CALORIMETRY

From Big Medical Encyclopedia

CALORIMETRY (Latin calor is warm + grech, metreo to measure, measure) — measurement of amount of heat generated (absorbed) during various physical, chemical or biological processes. To. biol, and biochemical, processes (bio-calorimetry) allows to characterize quantitatively power and heat effects separate biochemical, reactions, activity of cellular organellas and cells, fabrics and bodies, an organism in general (see. Metabolism and energy , Thermochemistry ).

According to laws thermodynamics (see) a potential energy of the chemical connections participating in a metabolism it is expressed by their heat content, or an enthalpy. In the course of multistage disintegration of these connections energy of chemical bonds or dissipates in the form of heat (primary warmth), or passes into different types of work (reduction of muscles, active transport of ions, a luminescence, osmosis, the electric phenomena and so forth) and also turns into heat (secondary warmth); a part of energy is used on processes of resynthesis biochemical, connections. Heat effect of chemical reactions depends only on a condition of mother substance and end products (the law of constant heat summation, 1840). In an organism heat cannot pass into other types of energy in this connection heat generated by a live object is an end product of power transformations, and quantity it — their exact measure.

At calorimetric researches sizes of thermal flows from a live object to the environment are measured and the amount of the developed heat and heat content of an organism is calculated; change of heat content is found on the basis of data on weight, heat capacity and change of temperature of an object.

Units of heat are the kilocalorie (kcal) or joule (J) according to the International System of Units (SI); 1 kcal = 4,187•10 3 J. Specific heat is measured in kcal/kg or J/kg; a thermal flow — in kcal/hour or W; a specific thermal flow — in kcal/m 3 • hour or W/m 2 (see also Units ).

The beginning of a biocalorimetry of animals and the person carry to C. Lavoisier's researches, Laplace (P. S. Laplace, 1780) which took measurements of thermal and gas exchange at Guinea pigs in an ice calorimeter, throughout the next century works of Senator (N. of Senator, 1872), Rosenthal (Y. Rosenthal, 1878), Sh. Richet (1385), M. Rubner (1890, 1894) and other researchers a technique and technique of calorimetric researches were considerably improved. In V. V. Pashutin's laboratory (1883, 1893) calorimeters were developed for a research of thermal exchange at animals and the person in whom about amount of the produced heat judged by temperature increase of water in an external (water) cover of a calorimeter. In these installations were created fiziol, conditions for stay of examinees throughout long experience and the accuracy of measurements is considerably increased. Further development of techniques of a biocalorimetry went in the direction of sensitization of devices, increase in accuracy of measurement of flows of heat and development of the installations and systems allowing to investigate thermal exchange of animals and the person under natural conditions of his life and work.

The thermal flow (F) between internal and external covers of a calorimeter at a constant temperature schedule is proportional to heat conductivity of the environment (λ) dividing covers, y temperature differences (Θ) between them: Ф = λΘ.

Several main types of the calorimeters: isothermal (C:I), compensation (KK), adiabatic (KA), gradient (KG), dynamic (CD) and microcalorimeters (MK) allocate.

In isothermal calorimeters λ it is very big, and warmth does not remain in the device, and quickly passes into the environment.

At the same time temperature difference between external and internal covers is very small and measurement presents it considerable difficulties. Nevertheless such design provides rather normal (thermal) conditions for a live object in the calorimetric camera since temperature in it does not increase and by that it is not brought hindrances in the course of a research. It is necessary to carry an ice calorimeter of Bunsen to devices of this kind. U. Etuoter (1904) considerably improved this device. Its installation represented the heat-insulated, ventilated camera, in a cut of people could take place and work freely. The generated heat was determined by an amount of water, proceeding through system of tubes, and its temperature before passing through a calorimeter. Trautmen c Webb (S. Y. Troutman, P. Webb, 1972) offered a calorimeter in the form of the suit fitting a body and consisting of plastic tubules and the isolating clothes covering all body surface except for the person and feet. Heat given by a body was determined by a circulation time of water in tubes and its temperature. However isothermal calorimeters have essential defect — difficulty of the accounting of heatlosses to the environment. This defect is partially eliminated in compensation and adiabatic calorimeters.

