n e u r o l o g i a i n e u r o c h i r u r g i a p o l s k a 4 9 ( 2 0 1 5 ) 4 5 – 5 1 Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.elsevier.com/locate/pjnns Review article Neurological complications of underwater diving * Justyna Rosińska , Maria Łukasik, Wojciech Kozubski Chair & Department of Neurology, Poznan University of Medical Sciences, Poznan, Poland a r t i c l e i n f o a b s t r a c t Article history: The diver's nervous system is extremely sensitive to high ambient pressure, which is the Received 5 August 2014 sum of atmospheric and hydrostatic pressure. Neurological complications associated with Accepted 24 November 2014 diving are a difficult diagnostic and therapeutic challenge. They occur in both commercial Available online 1 December 2014 and recreational diving and are connected with increasing interest in the sport of diving. Hence it is very important to know the possible complications associated with this kind of Keywords: sport. Complications of the nervous system may result from decompression sickness, Diving pulmonary barotrauma associated with cerebral arterial air embolism (AGE), otic and sinus barotrauma, high pressure neurological syndrome (HPNS) and undesirable effect of gases Neurologic decompression illness used for breathing. The purpose of this review is to discuss the range of neurological High pressure neurological syndrome symptoms that can occur during diving accidents and also the role of patent foramen ovale (PFO) and internal carotid artery (ICA) dissection in pathogenesis of stroke in divers. Pulmonary barotrauma # 2014 Polish Neurological Society. Published by Elsevier Urban & Partner Sp. z o.o. All Patent foramen ovale rights reserved. development of decompression sickness. Barotrauma results 1. Introduction from the Boyle–Mariotte law, according to which gas in the air spaces in the diver's body expands and increases in volume During diving, hydrostatic pressure is exerted on the diver's proportionally to the decrease of the surrounding pressure [1,2]. body in addition to the atmospheric pressure. According to The nervous system is particularly sensitive to the effects of Dalton's law, in the course of descent the increase of the high ambient pressure. The last two decades have seen the ambient pressure also causes an increase of the partial increasing popularity of recreational diving, but disregard for pressures of individual gases in the breathing gas mixture. basic safety principles resulting from knowledge of diving This contributes to the increased dissolution and transport of physiology lead to an increasing number of accidents associated gases, mainly nitrogen, in the tissues until saturation in with this activity. Complications of the nervous system proportion to the ambient pressure, as Henry's law states [1,2]. associated with diving can result in decompression sickness, During ascent, when the ambient pressure decreases, the pulmonary barotrauma-induced cerebral arterial gas embolism excess gas from the tissue is removed with exhaust air. When (AGE), ear and sinus barotrauma, high pressure neurological the change of the ambient pressure occurs more quickly than syndrome (HPNS) and the undesired effect of breathing gas in removal of nitrogen from the tissues, it may lead to the the form of nitrogen narcosis or oxygen toxicity. Differentiation supersaturation of an inert gas, which is the main cause of the of arterial thrombotic events associated with pulmonary * Corresponding author at: Department of Neurology, Przybyszewskiego 49, 60-355 Poznan, Poland. Tel.: +48 61 869 15 35; fax: +48 61 8691697. E-mail address: [email protected] (J. Rosińska). http://dx.doi.org/10.1016/j.pjnns.2014.11.004 0028-3843/# 2014 Polish Neurological Society. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved. 46 n e u r o l o g i a i n e u r o c h i r u r g i a p o l s k a 4 9 ( 2 0 1 5 ) 4 5 – 5 1 barotrauma from decompression sickness is not always ascent flows directly to the arterial circulation without the possible, and therefore there is frequent reference to the specific security filter provided by the pulmonary vessels. common concept of decompression illness (DCI) [3]. These two The classification proposed by Golding in 1960 includes two are often present together in the same patient. In addition, the types of decompression sickness. In type I the symptoms are differentiation is of little clinical importance because the usually mild and may manifest as malaise or fatigue, or may be treatment of both conditions is essentially the same. more specific, involving the skin, joints and muscles. This less severe type of decompression sickness is called the bends [5]. Type II decompression sickness is more severe and can affect 2. Neurologic decompression sickness the lungs, and both the vestibular and the nervous system. Neurologic symptoms of decompression sickness are associ- Neurologic decompression sickness is one of the most serious ated with both