From Big Medical Encyclopedia

GAS ANALYZERS — devices for measurement of concentration of gas in gas mixture.

Widely apply in the metallurgical, chemical and coal industry to the analysis of flue gases, definitions of gas composition of air of production rooms and in systems of automatic control of technological processes, in heatpower and nuclear power and in medical practice at a research gas exchange (see) for measurement of concentration of carbon dioxide gas, oxygen and nitrogen in the inhaled and exhaled gas mixture, for a research of blood gases and for measurement of concentration of gas indicator in artificially created mix during the definition of a number of parameters of breath.

By the principle of action of G. divide on mechanical (volume and manometrical), acoustic (sound and ultrasonic), thermal (termokonduktometrichesky and thermochemical), magnetic (thermomagnetic, magnitotermokonduktometrichesky, magnitoviskozimetrichesky, magnetomechanical), electrochemical, ionization, optical (absorbing and issue) and mass and spectrometer.

Mechanical G.' action is based on determination of content of any component in gas mixture by its allocation and measurement of change of volume of test with a constant pressure (in volume G.) or pressure at the constant volume of the measuring camera (in manometrical G.); acoustic G. are based on dependence of rate of propagation of a sound in gas mixture from concentration in it the defined component; in thermal G. thermal characteristics of gases are used; magnetic G. are based on paramagnetic properties of oxygen; electrochemical G.' action is based on measurement of any parameter of liquid (e.g., specific conductivity), about a cut gas reacted; in ionization G. dependence of the ionic current arising in the ionized gas mixture at its room in electric field on concentration of the defined component is used; in optical G. dependence of change of optical properties of gas mixture (e.g., index of refraction, the optical density, spectral absorption) from concentration of a component in mix is used. Mass and spectrometer G. are based on division of bunches of charged particles (ions) of the analyzed gases with a different ratio of mass of particles and a charge, catching of ions and registration of ionic currents of each component of an ion beam; the size of ionic current is a measure of maintenance of the defined component in gas mixture.

In the exhaled and inhaled air apply volume mechanical G. like Haldane (GVV-2) to measurement of content of carbon dioxide gas and oxygen, in Krom for absorption of carbon dioxide gas solution caustic is used heat (natron), for oxygen absorption — caustic solution of pyrogallol (sodium hyposulphite). Instrumental error of ±0,1% of the volume of test. In expired air apply a domestic manometrical gas analyzer of AUH-2 with a limy absorber to express measurement of content of carbon dioxide gas. Measurement ranges — from 0 to 10 about. %, absolute error ±0,2 about. %. The volume of test for one analysis — 100 cm3. The device is figurative, weight is 2,3 kg. Time of establishment of indications — no more than 1 min. The device can use directly at a bed of the patient.

For measurement of concentration of helium in helio-air mixture, the cut breathes inspected in the closed system, during the scoping of residual gas in lungs and irregularity of lung ventilation apply an automatic termokonduktometrichesky gas analyzer of TP-7102. The device consists of an adsorber for absorption of carbon dioxide gas, a dehumidifier with the dehydrated calcium chloride, the membrane pump for soakage of the analyzed mix, the rotameter for control of a consumption of gas mixture and the measurement unit, in Krom the measuring scheme G. — the compensation comparator of tension is placed. A sensitive element of this G. is the conductor heated by current surrounded with the analyzed gas mixture. Temperature and consequently, and resistance of the conductor depend on heat conductivity of gas mixture and, respectively, on concentration of the measured component. A measuring range — from 0 to 5 about. %. The main given error of ±2,5%. Time of establishment of indications — no more than 2 min. Device figurative.

Fig. 1. Scheme of a magnetomechanical rotor gas analyzer: 1 and 7 — poles of magnets; 2 — a rotor; 3 — an extension; 4 — a mirror; 5 — the lighter; 6 — a scale. Action of a gas analyzer is based on change of force, edges affects the rotor placed in magnetic field.
Fig. 2. Gas analyzer of carbon dioxide gas low-inertia GUM-3: 1 — the sensor mounted on a mobile bracket; 2 — the case containing the gas scheme, the amplifier, the electrical power unit; 3 — the showing device; 4 — the operating console; 5 — the self-recording device.

In the inhaled and expired air and in various complex gas mixtures, including in oxygen-helium, apply a magnetomechanical rotor gas analyzer of MM of G-7 (oxyanalyzer) to measurement of the oxygen content. Its action is based on measurement of force, edges affects the rotor placed in magnetic field (fig. 1) and surrounded with the analyzed oxygen-containing mix. Selection of gas mixture in the measuring camera of the device and removal it from the device is made by means of the membrane pump. Results of measurements are counted on a scale, otgraduirovanny in millimeters of mercury (measuring ranges: 70 — 170; 0 — 200; 0 — 400; 0 — 800) or on a scale, otgraduirovanny in percents by volume (a measuring range from 0 to 100). The device has an exit to a standard self-recording potentiometer. The main given error of ±2%, time of establishment of indications — no more than 20 sec. The scheme with a feed-back is applied to elimination of influence of change of temperature on instrument readings in it.

Apply an absorbing optico-acoustic gas analyzer of GUM-3 (fig. 2) to continuous registration of changes of content of carbon dioxide gas in an alveolar air. G.'s action is based on comparison of attenuation range of energy of infrared radiation by the reference and analyzed mixes. This G. can be used also for measurement of concentration of carbon dioxide gas in expired air in the closed systems. Measuring ranges — 0 — 8 about. % and 0 — 12 about. %. A consumption of the analyzed gas — to 2 l/min. Time of establishment of indications — no more than 0,35 sec. Speed of the movement of a chart tape — 0,02 — 50 mm/sec.

In the inhaled and expired air apply optical issue G. to measurement of content of nitrogen an azotograf of A-2M. In the device there are showing and registering devices. Measuring ranges: 0 — 12 and 0 — 80 about. %. The main absolute error on the showing device on the first range ±0,2 about. %, on the second ±1 about %. Changes of content of nitrogen are registered on a chart tape. The given error at registration of ±3% of a measuring range. Time of establishment of indications — no more than 0,1 sec.

Apply the special G. based on the volume and electrometric principles of action to a research of blood gases (see Acid-base equilibrium, devices), and also ion-selective electrodes (see).

See also Gasometry .

Bibliography: Wan Ya. Analyzers of gases and liquids, the lane from Czeches., M., 1970, bibliogr.; Iovenko E. N. Autoanalyzers and signaling devices of toxic and explosive substances in air, M., 1972, bibliogr.; To about m r about J., etc. Lungs, Clinical physiology and functional trials, the lane with English, M., 1961, bibliogr.; New devices of gasometry in modern medicine and physiology, under the editorship of M. I. Abdrakhmanov and V. F. Bogoyavlensky, Kazan, 1967; Pavlenko V. A. Gas analyzers, M. — L., 1965, bibliogr.; Syrkinap.E. Gasometry in medical practice, M., 1956, bibliogr.

N. S. Mironova, L. I. Nemerovsky.