A new, non-invasive test might help doctors better predict the risk of death for their patients with lung disease, say researchers in Spain. In a study published in the American Journal of Respiratory and Critical Care Medicine on March 15,1 doctors in Spain described the test as one that measures lung hyperinflation, in which tiny air sacs in the lung fail to deflate during breathing.
A Cluster of Lung Diseases
The test is aimed at patients with chronic obstructive pulmonary disease (COPD), an umbrella term used to describe a group of diseases that causes airflow blockage and breathing-related problems. It includes emphysema, chronic bronchitis, and in some cases, asthma. COPD is a leading cause of death in the United States.2
The primary cause of COPD is tobacco use, but asthma, exposure to air pollutants in the home and workplace, genetic factors, and respiratory infections also play a role. In the developing world, it's believed that indoor air quality plays a larger role in the development and progression of COPD than in the United States.
Estimates are that 10 million U.S. adults were diagnosed with COPD in the year 2000, but information from a national health survey suggested that as many as 24 million people in this country have the disease.2
Ties to Other Lung Diseases
People with COPD can also eventually develop pulmonary hypertension (PH), whose presence and severity are closely related to the prognosis of COPD.3 PH is a rare lung disorder in which blood pressure in the artery leading from the heart to the lungs rises to abnormal levels for no apparent reason. In the United States, up to 1,000 new cases of primary, or unexplained PH are diagnosed every year.4
Some people with emphysema, one of the diseases that falls into the COPD category, can also develop another lung disease: idiopathic pulmonary fibrosis.5
Is a New Prognostic Test Better?
In the study, chief investigator Ciro Casanova, MD, in the Respiratory Research Institute at Hospital Universitario la Candelaria in Tenerife, Spain and his colleagues tested the efficacy of the new test in a group of 689 patients with chronic obstructive pulmonary disease.
The test uses the ratio of inspiratory capacity (total volume of air that can be inhaled after a full exhalation) to total lung capacity—the volume of air contained in the lungs after the greatest possible inhalation.
Each patient was followed, on average, for nearly 3 years in the study. The test was compared to another test known as the BODE Index, which assesses a patient's prognosis by collecting information on body mass index (a measure of healthy weight in relation to height), airflow obstruction, dyspnea (shortness of breath), and exercise performance. The index consists of a 10-point score, with the highest scores indicating a higher risk of death.6
Some doctors have suggested that the BODE Index itself is better than a standard test for COPD known as FEV1, a measure of total forced expiratory volume in 1 second. This is due to other possible signs of the disease that the FEV1 test cannot detect.6 (Forced expiratory volume is the total amount of air that can be exhaled after a full inhalation.)
After analyzing results of the new test to that of the BODE Index during the nearly 3-year study, the researchers concluded that the newer test is as good as the BODE Index, if not better. During the study, 27 percent of the patients died, the investigators reported. They learned that 71 percent of the patients who died scored under 25% in resting lung hyperinflation as detected by the new test. That means most of the air sacs in the patients' lungs failed to deflate when exhaling.
The test appears to be more accurate, the investigators stated, than other indicators currently in use, most likely because it provides a direct analysis of functional lung impairment.
"We propose that this ratio be considered in the assessment of patients with chronic obstructive pulmonary disease," the investigators wrote.
1. Casanova C, Cote C, de Torres JP et al. Inspiratory-to-total lung capacity ratio predicts mortality in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2005 Mar 15;171(6):591-7. Epub Dec 10.
2. National Center for Environmental Health. Centers for Disease Control and Prevention (CDC). Facts about Chronic Obstructive Pulmonary Disease (COPD). Available at: http://www.cdc.gov/nceh/airpollution/copd/copdfaq.htm. Accessed March 17, 2005.
3. Barbera JA, Peinado VI, Santos S. Pulmonary hypertension in COPD: old and new concepts. Monaldi Arch Chest Dis 2000 Dec;55(6):445-9.
4. American Heart Association. Primary or unexplained pulmonary hypertension. Available at: http://www.americanheart.org/presenter.jhtml?identifier=4752. Accessed March 17. 2005.
5. Hiwatari N, Shimura S, Takishima T. Pulmonary emphysema by pulmonary fibrosis of undetermined cause. Respiration 1993;60(6):354-8.
6. Celli BR, Cote CG, Marin JM et al. The body-mass index, airflow obstruction, dyspnea, and exercise capacity index in chronic obstructive pulmonary disease. N Engl J Med 2004 Mar 4;350(10):1005-12.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
