Scuba diving is a popular recreational and professional activity with inherent risks. Complications related to barotrauma and decompression illness can pose significant morbidity to a diver’s hearing and balance systems. The common symptoms of otologic dysfunction are ear fullness or pain, hearing loss, tinnitus, and vertigo. Vertigo is one of the most hazardous symptoms to occur during diving. It is frequently accompanied by hearing loss and tinnitus. Vertigo is described in multiple phases of diving. However, many of these reports are not well documented, do not differentiate vertigo from nonvertiginous disequilibrium, or discuss vertigo only as an incidental observation.The purpose of this publication is to review the vestibular effects of diving

Milkov, Mario

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Varna Medical University Press: Journals

79Book of Proceedings - Symposium “Alumni Club and Friends” - Medical University – Varna,  March 6-8, 2020VESTIBULAR EFFECTS OF DIVING – А REVIEWMario MilkovDepartment of Dental Material Science and Propaedeutics of Prosthetic Dental Medicine, Faculty of Dental Medicine, Medical University of VarnaINTRODUCTION Divers occasionally suffer vestibular injury due to barotrauma or decompression illness (DCI) (15). Acute cases are usually recognized by a combination of vertigo, nausea and vomiting with a tendency to fall to the injured side and nystagmus to the contra-lateral side. The loss of peripheral vestibular function may be permanent, but in spite of this, there is often a nearly complete symptomatic recovery after weeks to months due to central vestibular compensation.AIMThe purpose of this publication is to review the vestibular effects of diving.MATERIALS AND METHODS The following research databases were used for the study: MEDLINE, Scopus, EMBASE and PubMed from January 2020 to August 2020, using the following keywords: marine medicine, vestibular system, diving.RESULTS AND DISCUSSION Less dramatic but much more common are mid-dle ear barotraumas and short episodes of vertigo during diving. Middle ear barotrauma is the most common medical problem in diving (24). It is char-acterized by ear pain, usually during descent, con-ductive hearing loss, and otoscopic signs of barotrau-ma to the middle ear (haemotympanum) or the tym-panic membrane (haemorrhage and/or rupture). The prognosis is usually excellent but repeated barotrau-mas may cause permanent hearing loss (5).Barotrauma is a pressure-mediated injury to tis-sue governed by Boyle’s law. As a diver descends and the pressure increases, the volume of the gas com-presses. This can result in a relative negative pressure in rigid- or semi-rigid-walled air-containing spaces in the body such as the middle ear or paranasal si-nuses. Negative pressure can cause mucosal oedema, haemorrhage and even perforation if the space can-not equalize. On ascent, the volume of gas increas-es as the ambient pressure decreases. If an air-con-taining space cannot equalize with the surrounding pressure, the expanding volume of the gas may result in a variety of head and neck pathologies, including middle ear perforation or pneumocephalus from si-nus barotrauma (7).Tinnitus, or spontaneous noise in the ear, is dif-ficult to quantitate because different patients expe-rience different types of noise. Also, the perception of severity and the effect on daily life vary. Tinnitus ABSTRACTScuba diving is a popular recreational and professional activity with inherent risks. Complications related to barotrauma and decompression illness can pose significant morbidity to a diver’s hearing and balance systems. The common symptoms of otologic dysfunction are ear fullness or pain, hearing loss, tinnitus, and vertigo. Vertigo is one of the most hazardous symptoms to occur during diving. It is frequently accompanied by hearing loss and tinnitus. Vertigo is described in multiple phases of diving. However, many of these reports are not well documented, do not differentiate vertigo from nonvertiginous disequilibrium, or discuss vertigo only as an incidental observation.The purpose of this publication is to review the vestibular effects of diving.Keywords: vestibular effects, diving, vertigo, otologic dysfunctionVestibular Eects оf Diving – А Review80ter. The diver may run out of air if forced to delay as-cent in order to eliminate vertigo. Vomiting under-water may cause suffocation if wearing a helmet with an oronasal inner mask. In spite of this, no danger-ous situations caused by alternobaric vertigo were re-ported by the divers in this study. This is in agree-ment with a study by Klingmann et al. (14).Alternobaric vertigo is a specific type of middle