Otoneurological symptoms in Brazilian fishermen exposed over a long period to carbon monoxide and noise

Anamnesis

A questionnaire was given with an emphasis on the otoneurological signs and symptoms.

Ear, nose, and throat (ENT) evaluation

It was performed in order to rule out any alteration that could affect the test.

Vestibular assessment

The fishermen were subjected to the following tests that make up the vestibular examination: Initially, vertigo and position/positioning nystagmus, spontaneous and semi-spontaneous, were researched.

Then for electronystagmography (ENG), a thermosensitive Berger Eletromedicina model VN316, made in the São Paulo, São Paulo, Brazil unit was used with three recording channels. An active electrode was attached with an electrolytic paste at a lateral angle for each eye and the frontal midline, forming an isosceles triangle that allows the identification of horizontal, vertical, and oblique eye movements and especially, the calculation of the angular velocity the slow-component eye velocity (SCV) of the nystagmus.

We used a Ferrante model COD 14200 made in São Paulo, São Paulo, Brazil, an adjustable height swivel chair, a model EV VEC visual stimulator, and air calorimeter model NGR 05; both the visual stimulator and air calorimeter were manufactured by Neurograff Eletromedicina, São Paulo, São Paulo, Brazil.

We compared the results with the normal standards obtained from epidemiological studies for the Brazilian population.[161718] Table 1 shows the criteria used to analyze each test as well as to distinguish central vestibulopathy from peripheral vestibulopathy.

The diagnosis of peripheral vestibulopathy was achieved by comparison with the normal standards and the absence of pathognomonic signs of central vestibular alterations:

• Calibration of eye movements, at this stage of the examination, the clinical aspect evaluated was the regularity of motion, making the study data comparable.
• Study of spontaneous nystagmus (eyes open and closed) and semi-spontaneous (eyes open). In this stage we evaluated the occurrence, direction, and inhibitory effect of ocular fixation (IEOF), and the maximum SCV value of the nystagmus.
• Study of pendular tracking for evaluation of occurrence and type of curve.

• Study of optokinetic nystagmus at a speed of 60^°/s, horizontally counterclockwise and clockwise. We evaluated the occurrence, direction, and maximum SCV counterclockwise and clockwise movements of the nystagmus.

• Study of pre-and postrotatory nystagmus in swivel chair testing, stimulating the lateral, anterior and posterior semicircular canals. For stimulation of the lateral (horizontal) semicircular canals, the head was bent forward 30^°. In the next step, to sensitize the anterior and posterior (vertical) semicircular canals, head positioning was 60^° backward and 45^° to the right, and then backward 60^° and 45^° to the left. The occurrence, direction, and counterclockwise and clockwise rotation frequencies of the nystagmus were observed.

• Study of pre- and postcaloric nystagmus were carried out on the patient positioned such that the head and trunk were inclined 60^° backward for adequate stimulation of the lateral semicircular canals. The irrigation time of each ear with air at 42^°C and 20^°C lasted 80 s for each temperature and the responses were recorded with eyes closed and then with eyes open to observe the IEOF. In this evaluation, the direction, the absolute values ​​of the SCV, and the calculation of the relationship of directional preponderance and labyrinthine preponderance of postcaloric nystagmus were observed.

Sound pressure level assessment on vessels

The evaluation of sound pressure levels followed the criteria and procedures set out in technical standard International Organization for Standardization (ISO) 9612: 1997 — Acoustics — Guidelines for the measurement and assessment of exposure to noise in a working environment and the standard developed by FUNDACENTRO, Normas de Higiene Ocupacional (NHO) 01. As described in Table 2, the evaluation of sound pressure levels was carried out in four different kinds of job with one specific location on board and three types of industrial fishing vessels in 2007. The vessels used were: A seiner, a drift net boat, and a trawler. The evaluations were carried out in the compartments of vessels where CO assessments were made. For comparison with the tolerance limits, a calculation was made of the standard exposure level (SEL) for 8 h of exposure while taking into account that the exposure for fishermen was 24 h. The measurement equipment for sound pressure levels used in the assessment of occupational exposure to noise belonged to FUNDACENTRO. To determine the dose or the average level, we used integrating meters for personal-use (noise dosimeters) that meet the specifications in ANSI S1.25 (1991), and integrating meters for the evaluator (sound pressure level meters) that meet the specifications of ANSI S1.4 (1983) and IEC 651 (1993) and are type 2.

