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Flight Physiology 101


The physiological significance is in the explanation of gas exchange ... Physiological. Sleep State. Fatigue. Alcohol. Psychological. Mental State. Psychosocial ... – PowerPoint PPT presentation

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Title: Flight Physiology 101

Flight Physiology 101
  • Jeremy Maddux, NREMTP

Functions of the Atmosphere
  • Source of oxygen and carbon dioxide
  • Shield against cosmic and solar radiation
  • Protective layer that consumes debris from space
  • Source of rain
  • Maintains the temperature and climate that
    sustain life on earth

Components of the Atmosphere
  • Gas percentages REMAIN THE SAME with changes in
    altitude the NUMBER of molecules in a given
    area decrease with altitude increases
  • Gases are compressible therefore pressures vary
    with altitude

Atmospheric Pressure
  • Atmospheric (barometric) pressure is the combined
    weight of all the atmospheric gases, creating a
    force upon the surface of the earth the cause
    of this force is gravity
  • The pressure of a column of the atmosphere can be
    measured in force / unit area
  • Pounds per square inch
  • Millimeters of mercury
  • Inches of mercury (Hg)

Average Barometric Pressures
Measures of Altitude
  • True Altitude
  • Altitude above mean sea level
  • Absolute or Tapeline Altitude
  • Altitude of aircraft above the surface
  • Pressure Altitude
  • Flown over the continental US above 18,000 feet
    and are referred to as flight levels
  • i.e., 18,000 feet FL 180

Measures of Altitude
  • An Altitude Reference standard day conditions
  • When the pressure is 29.92 inches of Hg (760 mm
    Hg) and the temperature is 59º F ( 15º C) a
    standard day exists
  • As barometric pressure changes locally, this
    altitude changes
  • Reflects standard conditions at sea level

Physiologic Divisions of the Atmosphere
  • Physiologic Zone
  • Physiologically Deficient Zone
  • Partial Space Equivalent Zone
  • Space Equivalent Zone

Physiologic Zone
  • Sea level to approximately 10,000 feet
  • Some references state 12,000 feet
  • The human body is adapted in this zone
  • Barometric pressure drops from approximately 760
    mm Hg to 485 mm Hg in this zone
  • Zone where non-pressurized aircraft operate safely

Physiologic Zone
  • Problems may develop in individuals who are
    exposed to higher altitudes than they are
    normally exposed if they
  • Remain at the altitude for prolonged periods
  • Exert themselves

Physiologic Zone
  • Symptoms of Prolonged Exposure
  • Shortness of breath
  • Dizziness
  • Headache
  • Sleepiness
  • Sinus and ear disturbances
  • Treatment
  • Supplemental oxygen
  • Descent

Physiologically Deficient Zone
  • 10,000 to 50,000 feet (or FL 500)
  • Most commercial aviation occurs in this zone
  • Human survival in this zone depends on
    pressurized cabins and/or supplemental oxygen
  • Barometric pressure drops to 87 mm Hg in this
  • Because of the reducing atmospheric pressure,
    hypoxia is a problem during ascent without
    artificial atmosphere

Partial Space Equivalent Zone
  • 50,000 feet to 120 miles
  • Similar to space
  • Pressurized suits required
  • Changes in gravity affect the body

Space Equivalent Zone
  • Above 120 miles
  • Artificial atmosphere/pressure suits mandatory
    for life
  • Weightlessness effects
  • Outer space

Gas Laws
  • The body responds to barometric pressure changes
    in temperature, pressure, and volume.
  • Boyles Law
  • Henrys Law
  • Charles Law
  • Daltons Law
  • Grahams Law

Boyles Law
  • At a constant temperature, a given volume of gas
    is inversely proportional to the pressure
    surrounding the gas
  • A volume of gas expands as the pressure
    surrounding the gas is reduced
  • As altitude increases / gas expands and as
    altitude decreases / gas compresses

Boyles Law
  • Boyles Law Formula
  • P1 x P2 P2 x V2 or V2 (P1V1) P2
  • Where
  • P1 initial volume (original altitude)
  • P2 final pressure (maximum altitude enroute)
  • V1 initial volume (volume of gas at original
  • V2 final volume (volume of gas at maximum

Boyles Law
  • Example
  • A patient with a pneumothorax (without
    intervention) has 500cc of trapped gas within the
    lung at liftoff from sea level (760 mm Hg). The
    flight travels up to 6,000 ft where barometric
    pressure is 609 mm Hg.
  • P1 760 V2 (760 x 500) 609
  • P2 609 V2 623cc
  • V1 500 V2 final volume of trapped air

Boyles Law
  • Clinical Significance
  • The amount of volume expansion is limited by the
    pliability of the structure or membrane which
    encloses the gas
  • PASG or Air Splints
  • Respiratory Rate and Depth changes
  • Flow rates of IV sets
  • ETT or Tracheal cuff pressures
  • Trapped gas effects within the body

Henrys Law
  • The amount of gas in solution is proportional to
    the partial pressure of that gas over the
  • As the pressure of the gas above a solution
    increases, the amount of that gas dissolved in
    the solution increases
  • Reverse is also true, as the pressure of the gas
    above a solution decreases, the amount of gas
    dissolved in the solution decreases and forms a
    bubble of gas within the solution

Henrys Law
  • In normal physiologic function, this law can be
    seen in the transfer of gas between the alveoli
    and the blood
  • This is significant physiologically for the
    occurrence of evolved gas disorder, aka
    decompression sickness
  • Explains the hypoxia experienced with increasing
    altitude as the pressure of gases is reduced
    with ascent, the amount of gases dissolved in
    solution decreases and this leads to hypoxia and
    may lead to nitrogen bubble formation

