From WebMD website, for whatever it's worth. Bulla is apparently another term for "bleb."
pneumothorax
Miller-Keane Medical Dictionary, 2000
(noo´´mo-thor´aks) accumulation of air or gas in the pleural cavity, resulting in collapse of the lung on the affected side. The condition may occur spontaneously, as in the course of a pulmonary disease, or it may follow trauma to, and perforation of, the chest wall or lung parenchyma.
SPONTANEOUS PNEUMOTHORAX. This condition occurs when there is an opening on the surface of the lung allowing leakage of air from the airways or lung parenchyma into the pleural cavity. Most often it occurs when an emphysematous bulla or other weakened area on the lung ruptures. Normally the pleural cavity is an airtight compartment with a negative pressure. When air enters the pleural cavity the lung collapses, producing shortness of breath and mediastinal shift toward the unaffected side (see also "mediastinal shift" MEDIASTINAL SHIFT).
Other symptoms of spontaneous pneumothorax are a sudden sharp chest pain, fall in blood pressure, weak and rapid pulse, and cessation of normal respiratory movements on the affected side of the chest.
Spontaneous pneumothorax may require no specific treatment beyond bed rest and the administration of oxygen to relieve dyspnea. The patient usually is more comfortable if allowed to sit up. In some cases "thoracentesis" THORACENTESIS and aspiration of air from the pleural cavity may be necessary. This allows for reexpansion of the lung. If air continues to leak from the defect in the lung surface a continuous closed-drainage apparatus is set up (see also "chest tubes" CHEST TUBES). As soon as the lung lesion heals and the lung is reexpanded, the patient is allowed to resume usual daily activities.
Tension pneumothorax is a particularly dangerous form of pneumothorax that occurs when air escapes into the pleural cavity from a bronchus but cannot regain entry into the bronchus. As a result, continuously increasing air pressure in the pleural cavity causes progressive collapse of the lung tissue. Emergency treatment-aspiration of air from the pleural cavity-is necessary in this disorder. If untreated, increased pressure within the pleural cavity will cause lung collapse and "mediastinal shift" MEDIASTINAL SHIFT.
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