High altitude physiology and deep sea physiology
High Altitude Physiology and Deep Sea Physiology
Physiological changes at high altitude, acclimatization, aviation, space and deep sea environments.
1 High Altitude Physiology
A person can ascend to this level without any adverse effect.
At high altitudes, barometric pressure is low.
However, amount of oxygen available in atmosphere is same as it is at sea level.
Due to low barometric pressure, the partial pressure of gases, particularly oxygen, decreases leading to hypoxia.
Carbon dioxide at high altitude is very much negligible and it does not create any problem.
2 Barometric Pressure and Partial Pressure of Oxygen at Different Altitudes
Barometric pressure decreases at different altitudes and accordingly the partial pressure of oxygen also decreases leading to various effects on the body.
Barometric pressure and partial pressure of oxygen at different altitudes and their common effects on the body are given below.
| Altitude (feet) | Barometric Pressure (mm Hg) | Partial Pressure of Oxygen (mm Hg) | Common Effects |
|---|---|---|---|
| Sea level | 760 | 159 | — |
| 5,000 | 600 | 132 | No hypoxia |
| 10,000 | 523 | 110 | Mild symptoms of hypoxia start appearing |
| 15,000 | 400 | 90 |
Moderate hypoxia develops with following symptoms:
|
| 20,000 | 349 | 73 |
Severe hypoxia appears with cardiorespiratory symptoms such as:
|
| 25,000 | 250 | 62 |
This is the critical altitude for survival.
|
| 29,028 | 235 | 49 | This is the height of Mount Everest. |
| 30,000 | 226 | 47 | Symptoms become severe even with oxygen |
| 50,000 | 87 | 18 | Hypoxia becomes more severe even with pure oxygen |
3 Changes in the Body at High Altitude
When a person is exposed to high altitude particularly rapid ascent, the body cannot cope with lowered oxygen tension, and the effects of hypoxia start.
Besides hypoxia, some other factors are also responsible for changes in the functions of the body at high altitude.
Factors Affecting Physiological Functions at High Altitude
- Hypoxia.
- Expansion of gases.
- Fall in atmospheric temperature.
- Light rays.
1. Effect of Hypoxia
Hypoxia produces various effects on physiological functions.
2. Effects of Expansion of Gases
Volume of gases increases when the barometric pressure is reduced.
So, at high altitude, volume of all gases increases in atmospheric air, as well as in the body due to decreased barometric pressure.
Expansion of gases in gastrointestinal tract causes painful distention of stomach and intestine.
It is minimized by supporting the abdomen with a belt or by evacuation of the gases.
Expansion of gases also destroys the alveoli.
During very rapid ascent from sea level to over 30,000 feet height, the gases evolve as bubbles of partially nitrogen, resulting in decompression sickness.
3. Effects of Reduced Atmospheric Temperature
Environmental temperature falls gradually at high altitudes.
Temperature decreases to about 0°C at the height of 10,000 feet.
It becomes −22°C at the height of 20,000 feet.
At the altitude of 40,000 feet, the temperature falls to −44°C.
Injury or frostbite occurs if the body is not adequately protected by warm clothing.
4. Effects of Light Rays
Skin becomes susceptible for injury due to many harmful ultraviolet rays of sunlight.
Moreover, ultraviolet rays reflected by the snow may injure the retina of the eye if it is not protected with suitable tinted glasses.
4 Mountain Sickness
Definition
It commonly develops in persons going to high altitude for the first time.
It develops within a day in these persons before they get acclimatized to high altitude.
Symptoms
In mountain sickness, the symptoms occur mostly in digestive system, cardiovascular system, respiratory system and nervous system.
1. Digestive System
Loss of appetite, nausea and vomiting occur because of expansion of gases in the gastrointestinal tract.
2. Cardiovascular System
Heart rate increases.
3. Respiratory System
Pulmonary blood pressure increases due to increased blood flow.
Blood flow increases because of vasodilation induced by hypoxia.
Increased pulmonary blood pressure results in pulmonary edema which causes breathlessness.
4. Nervous System
Symptoms of nervous system are headache, depression, disorientation, irritability, lack of sleep, weakness and fatigue.
Treatment
Treatment depends upon severity of sickness.