Henrys Law
  • Henrys Law Formula
  • P1 A1 P2 A2
  • Where
  • P1 original pressure of the gas above the
  • P2 final gas pressure above the solution
  • A1 amount of gas dissolved in solution at the
    original pressure
  • A2 amount of gas dissolved in solution at the
    final pressure

Henrys Law
  • Example
  • Bottle of soda
  • With the cap on, the gas within the solution is
    at equilibrium
  • With the cap removed, the gas pressure decreases
    and bubbles are released into the solution

Charles Law
  • The pressure of a gas is directly proportional to
    its temperature with the volume remaining
  • Temperature increases make gas molecules move
    faster, and greater force is exerted and volume
  • The law explains the temperature changes
    associated with rapid decompression, and pressure
    changes inducing temperature changes with an
    oxygen cylinder

Charles Law
  • Charles Law Formula
  • V1 T1 V2 T2
  • Where
  • V1 initial gas volume
  • V2 final gas volume
  • T1 initial absolute temperature
  • T2 final absolute temperature
  • Example
  • Shaving cream can placed into fire

Daltons Law
  • Describes the pressure exerted by a gas at
    various altitudes (pressures)
  • Each gas present in the atmosphere contributes to
    the total
  • The sum of the partial pressures is equal to the
    total atmospheric pressure

Daltons Law
  • As altitude increases gases exert less pressure
  • Explains the hypoxia that occurs with flight to
    higher altitudes
  • Example
  • Oxygen at sea level
  • O2 21 and PO2 21 x 760 mm Hg 159.22 mm Hg
  • Oxygen at 8,000 feet
  • O2 21 and PO2 21 x 565 mm Hg 118.65 mm Hg
    changes in altitude

Daltons Law
  • Daltons Law Formula
  • Where
  • Pt P1 P2 P3…Pn
  • Pt total pressure
  • P1…Pn partial pressures of constituent gases of
    the mixture

Daltons Law
  • Air sample at seal level
  • pO2 160 mm Hg 21
  • pN2 593 mm Hg 78
  • other 7 mm Hg 1
  • 760 mm Hg 100
  • Air sample at 18,000 feet
  • pO2 80 mm Hg 21
  • pN2 296 mm Hg 78
  • other 4 mm Hg 1
  • 380 mm Hg 100

Grahams Law
  • Law of gaseous diffusion
  • Gases diffuse or migrate from a region of higher
    concentration (or pressure) to a region of lower
    concentration (or pressure) until equilibrium is
  • The physiological significance is in the
    explanation of gas exchange
  • Oxygen moves from the alveoli into the blood and
    from the blood into the tissues due to this

The Stresses of Flight
  • Areas or methods in which persons involved in
    flight (patients and crew members) may be
    physiologically affected by the flight
  • Stress is anything that places a strain on the
    ability of a human to perform at optimum level

Types of Stresses
  • Physical
  • Size
  • Shape
  • Build
  • Physiological
  • Sleep State
  • Fatigue
  • Alcohol
  • Psychological
  • Mental State
  • Psychosocial
  • Motivation
  • Goal Direction
  • Money
  • Family
  • Pathological
  • Health / Wellness

The 9 Stresses of Flight
  • Hypoxia
  • Barometric Pressure
  • Thermal
  • Gravitational Forces
  • Noise
  • Vibration
  • Third-Spacing
  • Decreased Humidity
  • Fatigue

  • A state of oxygen deficiency sufficient to impair
  • There are four types
  • Hypoxic hypoxia
  • Hypemic hypoxia
  • Stagnant hypoxia
  • Histotoxic hypoxia

Hypoxic Hypoxia
  • AKA Altitude Hypoxia
  • Due to a lack of oxygen available for gas
    exchange within the alveoli
  • Causes
  • Decreased partial pressure of oxygen in inspired
  • Airway obstruction
  • Ventilation / Perfusion defects

Hypoxic Hypoxia
  • Occurrences
  • Improper function of oxygen delivery equipment
  • Loss of cabin pressurization
  • No use of supplemental oxygen with sustained
    cabin altitudes above 10,000 feet
  • Also seen in drowning victims or strangulation

Hypoxic Hypoxia
  • As altitude increases the partial pressure (PaO2)
    decreases (Daltons Law)
  • As the PaO2 falls in the alveoli, the amount of
    O2 which diffuses into the blood decreases
    (Henrys Law)
  • Results in a decrease in oxygen available to the

Changes in Oxygen Saturation in the Blood with
Altitude Increases
Hypemic Hypoxia (Anemic)
  • The inability of blood to accept sufficient
  • A reduction in the oxygen-carrying capacity of
    the hemoglobin (Hgb)

Hypemic Hypoxia (Anemic)
  • Causes
  • Anemia
  • Blood Loss / Donation
  • Carbon Monoxide (CO) Poisoning
  • Sickle Cell Disease
  • Sulfa Drugs
  • Excessive Smoking (related to CO levels)

Stagnant Hypoxia
  • Pooling of blood causes insufficient flow of
    oxygenated blood to tissues
  • Oxygen deficiency due to lack of movement of
    blood within the body

Stagnant Hypoxia
  • Causes
  • Gravitational Forces
  • Temperature Extremes
  • Prolonged Positive Pressure Breathing
  • Hyperventilation
  • Regional Vasoconstriction (e.g., tourniquets)
  • Heart Failure
  • Compromised Cardiac Output States

Histotoxic Hypoxia
  • Inability of tissue cells to accept and utilize
  • Metabolic disorder of the cytochrome oxidase
    enzyme system

Histotoxic Hypoxia
  • Causes
  • Cyanide Poisoning
  • Phosgene Gas
  • Carbon Monoxide (CO) Poisoning
  • Alcohol Ingestion
  • Narcotics

General Causes of Hypoxia
  • All hypoxias are additive
  • All hypoxias are insidious in presentation
  • All hypoxias cause intellectual impairment
  • All hypoxias occur between 15,000 and 35,000 feet

