Assessment of Sea Sickness in Naval Personnel: Incidence and Management.

BACKGROUND: Strategic, operational and tactical superiority of Navy hinges on extremely efficient warships which in turn depend on professionally competent sailors ready to undertake tasks to deliver timely, structured and metered response. Ships and their potentialities are tools to achieve the required strategic advantage which is dependent on the proficiency of sailors. Sailors who are fit ashore may be debilitated on board because of sea sickness. AIMS: To study the incidence and severity of sea sickness among 500 naval personnel from various ships. Setting and design: An observational study conducted from May 2019 to March 2020 among 500 naval personnel from various ships of the fleet.
MATERIALS AND METHODS: Motion Sickness Assessment Questionnaire (MSAQ) was used to collect data from personnel of different departments working in different part of ship aged between 20 to 50 years.
RESULTS: The majority suffered mild symptoms (78.78%) and did not require any medication. Their symptoms were selflimiting and settled on rest within 24 hours. Moderately severe symptoms were observed among 19.31 % personnel and had to be administered medication and rest for 24 hours. Only 1.91% had severe symptoms and had to be excused from duties along with medication and rest.
CONCLUSION: Sea sickness is unpleasant and has an adverse effect on employability of the sailors. It is mild and self limiting in majority of the personnel not requiring active intervention. Some personnel may require desensitisation along with pharmacotherapy. Copyright:

INTRODUCTION

Strategic, operational, and tactical superiority of Navy hinges on extremely efficient warships which in turn depend on professionally competent sailors ready to undertake tasks to deliver timely, structured, and metered response. Ships and their potentialities are tools to achieve the required strategic advantage which is dependent on the proficiency of sailors. Sailors who are fit ashore may be debilitated on board because of sea sickness. In critical military tasks, sea sickness would impede mission effectiveness if the naval personnel involved in important operations onboard experience sea sickness.

Sea sickness, a variant of motion sickness usually due to the roll and pitch movement of the ship, is a set of symptoms that occur in association with motion of a person or his or her surroundings, triggering a stress reaction that results in autonomic symptoms. It is characterised by various symptoms that progress through cold/hot sweating, salivation, and occasionally headache, to nausea and vomiting with incapacitation that can be severe.[12]

The onset of sea sickness is often insidious, with dizziness, drowsiness, and reduced alertness. It is a psychophysiological response with individual variations. For some even a minor stimulus like simply getting on board on a stationary vessel may be enough to precipitate an attack of sea sickness while others are immune to it. Some individuals may also experience “simulator sickness,” where playing complex video games on large screens or using virtual reality (VR) headsets can lead to similar symptoms even though the persons affected are not physically in motion.[3] Military organizations of some countries like France, Israel, United Kingdom, etc., employ an operational selection for naval and air force personnel.[45] In Indian Navy however there is no such operational selection on the basis of sea sickness.

MATERIALS AND METHODS

An observational study on incidence and severity of sea sickness among naval personnel was carried out from May 2019 to March 2020. Total 500 personnel from various ships of the fleet were included in this study. All the participants were apparently healthy and medically fit. Each participant had been deployed in the sea with an average 5 to 20 deployments per year. All personnel were from different departments working in different parts of ship aged between 20 to 50 years. Motion Sickness Assessment Questionnaire (MSAQ) as attached in 'Appendix A' was used to collect data. It contained information about personal particulars, anthropometric profile, average duration at sea, and symptoms of motion sickness encompassing gastrointestinal, central, peripheral, and psychosomatic. The data were then compiled and analyzed.

RESULTS

Table 1 shows the mean age of personnel was 30 years with SD 8.78.

Table 1

Anthropometric data

Parameters	Mean+/-SD
Age (Years)	30+/-8.78
Body weight (Kg)	58.7+/-5.69
Height (cm)	170+/-4.26

Table 2 shows that 62.2% personnel sailed for duration less than equal to 7 days at sea, 23.6% were for duration 8 to 14 days and rest 14.2% for more than 14 days at sea.

Table 2

Duration at Sea

Duration	Number (%)
</= 7 days	311 (62.2)
8-14 days	118 (23.6)
>14 days	71 (14.2)

Table 3 showing that 31.2% of personnel were having symptoms related to central––vestibular system, 28.4% were having gastrointestinal symptoms, 23.2% were having sopite syndrome-related symptoms and rest of the 17.2% were having peripheral autonomic symptoms.

Table 3

Types of Symptoms

Symptoms	Number (%)
Central (headache, spinning sensation, light headedness, malaise)	156 (31.20)
Gastrointestinal (nausea, belching, vomiting)	142 (28.40)
Sopite (withdrawl, apathy, lethargy)	116 (23.20)
Peripheral (sweating, cold/warm sensation, salivation)	86 (17.20)

Table 4 showing that 78.78% personnel were had self-limited minor inconvenience, not requiring any rest or medication or excuse from duty, 19.31% were having moderate symptoms requiring medication for sea sickness and rest for 24 hours, 1.91% were such individuals who had severe symptoms and required medication for longer duration along with rest and excuse from duties for more than 24 hours.

