Medicine

METHODICAL INSTRUCTION FOR STUDENTS OF THE 3 COURSE

MEDICAL FACULTY

LESSON № 15 (PRACTICAL – 6 HOURS)

Themes: 1. Tropical hygiene. A hygienical estimation of influencing of tropical climate on the conditions of life, capacity and health of population.– 3 hours.

2. Hygienical, toxicological and epidemiological problems of feed of population of tropical regions.

Organization and conducting of sanitary examination of food products and prepared meal in the countries of torrid zone. Methods of medical control after the feed of population of countries of tropical region.– 3 hours.

Aim:

1. Master hygienic peculiarities of working and living conditions of population in tropic and hot climate.

2. Master the method of assessment of heat exchange and organism thermoregulation of the body in tropic and hot climate.

3. Know types of population pathology in tropic and hot climate conditions.

4. Learn the social and hygienic, toxicological and epidemiological nutrition peculiarities of tropical regions population.

PROFESSIONAL ORIENTATION OF STUDENTS:

The most of the land belongs to tropics: almost all Africa, South Asia, south of East Asia, the most part of Latin America, Oceania. The most part of population lives in tropics and subtropics. Transitional zone adjoins to tropic zone (Mediterranean area, front and middle Asia, the south of the USA etc.) and it is characterized as tropic and mild zones from to medico –geographical point of view. WHO and UN specialists have developed medical measures to control living and working conditions in tropic climate and preventive measures which are implemented in countries of this climate. Calculation methods of heat load determination and overheating prevention and its pathology are of great importance among medical measures.

Rational nutrition and its provision in arid and humid areas with tropical climate is considered according to abovementioned natural peculiarities, social development of the countries, natural resources presence, which allow to solve economical and nutrition problems. For example countries of Middle East are rich with oil and despite the Arabian peninsula desert climate they trade and can receive food products from other countries. Due to these circumstances, the qualitative and quantitative sufficiency of population nutrition is satisfied.

METHODOLOGY OF PRACTICAL CLASS (9⁰⁰-12⁰⁰ hour).

Theme 1. A hygienical estimation of influencing of tropical climate on the conditions of life, capacity and health of population

Work 1. Methods of the assessment of human heat balance by calculation of heat emission

The assessment of human feeling of the heat/cold is performed comparing the heat production during work and heat emission. Heat emission is calculated as a sum of the irradiation, conduction and water evaporation.

The basic data are:

A) the human heat production in a calm state accounts to 0.8 – 1.5 kcal (3.34 – 6.27 kj) per 1 kg body weight per 1 hour, during hard work – 7-9 kcal/kg×h;

B) the body surface of “average” human (170 cm of height and 65 kg of body weight) is approximately 1.8 m² (see table );

C) 100 % of the body surface takes part in heat emission by conduction and sweat evaporation;

D) 80 % of the body surface takes part in heat emission by irradiation (see table ).

40 % of the body surface takes part in heat emission by irradiation relating to the one-sided heat radiation source.

Table

Dependence of the human body surface on body weight

Body weight, kg

Body surface, m²

100 %

80 %

1.323

1.058

1.482

1.186

1.535

1.228

1.635

1.308

1.729

1.383

1.830

1.464

1.922

1.538

2.008

1.606

2.098

1.678

2.188

1.750

2.263

1.810

2.338

1.870

100

2.413

1.930

1. Heat emission by irradiation (radiation) can be calculated using the following formula:

Q_irr_. = 4.5×(т₁ – т₂) s

(1)

Where: q – heat emitted by irradiation, kcal/h;

т₁ – body temperature, с;

т₂ – internal wall surface temperature, с;

s – body surface area, m².

2. Heat emission by conduction can be calculated using the following formula:

Q_con = 6(т₁ – т₂)  (0.5 + √‾v) s

(2.1)

Q_con = 7.2 (т₁ – т₂)  (0.27 + √‾v)s

(2.2)

Where : q – heat emitted by conduction, kcal/h;

6; 0.5 – constant coefficients if air movement is less than 0.6 m/s;

т₁ – body temperature, с;

т₂ – air temperature, с;

7.2; 0.27 – constant coefficients if air movement is higher than 0.6 m/s;

v – air movement, m/s;

s – body surface area, m².