spinal cord and rarely cerebral injury. Spinal complications of diving, resulting from the release of inert gas cord decompression sickness constitutes 50–60% of cases and bubbles, usually nitrogen, into the bloodstream and tissues it involves obstruction of both venous drainage, especially in after reduction of ambient pressure. The propensity for the the epidural vertebral internal venous plexus (Batson venous formation of nitrogen bubbles depends on the depth of the plexus) [15], and arterial circulation with a predilection to the dives, the residence time at a given depth and the rate of area supplied by the artery of Adamkiewicz. Changes are ascent [4]. Nitrogen bubbles can damage the nervous system as mainly located in the lower part of the thoracic spinal cord and a result of activation of the systemic inflammatory response, lesions of the lumbar or cervical part are rather uncommon. involving the cytokines and complement system as well as The most severe presentation is partial myelopathy of the mechanical disruption or compression of the brain, spinal thoracic segments [5,16] manifested by rapidly progressive cord, cranial and peripheral nerves and vascular occlusion, weakness of the lower limbs, paresthesias, dysesthesias and especially large veins [3,5]. White matter of the spinal cord is sensory loss in the trunk and lower extremities, pain in the particularly sensitive to nitrogen bubbles, due to the high lower back or pelvis and impaired function of the bladder and solubility of the inert gas in the lipid-rich myelin and relatively intestines [4]. Spinal cord decompression sickness may result poor blood flow in this tissue [6]. Neurologic decompression in specific residual symptoms in the form of sensation loss or sickness is more likely to occur in less experienced divers [7]. pain in the lower back. There are few reports of neurologic During descents the diver is exposed to elevated environmen- decompression sickness manifested as Brown–Séquard syn- tal pressure and an increased amount of inert gas dissolved in drome [17,18]. Divers with cervical and thoracic spinal canal the body tissue until saturation proportional to the ambient stenosis, mostly caused by disk degeneration, are at increased pressure. The desaturation occurs up to several hours after risk for the occurrence of spinal cord decompression sickness the dive and the presence of gas microbubbles is usually [19]. Cerebral decompression sickness constitutes 30–40% of asymptomatic. Repeated exposures contribute to accumula- cases and most commonly it involves the arterial circulation tion of these gas bubbles and the emergence of symptoms of [15]. In 90% of cases it occurs within six hours of ascent and decompression sickness. Risk factors of decompression more than 50% of patients develop symptoms within one hour sickness include breaking the principles of decompression, of ascent [3,5,20]. Cerebral symptoms occur alone or in frequent ascents and descents during a single dive (yo-yo combination with spinal decompression sickness [4]. The diving), repetitive diving in a single day, or plane flights or symptoms of brain damage depend on the location of the mountaineering trips within a short time after the dive emboli. They are often preceded by severe headache associat- associated with a reduction in ambient pressure and nitrogen ed with increased intracranial pressure, cerebral edema and supersaturation of the tissue. Patent foramen ovale (PFO), the congestion of blood in the venous sinuses. Perfusion disorders persistence of an embryonic defect in the interatrial septum, is in the area supplied by the anterior and middle cerebral present in about 26% of the general population. In patients arteries are the most frequent and in consequence multiple who have cryptogenic stroke the prevalence of PFO increases ischemic lesions in the frontal and parietal lobes occur. to about 40% [8,9]. Patent foramen ovale is one of the risk Behavioral and cognitive impairment as a result of cerebral factors of neurologic decompression sickness, most likely in decompression sickness may be persistent or slow to improve. the mechanism of paradoxical nitrogen emboli, especially in In decompression sickness the peripheral nervous system the case of compliance with the proper diving profile [10]. The is involved rarely and usually the nerves passing through the important role of cardiac right-to-left shunt for paradoxical gas anatomical spaces where gas bubbles can cause direct embolism in divers was indicated in 1986 [11]. Approximately mechanical pressure such as the facial, median or trigeminal 75% of divers who had experienced neurologic symptoms were nerve are affected [21]. found to have PFO [12]. Neurological complications and The diagnosis of neurologic decompression sickness is ischemic lesions in the brain assessed by MRI are significantly based on clinical signs and symptoms and should be suspected more frequent among divers with PFO [13].