Экологическая медицина = Ecological medicine. Учебное пособие

LABORATORY SESSION

In order to develop preventive recommendations, students are invited to assess the degree of addictive behaviour on alcohol, tobacco smoking, etc. according to the methodology developed at the Department of General­ Hygiene, Ecology and Radiation Medicine.

Questionnaire

for comprehensive rapid assessment of students’ addictive behaviour

Sex ____________. Age _______ years.

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The assessment is performed on a point scale in two successive stages. Stage 1. For each question, 1 point is for the answer “Change for the worse”, 2 points are for “Change for the better”, 0 points are for “Without

changes”.

Stage 2. Calculate the sum of points based on the results of the survey. On each question: 1–4 points – low dependency; 5–8 points – medium dependency; 9–12 points – maximum dependency.

This research algorithm is used for individual assessment and when evaluating behaviour in groups.

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Chapter 2

SOLAR RADIATION EFFECT ON THE HUMAN BODY

Motivational characteristic of the topic. Rational use of solar radiation promotes good health, increases its reactivity and resistance to adverse environmental factors. On the contrary, when there is insufficient insolation, particularly due to a deficiency of UV radiation, the individual’s health level decreases, susceptibility to infectious diseases increases, children may develop rickets.

Doctors of any speciality should be aware of the essence and role of solar radiation in human life, and must be able to give appropriate recommendations on the rational use of both natural and artificial radiation to strengthen and maintain good health.

The objective: to learn how to predict the possible negative effects of solar radiation on the human body.

Tasks:

1.  To become acquainted with the peculiar features of the biological effect of various solar radiation spectra on the human body.

2.  To determine the type of skin sensitivity.

3.  To master the technique for evaluating the risk of developing skin cancer.

4.  To learn how to calculate sunlight exposure time necessary for ensuring a person’s daily need for vitamin D.

Requirements for students’ initial knowledge level. To fully master the topic of the chapter, a student should revise the relevant material from the following disciplines:

1.  Medical and Biological Physics: “Electromagnetic radiation, specific power of radiation, wavelength, energy of a quantum”.

2.  Medical Biology and Genetics: “Biological effects of solar radiation”. 3.  The Normal Human Physiology: “Disturbance of physiological bal-

ance in the body with the sunlight deficiency”.

4.  Biological Chemistry: “Photochemical reactions occurring in the body when exposed to ultraviolet radiation”.

Review questions from the related disciplines:

1.  Characteristics of the physical properties of air. 2.  Characteristics of the chemical composition of air.

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3.  What are the mechanisms of the damaging effect of UV radiation? 4.  What is the role of the air in the emergence of non-communicable

diseases?

5.  What hygienic measures on protection of atmospheric air do you know?

Questions related to the topic of the chapter:

1.  Influence of the visible region of the solar spectrum and illumination on a person. “Winter depression” (affective seasonal disorder): concept, causes of development, clinical manifestations, prevention, and treatment.

2.  The definition of “biological rhythm”. Basic parameters. Classification and the desynchronisation problem of biological rhythms. Dynamic diseases.

3.  Meteosensitivity: the concept, classification according to the severity of clinical manifestations and types of meteopathic reactions.

4.  Features of the biological action of the infrared spectrum of solar radiation; application in medicine.

5.  What methods are available to measure the UV component of solar radiation?

6.  What is biodose, the minimum daily preventive dose, the optimal dose? Define these concepts.

7.  What is ultraviolet deficiency and how is it prevented?

8.  What are the results of excessive irradiation of the body with UV rays; how to prevent it?

LEARNING MATERIAL FOR THE CHAPTER

All organic life on Earth exists owing to solar radiation. The nature of the solar radiation influence on the human body and health is determined by its spectral composition: visible radiation provides the function of a visual analyser, infrared radiation has a thermal effect, ultraviolet radiation has a general stimulating, biological, erythemic, antirachitic, bactericidal effect. Rational use of solar radiation promotes good health, increases its reactivity and resistance to adverse environmental factors. On the contrary, when there is insufficient insolation, particularly due to a deficiency of UV radiation, the individual’s health level decreases, susceptibility to infectious diseases increases, children may develop rickets.

