THERMOMETRY

From Big Medical Encyclopedia

THERMOMETRY (Greek therme warmth, heat + metreo to measure, measure) — set of methods and ways of measurement of temperature, including in medicine measurement of body temperature of the person.

Measurement of temperature is a comparison of degree of a nagretost of the studied object with a standard scale of temperatures. In relation to average values the greatest distribution was gained by the scale of temperatures of Celsius determined by two defined points — temperature of boiling and temperature of freezing of water (thawing of ice) with a standard atmospheric pressure, the Crimea respectively hundred answer and zero units called by degrees Celsius (°C). By the size the degree Celsius is equal to one degree Kelvin (°k) which is the main unit of temperature (see. Units ). The Celsius scale is accepted in overwhelming number of the countries, however in the USA and Great Britain continue to use the Fahrenheit scale with unit degree Fahrenheit (°f); Fahrenheit temperature (tF) and Celsius temperature (tC) are connected by dependence of tF = 32 + 1,8 tC.

All methods of measurement of temperature divide on contact, based on transfer of heat to the device taking temperature by direct contact, and contactless when transfer of heat to the device is carried out by radiation through intermediate agent, usually through air. Contact methods allow to take temperature at preservation of interposition of the thermoreceiver and an object in traffic conditions of the last, to take measurements in any points in an object where it is possible to carry out the thermoreceiver. Contactless methods give the chance to take temperature of objects, contact with to-rymi is inadmissible, objects of the small sizes, the thermal contact with to-rymi is complicated or impracticable, to investigate distribution of temperature to body surfaces.

The errors caused by change of temperature of an object owing to distortion of its temperature profile made by the thermoreceiver, and also an inevitable difference of temperatures of the thermoreceiver and an object as a result of heat exchange of the thermoreceiver with the environment are inherent to contact methods. In the set thermal conditions when temperatures of an object and the thermoreceiver are stabilized, these errors are static. At the unsteady thermal conditions in addition there is a dynamic error of measurement connected with thermal inertia of the thermoreceiver. Decrease in errors is provided with use of more rational measuring techniques of temperature, designs of thermoreceivers etc.

The errors connected with the fact that the physical laws which are the cornerstone of these methods are fair only for absolutely black radiator from to-rogo on properties of radiation are inherent to contactless methods of measurement of temperature all real physical radiators differ (bodies and Wednesdays). According to Kirchhoff's law any physical body radiates energy less, than the black body heated to the same temperature. Therefore contactless devices for measurement of temperature, otgraduirovanny on a black radiator, will show smaller temperature, than valid.

Devices for measurement of temperature (thermometers) include a link of transfer of heat from the studied object to primary converter, primary converter or a thermosensitive link, a link of transformation of parameter of a condition of primary converter to directly displayed physical quantity, a link of display. Respectively thermometers differ on the nature of transfer of heat from an object to a thermosensitive link (contact and contactless); by the form transformations of heat energy in a thermosensitive link. At the same time various temperature and dependent properties of substances are used: thermal expansion of solids (dilatometric, bimetallic thermometers), liquids (mercury, spirit, etc.) and gases (manometrical thermometers), electrical resistivity (resistive electrothermometers), dielectric permeability (electrocapacity thermometers), thermoelectric effect (thermoelectric thermometers). In thermometers also different ways of display of results are used (position of a meniscus of liquid or an arrow of rather motionless scale, digital indication, graphic registration, visualization of the thermal field of an object on the screen of an electron-beam tube etc.).

In medicine and biology of T. it is widely used for measurement body temperatures (see), temperatures of environments and objects, with to-rymi the person, and also in clinicodiagnostic, microbiological, physiological and biochemical researches, a cryobiology contacts, cryotherapies (see), cryosurgeries (see), physical therapy (see), balneoterapiya (see), a space and air medicine (see. Air medicine, Medicine space), etc. The main place at measurements of temperature in medical practice is taken by contact T., the cut is the main advantage reliability of transfer of heat from an object to a thermosensitive link of the thermometer. However the basic possibility of heating of the thermoreceiver up to the temperature of the studied object often is limited to various methodical and efficiency factors. At measurement of body temperature, napr, in the place of contact of the thermoprobe with a body, local changes of a blood-groove, sweating take place, to-rye change temperature in the place of measurement; temperature of the thermoprobe is established not at once, and after transient phenomenon.

For measurement of body temperature use hl. obr. the medical mercury thermometer relating to liquid thermometers the principle of action to-rykh is based on thermal expansion of liquids. The mercury thermometer represents a transparent glass tank with sealed by a scale and the capillary having the expansion filled with mercury on the end. A temperature coefficient of expansion of mercury approximately in 500 times more a temperature coefficient of expansion of glass that provides noticeable movement of a mercury column in a capillary at a relative invariance of the sizes of the last. Range of measurement of temperature makes 34 — 42 °, scale interval 0,1 °. The mercury thermometer operates by the principle of the maximum thermometer: the mercury column remains in a capillary at the level of the highest rise during the heating and falls only during the stirring. It is reached by input in a capillary of the pin obstructing back motion of mercury; other end of a pin is sealed in a bottom of a tank. The mercury thermometer is used for measurement of temperature in an axillary hollow, an inguinal fold, a rectum, an oral cavity.