Signs / Symptoms of Hypoxia
  • Symptoms are the same regardless of the nature of
    the hypoxia
  • Early symptoms mimic alcohol intoxication or
    extreme fatigue
  • Each persons symptomology will vary as
    tolerances to hypoxic states vary
  • Each crew member must be familiar with their own
    symptoms and must observe their coworkers for
    presentation symptomology

Subjective (felt by you) Signs / Symptoms of
  • Apprehension
  • Blurred or double vision
  • Night vision decrements
  • Dizziness
  • Fatigue
  • Headache
  • Hot / Cold flashes
  • Nausea
  • Numbness
  • Tingling
  • Euphoria
  • belligerence

Signs / Symptoms of Hypoxia
  • Night vision decrements
  • Night vision is very subjective to hypoxia
  • Night vision is reduced by 25 at 8,000 feet
  • Cabin altitudes of 5,000 feet can alter night
  • Night vision adaptation requires 30 minutes
  • Looking at bright or white light erases
    adaptation and requires a re-adaptation period

Objective (noticed by others) Signs / Symptoms of
  • Increased rate of breathing
  • Cyanosis (late sign)
  • Impaired task performance
  • Loss of muscle coordination
  • Mental confusion
  • Unconsciousness

Symptomology Altitude Frequency of Occurrence
Stages of Hypoxia
  • There are 4 general stages
  • Indifferent Stage
  • Compensatory Stage
  • Disturbance Stage
  • Critical Stage

Indifferent Stage
  • Sea Level to 10,000 feet
  • O2 saturation 90 to 98
  • Stage of normal operations
  • Symptomology may appear with higher altitudes of
    this range
  • Most persons unaware of symptoms
  • Most common symptoms are increases in respiratory
    rate and decreases in night vision

Compensatory Stage
  • 10,000 to 15,000 feet
  • O2 saturation 80 to 90
  • Symptoms advance from previous stage
  • Efficiency is impaired
  • Night vision decreases 50

Compensatory Stage
  • Respiratory rate and depth increase related to
    air hunger
  • Blood pressure and heart rate increase
  • Nausea and vomiting (more pronounced in
  • CNS Symptoms
  • Headache
  • Amnesia
  • Decreased LOC
  • Belligerence
  • Fatigue
  • Apprehension
  • Evidenced by
  • Poor judgment
  • Impaired coordination
  • irritability

Disturbance Stage
  • 15,000 to 20,000 feet
  • O2 saturation 70 to 80
  • Stage when definitely aware of symptoms
  • Previous symptoms increase in intensity

Disturbance Stage (Symptoms)
  • CNS
  • Slowed thinking
  • Impaired mental functioning
  • Impaired short-term memory
  • Dizziness
  • Sleepiness
  • Loss of muscle coordination
  • Sensory
  • Increase in visual disturbances
  • Mainly peripheral
  • Tunnel vision
  • Numbness
  • Decreased awareness of pain
  • Decreased sense of touch

Disturbance Stage (Symptoms)
  • Personality
  • Euphoria
  • Aggressive or belligerent
  • Depression
  • Over confident
  • Performance
  • Decreased coordination
  • Slowed speech
  • Impaired handwriting
  • Cyanosis

Critical Stage
  • 20,000 to 30,000 feet
  • O2 saturation 60 to 70
  • Symptomology
  • Mental confusion
  • Incapacitation
  • Unconsciousness
  • Seizures
  • Inability to remain upright
  • Coma and death
  • Ignored signs and symptoms of hypoxia can result
    in death

Time of Useful Consciousness (TUC)
  • The interval of time from interruption of an
    adequate oxygen supply to the tissues to the loss
    of the ability to help yourself
  • The TUC is the time that the crew member has
    before LOSING CONSCIOUSNESS from hypoxia!
  • This is the amount of time the crew member has to
    self-administer oxygen in order to maintain
    consciousness at higher altitudes

Effective Performance Time (EPT)
  • The amount of time a crew member can effectively
    function with an insufficient supply of oxygen

Time of Useful Consciousness (TUC)
  • Explained by the gas laws
  • Henrys Law
  • O2 levels in the blood decrease in response to
    lower PaO2
  • Law of Gaseous Diffusion
  • Diffusion of gas from an area of higher
    concentration to an area of lower concentration
  • The greater the gradient the faster the rate of
    diffusion and thus a rapid drop in TUC with
    increases in altitude

Time of Useful Consciousness (TUC)
Time of Useful Consciousness (TUC)
  • A rapid decompression can reduce the TUC by 50
  • Flight team members must be aware of their status
  • Those who become incapacitated are a risk not
    only to themselves but to their patients and
    partners as well

Factors Involved in Hypoxia
  • Altitude
  • Rate of ascent
  • Duration of exposure
  • Individual tolerance
  • Physical fitness
  • Physical activity
  • Environmental temperatures
  • Self-imposed stresses

Prevention of Hypoxia
  • Cabin pressurization (discussed later)
  • Supplemental oxygen
  • Ensures adequate oxygen deliver to lungs
  • Oxygen adjustment calculation
  • Used to calculate increase in oxygen delivery to
    compensate for decreases in PaO2 associated with

Oxygen Adjustment Calculation
  • IO2 x BP1
  • BP2
  • Where
  • BP1 barometric pressure prior to ascent
  • BP2 barometric pressure at altitude
  • IO2 inspired O2

IO2 required at altitude
Oxygen Adjustment Calculation
  • Example
  • A patient is flown from seal level (760 mm Hg) to
    5,000 feet (632 mm Hg)
  • 21 x 760
  • 632
  • Example
  • A patient on .50 IO2 is flown from sea level (760
    mm Hg) to 5,000 feet (632 mm Hg)
  • 50 x 760
  • 632

