Should computed tomography of the chest be recommended in the medical certification of professional divers?

T oklu et al have raised the question of whether routine high resolution computed tomographic (CT) scanning of the chest should form part of the initial diving medical examination for occupational divers. The authors make this proposition in discussing their series of three divers in which pulmonary abnormalities were discovered on high resolution CT scan after occupational diving incidents. One case involved a bulla, the second multiple air cysts, and the last a subpleural bleb. The authors assume that the initial mechanism of injury in each case was pulmonary barotrauma associated with the lesions revealed. One could argue whether the second and third cases may have involved arterialisation of venous bubbles rather than pulmonary barotrauma, but any uncertainty does not invalidate consideration of the authors’ contentions. It is widely agreed that lung cysts, bullae, and blebs may all predispose to pulmonary barotrauma, and most authorities recommend disqualification from diving if such lesions are found. This report adds to others in which CT scans have revealed pulmonary abnormalities in diving accident victims where chest radiographs did not. 6 I have also managed a similar case of apparently undeserved arterial gas embolism after years of uneventful diving in a healthy man with a normal chest radiograph. Subpleural blebs were discovered on incidental CT scan several years later. Pulmonary barotrauma in divers often occurs in the provocative setting of uncontrolled ascent, with rapid gas expansion and the potential for high transthoracic pressures. 7 It is estimated that a normal lung will rupture if a transtracheal pressure of 75–80 mm Hg is exceeded, and pulmonary structural predisposition is not needed to explain such incidents. 9 Prevention of such cases should focus on psychological suitability for underwater work, training, equipment reliability, and operational diving practice. Where barotrauma initially appears ‘‘undeserved’’, as in the cases of Toklu et al, however, it is particularly tempting to search for predisposing pathology and assume cause and effect if lesions are discovered. Caution is necessary with such an approach as it tends to produce a self supporting literature. To better estimate risk would require at least several major case series from which the incidence of the purported predisposing factor(s) could be reliably estimated and compared with the incidence in suitable control populations. Herein lies a major limitation; no such large series exist in the diving medicine literature, and rapidly evolving medical imaging technology has not been matched with publication of the findings on control populations of healthy normals let alone divers specifically.