Table 4

Severity of Sea Sickness

Severity	(%)
Minor inconvenience, self limited not required rest	78.78
Moderate inconvenience, needed medication required rest for 24 hrs	19.31
Severe, required medication and excuse of duties>24 hrs	1.91

Table 5 shows that majority 54.5% were having sea sickness of first exposure and 26.5% were had symptoms even up to 10 exposures at sea. 5.4% were such that they had continued symptoms even after more than 10 exposures at sea.

Table 5

Incidence of sea sickness in relation to exposure to sea trip

Number of exposure	(%)
First	54.50
<10 exposure	26.50
>10 exposure	13.60
Always	5.40

DISCUSSION

Exposure to unfamiliar real or apparent motion at sea produces a psycho-physiological response with a complex set of symptoms affecting gastrointestinal, central, peripheral system. Once the triggering motion ceases, symptoms generally disappear completely within 24 hours.

Our study was conducted on 500 Naval personnel aged between 20 and 45 years [Table 1]. Data included anthropometry, types of symptoms with predominant system involvement, severity of sea sickness in relation to exposure and requiring medical intervention and rest or excuse from duty. In our study 62.2% personnel had sailed up to 7 days at sea, 23.6% for 8-14 days and 14.2% for more than 14 days [Table 2].

Among the symptoms those related to central nervous system (31.2%) were the most common namely dizziness, spinning sensation, light headedness, drowsiness followed by gastrointestinal system symptoms (28.4%) like nausea, vomiting, queasiness etc.

Early symptoms of incipient motion sickness with reduced alertness are also called “sopite syndrome” (from the Latin word sopire which means to lull or to put to sleep). The term describes a condition of withdrawal with increasing apathy and lethargy which the person affected may not even notice him- or herself.

In our study, 23.2% of personnel presented with sopite symptoms like feeling annoyed, irritated, drowsy, fatigue, uneasy feeling. Rest 17.2% presented with peripheral symptoms like feeling sweaty, cold, warm or hot sensation of body [Table 3].

The majority suffered mild symptoms (78.78%) and did not require any medication. Their symptoms were self-limiting and settled on rest within 24 hours. Moderately severe symptoms were observed among 19.31% personnel and had to be administered medication and rest for 24 hours. Only 1.91% had severe symptoms and had to be excused from duties along with medication and rest [Table 4].

Sea sickness on first exposure was noticed in 54.5% personnel, 26.5% personnel continued to have symptoms up to 10 exposures and 13.6% had symptoms even after 10 exposures of sea. Only 5.4% had symptoms of sea sickness each time they were sailed out [Table 5].

The scientific literature does not present a consistent picture on performance limitation due to sea sickness.[67] It is possible for the personnel to carry out their allotted task on the ship though with discomfort if they experience mild gastrointestinal symptoms like nausea, vomiting lasting for the transient duration. However, they experience apathy and depression with a resultant decrement in performance through cognitive, emotional, and motivational deficits.[6]

The pathophysiology of sea sickness is best explained by sensory conflict or neural mismatch theory.[89101112131415] Vestibular, somatosensory, and visual afferents provide information about body movements and body posture. The vestibular inputs are provided by the three semicircular canals i.e., horizontal, superior, posterior semicircular canals, stimulated by angular acceleration, and by the otolith organs i.e., saccule and utricle, which are stimulated by linear acceleration. Proprioceptive afferents from the neck muscles and the vertebral column maintain the position of the head relative to the torso. Visual inputs provide information on the body's own motion and/or that of its environment. The sense of joints movements, joint position, and acceleration is by proprioceptive afferents from the joints and skeletal musculature. Normally the three sensory channels (vestibular, visual, and proprioceptive) complement each other without contradiction. The afferents are connected to motor centers in the brainstem, which stabilize body position e.g., through the use of stabilization reactions. Sensory conflicts are the most current explanation of motion sickness. The conflict type is tabulated in Table 6 given below.[9]

Table 6

Types of kinetogenic sensory conflict

Conflict type	Category AConflicting sensory informationVisual (VIS) Vs Vestibular (VES)	Category BConflicting sensory InformationSemicircular canals (SC) Vs Otolith Organs (OT)
Type 1Conflicting motion-related input from two sensory systems	A1 VIS≠VES– Watching waves over the side of a swaying ship– Making head movements while wearing an optical device that distorts the visual field or inverts it by means of a prism	B1 SC≠OT– Vestibular Coriolis reaction. Head movement about an axis not identical with the body‘s axis of rotation, e.g., nodding the head while revolving on a rotating chair(Lansberg provocation test)
Type 2First input signals motion,second input does not	A2 VIS+VES –– Pseudo motion sickness, simulator sickness– In a stationary simulator or cinema, watching a film shot from a moving vehicle or aircraft subjected to linear and/or angular accelerations	B2 SC+OT–– Caloric nystagmus– Alcohol-related nystagmus. Head movements during weightlessness (space sickness)
Type 3Second input signals motion, first input does not	A3 VIS – VES+– Riding inside a jolting vehicle without any external visual reference– Reading a book below deck on board ship	B3 SC – OT+– Rotation at a constant speed about the body’s long axis when horizontal (barbecue rotation)

