Respiration, Hypoxia & Anoxia,
Drowning & Hyperventilation
Respiration
What is Respiration?
Respiration is the process by which OXYGEN (O2) is transported from the air that is breathed to the body tissues, and by which CARBON DIOXIDE (CO2) produced in these tissues is vented to the air. This process becomes clear when the composition of inhaled (breathing in) and exhaled air (breathing out) is examined.
|
% Composition |
Inhaled Air |
Exhaled Air |
|
Nitrogen, N2 |
78 |
78 |
|
Other |
» 1 |
» 1 |
|
Oxygen, O2 |
21 |
16 |
|
Carbon dioxide, CO2 |
Trace |
5 |
It is apparent that whilst the air has been in the lungs, some of the oxygen has been used and a small amount of carbon dioxide added. Note that nitrogen is not involved in this process (i.e. it is non-metabolic), so that its contribution remains unaltered. It is important for other reasons (e.g. it is responsible for nitrogen narcosis and decompression sickness).
Why is Respiration necessary?
In the same way that a fire needs oxygen to burn, i.e. to release the chemical energy in the fuel (e.g. coal), a human body needs oxygen to release energy from food. Carbon dioxide is a waste product of this process and needs to be removed from the body. The process is known as metabolism i.e.
Food + O2 = Energy + CO2 + waste products
How is breathing accomplished?
Air is drawn into the lungs by the action of intercostal muscles and the diaphragm. To breathe in, the rib cage is pulled up and the diaphragm down. This increases the volume of the lungs, causing the internal pressure to fall and air to move in to fill the space. Breathing out is the reverse of this action. The lungs are ‘squeezed’ by letting the rib cage fall and pulling the diaphragm up, which results in the air being pushed out.
Airways
The path by which air enters the lungs is as follows:
Mouth & Nose => Larynx => Trachea => Bronchi => Lungs (Alveoli).
It leaves in the reverse direction
The Lungs
The lungs are the organs where the exchange of gases between the atmosphere and the blood takes place. They occupy, along with heart, almost all of the chest cavity. The lungs are rather dense organs, similar in structure to a sponge. The holes in this ‘sponge’ are represented by air spaces, within which air is continually moving in and out and the structure of the sponge is the small blood vessels, called CAPILLARIES, which contain de-oxygenated blood. These air spaces are actually microscopic sacs, called ALVEOLI. Their function is to allow the transfer of O2 and CO2 between the air in the sac and the de-oxygenated blood surrounding it, with O2 moving from the air to the blood and CO2 from the blood to the air. The lungs are completely filled with alveoli, providing a surface area equal to the size of a tennis pitch over which gaseous exchange can occur.
(1) Respiratory Bronchiole (sometimes called terminal bronchiole)
(2) Alveolar duct
(3) Alveoli
Oxygen is transported round the body via the blood. It is principally carried via RED BLOOD CELLS. These are shaped like discs, to maximise their surface area and so make gaseous exchange easier. The cells are full of a compound called HAEMOGLOBIN, which has a strong affinity to oxygen. When oxygen comes into contact with a molecule of haemoglobin, it seizes it and forms a molecule of OXYHAEMOGLOBIN. This moves around the body to where it is needed, whereupon the oxygen is released and the molecule reverts to being haemoglobin. Oxygen also dissolves in the blood plasma and is transported in that way. Carbon dioxide is also transported via the blood, mostly in solution.
The Circulatory System
Blood is transported around the body by means of a highly efficient pump: the heart. It circulates blood within a closed circuit system known as the CIRCULATORY SYSTEM. This circulation takes oxygenated blood (oxygen rich, little carbon dioxide) from the lungs to those tissues which require it and de-oxygenated blood (oxygen depleted, carbon dioxide rich) back to the lungs, where the CO2 is vented and more O2 is captured.
Where does the desire to breathe originate?
The breathing rate (i.e. the number of breaths taken per minute) varies depending on the work rate. Thus the harder the work rate, the more air is taken. This occurs because energy is being burned faster and so there is a need to consume more oxygen.
Hypoxia & Anoxia
What Are Hypoxia & Anoxia?
It has already been established that a body’s demand for oxygen varies proportionally with the workload. Hypoxia describes a situation where an insufficient amount of oxygen is received. This term can apply to the entire body or to specific organs e.g. the brain. It is defined as a partial lack of oxygen. If steps are not taken to increase the supply of oxygen, Anoxia can result, which is the complete absence of oxygen. Body cells cannot survive without oxygen. Brain cells are particularly sensitive and can die within as little as 4 minutes.