The principle of work of compensation calorimeters is as follows. There are two absolutely identical, similarly located and heat-insulated calorimetric cameras in one of which the studied object, and in other (control) — a source of heat is located, usually physical. nature. The special device registers during experiences temperature difference between covers of both calorimeters and automatically maintains these temperatures at the identical level, respectively warming up a control calorimeter. Thus any are as if compensated, including and hardly considered, heatlosses to the environment. Knowing the amount of heat which is marked out in the control camera and necessary for an equilibration of temperatures and believing that the thermolysis of both calorimeters is identical, it is possible to define amount of heat generated by the studied object.

Since Tangl's researches (F. Tangi, 1913) and Hari (P. Hari, 1925) compensation calorimeters were widely adopted relatively, however bulkiness and high cost of these devices, impossibility of ensuring full identity of heat exchange for both calorimetric cameras and some other reasons limited their use.

Fig. 1. A symbolic circuit of a microcalorimeter (across Kalva): 1 — the working camera (a zone of storage of heat); 2 — the external camera which is well carrying out heat with the thermocouples (3) located in it which are connected to a galvanometer (And); 4 — a zone of calorification.

In microcalorimetric installations the listed shortcomings are absent. The combination of isothermal and compensation calorimeters allowing to investigate heat release of yeast, cultures of microbes, newborn animals and other objects was offered Kalva and Pratt (E. Calvet, H. Prat, 1963). Their device consists of two microcalorimetric cameras, one of which is a working calorimeter, and the second — control. Heat is brought out of the working camera and dissipates in the metal block, in Krom is evenly distributed apprx. 1800 thermocouples (fig. 1). The control calorimeter serves only for ensuring constancy of experimental «zero» at change of temperature of an external cover and compensation of heat release in a working calorimeter; accuracy of such calorimeters reaches 1%.

Full independence of heat exchange in a calorimeter from influences of the environment is reached in adiabatic calorimeters. According to the equation F = λΘ in these devices λ = 0, and consequently, and F = 0. Temperature of an external cover is equal internal that is reached by heating or cooling of the device by means of special system of thermoregulation.

The adiabatic method is offered by Paerson (S. S. to Person, 1849) and entered into practice of heat-exchanging researches by Richards (T. W. Richards) with sotr. (1905). L. N. Kurbatov et al. (1953) created two models of an adiabatic calorimeter for large (dogs, cats, rabbits) and small animals (mouse).

Installation consists of 4 main nodes: calorimetric camera, thermostatic cover, temperature-controlled and measuring schemes.

Calculations of direct heat production (Θ) are made on a formula:

Θ = CΔR + MCM (t2 — t1) + λV (e2 — e1), (1)

where ΔR — the change of electric resistance determined by a Wheatstone bridge; With — heat capacity of a calorimeter; M — the weight of an animal; St — heat capacity of a body of an animal; t1 and t2 — initial and final body temperatures; λ — vaporization heat; V \volume of the calorimetric camera; e1, e2 — initial and final air humidity.

A lack of adiabatic calorimeters is increase in their temperature in the course of experience and nek-paradise inertness of measurement of heat exchange.

Fig. 2. Scheme of a gradient calorimeter: and — the general scheme of installation — the scheme of a gradient layer.

Thermal inertness of devices and dependence of heat exchange in a calorimeter from changes of temperature in the environment were substantially overcome in gradient calorimeters (fig. 2). The inner surface of their calorimetric camera is covered with a thin uniform coat of the isolating material. The gradient of temperature of an inner and outer surface of a layer is proportional to the speed of carrying out heat from the studied object which is in the calorimetric camera. Transition from one level of a thermolysis to another leads to bystry increase or decrease in a gradient. The gradient of temperature and speed of its change depend on thickness of an insulation layer. The average size of a temperature gradient is independent of the size, a form and an arrangement of a source of heat and of ways of heat waste by an organism (evaporation, carrying out, radiation).