Visible radiation is a narrow range in the spectrum of electromagnetic radiation from the Sun (from 400 to 760 nm), but in terms of physiological and hygienic significance it takes a leading place among environmental

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factors. Daylight has a beneficial effect on the body, stimulates its vital activity, improves the psycho-emotional state of a person (especially a patient). Under its influence metabolism in the body is intensified, haematopoiesis processes are activated, the work of the endocrine glands improves, etc. The illumination mode plays an essential role in the regulation of biological rhythms. In almost all living beings, from protozoa to humans, the state and functions of systems change rhythmically. These changes often correspond to the circadian rhythm associated with the rotation of the Earth, although there are other periodic fluctuations corresponding to the tidal, lunar, or annual cycles.

Biological rhythms are fluctuations in the change and intensity of processes and physiological reactions. They are based on changes in the metabolism of biological systems due to the influence of external and internal factors. Factors that affect the rhythmicity of processes occurring in a living organism have been defined as “synchronisers” or “time sensors”. In the nature of the biological rhythm inherent in every living organism, there are two components: exogenous (external) and endogenous (internal). The biorhythm endogenous component (the daily rhythm of physiological functions) is genetically fixed and inherited, the exogenous component (any influence of external factors) is caused by external time sensors.

External factors include: changes in illumination (photoperiodism), temperature (thermoperiodism), magnetic field, intense cosmic radiation, tides, seasonal and solar-lunar influences; social influences that are characteristic of humans.

Internal factors include neurohumoural processes occurring at a certain, genetically fixed rate and rhythm.

In the natural environment, there are no contradictions between the components of the diurnal rhythm. Artificial violation of exogenous rhythm component (artificial illumination, sleep disturbance, working night shift, changing time zones) is often a trigger mechanism for violation of organism adaptation processes to environmental conditions. Since endogenous rhythms only approximately correspond to the diurnal rhythm, they are called circadian (lat. “circa” – about, “dies” – day). Humans have more than 100 different physiological parameters cyclically changing with a period of 24 hours. Thus, the body temperature is minimal early in the morning and reaches its maximum in the evening, becoming about 1–1.5 °C higher. The diurnal sleep / wake cycle is the most pronounced, therefore many functional changes of the body usually occurring with the onset of sleep (e.g., decrease in body temperature, heart and respiration rate) were considered causally related to it.

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Infrared (thermal) radiation represents the majority (~58%) of the solar electromagnetic spectrum. IR radiation with a wavelength (λ) of 760– 3,000 nm reaches the Earth’s surface, while longer wavelengths are trapped by the atmosphere. IR radiation, when it encounters molecules and atoms of various substances on its way, intensifies their vibrational motion and thus causes a thermal effect. It penetrates through the atmosphere, the water column and the soil, through window glass and clothing. The shortest infrared radiation (760–1,000 nm) penetrates body tissues, including the bones of the skull to a depth of 4–5 cm. When acting locally on tissues, IR radiation somewhat accelerates biochemical reactions, enzymatic and immunobiological processes, cell growth and tissue regeneration, increases blood flow. Intensity of heating of subcutaneous tissue and internal organs decreases due to blood circulation. Further exposure to IR radiation intensifies deep tissue warming, which may lead to heatstroke or sunstroke.

The active decomposition products formed under the influence of ­infrared radiation on the skin, and the nerve impulses coming from it, spread the local effect of the radiation to the whole organism. This effect (humoural and nervous) normalises the tone of the vegetative nervous system, relieves excessive tension, weakens muscle and vascular tone, achieves analgesic and anti-inflammatory effect. Due to this, IR radiation is used in medical practice (physiotherapy).

Thermal radiation intensity in SI is measured in Joules (J), Kilojoules (kJ), Megajoules (MJ) per square meter per hour [MJ/(m2h)]. An off-sys- tem (obsolete) unit [cal/(cm2 min.)] is found in old manuals, reference books and on the scales of measuring instruments – actinometers. The intensity of the Sun’s total thermal radiation at the border of the Earth’s atmosphere (solar constant) is 4.87 MJ/(m2h) or [1.94 cal/(cm2 min.)]. At the Earth’s surface in temperate latitudes it does not exceed 3.77 MJ/(m2 h) or [1.5 cal/(cm2 min.)] (Table 2.1).

