BIO
1.
Students will learn how to perform various tests of pulmonary function such as the forced expiratory vital capacity (FVC) test, the slow expiratory vital capacity (SVC) test, and the maximal voluntary ventilation (MVV) test.
2.
Students will also practice evaluating the results of the various pulmonary function tests.
Spirometry is the measurement of lung volume changes during specific breathing maneuvers. In this laboratory this will be done using the Koko Spirometer , which is a sophisticated pneumotachometer and associated software used for quantifying air volumes and flow rates. The
Pneumotachometer, or pneumotach , is the device through which you will inhale from and exhale into, using a specially designed and presterilized mouth filter.
During the various breathing maneuvers the pneumotach sends a signal to the connected laptop computer which has the Koko Spirometry Software . This software enables the computer to evaluate and eventually store patient information and data from the various breathing maneuvers. Since these breathing maneuvers are used for analysis, they are also referred to as “tests”.
The data, depending on the breathing maneuver, can be analyzed and expressed in graph form as the volume of air inhaled versus time, or the volume of air exhaled versus time. This type of graph is a classic spirogram . In addition, the Koko Spirometer System can also express the data in two other ways. One way the data can be expressed is as a graph of air flow versus time. Air flow is a rate measurement expressed as liters per second (L/s). It is the velocity of air flow either for expiration or inspiration, depending on the maneuver. Another way the data can be expressed, is as a flowvolume curve . In a flow-volume curve the horizontal axis marks the volume, (liters) and the vertical axis marks the flow rate (or simply the flow, L/s). In other words, the flow-volume curve shows how the velocity of air movement, either into or out of the lungs, varies after different volumes have been either inspired or expired. It demonstrates that the flow rate decreases rapidly the greater the volume of air exhaled from the lungs. The shape of the curve on this graph varies between normal individuals and those with various pulmonary disorders (to be discussed later).
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SPECIFIC BREATHING MANEUVERS (TESTS)
A) The FVC Test
The most commonly used, and most powerfully predictive test, in general, is the Forced
Expiratory Vital Capacity (FVC) test. In this test, the subject inhales as much as possible, and then exhales as much and as fast as possible. In other words, the subject makes a maximal inspiration followed by the most rapid and complete expiration the subject can make.
It is important that in the lab groups, one student should serve as a coach to encourage the subject to make a maximal expiratory effort, and to keep on exhaling until absolutely no more air can be expelled. During expiration in this, and other tests, the subject must be careful not to inhale or exhale nasally.
Many parameters can be calculated from this one maneuver. These include the FVC, FEV1,
FEV1/FVC ratio, PERF, and PIRF. The FVC is the vital capacity measured using this technique
(the forced expiratory vital capacity). Recall that vital capacity is the sum of the tidal volume, and inspiratory and expiratory reserve volumes. The FEV1 is the forced expiratory volume measured at the one second point into expiration. The FEV1 can be considered both as a volume and as an average flow rate over the first one second of forced expiration. Another important parameter is the
FEV1/FVC ratio which is usually expressed as a percent. Typical values for this ratio are somewhere between 70 to 80%. The PERF is the peak expiratory flow measured in liters per second (L/s). This is the value for the highest flow rate measured in this maneuver. Similarly, the
PIRF is the peak inspiratory flow rate measured in this maneuver, which again is expressed as liters per second (L/s).
One last, but extremely important piece of information this test provides is the shape of the flowvolume curve. There are two “halves” to this flow-volume curve – a top half above the horizontal axis, and a bottom half below the horizontal axis. Together, these two halves make up what is called the Flow-volume Loop . The top half of the loop shows how the rate of flow for expiration changes at different volumes, whereas, the bottom half of the loop shows how the rate of flow for inspiration changes at different volumes. An example of this FVC Flow versus Volume graph is shown below. Note that, by convention, the expiratory flow rate values are positive, and the inspriatory air flow values are negative. Also note, that the horizontal axis represents positive values (liters), which are relative to expiratory volumes. The curve on the graph moves from left to right during expiration until the maximal expiratory volume is reached. Then, when the subject inhales, the curve moves back toward zero (right to left) since the expiratory volume is “taken back”, and it does this below the horizontal axis. The shape of the flow-volume curve is very useful for evaluating obstructive and restrictive pulmonary diseases.
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Expir
Flow
(L/s)
Inpir
Flow
(L/s)
Figure 1 Typical Flow-Volume Curve
The FVC test is so frequently used because of its high sensitivity toward detecting diseases that affect the mechanical aspects of lung function such as emphysema, chronic bronchitis, and asthma.
B) The SVC Test
Another test involves having the subject both inhale and exhale maximally, but slowly. This is called the Slow Vital Capacity Test ( SVC ). Usually the SVC and FVC are very similar, however in cases of airway obstruction, such as asthma, the FVC can be considerably smaller than the SVC due to bronchial constriction during forced expiration. The curve to be generated here in this test is
SVC Volume versus Time .
C) The MVV Test
In the test for the Maximal Voluntary Ventilation ( MVV ), the subject breathes in and out repeatedly as hard and as fast as possible for about 15 seconds. This test is not very specific for any particular pulmonary disorder, but it does correlate well with the subject’s exercise capacity. In other words, subjects who are in better cardiovascular condition usually perform better than those
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who are not in good condition. The curve to be generated here in this test is MVV Volume versus
Time .
