 Neurologic
Issues in Aviation*
Disturbances
of Awareness or Consciousness
Dizziness
is a symptom with numerous causes. Determine what the patient means by
"dizziness" by asking what they feel such as: about to pass out
(pre-syncope), a spinning sensation or illusion (vertigo), trouble walking
without vertigo or pre-syncope (dysequilibrium), lightheadedness with or without
anxiety. Not all dizziness involves vertigo (spinning). Check for red flags that
may indicate an ominous cause: fever, stiff neck, head trauma (more than mild),
cranial nerve dysfunction, severe headache, difficulty mentating, seizure,
double vision, difficulty swallowing or talking, severe depression (suicide
risk), suspected toxin, medication or illegal drug exposure, infection, alcohol
(subdural), chest pain, difficulty breathing, severe hypertension or hypotension,
or history suggestive of DCS. If vertigo (spinning) is the only symptom and head
movement triggers it then Benign Positional Vertigo is the most likely
diagnosis. Other common causes of dizziness in the military population include:
heat exhaustion, motion sickness, dehydration, head trauma, vasovagal, toxin
exposure, electrolyte disturbance, drugs, alcohol, hyperventilation, sleep
deprivation and psychiatric. Aviators may experience "dizziness" while
flying secondary to various illusions or hypoxia.
Headache
in the aviation environment can be distracting to the point that safety of
flight could be compromised. Medications used to treat headache can have side
effects with similar concerns. The most common headache is tension type
characterized by gradual onset, steady bilateral pain that is not throbbing and
is long lasting. Similar headaches can be associated with stress, dehydration,
fasting, withdrawal from coffee or medications, exposure to a toxin, associated
with an infection, endocrine dysfunction, following head trauma, sleep
depravation, or depression. Migraine is a type of headache characterized by
unilateral throbbing pain that lasts for hours to days and is associated with
nausea, vomiting, photophobia, sound sensitivity, is aggravated by physical
activity and may be preceded by an aura. Visual aura that is most described is
the fortification spectra (see figure 1). Cluster headaches are severe and
recurring but fortunately usually short in duration. The pain is boring, sharp
around an eye that is red with a droopy eyelid, lacrimation, nasal congestion
and often occurs during REM sleep. The headache associated with a sinus
infection is characterized by local pain behind the eyes with malaise, nasal
discharge and fever. The vast majority of headaches are benign but bacterial
meningitis, subarachnoid hemorrhage and brain tumors do occur in the military
population. Headache red flags include: fever, stiff neck and
"explosive" onset over several minutes with nausea and vomiting,
alterations in consciousness, third nerve palsy or any neurologic dysfunction.
Motion
Sickness in
the aviation environment is generally detected and treated early in flight
training. Symptoms include cold sweating, nausea, drowsiness, yawing, facial
pallor, salivation, lethargy, apathy, headache and vomiting. Airsickness is
motion sickness in the flight environment and can cause poor flight performance
and affect motivation. A Self Paced Airsickness Desensitization Program (SPAD)
at the Naval Operational Medicine Institute in Pensacola has a 60% success in
treating motion sickness (see figure 2).
Head
Trauma
resulting in loss of consciousness (LOC) or post traumatic amnesia (PTA) can be
classified as PTA+LOC: minor <5 min, mild >5min but <1hr, moderate 1-24
hrs, and severe >24 hrs, traumatic brain injury. A careful and accurate
estimation of this time is important because it determines how long an aviator
must be observed before a waiver to return to flying can be submitted following
a head injury. Following head trauma even without LOC or PTA, posttraumatic
symptoms can occur and include: headache, dizziness, sleep disturbance, blurred
vision, poor concentration, memory disturbance, irritability, depression, and
personality change. Posttraumatic seizures are the most significant aeromedical
concern following head trauma. The risk is proportional to the level of injury
and diminishes with time.