Chemical agent evaluation for CO in vessels

CO environmental assessments [Table 2] were carried out in 2007 on board when the three fishing vessels were on normal fishing activity by a researcher from FUNDACENTRO. The evaluated vessels belonged to fishing companies located in the municipalities of Itajaí, Santa Catarina, Brazil and Navegantes, Santa Cararina, Brazil and were of different types of fishing categories. Vessel A was a drift net boat and vessel B was a trawler, both with 6-men crew; vessel C was a seiner, with a 14-men crew.

For the environmental assessment, the reagent tubes for direct reading by diffusion, specific to CO, manufactured by Dräger, CO 50/a-D was chosen. The evaluations carried out on fishermen were personal sampling and environmental assessment and an environmental sampling to check for CO emissivity in the engine, the most likely location for emissions, and the risk it posed to the occupants. The exhaust pipe of the engine is usually above the ceiling of the vessel control room and is less likely to reach the crew due to its dissipation by wind. For personal sampling, diffusion tubes were attached to the lapel of the fishermen selected for evaluation, and at the time the evaluation began, the tube was broken on one side allowing CO existing in the environment into the tube by a diffusion process permitting it to react with the indicator layer, coloring it. The tube remained open throughout the sampling period and was positioned in the breathing zone of the fisherman. Sampling was carried out during the working day, from the moment it was attached to the worker's lapel until the time he returned to port upon completion of work. However, this time the sample was limited to a maximum 8-h period specified in the instructions provided by the tube manufacturer and removed at this time by the worker who then made a mark on the tube using a permanent ink pen. Once on land, the concentrations were calculated.

To calculate the concentration versus time of assessment, the following formula was used:

[CO concentration (ppm) = Indicator on detection tube/evaluation period (hours)].

The fishermen selected were pilots, cooks, fishermen who were smokers, and deck hands who had indicated that they often smell gases from the burning fuel, diesel oil. For environmental sampling, the tubes were placed on the machinery near the central location of the pilots at their breathing zone level. The sampling time was also limited to a maximum of 8 h, according to the instructions accompanying the diffusion tubes. During the CO assessments, it was observed that the fishermen smoked often.

Statistical analysis

We applied the Difference of Proportions and Fisher's tests in order to compare the results of the vestibular examination (analyzing normal and abnormal results and correlating them with age and length of service) and the Fisher's and chi-square tests (correlating the results of the vestibular examination with the symptoms of tinnitus, dizziness, and hearing loss). It was set at 0.05 or 5% as the level for rejecting the null hypothesis.

Information that is already known on this topic

In analyzing the medical history, the occurrence of multiple diverse clinical and otoneurological symptoms was verified that were mainly tinnitus, dizziness, and hearing loss. According to the literature, tinnitus is the first warning of exposure to excessive sound stimuli and may indicate an increased susceptibility to injury. This is an important symptom in preventing NIHL and is one of the main predictors of disadvantages generated in workers exposed to noise. Tinnitus is one of the three major otoneurological manifestations, along with sensorineural hearing loss and dizziness.[2021] It is regarded as a physiological disorder resulting from abnormal neural activity in the auditory pathways.[22] Current conceptions suggest the existence of involvement of the peripheral and central auditory systems, afferent and efferent, and the interaction with other systems.[22] Dias et al.[23] evaluated 284 workers and found a prevalence of 63.0% in NIHL and tinnitus in 48.0% of the cases evaluated. In another study[24] carried out among 20 factory workers exposed to occupational noise for more than 10 years, the authors found that prolonged exposure to noise could cause vestibular symptoms that are initially neglected most of the time for being subtle.

Several structures are involved in balance and changes in vestibular and/or auditory systems can often be the cause of body instability.[25] Okamoto and Santos,[26] in correlating noise with vestibular symptoms, observed that during or after exposure to noise, many patients had vestibular disorders such as vertigo with or without neurovegetative symptoms, an unsteady gait, nystagmus, fainting, and pupil dilation. It is known that the auditory impulse, before reaching the cerebral cortex, passes through several subcortical stations that explain the presence of nonauditory effects induced by noise.[26]

Studies carried out[27] on 258 men from the military service in Israel who were exposed to intense impulse and impact noises showed a vestibular dysfunction (not specifying type) when asymmetric hearing loss occurs. According to the authors, there is an association between the severity of hearing loss and vestibular symptoms.

