Airsickness - VSA 2009 October 2009 Airsickness VSA Lecture Series 2009 1 Airsickness Notes prepared on airsickness – causes, symptoms, prevention and treatment. Prepared by Jeff Farrow, GGC for the VSA Winter Lecture Series, 2009 Problem for newcomers to the sport, early cross country pilots been taken cross country and for TIF’s/F&F’s Airsickness 2009 Airsickness - VSA 2009 Definition October 2009 ■ Simplistically one of a number of motion induced sicknesses ■ Misnomer – Doesn’t need motion to induce – Not an illness, is physiological ■ Motion Mal-adaptation Syndrome ■ Caused by conflicting stimuli from the various balance organs 2 Definition Types Simply though of as one of a number of forms of motion induced sickness including Vestibular Visual imbalance seasickness airsickness carsickness swing-sickness (carnival rides) camel-sickness (Laurence of Arabia) Canal-Otolith space-sickness Misnamed It can be the absence of motion as well as presence of motion that can be the issue simulator sickness virtual reality sickness Cinerama sickness (IMAX etc) It is not an illness or sickness, but a normal physiological response experienced by all if provocation is severe enough More accurately defined as a motion mal-adaptation syndrome Caused by mismatched/absent signals from the various balance organs particularly the eyes, the labyrinth, and the proprioceptor system (muscles and joint position senses) The only individuals who are immune to motion sickness are those who have had their vestibular systems destroyed Airsickness 2009 Airsickness - VSA 2009 Incidence October 2009 ■ Initial individual susceptibility varies ■ Individuals develop tolerance with time and experience ■ Incidence – 99% life-raft in heavy seas – 20% USN ab initio trainees *(non-pilot aircrew) – 12% USN advanced trainees* – 8% RPT in severe turbulence – 7% USN in Flight readiness Sorties * – <1% civil RPT operations 3 Incidence Individual susceptibility varies widely, and depends predominately on the type of the motions, as well as a on a number of factors which will be discussed shortly. Individuals usually develop tolerance with continued exposure given time enough to adapt and as long as they don’t develop excessive anxiety over the condition. This is a process called adaptation. This acquired tolerance gradually fades with time, so repeated exposure is needed. This retention also varies with individuals Been a number of studies usually on service recruits. Pre-recruitment questionnaires for RAF had the incidence at 3.6%, increased to 59% on post-acceptance confidential questionnaires Airsickness 2009 Airsickness - VSA 2009 Signs & Symptoms October 2009 ■ Prodrome – Stomach awareness ■ Incipient signs – Nausea – Circumoral or facial pallor – Sweating – Apathy, introspection and poor concentration ■ Avalanche Phenomena – Salivation, flushing, light headedness – Vomiting 4 Symptoms and Signs The cardinal symptoms is nausea The sequence: Stomach awareness - epigastric discomfort and unfamiliar sensation of awareness Prodrome - Nausea of increasing severity Circumoral or facial pallor Sweating (thermal not emotive) Avalanche phenomena - Salivation, flushing, light headedness, apathy and lack of concentration (instructor may interpret as lack of aptitude/skill) VOMITING Airsickness 2009 Airsickness - VSA 2009 Sequelae October 2009 ■ Often initial transient relief of symptoms, but the cycles repeats with waxing and waning of symptoms ■ Results – Short term - Increasing prostration and inability to function – Medium - Electrolyte and hydration issues – Long term - Apathy, depression, suicide 5 Sequelae Vomiting may be followed by temporary relief of symptoms, but if the provocation continues the symptoms recur, with Short term - increasing prostration, and inability to function. Medium term - dehydration and electrolyte disturbance (hypokalemia, ketosis), can result in cardiac arrhythmias or mental changes Long term - apathy, depression and suicide (in the setting of life boats) Airsickness 2009 Airsickness - VSA 2009 Associated Symptoms October 2009 ■ Associated symptoms more variable – Belching and flatulence early – Hyperventilation – Sighing and yawning – Headache or buzzing sensation ■ Post vomiting somnolence ■ Somnolence can be the main symptom instead of nausea in those partially adapted 6 Associated Symptoms Early stages increased salivation, belching and flatulence precede the development of nausea Hyperventilation is occasionally seen, more often sighing and yawning Somnolence Typically following withdrawal of the provocation feelings of lethargy and somnolence persist for hours. Some individuals the only symptoms evoked by motion is an inordinate desire to sleep. This is typically seen in conditions where the stimulus is low enough that there