Chest
Topics in Practice ManagementOptimizing Performance of Respiratory Airflow Resistance Measurements
Section snippets
Clinical Indications
The following are indications for Raw measurements16: (1) evaluating airflow limitation beyond spirometry; (2) determining bronchodilator responsiveness; (3) determining bronchial hyperreactivity to methacholine, histamine, or isocapnic hyperventilation; (4) differentiating types of obstructive lung diseases having similar spirometric configurations; (5) following the course of disease and response to treatment; and (6) distinguishing respiratory muscle weakness from obstruction as the cause of
Airflow Perturbation/Oscillatory Resistance
Forced oscillatory resistance is the most commonly used airflow perturbation method, available commercially in the United States as impulse oscillometry (IOS). IOS measures Rrs regardless of lung volume. In both IOS and simpler airflow perturbation devices (APDs), measurement of Rrs provides more useful information if end-expiratory lung volume is known. Therefore, an inspiratory capacity (IC) effort should be included prior to completion of airflow perturbation test sessions. Patients with
Plethysmography Test Performance
Performing Raw measurements by plethysmography requires enclosure of the patient in a total-body plethysmograph designed to measure pressure and flow changes. The test procedure requires < 10 min to perform multiple trials within preset acceptability and repeatability criteria. Patients are instructed in the correct techniques while the plethysmograph door is open. The instructions include the need for relaxing and breathing normally between trials, supporting the cheeks during trials,
Reporting Results
Report Rrs in centimeters of water per liter per second at the lowest frequency measured (usually 5 Hz). Report the fall in Rrs between 5 Hz and 15 Hz (R5-R15), designated f-dR in the same units. Report the IC both before and after bronchodilator. Unlike plethysmography, which measures absolute TGV, Rrs measurements during normal breathing are subject to the patient's chosen respiratory pattern. The IC effort required just before ending the test session provides an index within the vital
Clinical Evaluation
Rrs should be displayed graphically at different oscillatory frequencies (Fig 2). Determine whether Rrs decreases with increasing oscillation frequency (f-dR), demonstrating airflow obstruction, or whether Rrs is constant (normal subjects in group A, Fig 2) independent of oscillation frequency. This feature is paramount in clinical interpretation of small airway impairment.
Plethysmograhic sRaw loops have definite shapes indicative of specific airway disorders24, 25 and are as important to
Practice Management
Report Raw measurements with current procedural terminology code 94360,26 for both oscillatory and plethysmographic methods. If plethysmographic lung volumes are reported with current procedural terminology code 93720 (plethysmography, total body), then 94360 is bundled into plethysmography and cannot be reported separately.27
Raw reimbursement varies regionally in the United States based on local carrier decisions.28 Medical necessity is supported by the use of International Classification of
Summary
Raw provides useful clinical information for diagnosis and monitoring of lung disease beyond spirometry. A direct measure of airway status, Raw is useful in individuals unable to provide adequate effort during spirometry. Rrs falls with increasing oscillation frequency (R5-R15) that provides a surrogate for frequency dependence of compliance, and reflects small airway impairment. R5-R15 and sGaw are particularly useful for assessing changes in airway caliber after bronchodilator administration.
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