Pulmonary Function Laboratory
Objectives:
Determine your own lung volumes and capacities using spirometry.
Perform and quantify your own forced expiratory and flow-volume maneuver.
Compare your lung static and dynamic pulmonary function results to predicted lung values.
Perform or watch a maximal breathing capacity maneuver.
Examine how PTFs are used to diagnosis restrictive and obstructive lung diseases.
Introduction:
Pulmonary function tests (PFTs) is a battery of studies that include simple spirometry.
Spirometric PFT is a valuable tool to evaluate respiratory function and an important adjunct to
the patient history, lung imaging, and invasive testing such as bronchoscopy and lung biopsy.
The overall approach is to compare the measured values for an individual with normative values
derived from population studies. Therefore, the percent predicted normal is used to define
normal as well as to grade the severity abnormality. Clinicians must become familiar with PFT as
spirometry assesses functional status of the lungs as it relates to:
-how much air volume can be moved in and out of the lungs.
-how fast the air in the lungs can be moved in and out.
-how stiff are the lungs and chest wall – compliance.
-screening for the presence of obstructive and restrictive diseases.
-documenting the progression of pulmonary disease - restrictive or obstructive.
-documenting the effectiveness of therapeutic intervention.
-evaluating patients prior to surgery. Significant reductions in VC (less than 20 cc/Kg of ideal
body weight) indicate that a patient is at risk for postoperative respiratory complications as VC
reflects the patient's ability to take a deep breath, to cough, and to clear the airways of excess
secretions.
Equipment:
The primary instrument used in pulmonary function testing is the spirometer. It is designed to
measure changes in volume and can only measure lung volume compartments that exchange gas
with the atmosphere. Modern spirometers of have pneumotachographs that also measure flow.
Many systems have printouts that show the predicted values next to the observed.
Dynamic Volumes: Definitions–
FVC, after taking in the deepest possible breath, is the volume of air which can be forcibly and
maximally exhaled out of the lungs until no more air can be expired.
FEV1 is air volume forcibly exhaled from the lungs during the1st second of a FVC test.
FEV1/FVC (FEV1%) - % air expelled from the lungs during the 1st second of forced exhalation.
FEV3 - This volume is close to the FVC in the healthy individual.
FEV3/FVC (FEV3%) - % of the total FVC was expelled during the 1st 3 seconds of a FVC test.
PEFR is maximum flow rate achieved during the FVC test. This is a useful measure to see if
treatment improves obstructive diseases like asthma.
PIFR is maximum inspiratory flow rate achieved during a flow-volume loop. This is a useful
measure to see if airway obstruction is anatomically extra- or intrapulmonary.
FEF25%-75% measures volume of air expelled during the middle half of the FVC test. Many
physicians like to look at this value because it is an indicator of obstructive disease.
Slow Vital Capacity (SVC) Test- performed by slowly and completely blowing out all of the air
from the lungs. It eliminates airway compression that accompanies a strong forced expiratory
effort. Hence, VC may be larger after a SVC test because there is little or no airway collapse
during slow expiration. If VC improves, then it can be assumed that a small FVC is caused by
airway collapse and does not indicate the presence of restrictive disease. If VC does not improve
either with the inhalation of a bronchodilator or does not improve with the administration of a
SVC test, then restrictive pathologies must be considered as a possible cause for a small VC
result.
Conditions:
Gas volumes vary with temperature and pressure (Boyle’s law). Therefore the conditions during
which PFTs are measured must be recorded. Today we will not require these conversions. You
will routinely see the conditions abbreviated as:
BTPS body temperature and pressure, saturated.
ATPS ambient temperature and pressure, saturated.
STPD standard temperature (0 ºC), barometric pressure at sea level (101.3 kPa) and dry gas:
Tables of conversion factors between BTPS, ATPS and STPD are available.
Temp.
ºC
16
17
18
19
20
Corr.
factor
1.123
1.118
1.113
1.107
1.102
Gas Volume Conversion:
Conversion from ATPS to BTPS conditions
Temp.
Corr.
Temp.
Corr.
Temp.