The ultraviolet part of the solar spectrum is the most biologically active. Its intensity and spectral composition constantly change depending on the season of the year, the state of the atmosphere, the amount of water vapour, aerosols, the height of the sun above the horizon, the dust level and annual pollution of atmospheric air. One of the main characteristics is wavelength (from 200 to 400 nm). In addition, there is a division into 3 groups, depending on the wavelength:

1)  ultraviolet A radiation (UVA) – 400–320 nm;

2)  ultraviolet B radiation (UVB) – 320–280 nm;

3)  ultraviolet C radiation (UVC) – 280–200 nm.

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Table 2.1. Galanin’s scale for subjective assessment of heat radiation intensity

UV radiation has a wide biological effect. Penetrating into the tissue to the depth of 0.5–1.0 mm, it actively affects the immunological resistance of the body, increasing the activity of hypothalamic-pituitary-adrenal system, leads to the activation of biochemical processes and thus affects the cell metabolism. The rate of chemical processes in the body increases, which improves metabolic and trophic processes, accelerates growth and regeneration of body tissues, increases resistance to infection and improves physical and mental performance.

Under the influence of significant doses of UV rays, erythema occurs on the skin, reaching its maximum development after 18–20 hours, which is eventually replaced by pigmentation, i.e., tan on day 7–9. The processes emerging during erythema formation are the basis of analgesic, anti-in- flammatory, resorbing actions.

The specific biological effect of UV radiation is the formation of endogenous vitamin D, which occurs in the skin under the influence of small doses of UVA radiation with a wavelength of 315–365 nm. Dehydrocholesterol in the skin is converted into vitamin D3. The latter is involved in the regulation of phosphorus-calcium metabolism in the body.

An important feature of the UVC rays is their bactericidal effect. It is based on the direct effect of these rays on microorganisms. During absorption of radiant energy, complex biochemical processes occur in the microorganisms, leading ultimately to their death.

Speaking about the biological effects of UV radiation, it is worth mentioning possible side effects. Thus, when exposed to excess disposable UV irradiation it is possible to note:

1.  The occurrence of photochemical burns in the form of erythema, blisters, headache. Photophthalmia is possible as well. In this case, there is

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an increase in lipid peroxidation, which leads to cell membrane damage and cell death.

2.  Exacerbation of chronic diseases such as tuberculosis, rheumatism, etc., because the increased formation of melanin increases the need for essential amino acids, vitamins, calcium salts, which adversely affects the course of the chronic process.

3.  When exposed to UVC radiation with a wavelength of 200–280 nm, cholecalciferol is inactivated into its toxic derivatives.

Prolonged exposure to excessive UV radiation may result in: yyformation of peroxide and epoxy substances with mutagenic effect; yyskin cancer induction;

yyincreased photosensitisation;

yyoccurrence of photo-allergies in certain population.

Methods of measurement and regulation of UV radiation. The beneficial effect of UV radiation can be ensured by regulating its intensity and erythemic radiation dose, as well as a clear control of the irradiation process. Currently, three methods are used for this purpose: biological, photochemical, and photoelectric.

Biological method is widely used in medical practice. It is based on determination of erythemic – biological dose (vitadose) of irradiation. Biodose is the smallest amount of UV exposure (or minimum exposure time) that causes (after 8–14 hours) the occurrence of barely noticeable redness on an untanned skin area (determined with the Gorbachev’s biodosimeter).

The dose that prevents hypoand avitaminosis D, disorders of phos- phorus-calcium metabolism, and other adverse effects of light starvation is called a prophylactic dose and is 1/8 of the erythemic dose. The physiological dose of UV radiation (in terms of its adaptogenic effect) is 1/4–1/8 of the erythemic dose.

