What is Radiation Sickness?
Radiation sickness is formed under the influence of radioactive radiation in the dose range of 1-10 Gy or more. Some changes observed during irradiation in doses of 0.1-1 Gy are regarded as preclinical stages of the disease. There are two main forms of radiation sickness that form after a general relatively uniform exposure, as well as during very narrowly localized irradiation of a specific segment of the body or organ. Combined and transitional forms are also noted.
Pathogenesis during Radiation Sickness
Radiation sickness is divided into acute (subacute) and chronic forms depending on the temporal distribution and the absolute magnitude of the radiation load, which determine the dynamics of developing changes. The peculiarity of the mechanism of development of acute and chronic radiation sickness precludes the transition of one form to another. The conditional boundary that delimits acute or chronic forms is the accumulation over a short period (from 1 hour to 1-3 days) of the total tissue dose equivalent to that from exposure to 1 Gy of external penetrating radiation.
The development of the leading clinical syndromes of acute radiation sickness depends on the doses of external radiation, which determine the variety of observed lesions. In addition, the type of radiation plays an important role, each of which has specific features that are associated with differences in their damaging effects on organs and systems. So, a-radiation is characterized by a high ionization density and low penetrating ability, and therefore these sources cause a spatially limited damaging effect.
Beta radiation, with low penetrating and ionizing ability, cause tissue damage directly in parts of the body adjacent to a radioactive source. On the contrary, gamma radiation and x-ray radiation cause deep damage to all tissues in the area of their action. Neutron radiation causes a significant heterogeneity of damage to organs and tissues, since their penetrating ability, as well as the linear energy loss along the neutron beam in the tissues, are different.
In the case of irradiation with a dosage of 50-100 Gy, CNS damage determines the leading role in the mechanism of the development of the disease. With this form of the disease, death is usually observed on the 4th-8th day after exposure to radiation.
When irradiated in doses of 10 to 50 Gy, the symptoms of damage to the gastrointestinal tract with rejection of the small intestinal mucosa leading to death within 2 weeks come to the fore in the mechanism of the development of the main manifestations of the radiation clinical picture of the disease.
Under the influence of a lower dose of radiation (from 1 to 10 Gy), the symptoms typical of acute radiation sickness are clearly traced, the main manifestation of which is the hematological syndrome, accompanied by bleeding and all kinds of complications of an infectious nature.
Damage to the organs of the gastrointestinal tract, various structures of both the brain and the spinal cord, as well as the blood forming organs, is characteristic of exposure to the above radiation doses. The severity of such changes and the speed of development of violations depend on the quantitative parameters of exposure.
Symptoms of Radiation Disease
The following phases are clearly distinguished in the formation and development of the disease: Phase I – primary general reaction; Phase II – apparent clinical well-being (fast, or latent, phase); III phase – pronounced symptoms of the disease; IV phase is the period of restoration of structure and function.
In the event that acute radiation sickness proceeds in a typical form, four degrees of severity can be distinguished in its clinical picture. Symptoms characteristic of each of the degrees of acute radiation sickness are due to the dose of radiation that occurred in this patient:
- a mild degree occurs when irradiated in a dose of 1 to 2 g;
- moderate severity – the radiation dose is from 2 to 4 g;
- heavy – the dose of radiation ranges from 4 to 6 g;
- an extremely severe degree occurs when irradiated in a dose exceeding 6 g.
If the patient received a dose of radiation at a dose of less than 1 g, then we have to talk about the so-called radiation injury, which occurs without any obvious symptoms of the disease.
The severe degree of the disease is accompanied by restoration processes that take a long time for 1-2 years. In cases where there are any changes that become persistent, in the future we should talk about the consequences of acute radiation sickness, and not about the transition of the acute form of the disease to chronic.
Phase I of the primary general reaction is observed in all individuals when irradiated in doses exceeding 2 g. The time of its appearance depends on the dose of penetrating radiation and is calculated in minutes and hours. The characteristic signs of the reaction are nausea, vomiting, a feeling of bitterness or dry mouth, weakness, fatigue, drowsiness, headache.
Perhaps the development of shock-like conditions, accompanied by a decrease in blood pressure, loss of consciousness, possibly an increase in temperature, as well as diarrhea. These symptoms, as a rule, occur during irradiation in doses exceeding 10 g. Transient reddening of the skin with a slightly bluish tinge is detected only in parts of the body exposed to irradiation in a dose exceeding 6-10 g.
In patients, there is some variability in the pulse and blood pressure with a tendency to decrease, a uniform general decrease in muscle tone, trembling of the fingers, and a decrease in tendon reflexes are characteristic. Changes in the electroencephalogram indicate moderate diffuse inhibition of the cerebral cortex.