Symptoms can be reverted by returning to lower altitude or by breathing oxygen.
Medical attention is required if symptoms are very severe.
5 Acclimatization
Definition
While staying at high altitudes for several days to several weeks, a person slowly gets adapted or adjusted to low oxygen tension, so that hypoxic effects are reduced.
It enables the person to ascend further.
Changes During Acclimatization
Various changes during acclimatization help the body to cope with adverse effects of hypoxia at high altitude.
Following changes occur in the body during acclimatization.
1. Changes in Blood
During acclimatization, RBC count increases and packed cell volume rises from the normal value of 45% to about 59%.
Hemoglobin content in the blood rises from 15 to 20 g%.
So, oxygen carrying capacity of the blood is increased.
Thus, more oxygen can be carried to tissues in spite of hypoxia.
Increase in RBC count, packed cell volume and hemoglobin content is due to erythropoietin that is released from juxtaglomerular apparatus of kidney.
2. Changes in Cardiovascular System
Overall activity of cardiovascular system is increased in high altitude.
There is increase in rate and force of contraction of heart, cardiac output and blood pressure.
Hypoxia-induced vasodilation increases the vascularity in the body.
So, blood flow to the vital organs such as heart, brain and muscles increases.
3. Respiratory System
- Pulmonary ventilation increases up to 65% due to stimulation of chemoreceptors. This helps the person to ascend several thousand feet.
- Pulmonary hypertension develops due to increased cardiac output and pulmonary blood flow.
- Diffusing capacity of gases increases in the alveoli due to the increase in pulmonary blood flow and pulmonary ventilation. It enables more diffusion of oxygen into blood.
4. Changes in Tissues
Both in human beings and animals residing at high altitudes permanently, cellular oxidative enzymes are more than in the inhabitants at sea level.
Even when a sea level inhabitant stays at high altitude for certain period, quantity of the oxidative enzymes is not increased.
So, the elevation in quantity of oxidative enzymes occurs only in fully acclimatized persons.
An increase in the number of mitochondria is also observed in these persons.
6 Aviation Physiology
Flying affects the body through accelerative forces and gravitational forces, which are developed during flight maneuvering.
Pilots and other crew members of aircraft are trained to overcome the effects of these forces.
Accelerative Force
Acceleration means change in velocity.
Flying straight in horizontal plane with constant velocity has minimum effects on the body.
However, changes in velocity produce severe physiological effects.
Accelerative forces are developed in the flight during linear, radial or centripetal and angular acceleration.
Gravitational Force: G Unit
Gravitational force (G force) is the major factor that develops accelerative force.
Force or pull of gravity upon the body is expressed in G unit.
On the earth, this pull is responsible for body weight.
Force of gravity while sitting, standing or lying position is considered to be equal to body weight and it is referred as 1 G unit.
While traveling in an airplane, elevator or a car, if there is a sudden change in speed or direction, the passengers are thrown or centrifuged in opposite direction.
It is because of change in G unit.
Types of G Unit
Positive G
Positive G is increase in G unit.
It occurs while increasing the speed (acceleration).
Negative G
Decrease in G unit is called negative G and it occurs while decreasing the speed (slowing down, deceleration).
G unit is altered during the change in direction also.
While flying, both positive G and negative G cause physiological changes in the body.
Body can be protected from the effects of G forces, particularly positive G by using abdominal belt and anti-G suit.
7 Space Physiology
Major differences between the environments of earth and space are atmospheric factors, radiation and gravity.
All the three factors challenge human survival in space.
Atmospheric factors are atmospheric pressure, temperature, humidity and gas composition.
Spacecraft and Space Suit
Spacecraft or spacelab is provided with stable and sophisticated environmental control system, which maintains all the atmospheric factors close to earth’s atmospheric conditions.
Astronauts also wear launch and entry suit (LES) which is a pressurized suit that protects the body from space environment.
Weightlessness
Another factor which affects the body in the space is weightlessness.
Weightlessness is because of absence of gravity (microgravity).
8 Deep Sea Physiology
In high altitude, the problem is with low atmospheric pressure.
In deep sea or mines, the problem is with high barometric pressure.
High barometric pressure in deep sea produces two major problems:
- Compression effect on the body and internal organs.
- Decrease in volume of gases.
