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Interpretation of PFT's

VIEWS: 403 PAGES: 6

									                            INTERPRETATION OF PFTs
                               Francis W. Chan, M.D.
                                      Week 16

Educational Objectives:

        1. Understand the physiologic basis of the measurements obtained during PFT testing
        2. Develop strategies to interpret PFTs for obstructive and restrictive diseases
        3. Interpret mixed obstructive/restrictive findings on PFTs


Note:

The lung volumes and % predicted values may not be accurate in comparison to the true
published matched patient age/sex values. The values should merely be used for the problem
solving exercise.

CASE ONE:

A 39-year-old woman with no significant PMH now presents to your office with a three-
month history of cough and episodic shortness of breath at night. She is a lifetime non-
smoker and has been very active, running three days a week. Her exam is significant for a
normal cardiac exam with no murmurs or gallops and lungs that are clear to auscultation
bilaterally. She appears comfortable with a RR 12 and O2sat of 99% RA.


Questions:

   1. What is on your differential diagnosis for her presentation and symptoms?
      Ultimately, what do you think is her most likely diagnosis?
      The differential for chronic cough includes asthma, postnasal drip (now referred to
      Upper Airway Cough Syndrome), GERD, post URI cough, ACE inhibitor use, chronic
      bronchitis, bronchiectasis, or lung cancer. Her other symptoms of nocturnal SOB are
      suggestive of either a cardiac etiology such as CHF or pulmonary etiology such as
      asthma. Based on her history of chronic cough, nocturnal SOB, and good exercise
      tolerance, the most likely etiology for her dual symptoms is asthma.
CASE ONE CONTINUED:

She is sent for PFTs, and her values are as follows:
                      Pre-bronchodilator     % Predicted   Post-bronchodilator   % change

FVC                           2.4                85                2.7               12

FEV1                          1.5                63                2.0               34

FEV1/FVC                      58%                                  75%               29

DLCO                                             99


   2. Qualitatively describe the FVC (forced vital capacity), FEV1 (forced expiratory
      volume in 1sec), FEV1/FVC ratio, TV (tidal volume), RV (residual volume), and
      TLC (total lung capacity). What do each of these terms mean?
      FVC                  The largest amount of air that can be expired after a maximal
                           inspiratory effort.
      FEV1                 The volume of air expired in the first second of an FVC maneuver
      FEV1/FVC ratio       The fraction or percentage of the FVC volume that can be blown
                           out in the first second of the FVC maneuver. The normal range in
                           a healthy adult is 75-80%.
      TV                   The amount of air that moves into the lungs with each normal
                           inspiration/exhalation.
      RV                   The volume of air remaining in your lungs after a maximal
                           expiratory effort.
      TLC                  The total volume of air in your lungs. (FVC + RV = TLC)

       See diagram on following page.
:

    3. What is her diagnosis? Based upon what?
       The patient has asthma. By the ATS guidelines, she has a significant bronchodilatory
       response (an increase in either FVC or FEV1 of 12% or more AND a 0.2L or more
       increase from her baseline).

CASE TWO:

A 59-year-old woman with SLE and a history of tobacco use (10 pack-years) presents with
SOB of two months duration with no associated cough, no orthopnea or paroxysmal
nocturnal dyspea (PND), and no lower extremity swelling. Her exam is significant for dry
crackles bilaterally. She is sent for PFTs, and her values are as follows:
                      Actual        % Predicted

FVC                    2.0             62
FEV1                   1.7             71
FEV1/FVC              85%
RV                    1.0              42
TLC                   2.9              57
DLCO                                   65
   4. What type of lung physiology does this patient have? Upon what do you base this
      interpretation?
      She has a restrictive defect with significantly decreased diffusion capacity. By the
      suggested ATS/ERS guidelines and algorithm for evaluating PFTs, any patient with a
      diminished FVC and TLC has restrictive disease. Her diminished FVC at 62% of
      predicted indicates restrictive physiology which is further confirmed by her TLC that is
      57% of predicted. Her preserved FEV1/FVC ratio does not suggest obstruction. Her
      lung disease is likely due to longstanding SLE.

CASE THREE:

A 65-year-old man with a history of tobacco use (50 pack-years) presents with worsening
SOB of three to four months duration. He has an associated cough that is worse in the
mornings, no orthopnea or PND, and no lower extremity swelling. He used to work in
construction. His exam is significant for a benign cardiac exam and bilateral dry crackles
with scattered expiratory wheezes. He smells of cigarettes. He is sent for PFTs, and his
values are as follows:
                     Actual       % Predicted
FVC                  2.3            65
FEV1                 1.4            70
FEV1/FVC             61%
RV                   1.6
TLC                  2.9            62
DLCO                                58


   5. What type of lung physiology does this patient have?
      This patient has a mixed obstructive and restrictive physiology with significantly
      decreased diffusion capacity. In looking at his FEV1/FVC ratio we see that it is
      decreased at 61%, suggesting an obstructive picture. In a typical isolated obstructive
      defect, the FEV1/FVC ratio is decreased primarily due to a decreased FEV1 with a
      relatively normal FVC and a normal to increased TLC (due to air trapping). In this
      patient, the FVC is also significantly decreased to 65% of predicted. Furthermore, if you
      also look at the patients TLC, it is also decreased at 62% of predicted. The decreased
      FVC and TLC suggest a restrictive defect superimposed on the obstructive physiology.
CASE FOUR:

A 38-year-old man with no PMH presents with recurrent episodes of SOB over the past one
to two months. He is a lifetime smoker since age 15 and has smoked between one and three
packs per day. His exam is significant for a benign cardiac exam and diffuse wheezes
bilaterally. You have access to PFTs in the office, and you send him straight for evaluation.
His results are:

              Actual                % Predicted
FVC           2.7                   74
FEV1          2.1                   80
FEV1/FVC      78%
TLC           4.7                   101
DLCO                                85


   6. What is his lung physiology?
      This patient has an obstructive physiology. On first glance, his FEV1/FVC ratio is
      normal. However, his FVC is decreased to 74% of predicted. This might otherwise be
      suggestive of a restrictive defect except for the fact that he has a normal to increased
      TLC. In this scenario, his FEV1/FVC ratio is within normal range due to a simultaneous
      decrease in both the FEV1 and FVC. In going back to the answer from Question #2, the
      TLC = FVC + RV. If the TLC is normal (or slightly increased) and the FVC is
      decreased, this must mean that the RV has increased. This represents air trapping. In
      summary:
          his FEV1 is decreased, suggesting obstruction
          his TLC is normal, arguing against restriction
          his FVC is decreased due to the relative increase in his RV, which is suggestive of
             air trapping.

        Therefore, he has obstructive disease with a decreased DLCO likely due to his tobacco
       use. See the algorithm on the following page.

Primary References:

   1. Figure 2 from Pellegrino R et al. European Respiratory Journal. 2005.
   2. Evans SE and Scanlon PD. Current Practice in Pulmonary Function Testing. Mayo
      Clinic Proc. 2003; 78: 758-763.

Additional References:

   1. Ganong WF. Review of Medical Physiology, 22nd Ed.
   2. Pellegrino R et al. Interpretive strategies for lung function tests. ATS/ERS Task Force:
      Standardization of Lung Function Testing. European Respiratory Journal. 2005; 26:
      948-968.
Pellegrino R et al. Eur Respir J 2005

								
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