Pulmonary Function Testing Sandra B. Weibel MD Thomas Jefferson University

Objectives To review the basic principles of performing lung function studies and the physiology To understand the calibrations and to be able to assess that lung function studies are performed according to standards To understand basic interpretation

Indications Differential diagnosis of dyspnea Provides objective assessment of symptoms versus severity Determine fitness for surgery To guide therapy To follow the course of a disease

Physiologic classification of disease Obstructive Impairment- Airway limitation due to the resistive properties of the respiratory system Restrictive Impairment- Loss of volume capacity of the lung due to loss of air space units or inability to expand the respiratory system

Obstructive Processes L ocal obstruction A sthma C hronic bronchitis (COPD) E mphysema

Restrictive Processes P leural disease A lveolar filling processes I nterstial lung disease N euromuscular diseases T horacic cage abnormailites

Spirometry Most widely performed study and is important in initial screening of patients Easily and quickly performed in many settings

Types of spirometers Types include flow (pneumotach) or volume (water seal, rolling and diaphragm) Water seal device previoisly most commonly used in pulmonary function labs of the volume Collect exhaled gas and act as a reservoir for inhaled gas Composed of a mouthpiece, bell system and a pen on a rotating drum

Volume Displacement Spirometer

Flow Spirometry

Calibration of spirometer Warmed up and temperature controlled Barometric pressure and temperature recorded Volume calibration with 3L syringe (within 3%) Flow spirometer tested at 3 flow rates between 2 and 12L

Quality Control

Prior to testing

Performing the maneuver It is a forced expiratory maneuver and the patient must be sitting upright in a chair with lips around a mouthpiece After a maximal inspiration, a forced and rapid expiration is made Quality of the maneuver needs to be assessed noting that the patient started at zero, had a maximal initial efffort and lasted 6 seconds.

Measurements FVC FEV1 FEV1/FVC Also FEF25-75 and TET

FVC Measurement

FEV1 Measurement

Flow volume

Interpretation First need to assess the quality of the maneuvers Choice of reference values Use of LLN Compare to previous tests Race adjustments

Interpretation Restrictive Lung Obstruction FVC AND FEV1 decreased FEV1/FVC normal FEV1 main distinguishing feature Obstruction FEV1 decreased FVC Normal FEV1/FVC are low

Pitfalls in Interpretation Predicted need to fit your population Non Caucasians have lower lung volumes and this may need to be addressed Prior to interpretation the test needs to be assessed to see if it meets standards Machines need to be calibrated daily to ensure accuracy

Effort

Poor effort

Interpretation The patient’s data is compared to predicted Predicted values are obtained after studying populations of normal nonsmokers and then regression equations developed Regressions are based on sex, height, and age.

Predicted Values

Decline in PFTS

References Many different ones used in past Knudson Crapo etc Current recommendation is NHANES III This studied over 7000 individuals Included Caucasians, blacks and Mexican Americans

Interpretaion Normal is > 80% of predicted Mild impairment 65-79% Moderate 50 -64% Severe < 50%

Interpretations

Flow Volume Loops Inspiratory loops can also be obtained to evaluate for the presence of large airway obstruction Theory changes in pressure outside and inside the thoracic cage will cause changes in airway diameter These airway changes can cause a limitation to airflow if large enough

Extrathoracic Obstruction

Intrathoracic Obstruction

Fixed Obstruction

Large Airway Obstruction

Bronchodilator Response

Bronchodilator testing No short acting agents for 4 hrs No long acting beta agonists for 12 hrs No theo for 12 hrs No smoking for 1 hr Beta agonist given recommended 4 puffs and wait 10-15 minutes later

Performance of the Maneuver

Peak Flow Measurements Convenient portable device for measuring peak expiratory flow in l/min May be less reliable than spirometry but easy to use and inexpensive Useful to follow the course of asthma and to possibly look and work exposure Technique

Lung Volumes May be measured by multiple methods Is important to understand what volumes the lung is composed of The total volume of the lung is TLC The subdivisions include ERV, IRV, TV,and RV Capacities are composed of 2 or more volumes.