.25 IO2 required
.60 IO2 required
Oxygen Delivery / Adjustment Altitude Chart
Positive Pressure Breathing
  • Method of maintaining an adequate alveolar pO2 at
    high cabin altitudes (above 40,000 feet)
  • Positive pressure drives the O2 to diffuse
  • Causes a reversal of the breathing cycle to
    passive inspiration and very active expiration

Positive Pressure Breathing
  • Tendency to hyperventilate must be monitored, and
    controlled with training
  • Use is limited in duration due to physiological
    effects of decreased venous return to the heart
    (stagnant hypoxia)
  • Other limitations include very difficult speech
    over forced airflow, poor communication, and a
    feeling of claustrophobia in some individuals

Treatment of Hypoxia
  • Prevention
  • Recognition of symptoms
  • Monitor patient for symptoms / response
  • Supplemental oxygen
  • Oxygen cylinder capabilities

Oxygen Concentration Available with Common
Adjuncts at Sea Level
Oxygen Cylinder Capabilities
  • 1 cubic foot of gas 28.3 liters of oxygen
  • Various cylinder sizes and capabilities
  • D cylinder 12.7 cu.ft. 359.4 liters
  • E cylinder 22 cu.ft 622.6 liters
  • F cylinder 55 cu.ft. 1,556.5 liters
  • G cylinder 187 cu.ft. 5,292 liters
  • H/K cylinder 244 cu.ft. 6905.2 liters

Calculation of Duration of Oxygen Availability
  • cu.ft. x 28.3 x (PSI 2200)
  • liter flow
  • Where
  • cu.ft. capacity of tank in cubic feet
  • 28.3 liters of oxygen per cu.ft. of gas
  • PSI Psi reading on gauge of cylinder
  • 2200 a constant (maximum psi when full)

duration in minutes
Calculation of Duration of Oxygen Availability
  • Example
  • D cylinder
  • 12.7 cu.ft. x 28.3 x (1,500 2,200) 245.05
  • 10 liters per minute 10 lpm
  • 24.5 minutes of available oxygen

Liquid Oxygen (LOX)
  • Each liquid liter 860.3 gaseous liters
  • 860.3 gaseous liters 30.38 cu.ft.
  • System capacity varies with size of container
  • Common size for HEMS is 25 liquid liters
  • 25 liquid liters 21,507.5 gaseous liters
  • 21,507.5 gaseous liters 759.5 cu.ft.

Barometric Pressure (Boyles Law)
  • Gases within the body are influenced by pressure
    changes outside the body
  • Ascent pressure is decreased and gases expand
  • Descent pressure is increased and gases
  • The body can withstand changes in total
    barometric pressure as long as the air pressure
    within the body cavities is equalized to ambient

Barometric Pressure
  • Body cavities most often affected
  • Gastrointestinal tract
  • Middle ear
  • Paranasal sinuses
  • Teeth
  • Respiratory tract

Gastrointestinal Tract
  • Most frequently experienced with a rapid ascent
    (decrease in barometric pressure)
  • Symptoms result from gas expansion
  • Above 25,000 feet distention could be large
    enough to produce severe pain
  • May produce interference with breathing

Gastrointestinal Tract
  • Sources of Gas
  • Swallowed air (including gum chewing)
  • Food digestion
  • Carbonated beverages
  • Treatment
  • Belching or passing flatus
  • Expulsion aided by walking or moving about
  • Massage the affected area
  • Loosen restrictive clothing
  • Use of a gas reducing agent (Pepto Bismol)
  • Descent to a higher pressure

The Middle Ear
  • Ascent to altitude
  • As barometric pressure decreases with ascent, gas
    expands within the middle ear
  • Air escapes through the eustachian tubes to
    equalize pressure
  • As pressure increases, the eardrum bulges outward
    until a differential pressure is achieved and a
    small amount of gas is forced out through
    eustachian tube and the eardrum relaxes

The Middle Ear
  • Descent to altitude
  • Equalization of pressure does not occur
  • Eustachian tube performs as a flutter valve and
    allows gas to pass outward easily, but resists
    the reverse
  • During descent the ambient pressure rises above
    that inside and the eardrum is forced inward
  • If pressure is not equalized
  • Ear block may occur and it is extremely difficult
    to reopen the eustachian tube
  • The eardrum may not vibrate normally and
    decreased hearing results

Ear Block (Barotitis Media)
  • Symptoms
  • Ear congestion
  • Inflammation
  • Discomfort
  • Pain
  • Temporary impairment of hearing
  • Bleeding (severe cases)
  • Vertigo
  • Contributing Factors
  • Flying with head cold
  • Flying with a sore throat
  • Otitis media
  • Sinusitis
  • Tonsillitis

Ear Block (Barotitis Media)
  • Treatment
  • Yawning or swallowing
  • Valsalva maneuver
  • Nasal sprays best used prior to descent
  • Pain medications
  • For infants / children provide a bottle / straw
    to suck
  • Politzer bag used to force air through the
    eustachian tube
  • Ascend to safe altitude where symptoms subside
    and then slowly descend

Ear Block (Barotitis Media)
  • Prevention
  • Stay ahead of your ears
  • Valsalva during descent
  • Use self-medications with vasoconstrictors with
  • Rebound effects of nasal sprays may not allow
    swelling to subside

Delayed Ear Block
  • Occurs in situations where crew members breath
    100 oxygen at altitude or in an altitude
    chamber, especially if oxygen was maintained
    during descent to ground level
  • Symptoms occur 2 to 6 hours after descent
  • Oxygen in the middle ear is absorbed and creates
    a decreased pressure
  • Prevention valsalva numerous times after
    altitude exposure to prevent absorption

The Sinuses
  • Most often involves frontal sinuses (above each
    eyebrow) and maxillary sinuses (both cheeks)
  • Sinus ducts have openings into the nasal passage
  • Gas vented with increases upon ascent most often
    without problems
  • With descent, air moves back out through the
    ducts if they are open
  • If the openings are swollen or are malformed, a
    blockage may occur