The threshold erythemic biodose is not constant and depends on gender, age, health, and other individual characteristics. The biodose is determined experimentally for each case or selectively for the most impaired individuals who will be exposed to irradiation.

Photochemical method of determining the degree of erythemic irradiation caused by UV radiation is based on the decomposition by the latter in the presence of uranyl nitrate of a titrated solution of oxalic acid. One erythemic dose corresponds to 4 mg of decomposed oxalic acid per 1 cm2 of the irradiated solution surface.

Photoelectric (physical) method is based on determining the intensity of UV radiation using special devices, i.e., ultraviolet meters or UV meters

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(UVM-71). These devices allow determining the energy (physical) value of UV radiation, i.e., the degree of energy irradiation to estimate the intensity of UV radiation and the nature of its distribution on the surface in the premise volume. Measurement results are indicated in watts per square meter and in watt derivatives (W/m2, mW/m2, μW/m2). With the help of these devices, it is possible to determine the amount of irradiation, i.e., dose of energetic irradiation, for dosing radiation separately in erythemic (290–340 nm) and bactericidal (220–290 nm) ranges – W/(m2/h), mW/(m2/h), μW/(m2/h).

Indications and contraindications for UV irradiation

General indications include:

yyprevention of solar insufficiency, and at the same time hypovitaminosis; yyprevention and treatment of rickets;

yyprevention of lowering the overall resistance of the body in the win- ter-autumn period;

yyprevention of infections;

yyprevention of a decrease in mental and physical performance. Local indications include erythemotherapy for inflammatory diseases of

internal organs, such as: yybronchitis; yygastritis; yyrheumatism; yytonsillitis; yyangina; yybronchial asthma.

It is generally believed that UV therapy is most effective in childhood and adolescence, due to the fact that metabolic processes are still very labile and not fully formed. Besides, UV radiation is used in surgery, traumatology, dermatology.

Contraindications in the application of UV radiation include: yymalignant tumours;

yysusceptibility to bleeding; yyactive pulmonary tuberculosis; yydysemia;

yycachexia; yyhyperthyroidism;

yysystemic lupus erythematosus; yycirculatory inefficiency of I, II degree.

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The following factors are critical in the development of pathology: yyradiation dose;

yyradiation spectral characteristics; yyindividual sensitivity; yyexposure frequency.

It has been found that different spectral ranges of UV radiation affect human skin differently, the main reaction of which is the development of erythema. For example, the skin is 100 times more sensitive to UV radiation with a wavelength of 298 nm than with λ = 319 nm. The contribution of different UV ranges in the formation of erythema reflects the so-called erythemal action spectrum (EAS), the values of which are expressed in the UV flow rate per unit area (W/m2). According to the recommendations of international organisations, 0.25 W/m2 should be considered as the maximum value of the EAS. In everyday practice, when monitoring the level of UV radiation, many countries use the ultraviolet radiation index (UV index), which is reported to the population through the mass media. The UV index is calculated by multiplying the EAS by a factor of 40. Accordingly, the UV index with the maximum permissible recommended exposure to UV radiation with an EAS equal to 0.25 W/m2 will be equal to 10 (0.25 W/m2 × 40 = 10).

The World Health Organisation (WHO) recommends the following gradation of UV indices:

yy1–2 is low; yy3–5 is medium; yy6–7 is high; yy8–10 is very high;

yy11 or more is extreme.

In the summer on the territory of the Republic of Belarus, the UV index ranges from 5 to 8. It is known that each person has individual skin sensitivity to the action of UV radiation. There are four main types of skin sensitivity. To determine the type of skin sensitivity, use a special test provided below.

For a person, the value characterising the UV radiation effect is the minimal erythema dose (MED). This is a dose of UV radiation that causes hyperemia or erythema on the unburnt skin after 8–10 hours. One unit of MED was calculated to correspond to the energy of 250 J/m2 and it causes this effect in people with type II skin sensitivity. Other types of skin sensitivity have their own values of flux density (Table 2.2). Accordingly, the radiation exposure permissible limit (PL) is calculated, corresponding to the UV radiation dose for skin sensitivity type II.

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