ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

RV is the volume of gas remaining in the lung after maximal (complete) exhalation regardless of the lung volume at which expiration was started. It requires maximal expiratory efforts and cannot be obtained in non-cooperating subjects. It is indirectly determined by subtracting the ERV from FRC, or VC from TLC. It is usually elevated in obstructive lung diseases and reduced with restrictive lung diseases. While spirometry may suffice in the diagnosis and monitoring response to therapy in obstructive lung diseases such as COPD or asthma, lung volume measurements are essential in the diagnosis of restrictive lung disease and often very helpful in complex or mixed lung conditions.

Indications and Contraindications Table 8.1

Indications for measuring lung volumes include Establish or confirm a “restrictive ventilatory defect” or in diagnosing hyperinflation and abnormal distensibility as may occur in patients with emphysema (2). Differentiating types of lung disease processes characterized by airflow limitation that have similar forced expiratory configurations (2). Assess response to therapeutic intervention (e.g., drugs, transplantation, radiation, chemotherapy, and lobectomy). Aid in the interpretation of other lung function tests. Evaluate cause of pulmonary disability. Make preoperative assessments in patients with compromised lung function (known or suspected) when the surgi- Relative contraindications for measuring lung volumes include Relative contraindications for performing static lung volumes include those also considered for spirometry (3): 1. Hemoptysis of unknown origin 2. Pneumothorax 3. Unstable cardiovascular status 4. Thoracic, abdominal, or cerebral aneurysms 5. Recent eye surgery Presence of an acute disease that might interfere with test performance (e.g., nausea, or vomiting) Recent surgery of thorax or abdomen With respect to total-body plethysmography, such factors as claustrophobia, upper-body paralysis, obtrusive casts, or any factor that could limit the patient’s access into the chamber is a concern. In addition, temporary interruption of supplemental oxygen (O 2 ) and intravenous fluids may be contraindicated. With respect to the multiple-breath dilution or washout methods, in patients with very severe chronic obstructive pulmonary disease (COPD) factors such as depressed ventilatory drive during FRC N2 (due to breathing 100% O 2 ), and induced hypercapnia and/or hypoxemia during FRC He (due to failure to adequately remove carbon dioxide [CO 2 ] or add O 2 ), need to be considered and addressed. cal procedure is known to affect lung function. Quantify the amount of nonventilated lung. Table 8.2

74