Prepare for the PANCE with this comprehensive topic on pulmonary function testing (PFT) in asthma assessment. Follow the case of a 29-year-old man presenting with dyspnea and dry cough, with a history of childhood asthma. Explore the vital signs, lung auscultation, and laboratory findings to determine the most likely PFT results for this patient. Ideal for physician assistant students and professionals seeking a deeper understanding of PFT interpretation and its significance in diagnosing and managing respiratory conditions. Ace your PANCE exam and excel in clinical practice with this valuable resource.
A 29-year-old man presents to the primary care clinic due to two months of mild intermittent dyspnea and dry cough. The patient was diagnosed with mild intermittent asthma as a child based on symptoms and previously used an albuterol inhaler when playing outside or playing sports, but has not used an inhaler during the last ten years. Vital signs are within normal limits. Lung auscultation demonstrates diffuse wheezing and decreased air movement bilaterally. Serum white blood cell count is 7,000/mm3 (4,500-11,000/mm3) and hemoglobin is 14.5 g/dL (13.5-17.5 g/dL). Which pulmonary function test (PFT) findings would most likely be found in this patient?
A. Decrease in FEV1 following methacholine administration
B. Increase in FEV1 from 400 mL to 420 mL following albuterol administrationC. DLCO of 110% with normal PFTs
D. DLCO of 75% with normal PFTsE. Flattened flow-volume loop in inspiration and expiration
Scroll down to find the answer!
The correct answer to today’s PANCE® Question is…
A. Decrease in FEV1 following methacholine administration
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s PANCE® Question are…
B. Increase in FEV1 from 400 mL to 420 mL following albuterol administration
Incorrect: Asthma is diagnosed if the FEV1 improves by ≥12% following bronchodilator therapy.
This degree of response of 5% is inadequate to diagnose asthma and would require further testing.
C. DLCO of 110% with normal PFTs
Incorrect: An isolated increased DLCO may indicate pulmonary hemorrhage, polycythemia, or a left-to-right shunt. This patient likely has asthma, which would lead to a reduced FEV1/FVC and bronchodilator response in FEV1 of ≥12%. Asthma is not associated with significant changes in DLCO.
D. DLCO of 75% with normal PFTs
Incorrect: An isolated decreased DLCO may indicate pulmonary hypertension or anemia. This patient likely has asthma, which can be diagnosed with PFTs showing a reduced FEV1/FVC and bronchodilator response in FEV1 of ≥12%. Asthma is not associated with significant changes in DLCO.
E. Flattened flow-volume loop in inspiration and expiration
Incorrect: A flattened loop in inspiration and expiration would be seen in fixed upper airway obstruction, such as tracheal stenosis. Asthma demonstrates a fixed lower airway obstruction pattern (normal inspiratory loop and a “scooped out” expiratory loop).
Main Explanation
This patient with a history of asthma as a young child who is now presenting with a cough, shortness of breath and wheezing, likely has asthma. Asthma is an obstructive lung disease characterized by episodic inflammation and hyperresponsiveness of bronchial smooth muscles. These episodes lead to the narrowing of airways, causing decreased and turbulent airflow, which manifests in shortness of breath and wheezing. Asthma can be diagnosed with pulmonary function tests (spirometry).
A decreased FEV1/FVC ratio indicates obstructive disease (generally asthma or COPD). Providers can give patients an inhaled short-acting beta-agonist and then re-measure FEV1. If the FEV1 increases by ≥12%, this positive response is diagnostic of asthma; however, patients can undergo further spirometric testing if asthma is suspected but the FEV1 increase is <12%. A dramatic decrease in FEV1 after provocation (e.g., exercise, methacholine challenge) is also diagnostic of asthma. Flow-volume loops are also used as part of PFTs to evaluate for obstructive lung disease, but these loops cannot differentiate between COPD and asthma.
Major Takeaway
Asthma is characterized by episodic reversible bronchial inflammation and hyperreactivity. Patients with an obstructive pattern on PFTs (decreased FEV1/FVC ratio) should be given a short-acting beta-agonist and have their FEV1 remeasured to assess for reversibility. An increase in FEV1 by ≥12% is diagnostic of asthma. A severe decrease in FEV1 with provocation testing (e.g., exercise, methacholine) also indicates asthma.
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