ºC
factor
ºC
factor
ºC
21
1.097
26
1.069
31
22
1.091
27
1.063
32
23
1.086
28
1.057
33
24
1.080
29
1.051
34
25
1.074
30
1.045
35
V (STPD) =
BP-47
760
x
273
310
Corr.
factor
1.039
1.033
1.026
1.020
1.013
x V (BTPS)
Measurements:
Each individual should perform the PFTs. Obtain a new mouthpiece and filter for each
individual. Begin this laboratory by selecting a “patient” and a “PFT technician” from your
group. Connect these to the pneumotachograph. The technician has the patient begin by breathing
normally (resting TV) through the pneumotachograph. Begin recording by selecting the start
button on the computer screen. Stop the recording after dozen or so breaths. Highlight from the
volume trace a “typical” TV. Select the magnifier and then with the cursor determine TV and
record its value on the data sheet.
Start recording again. Resume breathing through the spirometer. After several breaths have the
patient passively exhale to FRC by relaxing all muscles of ventilation pausing. Thereafter instruct
the patient to inhale maximally then forcefully and maximally exhale, continuing to exhale for
at least 5 seconds. You may have to practice this maneuver several times before performing it
correctly. Stop the recording. From this series of maneuvers and by knowing the TV above,
determine the patient’s lung volumes and capacities listed below and record them. Highlight
from the volume trace segments of the maneuver that will allow you to determine each variable
listed in the following data table.
Static Volumes - Expressed as liters:
Observed
Predicted
% of Predicted
________________
________________
TV ________________
VC ________________
ERV________________
IRV ________________
IC ________________
RV
________________
TLC
________________
FRC
________________
Use the computer to link with the Johns Hopkins Hospital web site to help determine the
predicted values as well as the equations presented on the following page.
The Johns Hopkins Hospital prediction equations:
VC = 0.1626*Height (inches) - 0.031*Age(years) - 5.335 [Men]
VC = 0.1321*Height(inches) - 0.018*Age(years) - 4.360 [Women]
RV = 0.0687*Height(inches) + 0.017*Age(years) - 3.447 [Men]
RV = 0.0813*Height(inches) + 0.009*Age(years) - 3.900 [Women]
Total lung capacity (TLC) is found by adding predicted values for RV and VC.
FRC = 0.1295*Height(inches) - 5.19 [Men]
FRC = 0.1220*Height(inches) - 5.01 [Women]
Assessing your dynamic lung function:
Consider the first “FVC maneuver” as practice. Now perform a FVC maneuver to analyze your
dynamic lung function. Resume recording but do not have your mouthpiece in place. Inhale
maximally, pause, reposition your mouthpiece and then exhale as forcefully and maximally as
possible. Continue this maximal expiratory effort for as least 5 seconds. The PFT technician
should aggressively encourage the “patient” to continue the maneuver for 5 seconds (like a
cheerleader) while monitoring the expiratory trace. Highlight Channels 1 and 2, then select from
the Spirometry button on the menu. Then select Report and Data Window to determine or
calculate the variables listed below:
Observed
Predicted
FVC
___________
FEV1
___________
________________
FEV1/FVC
___________
________________
FEV3
___________
FEV3/FVC
___________
FEV5
___________
FEV5/FVC
___________
Determination of predicted variables:
FEV1%= 91.4 – (0.2*Age in years)
Predicted values for FEV1 are computed by multiplying the predicted FEV1% by the
predicted FVC.
Flow-Volume Loop:
Breathing normally for several tidal breaths, then inspire forcibly and maximally then expire
forcibly and maximally repetitively for about 5 cycles. Stop the maneuver. Highlight Channels 1
and 2 over several tidal breaths and the forced inspiratory and expiratory cycles. Select the FlowVolume under Spirometry on the menu. Examine the trace. Use the cursor to determine the
variables:
PEFR_______________.
PIFR________________.
Which has the greatest flow rate: inspiration or expiration?________________.
What is your VC during this maneuver?__________________.
What percentage is it of your VC determined above?_________________.
Contrast the inpiratory and expiratory flow profile. List several reasons why the expiratory phase
flow rate decreases as trace progress from TLC to RV:
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Determine a Subject's MBC (MVV) _____________________________________________
Maximal Voluntary Ventilation (MVV) is determined by having an individual breathe in and out
as rapidly and forcefully as possible for 10, 12 or15 seconds but blowing only into a measuring
apparatus (not inhaling air form it). This test reflects the status of the respiratory muscles,
compliance of the thorax-lung complex and airway resistance. Surgeons like this test value
because it is a quick and easy way to assess the strength of the patient's pulmonary musculature
prior to surgery. A poor performance on this test suggests that the patient may have pulmonary
problems postoperatively due to muscle weakness. One major cautionary note is that this test is
effort dependent and therefore can be a poor predictor of true pulmonary strength and
compliance. Consider what effect expiring pain during this maneuver will have on its results.