The Sinuses
  • Symptoms
  • Severe pain
  • Possible epistaxis
  • Possible referred pain to teeth
  • Treatment
  • Equalize pressure as quickly as possible
  • Valsalva is sometimes effective
  • Coughing against pressure is effective
  • Ascent to safe altitude then slow descent
  • Nasal sprays may help

The Sinuses
  • Prevention
  • Try to maintain an equalized pressure
  • Keep ahead of your ears

The Teeth (Barodontalgia)
  • Incidence is low
  • Pain is excruciating
  • Altitude of occurrence varies greatly with
  • Air trapped within teeth expands with ascent
  • Confirmed barodontalgia is experienced in
    previously restored defective teeth
  • Untreated caries may cause pain at altitude
  • Rarely caused by a root abscess with a small
    pocket of trapped gas

The Teeth (Barodontalgia)
  • Treatment / Prevention
  • Descent
  • Pain medications
  • Good dental hygiene

The Respiratory Tract
  • Hypoxia
  • Pneumothorax
  • Diagnosis and treatment prior to flight
  • Existing pneumothorax left untreated will expand
    with pressure decreases
  • If the lung tissue continues to be compressed due
    to trapped gas expansion, intrathoracic pressure
    will increase
  • Vascular structures within the chest may become
  • Potential tension pneumothorax

Effects Upon Mechanical Ventilators
  • Pneumatic controlled and powered
  • With decreased barometric pressure and increased
  • Increased inspiratory time
  • Increased tidal volume
  • Increased flow rate
  • Increased expiratory time
  • Decreased rate
  • Opposite with descent

Effects Upon Mechanical Ventilators
  • Electronic controlled and powered
  • No effect on controls from altitude / pressure
  • Flow rate of O2 may change
  • Patient tidal volume may change

  • Air medical operations place crew members and
    patients in situations within a wide range of
  • Ambient temperature decreases with increasing
  • Atmospheric temperature decreases 2 C for each
    1,000 ft increase in altitude
  • Weather temperature variations can create air
    turbulence monitor for motion sickness and
    increased fatigue

  • Variations in Temperature Contribute to
  • Stress
  • Fatigue
  • Motion sickness
  • Dehydration
  • Disorientation
  • Contributing Factors
  • Circulating air within cabin
  • Amount of time exposed to thermal stress
  • Type of clothing
  • Personal physical conditioning

Heat Loss
  • Minimizing Heat Loss Enroute
  • Warm cabin environment
  • Blankets and layering
  • Avoid direct contact with cold surfaces
  • Remove wet clothing
  • Limit surface are of any wet dressings
  • Preventive Measures
  • Keep clothing dry
  • Limit exposure to mechanisms of heat loss
  • Radiation
  • Conduction
  • Evaporation
  • Convection
  • Avoid alcohol
  • Monitor wind chill
  • Wear layer of clothing

Gravitational Forces
  • The force of gravity on a human body is referred
    to as G
  • 1 G is the force exerted upon a body at rest
  • During flight, an aircraft moves and maneuvers
    through the atmosphere with force (thrust) and
    centrifugal forces are applied along various axes
  • These forces also apply to occupants

Gravitational Forces
Gravitational Forces
  • Physiological Effects of G Forces
  • G forces affect blood pooling
  • Influenced by
  • Weight and distribution
  • Gravitational pull
  • Centrifugal force
  • Positive Gz
  • Blood pooling in lower extremities
  • Increased intravascular pressures
  • Stagnant hypoxia
  • Negative Gz
  • Stagnant hypoxia
  • Blood pooling in upper body
  • Headache

Gravitational Forces
  • Variations in G Force Application
  • Motion sickness
  • Vestibular apparatus within the middle ear
  • Balance center is sensitive to changes is G force
  • Excessive, abnormal or abrupt changes lead to
    motion sickness syndromes
  • Spatial disorientation
  • Inability to correctly orient oneself with
    respect to the horizon
  • Body senses which assist in maintenance /

Body Senses Which Assist in Maintenance of
Balance / Equilibrium
  • Vision
  • Most valid sense for maintaining orientation
  • Vestibular Apparatus
  • Otolith Organs
  • Proprioception System

Vestibular Apparatus
  • The structures for balance maintenance
  • Located in the inner ear (semicircular canals)
  • Monitors angular acceleration
  • Three / ear on each axis yaw, pitch, roll
  • Each canal is a bony, fluid-filled structure
  • Enlarged area containing a sensory structure

Otolith Organs
  • Monitor linear acceleration
  • Located in same bony labyrinth as semicircular
  • Composed of sensory hairs
  • Hairs project into a membrane containing
    crystalline particles
  • Gravity causes particles to bend hair cells

Proprioception System
  • Often referred to by pilots as seat of the
  • Acceleration causes a feeling of pressure in
    various parts of the body
  • Least reliable of the balance systems

Types of Spatial Disorientation
  • Leans
  • A false sense of being moved in a nonlevel flight
    resulting in leaning to one side or the other
    (most common)
  • Graveyard Spin / Spiral
  • A false sense of spinning

Types of Spatial Disorientation
  • Coriolis Illusion
  • Most severe vestibular illusion occurs when the
    semicircular canal fluid flows in two planes of
    rotation simultaneously
  • The aircraft must be turning
  • Rapid head movement
  • Occulogravic Illusion
  • A false sensation of climbing

Spatial Disorientation
  • Prevention
  • Use visual clues from the horizon
  • Minimize head movement
  • Pilots
  • Rely on instruments
  • Treatment
  • Relax
  • Allow sensation to subside
  • Do not panic
  • Do not make rapid or sudden head movements
  • Pilots
  • Rely on instruments

