Respiratory physiology and pathophysiology
Practice questions with explanations

B. It reflects large airway calibre and effort, so it detects obstruction but is effort-dependent and less sensitive to small airway disease

Because it depends on effort and technique, a low reading may reflect poor technique rather than obstruction, and it is compared against the individual's personal best rather than a predicted value. Spirometry provides more information, but peak flow's portability makes it valuable for home monitoring in selected patients.

A. The FEV1/FVC ratio, reduced in obstruction and preserved or increased in restriction

In obstruction, expiratory flow is limited so FEV1 falls more than FVC and the ratio drops below 0.7. In restriction, both fall proportionally as lung volumes are reduced, so the ratio is preserved and total lung capacity is low. Asthma, COPD and bronchiectasis are obstructive; interstitial lung disease, obesity, neuromuscular weakness and chest wall disease are restrictive.

B. Air in the pleural space abolishes the negative pressure, allowing the lung to collapse and impairing ventilation

The lung's elastic recoil is opposed by negative intrapleural pressure; admit air and the lung recoils inward. A tension pneumothorax develops when a one-way valve lets air in but not out, raising intrathoracic pressure until venous return and cardiac output fail, which is a clinical diagnosis requiring immediate decompression rather than a chest x-ray.