clearance in medicine

From Big Medical Encyclopedia

CLEARANCE in medicine (English. clearance) — speed of clarification of a blood plasma, other environments or body tissues from any substance in the course of its biotransformation, redistribution in an organism and (or) allocations from an organism.

The concept «clearance» of medicine was formulated in 1929 by Van-Slayk (D. D. Van Slyke) et al. applicable only to clarification of plasma from the substances emitted by kidneys, in particular from urea. At the same time To. was defined as extent of clarification from any substance of the blood plasma which passed through kidneys in 1 min. In the next years in connection with broad use in diagnosis of indicator paints and radioisotopes the concept «clearance» began to be used for designation not only an indicator of clarification of plasma, but also speed of decrease of indicator substance from the studied volume of any fabric, body. However the traditional use of the concept «clearance» (in relation to clarification of plasma) is steadiest.

In the developed terminology clarification of plasma from any substance is designated as To. this substance, e.g. To. inulin, To. creatinine. In formulas K. designate a symbol With, near the Crimea in abbreviated form designate substance, e.g. Cin — To. inulin. Depending on that what role of body in clarification of plasma is studied, speak about renal To., hepatic To. etc. There is also a concept of the general, or total plasmatic To. (Erased), size to-rogo characterizes the speed of clarification of plasma from substance irrespective of mechanisms of clarification (allocation by excretory bodies, biotransformation with loss of initial properties, etc.). Having defined at the same time general plasmatic To. and intensity of clarification from this substance a kidney or a liver, calculate a role of these bodies generally plasmatic K. Tak the leading role of kidneys in clarification of plasma from penicillin, inulin, a paraaminogippurata (PAGE) and the leading role of a liver in was shown, e.g., To. bromsulfoftalein and the Bengalese pink.

For definition of the general plasmatic To. indicator substance is once injected in a vein and through certain time slices collect several blood samples for studying of dynamics of concentration of the entered substance in plasma. Falling of concentration in blood of some substances, e.g. PAGE, happens on an exponent (for equal time terms concentration decreases on an identical relative part of initial size), other substances, napr, a bromsulfoftaleina, ethanol, a tsitemben — in the form of linear relation (concentration decreases by identical absolute value for equal time slices), and some substances have a curve of decrease in concentration in blood in the form of the wrong function. Depending on the nature of falling of concentration of substance in a blood plasma for calculation To. use various formulas.

Total plasmatic To. calculate by formula

Str = I/S

where I — amount of the substance entered into blood, S — the area under a curve of concentration of substance in plasma (on ordinate axis) during the research (on abscissa axis). At the exponential nature of curve concentration not to determine the area under it, use formula

Str = I*0,693/P 0 T 1/2

where P 0 — initial concentration in plasma in mg/ml, T 1/2 — time (in minutes or in hours) reduction of concentration of substance in plasma twice, I — amount of the entered substance.

A role of separate bodies in To. any substance it can be established on distinction of concentration of this substance in plasma of the blood inflowing to body and flowing from it. About this difference it is possible to judge also by distinction of concentration of substance in plasma and in the emitted liquids (for excretory bodies). To. substances, caused by secretory function,

V*K/P

where V — the volume of a secret (ekskret) received for a unit of time (usually in ml/min.), To — concentration of substance, i.e. quantity in 1 ml of a secret (e.g., urine, bile), P — concentration of substance in plasma is determined by the general formula C =. It is methodically essential that for definition of the general plasmatic To. make a single injection of substance; for measurement organ, in particular renal, To. it is preferable continuous infusions to maintain concentration of test substance in plasma on a fixed level.

Clinical value clearance tests

the broadest use and development clearance tests was gained in studying of renal functions. With the help clearance tests define a renal plazmotok, glomerular filtering, a reabsorption and secretion (see. Kidneys ). At the same time use distinctions in renal To. different substances. Definition of a renal plazmotok is based on measurement To. Cardiotrastum, PAGE, or a gippuron of which the blood plasma is completely cleared at single passing through cortical substance of a kidney. For measurement of glomerular filtering define To. substances which are filtered, but do not cosecrete and do not reabsorbirutsya (inulin, sodium thiosulphate, polyethyleneglycol 1000, Mannitolum). The received result is led to a standard body surface (1,73 m 2 ). To. inulin at the person PAGE — 624 ml/min. on 1,73 m is equal 127, and clearance 2 . As long infusions in a vein of solutions of inulin and other substances used for definition of glomerular filtering it is difficult, in clinic quite satisfactory results are yielded by its measurement on To. endogenous creatinine. When substance is emitted only with a kidney, it is possible to define it To. without capture of urine if rate of administering of substance is regulated so that concentration it in plasma was maintained on a fixed level, then the amount of the entered substance is equal it To.

