Which mechanism is primarily responsible for a spontaneous pneumothorax?

A spontaneous pneumothorax primarily occurs due to the rupture of subpleural apical blebs, particularly in individuals who may have underlying lung conditions or are tall and thin. These blebs are small air-filled sacs located at the apex of the lungs, and during instants of high negative intrapleural pressure, such as during vigorous physical activity, coughing, or even at rest, these blebs can rupture, allowing air to escape into the pleural space.

This mechanism results in a situation where air collects in the pleural cavity, compromising lung expansion and leading to a potentially significant respiratory distress. The involvement of high negative intrapleural pressures is critical as it contributes to the rupture of these blebs, thus making option D the correct choice as it accurately describes the physiological occurrence leading to a spontaneous pneumothorax.