The role of atmospheric pressure variation in the development of spontaneous pneumothoraces

It has been postulated that spontaneous pneumothoraces (SP) develop because of rupture of subpleural blebs, and that atmospheric pressure changes (ΔAP) may be contributory. A 5-year retrospective analysis of SP admissions was carried out to determine if ΔAP do play a role in SP development. Using a 36-yr record of hourly ΔAP, a normative background for ΔAP was constructed. A fall in AP below the fifth, or a rise above the ninety-fifth percentile during these time periods, was classed as 'unusual'. Atmospheric pressure changes in the 4 days prior to SP were analyzed. The expected frequency of SP occurring by chance, if no relationship to ΔAP existed, was also calculated. A total of 192 cases of SP was analyzed. Traumatic pneumothoraces were excluded. The majority of cases (72%) had been exposed to at least one 'unusual' ΔAP in the 4 days prior to onset of symptoms. Among those with four or more 'unusual' exposures, SP occurrence was significantly more frequent than expected by chance alone (p < 10^-10). A strong positive association between ΔAP and SP was not found in all cases, as ΔAP are unlikely to be the only causative factor for SP. This finding of a relationship with ambient pressure changes lends support to the theory that SP develop as a result of rupture of subpleural blebs.