Motion Sickness
  • Treatment
  • Oxygen
  • Supine position
  • Limit head movement
  • Visual fixation on a point outside the aircraft
  • Cool air blown to face
  • Symptoms are subjective and so are the cures!
  • Prevention
  • Fear and anxiety contribute
  • Motivation is a key factor in prevention
  • Eating prior to flying may help

Clinical Applications Patient Positioning
  • To transverse the Gs if at all possible is
  • Counter the effects of the force by positioning
    opposite the direction of force
  • Most EMS aircrafts do not have significant
    problems with G forces
  • Ascent, descent, and banking are when effects are
    felt most often
  • When encountered, most G forces in air medical
    transport are transient and limited in effect

  • Transmitted through a medium such as air, solid,
    or liquids
  • Hertz one oscillation per second
  • Frequency number of times each second that
    these oscillations occur
  • Audible range for the human ear
  • 20 to 20,000 Hz

  • Pitch description of frequency in terms of
    higher versus lower on a scale
  • Intensity loudness, or a measure of sound waves
    in the ear canal measured in decibels
  • Decibel measure of the pressure of noise /
    sound (dB)
  • Human heart 10 dB
  • Jet engine at full power 170 dB

Effects of Hazardous Noise
  • Repetitive exposure can interfere with job
    performance and safety
  • Temporary or permanent hearing loss may occur
  • Interference with communications
  • Produces side effects of fatigue and headache
  • Hearing loss is insidious is nature by the time
    most crew members notice a change in hearing
    capabilities, permanent damage has occurred

Duration of Exposure to Noise
  • A relatively non-hazardous noise can become
    hazardous with prolonged duration of exposure
  • Hazardous exposure
  • 80 dB for 16 hours is permissible unprotected
  • For each 4 dB increase above 80 dBA, the time
    limit is reduced by one half
  • Unprotected exposure to levels above 114 dBA is
    not safe at any time level (hearing protection)

Duration of Exposure to Noise
  • A good measure to remember is noise intensity
    that affects normal voice communication is the
    approximate level which begins the threat of
  • If after exposure to noise, you notice a fullness
    or ringing in your ears, assume you have been
    overexposed to noise

Daily Exposure Time Limits for Noise
Sources of Noise (Aircraft)
  • Engines
  • Blades
  • APU
  • Radio / Communications
  • Wind
  • It is common for the noise level inside the cabin
    of both fixed and rotor wing aircraft to remain
    100 to 125 dB

Modification of Noise Risk
  • Distance from source
  • Angle from source (varies with nature of sound
  • Location of source of noise
  • Varies considerably at locations within aircraft
  • Flight phase noise level varies with flight
  • Acoustical insulation within aircraft bulkhead
  • Monitor for flight line noise sources
  • APU, air conditioner units

Reduce Time of Exposure
  • A risk to hearing may exist even with noise
    reduction and use of personal protective gear
  • Put noise attenuating devices on IMMEDIATELY when
    entering noise / aircraft area

Protection from Noise Exposure Hazards
  • Earplugs
  • Variation in size texture may alter
  • Best for reduction of low frequency noise
  • Very effective to 115 dB
  • Earmuffs
  • More comfortable / convenient
  • Easily donned / removed
  • Interfere with headgear
  • Better for higher frequency attenuation

Protection from Noise Exposure Hazards
  • Headsets / Helmets
  • Best for higher frequency attenuation
  • Not very effective for low frequency noise
  • Enable voice communication with mounted microphone
  • Combination
  • Best when exposed to combination of high and low
    frequency with high intensity noise
  • Noise Reduction
  • Eliminate the noise or reduce its level

Effects of Noise Exposure
  • Air crew members must have audiometer
    examinations regularly
  • Symptoms
  • Distraction from task
  • Fatigue
  • Fullness / ringing in ears
  • Nausea
  • Headache
  • Mild vertigo
  • Temporary or permanent hearing loss

Operational Considerations
  • All air crew members and patients on aircraft
    MUST wear hearing protection
  • Noise interferes with certain patient care
  • Auscultation
  • Percussion
  • Alarm monitoring
  • Communication / speech with patient
  • Use of Doppler as alternative
  • Development of astute palpation and observation
    skills a MUST

  • Defined as rapid up and down or back and forth
    rhythmic movement
  • Described using the same parameters as sound
  • Frequency
  • Intensity
  • Time
  • Additional factors include
  • Plane of vibration
  • Direction of application

  • Vibrations of low frequency and high intensity
    are of most concern to human health
  • Range of 1 to 100 Hz is most hazardous
  • Human skull resonates at 20 to 30 Hz
  • Human eye resonates at 60 to 90 Hz
  • These vibrations may elicit a physiologic
    response which is distressing
  • Vibration energy is passed through the body
    acoustically or directly mechanically

Sources of Vibration
  • Aircraft power plant (engines)
  • Rotors / Propellers

Effects of Exposure to Vibration
  • Loss of appetite
  • Loss of interest
  • Perspiration
  • Air sickness
  • Nausea / emesis
  • Increased heart rate
  • Increased respiratory rate
  • Increased metabolic rate
  • Decreased motor function ability
  • Decreased ability to concentrate on task
  • Severe or prolonged exposure
  • Fatigue
  • Discomfort
  • Pain

Protection from Vibration
  • Limitation
  • Isolation of vibration source
  • Restraint of the body
  • Limiting vibration to internal organs is critical
    to prevent impairment of normal physiologic
  • Protection
  • Avoid direct contact with source of vibration
  • Use of protective helmets / harnesses
  • Good physical conditioning of crew members to
    increase tolerance

Third Spacing
  • Decreasing barometric pressure (ambient) may
    cause leakage of intravascular space fluid into
    extravascular tissues
  • Hypoxia-induced peripheral vasoconstriction may
    accentuate this
  • Aggravated additionally by
  • Temperature changes
  • Vibration
  • G-forces

