Pulmonary Function Testing

Sandra B. Weibel MD

Thomas Jefferson University

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– 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

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– 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 – 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