has been adaptation without malaise. Seems reminiscent of the infantile response of sleep to repetitive motion Airsickness 2009 Airsickness - VSA 2009 Physiology October 2009 ■ Equilibrium is maintained by – Visual system – Vestibular system – Proprioceptive system ■ Integrated in the CNS – Brain stem and cerebellum – unconscious regulation of balance – Cerebral cortex – conscious appreciation of balance 7 Physiology The bodies equilibrium is maintained by a number of senses. Visual – Image projected on the retina. Orientate static equilibrium and slow angular and linear velocities. Not effective with faster movement, or if eyes closed. Vestibular – measures static (gravitational) orientation, angular movement, linear and angular acceleration. Less effective with constant linear movement. Effective in darkness and higher speed Proprioceptive . Stress detectors in the muscle and joint ligaments, and pressure detectors in the skin and subcutaneous tissues. Useful for determining gravitational equilibrium, acceleration and linear motion (eg air on body running). Limited sensitivity, affected by change in G-load. High input from the neck area to compensate for the specialist senses being in the head Input from these receptors is to the CNS, initially to the brain stem and cerebellum but ultimate appreciation of balance is in the temporal lobe of the cortex. Airsickness 2009 Airsickness - VSA 2009 Vestibular Apparatus October 2009 8 Vestibular Apparatus Cochlea – hearing Saccule – hearing and vibration sense in lower species, non-functional in humans Utricle contains the macula or otolith. Consists of hairs topped with denser (x3) rocks. The hairs are connected to nerve fibres. Accelerational forces, including centrifugal and gravitational forces, act on these rocks and bend the hairs. Asymmetry in the length of the hairs gives directional information (the kinocilium is always located to one side of the group of hairs). Different groups of hair cells are orientated in different directions so different groups are stimulated by different positions in space. Detect – static equilibrium, gravity pulls down on the rocks bending the hair. - linear acceleration, inertia displaces the rocks bending the hairs - constant angular velocity, changing orientation leads to changing groups of hairs being stimulated Semicircular canals in three different axes (with head bent forward 30° external horizontal, superior forwards and 45° outwards, posterior backwards and 45° outwards). The ampullae contain a gelatinous vane of similar density to the fluid in which hairs are embedded, with nerve fibres connected to them (the cupule). Movement of the vane in one direction stimulates the nerve, in the other direction inhibits it. Detect – angular acceleration causes the canals to turn and the fluid to remain still due to inertia, this causes a flow of fluid which bends the cupule generating a signal (say an increase). With constant rotation the fluid catches up due to friction and the signal settles back to a resting tone. With deceleration the reverse occurs, the fluid keeps moving for a while, the vane bends the other way, and the hair cells generate the opposite signal (a decrease). Sensitivity 1°/sec 2. By detecting changes in acceleration these organs will predict a change in position before it occurs (the otolith only after it occurs) enabling one to maintain balance. Also maintain visual fixation during fast rotation through nystagmus Airsickness 2009 Airsickness - VSA 2009 CNS Mechanisms October 2009 9 CNS Mechanisms - The various equilibratory inputs converge at the level of the brain stem. (level of these depend on receptivity). - They are transmitted to the cerebellum where they are compared with a stored copy of expected motion cues accumulated from previous experience. (retention) (mal de debarquement) - The output of this centre is a mismatch signal, transmitted through to the motor control system as well as updating the internal model (adaptation) - A sustained mismatch signal gradually accumulates (slow onset of symptoms) and may reach a threshold to stimulate the motion sickness response. This mechanism must also include some degree of leak as adaptation can occur without motion sickness. These features are suggestive of a neurohumoral mechanism though the factors involved have not been identified. - These factors act in turn on the vomiting centre of the medulla oblongata (brainstem) Why Vomiting? Motion sickness is not a sensation that would be expected in unaided man. Without technology or domestication of animals there are no likely situations where unaided man would develop motion sickness. The vestibular mechanism are complex neural mechanisms relatively exposed to the blood stream compared to the CNS behind the blood