Third Spacing
  • Effects Physiologically of Third Spacing
  • Seen on long distance transports
  • Seen on high altitude flights
  • Signs / Symptoms
  • Edema
  • Generalized
  • Dependent
  • Dehydration
  • Increased heart rate
  • Decreased blood pressure

Third Spacing
  • Prevention / treatment of symptoms
  • Encourage fluids
  • Movement / ambulation when possible
  • Avoid excessive vibration
  • Monitor / protect against temperature extremes

Decreased Humidity
  • Amount of water vapor in the air decreases as
    altitude increases
  • 90 of the water vapor in the atmosphere is
    concentrated below 16,000 feet
  • Pressurized aircraft cabins recirculate air
    approximately every 3 minutes without
  • Flight for extended periods at high altitudes
    exposes crew / patients for dehydration

  • Physiology
  • Decreased available moisture to respiratory
    membranes causes inflammation and decreased
    efficiency of gas exchange
  • Respiratory secretions become thickened and
    further interfere with gas exchange
  • Increases risk of hypoxia
  • Stimulation of the hypothalamus to increase basal
    metabolic rate and oxygen demand

  • Signs / Symptoms
  • Thirst
  • Heat cramps
  • Headaches
  • Diminished task performance
  • Restlessness
  • Fatigue

Sources of Dehydration
  • Normal daily bodily losses approx 1 quart
  • Urination
  • Bowel
  • Respiration
  • Skin
  • Sweating
  • Profuse sweating can release 2 to 4 quarts an hour
  • Pressurized aircraft cabins
  • Not enough oral fluid intake
  • Carbonated beverages further complicate and
    decrease water absorption in the GI tract
  • Coffee / alcohol increase water loss

  • Prevention / Treatment
  • Drink more WATER
  • Maintain hydration to prevent dehydration /
  • Increase patients fluid intake (monitor closely
    high risk patients)
  • Burn
  • Pre-existing dehydration states

  • A decrease in skill performance related to
    repetitive use and duration
  • Also includes personal evaluation of a sense /
    feeling / perception of tiredness, discomfort or
    disorganization of muscular coordination
  • Aggravated by physical, physiological, and
    psychological states

  • INSIDIOUS in onset
  • Noted by aviation community for many years as
    having a strong impact on flight safety and
  • As length of fatigue increases, performance may
    become compromised and degraded, irritability
    increases, and random mistakes may occur
  • Lowers thresholds for other stressors
  • Fatigue factors are cumulative

Causes of Fatigue
  • Extended flight times
  • Insufficient rest
  • High noise levels
  • Long periods of inactivity / limited movement
  • Pressurized / artificial cabins
  • Vibration
  • Barometric pressure changes
  • Variations in temperature
  • G-forces on takeoff / landing
  • Poorly designed seats / restraints
  • Circadian rhythm alteration

Circadian Rhythm Alteration
  • Circadian (about a day)
  • Time period approx 24 hours (variation between 20
    and 28)
  • Referred to as the rhythmic biological clock to
    which functions are geared
  • Intrinsic sleep / wake cycle or the external day
    / night cycle
  • Diurnal variations in a persons
  • Body temperature
  • Heart rate
  • Performance
  • Hormone secretion

Time Zone Changes During Flight
  • Jet Lag
  • Studies have shown that complex bodily functions,
    such as those measurable by reaction time,
    performance and decision time are affected by
    rapid shifts through several time zones
  • Without proper preparation and planning, it takes
    one 24-hour period per one hour shift in time
    zone to recover
  • Crossing 4 time zones 4 x 24 hours to adjust
    bodily cycles

Types of Fatigue
  • Acute single-mission skill fatigue
  • Results from repeating tasks during long flights
    or from numerous repetitive short flights
  • Very common
  • Healthy persons recover with rest / sleep
  • Symptoms
  • Tiredness
  • Lassitude
  • Loss of coordination
  • Inattention to details

Types of Fatigue
  • Chronic skill fatigue
  • Occurs when recuperative time is insufficient
  • Overlapping with factors of acute fatigue
  • Can occur with any repetitive maximum effort
    program / job

Increasing Personal Resistance to Fatigue
  • Sleep
  • Know personal requirements
  • Physical conditioning
  • Exercise recreation
  • Proper diet
  • Wear use personal protective gear
  • Hearing protection
  • Oxygen at altitude
  • Vary the routine
  • Range of motion if confined to seat
  • Minor diversions to break monotony
  • Avoid dehydration
  • Water snacks
  • Personal concerns
  • Personal problems brought to work

Self Imposed Stressors / Human Factors
  • Stress can be ANYTHING that places a strain on an
    air crew members ability to perform at optimum
  • Certain stresses are inherent within the aviation
  • Acceleration forces, hypoxia, barometric pressure
  • Numerous others are a result of outside actions
    taken by the air crew member, which decrease
    tolerance to the routine stressors of flight

Self Imposed Stressors
  • Alcohol
  • Effects are magnified at attitude
  • 1 drink at 10,000 feet equals 2 to 3 drinks at
    sea level
  • Reduction of ability of the brain cells to
    utilize oxygen enhances hypoxia, which further
    impairs judgment and skill
  • Additive effect of dehydration
  • Chronic use effects as well as acute ingestion
    threaten safe flight

Self Imposed Stressors
  • Drugs
  • Self-medication has two potential dangers to safe
  • Drugs mask unsafe conditions
  • Drugs can make the crew member unsafe
  • Treatment of illness requires a drug that treats
    the cause not just the symptom
  • Air crew members who utilize over-the-counter
    (OTC) drugs must responsibly evaluate the impact
    of these drugs on their performance and the
    safety of the mission