Seizures
in aviators are of obvious concern because of the almost certain risk of injury
to self or others. Although partial seizures are not fully incapacitating as
Grand Mal (generalized) seizures, they can interfere with critical tasks and
have the potential to secondarily become generalized. Seizures are more likely
following sleep deprivation, heavy alcohol use, illicit drug use, severe head
trauma, brain infections bleeding or tumors. Post-ictal confusion following a
seizure helps to distinguish it from syncope.
Syncope
is most often caused by vasodepressor (vasovagal), neurogenic, orthostatic, and
cardiac etiologies. Transient loss of consciousness from a two-thirds reduction
or more of cerebral blood flow differs from seizure in several ways. The rapid
return to normal level of attentiveness, facial pallor and sweating, occurring
only in upright posture or precipitated by anxiety or pain (e.g. venipuncture)
are typical features of syncope. Lightheadedness, with loss of peripheral vision
"graying out" and unconsciousness can occur during flight when blood
flow to the brain is reduced by "G" forces (G-LOC). Typical features
of seizure include focal sensory or motor phenomena, auras, bladder
incontinence, tongue or cheek bites, muscle soreness, lethargy and unnatural
need to sleep, headache and post-episode (post-ictal) confusion. Correct
diagnosis of loss of consciousness is essential and aviators are grounded until
the diagnosis is clear and is not likely to recur.
Convulsive
Syncope may
be confused with seizure and may be experienced in 12% of syncope cases. The
convulsive movements are identical to those seen in seizure but are due to more
severe or prolonged diminution of blood flow to the brain. This is most often
seen when a person is maintained in the upright or sitting position following
syncope in an attempt to prevent injury. Falling to the ground serves an
important compensatory role in syncope.
Hypoxia
in the aviation environment can result in loss of consciousness. Typical
symptoms include decrease in night vision, drowsiness, air hunger, apprehension,
fatigue, nausea, headache, dizziness, hot and cold flashes, euphoria, blurred
vision, tunnel vision, numbness, tingling, poor judgment and coordination,
difficulty talking, unconsciousness, convulsions, circulatory failure and in the
critical stage, death.
Hyperventilation
causes in increase in blood pH, vasoconstriction of blood vessels supplying the
brain, resulting in a drop in the oxygen concentration and unconsciousness if
severe enough.
Excessive
Daytime Sleepiness
(EDS) is a symptom common to several sleep disorders. It is also a common
complaint during sustained flight operations and is due to inadequate
restorative sleep. Regardless of the cause, EDS can result in mishaps from
fatigue, poor concentration, inattention or inadvertently falling asleep. Sleep
disorders associated with EDS are Sleep Apnea Syndrome, Narcolepsy, Periodic
Movements of Sleep, and Restless Legs Syndrome. An overnight polysomnogram and
multiple sleep latency test aid in the diagnosis of these sleep disorders.
Toxin
exposure from
environmental hazards in the aviation environment can result in confusion,
delirium, delusions, coma and death. Organic hydrocarbons (jet fuel), solvents,
carbon monoxide and other combustion products are common toxins. Others include
alcohol, drugs, medications, heavy metals, food poisoning, and organophosphates
(insecticides, nerve agents).
Heat
exhaustion
results from excessive sweating without fluid replacement causing fatigue,
weakness and anxiety. The individual has cold, pale, clammy skin and disordered
mentation with a slow pulse and low blood pressure. Heatstroke differs in that the skin is hot, flushed and usually dry
with a rapid pulse and no drop in blood pressure. Disorientation may briefly
precede unconsciousness or convulsions, the temperature climbs rapidly to 40º C
(104º F) or higher and is a medical emergency.
Acute
infections such
as meningitis, septicemia and toxic shock can cause mental confusion and are
medical emergencies.
This section was
contributed by CDR Henry Porter, MC, USN (FS).
*Source:
Operational Medicine 2001, Health
Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau
of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington,
D.C., 20372-5300 |
