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Chapter 3. Pulmonary Function Study Assessments. Introduction. Pulmonary function studies are used to: Evaluate pulmonary causes of dyspnea Differentiate between obstructive and restrictive pulmonary disorders Assess severity of the pathophysiologic impairment
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Chapter 3 Pulmonary Function Study Assessments
Introduction • Pulmonary function studies are used to: • Evaluate pulmonary causes of dyspnea • Differentiate between obstructive and restrictive pulmonary disorders • Assess severity of the pathophysiologic impairment • Follow the course of a particular disease • Evaluate the effectiveness of therapy • Assess the patient’s preoperative status
Table 3-1. Lung Volumes and Capacities of Normal Recumbent Subjects 20 to 30 Years of Age
Table 3-2. Restrictive Lung Disorders: Lung Volume and Capacity Findings
Table 3-4. Obstructive Lung Disorders: (Lung Volume and Capacity Findings)
Table 3-5. Anatomic Alterations of the Lungs Associated with Obstructive Lung Disorders: (Pathology of the Tracheobronchial Tree)
Figure 3-1. Visual comparison of lung volumes and capacities in obstructive and restrictive lung disorders. (From Wilkins RL, Stoller JK, Scanlan CL: Egan’s fundamentals of respiratory care, ed 9, St Louis, 2009, Elsevier.)
Indirect Measurements of the Residual Volume and Capacities Containing the Residual Volume • Closed-circuit helium dilution test • Open-circuit nitrogen washout test • Body plethysmography
Forced Vital Capacity (FVC) • The FVC is the total volume of gas that can be exhaled as forcefully and rapidly as possible after a maximal inspiration.
Figure 3-2. Forced vital capacity (FVC). A is the point of maximal inspiration and the starting point of an FVC maneuver. Note the reduction in FVC in obstructive pulmonary disease.
Forced Expiratory Volume (FEVT) • The maximum volume of gas that can be exhaled over a specific period is the FEVT. • This measurement is obtained from an FVC measurement. • Commonly used time periods are 0.5, 1.0, 2.0, 3.0, and 6.0 seconds • The most commonly used time is 1 second (FEV1 ).
Figure 3-3. Forced expiratory volume timed (FEVT). In obstructive pulmonary disease, more time is needed to exhale a specified volume.
Forced Expiratory Volume (FEVT) (Cont’d) • In the normal adult, the percentage of total volume exhaled during these time periods: • FEV0.5: 60% • FEV1: 80% • FEV2: 94% • FEV3: 97%
Forced Expiratory Volume in 1 Second/ForcedVital Capacity Ratio (FEV1/FVC Ratio)(also abbreviated as FEV1%)
FEV1/FVC RatioorFEV1% • The FEV1/FVC ratio compares the amount of air exhaled in 1 second with the total amount exhaled during an FVC maneuver.
FVC, FEV1, and FEV1% • Clinically, the FVC, FEV1, and FEV1% are commonly used to: • Assess the severity of a patient’s pulmonary disorder and • Determine whether the patient has an obstructive or a restrictive disease
FVC, FEV1, and FEV1% (Cont’d) • The primary pulmonary function study difference between an obstructive and a restrictive lung disorder are as follows: • In an obstructive disorder, the FEV1 and FEV1% are both decreased. • In a restrictive disorder, the FEV1 is decreased and FEV1% is normal or increased.
Forced Expiratory Flow25%-75% • The FEF25%-75% is the average flow rate generated by the patient during the middle 50% of an FVC measurement. • FEF25%-75% is used to evaluate the status of medium-to-small airways in obstructive lung disorders.
Figure 3-4. FEF25%-75%. This test measures the average rate of flow between 25% and 75% of an FVC.
Forced Expiratory Flow200-1200 • The FEF200-1200 measures the average flow rate between 200 and 1200 mL of an FVC. • The FEF200-1200 provides a good assessment of the large upper airways.
Forced Expiratory Flow200-1200 (Cont’d) • The FEF200-1200 measures the average flow rate between 200 and 1200 mL of an FVC. • The FEF200-1200 provides a good assessment of the large upper airways.
Figure 3-5. FEF200-1200. This test measures the average rate of flow between 200 mL and 1200 mL of an FVC.
Peak Expiratory Flow Rate • The PEFR is the maximum flow rate generated during an FVC maneuver.
˙ ˙ Figure 3-6. PEFR. The steepest slope of the DV/DT line is the PEFR (V).
Maximum Voluntary Ventilation (MVV) • The MVV is the largest volume of gas that can be breathed voluntarily in and out of the lungs in 1 minute. • Note: The patient effort during the MVV is for only 12 to 15 seconds. The total 1 minute MVV is extrapolated from these data.
Flow-Volume Loop • The flow-volume loop is a graphic illustration of both a forced vital capacity (FVC) maneuver and a forced inspiration volume (FIV) maneuver.
Flow-Volume Loop (Cont’d) • Depending of the sophistication of equipment, several important pulmonary function study values can be obtained, including: • FVC • FEVT • FEF25%-75% • FEF200-1200 • PEFR • Peak inspiratory flow rate (PIFR) • FEF50% • Instantaneous flow at any given lung volume during forced inhalation and exhalation
Figure 3-9. Flow-volume loop demonstrating the shape change that results from an obstructive lung disorder. The curve on the right represents intrathoracic airway obstruction.
Figure 3-7. Volume-time tracing for a maximum voluntary ventilation (MVV) maneuver. Note: the patient actually performs the MVV maneuver for only 12 sec, not 60 sec.
Figure 3-10. Flow-volume loop demonstrating the shape change that results from a restrictive lung disorder. Note the symmetric loss of flow and volume.
Table 3-8. Obstructive Lung Diseases: Forced Expiratory Flow Rate and Volume Findings
Pulmonary Diffusion Capacity • The pulmonary diffusion capacity of carbon monoxide (DLCO) measures the amount of carbon monoxide (CO) that moves across the alveolar-capillary membrane.
Table 3-9. Pulmonary Diffusion Capacity of Carbon Monoxide (DLCO)