In the present study, we observed a change in the peripheral vestibular system in 17 patients; this change was found in the caloric test, with predominance of irritative peripheral vestibular dysfunction. In the literature, there was a scarcity of studies involving the vestibular system and the activity of fishing. We emphasize the research of Kumar, Vivarthini, and Bhat[15] who applied vestibular evoked myogenic potentials (VEMP) in individuals with NIHL and observed significant changes in elongation and reduction of n23 latency in p13-n23 intervals, thus demonstrating an involvement of this important otoneurological examination. VEMP was abnormal in 67.0% of the cases with NIHL. The authors concluded that the possibility of vestibular dysfunction, especially in the saccule, was high in these cases. This result is in accordance with the study of Tseng and Young[28] that observed a large number of saccular changes in 30 patients with NIHL. Teixeira, Körbes, Rossi et al.[29] assessed a balance by examining the computerized dynamic posturography (CDP) in 16 workers exposed to occupational noise of a printing company and observed alterations in balance in the assessment of all the stages tested that evaluate somatosensory, visual, vestibular, and balance functions. The authors reported that high levels of sound pressure can alter balance by the activation of the saccule's sensory cells that are sensitive to both labyrinthine and acoustic stimuli.

With respect to CO poisoning, Kowaska[30] studied 50 patients and the results showed bilateral hearing loss in different degrees in 42.0%, retrocochlear impairment in 80.0%, deafness in 6.0%, and vestibular dysfunction in 86.0% of the patients. In another study[31] conducted on workers exposed to CO, 66.0% had hearing loss and 76.5% had vestibular dysfunction. According to the author, these data confirmed the toxic effects of CO.

When comparing the results of the vestibular examination with complaints of dizziness, this difference becomes relevant. According to Cohen,[32] dizziness may hinder the performance of the individual in performing activities requiring rapid movements of the head and also on tasks involving trunk and head flexion. This explains the significance that occurs with the symptom of dizziness since this type of profession sometimes requires jerky movements of the trunk and head.

When we compared the results of the vestibular examination to the age and length of service, we observed the results to be significant. This demonstrates that the individual enters this profession early and works for a long period in most cases, going through several generations that entails combined exposure to CO and NIHL for a long period. These characterize fishermen as a risk population for future vestibulocochlear problems.

Main finding of this study

The most evident otoneurological symptoms were: Tinnitus, dizziness, and hearing loss while several more clinical symptoms reported were: Fatigue, anxiety, and depression.

Alterations in the vestibular examination occurred in 43.3% of the fishermen and were found in the caloric test, with predominant dysfunction of the peripheral vestibular system of the irritative type.

The otoneurologic complaints were frequent and allowed to verify the importance of the labyrinthine examination and the need to adopt preventive measures regarding exposure to noise and CO, as they may cause and/or enhance several manifestations compromising the vestibular system that may affect the quality of life of these workers.

What this study adds

According to the Ministry of Health in Brazil,[33] some chemical exposures may pose a potential health risk causing serious ototoxic effects and damaging a person's hearing and balance functions. Ototoxins can be ingested, inhaled, and absorbed. The chemicals may have endogenous and exogenous origins, the latter including aminoglycosides, diuretics, and chemicals used at work as well as cigarette smoke and alcohol. For the authors,[34] the distinct ototoxic effects of substances in the chemical composition of smoke can synergistically affect the auditory and vestibular systems when combined with noise exposure. Studies of 100 fishermen in Greece[35] reported that health risk factors included alcohol, consumption of fatty foods, smoking, and lack of exercise. Fort, Massardier-Pilonchéry, and Bergeret[36] suggest that stressful working conditions can lead fishermen to higher consumption of and dependence on tobacco and alcohol.

Regarding vibration, the authors[37] investigated the effects of sound on body stability and found that sounds with higher amplitudes and low frequencies can vibrate the vestibular system more than sounds at a high frequency, leading to increased instability. Each structure of the human body responds to different vibratory stimuli; however, the risks to health caused by vibrations are poorly known but can, in general, cause discomfort, pain, nausea, and vomiting.[38]

Exposure to any of these factors (smoking, alcohol, and vibration) can significantly increase the risk of developing major vestibulocochlear alterations, thus demonstrating the importance of clinical monitoring and control tests in the fishing industry. In this way, we can develop educational activities and thereby minimize the effects caused by the interaction of these harmful agents to occupational health.

This study is important for the preservation of workers’ health, its social and economic aspects, and the importance of fishing in Brazil as a job. This is especially true for some coastal municipalities where fishing plays an important role and in places that offer few economic alternatives, where manual laborers are employed who have little or no qualification; in some cases, fishing is the only employment opportunity.

In the literature, we found few Brazilian and international references that addressed the study of vestibulometry in industrial fishermen with which we could have compared our findings. This alone demonstrates the relevance of the subject studied, thus encouraging the continuation of research and new studies on the subject. In this way, we may in the near future plan actions that can minimize the symptoms caused by combined exposure to CO, tobacco, alcoholic beverages, and NIHL for a long period in the performance of this profession.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.