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Chapter 6

PFTs for the PCP: Part 1

Nirav Shah, MD, Paul Simmons, MD, and Neda Frayha, MD
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19:07

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PFTs? Easy as ABC! Pulmonologist Dr. Nirav Shah is back, this time walking Neda and Paul through pulmonary function tests in a super clear, straightforward way.

Pearls:

  • In-office spirometry is a great first step to understanding undifferentiated dyspnea, followed by PFTs and referral to pulmonology.
  • Cardiopulmonary exercise testing (CPET) is another diagnostic tool after PFTs that gives dynamic cardiac and pulmonary function information.

 

  • Pulmonary Function Tests (PFTs) components:

    • Spirometry- how much air gets into and out of your lungs

    • Lung volumes - how much air fits into your lung

    • Diffusion capacity - how well your lung exchanges oxygen and carbon dioxide
  • When to get them?

    • Unexplained shortness of breath, cough, wheezing

  • Categories of disease that PFTs help understand:

    • Obstructive lung disease (asthma, COPD)

    • Restrictive lung disease (idiopathic pulmonary fibrosis or interstitial lung diseases, scoliosis)

    • Diffusion limitations (COPD, interstitial lung disease)
  • Office-based spirometry:

    • Can be done in the office and they are pretty good at ruling out abnormality. However, interpretation of individual numbers (and not just the ratio) is important. If spirometry looks off then go to formal PFTs.

    • Steps:

      • 1. Hold a mouthpiece in the mouth while plugging the nose

      • 2. Take normal breaths on the spirometer to get the tidal volume

      • 3. Take a big breath in and then exhale as forcefully as you can to get the forced vital capacity
      • ** You can always redo it, so there is no messing up! **

  • Plethysmography:

    • Used to determine the total lung volume

    • The patient sits in a glass box so that you can calculate how much air is in the box and how much is being displaced → the residual volume is in their lungs
    • Good to let patients know they will be in a closed space if they have any issues with claustrophobia

    • Other ways to measure if they can’t tolerate the glass box:

      • Helium dilution- patient breaths in a known concentration of helium and the spirometer measures the new concentration of helium. The leftover is the residual lung volume

      • Nitrogen washout- similar to helium dilution in that a known concentration of nitrogen is inhaled and then exhaled. The difference is used to calculate residual lung volume

    • With lung volumes, if the FVC is lower than expected this should be a tip-off that total lung volumes may also be abnormal and the patient has a restrictive lung disease

  • Diffusion capacity:

    • Determined by the alveolar-capillary membrane

    • Things that affect this membrane:
      • Alveolar scarring - idiopathic pulmonary fibrosis or interstitial lung disease

      • Decreased alveolar volume - emphysema leading to the reduced surface area

      • Capillary - pulmonary hypertension because the capillary gets thickened

  • Interpreting spirometry:

    • Flow-volume loops:
      • The upper half is exhalation

      • The bottom half is inhalation
      • Variability in the overall shape of the curve can help identify obstructive vs. restrictive processes as well as a variable or fixed obstruction

      • Obstructive pattern: looks like a scooped out chair. A more severe pattern will have a lower back to it.

      • Restrictive pattern: squished egg shape

    • Interpreting the numbers:

      • Look at the loops first to give you a sense of what you might be looking for

      • FEV1/FVC ratio < 70% → obstructive
        • If total lung capacity is >120% predicted (based on demographics) = obstructive (hyperinflation)

      • FEV1/FVC ratio >= 100% + total lung capacity < 80% → restrictive

  • Prepping your patient for PFTs:

    • They may have lightheadedness and that’s to be expected

    • Review the process with them

    • Abstain from short-acting bronchodilator 4 hours prior to the PFTs because the test may actually want to look at the pre-and post-bronchodilator response

    • If they are only a daily or twice daily LABA or LAMA, hold it for 12-24 hours

  • Cardiopulmonary exercise testing (CPET):

    • Useful after PFTs, cardiac echo and maybe a trial of medication and still no improvement in dyspnea

    • In the test, the patient exercises while being connected to a device the measures oxygen consumption and CO2 production

    • Generally ordered by a pulmonologist

 

References:

  1. Coates AL, Tamari IE, Graham BL. Role of spirometry in primary care. Can Fam Physician. 2014; 60(12):1069–1077.
  2. Gabrovska M, Bourgeno HA, Ninane V. Contribution of four pulmonary function tests to diagnosis in primary care. European Respiratory Journal 2018; 52 (suppl 62) PA4198; DOI: 10.1183/13993003.congress-2018.PA4198
  3. Joint Statements on Lung Function Testing by the American Thoracic Society and European Respiratory Society:
  4. Miller MR, Crapo R, Hankinson J, et al. General considerations for lung function testing. Eur Respir J. 2005; 26(1):153-161.
  5. Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005; 26(5):948. 

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