Local measurements of temperature (local T.) are carried out by means of electrothermometry (measurement of body temperature by electrothermometers). The dot thermoprobes having the area of contact with the studied object 1 — 2 mm2 are used. Their thermosensitive link is the thermoresistor — the semiconductor resistor, electric resistance to-rogo depends on temperature. Because of the small sizes and weight (microthermoresistor) it has small thermal inertia. Serially released medical TPEM-1 electrothermometer contains three such thermoprobes — for measurement of temperature of skin, soft tissues and perigastriums. The device has two scales with a general range of 16 — 42 °C scale interval 0,2 °. Electrothermometers are widely used for segmented T., and also for long overseeing by body temperature during surgeries, at seriously ill patients, in the conditions of resuscitation. At long observations thermoprobes usually enter into a rectum, sometimes into a gullet.

Temperature went to cavities. - kish. a path in some cases measure telemetric by means of the swallowed inspected radiopill representing the tiny radio transmitter connected to the sensor of temperature. As a thermosensitive link of the sensor serves the segnetokeramichesky element, dielectric permeability to-rogo changes depending on temperature, causing corresponding changes of frequency of the transferred fluctuations. These fluctuations are perceived by the receiving device which is out of the body inspected.

Apply the contactless termografiya (radiation thermometry, or thermovision) based on perception by special sensors of infrared radiation from a body surface to receiving a thermotopographical picture of certain areas of a body, or a contact liquid crystal termografiya, a cut property of liquid crystals to change color at change of temperature of the contacting environment (see is the cornerstone. Termografiya ). Two routes of administration of liquid crystal T were outlined. in medicine: drawing on a body surface of thermocompositions — special thermosensitive pastes and application of a termokhromny film.

The thermometry of a body — measurement of body temperature (see) — is an important and obligatory component of inspection of the patient (see), has great diagnostic value, allows to distinguish feverish and hypothermal states (see Fever, Cooling of an organism). Measurement is performed more often by means of the medical (mercury) thermometer. Are used as well electrothermometers. Temperature is taken in an axillary hollow, is more rare in an inguinal fold, an oral cavity, a rectum (at children) or in a vagina. At measurement of temperature in an axillary hollow or in an inguinal fold skin should be wiped previously dry. Before introduction to a rectum the thermometer is greased with vaseline. Duration of measurement of temperature in an axillary hollow makes about 10 min. That the thermometer densely adjoined to skin, the shoulder is pressed to a breast. At the seriously ill patients who are in unconsciousness and also at children the thermometer is held in an axillary hollow a certain position of a hand of the patient. Temperature is taken, as a rule, by 2 times a day (in 7 — 8 hours of morning and in 17 — 19 hours of evening), if necessary measurement is taken more often, by each 2 or 4 hours. After measurement of temperature the thermometer should be wiped disinfecting r-rum or to place it in a vessel with such solution.

Standard temperature at measurement in an axillary hollow should be considered 36,4 — 36,8 °. The most high temperature is during the day observed between 17 and 21 hour, and the lowest — between 3 and 6 hours of morning; the difference of temperatures at the same time at healthy faces, as a rule, does not exceed 0,6 °. After food, big physical and emotional tension, in the hot room body temperature increases a little. Temperature also depends on age; at children it is higher on average on 0,3 — 0,4 °, than at adults, in old age can be slightly lower. Asymmetry of axillary temperature meets very often (54%), at the same time at the left it is slightly higher.

Important a wedge, measurement of the skin temperature which is an indirect indicator of intensity of exchange processes in skin and the subject fabrics and also extents of their blood supply matters. At the same time its absolute values usually are not considered since temperature of skin to a large extent depends from (temperature and humidity of the environment, intensity of a blood-groove, local reaction of fabric, intensity of sweating etc. The difference of temperature of the skin taken on its strictly symmetric sites is considered, as a rule; the difference of temperature on symmetric sites exceeding 0,5 ° is considered a symptom of pathology. Measurement of temperature of skin of separate segments of extremities (segmented T.) it is used at diagnosis of disturbances of peripheric circulation. In usual conditions fall of temperature of skin of extremities goes in the direction from proximal departments to distal. Temperature difference of skin, measured over an ileal or axillary artery and the I finger of foot or the IV finger of a brush, carries the name of a skin temperature coefficient. Normal its size makes 3,8 — 4 ° for upper extremities and 4,9 — 5,2 ° for lower. In case of pathology it increases. The inflow of blood to the periphery is worse, the skin temperature coefficient is higher.

Segmented T., as well as local, it is carried out by means of electrothermometers. Measurement is taken after 10 — 15 min. adaptation of the room inspected to temperature, in Krom examination is conducted. T. bodies can be carried out also by remote methods T. So, by means of a termografiya it is possible to study the nature of distribution of temperature within all body or its certain areas. Especially valuable information is given by a termografiya of pair bodies and extremities. Termografiya is successfully applied at diagnosis of disturbances of blood circulation (see), pathologies of blood vessels (see), at detection of malignant tumors of a mammary gland, etc.

T. skin it is used also during the studying of mechanisms of sweating normal and pathologies (see. Sweating ), mechanisms of thermal control (see) in general.

Great diagnostic value at gastroenterological researches has T. went. - kish. a path by means of a radiopill, to-ruyu swallows inspected. The receiving device perceiving information transferred by a radiopill is located out of a body (see Telemetry).



Bibliography: Butchers And. JI. Propaedeutics of internal diseases, page 67, M., 1957; Propaedeutics of internal diseases, under the editorship of V. of X. Vasilenko and A. L. Grebene-va, page 59, M., 1982; Temperature and its measurement, under the editorship of A. Armand and K. Vulfso-n, lane with English, M., 1960; Sh to l I r B. S. Diagnosis of internal diseases, Kiev, 1972.


E. K. Lukyanov, V. S. Salmanovich; S. M. Kamenker (thermometry of a body).

Яндекс.Метрика