Learning Objectives List the three categories of pulmonary function tests. State the primary purposes of pulmonary function testing. Describe the pathophysiologic patterns associated with obstructive and restrictive lung disease. State what is meant by the term spirometer, and list the parameters that can be measured by it.
Learning Objectives (cont.) List and describe the four general principles that should be considered for tests of pulmonary function. List and describe the measurements that indicate pulmonary mechanics. Describe the purpose and technique for the bronchial challenge test. List and describe the four volumes and four capacities that can be measured with pulmonary function testing.
Learning Objections (cont.) Describe the purpose and techniques used to measure diffusion capacity. Interpret pulmonary function reports.
PFTs will measure: Dynamic flow rates of gases through airways, Lung volumes & capacities Ability of lungs to diffuse gases
Purposes of PFT Identify & quantify changes in pulmonary function due to disease Evaluate effectiveness of therapy Perform epidemiological surveillance for pulmonary disease Assess patients for risk of postoperative complications Determine pulmonary disability
All of the following are contraindications to pulmonary function testing, except: • Hypertension • Pneumothorax • Pulmonary Embolism • Myocardial Infarction
Pathophysiologic Patterns • Two major categories of pulmonary disease exist: • Obstructive • Restrictive • Primary abnormality in obstructive disease is increased airways resistance • Primary problem in restrictive disease is decrease in either lung compliance or lung volumes or both • Some pulmonary diseases cause both obstructive & restrictive disease
PFT Equipment • Two general types of measuring devices exist, those that: • Measure volume • Measure flow • Volume-measuring devices - spirometers • Flow-measuring devices - pneumotachometers • Every measuring device has capacity, accuracy, error, resolution, precision, linearity, & output
Elements of Quality Assurance • Accuracy & precision of measuring instruments • Performance of Respiratory Therapist (RT) • Test results when measuring a standard
All of the following are pathophysiological patterns of pulmonary diseases, except: • Restrictive diseases will decrease lung compliance • Obstructive diseases will increase airway resistance • Restrictive disease will increase lung volumes • Some pulmonary diseases can cause both obstructive and restrictive disease
Principles of Measurement • Most pulmonary function laboratories have 3 components. • Performing spirometry to measure airway mechanics • Measuring lung volumes & capacities • Measuring diffusion capacity of lung • All 3 components are required when purpose of PFT is to identify presence & degree of pulmonary impairment
Spirometry • Tests of pulmonary mechanics • Forced vital capacity (FVC) • Forced expiratory volume in 1 second (FEV1) • Other forced expiratory flow measurements • Maximum voluntary ventilation • These measurements assess ability of lungs to move large volumes of air quickly through airways
Forced Vital Capacity Most common test of pulmonary mechanics Many measurements are made while patient is performing FVC maneuver FVC is an effort-dependent maneuver requiring careful patient instruction & cooperation To ensure validity, each patient must perform at least 3 acceptable FVC maneuvers
Other Measures of Pulmonary Mechanics FEV1 - volume of gas exhaled in first 1-second of FVC maneuver FEV1/FVC - calculated by dividing largest FEV1 by largest FVC FEF200-1200 - average flow rate early in FVC maneuver FEF25-75 - measure of flow during middle 50% of FVC PEFR - highest point on flow-volume graph
What is the most commonly used test of pulmonary mechanics: • Forced expiratory flow measurements (FEV1) • Forced vital capacity (FVC) • Maximum voluntary ventilation (MVV) • Helium dilution technique
Maximal Voluntary Ventilation (MVV) • Effort-dependent test; patient asked to breathe deep & fast for 12 seconds • Results reflect: • Patient effort • Function of respiratory muscles • Ability of chest wall to expand • Patency of airways
Quality Assurance of Spirometry • 3.0 L syringe used for accuracy & precision of volume or flow • Multiple strokes at various injection speeds • Average volume should meet the +/- 3% standard • 95% expected performance range should be determined • Technologist performance should be observed & reviewed periodically
Significance of Results • Normal FEV1 = 5.6 L for average 20-year-old man • FEV1 is reduced with both obstructive & restrictive lung disease. • FEV1/FVC should be at least 70% • Reduced with obstructive disease • Normal with restrictive disease • Other measures of expiratory flow are also reduced when obstructive disease is present
Significance of Results (cont.) Normal MVV for males is 160 to 180 L/min & slightly lower in females MVV is reduced in patients with moderate to severe obstructive lung disease MVV may be normal or slightly reduced in patients with restrictive disease Undernourished patients may have reduced MVV
Reversibility If obstruction is present, reversibility must be evaluated Done by performing spirometry before & after therapy Bronchodilator is administered by small-volume nebulizer or MDI Reversibility indicates effective therapy Reversibility is defined as 15% or greater improvement in FEV1 & at least 200-ml increase in FEV1
If FEV1/FVC is less than 70%, this would indicate; • Obstructive disease • Obstructive and restrictive disease • Restrictive disease • Patient is in the normal range
Lung Volumes & Capacities • Lung Volumes • Tidal volume • Inspiratory reserve volume • Expiratory reserve volume • Residual volume • Lung Capacities • Total lung capacity • Inspiratory capacity • Functional residual capacity • Vital capacity
The functional residual capacity consist of which two lung volumes • Tidal volume and inspiratory reserve volume • Tidal volume and expiratory reserve volume • Inspiratory reserve volume and residual volume • Expiratory reserve volume and residual volume
Techniques for Measuring RV • Helium dilution • Based on fact that known amount of helium will be diluted by size of patient’s RV • Nitrogen washout • Based on fact that 79% of RV is nitrogen • Volume of nitrogen exhaled ÷ 0.79 = RV • Body box • Applies Boyle’s law to measure RV
Quality Assurance for Measuring Lung Volume • Helium dilution & nitrogen washout • Accuracy & precision of volume & flow measuring device • Accuracy & linearity of gas analyzer • Leak test must be acceptable range • Plethysmography • Box & mouth pressure transducers must be calibrated & accurate
Significance of Results TLC, FRC, & RV increase with obstructive disease & decrease with restrictive impairment Normal tidal volume is 500 to 700 ml (5 to 8 ml/kg of predicted body weight); VT measurement alone not helpful Normal TLC is about 6 L Normal VC is about 4.8 L in adult; results vary with age, gender, height, & ethnicity
Diffusing Capacity Most PF labs use carbon monoxide to measure the diffusion capacity of the lungs Results reported in ml/min/mm Hg Results may be low in both obstructive & restrictive lung disease Emphysema & pulmonary fibrosis are two common causes of reduced DLCO
Interpreting the DLCO Factors that Decrease DLCO Factors that Increase DLCO Polycythemia Exercise Congestive heart failure • Anemia • Carboxyhemoglobin • Pulmonary Embolism • Diffused pulmonary fibrosis • Pulmonary emphysema
Quality Assurance for Measuring Diffusing Capacity • Accuracy & precision of volume or flow measuring device • Accuracy & linearity of gas analyzer • Test acceptability & repeatability • Measuring diffusing capacity of 3.0 L to provide quality control standard
Which one of these factors can decrease the diffusing capacity of the lung: • Polycythemia. • Exercise. • Congestive heart failure. • Pulmonary emphysema.
PFT Report Interpretation • FEV1/FVC ratio is good place to start; reduced (<70%) with obstructive lung disease • If TLC less than 80% of predicted normal & FEV1/FVC is normal - restrictive disease is present • If DLCO is <80% of normal - diffusion defect is present • Reduced surface area = emphysema • Thickened AC membrane = pulmonary fibrosis