As definition renal To. it is connected with a research of concentration of test substance in urine, it is necessary to consider transport of water in kidneys, and also their ability not only to excrete, but also to hold some substances in an organism. In the latter case concentration of substance in urine will be less, than in a blood plasma. To define whether there is excretion a kidney of this substance, use calculation To. for

a formula C = V (U — P) / P,

where U — concentration of substance in urine. For substances which concentration in urine is lower, than in plasma, the received size K. will be negative; it will indicate that substance keeps in plasma, and excess of water is distinguished. A concept about positive and negative To. important for the characteristic osmo-and ionoreguliruyushchy function of kidneys.

Use as test substances of radioisotopes significantly expanded opportunities clearance tests in a wedge, to practice and raised their wedge, the importance. Over heart determine an effective renal plazmotok and a blood stream by a curve of recession of radioactivity. Substances, To. which it is used for definition of glomerular filtering, but the radioisotopes having in a molecule (inulin - 131 I, EDTA- 51 Cr, EDTA- 169 Yb), allow to make a research without collecting urine that gives the chance to define glomerular filtering at a hypouresis. The isotope renografiya allows to estimate funkts, a condition of kidneys at their various diseases, evakuatorny function of upper uric ways; it is used for overseeing by a state and function of a transplantirovanny kidney (see. Renografiya radio isotope ).

The clearance tests in hepathology is applied to studying of poglotitelnovydelitelny function liver (see). At the same time enter the substances absorbed by a liver and emitted with bile into an organism (bilirubin, bromsulfalein, an azoruby-S, Bengalese pink, vofaverdin, uyeverdin, etc.). Use more often bromsulfoftaleinovy test (see) and vofaverdinovy test (see).

For definition hepatic parenchymatous To. apply Bengalese pink, marked 131I which possesses the expressed gepatotropnost. Curves To. process by means of the exponential equation, calculating a half-cycle of elimination, time of the maximum level of radiation over a liver and time of emergence of drug in Intestines. At diseases of a liver the speed and attenuation range and attenuation range and excretion of paint decrease: at defeat of polygonal cells process of absorption suffers to a large extent, and at an inflammation, and especially disturbance of passability of bilious ways — excretory function. Comparison of indicators of clarification from blood preparation and a liver is especially important. In case of an obstacle to outflow of bile the normal or low-changed decrease of drug from blood at its slowed-down removal from a liver is observed; simultaneous disturbance of absorption of the Bengalese pink allows to assume defeat of a parenchyma. With the help the clearance tests is obviously possible identification of anicteric forms of a viral hepatitis, predictive assessment of the recovery period after an acute viral hepatitis, extent of defeat and dynamics of process at hron, diseases of a liver.

For studying of a regional blood-groove use a method of so-called fabric clearance — the speed of elimination of isotopes 133Xe, 85Kr, albumine, marked 131I, etc. from the studied fabric (body), in a cut the depot of drug is created.

The perspective of use clearance tests in a wedge, researches steadily extends. With their help study exchange of a number of substances, napr, albumine, longevity of erythrocytes, products of bilirubin, biol, a cycle of hormones, speed of consumption of professional actors and factors of coagulant and anticoagulative system of blood.

Definition plasmatic To. finds application during the studying of pharmacokinetics of medicines, for studying of absorption of drugs from went. - kish. a path, their distribution in an organism, a role of various bodies in their allocation or destruction. Besides, on To. judge efficiency of clarification of an organism from endogenous and exogenous substances during the use of such methods of treatment as hemodialysis (see), peritoneal dialysis (see), hemosorption (see), limfosorbtion (see), plasma exchange (see), exchange substitution of blood.



Bibliography: Gekhmosorbtion, under the editorship of Yu. M. Lopukhin, M., 1977; r and f N of e of a black grouse Y., etc. Value of plasmatic clearance in studying of kinetics of antibiotics, Antibiotics, t. 5, No. 3, page 56, 1960; Lopukhin Yu. M. and M about-lodenkov M. N. Gemosorbtion, M., 1978; Fundamentals of hepathology, under the editorship of A. F. Blyuger, page 116, Riga, 1975; Shyuk O. A functional research of kidneys, the lane from Czeches., Prague, 1975, bibliogr.; I r about sh e in with to and y A. Ya. Clinical nephrology, L., 1971; Koi-shanp our E. Renal physiology, Philadelphia, 1976.


Yu. V. Natochin, M. E.Semendyaeva.

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