A 22-year-old woman presents to the emergency department with shortness of breath. She was hiking when she suddenly felt unable to breathe and had to take slow deep breaths to improve her symptoms. The patient is a Swedish foreign exchange student and does not speak any English. Her medical history and current medications are unknown. Her temperature is 99.5°F (37.5°C), blood pressure is 127/68 mmHg, pulse is 120/min, respirations are 22/min, and oxygen saturation is 90% on room air. Physical exam is notable for poor air movement bilaterally and tachycardia. The patient is started on treatment. Which of the following parameters including forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and diffusing capacity of carbon monoxide (DLCO) most appropriately describes this patient's underlying pathology?
Increased FVC
Decreased airway tone
Normal DLCO
Increased FEV1/FVC
Normal DLCO
This patient who presents with dyspnea and poor air movement bilaterally most likely has an acute asthma exacerbation. DLCO is the one parameter that is normal in these episodes.

Asthma is an obstructive lung disease that results in intermittent episodes of respiratory compromise. Asthma presents with shortness of breath typically secondary to an allergen/antigen or with exposure to exercise or cold air that causes bronchospasm. Pulmonary function testing will typically reveal a decreased FEV1, a decreased FVC, and a decreased FEV1/FVC in both asthma and emphysema. The DLCO will be normal in asthma in contrast to emphysema where the DLCO is decreased. Patients should be treated with inhaled beta-adrenergic agonists and corticosteroids for acute exacerbations.

Peng et al. review the evidence regarding patients who have COPD versus asthma. They discuss how patients with COPD have reduced DLCO. They recommend measuring parameters to distinguish between these entities.

Incorrect Answers:
Answer A: Decreased airway tone does not describe asthma. Rather, hyperreactive airways with increased tone describes an asthma attack. Decreased airway tone may be seen in patients with connective tissue diseases such as Ehlers-Danlos syndrome.

Answers 2-4: Increased FEV1, FEV1/FVC, and FVC do not describe asthma. All of these laboratory values are decreased in asthma and emphysema. Increased respiratory performance can be seen in patients who are athletes or training for marathons.

Bullet Summary:
Both asthma and emphysema present with a decreased FEV1, FVC, and FEV1/FVC; however, asthma has a normal DLCO while COPD has a reduced DLCO.