The size of a thermal flow is characterized by the equation:

Θ = A(λ/D) ΔT, (2)

where Θ — a thermal flow; And — the area of the insulating layer; λ — heat conductivity of the insulating layer; D — thickness of the insulating layer; ΔT — temperature difference of an inner and outer surface. Temperature is registered by means of mednokonstantanovy thermoelements. High sensitivity of gradient calorimeters is reached, on the one hand, by the choice of material and uniformity of a gradient layer, and with another — existence of a large number (to 10 thousand) evenly located thermocouples that, however, complicates calorimetric systems of this type.

In 1973 G. Spinnler with sotr. described a calorimeter for the person with the new type of a gradient layer allowing it is long with high precision to register a thermolysis both from the surface of skin, and due to breath. Sizes of the calorimetric camera 182 X 75,5 X 136 cm. The insulation layer is made of epoxy 2,4 mm thick with copper or nickel contours on the internal and outside parties of a gradient layer. Since the electric resistance of contours is function of temperature, the thermal flow was measured on the basis of a difference of resistance of the chains included in the scheme of a Wheatstone bridge.

The calorimeters of gradient type representing the suit which is closely fitting a body of the person and allowing it to move freely gained distribution. These calorimeters (space suits, pneumosuits) are created in a complex and on the basis of the special means isolating the person from action of various harmful environmental factors (a research in space, under water, at high and low ambient temperatures, changes of a gaseous fluid etc.).

The method of a direct calorimetry of the person in antitack agents of protection is developed. The sensor of measurement of heat release of the person is executed in the form of underwear, the knitted basis to-rogo joins thermosensitive elements. One of sensors densely adjoins to a body of the person, another contacts to the environment. These elements are divided by a layer of the isolating material (a gradient layer).

Go also Kasirk (G. L. Hody, J. J. Kacirk, 1972) suggested to use as a gradient calorimeter underwater germokostyum, supplied with sensors and closing a body surface, except for a face, hands and feet. However such isolating suits have a shortcoming since in them there are uncovered a head and distal departments of extremities that can influence thermal exchange considerably.

Dynamic calorimetric cameras make of the thin, well carrying out heat material giving the chance to take measurements of intensity, heat release at animals for short pieces for a long time.

Fig. 3. Dynamic calorimeter

In the dynamic calorimeter represented in the figure 3, ambient temperature can change randomly over a wide range due to change of temperature of a temperature-controlled cover of a calorimeter, edges plays a role of the environment for the camera. The device is provided with systems of ventilation, gasometry.

Calorimeters have high sensitivity, a small inertance and allow to take measurements of a thermal flow with an accuracy of 2%.

Sensitization of calorimeters created premises to creation of microcalorimeters by means of which calorification is defined during biochemical, reactions, by cultures of microorganisms, etc. Kalva can carry to microcalorimeters the calorimeter described above and Pratt.

In a thermoelectric differential calorimeter of N. I. Putilin et al. (1969) high sensitivity at rather low inertance allow to measure heat production of the isolated muscles in time. Benzinger (T. H. Benzinger, 1967) offered the gradient microcalorimeter capable to catch heat generated by microorganisms, to study heat energy at hydrolysis of ATP, at reaction of antigens with antibodies and so forth.

The actual heat production of a live object (Θ) is defined by the equation:

Θ = Θкал + Θ H 2 O ± ΘT, (3)

where Θкал — heat lost by an object by convection, carrying out, radiation; Θ H 2 O — heat lost by an object at loss of moisture (evaporation); ΘT — the amount of heat given or detained by a body of an animal for this interval of time depending on change of temperature of his body determined by a formula: ΘT = CMΔt, where With — the mean specific heat of a body, M — weight, Δt — temperature difference of a body for this interval of time.

At calorimetric calculations nek-ry complexity is represented by determination of size ΘТ. It is known that temperature of various body parts is not identical owing to existence of cross and longitudinal gradients of temperature of a cover of a body (skin, hypodermic cellulose, superficial muscles and extremities) and depending on different conditions can change by several degrees. Temperature of internals is more uniform and stable, its fluctuations do not exceed 0,5 — 1,5 °. However fabrics of a cover make apprx. 50% of body weight and therefore shifts of its temperature by several degrees can affect considerably size ΘT. At exact calorimetric calculations body temperature (T) is determined by formulas of «mixing» in which in a certain proportion temperature of internals (rectal temperature, Tp) and temperature of a cover of a body (skin temperature, Tk) is considered. Various formulas such are known:

T = 0,65Tp + 0,35TK; t = 0,8tr + 0,2TK;

T = 0, Tr + 0,3tk.

