flight physiology 101 jeremy maddux, nremtp. functions of the atmosphere source of oxygen and carbon...
TRANSCRIPT
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
Oxygen 21%
Nitrogen 78%
Others 1% 0
50
100
1st Qtr
Oxygen
Nitrogen
Others
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 PressuresAltitude
(1000 feet)
Barometric Pressure mm Hg
Psi Temperature Cº Temperature Fº
0 760 14.70 + 15.0 + 59.0
1 733 14.17 + 13.0 + 55.4
2 706 13.87 + 11.0 + 51.8
3 681 13.67 + 9.1 + 48.38
4 656 12.69 + 7.1 + 44.78
5 632 12.23 + 5.1 + 41.18
6 609 11.78 + 3.1 + 37.58
7 586 11.34 + 1.1 + 33.98
8 565 10.92 - 0.9 + 33.67
9 542 10.51 - 2.8 +26.96
10 523 10.11 - 4.8 + 23.36
12 483 9.35 - 8.8 + 16.6
14 447 8.63 - 12.7 +9.4
16 412 7.97 - 16.7 +1.94
18 380 7.34 - 20.7 - 5.26
20 349 6.75 - 24.6 - 12.28
24 295 5.70 - 32.6 - 26.68
28 247 4.78 - 40.5 - 40.9
30 228 4.36 - 44.4 - 47.92
32 206 3.98 - 48.4 - 55.12
36 171 3.30 - 55.0 -67
42 128 2.47 - 55.0 -67
48 96 1.86 - 55.0 -67
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
1. Physiologic Zone
2. Physiologically Deficient Zone
3. Partial Space Equivalent Zone
4. 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
zone• 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.– Boyle’s Law– Henry’s Law– Charles’ Law– Dalton’s Law– Graham’s Law
Boyle’s 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
Boyle’s Law
• Boyle’s 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
altitude)• V2 = final volume (volume of gas at maximum
altitude)
Boyle’s 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
Boyle’s 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
Henry’s Law
• The amount of gas in solution is proportional to the partial pressure of that gas over the solution
• 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
Henry’s 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
Henry’s Law
• Henry’s Law Formula– P1 ÷ A1 – P2 ÷ A2– Where
• P1 = original pressure of the gas above the solution
• 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
Henry’s 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 constant
• Temperature increases make gas molecules move faster, and greater force is exerted and volume expands
• 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
Dalton’s 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
Dalton’s 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
• THE PECENTAGE OF OXYGEN REMAINS THE SAME with changes in altitude
Dalton’s Law
• Dalton’s Law Formula– Where
• Pt = P1 + P2 + P3…Pn– Pt = total pressure– P1…Pn = partial pressures of constituent gases of the
mixture
Dalton’s 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%
Graham’s 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 reached
• 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 phenomenon
The Stresses of Flight
• Areas or methods in which persons involved in flight (patients and crew members) may be physiologically affected by the flight environment
• 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
Hypoxia
• A state of oxygen deficiency sufficient to impair function
• 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 air– 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
victims
Hypoxic Hypoxia
• As altitude increases the partial pressure (PaO2) decreases (Dalton’s Law)
• As the PaO2 falls in the alveoli, the amount of O2 which diffuses into the blood decreases (Henry’s Law)
• Results in a decrease in oxygen available to the tissues
Changes in Oxygen Saturation in the Blood with Altitude Increases
Altitude (feet) Oxygen Saturation PaO2
10,000 87% 60
12,500 85% 50
18,000 48% 26
25,000 9% 7
35,000 0% 0
Hypemic Hypoxia (Anemic)
• The inability of blood to accept sufficient oxygen
• 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 oxygen
• 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
REMEMBER – AT 18,000 FEET
YOU ARE AT ½ ATMOSPHERE
Signs / Symptoms of Hypoxia
• Symptoms are the same regardless of the nature of the hypoxia
• Early symptoms mimic alcohol intoxication or extreme fatigue
• Each person’s 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 Hypoxia
• 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
vision– 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 Hypoxia
• Increased rate of breathing
• Cyanosis (late sign)
• Impaired task performance
• Loss of muscle coordination
• Mental confusion
• Unconsciousness
Symptomology & Altitude Frequency of Occurrence
5,000 ft 10,000 ft 15,000 ft 18,000 ftBlurred vision Hyperventilation Belligerence Cyanosis
Tunnel vision Impaired task management
Euphoria Confusion
Decreased night vision
Air hunger Sleepiness Poor judgment
Apprehension Slow thinking Muscle coordination
Fatigue
Headache
Dizziness
Numbness / Tingling
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 pediatrics)
• 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
DO NOT CONFUSE WITH EFFECTIVE PERFORMANCE TIME (EPT)
Effective Performance Time (EPT)
• The amount of time a crew member can effectively function with an insufficient supply of oxygen – NOT TIME OF USEFUL CONSCIOUSNESS
(TUC)
Time of Useful Consciousness (TUC)
• Explained by the gas laws– Henry’s 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 UsefulConsciousness (TUC)