The relative incidence of some of these symptoms in 10 US navy flights studied by Kennedy and colleagues confirms similar findings.[16] Data from other studies also support these findings.[1718]

The ways to prevent sea sickness is to avoid exposure to provocative motion exposure and adaptation. Some of the measures are hydration, fresh air, keeping sight on fixed object, suitable position in the middle of the ship and antiemetics and antihistaminics.[19] Adaptation is the most potent prophylaxis. Various desensitization therapies are used for adaptation including stimuli like vertical linear oscillation and optokinetic stimulation in the belief that there will be a better adaptation to the dynamic environment.[20] The desensitization therapy has been successfully used for air crew and the same can be applied to sailors too.[202122] Desensitization physiotherapy also includes reactive motion and body positioning exercises by actively synchronizing body movements with motion including head tilts.

Nondrug therapy for sea sickness includes behavioral strategy like habituating to motion pattern, reducing intersensory conflict, and synchronizing the visual system with the motion [Table 7].[2324]

Table 7

Behavioural strategies to prevent or minimize symptoms of motion sickness

*Behavioural Therapy	Measures/features	**Level of evidence
Habituating to the motion pattern	(i) Habituate through prolonged exposure at sea(ii) Support habituation e.g., with physiotherapy exercises – Reactive exercises, wilful counter movements of the head	AC
Reducing intersensory conflict	Reduce vestibular stimuli– Avoid movements outside the axes of motion– Avoid low-frequency movements, especially vertical ones (e.g. pitching of a ship)– On a ship: amidships is better than at the bow or stern; focus on the horizon
Synchronizing the visual system with the motion	Focus on the horizon and on a distant point– If watching the horizon is not possible, it may help to close eyes and minimize head movements-- Optokinetic exercises and visual fixationUse an ‘artificial’ horizon– E.g. head-mounted displays or special glasses that provide informationabout the horizon	C
Actively synchronizing the body with the motion	Perform active synchronizing movements (e.g., tilt head into turns), walk around actively, take over steering/control, if possible	C
Breathing technique	Practice active deep diaphragmatic breathing	C

** Evidence level (SORT rating). A: Consistent, high-quality patient-oriented evidence. B: Inconsistent or limited-quality patient-oriented evidence. C: Consensus, disease-oriented evidence, usual practice, expert opinion, or case series

At sea the intersensory conflict can be minimized by looking in the direction of ship movement or gazing at the horizon.[23] Head-mounted display having an artificial horizon or horizon information will also decrease the intersensory conflict.

Medical management of sea sickness includes centrally acting anticholinergic drug-like scopolamine, which is probably the most effective, usually used as1.5 mg transdermal patch applied 6-8 hrs before exposure, it is effective for 72 hrs. Common adverse effects are dry eyes, dry mouth, and light sensitivity. Other drugs like antihistaminics have also been shown to be effective in motion sickness and they include, in ascending order of sedating potential, Cinnarizine, dimenhydrinate, diphenhydramine, and promethazine. Cinnarizine is the most commonly used antihistaminic for dizziness and vertigo due to varying pathogenesis. It is used mainly for acute episode in a dose of 25 mg thrice a day for not more than 4 – 7 days. Common side effects of its use are drowsiness, dry mouth, and stomach pain.[2324]

Avoiding foods with high histamine content, such as tuna, some kinds of cheese, processed food and red wine might be helpful. Some natural remedies like ginger and Vitamin C to repress sea sickness are also recommended by some studies. Ginger contains certain substances that antagonize 5HT3 receptors, which has an important role in the vomiting center.[25] High-dose vitamin C was found to reduce the symptoms of sea sickness because of some anti-histaminergic effect without identifiable adverse effects, in a prospective, double-blind, placebo-controlled study.[26]

In some cases good response had been found by application of transcutaneous electrical nerve stimulation (TENS) and by general stress-reduction measures such as listening to pleasant music or exposure to good odours, aroma and fragrance.[27282930]

CONCLUSION

Sea sickness is a classical type of motion sickness producing a set of symptoms on exposure to environment in which there is a conflict of vestibular and visual sensory input generating a stress reaction that results in autonomic symptoms. It is observed that sea sickness is troublesome for personnel onboard deployed in operations especially young sailors on first exposure to sailing. Once the triggering stimuli disappear symptoms get controlled within 24 hours with some exceptions. These personnel can then be managed by behavioral desensitizing habituation methods in combination with drugs like H1-antihistamines and anticholinergics.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Central	Gastrointestinal	Sopite related	Peripheral
I felt dizzy	I felt sick to my stomach	I felt annoyed/irritated	I felt sweaty
I felt like I was spinning	I felt nauseated	I felt drowsy	I felt clammy/cold sweat
I felt as if I may faint	I felt as if may Vomit	I felt tired/fatigued	I felt hot/warm
I felt lightheaded	I felt queasy	I felt uneasy