In turn Shopping malls express as «the weighted average temperature of the skin» representing the sum of these or those sites of a skin surface, private from division of temperature, into a share of these sites in the total area of an integument.

The characteristic of stable thermal exchange of the person requires creation of conditions of so-called thermal comfort, i.e. sets of conditions of air and radiant heat in which the person subjectively tests pleasant heat are kept by normal thermal exchange, keeps the standard temperature of the body and does not emit sweat.

With the help To. applicability of the law of conservation and transformation of energy and the second beginning of thermodynamics to live organisms is shown (see. Thermodynamics ), an opportunity and borders of use of gas exchange (indirect To.) for the characteristic of energy balance of animals and the person in the conditions of norm and pathology. Calorimetric researches are necessary for studying of a heat balance of an organism or its parts at endogenous and exogenous disturbances of thermal exchange.

A calorimetry in the conditions of norm and pathology. Use of calorimeters allows to measure precisely amount of heat released by an organism and to give the chance to compare the size of all energy released by an organism in the form of heat with amount of absorbed oxygen and the emitted carbon dioxide gas, i.e. with size gas exchange (see). Considerable coincidence between the results received at a research of energy balance by methods of a straight line To. and definitions of intensity of gas exchange at the person in the conditions of rest, allowed to consider the last method as a method indirect To. As an energy source in an organism are oxidizing processes at which oxygen is consumed and carbon dioxide gas, definition of gas exchange for assessment of the power processes of an organism which are followed by calorification is formed it is justified. Oxygen consumption and formation of carbon dioxide gas happens in all bodies and fabrics. The attitude of the carbon dioxide gas which is emitted from an organism towards amount of the consumed oxygen unequally also depends on preferential oxidation of carbohydrates, fats or proteins. This relation received the name respiratory coefficient (see). Its definition gives the chance to judge qualitative features of a metabolism, napr, dominance of oxidation of carbohydrates or fats. Other indicator of power exchange — a caloric equivalent of oxygen is closely connected with a respiratory coefficient (i.e. the amount of heat which is marked out by an organism at consumption of 1 l of oxygen). Its size fluctuates from 4,7 kcal at oxidation of fats to 5 kcal at oxidation of carbohydrates. Besides, release of strictly certain amounts of energy at oxidation of proteins, fats and carbohydrates will give the chance of their replacement in the ratios corresponding to warmth of their combustion (the so-called law of an izodinamiya).

Originally gas exchange at the person and at animals was defined in the special cameras having a loop system, napr in the respiration camera of Shaternikov (see. Shaternikova camera ), in a cut continuous air circulation, cleared of carbon dioxide gas, and continuous intake of oxygen provided a possibility of long stay in the camera of the person or an animal. The advantage of devices of the closed type is that required sizes decide by them without intermediate measurements on a fine precision, there is an opportunity to write down a soprogramma. It is possible to carry to shortcomings what in the course of the research of people breathes artificially made gas mixture and that they are applied by hl. obr. in the conditions of rest. The specified shortcomings are absent in devices of open type in which breath is carried out by free air. In expired air concentration of oxygen and carbon dioxide gas is defined, the respiratory coefficient is precisely counted. The greatest distribution in clinic was gained by Douglas's devices — Haldane in which expired air gathers in a special rubber bag, is analyzed by means of sets of absorbers of oxygen and carbon dioxide gas, and volume is measured by a wet gas meter. For a research of gas exchange also «BELLAU» devices, «Spirolit», PGI-1 and PGI-2 including gas analyzers and counters of expired air are used.

Methods K. allowed to check experimentally the law of conservation and transformation of energy in an animal organism, showed full applicability it to life activity in fiziol, conditions. They allowed to open at the person and animals the daily periodical press of heat production, dependence of heat exchange on the size of a body surface («the law of a surface» of Rubner, 1883), influence on the level of energy balance of work, food, ambient temperature, and also age.