Helium Dilution Technique Uses an inert gas, helium and by a closed circuit technique, allow it to come to equilibrium and FRC is measured May underestimate lung volumes in bullous lung disease

Lung volume measurements FRC is directly measured as well as SVC Other volumes and capacities can be calculated Lung volume measurements are important to confirm RLD TLC and RV the usual volumes assessed

Nitrogen Washout Determine FRC by multiple breath open circuit nitrogen washout Involves having nitrogen in patients lung being washed out by inhaling 100% O2 for several minutes. Widely used, easy to perform but may underestimate bullous lung disease

Nitrogen Washout Performed by having the patient breath comfortably for several minutes and then turn in to 100% O2 at FRC. Monitor N2 concentrations and test ends when falls below 1% Easy to see leaks

Nitrogen Washout Concept is C1V1= C2V2 C1 = Nitrogen concentration at the start of the test V1 = FRC volume C2 =N2 concentration in exhaled volume V2 = Total exhaled volume during O2 breathing period Nitrogen is measured by photoelectric principle

Body Plethsymography Is a sealed box with a fixed volume Uses Boyle’s Law that changes in pressure are brought about by changes in volume for the person seated in the box P1V1= P2V2

Body Plethysmograph

Lung volume measurements FRC is directly measured as well as SVC Other volumes and capacities can be calculated Lung volume measurements are important to confirm RLD TLC and RV the usual volumes assessed

Interpretation RLD OLD TLC is reduced in all Predicted values and interpret same as FVC and FEV1 OLD TLC can be increased and is then called hyperinflation (120%) RV can be increased in asthma and COPD indicating air trapping

Diffusing Capacity Provides information about the transfer of gas between the alveoli and the pulmonary capillary bed It is the only noninvasive test of gas exchange Performed by a single breath technique and uses CO as the inert gas

Diffusing Capacity Diffusion of a gas is dependent of the area, the concentrations, the thickness of the membrane and the diffusing properties of the gas Diffusion is the rate at which a gas is transferred across the alveolar capillary membrane, the plasma, the RBC and ultimately combined with Hgb

Diffusing Capacity CO is typically used because it is freely diffusable It usually is not present in significant amounts in the blood except in some heavy smokers Helium or methane is also used to measure volume A single maximal inspiration is taken and held for 10 sec

Diffusing Capacity Normal result is >80% Can be reduced in interstitial diseases such as sarcoid or asbestosis Can be reduced also in emphysema or pulmonary vascular diseases False low measurements in anemia or lung resection and elevated in alveolar hemm

Summary Spirometry- Most commonly performed and useful screening test. Lung volumes- Can be measured several different ways. Are used to evaluate for restrictive disease and will also show air trapping Diffusing Capacity - Transfer of gas across the alveolar membrane

Selecting Tests Who should get what test Who cannot get certain tests Which method of lung volume testing Inpatients

Case 1 A 25 year old female comes to your office complaining of chest tightness and shortness of breath with running. Exam is normal What tests would you order?

Spirometry Pre Post FVC 2.64 90% FEV1 1.83 79% FEV1/FVC 69 TET 5.0 FEFmax 4.85 L/S Post 3.12 106% 2.21 95% (18%) FEV1/FVC 71 TET 5.5 FEFmax 5.02 L/S

Case 2 A 58 year old male presents to office complaining of dyspnea on exertion over the last 6 months. He has a dry cough but no other complaints. He has smoked 1ppd for 35 years and works in construction.

PFTS FVC 1.43 48% FEV1 1.30 57% FEV1/FVC 91 TLC 3.05 63% RV1.53 68% Dsb 5.78 24% Dsb(adj) 7.8 33% VA 2.3 42% D/VA 2.51 57% Hsb 11.4

Causes of Hypoxemia Hypoventilation Elevated altitude Shunt V/Q mismatch Impairment of diffusion

Hypoxemia Daltons Law In a gaseous mixture the partial pressure of each gas in the mixture is independent of the other gases and the total pressure of the mixture is equal to sum of all the gases and must equal barometric pressure PB=PA=PN2+PH2O+ PO2 +PCO2

Alveolar Oxygen

Hypoxemia Nitrogen concentration is fixed and minimal variation in water vapor pressure PA (alveolar pressure) is mainly determined by PCO2 and PO2 and there is an inverse relationship pAO2 = (PB- PH2O) x FiO2 - PaCO2/R From this can calculate PA-a gradient Normal 10-20

V/Q Mismatch

Hypoxemia Calculate A-a gradient if normal than hypoventilation or altitude If >20 then V/Q mismatch, shunt or diffusion Shunt does not respond to O2