The human body is made up of a number of cells with different forms and functions that all need to be continuously supplied with oxygen in order to produce energy. Oxygen, which is one of the basic elements of the atmospheric air, enters our body through the respiratory organs, feeding all the cells via the bloodstream.
THE RESPIRATORY SYSTEM
The function of the respiratory organs is to supply the body with the gasses surrounding it; this is done by its absorption into the blood through the following organs:
The respiratory airways: which connect the lungs with the outside.
The alveoli, the place where gas enters the bloodstream. The capillaries, which link the alveoli with the heart. The respiratory airways are divided in two sections: upper and lower. The upper airways are nose, mouth, sinuses, pharynx and larynx: their function
is to carry air to the lungs while purifying and adding moisture to it. The lower airways are trachea, bronchi, bronchioli and alveoli.
The bronchioli and alveoli make up the pulmonary mass inside which the respiratory exchange takes place.
THE ALVEOLI AND THE CAPILIARIES
These are the organs used for the gas exchange and have a vast surface area (between 40 and 100 square metres in adults). Oxygen and carbon dioxide are transferred from the breathed air into the blood, because of the difference in partial pressure, through the membrane of the pulmonary alveolus.
Once oxidised the blood carries to the left atrium via the pulmonary veins prior to being distributed throughout the body.
THE CARDIO – CIRCULATORY
SYSTEM
The function of the cardio-circolatory system is to transport and distribute oxygen and to remove residues and carbon dioxide. The main element of the system is the heart, which is divided vertically in two sections:
– the left side of the heart is responsible for the transportation of the blood enriched in oxygen
– the right side of the heart is responsible for the transportation of the blood charged with carbon dioxide and poor in oxygen.
It is in turn divided horizontally into two parts:
– the atria, in the upper part, which receive the blood.
– the ventricles, in the lower part, which pump the blood.
The right ventricle pushes the blood towards the lung via the pulmonary arteries, and returns, oxidised blood, through the pulmonary veins, which go to the left atrium. From here the blood passes into the left ventricles where is then pumped throughout the body via the arteries after which it returns through the veins to the right atrium.
Cardiac movement is divided into two phases: “systolic” and “diastolic”. The systole is a contraction and enables the release of the blood; the diastole is dilatation that allows the heart to be filled with blood.
Cardiac movement in adults is approximately 60 to 80 beats to the minute while in children and old people this tends to increase.
Blood is carried by:
– the main arteries: these are thick and wide, and are resistant to high blood pressure
-the arteriole: these are small in width and regulate the flow of blood according to the requirements of the various organs
– the capillaries: here the blood slows down considerably to allow tissue exchange. From the capillary the blood goes into the venule, then into the larger veins and finally to the vene cavae that return to the heart.
Human metabolism
Every time we make a movement we use energy which asks more of our body, requiring a change in the metabolism in order to satisfy this new demand. For example, if we draw on a muscular structure to make a movement we set off a chain of events:
– The need for oxygen, vital for the production of muscular energy, increases, as a result, the breathing rate increases in order to oxidise the blood, and to increase the CO2 wash out.
– The heart rate also increases in order to pump blood more quickly through the body.
– There will also be an increase in the body temperature.
If any of these delicate balancing mechanisms are altered an emergency situation will arise.
These emergency situations can, in a context of diving, be grouped into the following categories:
–accidents due to excess of carbon dioxide (shortness of breath)
-accidents due to lack of oxygen (hypoxia)
-accidents due to water temperature (hypothermia or hyperthermia)
-accidents due to the breathing of compressed air (embolism)
SHORTNESS OF BREATH
A particularly strenuous action or heightened emotional tension can bring on shortness of breath, which is characterised by the difficulty in satisfying an increased need for oxygen with one’s breathing. It can take more effort to breathe underwater, because of the different ambient pressure, the resistance due to the equipment and the low temperature. At its worst, this can lead to shortness of breath.
Normally, shortness of breath is preceded by an increase in the breathing rate. If the cause is not dealt with breathing becomes faster and faster without, however, adequate oxidisation having taken place.
A feeling of anxiety and a suffocating sensation arises which can lead to panic and therefore more serious risks. To prevent shortness of breath a regular breathing pattern (10/ 12 breaths a minute) with equal inhalation and exhalation times must be maintained.
The diver who feels the first symptoms of shortness of breath must immediately stop all activity, remain still and try to re-establish his regular breathing pattern, which can be achieved with the use of respiratory stop.
The diver’s companion must be alerted to his condition as soon as possible: the two should then slowly reascend to the surface together.
HYPOXIA
Hypoxia refers to the situation whereby the amount of oxygen required by the cells exceeds that which is available to the body. When scuba diving, hypoxia can occur after a sudden interruption of the air supply or can develop gradually. In the former case the cause can be a malfunction in the equipment or exhaustion of the air reserves, something which should never happen if the dive has been well planned.
In the latter case, incorrect breathing or excessive physical exertion causes the lack of oxygen. The symptoms of hypoxia include inability to concentrate and impaired movement.
The diver suffering from hypoxia should be taken to the surface as soon as possible, treated with oxygen and, if necessary, given artificial respiration. If the oxygen supply proves to be insufficient there will also be an increase in carbon dioxide and therefore the problem of hypercapnia, or asphyxia.