Altitude in Feet / Flight Level TUC
12,000 to 20,000 feet (FL 200) 20 to 30 minutes
25,000 feet (FL 250) 3 to 5 minutes
30,000 feet (FL 300) 1 to 2 minutes
35,000 feet (FL 350) 30 to 60 seconds
40,000 feet (FL 400) 15 to 20 seconds
50,000 feet (FL 500) 9 to 12 seconds
Time of UsefulConsciousness (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 altitude
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
FIO2 SL 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000
.21 159 153 148 143 138 132 128 123 118 113 109
.22 167 161 155 150 144 139 134 129 124 119 115
.24 182 176 170 163 157 152 146 141 135 130 126
.28 213 205 198 191 184 177 170 164 158 152 147
.30 228 220 212 204 197 190 183 176 169 163 157
.34 258 250 240 232 223 215 207 199 192 184 178
.36 274 264 254 245 236 228 219 211 203 195 188
.40 304 293 283 272 262 253 244 235 226 217 209
.44 334 322 311 300 289 278 268 258 248 238 230
.50 380 366 353 341 328 316 304 293 282 271 262
.55 418 403 389 375 361 348 335 322 310 298 288
.60 456 440 424 409 394 379 365 352 339 325 314
.65 494 476 459 443 427 411 396 381 367 352 340
.70 532 513 495 477 459 443 426 410 395 379 367
.75 570 550 530 511 492 474 457 410 423 406 393
.80 608 586 565 545 525 506 487 469 452 434 419
.85 646 623 601 579 558 537 518 498 480 461 445
.90 684 660 636 613 591 569 548 528 492 489 471
.95 722 696 671 647 623 601 579 557 536 515 498
1.00 760 733 707 681 656 623 609 586 565 542 524
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
Device Liters / Minute % IO2
Nasal Cannula 1 24
Nasal Cannula 2 28
Nasal Cannula 3 32
Nasal Cannula 4 36
Nasal Cannula 6 44
Simple Mask 5-6 40
Simple Mask 6-7 50
Simple Mask 7-8 60
Partial Nonrebreather Mask 7 70
Partial Nonrebreather Mask 8 80
Partial Nonrebreather Mask 10 > 90
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(Boyle’s 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 contract
• The body can withstand changes in total barometric pressure as long as the air pressure within the body cavities is equalized to ambient pressure
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 automatically– 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– DO NOT FLY WITH A HEAD COLD– “Stay ahead of your ears”
• Valsalva during descent
– Use self-medications with vasoconstrictors with caution
• 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– DO NOT FLY WITH A COLD– 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
individuals• 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 compromised
– Potential tension pneumothorax
Effects Upon Mechanical Ventilators
• Pneumatic controlled and powered– With decreased barometric pressure and
increased altitude• 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
changes
– Flow rate of O2 may change
– Patient tidal volume may change
Thermal
• Air medical operations place crew members and patients in situations within a wide range of temperatures
• Ambient temperature decreases with increasing altitude
• 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
Thermal
• 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
Direction of Force Standard Terminology
Pull head toward feet +Gz
Pull foot toward head -Gz
Pull from chest to back +Gz
Pull from back to chest -Gz
Pull from right to left +Gz
Pull from left to right -Gz
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 /
equilibrium
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 canals
• 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 pants”
• 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 ApplicationsPatient Positioning
• To “transverse the G’s” if at all possible is optimum
• 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
Noise
• 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
Noise
• 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
exposure• 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 hearing
• 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
Decibels (dB) Exposed
Permissible Unprotected Exposure Time Limit
80 16 hours
84 8 hours
88 4 hours
92 2 hours
96 1 hour
100 30 minutes
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
waves)• Location of source of noise
– Varies considerably at locations within aircraft
• Flight phase noise level – varies with flight phases
• 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 effectiveness
– 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 procedures– Auscultation– Percussion – Alarm monitoring– Communication / speech with patient
• Use of Doppler as alternative• Development of astute palpation and
observation skills a MUST
Vibration
• 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
Vibration
• 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 performance
• 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 function
• 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 humidification
• Flight for extended periods at high altitudes exposes crew / patients for dehydration
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
Dehydration
• 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
Dehydration
• Prevention / Treatment– Drink more WATER– Maintain hydration to prevent dehydration /
