I came across this question when I was browsing the Malaysian Diving Community forum, thus decided to write a little about it. I have to justify that I am not an expert in the field of haematology but just an aid to my fellow divers and bloggers.
The red blood cell is a component of the blood. These specialised cells are like flattened discs, which gives them a much greater surface area with which to exchange oxygen and carbon dioxide in the lungs and with body cells.Red blood cells are able to carry oxygen so efficiently because of a special protein within it called haemoglobin which is also responsible for its colour.
Haemoglobin contains a haem group that has an iron atom at its centre. When the iron is bound to oxygen, the haem group is red in colour (oxyhameoglobin), and when it lacks oxygen (deoxygenated form) it is blue-red.
Haemoglobin is composed of four polypeptide chains, which in adults consist of two alpha (a) globin chains and two beta (b) globin chains. Each polypeptide has a haem prosthetic group attached, where each haem can bind one oxygen molecule - so there are four haem groups per haemoglobin molecule that together bind four oxygen molecules.
So, like all things in life, nothing is perfect. Abnormalities of these haemoglobin are called haemoglobinopathies. There many such haemoglobinopathies and among the popular ones are the thalassemia and the sickle cell disease.
They are different in that Thalassemia is due to defective or deficient production of the alpha(a) or beta(b) chain whereas Sickle Cell is due to the production of a mutant form of beta chain and is better known as HbS
However, they are similar in that they are genetic disorders and are passed down in a similar fashion. Some may even have both but this is more common among the African and Mediterranean population.
From legends, Thalassa (”sea”) was a primordial sea goddess and she was the personification of the Mediterranean Sea, Haima is Greek for blood. When the production of ? globin is deficient then it is called a thalassaemia, while in ? thalassemia the production of ? globin is defective.
The is a higher estimated prevalence among the Chinese and Malays in Malaysia and the commoner type is of beta thalassaemia which can present itself as either major, minor or intermedia. b-thalassaemia major means that the genetic mutations are more severe and causes one to require frequent blood transfusion whereas b-thalassaemia minor may live quite a normal life with just fatigue as their complaint. More often they may not even be aware of their condition.
Thalassemia major (Cooley anemia) is characterized by transfusion-dependent anemia, massive splenomegaly, bone deformities, growth retardation, and peculiar facies in untreated individuals, 80% of whom die within the first 5 years of life from complications of anemia.
Carriers of this condition have some degree of protection against malaria and have some protection against coronary heart disease.
Our famous Zidane is also a carrier. This comes to show that carriers would not generally have problems with vigorous activities and therefore diving is safe for them. However, a full edical screening is necessary. A peripheral blood film and an haemoglobin electrophoresis are essential apart from complete blood counts and iron studies.
As the saying goes, prevention is better than cure, successful prevention programs in different parts of the world have resulted in an impressive decline in the number of patients with severe forms of thalassemia. In addition to the effective prenatal diagnosis, other measures such as premarital screening programs,genetic counseling, and restrictions on issuing marriage certificates and licenses also proved to be effective.
Sickle Cell Anaemia
The abnormal b chain reduces the amount of oxygen inside the red blood cell, altering its shape, changing them from a flattened disc to a sickle or crescent shape. Sickle blood cells are hard, inflexible and tend to clump together, causing them to get stuck in blood vessels as blood clots, thereby blocking the flow of blood. This can cause pain, blood vessel damage and a low red blood cell count (anaemia).
The disease is chronic and lifelong. Individuals are most often well, but their lives are punctuated by periodic painful attacks. In addition to periodic pain, there may be damage of internal organs, such as stroke. Lifespan is often shortened with sufferers living to an average of 40 years.
Low oxygen concentration causes more red blood cells to sickle. Repeated episodes of sickling causes loss of this elasticity and the cells fail to return to normal shape when oxygen concentration increases. These rigid red blood cells are unable to flow through narrow capillaries, causing vessel occlusion and ischemia. Therefore, these group of patients are not recommended for diving.