OTC Prescription Drug Hazards
  • Caffeine
  • Nervousness
  • Indigestion
  • Insomnia
  • Increased heart rate blood pressure
  • Diuretic effect
  • Antihistamines
  • Depressant
  • Drowsiness, dry mouth, impaired depth perception
  • Amphetamines
  • Force the body beyond normal capacities
  • Recovery times enhanced
  • Narcotics
  • Drowsiness
  • Respiratory depression
  • Tranquilizers
  • Cause stuffy nose, constipation, blurred vision,
  • Nasal decongestants
  • Rebound congestion

OTC Prescription Drug Hazards
  • Air medical crew members who self-medicate MUST
    be aware of
  • Predictable side effects
  • Overdose potentials
  • Allergic reactions
  • Synergistic effects

  • Poor diet contributes to fatigue
  • Often during long flights, reliance is placed
    upon glycogen stores rather than eating a meal at
    regular intervals
  • Crash or fad diets are a potential threat to
  • Diet pills are amphetamines and are a hazard

  • Tar
  • Causes swelling and prevents natural cleansing of
  • Nicotine
  • Potent drug which affects nervous tissue and
  • May cause
  • Skeletal muscle weakness and twitching
  • Abdominal cramping, nausea, emesis
  • Alters circulation of blood and nerve impulses
  • Increases heart rate
  • Decreases individual ability to adapt to other

  • Carbon Monoxide (CO)
  • Air medical crew members who smoke have 5 to 10
    total hemoglobin saturated with CO
  • Will result in mild hypoxia at 8,000 feet
  • Flying with a cabin altitude of 10,000 feet (very
    common in commercial fixed wing flights) will
    result in feeling physiologic effect of 15,000
  • Decreased night vision accuracy related to hypoxia

Physical Fitness
  • Physical fitness is more than muscle conditioning
  • Regular aerobic / strenuous exercise increases
    the efficiency of supply and delivery of oxygen
    to the tissues, and reduced heart rate and blood
  • Air medical crew members who maintain good
    physical conditioning are better able to sustain
    prolonged exposure to stressors of flight

Personal Stress
  • Flying is a stressful job by nature
  • Patient care can be stressful
  • Duties often require intense concentration
  • Individuals who are experiencing outside personal
    stress cannot devote entirely to critical tasking
    at work
  • Personal stress is not easy to leave away from
  • Constant effort must be maintained to avoid,
    reduce, or eliminate personal problems from
    interfering with work

  • Anticipate effects of the stresses of flight
    prior to transport
  • Initiate interventions appropriately
  • Monitor for hypoxia
  • Avoid flying with a head cold
  • Avoid gas producing foods
  • Deep ahead of barometric pressure changes
  • Develop effective stress management and time
    management techniques
  • Minimize self-imposed stressors

Pressurized Cabin / Artificial Atmosphere
  • Mechanical method to maintain a greater than
    outside ambient pressure within an aircraft cabin
  • Protective environment against decreased
    temperature and pressure
  • Each type and design of aircraft varies in
    capabilities and the air medical crew must be
    familiar with the aircraft they are working within

Advantages of a Pressurized Cabin
  • Reduces possibility of hypoxia and evolved gas
  • Reduces gastrointestinal gas expansion
  • Cabin temperature, humidity, and ventilation are
  • No use of encumbering life support equipment
  • Minimizes fatigue and discomfort
  • Able to easier protect from barotrauma by slow
    cabin descent

Disadvantages of a Pressurized Cabin
  • Increase in aircraft weight and size
  • Additional engineering, equipment, engine power
    and maintenance
  • Decrease in maximum payload capabilities of
  • Controls required to monitor for contamination by
    smoke, fumes, CO, CO2
  • Decompression hazard

Slow Decompression
  • Cabin pressure is depleted in greater than 3
  • May occur undetected
  • Descent to 10,000 feet required if no
    supplemental O2 available
  • Use of supplemental O2 until descent
  • Evolved gas disorder and hypoxia possible

Rapid Decompression
  • Occurs in under 3 seconds
  • Lungs decompress faster than the cabin
  • Hypoxia risk dependent upon altitude
  • Emergency procedures
  • Oxygen on yourself
  • Oxygen on others
  • Unclamp and clamped tubes
  • Secure yourself / others
  • Descend

Explosive Decompression
  • Change in cabin pressure faster than the lungs
    can decompress
  • Lung damage possible
  • Decompression sickness probable

Factors Affecting Severity of Decompression
  • Volume of pressurized cabin
  • Size of the opening (larger faster)
  • Differential ration (greater faster)
  • Flight altitude
  • Higher altitudes create greater threats for
    physiological consequences
  • Remember your Time of Useful Consciousness (TUC)

Physical Indicators of Decompression
  • Flying debris
  • Fogging (related to temperature drop)
  • Temperature drop
  • Pressure decrease symptoms
  • Windblast

Decompression Sickness (Dysbarism) 2 Types
  • Trapped Gas
  • Gas within bodily cavities / organs
  • Boyles Law
  • Symptoms occur rapidly
  • Evolved Gas
  • Effects produced by evolution of gas from tissues
    and fluids of the body
  • Henrys Law

Decompression Sickness
  • When the atmospheric pressure is decreased
    rapidly to certain critical values, the nitrogen
    pressure gradient between the body and the
    outside air is such that nitrogen will come out
    of solution in the form of bubbles
  • Can occur in the blood, other fluids, or in the
  • Symptoms do not appear rapidly

Severity and Rapidity of Onset Related to
  • Rate of ascent
  • More rapid sooner symptoms appear
  • Altitude
  • Below 25,000 feet is rare
  • Above 25,000 feet may occur after leveling off
  • Duration of exposure
  • Physical activity
  • Exercise lowers the threshold for manifestations,
    particularly the bends
  • Individual susceptibility
  • Unpredictable

SCUBA Diving
  • Greatly lowers threshold altitude f
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