HYPOTHERMIA
Every time that our body undergoes a loss of heat it responds by trying to maintain a constant temperature in the central zone. In a prolonged stay in cold water, for example, the body automatically protects this central zone (which includes all the vital organs) as a result of which hypothermia may occur. Hypothermia is caused by a lowering of the body temperature to about 30 degrees C and can lead to serious clinical problems. At first an increase in the heartbeat occurs, to try to deal with the negative situation, but when the temperature drops to below 34 degrees C, the heart beat starts to slow down. Below 30 degrees potentially very serious heart problems can occur. Hypothermia affects the respiratory functions, causing reduction of breathing.
It also reduces the brain activity causing anxiety, disorientation and coma. It is therefore
very important to be properly equipped, but above all to have a sensible attitude. Treatment of hypothermia consists of preventing a further decrease of body temperature: it is therefore necessary to remove the diver ‘s wet clothing and to dry him, cover him with blankets, and keep him warm all over. It must be remembered that it is very dangerous to give alcoholic drinks to someone suffering from hypothermia, because the resulting dilatation of the blood vessels would allow the colder blood at the extremes of the body to reach the vitals organ more quickly.
HYPERTHERMIA
This occurs after excessive exposure to external heat. When the diving suit is left on under the sun for considerable time. The body can no longer compensate for the increase in his own temperature. Symptoms such as light-headless, headache, excessive sweating, respiratory difficulties, and even loss of consciousness may occur. It is recommended that the diver be undressed, taken to a cooler environment and given plenty of water to drink.
Diving accidents
EMBOLISM
During ascent the air in the lungs tend to expand. If for any reason the breath is held during ascent in a Scuba diving this expansion of the air after having enlarged the lungs to their maximum causes a progressive distension of the pulmonary alveoli, if the diver continues to ascend without breathing out the overdistension of the lung can results in a pulmonary barotrauma (a wounding of the lungs caused by pressure) in this case the alveoli membrane is stretched to a such a degree that tiny air bubbles are able to pass into the blood stream, or can tear and cause the release of larger bubbles. Regular and continuous breathing is, however, sufficient to eliminate excess air and maintain normal lung volume. A risk of pulmonary overdistension occurs in the last ten metres below the surface where the variation in the pressure volume ratio is at his greatest. The reduction in pressure in the last ten metres of ascent towards the surface is 50% (from
2 to 1 atm), while the same distance, but from 20 to 10 metres, sees the 33% drop in pressure (from 3 to 2 atm). This considered, it is important remembering to never hold one’s breath during ascent, even in the pool. The seriousness of a pulmonary distension depends on the effect that pressure has exerted on the walls of the pulmonary alveoli: distension or laceration of tissue.
The most serious consequence of pulmonary overdistension is the passing of air bubbles from the alveoli into the blood stream and is commonly known as air embolism syndrome. The air bubbles that pass from the lacerated alveoli to the adjacent tissues can, on the other hand, causes pneumothorax, mediastinal emphysema, subcutaneous emphysema.
AIR EMBOLISM SYNDROME
The bubbles escaping from the laceration of the pulmonary alveolus, once they have reached and been pushed along the aorta, can reach any part of the body and may stop in the small vessels. This can block circulation of the blood, and therefore of oxygen in the areas below the embolus.
Symptoms and effects
Air embolism syndrome is generally traumatic and usually occurs in the first moments of surfacing or even before reaching the surface. The symptoms include dizziness, vertigo, impaired vision, breathing problems, heart disturbances, and paralysis.
PNEUMOTHORAX
It occurs when considerable quantity of air that escaped from the alveolus remains trapped between pleura. The lung, then stop to function due to the lack of vacuum between the pleurae.
Symptoms and effects The symptoms of pneumothorax consist of intense chest pain
along with coughing of blood and considerable difficulty in breathing.
MEDIASTINAL EMPHYSEMA
When the air that leaves the exits from the alveoli head towards the inside of the rib cage, so remaining trapped between the tissues around the heart and the major large blood vessels and causing an irregular return of venous blood as well as abnormal pressure on the respiratory airways pulmonary sac, the result is mediastinal emphysema.
Symptoms and effects
The first symptom is a pain in the inside of the rib cage. In addition, the trapped air that presses against the lungs, the heart, and the large blood vessels, inhibiting breathing and circulation, causes breathing difficulties and possible loss of consciousness.
SUBCUTANEOUS EMPHYSEMA
Subcutaneous emphysema occurs when air bubbles that have escaped from a laceration of lung tissue are forced toward the neck causing it to swell at the front.
Symptoms and effects
The symptoms are a “sense of swelling” at the neck and a change in the sound of the voice.
Subcutaneous emphysema is often associated with mediastinal emphysema.
TREATMENT OF PULMONARY OVERDISTENSION
The only effective treatment for air embolism syndrome is immediate recompression in a hyperbaric chamber and the administration of large quantity of water to make the blood more fluid and so reduce the risks of obstruction by the bubbles. The administration of oxygen or artificial respiration is of use only as first aid on the way to the hospital.