During the first days after irradiation in the peripheral blood, neutrophilic leukocytosis is observed with no noticeable rejuvenation in the formula. Subsequently, over the next 3 days, the level of lymphocytes in the blood decreases in patients, this is due to the death of these cells. The number of lymphocytes after 48-72 hours after irradiation corresponds to the received dose of radiation. The number of platelets, red blood cells and hemoglobin in these periods after irradiation does not change against the background of myelocaryocytopenia.
In the myelogram, after a day, an almost complete absence of such young forms as myeloblasts, erythroblasts, a decrease in the content of pronormoblasts, basophilic normoblasts, promyelocytes, myelocytes is revealed.
In the first phase of the disease, with radiation doses exceeding 3 Gy, some biochemical shifts are detected: a decrease in the content of serum albumin, an increase in blood glucose with a change in the sugar curve. In more severe cases, moderate transient bilirubinemia is detected, indicating thereby metabolic disturbances in the liver, in particular, a decrease in the absorption of amino acids and increased protein breakdown.
Phase II – the phase of imaginary clinical well-being, the so-called latent or latent phase, is noted after the disappearance of signs of the primary reaction 3-4 days after irradiation and lasts for 14–32 days. The well-being of patients in this period improves, only a certain lability of the pulse rate and blood pressure level remains. If the radiation dose exceeds 10 g, the first phase of acute radiation sickness directly goes into the third.
From the 12-17th day in patients exposed to radiation in a dose exceeding 3 g, baldness is detected and progresses. Other skin lesions occur during these periods, sometimes being prognostically unfavorable and indicating a high dose of radiation.
In the second phase, neurological symptoms become more distinct (impaired movement, coordination, involuntary trembling of the eyeballs, organic mobility, symptoms of mild pyramidal insufficiency, decreased reflexes). On the EEG, the appearance of slow waves and their synchronization in the rhythm of the pulse are noted.
In peripheral blood, by the 2-4th day of the disease, the number of leukocytes decreases to 4 × 109 / l due to a decrease in the number of neutrophils (first decrease). Lymphocytopenia persists and progresses somewhat. Thrombocytopenia and reticulocytopenia join on the 8-15th day. The number of red blood cells is not significantly reduced. By the end of phase II, a slowdown in blood coagulation is detected, as well as a decrease in the stability of the vascular wall.
In the myelogram, a decrease in the number of more immature and mature cells is detected. Moreover, the content of the latter decreases in proportion to the time elapsed after irradiation. By the end of phase II, only mature neutrophils and single polychromatophilic normoblasts are found in the bone marrow.
The results of biochemical blood tests indicate a slight decrease in the albumin fraction of serum proteins, normalization of blood sugar and serum bilirubin.
In the III phase, proceeding with severe clinical symptoms, the timing of the onset and the degree of intensity of individual clinical syndromes depend on the dose of ionizing radiation; the duration of the phase ranges from 7 to 20 days.
The dominant in this phase of the disease is the defeat of the blood system. Along with this, there are suppression of immunity, hemorrhagic syndrome, the development of infections and auto-intoxication.
By the end of the latent phase of the disease, the condition of the patients worsens, resembling a septic state with characteristic symptoms: increasing general weakness, rapid pulse, fever, lowering blood pressure. Swelling and bleeding of the gums are expressed. In addition, the mucous membranes of the oral cavity and gastrointestinal tract are affected, which is manifested in the appearance of a large number of necrotic ulcers. Ulcerative stomatitis occurs when irradiated in doses of more than 1 Gy on the oral mucosa and lasts about 1-1.5 months. The mucous membrane is almost always restored completely. At high doses of radiation, severe inflammation of the small intestine develops, characterized by diarrhea, fever, bloating and soreness in the ileum. At the beginning of the 2nd month of the disease, radiation inflammation of the stomach and esophagus is possible. Infections are most often manifested in the form of ulcerative-erosive tonsillitis and pneumonia. Autoinfection, which acquires pathogenic significance against the background of pronounced inhibition of hematopoiesis and suppression of the immunobiological reactivity of the body, has a leading role in their development.
Hemorrhagic syndrome manifests itself in the form of hemorrhages, which can be localized in completely different places: the heart muscle, skin integument, the mucous membrane of the respiratory and urinary tract, the gastrointestinal tract, central nervous system, etc. The patient experiences heavy bleeding.
Neurological symptoms are a consequence of general intoxication, infection, anemia. Increasing general lethargy, adynamia, dimming of consciousness, meningeal symptoms, increased tendon reflexes, and decreased muscle tone are noted. Usually, signs of increasing edema of the brain and its membranes are detected. Slow pathological waves appear on the EEG.