3. The maximum amount of water evaporated from the body surface can be calculated using the following formula:

Р_evap = 15(f_max – f_abs)  (0.5 +√‾v)s

(3.1)

Where: р_evap – water. Evaporated from body surface under this conditions, ml/h;

15 – constant coefficient;

F_max – maximum humidity under skin temperature of the body;

F_abs – absolute humidity under currant air temperature.

“f_abs” – can be calculated using the following formula:

(3.2)

Where: f _max– maximum humidity under air temperature, hg mm. ;

f_rel_.– relative humidity under current air temperature, %;

(f_max – f_abs) – physiological humidity deficit, hg mm.;

v – air movement, m/s;

s – body surface area, m².

Quantity of emitted heat may be calculated by multiplication of the result by 0.6 (calorie evaporating coefficient of 1 g of water). Or by putting the coefficient “9” in formula (3.1) instead of “15” (0.6×15 = 9). It is necessary to remember that an adequate heat self-feeling remains stable if sweat evaporation is not more than 250 ml (it takes 150 kcal).

Work 2. Hygienic standards and calculation methods of heat load of organism in hot and tropic climate conditions

1. Maximum allowable equivalent-effective temperature (EET) indices.

Table 1

Labour mode

Labour intensity

light

medium

hard

Without breaks during the shift

30.4

28.9

26.1

With breaks:

-every 3 hours

32.7

29.9

27.6

-every 2 hours

33.3

31.0

29.9

-every 1 hour

35.0

32.7

30.4

-every 30 min

38.2

35.5

34.4

- every 20 min

40.5

37.7

35.0

For people acclimatized to high temperature

32.2

29.4

28.9

For non-acclimatized to high temperature people

30.2

27.4

26.9

EET and resultant temperatures are calculated by means of tables and nomograms

Work 3. Wet bulb globe temperature determination method and its hygienic assessment according to Yanglow and Minard (1955).

Wet bulb globe temperature (WBGT) is an integral index of environment temperature which takes into account temperature, air humidity, radiant temperature and it is calculated by the following formula (1):

WBGT = 0.1 t_dry + 0.7 t_wet + 0.2 t_bulb, (1)

where, WBGT – is wet bulb globe temperature;

t_dry – temperature according to dry thermometer of psychrometer indices;

t_wet – temperature according to wet thermometer of psychrometer indices;

t_bulb radiant temperature according to the black globe thermometer.

According to Yanglow and Minard (1955) if WBGT exceeds 29.4⁰C physical load for non-acclimatized people is limited. Under 31.1⁰C WBGT physical load is excluded. Under 32.2⁰C WBGT physical load is excluded for acclimatized people too.

Work 4. Heat–Load Index (HL) according to Belding and Hatch calculation.

According to this method heat-load is calculated by the formula (2);

HL = М  С  R – Е_max_. kcal/hour, (2)

where: M - intensity of metabolism during work: light work –170 kcal per hour; medium - 300 kcal per hour; hard – 420 kcal per hour;

R – heat exchange through radiation, kcal per hour;

C- heat exchange through convection, kcal per hour;

E_max- maximum acceptable heat loss through sweat evaporation, kcal per hour.

Loss (-) or income (+) of heat by radiation R is calculated by formula (3):

R = 11×(t_bulb - 35) kcal/hour, (3)

where: t_globe – mild radiation temperature according to the globe black thermometer;

Losses (-) or income (+) of heat by convection is calculated by formula (4):

С = 6×v⁰^.⁶×(t_dry- 35) kcal/hour, (4)

where: v - air movement, m/sec. (v is in the table 2);

t_dry – air temperature according to dry temperature of psychrometer;

35 – surface body temperature.

Table 2

v m/sec

0.05

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

v⁰^.⁶

0.17

0.25

0.38

0.49

0.58

0.66

0.74

0.81

0.87

0.94

0.99

Maximum heat loss through sweat evaporation (E_max) is calculated by formula (5):

Е_max.= 12×v⁰^.⁶ ×(42 - р) kcal/hour, (5)

where: p - maximum water pressure, Hg mm under dry thermometer of psychrometer.

In case of wearing light clothes calculation result of heat load by formula (2) is divided by 3.

