Imaging Regional Lung Defect Severity

Recently, The Center for Disease Control and Prevention (CDC) announced that chronic obstructive pulmonary disease (COPD) had escalated to the 3rd leading cause of death in this country. John Walsh (President, COPD Foundation) remarked that "It's unacceptable that COPD has gone from the fourth leading cause to the third twelve years sooner than what was originally projected. This wakeup call intensifies our declaration of war on COPD and points to the importance of improved awareness, prevention, detection and treatment to decrease the burden of COPD". Although there have been significant advances in care, the COPD epidemic persists, leading to approximately 137,082 deaths/yr. in the US alone. COPD represents the only disease in the top ten causes of death that has consistently increased in frequency over the past 4 decades only showing a slight decrease (\~4%) in the preliminary data for deaths in 2009 recently released. The economic burden of COPD in the US in 2010 is estimated at 29.5 billion dollars in direct costs (an increase of 63% from 2002) and another 20.5 billion in productivity loss. Consequently COPD represents one of the largest uncontrolled disease epidemics in the U.S.; it currently includes 15-20 million diagnosed cases with perhaps a similar number undiagnosed. In the U.S., there are approximately 90 million current or former smokers thus; a huge population is at risk of developing COPD. COPD is defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) as a disease state characterized by airflow limitation that is not fully reversible. There is clear recognition that COPD includes both emphysema and small airway disease; however, there is little appreciation of how to identify COPD early - before there is significant airflow obstruction and clinical impairment. It has long been appreciated that better characterization of pulmonary disease requires assessing the lung regionally. To this end computed tomography (CT) is gaining prominence by distinguishing airways-predominant vs. emphysema-predominant COPD. CT can also add functional information regarding perfusion or ventilation, but concern is increasing regarding radiation dose and increased cancer risk. The introduction of 3-Helium (3He) MRI enables longitudinal and sensitive imaging of ventilation, while adding contrast like the apparent diffusion coefficient (ADC) to reveal emphysema. Unfortunately the world supply of 3He is miniscule, and 3He ADC has failed to measure disease progression. Thus, attention has turned to 129-Xenon (129Xe) MRI and the Duke group has now shown clinical 129Xe MRI with similar quality to 3He, including ADC contrast. Ultimately, however, the dissemination of the hyperpolarization technology required to acquire these scans remains problematic and acts as a hindrance in using it in clinical trials. Consequently another imaging biomarker is required, and hence perfluoropropane/oxygen mixtures are being considered. To treat patients, or to develop new therapies for a disease, requires the ability to phenotype the condition, monitor progression/response, and to do so non-invasively and longitudinally. Improved measurements will be critical to drive progress in treating chronic diseases such as COPD that affect over 15 million US patients, but progress slowly and respond to therapy slowly. Clinical trials of treatments of lung airway disease often require very large numbers of subjects due to the limited sensitivity of global ventilation assessment or other clinical measures (e.g. number of exacerbations per year). The question of regional ventilation in disorders such as COPD is becoming increasingly important. An editorial in the New England Journal of Medicine (NEJM) addressed the concerns of using changes in Forced Expiratory Volume in 1 second (FEV1) as an endpoint in treatment trials. The comments were related to the Understanding Potential Long-Term Impacts on Function with Tiotropium trial (tiotropium vs. placebo (UPLIFT). In this study, reported in the same issue, patients using standard respiratory medications (except inhaled anticholinergic drugs) were randomized to their existing treatment with either tiotropium or placebo and followed for a 4-year period. While the treatment group using tiotropium had improvements in lung function, quality of life (QOL) and fewer exacerbations in the 4-year study, there was no significant change in the rate of decline in FEV1 either before of after bronchodilator administration. In a separate study called Towards a Revolution in COPD Health (TORCH), trial patients were randomized to a combination treatment (fluticasone and salmeterol), each of the agents alone or placebo. TORCH patients were followed for a 3-year period where the primary outcome was death from any cause. The reduction in mortality did not reach statistical validity although there were benefits in secondary outcomes (e.g. frequency of exacerbations, spirometric values). The difference in FEV1 for the dual agent arm versus placebo was 0.092 liters (95% confidence interval (CI) 0.075 - 0.108, p\<0.001) although the mean baseline FEV1 for the treated and placebo group was 1.24 and 1.26 liters respectively yielding a 7% difference in the FEV1, a difference not generally considered clinically relevant. The dominant question in the editorial and one facing studies of COPD is the heterogeneity of the disorder and the current lack of a good diagnostic tool for stratification/screening of potential subjects for a treatment study. Potentially radiographic or non-radiographic imaging may become a tool to assist in such screenings or even serve as an endpoint. Avoiding such failures requires developing measurements with greater sensitivity and specificity. Clearly, COPD is a major health issue in this country and current treatment strategies are limited. The limits of global pulmonary function testing are recognized as a stumbling block in the development and evaluation of new therapeutic tools for these diseases. These new imaging biomarkers (PFx's) for evaluation of regional ventilation should be an important step in decreasing the impact of these diseases in the US and perhaps worldwide. The central hypothesis and current observation is that PFx gases, when used as contrast agents, provide functional images of the lung airways including important regional ventilation information such as ventilation defect severity and gas trapping. We will test the central hypothesis and accomplish the overall objective by addressing the following specific aims: Primary Study Aims/Secondary Aims Aim 1: Determine quantitative measures of lung ventilation performance in terms of direct measures of gas trapping measured during washout of the perfluorinated gas mixture. Sub-aim 1.1: Compare gas trapping from AIM 1 with air trapping by high-resolution computed tomography (HRCT) using conventional analysis procedures. Sub-aim 1.2: We will accomplish this aim (as well as Aim 2) in a well-characterized cohort of subjects with COPD and subjects with normal global pulmonary function tests (non-, ex- and current smokers). This cohort will provide the basis for the cross sectional evaluation of the imaging markers in all aims with respect to disease severity (e.g. GOLD status) and risk factors (e.g. smoking) Aim 2: Determine ventilation defect severity by comparing regional gas signal during wash-in of the perfluorinated gas mixture to steady state in the same cohort. The outcomes of the work proposed in the aims is expected to demonstrate a novel quantitative approach for ventilation defect and gas trapping evaluation of regional lung function in humans that would be easily deployed for multi-center studies. It should also provide a set of biomarkers that could better inform evaluation of new treatments. In each of these 250 subjects, after obtaining informed consent, an array of clinical, physiologic, imaging, and disease impact data will be collected on dedicated computerized case report forms. The goal is to categorize the disease from structural, functional, and clinical perspectives. The specific data to be collected have been shown in multiple studies to be useful in describing clinical phenotypes and helped characterize subjects. They can predict functional status and can also demonstrate and predict responders to various therapeutic interventions.