About oxygen and alveolar air:
partial pressure of oxygen @ 10,000 feet 55 mm hg above cabin heights of 10,000 feet oxygen needs to be added is to be sufficient to maintain an alveolar partial pressure of 103 mm hg which is equivalent to breathing air at sea level. oxygen is added as per the altitude and keep adding to maintain 103 mm hg. which is a sea level oxygen partial pressure. Stage reaches when one hundred percent oxygen is required to maintain the 103 mm hg-This stage reaches @ 33,700 ft. we can continue flying till the alveolar partial pressure of 55 mm hg (equivalent of breathing air @ 10,000 FT) - This partial pressure is reached @ 40,000 ft above this 100% oxygen must be supplied @ an increase pressure (Pressure breathing) but this is more relevant for military crew and Concorde crews who fly at high altitude.
Threshold of oxygen requirements summary-
up to 10,000 feet Air only
10,000 - 33,700 feet Oxygen / Air mixture
33,700 - 40,000 feet 100% Oxygen
above 40,000 feet 100% Oxygen under pressure
Smoking and Anaemic Hypoxia-
smoking produces carbon-monoxide which is inhaled, as the hemoglobin in the red blood cells has much greater affinity
to this carbon monoxide than to carbon than to oxygen it reduces the availability of hemoglobin to transport oxygen. heavy
smoking produces 8-10 percent carboxyhemoglobin in the blood, a regular smoker will start to suffer
from hypoxia approximately 4000-5000 ft below that of a non-smoker.
Hypoxia and Hyperventilation symptoms are hard to Distinguish:
Hypoxia: Breath rate to be increased to raise the level of oxygen in blood whereas in hyperventilation
breath rate should be slow down then normal to raise the carbonic acid level in blood.
*DO NOT ASSUME HYPERVENTILATION IF IT COULD BE HYPOXIA
HYPERVENTILATION- After Unconsciousness- RECOVERY
HYPOXIA - After Unconsciousness- DEATH
Q. Why we do not maintain the CABIN ALTITUDE at sea level pressure ?
A. Ideally it should be but this is impractical because of aircraft weight and fuselage strength limitations.
All about cabin pressurization-
commercial airliners flying @ 30,000 feet produces an internal cabin pressure equivalent to 6,000 ft with max limit of 8,000 ft. the pressure
differential across the aircraft skin is normally designed not to exceed 8-9 p.s.i.
the rate of change of cabin pressure > 500 ft per minute: on ascend
> 300 ft per minute: on descend
Decompression sickness: Is due to the the nitrogen which comes out of blood while forming
bubbles like as in fizzy drinks when bottle of soft drink is opened formation of bubbles
occurs and pressure allowed to drop.
Decompression sickness (DCS) occurs while any ascent to altitudes over 25,000 ft
it is more likely the higher and longer exposure to altitudes above 18,000 ft
it is unlikely to occur below 14,000 ft.
person suffered from DCS may collapse and in rare cases DCS may occur
or persist after descent and go on to cause DEATH.
symptoms: DCS caused pain in joints due to leakage of nitrogen as a bubble causing pain in body joints like knee, shoulder etc and pain is called BENDS.
skin causes the creeps when sufferer feel the small compact colony of ants crawling over, or just under, the skin.
Respiratory systems known as CHOKES causes piercing pain in respiratory system.
Brain it affects as STAGGERS, patient may loose mental control, chronic paralysis or may even permanent mental disturbance.
DCS can be avoided by Pre-Oxygenation before expose to high altitudes, it reduces the body storage of
nitrogen as much as possible.
To cure DCS: Sufferer should be put on to a 100% Oxygen supply. Land as soon as possible and before that
descent to a level at which the symptoms are relived.
While diving body is exposed to 2 atm pressure (1 atm by air above the water and 1 atm by water itself)
In scuba diving, air under pressure is used and this increases the amount of nitrogen in the body.
On ascend this may come out of blood and giving rise to DCS.
DO NOT FLY WITH IN 12 HOURS OF SWIMMING USING COMPRESSED AIR AND AVOID FLYING FOR 24 HOURS IF DEPTH OF 300 FEET HAS BEEN
EXCEEDED. (AT 30 FEET THE PRESSURE IS EQUAL TO A SEA LEVEL PRESSURE THAT IS: 760 MM HG.)