Flight Physiology & Gas Laws Flashcards
Boyle’s Law
As altitude increases the atmospheric pressure decreases and gas in an enclosed space will expand
P1 V1 = P2 V2
P = Pressure (Atmosphere's - ATM) V = Volume P,V = Inverse relationship
Charles Law
Charles Law states that the relationship between temperature and volume are proportional at a constant atmospheric pressure.
As the temperature goes up, gas volume expands
As the temperature goes down, volume decreases
Gay Lussac’s Law
For a given mass and constant volume of a gas, the pressure exerted on the sides of its container is directly proportional to its absolute temperature
Dalton’s Law
The total pressure of a gas mixture is the sum of the partial pressures of all gases.
Also describes how a pressure is exerted by a gas at various altitudes, and how that pressure affects the partial pressure of the said gas
Henry’s Law
The amount of gas dissolved in a solution is directly proportional (+:+) to the pressure of the gas over the solution
Fick’s Law
The rate of diffusion of a gas across a permeable membrane is determined by:
- The chemical nature of the membrane itself,
- The surface areas of the membrane,
- The partial pressure gradient of the gas across the membrane,
- The thickness of the membrane.
Graham’s Law
the rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
This means that diffusion will happen at a faster rate if the gas is thinner and at a slower rate if the gas is heavier
Expected temperature change on ascension
Every 1000 feet ascended the temperature will decrease by 2oC
Every 150 meters ascended the temperature will decrease by 1oC
Stressors of Flight
Hypoxia
Noise
Vibration
Gravitational forces
Flicker vertigo
Spatial disorientation
Fatigue
Barometric pressure
Thermal changes
Decreased humidity
Formula for bedside PaO2
PaO2 = (700 torr ∗ [FiO2 Percentage]) - 50
Observable effects of hypoxia
Hyperventilation
Confusion
Poor decision making
Cyanosis (late)
Subjective effects of hypoxia
Fatigue
Anxiety
Nausea
Headache
Euphoria
Numbness/Tingling
Agitation
Blurred vision
Hot/Cold flashes
Stages of hypoxia (from least to most severe)
- Indifferent Stage
- Compensatory Stage
- Disturbance Stage
- Critical Stage
Formula for FiO2 at a new altitude
(%FiO2 x P1) / (P2)
P1 = Current pressure
P2 - New pressure
Indifferent Stage of Hypoxia
Occurs at altitudes 0 to 10,000 ft
SpO2 ranges from 90% to 100%
Decrease in night vision @ 4000 ft
Compensatory Stage of Hypoxia
Occurs at altitudes 10,000 to 15,000 ft
SpO2 ranges from 80% to 90%
Night vision < 50% of usual capability
CNS symptoms start (poor judgement, decreased coordination, etc.)
Disturbance Stage of Hypoxia
Occurs at altitudes of 15,000 to 20,000
SpO2 of 70% to 80%
Worsening CNS symptoms (memory loss, not understanding of speech, etc.)
Hyperventilation
Critical Stage of Hypoxia
Occurs at altitudes of 20,000 to 25,000 ft
SpO2 of 60% to 70%
Rapid unconsciousness and coma rapidly followed by death
Seconds of useful consciousness after decompression at high (40,000’ ft +) altitudes
9 seconds or less
Quick way to calculate ATM under 6000 ft
Every 1500’ up is 0.5 ATM loss
What is pulmonary shunt?
When oxygenation fails to occur at the alveoli, leading for unoxygenated blood to be circulated
What ventilator setting can assist with pulmonary shunt
Adding or increasing PEEP
Barotrauma to consider to provider
Barotitis media - Ear infection causing pain on ascent and descent
Barodentalgia - Oral abscess or cavity that expands on ascent
Barobariatrauma - Displacement of nitrogen causes nitrogen narcosis
Patient/Equipment considerations for barotrauma
Any cavity filled with air will expand on ascent. Will severely worsen a pneumothorax or perf a stomach filled with air
Any equipment that has air in it will expand on ascent (ex. air splints, pressure bags, etc.)