If in a children's organism the high level of a metabolism and energy is noted, then a nek-swarm decrease in oxidizing processes is observed with age. So, the minute volume of breath expected a weight unit at the seven-months child equals 500, two-year-old — 330, and at adult 100 — 120 ml. Age decrease in energy balance is characterized by constancy and does not change in various conditions of the environment (K. M. Maksutov, A. T. Tynybekov, 1969). The metabolism at starvation is studied, specific dynamic action of food, its components is investigated: proteins, fats, carbohydrates. So, the level of energy balance at preferential fatty and proteinaceous food at usual ambient temperature was much higher (respectively for 14,3 and 34,7%), than at the mixed food (R. Akhmedov, 1966). To. widely use a dignity at the solution of various questions. - a gigabyte. character, approbation of special equipment etc. It is shown, e.g., that improvement of working conditions on automobile works of I. A. Likhachev led to reduction of energy costs which averaged 3650 kcal a day (A. P. Borisov, N. G. Shchepkin, 1966) that is 550 kcal less, than energy costs of working same workshops of the plant on data of the 30th. Studying of influences of active recreation on power exchange at persons of young and advanced age showed the progressing reduction of oxygen consumption, and also oxygen «cost» of the performed work. It is established that the dosed active recreation, providing more fiziol, «entry» of an elderly organism into work (E. G. Yanenko, 1968), promotes elimination of the pulmonary insufficiency developing with age.

To. found broad application in clinic during the determination of level standard metabolism (see). There are many data on indicators of standard metabolism at atherosclerosis, rheumatic cardites, an idiopathic hypertensia, various manifestations of cardiovascular insufficiency, infectious and toxic damages of a liver etc. Studying of standard metabolism at patients with hron, the diseases of lungs which are followed by emphysema showed its preferential increase. In particular, strengthening of operation of the device of external respiration, a bronchopulmonary infection, heart failure, a hyperthyroidism etc. can be factors of increase in standard metabolism. At the same time lack of increase or even decrease in standard metabolism at patients with the expressed emphysema of lungs and heart failure is considered as manifestation of absolute insufficiency of all respiratory and circulator system, as a result the cut is not provided the increased need of an organism for oxygen. At atherosclerosis the preferential decrease in a respiratory coefficient testimonial of considerable disturbance of a lipometabolism is stated. Increase in standard metabolism at patients with a septic endocarditis and other diseases is noted.

Improvement of methods of a microcalorimetry allows to study power processes in various microorganisms, the burgeoning seeds (under the influence of humidity, temperature etc.). Wide use of methods fiziol. To. showed limitation of a method indirect To. If at researches at rest or at easy physical. to loading the indicators of energy expenditure defined direct and indirect To., practically match, at an intensive fiziol, the activity connected with tension of energy and thermal balance, results of straight lines and indirect calorimetric researches significantly disperse. Considerable discrepancies in results are noted also at a research of some patol, conditions of the person. The last strengthens at the researches demanding exclusive accuracy, a tendency or to refuse simple and available methods indirect To., or to carry out them with simultaneous control of a straight line To.


Bibliography: Gorodinsky S. M., Glushko A. A. and Nuts B. B. A calorimetry in Antitack agents of protection of the person, M., 1976; Dulnev G. N., Pilipenko N. V. and P l and tun E. S. Dinamichesky bio-kalorymetr, Izv. vyssh. uchebn. institutions, Instrument making, t. 14, No. 5, page 111, 1971, bibliogr.; To Kalva E. and Pratt A. Mikrokalorimetriya, lane with fr., M., 1963, bibliogr.; Cherednichenko L. K. A physiological calorimetry, M. — L., 1965; Lavoisier A. L. et de Lapias e P. S. Memoire sur la chaleur, Mesh. Acad. Sci. (Paris), p. 355, 1780; Spinnler G. o. Human calorimeter with a new type of gradient layer, J. appl. Physiol., v. 35, p. 158, 1973.

L. K. Cherednichenko; V. G. Zilov (physical.).

Яндекс.Метрика