Pulmonary Function Tests

1. Pulmonary Function Tests J.B. Handler, M.D. Physician Assistant Program University of New England

2. ARDS- adult respiratory distress syndrome DLCO- diffusion capacity for carbon monoxide Ht- height Wt- weight SOB- short of breath Pred- predicted Meas- measured PFT- pulmonary function test ABG- arterial blood gas Abbreviations

3. PFT’s: Indications • Detect abnormalities and severity of lung function in presence of disease. • Monitor course of disease. • Baseline pulmonary function prior to surgical, medical or radiation therapy. • Differentiation of obstructive vs restrictive disease. • Evaluate response to therapy, reversibility. • Determine the preoperative risk of thoracic surgery.

4. Lung Volumes Images.google.com

5. Tidal Volume (TV): amount of air inhaled and exhaled at rest; normal= 500-750 ml. Inspiratory Capacity (IC): beginning of normal inhalation to maximum inspiration. Lung Volumes IC Images.google.com

6. Inpiratory Reserve Volume (IRV): Volume measured from “top” of the TV (point of normal exhalation) to maximum inspiration. Expiratory Reserve Volume (ERV): Volume measured from the “bottom” of the TV (point of normal inhalation) to maximum expiration. Lung Volumes Images.google.com

7. Residual Volume (RV): The amount of air left in the lungs following full exhalation to the ERV.. Functional Residual Capacity (FRC) = ERV + RV: amount of gas remaining in the lungs at the end of the tidal volume. Lung Volumes Images.google.com

8. Vital Capacity (VC): volume of air measured from full inhalation to maximum exhalation Total Lung Capacity (TLC): summation of the RV + vital capacity. Lung Volumes Images.google.com

9. Spirometer

10. Spirometry • Forced Vital Capacity (FVC)- Following full inspiration, patient exhales as rapidly as possible, forcibly and completely- volume of air exhaled is measured; takes 5-6 seconds with majority in 1 second. Wide range of normal (see below). • Volume obtained is expressed as a % of predicted normal. Normals are based on volumes obtained from thousands of healthy individuals of similar age, sex, ht and wt and race. Normal 80% of predicted.

11. Spirometry • FEV1:Amount of air forcibly exhaled in the 1st second of the FVC maneuver (80% of FVC volume). Normal 80% predicted; wide range of normal (see below). • Volume obtained is expressed as a % of predicted normal. Normals are based on volumes obtained from thousands of healthy individuals of similar age, sex, ht and wt and race. Normal  80% of predicted.

12. Spirometry • FEV1/FVC: Very important ratio; when reduced, helps identify presence of obstructive disease. Percentage reduction correlates with severity of obstruction; normal is 75-80+%. Normal (or ) in patients with restrictive disease. • Obstructive airway disease: Asthma, COPD. • Restrictive disease: Interstitial lung disease, kyphoscoliosis, pleural disease & others).

13. Peak Expiratory Flow Rate • Measured using simple hand held device. • Occurs within the first milliseconds of forced expiration and is a measure of maximum airflow rate. • Wide variation in normal ranges (age, ht and sex) adult males: 400-700L/minute.adult females: 300-600L/minute. • Effort dependent. • When abnormal- indicator of large airways obstruction.

14. Peak Expiratory Flow Rate • Clinical use: Assessment of patients with asthma. • Patient determines “personal best” PEFR when most healthy, between asthma attacks. • PEFR often precedes symptoms. • Guide for responsiveness to meds, worsening of episodes, when to get help, etc.

15. Diffusion Capacity • Tests gas exchange across the alveolar-capillary membrane. • Per minute transfer of gas- Carbon Monoxide measured from alveoli to blood; DLCO. • Decreased if thickened alveolar capillary membrane (pulmonary fibrosis, ARDS), or following loss of surface area of the alveoli. • Most useful and decreased in interstitial lung disease (lecture to follow). • Normal mean is 25-30 mL/min/mmHg.

16. Application of PFT’s • Obstructive disease: asthma, COPD, bronchiectasis. • Pattern: FVC normal or decreased mildly.FEV1 decreased; reduction reflects severity. • FEV1/FVC decreased- reflects severity. • Response to bronchodilator indicates reversible component.

17. Application of PFT’s • Restrictive disease: pulmonary fibrosis, sarcoidosis, kyphoscoliosis, neuromuscular disease, others. • Pattern: FVC decreased, often markedly.FEV1 decreased, often markedly. • FEV1/FVC normal or increased. • No response to bronchodilator.

18. Problem Solving 22 y.o male with cough, SOB, and wheezing. • FVC – 3.63L (pred), 3.23L (meas), 89% pred • FEV1- 3.24L (pred), 2.24L (meas), 69% pred • FEV1/FVC 69% (meas)Post bronchodilator: • FVC- 3.23L • FEV1- 2.70L (meas) 83% pred • FEV1/FVC 84% (meas) • Interpretation: mild obstructive airways disease with post bronchodilator reversibility. • Diagnosis: Asthma

19. Problem Solving • 45 y.o black man with progressive shortness of breath. • FVC- 3.05L (pred), 0.81L (meas), 22% predicted • FEV1- 2.9L (pred) 0.69L (meas), 24% predicted • FEV1/FVC 97% (meas) • No change post bronchodilator • Interpretation: Severe restrictive disease; no evidence of airway obstruction. • Diagnosis: Sarcoidosis

20. Pulse Oximetry • Measures per cent oxygenation of hemoglobin (oxyhemoglobin). • Non-invasive; measures absorption of light passing through tissue, then calculates O2 saturation of arterial blood. • Measured via electrodes placed on skin- fingertips, ear lobes. • Normal = 97%

21. Arterial Blood Gas Measurement • Requires arterial puncture • pH of arterial blood • PO2: partial pressure of oxygen (mmHg) • PCO2: partial pressure of carbon dioxide (mmHg) • HCO3: calculated- bicarbonate; proportional to dissolved CO2 in blood.

22. O2-Hemoglobin Dissociation Images.google.com