Primary spontaneous pneumothorax occurs in patients without underlying pulmonary disease, classically in tall, thin young men in their teens and 20s. It is thought to be due to spontaneous rupture of subpleural apical blebs or bullae that result from smoking or that are inherited. It generally occurs at rest, although some cases occur during activities involving reaching or stretching. Primary spontaneous pneumothorax also occurs during diving and high-altitude flying because of unequally transmitted pressure changes in the lung.
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