FACTORS AFFECTING THE RESULTS IN NORMAL SUBJECTS
There are a variety of factors that can affect the FVC, SVC, and MVV test results. Some of these are listed below.
(i) FVC and FEV1 values in adults decline with increasing age.
(ii) Most spirometric values increase with increasing height.
(iii) Spirometric values tend to decrease with increasing obesity.
(iv) Spirometric values are usually lower in women than in men of equal size.
(v) There are also race differences due to different ratios of height to lung volumes.
TYPICAL FLOW-VOLUME LOOP CURVE PATTERNS IN DISEASE
The purpose of this laboratory is to help the student learn about parameters and flow-volume loops obtained from normal-healthy individuals. Nonetheless, information is provided below to illustrate the power of this technique in evaluating problems in pulmonary function.
Flow-volume loops show distinct shapes for people with obstructive and restrictive pulmonary diseases compared to those from healthy people. In people with obstructive defects there is a decrease in the maximal expiratory flow such that rapid emptying of the lung is not possible. This results in an expiratory curve (of the flow-volume loop) which decreases in a concave fashion.
Usually, this defect is also associated with a decrease in the forced expiratory vital capacity (FVC).
This is shown below in the graph on the next page. Examples of obstructive defects are emphysema, chronic bronchitis, and asthma.
A restrictive defect is one where the FVC is reduces by congestive heart failure, lung resection
(partial removal of a lung), a lung tumor, an enlarged heart, pregnancy, obesity, or neuromuscular disease (among others). This defect is associated with an expiratory curve (of the flow-volume loop) that decreases rapidly with a greater slope than normal. This is shown in the illustration below.
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Figure 2. Typical Flow-Volume Curve Patterns for Normal Individuals, and
Individuals with Obstructive Pulmonary Disease or Restrictive Pulmonary Disease
The table below is provided to show how the different parameters of pulmonary function testing vary with different diseases compared to normal results.
Table 1. Changes in Pulmonary Function Tests in Disease
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PROCEDURE
A. How to Connect the Laptop and Pneumotach and Calibrate the Instrument.
B. How to Get Started and Create a Patient (Student) Record
1.
Double click on the “Koko PF Testing” icon.
2.
The main menu will then appear on screen.
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Click on the male/female icon on the left. The “Enter/Edit Patient Information” window will appear.
4.
At the bottom left under Patient, click “New…”
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Enter the student information. ( You can ignore Diagnoses and comments .)
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When finished, click “OK”
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Enter information for every other student in your group that will perform the tests.
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Then click “Close” at the bottom.
C: How to perform the FVC Test (forced expiratory vital capacity)
1.
Click on the “FVC” icon
2.
Click on the “male/female” icon. Select the student to be tested. (To bring up the student, you may need to enter the last name and click “Show all matches”.)
3.
Click “Close”.
4.
When you are ready to start the test click on the green button and then click “OK” for the previously entered pneumotach environment values.
5.
Follow the instructions as they come up on the screen. (Again, the subject must be careful to not breath nasally in this or any of the other tests.)
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Once the student has done the test successfully (the screen will let you know if you did the test correctly), you can save the efforts by clicking “Yes” when asked.
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Save results on the hard drive of the laptop by clicking on the disc icon (fifth icon from right).
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To perform the FVC test on another student click the male/female icon, enter the last name, press “Show all matches” and then press “OK” at the bottom.
9.
To exit this test, click on the upper right corner [X].
Printing should be done after all the tests (FVC, SVC, and MVV) are completed and stored on the hard drive of the laptop computer.
NOTE: You can use the incentive graphic by pressing on the incentive icon (the kite). If the FVC test were done in a clinical setting, the clinician would verify that the two best FVC and FVC1 tests gave values within 5% of each other. It is not necessary to do this in this laboratory.
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D: How to perform the SVC Test (slow vital capacity).
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Click on the “SVC test” icon
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Click the “male/female” icon and select the student as you did before.
3.
When ready to perform test, click on the green button, and follow the instructions.
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Save your data as you did before.
5.
To exit this test, click on the upper tight corner [X].
E: How to perform the MVV Test (Maximum Voluntary Ventilation)
1.
Click on the “MVV test” icon.
2.
Click the “male/female” icon and select the student as you did before.
3.
When ready to perform test, click on the green button, and follow the instructions.
Remember that the subject will be repeatedly inhaling and exhaling as deeply and quickly as possible.
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Save your data as you did before.
5.
To exit this test, click on the upper tight corner [X].
F: Printing Results.
1.
The printer port and the pneumotach port in the laptop are the same, so first carefully remove the pneumotach cable from the laptop computer.
2.
Put the pneumotach back in its box.
3.
Carefully connect the printer cable to the same port in the laptop computer.
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Go to the main menu of the Koko Spirometry software and click on the “printer” icon.
5.
Toward the bottom it should say that the printing option is a “202 Report”. If it doesn’t, you have to press “select report design” and then select the “202 Report”.
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Now press the “Print” button.
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It takes about 6 minutes to print the two pages of each report.
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After all reports have printed, carefully disconnect the printer cable from the laptop computer and inform the instructor that the units are ready to be put away.
1. Interpretation of Pulmonary Function Tests: A Practical Guide. Eds Hyat, Scadon , and
Nakamura (1997)
2. Pulmonary Function Testing: A Guide for the Student and House Officer. Edited by A. Miller
(1987)
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