ear barotrauma that occurs if the reduction of mid-dle ear pressure is not equivalent in the bilateral mid-dle ear spaces. If the pressure differential exceeds a threshold of 45 mmHg, asymmetric stimulation of the labyrinths will occur, resulting in what is called alternobaric vertigo (16). Symptoms include nausea, vomiting, disorientation, and generalized malaise. The sensation of vertigo may persist for 1 to 2 hours after ascent but gradually disappears without ther-apy. Divers may be particularly susceptible to alter-nobaric vertigo if they have had previous injury or infection of either labyrinth. In susceptible divers, use of moderate doses of antihistamines or decon-gestants prior to diving may prevent symptoms, al-though these medications are not recommended for routine use before diving as they may potentiate re-verse squeeze. Although symptoms are usually mild, they may occur underwater, which is a serious prob-lem that may lead to aspiration and drowning (18). The disorder must be differentiated from inner ear decompression sickness, which is described later and is usually associated with deeper, prolonged diving.Transient symptoms suggestive of vestibular sys-tem dysfunction (vertigo, dizziness, and nausea) have been reported in association with high-pressure ner-vous syndrome (2,4). Later studies (1,3,9,10) have indicated that these symptoms are not accompa-nied by demonstrable electronystagmographic nys-tagmus but are associated with decrements in pos-tural equilibrium and bilaterally equal increases in can occur with middle ear disease that results in a conductive hearing loss but usually occurs with in-ner ear or central auditory pathway disease. With the former, tinnitus is thought to represent the sounds of cochlear and intracranial blood flow that are per-ceived because the conductive hearing loss results in a loss or a decrease of the masking effect of the usu-al background noise. Patients may describe a rush-ing, pulsatile sound that can often be timed with the pulse. With inner ear disease, tinnitus is thought to be due to the spontaneous firing of injured but via-ble auditory neurons or cochlear hair cells. However, this is not well understood: destructive labyrinthec-tomies or 8th cranial nerve sections in patients with recurrent and disabling vertigo, tinnitus, and non-functional hearing due to Meniere disease—which usually relieve the vertigo—have frequently not re-lieved the tinnitus.Vertigo while diving is common (Table 1). Ed-monds et al. (6) undertook a complete review of the various causes of dizziness in diving. Their classifi-cation is basically broken down into those causes of vertigo due to unequal vestibular stimulation, in-cluding caloric stimulations, barotrauma, and de-compression sickness; and those due to unequal ves-tibular responses to equal stimuli, such as the result of one vestibular apparatus being more sensitive than the other. Affected persons might have vertigo with caloric stimulation resulting from equal amounts of cold water entering the external ear canals. Also in-cluded in this group are divers who experience ver-tigo resulting from a unilateral hypofunctioning ves-tibular end-organ in situations in which equal and symmetrical pressure changes occur in the middle ear cavities during ascent and descent.In addition, this classification includes dizziness noted with nitrogen narcosis; the dizziness, nau-sea, and tremor described in the high-pressure ner-vous syndrome; and the dizziness noted during oxy-gen toxicity and sensory deprivation. Here, we offer a modification of this classification, which separates diving otologic injuries into those with usually tran-sient otologic dysfunction and those with permanent otologic inner ear injury.Alternobaric vertigo is a short spell of vertigo, which usually occurs during ascent, and is thought to arise because of asymmetric pressure in the middle ears during equalization. The lifetime prevalence in divers has been reported to be close to 30% (14). Oth-er causes of vertigo in diving are inner ear barotrau-ma, DCI, caloric stimulation, nitrogen narcosis or, in deep diving, the high-pressure nervous syndrome (11). Strong vertigo may lead to panic and irrational behaviour, which may be dangerous while under wa-Decompression sicknessHypoxiaHypercarbiaNitrogen narcosisSeasicknessAlcoholic hangoversSensory deprivationHyperventilationImpure breathing gasUnequal caloric stimulationDifficulties with middle ear pressure equilibrationTable 1. Causes of vertigo in divers81Mario Milkovthe vestibulo-ocular reflex. Thus, such symptoms during high-pressure nervous syndrome are thought to be related to dysfunction in more centrally