Barometric Pressure at Different Depths
At sea level, the barometric pressure is 760 mm Hg, which is referred as 1 atmosphere.
At the depth of every 33 feet (about 10 m), the pressure increases by 1 atmosphere.
Thus, at the depth of 33 feet, the pressure is 2 atmospheres.
It is due to the air above and is the weight of water itself.
Barometric Pressure and Effects at Different Depths
| Depth (feet) | Atmospheric Pressure (atmosphere) | Effects on the Subject |
|---|---|---|
| Sea level | 1 | — |
| 33 | 2 | — |
| 66 | 3 | — |
| 100 | 4 | Symptoms of nitrogen narcosis appear |
| 133 | 5 |
Lack of concentration Becomes jovial and careless |
| 166 | 6 | Starts feeling drowsy |
| 200 | 7 |
Feels fatigued and weak Becomes very careless |
| 233 | 8 |
Loses power of judgment Unable to do skilled work |
| 266 | 9 | Becomes unconscious |
9 Effect of High Barometric Pressure: Nitrogen Narcosis
Definition
Nitrogen narcosis means narcotic effect produced by nitrogen at high pressure.
Nitrogen narcosis is common in deep sea divers who breathe compressed air (air under high pressure).
Breathing compressed air is essential for a deep sea diver or an underwater tunnel worker in order to equalize the surrounding high pressure acting on thoracic wall and abdomen.
Symptoms of Nitrogen Narcosis
- First symptom starts appearing at a depth of 120 feet. The person becomes very jovial, careless and does not understand the seriousness of the conditions.
- At 150 to 200 feet depth, the person becomes drowsy.
- At 200 to 250 feet depth, the person becomes extremely fatigued and weak. There is lack of concentration and judgment. Ability to perform skilled work or movements is also lost.
- Beyond the depth of 250 feet, the person becomes unconscious.
Mechanism of Nitrogen Narcosis
Nitrogen is soluble in fat.
During compression by high barometric pressure in deep sea, nitrogen escapes from blood vessels and gets dissolved in fat present in various parts of the body, especially neuronal membranes.
Dissolved nitrogen acts like an anaesthetic agent suppressing neuronal excitability.
Nitrogen remains in dissolved form in fat till the person remains in deep sea.
When the person ascends up, decompression sickness develops.
10 Decompression Sickness
Definition
It is also known as dysbarism, decompression sickness, caisson disease, bends or diver’s palsy.
Causes of Decompression Sickness
High barometric pressure at deep sea leads to compression of gases in the body.
Compression reduces the volume of gases.
Among the respiratory gases, oxygen is utilized by tissues.
Carbon dioxide can be expired out.
But nitrogen, which is present in high concentration, i.e. 80%, is an inert gas.
So, it is neither utilized nor expired.
When nitrogen is compressed by high atmospheric pressure in deep sea, it escapes from blood vessels and enters the organs.
As it is fat soluble, it gets dissolved in fat of the tissues and tissue fluids.
It is very common in the brain tissues.
Symptoms of Decompression Sickness
- Severe pain in tissues, particularly the joints, produced by nitrogen bubbles in the myelin sheath of sensory nerve fibers.
- Sensation of numbness, tingling or pricking (paresthesia) and itching.
- Temporary paralysis due to nitrogen bubbles in the myelin sheath of motor nerve fibers.
- Muscle cramps associated with severe pain.
- Occlusion of coronary arteries followed by coronary ischemia, caused by bubbles in the blood.
- Occlusion of blood vessels in brain and spinal cord also.
- Damage of tissues of brain and spinal cord because of obstruction of blood vessels by the bubbles.
- Dizziness, paralysis of muscle, shortness of breath and choking.
- Finally, fatigue, unconsciousness and death.
Prevention of Decompression Sickness
Decompression sickness is prevented by taking proper precautionary measures.
While returning to sea level, the ascent should be very slow with short stay at regular intervals.
Stepwise ascent allows nitrogen to come back to the blood without forming bubbles.
It prevents the decompression sickness.
Treatment
If a person is affected by decompression sickness, first recompression should be done.
It is done by keeping the person in a recompression chamber.
Then, he is brought back to atmospheric pressure by reducing the pressure slowly.
Oxygen therapy may be useful.