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syncope there is collapse of peripheral resistance (relaxation of the peripheral arterial sphincter). This is
the predominant mechanism in most cases of syncope, as opposed to cardio-inhibitory syncope
characterized by bradycardia. Sudden syncope is almost always of cardiac origin (cardio-inhibitory).
Syncope is a disturbance of homeostasis, the balance between cardiac output, blood volume, and
peripheral resistance.
It is important to distinguish syncope clinically from other conditions, most importantly seizure. History
is paramount, and the medical assessor should consider the following:
1. Postural Setting: Syncope characteristically occurs in the upright position, is unusual while
sitting, and is rare in recumbency.
2. Prodrome: In vasodepressor syncope a significant prodrome of 2-5 minutes is common, during
which distinct symptoms may occur. Visual symptoms (darkened vision or constricted visual
fields, bleached white or yellow vision) point to retinal, not cerebral, ischaemia, indicating an
extracerebral event. Nausea, queasiness, yawning, lightheadedness, pallor, and sweating are
other usual features.
3. The Syncopal Event: Syncope is brief, lasting 10-15 seconds with little or no confusion. The
individual is pallid, with shallow or imperceptible respirations. Collapse is a hypotonic event in
which the individual softly folds into a heap (syncopal slump).
ICAO Preliminary Unedited Version — October 2008 III-10-6
4. Convulsive Accompaniments and Urinary Incontinence: Brief convulsive twitching or tonic
posturing occurs in ten per cent of individuals with syncope, and urinary incontinence occurs in a
similar proportion. Care must be taken to avoid interpreting these features as indications of
epileptic seizure.
5. Syncopal Setting: Specific circumstances are often associated with syncope. These include
worry, fear, micturition, physical exertion (weightlifter’s syncope), medical procedure such as
venipuncture, pain, sight of blood, and others.
When determining the aeromedical significance of syncope, the medical assessor must search for the
mechanism of its occurrence. Fortunately, benign situational syncope is the most common event. Other
causes include orthostatic events related to medication, blood loss, dehydration, and other mechanisms.
Disturbances of cardiac output and disturbances of cardiac rhythm must also be considered. Seizures may
mimic syncope, and differentiating syncope from seizure has clear aeromedical implications. The nature
and direction of evaluation for syncope is guided by the clinical setting. Once potentially serious
mechanisms of syncope have been ruled out, medical certification can be considered.
Operational implications:
Syncope should be considered disqualifying for all classes of medical certification until the cause for
syncope is identified and the risk for recurrence has been determined.
Aeromedical considerations:
Fortunately syncope is mostly benign and often situational. Medical certification is appropriate when the
benign nature of the event has been identified and potentially serious mechanisms of syncope have been
considered and excluded. If treatment or other countermeasures are employed, an observation period
ranging from three months to one year might be appropriate. A three month period might be appropriate
when one or two fully explained benign events have occurred over time, whereas multiple recurrent
episodes requiring treatment may warrant a six to twelve month period of observation before medical
certification is considered. Restriction to multicrew operations and non-safety-sensitive air traffic control
duties, at least for a period, may further mitigate the risk.
Seizure Disorder
A seizure is an abnormal paroxysmal excessive discharge of cerebral cortical neurons. Epilepsy, seizure
disorder, and convulsive disorder are synonymous terms. Epilepsy is defined as a tendency towards
recurrent, unprovoked seizures. An individual must experience recurrent (i.e. at least two) seizures to
qualify for a diagnosis of epilepsy.
Not all seizures represent epilepsy. For example acute symptomatic seizures can occur with insulin
induced hypoglycaemia, hypoxia from cardiac arrest, hyponatraemia, acute infection (e.g. pneumococcal
meningitis with high dose penicillin) and other symptomatic precipitants. These conditions do not portend
chronic seizure potential. On the other hand, symptomatic seizures related to a subdural haematoma six
months earlier imply a glial scar and likely recurrent seizures.
For aeromedical purposes, a basic seizure classification suffices:
1. Generalized from Onset: At seizure onset, as the name implies, simultaneous epileptiform
discharges appear in all areas of the cortex. Idiopathic grand mal epilepsy is a prime example of
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Manual of Civil Aviation Medicine 2(26)
