increased from 67±26% to 78±19% (P=0.04). Eastern Cooperative Oncology Group and dyspnea scores improved in 83% and 75% of the patients, respectively. ConclusionsaOCT provides real-time measurements of obstructing central airway lesions that can assist therapeutic interventions such as selection of endobronchial stents and airway dilatation procedures.

Thoracic ultrasound recognition of competence: A position paper of the Thoracic Society of Australia and New Zealand

The ability to perform bedside thoracic ultrasound is increasingly recognized as an essential skill for thoracic clinicians, extending the clinical examination and aiding diagnostic and therapeutic procedures. Thoracic ultrasound reduces complications and increases success rates when used prior to thoracentesis or intercostal chest tube insertion. It is increasingly difficult to defend performing these procedures without real or near‐real time image guidance. To assist thoracic physicians and others achieve and demonstrate thoracic ultrasound competence, the Interventional Pulmonology Special Interest Group (IP‐SIG) of the Thoracic Society of Australia and New Zealand (TSANZ) has developed a new pathway with four components: (i) completion of an approved thoracic ultrasound theory and hands‐on teaching course. (ii) A log of at least 40 relevant scans. (iii) Two formative assessments (following 5–10 scans and again after 20 scans) using the Ultrasound‐Guided Thoracentesis Skills and Tasks Assessment Tool (UG‐STAT). (iv) A barrier assessment (UG‐STAT, pass score of 90%) by an accredited assessor not directly involved in the candidates training. Upon completion of these requirements a candidate may apply to the TSANZ for recognition of competence. This pathway is intended to provide a regional standard for thoracic ultrasound training.

Atrial Fibrillation and Sleep Apnoea: Guilt by Association?

Atrial fibrillation (AF) and obstructive sleep apnoea (OSA) are both common, often underdiagnosed conditions with serious sequelae. An association between these two conditions has been recognised but the nature of this relationship remains a topic of active debate. Despite that lack of strong, randomised controlled trials, there is a considerable body of data indicating that not only does untreated OSA provide the substrates and triggers for AF but that OSA, itself, is also a therapeutic target for the management of cardiovascular disease in general and of AF in particular.