Decompression illness

Abstract: A relationship between migraine with aura and the presence of right-to-left shunts has been reported in two studies. Right-to-left shunts are also associated with some forms of decompression illness. While conducting research in divers with decompression illness, it was our impression that divers with a large shunt often had a history of migraine with aura in everyday life and after dives. Therefore we routinely asked all divers about migraine symptoms. The medical records of the last 200 individuals referred for investigation of decompression illness were reviewed to determine the association between right-to-left shunts and migraine aura after diving, and migraine in daily life unconnected with diving. Migraine with aura in daily life unconnected with diving occurred significantly more frequently in individuals who had a large shunt which was present at rest (38 of 80; 47.5%) compared with those who had a shunt which was smaller or only seen after a Valsalva manoeuvre (four of 40; 10%) or those with no shunt (11 of 80; 13.8%) (P<0.001). Hemiplegic migraine occurred in 10 divers, each of whom had a shunt that was present at rest; in eight of these cases the shunt was large. The prevalence of migraine without aura was similar in all groups. Post-dive migraine aura was significantly more frequent in individuals who had a large shunt present at rest (21 of 80; 26.3%) compared with those who had a shunt that was smaller or only seen after a Valsalva manoeuvre (five of 40; 12.5%) or no shunt (one of 80; 1.3%) (P<0.001). Thus individuals with a large right-to-left shunt have an increased prevalence of migraine with aura in daily life unconnected with diving, and they also have an increased incidence of migraine aura after dives, but only when the dives liberate venous bubbles. These data suggest the possibility that, in some individuals, right-to-left shunts have a role in the aetiology of migraine with aura. The observations suggest that paradoxical gas embolism may precipitate migraine with aura.

Abstract: There is dispute as to whether paradoxical gas embolism is an important aetiological factor in neurological decompression illness, particularly when the spinal cord is aected. We performed a blind case-controlled study to determine the relationship between manifestations of neurological decompression illness and causes in 100 consecutive divers with neurological decompression illness and 123 unaected historical control divers. The clinical eects of neurological decompression illness (including the sites of lesions and latency of onset) were correlated with the presence of right-to-left shunts, lung disease and a provocative dive profile. The prevalence and size of shunts determined by contrast echocardiography were compared in aected divers and controls. Right-to-left shunts, particularly those which were large and present without a Valsalva manoeuvre, were significantly more common in divers who had neurological decompression illness than in controls (P ! 0.001). Shunts graded as large or medium in size were present in 52% of aected divers and 12.2% of controls (P ! 0.001). Spinal decompression illness occurred in 26 out of 52 divers with large or medium shunts and in 12 out of 48 without (P ! 0.02). The distribution of latencies of symptoms diered markedly in the 52 divers with a large or medium shunt and in the 30 divers who had lung disease or a provocative dive profile. In most cases of neurological decompression illness the cause can be determined by taking a history of the dive profile and latency of onset, and by performing investigations to detect a right-to-left shunt and lung disease. Using this information it is possible to advise divers on the risk of returning to diving and on ways of reducing the risk if diving is resumed. Most cases of spinal decompression illness are associated with a right-to-left shunt.

Abstract: Dear Sirs, Sandra Rea Torti et al., in the June issue of the Journal ,1 report on a group of divers, examined for patency of the foramen ovale (PFO), and claim to be able to calculate the relative risk for decompression illness (DCI) when a diver has a PFO. Where it is true that in large samples with a low occurrence of a disease in proportion to a risk factor, the Odds Ratio may approach the value of the Relative Risk, in this series that claim is unjustified.2 First of all, the authors undertook a retrospective …

Abstract: OBJECTIVE—Large flap valve patent foramens may cause paradoxical thromboembolism and neurological decompression illness in divers. The ability of a self expanding Nitinol wire mesh device (Amplatzer septal occluder) to produce complete closure of the patent foramen ovale was assessed. PATIENTS—Seven adults, aged 18-60 years, who had experienced neurological decompression illness related to diving. Six appeared to have a normal atrial septum on transthoracic echocardiography, while one was found to have an aneurysm of the interatrial septum. METHODS—Right atrial angiography was performed to delineate the morphology of the right to left shunt. The defects were sized bidirectionally with a precalibrated balloon filled with dilute contrast. The largest balloon diameter that could be repeatedly passed across the septum was used to select the occlusion device diameter. Devices were introduced through 7 F long sheaths. All patients underwent transthoracic contrast echocardiography one month after the implant. RESULTS—Device placement was successful in all patients. Device sizes ranged from 9-14 mm. The patient with an aneurysm of the interatrial septum had three defects, which were closed with two devices. Right atrial angiography showed complete immediate closure in all patients. Median (range) fluoroscopy time was 13.7 (6-35) minutes. Follow up contrast echocardiography showed no right to left shunting in six of seven patients and the passage of a few bubbles in one patient. All patients have been allowed to return to diving. CONCLUSION—The Amplatzer septal occluder can close the large flap valve patent foramen ovale in divers who have experienced neurological decompression illness. Interatrial septal aneurysms with multiple defects may require more than one device. Keywords: patent foramen ovale; decompression illness; Amplatzer septal occluder