fatigue– Increase patient’s fluid intake (monitor closely
high risk patients)• Burn• Pre-existing dehydration states
Fatigue
• 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
Fatigue
• INSIDIOUS in onset• Noted by aviation community for many years as
having a strong impact on flight safety and efficiency
• 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 person’s– 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 member’s ability to perform at optimum level
• Certain stresses are inherent within the aviation environment– Acceleration forces, hypoxia, barometric pressure
changes
• 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
flight• 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, drowsiness
• 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
Diet
• Poor diet contributes to fatigue• Often during long flights, reliance is placed upon
glycogen stores rather than eating a meal at regular intervals
• Hypoglycemia is a SAFETY THREAT TO YOURSELF, YOUR CO-WORKERS, AND YOUR PATIENTS
• Crash or fad diets are a potential threat to safety• Diet pills are amphetamines and are a hazard
Tobacco
• Tar– Causes swelling and prevents natural cleansing of
alveoli
• Nicotine– Potent drug which affects nervous tissue and muscle– 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 stress
Tobacco
• 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 feet
– 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 pressure
• 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 work
• Constant effort must be maintained to avoid, reduce, or eliminate personal problems from interfering with work
Prevention
• 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 disorders
• Reduces gastrointestinal gas expansion• Cabin temperature, humidity, and ventilation are
controllable• No use of encumbering life support equipment
(suits)• 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 aircraft
• Controls required to monitor for contamination by smoke, fumes, CO, CO2
• Decompression hazard
Slow Decompression
• Cabin pressure is depleted in greater than 3 seconds
• 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 AffectingSeverity 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 Indicatorsof 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– Boyle’s Law– Symptoms occur
rapidly
• Evolved Gas– Effects produced by
evolution of gas from tissues and fluids of the body
– Henry’s 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 tissues
• Symptoms do not appear rapidly
Severity and Rapidityof 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 for the occurrence of decompression sickness when flying
• Cases of decompression sickness have occurred in individuals who fly in cabins as low at 5,000 feet – If within 6 hours of diving– Recommended at least 24-hour delay
between diving with SCUBA and flying
Decompression Sickness (DCS)
• Skin manifestations– Mild– Mottled and diffuse rash– Tingling of the skin– Believed to be caused by bubbles of gas evolving
under the skin– Symptoms themselves are not serious HOWEVER
they are a WARNING that bubbles may form elsewhere
– Continued exposure may lead to more serious forms of decompression sickness
Decompression Sickness (DCS)
• The Bends– Generally located around / near articulating
joints of the body– Pain from mild to unbearable– Factors of exercise, increased altitude, and
increased time of exposure will increase severity of symptoms
– Descent to below altitude of onset
Decompression Sickness (DCS)
• The Chokes– Rare but potentially life-threatening– Nitrogen bubbles in the blood vessels of the lungs– Symptoms
• Deep and sharp pain or burning sensation under the sternum• Shortness of breath• Dry, progressive, nonproductive cough• Feeling of suffocation with decreasing ability to take a breath
– Results in hypoxia
Decompression Sickness (DCS)
• False Chokes (NOT DCS)– Caused by mouth breathing and cool, dry
aircraft air– Throat irritation and discomfort– Relieved with fluid intake
Decompression Sickness (DCS)
• Neurologic Manifestations (CNS)– Very rare– Rarely may effect brain or spinal cord– More common
• Visual disturbances (blind spots, flushing, or flickering vision – Scotoma)
• Persistent headache• Partial paralysis• Inability to speak or hear• Loss of orientation
Decompression Sickness (DCS)
• Emergency Treatment– 100% oxygen for everyone onboard– Declare an emergency– Descent as rapidly as possible– Immobilize affected areas– Treat shock– Land as soon as possible– Medical evaluation by a QUALIFIED flight surgeon /
hyperbaric physician ASAP– Decompression chamber therapy if required
Unpressurized Aircraft
• Altitude within the cabin equals aircraft altitude• Little control is available over the effects of the
gas laws• Effects seen in human discomfort and
equipment effectiveness• Programs that operate at high altitudes
(mountains or high plains) with unpressurized aircraft need be aware and alert for altitude symptomology
Unpressurized Aircraft
• Air pressure changes in– Body cavities / hollow
organs– Tube cuffs – Enclosed equipment
with fluid / air interference
• Respiratory variations– FiO2
– Tidal volume– Respiratory rate
The End!
Any Questions?