Pulmonary function testing in asthma commonly shows what pattern?

• A. Reduced flowrates (PEFR, FEV1, FVC)
• B. Reduced DLCO only
• C. Increased diffusion capacity
• D. Normal spirometry

Answer: (A)

Asthma mainly causes reversible obstruction of the airways, so pulmonary function tests show reduced expiratory flow. The hallmark is a drop in how fast air can be expelled, especially the FEV1 and the peak expiratory flow, which also lowers the FEV1/FVC ratio. This reflects dynamic airway narrowing from bronchial smooth muscle constriction and inflammation. The diffusion capacity (DLCO) is typically normal in asthma because gas transfer across the alveolar membrane isn’t inherently impaired, unlike in diseases such as emphysema or interstitial lung disease. While well-controlled or mild asthma can yield near-normal spirometry, the common pattern when obstruction is present is reduced flow rates, which is why that option best describes the typical PFT pattern in asthma.