Authors recommend allowable values of heat–load index in the range of no more than 400-600 kcal per hour. It should be mentioned that with air movement increase sweat evaporation intensity increases proportionally. Thus this method is used in conditions of weak air movement.

Theme 2. Hygienical, toxicological and epidemiological problems of feed of population of tropical regions.

Students receive situational tasks (prepared by the chair) and complete them on their own.

INDIVIDUAL STUDENTS PROGRAM

Theme 1. A hygienical estimation of influencing of tropical climate on the conditions of life, capacity and health of population

Control questions

1. Hygienic characteristic of climate and weather in tropic and hot climate.

2. Hygienic peculiarities of solar radiation in tropic climate.

3. Hygienic peculiarities of daily and seasonal microclimate fluctuation (air temperature, radiant temperature, humidity, air movement speed) in hot deserts and humid tropic conditions.

4. meteorological factors’ complex influence on heat exchange and other physiological processes in the organism in tropic and desert climate conditions.

5. Hygienic characteristics of savannah, steppe, arid areas and humid tropic forest climate.

6. Health disorders and diseases typical for tropic and hot climate and their prophylactics.

7. human adaptation and acclimatization in hot and tropic climate.

8. Personal hygiene peculiarities in hot and tropic climate: hygiene of skin, clothes, hygienic principles of day regimen and their substantiation.

9. Peculiarities of inhabited area planning and build-up in arid and humid tropic climate.

10. Peculiarities of sanitary infrastructure of settlements in tropic climate. Water supply, sewerage system, solid waste disposal. The role of green vegetations in microclimate conditions improvement in inhabited areas.

11. residential hygiene in hot climate. Planning peculiarities of different types of buildings according to their insolation and influence on residential microclimate conditions. Optimal windows orientation, its scientific substantiation. Sun protection devices.

12. Hygienic requirements to natural and artificial residential and industrial premises ventilation in tropic climate.

13. Air conditioning in residential, public and industrial premises as microclimate optimization measure.

14. Peculiarities of requirements to natural lighting of residential premises in tropic conditions. Natural lighting and microclimate optimization measures interrelations. Venetian blind influence on these factors.

15. Hygienic peculiarities of building materials and constructions which are used for building in tropic climate.

16. Organization and working regimen peculiarities in arid and humid climate. Microclimate parameters in which physical work is impossible.

17. Calculation methods of the assessment of tropical climate influence on heat condition of organism.

Theme 2. Hygienical, toxicological and epidemiological problems of feed of population of tropical regions. Organization and conducting of sanitary examination of food products and prepared meal in the countries of torrid zone. Methods of medical control after the feed of population of countries of tropical region

Control questions

1. Rational nutrition and conditions of its provision.

2. Social and hygienic peculiarities of nutrition of different age and sex population groups in tropical regions.

3. Physiological and hygienic basics of rational nutrition in tropical conditions.

4. Organism energy, protein, fat, carbohydrate requirements and their quantity and balance peculiarities in tropical climate.

5. Vitamins, mineral salts, microelements, taste substances (spices) role in nutrition of tropical regions population.

6. Hot climate influence on food and some its components assimilation. Metabolism and nutrition pattern peculiarities in tropical regions.

7. Hygienic characteristics of food products, used by population of arid and humid tropical regions.

8. General characteristic of alimentary diseases of tropical regions population.

9. Malnutrition and complete starvation diseases (protein and energy insufficiency) among tropical regions population.

10. Vitamin deficiency diseases (hypo- and avitaminosis) among tropical regions population. Polyunsaturated fatty acids deficiency diseases.

11. Mineral and microelements deficiency diseases among population of tropical regions.

12. Overeating diseases in tropical regions.

13. Diseases caused by poor quality of food intake (foodborne diseases, helminthosis, food poisoning, ferrnentopathies).

14. Methods of medical control over tropical regions population nutrition.

15. Calculation methods of the population nutrition assessment. Alimentary calorimetry method.

16. Sanitary inspection of food products and ready meals, its usage in tropical region counties.

17. Food products storage and preservation peculiarities in tropical conditions, usage of preservatives and antibiotics.

18. Methods and measures of prevention of the foodborne diseases, infections and invasions with alimentary transmission mechanisms, food poisoning.

SEMINAR DISCUSSION OF THEORETICAL ISSUES (12³⁰ – 14⁰⁰ hour).