The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

Unraveling the Mysteries of the Box

Susan Blonshine BS, RRT, RPET

Whole body plethysmographic lung volume determinations and the measurement of airway mechanics are gradually becoming a standard of care for the diagnosis and management of pulmonary disease. As technology has improved plethysmograph designs and incorporated multiple tests, the economic feasibility of performing these tests as advanced. The clinical utility of whole body plethysmograph measurements continues to expand. Understanding performance and application of plethysmographic procedures in order to perform thoracic gas volume measurements and airway mechanics is imperative to answer specific clinical questions.

Test quality aspects must be incorporated to assure reproducible and valid results. The test quality aspects include:

1. Quality Control

2. Test Performance

3. Test Measurement and Review

4. Error Recognition

5. Data Reduction

6. Result Reporting

7. Technologist Statements

Two primary measurement methods for thoracic gas volume and airway resistance are discussed in the literature: a quiet breathing technique and a panting maneuver. The primary method used in the United States is a panting maneuver. During the maneuver performance, several physiologic assumptions are made which include; mouth pressure is equal to alveolar pressure, abdominal gas does not affect the measurements and the respiratory exchange ratio is one.

Gas dilution methods may underestimate the "true" lung volume in the presence of significant (diffuse) obstruction, bullae, cavities, and cysts, a focal obstruction of an airway, dependent airway closure above FRC and in significant regionalized parenchymal or pleural disease. Plethysmographic volumes are accurate even in the presence of severe obstruction. The identification of restrictive patterns is based on TLC.

Airway mechanics are more sensitive to airway narrowing than forced expiratory flows. The site of airway disease, central vs. peripheral, may be identified with specific airway resistance or specific conductance measurements. If used alone, airway mechanics eliminate the bronchoactive effect of lung inflations. If used in conjunction with spirometry, airway mechanics provide a basis for a more specific characterization of the disease. Airway mechanics also serve as an important adjunct to bronchial provocation testing.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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