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Pulmonary Medicine

Pulmonary Function Lab Offers Uncommon Tests

11/02/2010

CU-Pulmonary FunctionUCLA’s nationally renowned Pulmonary Function Laboratory offers comprehensive inpatient and outpatient pulmonary function tests. The labs contain seven testing stations that are used to administer more than 15,000 tests annually, including spirometry, lung volume tests, diffusion tests, cardiopulmonary exercise testing and oxygen titration.

UCLA also offers two uncommon but useful assessments: hypoxia-altitude simulation testing (HAST) for high-altitude hypoxia, and the methacholine challenge for the diagnosis of asthma.

HAST

Thousands of patients with underlying pulmonary disease experience medical emergencies every year as a result of induced hypoxia at higher altitudes, especially during air travel. While some of these patients suffer from chronic diseases such as asthma or pulmonary fibrosis, the vast majority suffer from Chronic Obstructive Pulmonary Disease (COPD), a smoking-related lung condition with symptoms including emphysema and damage to small airways. Most airlines offer supplemental oxygen to passengers at risk of developing hypoxia. HAST determines how much supplemental oxygen a patient needs to stay properly oxygenated in flight.

Patients with severe COPD who already require oxygen at low elevations are obvious candidates for HAST before air travel. But a significant proportion of COPD patients with only mild respiratory symptoms can benefit from HAST, as they are also at risk of developing induced hypoxia in flight.

The risk arises because the cabin pressure maintained in most commercial airliners reduces the oxygen saturation levels of the breathable air to about 15 percent, a concentration equivalent to what is found at about 8,000 feet above sea level. (At sea level, the concentration of oxygen in the air is about 20 percent.) Both the American Thoracic Society and the European Respiratory Society recommend that COPD patients with arterial blood oxygen of less than 75-100 mm Hg at sea level undergo HAST before traveling by plane. The recommendations are based on research completed in 1984 by a team of UCLA physicians who published their findings in a widely cited paper. (AM Rev Respir Crit Care Med 1984 Vol 130 p 980-86)

Two ways to administer HAST

To undergo HAST, patients breathe a reduced-oxygen mixture of gases to simulate the oxygen available at altitude. Patients are monitored by either pulse oximetry for oxygen saturation or repeated arterial blood gas determinations using an arterial line to evaluate changes in carbon dioxide levels as oxygen is increased. Oxygen is added until ideal oxygenation levels are obtained. The test can be administered two ways. For air travel simulation, the patient is seated at rest, while breathing a gas mixture that simulates commercial airline cabin air. Ambulatory patients traveling to high-altitude destinations can take the test while walking on a treadmill to determine the appropriate oxygen prescription for activity. Altitudes other than 8000 feet can be simulated when appropriate.

Methacholine challenge

Physicians typically measure airway obstruction in patients who suffer from asthma with a spirometer, which is commonly found in doctors’ offices. Some asthmatics who suffer from coughing rather than wheezing symptoms are more difficult to diagnose, as they often perform normally on spirometer tests. The methacholine challenge can clarify the diagnosis of asthma in a patient who might not be identified by spirometer tests or who suffers from occasional symptoms.

Patients breathe in a saline solution containing a small concentration of metha-choline in an attempt to induce temporary broncho-constriction. The concentration of methacholine is incrementally raised to a maximum of 25 mg/ml while the patient undergoes serial spirometer tests. While non-asthmatics do not react, all asthmatics, even those who have no wheezing symptoms, will react at low concentrations.

UCLA’s Pulmonary Function Laboratory, which is managed jointly by Ronald Reagan UCLA Medical Center and the Division of Pulmonary & Critical Care Medicine, is one of the few centers in Southern California that offers the uncommon but highly useful HAST and methacholine challenge tests.

HAST and methacholine challenge underutilized

While hypoxia altitude simulation tests (HAST) and methacholine challenge have traditionally made up only a small proportion of the 15,000 pulmonary tests administered by the labs every year, the numbers are starting to grow.

“These tests are highly useful, but underutilized in the com-munity,” says Eric Kleerup, M.D., medical director of the Pulmonary Function Laboratory. “They’re not the kind of tests most doctors can do in their offices.”

HAST is especially useful for COPD patients who are at risk of suffering from hypoxia during air travel. Methacholine challenge, which can identify asymptomatic asthmatics, is a practical way to confirm or rule out asthma for state disability claims of patients with normal spirometer results.

“The methacholine challenge is not done in people with obvious asthma, but if there’s a question about the diagnosis, the test is very helpful,” Dr. Kleerup says.

Participating Physicians

Eric Kleerup, M.D.
Medical Director, Pulmonary Function
Clinical Professor of Medicine
Pulmonary and Critical Care Medicine

Christopher B. Cooper, M.D.
Medical Co-Director
Exercise Physiology Laboratory
Professor of Medicine and Physiology
Pulmonary and Critical Care
Medicine Physician

Contact Information
UCLA Medical Subspecialty Suite - Pulmonary
200 UCLA Medical Plaza Suite #302
Los Angeles, Ca 90095
(310) 825-8061





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