How It Can Occur?
Hypoxia can occur for a number of reasons:
· There is an obstruction of the airway
· There is too little oxygen in the breathing gas (i.e. partial pressure < 0.14 atm);
· The lung(s) are damaged or diseased e.g. a burst lung;
· Carbon monoxide poisoning has occurred (CARBOXYHAEMOGLOBIN);
· The heart is unable to pump with sufficient force to supply all the body tissues
· An extraordinary incident such as hyperventilation or drowning
There are many symptoms of hypoxia, depending on its severity:
· drowsiness
· lack of co-ordination
· headache
· increased respiration and pulse rate
· lips/nails/ear lobes turning blue (cyanosis)
· unconsciousness and death
Restore a supply of oxygen (at least 0.16 Bar absolute) as soon as possible, using pure oxygen if available. If the victim is not breathing, EAR and perhaps ECM will be necessary.
D
Drowning prevents oxygen from reaching the body tissues i.e. it causes hypoxia. The term, strictly speaking, should only be applied if death occurs. Individuals who inhale water but are resuscitated have experienced a ‘near drowning’ situation. Drowning is the ultimate cause of death in most diving fatalities.
· Blue or Dry Drowning
No water enters the lungs as a result of an EPIGLOTTAL SPASM, which seals off the trachea. However, water may enter the stomach. Hypoxia will occur and, unless breathing is restored, anoxia will result followed by death.
· White or Wet Drowning
This is a much more severe, and more likely to be fatal, form of drowning, in which water enters the lungs. There are two types:
Seawater Drowning: Water is removed from the blood by osmosis, leading to HAEMOCONCENTRATION. This can put a great strain on the heart.
Freshwater Drowning: This is the more severe situation. Water rapidly enters the bloodstream, again by osmosis, causing HAEMODILUTION. This causes the red blood cells to burst and subsequent heart fibrillation, leading to rapid death from hypoxia or heart attack.
Treatment
Clear the airway, and apply EAR/ECM as necessary. Always seek professional medical help: secondary drowning ,due to the lungs filling up with fluid because of damage to the alveolar membrane, can occur up to twelve hours after the original incident.
Hyperventilation
How Does It Occur?
The object of hyperventilation, before a breath-holding dive, is to increase the length of time the diver can remain underwater. It may be accomplished by taking a series of very deep breaths prior to breath-holding and commencing the dive. This, in effect, significantly reduces the level of CO2 in the body and only marginally increases the O2 level. Thus the CO2 breathing trigger is at an artificially low level at the start of the dive. During the dive, especially with the diver finning hard, O2 is being used up rapidly. However, the desire to breathe is suppressed due to the low level of CO2 The outcome of this is that the secondary receptors in the heart and brain detect the lack of O2 , before the CO2 trigger is reached. The diver then lapses into unconsciousness.
Why Does It Happen?
After the first two or three breaths the haemoglobin in the blood is saturated with oxygen. Subsequent breaths add no more oxygen, but remove more and more CO2 from the bloodstream, increasing the pH of the blood. When the dive begins, the body starts to use up the available oxygen, generating CO2 in the process. However, because the amount of CO2 in the blood was reduced to a low level by hyperventilating, it does not build up to the level at which a breathing reflex is triggered until well after the diver has used up all the available oxygen in the blood. As a result the individual become seriously hypoxic and finally anoxic. The problem is exacerbated with depth and is common in persons engaged in commercial spear-fishing.
What is the Safe Way to Swim Underwater?
Take only 2 medium deep breaths, at most, before setting off on a breath-holding dive. Never overwork or linger at depth. Snorkel divers, like their aqualung counterparts, should always operate in pairs. One should remain on the surface whilst his/her buddy is diving. The divers should arrange to be buoyant from 10m upwards, as problems normally occur on ascent or at the surface.
Principles of EAR
When somebody has stopped breathing, they will become increasingly hypoxic, and finally anoxic. To prevent certain death it is essential to commence Expired Air Resuscitation (EAR) on the victim as soon as possible. The aim is twofold:
1. To provide the casualty with the oxygen that they cannot provide themselves;
2. The air that is expired contains more carbon dioxide than is breathed in, so that it is more likely to trigger a breathing reflex in the victim and cause them to start breathing again.
3. The normal procedure is to give two breaths every 10 seconds, either mouth-to-mouth (on land) or mouth-to-nose (in water).
End of lecture