Rapid changes in atmospheric pressure, particularly those associated with thunderstorms, often precede "micro-epidemics" of idiopathic spontaneous pneumothorax (ISP), a European research team reports in the June issue of Chest.

Lead author Dr. Marco Alifano and associates identified records of patients with ISP from two hospitals in Bologna, Italy, between 2000 and 2004. They also obtained records of meteorological statistics for the same period.

There were 294 ISP events that occurred in 271 days. Eighty-four percent of pneumothorax cases occurred in 76 clusters, at a mean of 3.2 episodes per cluster.

Dr. Alifano, from Hotel-Dieu Hospital in Paris, and colleagues observed a significant relationship between clusters and wide differences in mean atmospheric pressure the previous day. The association was particularly strong for days in which thunderstorms occurred.

"Pneumothorax occurred on 54% of days with storms, but only 17% of days without storms (p < 0.0001)," the investigators write.

They suggest that "a transpulmonary pressure gradient originated by the lowering of the atmospheric pressure may result in rapid distension of weakened blebs/bullae walls with the subsequent occurrence of rupture and pneumothorax."

In contrast, incidence of ISP was not associated with any particular season, atmospheric temperature or other environmental factors.