_____________________________________________________________________________
_____________________________________________________________________________.
Notice the apnea after this maneuver of hyperventilation. It is call apnea vera.
Caution: One may become light headed or may faint. Take the necessary precautions.
Discussion:
Pulmonary function abnormalities can be grouped into two main categories: obstructive and
restrictive defects. This grouping of defects is based on the fact that the routine spirogram
measures two basic components - air flow and volume of air out of the lungs. Generally the idea
is that if flow is impeded, the defect is obstructive and if volume is reduced, a restrictive defect
may be the reason for the pulmonary disorder.
Obstructed Airflow: Flow can be reduced for a number of reasons:
-narrowing of the airways due to bronchial smooth muscle contraction as in asthma
-narrowing of the airways due to inflammation and swelling of bronchial mucosa and the
hypertrophy and hyperplasia of bronchial glands as in bronchitis
-material inside the bronchial passageways physically obstructing the flow of air as in excessive
mucus plugging, inhalation of foreign objects or the presence of invasive tumors
-destruction of lung tissue with the loss of elasticity and hence the loss of the external support of
the airways as in emphysema
-external compression of the airways by tumors and trauma
Restricted Airflow "Restriction" in lung disorders always means a decrease in lung volumes.
There are a variety of restrictive disorders:
-Intrinsic Restrictive Lung Disorders: sarcoidosis, tuberculosis, pnuemonectomy (loss of
lung), pneumonia
-Extrinsic Restrictive Lung Disorders: scoliosis, kyphosis, snkylosing spondylitis, pleural
effusion (fluid in the pleural cavity), pregnancy, gross obesity, tumors, ascites, pain on
inspiration - pleurisy, rib fractures
-Neuromuscular Restrictive Lung Disorders: generalized weakness – malnutrition, paralysis
of the diaphragm, myasthenia gravis, muscular dystrophy, poliomyelitis, amyotrophic lateral
sclerosis - Lou Gerig's disease
The PFT Before and After Aerosol Bronchodilators
Patients are almost always tested twice - once before bronchodilators are given and once after.
This assesses the reversibility of the airway obstruction. A Beta-2 selective sympathomimetic is
nearly always used is. If two out of three measurements improve FVC increases10% or more,
FEV1 increases 200 ml or 15% of the baseline FEV or FEF25% - 75% increases 20% or more;
then it can be said that the patient has a reversible airway obstruction that is responsive to
medication.
A Systematic Way To Interpretation
Step 1. Look at the forced vital capacity (FVC) to see if it is within normal limits.
Step 2. Look at the forced expiratory volume in one second (FEV1) and determine if it is
within normal limits.
Step 3. If both FVC and FEV1 are normal, then you do not have to go any further - the
patient has a normal PFT test.
Step 4. If FVC and/or FEV1 are low, then the presence of disease is highly likely.
Step 5. If the %predicted for FEV1/FVC is 88%-90% or higher, then the patient has a
restricted lung disease. If the %predicted for FEV1/FVC is 69% or lower, then the patient has
an obstructed lung disease.
How Do You Tell If The Patient Is Normal or Has Mild, Moderate or Severe Pulmonary
Disease?
There are a number of systems which physicians use to determine the severity of disease. Here is
one that is commonly used:

Mild: FVC % or FEV1 % is 60-79% of predicted and FEV1/FVC % is 60-69% of
predicted

Moderate: FVC % or FEV1 % is 40-59% of predicted and FEV1/FVC % is 40-59% of
predicted

Severe: FCV % or FEV1 % is40% or less of predicted and FEV1/FVC % is 40% or less
of predicted
Questions:
1. Name the major muscle groups involved in inspiration and expiration.
2. Name which volumes and capacities cannot by measured by spirometry.
3. What is the difference between a volume and capacity?
4. What causes apnea vera after a MVV maneuver?
5. Give 2 reasons why vital capacity and MVV decrease with age.