Methods of Complex Estimation of Microclimate. Types of Disturbance of Thermoregulation in Conditions of Hot Climate

Key Questions

1. Bases of physiology of a human heat exchange and its connection with a microclimatic condition of the environment.

2. Hygienic significance and technique of estimation of organism physiological reactions, which manifest the condition of the thermoregulation system.

3. Methods of complex estimation of microclimate:

· katathermometry

· effective temperatures;

· equivalent-effective temperatures

4. Application of methods of complex estimation of microclimate.

5. The disorders in a health condition and diseases which occur due to effect of discomfort microclimate on the man. Measures of their prevention.

Learning Objectives and Their Concrete Definition

1. Estimation of cooling ability of air (CAA) by method of katathermometry.

For the purpose a katathermometer (see the description in the previous lesson)is placed into hot water (about 80°C) and heated up until the spirit rises up to half of top expansion of a capillary. After that the device is wiped and hung up on a support or held on the outstretched arm in place of investigation, being protected from effect of sun energy by means of a small screen (cardboard, plywood). Then, keeping an eye on the stop watch, it should be found out, how much time it takes the spirit to go down from 38 to 35°; the experiment is repeated twice and the average value is calculated.

CAA (cooling ability of air) is estimated by the formula:

 

Н = F/t (mCal per second/cm2),

 

where F — a katathermometer factor (it is indicated on the back side of each device),

t — time of cooling a katathermometer.

The normal CAA = 5.5-7.0 mCal per second/cm2; if this parameter is lower than the norm, there will be overheating, if it is higher — overcooling.

2. A technique of estimation of effective temperatures by nomogram.

A total effect of temperature, humidity and air movement are expressed now in degrees of effective temperature. The indications of dry and wet thermometers of a psychrometer, as well as data about speed of air movement are necessary for estimation of effective temperature by nomogram. Having obtained them, the procedure is as follows: points on the right and left scales of nomogram corresponding to indications of dry and wet thermometers are connected by a line. The place of intersection of this line and the curve of appropriate speed of air movement gives the value of effective temperature.

Example: The temperature of the dry thermometer of psychrometer is 24°С, the temperature of the wet thermometer of psychrometer is 16°С. Air speed is 30 m/min. Determine the effective temperature under these cinditions.

Solution: On the left-hand side of nomogram we find the temperature of the dry thermometer; on the right-hand side of nomogram — the temperature of the wet thermometer. We superimpose bar on both retrieved points. We see that the bar intersects a curve of air movement speed corresponding to 30 m/min in a point marked by figure 20. This figure will thus be considered the effective temperature. On the basis of numerous observations the following norms of effective temperatures are distinguished:

a) The zone of comfort is 17.2–21.7° effective temperatures. At these temperatures 50 % of people feel well and comfortable.

b) The line of comfort is 18.1-18.9° effective temperatures. At these temperatures 100 % of people feel well and comfortable.

 

3. Definition of equivalent-effective temperatures. There is a special table, according to which we can find out the optimal microclimate for a person at different values of temperature, humidity and speed of air movement so, that heat sensation of organism is as if in a zone of comfort.

Algorithm of Practical Work of Students

The first stage. Testing the initial level of knowledge and skills.

The second stage. Active participation in discussion of key questions on the theme of the lesson.

The third stage. Independent work on estimation of CAA, speed of air movement in a premise, determination of effective temperatures.

The fourth stage. Solving situational tasks and final testing on the given theme.

Self-control Test

1. Where are the centers of thermoregulation in a human organism?

A. brain cortex

B. hypothalamus

*C. medulla oblongata

D. cerebellum

E. reticular formation

2. What are the devices for estimation of cooling ability of air?

A. psychrometer

B. thermograph

C. hygrometer

D. anemometer

*E. katathermometer

3. Specify the zone of comfort according to effective temperatures (in ° ET):

*A. 17.2-21.7

B.18.0-22.0

С. 20.1-23.5

D.18.0-20.0

E.16.0-18.0

4. What factors influence the intensity of cooling the heated body?

*A. air temperature, air humidity, speed of air movement

B. air temperature, air humidity

C. air temperature, speed of air movement

D. air temperature

E. air humidity; radiation temperature

5. At harvesting grain in July the air temperature outside was 31°С; in the cabin of combine harvester — 35°С, speed of air movement — 0.2 m/sec, relative air humidity — 55 %, temperature of sides and roof of the cabin — 45 oС. Normalization of microclimate in the cabin is possible by means of

A. thermal isolation of sides and roof

B. decrease of air humidity

C. increase of air humidity

*D. cooling of the air

E. increase of speed of air movement

6. In patient with pneumonia the body temperature has increased up to 39°С, the skin integuments have turned pale and become dry, gooseflesh occurred. What disturbances of thermoregulation caused these manifestations of fever?

A. dilatation of vessels, increase of perspiration, prevalence of heat production

*B. vasoconstriction, decrease of perspiration, prevalence of heat production

C. decrease of heat production, relaxation of tonic muscles and vessels

D. disintegration of brown fat

E. balance of heat production and heat emission

Problem Solving

1. The dry thermometer shows 20°C, and the wet one — 16°C. The speed of air movement is absent. Determine the effective temperature under the given conditions (according to nomogram).