located structures and not to unilateral end-organ or prima-ry vestibular neuron dysfunction.Motion sickness is commonly experienced during sea, air, and car travel and is characterized by nau-sea, vomiting, cold sweats, yawning and hyperven-tilation, and pallor. The current accepted theory of neural input mismatch involves differences between real sensory input from the proprioceptive, vestibu-lar, and visual systems compared with expected sen-sory input patterns to the central nervous system, which were programmed while the patient learned to crawl and ambulate during infancy (21).Divers commonly experience motion sickness on the boat or in the wave motion zone during decom-pression. Most symptoms resolve upon entering the water and with descent. Habituation from continu-ous exposure can develop in 2 to 3 days. Nervous-ness, female gender, young age, and dehydration from overindulgence in alcohol have all been cited as contributors to motion sickness (6). Positioning one-self amidships while concentrating on the horizon has been suggested to help prevent or reduce the se-verity of symptoms.As a diver descends and ambient pressure in-creases, progressively higher pressure gas is delivered to the lung and more inert gas dissolves in the blood stream. The amount of inert gas that dissolves in a given tissue is proportional to the maximum depth and bottom time, as well as the perfusion and diffu-sion characteristics of that tissue. As a diver ascends, the additional inert gas load comes out of solution at the level of the alveolus and is exhaled. If the rate of ascent exceeds the rate of alveolar gas exchange, in-ert gas will dissolute inside the diver, forming bub-bles within the circulation and in tissues. The sever-ity and nature of the decompression sickness injury vary from mild systemic, musculoskeletal and cuta-neous manifestations to severe, life-threatening cen-tral nervous and cardiorespiratory symptoms.A recent study showed that vestibular symptoms were more common in retired offshore divers than in age-matched controls (12). The symptoms were re-lated to a previous history of DCI, which is not sur-prising, given the fact that vestibular involvement has been reported to be relatively common in DCI (20). Some residual symptoms are common after vestibu-lar lesions. In the absence of manifest DCI, one might speculate whether repeated minor traumas to the in-ner ear may accumulate and give rise to permanent symptoms (13). This would be important since ves-tibular symptoms often have a significant negative impact on quality of life (19,25).Long-term vestibular symptoms have been demonstrated in retired offshore divers (12). In con-trast to this, no evidence of long-term vestibular ef-fects was found in this study. Further follow-up of the younger divers is desirable.Klingmann et al. (16) found that the lifetime in-cidence of DCI increased with decreasing diving ex-perience. Possibly, a certain diving frequency is re-quired in order to achieve and retain the skills neces-sary to avoid acute injuries.A study found that military divers, even without a history of DCI, had more white-matter lesions on brain magnetic resonance imaging than nondiving controls (8). The same article also reviewed the ev-idence from previous conflicting studies. Without a dose–response relationship, it is difficult to deter-mine whether injuries are due to the diving or to oth-er factors that separate divers from non-divers. Such a relationship has been found between diving expo-sure and hyperoxic lung damage (23), but the inner ear appears to be less sensitive than the lung to hy-peroxia (18).CONCLUSIONIn conclusion, transient dizziness and vertigo is common during and shortly after diving. Although these symptoms appear to be mostly benign, they may be difficult to distinguish from inner ear baro-trauma and DCI. Diving carries a definite risk of acute injuries, and a high degree of vigilance is nec-essary to prevent these from happening. However, there was no indication in this study that frequent diving per se, in the absence of acute injuries, leads to permanent vestibular dysfunction.Address for correspondence:Mario MilkovFaculty of Dental MedicineMedical University of Varna84 Tzar Osvoboditel Blvd9002 Varnae-mail: mario.milkov@gmail.comVestibular Eects оf Diving – А Review82REFERENCES1.  Adolfson JA, Goldberg L, Berghage TE: Effects of increased ambient air pressures on standing steadiness in man. 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Vestibular effects of diving – а review

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Vestibular effects of diving – а review

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