2. Determine CAA and speed of air movement in the corridor of a hostel, if F-factor of katathermometer is 630, time of its cooling — 90 sec. Temperature in the premise is 21.0°С.

3. What can the thermal health state of the man in a habitable room be, if the air temperature ranges within the limits of 18-20°C, difference in horizontal and vertical directions is 2.0-2.5°С respectively?

Standard Answers

1. According to nomogram we find the point of intersection of the line showing the temperature of dry and wet thermometers with the line of speed of air movement = 0. The answer: ET = 18.5°.

2. The ratio of F:t = CAA = 630/90 = 7.0 mCal/cm 2 /sec, that corresponds to the norm. According to Hill’s formula we determine the speed of air movements, which is equal to Н = 7.0; Q = 36.6 — 21 = 15.6°. Hence Х = 0.36 m/sec, that is a norm.

3. It is satisfactory, as all parameters are within the limits of the norm.

Sources of Information

S. Shibanov. Lectures on Common hygiene and Ecology. Simferopol. 2003. 130p.

Park’s Textbook of Preventive and Social Medicine. India, 2000.— 16th edition.— 660p.

 

 

Theme No 4.

Weather and Health. Prevention of Heliometeotropic Reactions. Climate and Problems of Acclimatization

In spite of the fact that the influence of weather on the man is known for a long time, this problem is still insufficiently investigated and even now it is little used by doctors in their practice. It is conditioned by the following:

· The concept of “weather” is very complex; it has many components, which are not well investigated in meteorology.

· Up to now the mechanisms of development of meteotropic reactions in the organism are not well investigated.

The Concept of Weather and Climate

Weatheris adynamic set of physical properties of surface air (troposphere) for a short time interval (hours, day, weeks).

Climate is a long-term mode of weather naturally repeated in the given area; its parameters are: an average monthly temperature of air, an average number of rainy days, etc.

Thus, weather is a changeable phenomenon, while climate is a statistically constant concept.

The basic weather-forming factors are:

· Heliophysical — intensity of a solar radiation and a solar activity

· Geophysical — intensity of a geomagnetic field, geomagnetic storms

· Electric condition of atmosphere — intensity and gradient of electric field, air ionization, etc.

· Meteorological — temperature, humidity, speed and direction of air movement, atmospheric pressure

· Synoptic — cloudiness, atmospheric precipitation

· Chemical structure of atmosphere — content of oxygen, СО2, pollutants in atmospheric air.

All these factors are interrelated and affect a person in a complex way; there is a difficulty of their all-round evaluation.

Meteorological factors are sharp fluctuations of temperature and atmospheric pressure: the greater the differences — the more biotropic the weather is. These factors are most investigated as reasons of development of meteotropic reactions (MR).

A certain role is played by changes of chemical composition of atmosphere — under some weather conditions there may be the decrease of absolute content of oxygen in the air by 60 g/m3 and over. The annual tendency of oxygen content is increasing in winter and decreasing in summer; the maximal fluctuations are in autumn and spring (the factor of an interdaily variability is more than 50 %).

An electric condition of atmosphereincludes:

· The content of positive or negative aeroions in the air

· The gradient of the electric field of the Earth

Synoptic factors are caused by atmospheric circulation of warm and cold air masses. There are 3 types of air masses — warm, cold, neutral (local). At their movement the atmospheric fronts are formed — warm, cold, occlusions (mixture of warm and cold masses).

The frequency of changing air masses is on average once per 5-6 days, but it may be more or less often — it depends on type of atmospheric circulation:

· Cyclone is an atmospheric whirlwind with low pressure in the center and movement of air masses counter-clockwise. It occurs more often in winter, on average about 40 cyclones per year occur above Europe. It is characterized by unstable weather — cloudiness, atmospheric precipitation, hurricanes, typhoons; there is great difference of atmospheric pressure, temperature, content of О2. The weather is biotropic.

· Anticycloneis an atmospheric phenomenon with a high pressure in the center and movement of air clockwise. The weather is clear — very hot in summer or frosty in winter. There are no sharp differences of weather factors, the weather is more favourable.

 

Heliophysical factors.Up to now these factors are insufficiently taken into account at estimation of weather, though the ingenious founder of heliobiology A. L. Chizhevsky in 1920s determined the influence of solar activity on living organisms, including people. There are data on coincidence of periods of increased solar activity with revolutions, wars, epidemics, even with frequency of car accidents. The difficulty of studying this question consists in cyclic changes of solar activity having different periodicity — 11 years, 22 years, 60 years and over, which can overlap each other and are poorly studied. The most investigated are 11-12-year cycles; the beginning of the last 24th cycle known to mankind is 1997, thus the maximal activity is in the middle of the cycle (2001-2002 years).

Parameters of solar activity include the following:

· Wolf index (W) — amount of spots on the Sun,

· index S — the total area of spots,

· intensity of radioactive radiation of the Sun on the wave of 10.7 cm,

· the solar wind is the corpuscular streams (protons, electrons, etc.) from the Sun which carry away with themselves the magnetic fields and form the spiral-sector structure of interplanetary magnetic field (IMF) of + and -- signs.

Every 6-7 days, while moving in orbit, the Earth gets in IMF of other sign that results in changes of geophysical parametersof electromagnetic field of Earth (EMF), its deviation from a usual level named "magnetic storms", which may be planetary and local or by intensity — weak, moderate and strong.