PNEVMOTAKHOGRAFIYA (grech, pneuma air +-a takhografiya) — the method of a research of mechanics of breath based on record of speed of the movement and volume of the inhaled and expired air. The record received at the same time is called pnevmotakhogrammy. P.'s use in physiology began Fleysh after the invention (And. Fleisch, 1925) the pneumotachograph and creation by Neer-gard and Virts (To. Neergaard, To. Wirz, 1927) pnevmotakhografichesky technique. The pneumotachograph is a part of a number of the modern devices and devices used for diagnosis (respirators, a whole-body plethysmograph, etc.). Independent application for the purpose of measurement of resistance of respiratory tracts of P. is found by hl. obr. in physiology.
Value of a research of mechanics of breath consists that at many diseases of lungs increase in resistance of respiratory tracts and change of elastic properties of lungs is observed. Costs of work of breath at such patients even at rest are much higher, than at healthy people. At increase in minute volume of breath of costs of work of breath at patients increase much quicker that limits a possibility of further growth of minute volume of breath (see. Respiratory insufficiency ).
Pneumotachographs work on an open circuit, i.e. at inhalation by the patient of an ambient air. The simplest pneumotachographs consist of the converter of air consumption in an electric signal and a regrtstrator. With their help define rate of volume flow of the movement of air at quet and forced ventilation, a respiration rate, duration of a breath and exhalation. Converters can be termoanemometrichesky or acoustic. There are also converters working on pressure difference (with the narrowing device, with a resistance of viscous friction), etc. Converters with a resistance of viscous friction and elements of selection of pressure on the site of streamline flow which provide direct proporshchyunalny dependence of a difference of pressure (pressure difference) on the air consumption passing through resistance are most eurysynusic. The majority of pneumotachographs is supplied with the integrator allowing along with pnevmotakhogrammy to write down a spirogramma (see. Spirography ), devices for calculation of parameters of a pnevmotakhogramma and a spirogramma and the devices transforming results of measurements to figures on the light indicator, on the screen etc. On a pnevmotakhogramma, except the parameters of mechanics of breath called earlier, define also distensibility of lungs, work of breath, etc. Distensibility of lungs normal makes 0,15 — 0,35 l/cm w.g., at diseases of lungs, napr, at fibrosis, it much less can also make 1/20 normal values. Work of breath in the conditions of rest at the healthy person does not exceed 0,5 kgm / mines, at patients with a high resistivity of respiratory tracts it can reach 2 — 3 kgm / mines and more.
Some types of pneumotachographs are supplied with devices for registration and measurement of alveolar and transpulmonic pressure, devices for registration of curves volume — pressure and volume — a flow, and also such parameters of mechanics of breath as resistance to an air flow prp breath, work of breath etc.
of P. at artificial ventilation of the lungs helps (manually or automatically) to provide the mode of breath, physiologic for the patient.
The maximum rate of volume flow of air at the forced exhalation at adults makes 4 — 8 l/sec., can reach 12 l/sec., at patients with disturbances of bronchial passability it decreases and in hard cases there can be less than 1 l/sec. At healthy people the greatest value of rate of volume flow at the forced exhalation is observed on average in 0,1 sec. after the beginning of an exhalation, and then speed gradually decreases. At patients the greatest value of speed at the forced exhalation is reached also quickly, as well as at healthy (fig. 1), but then sharply falls, and the exhalation proceeds at the lowered speed.
Such parameter as airway resistance gives big informational content, especially at inspection of patients with bronchial stenoses. In a norlga airway resistance is from 2 to 8 cm of waters. Art./l/sec. At patients with asthma during an attack it can reach values of 28 cm of waters. Art./l/sec. and above.
Most foreign firms apply the so-called tube of Fleysh presenting itself a respiratory tube with a resistance placed in it in the form of the channels parallel to an axis of a tube, educated the coiled metal tapes imposed at each other to P. (flat and corrugated). External channels in the sections located perpendicular to an axis of a tube through separate openings and cameras (collectors) connect to the converter, napr, to the converter of pressure difference in an electric signal. Fleysh's tube has shortcomings: it easily gets littered, and its sanitary cleaning is complicated, in the course of work demands heating (for prevention of formation of condensate), because of selection of pressure only from external channels P.'s testimonies are influenced by local indignations of a flow.
In the USSR instead of Fleysh I. S. Mironovoy's tube the converter of an expense with a resistance in the form of a tube with plane-parallel channels and elements of selection of pressure from each channel through cracks (openings) and collectors is offered. The big cross-sectional area of flat channels, than channels in Fleysh's tube, with the same their height provides smaller degree of a contamination at operation and the best conditions for sanitary cleaning, does not demand heating; selection of pressure from each channel excludes influence of local indignations of a flow on indications of the Item.
For the purpose of measurement of alveolar pressure use the device for short-term (within 0,1 — 0,2 sec.) with a frequency of 1 — 2 Hz of overlapping of a flow between the patient and resistance by means of, e.g., gate and the electromanometer connected to a respiratory tube on the site between the patient and resistance. Record of curves volume — pressure and volume — a flow is made by means of an oscillograph or the two-coordinate recorder.
In the USSR the pneumotachograph with the integrator is issued. Measuring ranges of a volume flow of 0—3, 0—6 and 0 — 12 l/sec.; volume of 0 — 1 and 0 — 5 l; alveolar pressure About — 100 mm w.g.; transpulmonic pressure from — 700 to — 300 mm w.g.; minute volume of breath from 6 to 150 l/min. Resistance to an air flow at an expense of 60 l/min — no more than 5 mm w.g.
There are two groups of the pnevmotakhografichesky techniques allowing to measure resistance of respiratory tracts at independent breath: interruption of an air flow and the forced oscillations. On one of them (fig. 2) the examinee breathes via the pneumotachograph. The differential manometer registers a pnevmotakhogramma. By means of the special gate the air flow is periodically blocked on 0,1 — 0,2 sec. At the time of overlapping Occurs to a vyravnivanyaa of pressure in alveoluses and a tube. On the written-down pnevmotakhogramma emissions correspond to the size of alveolar pressure. The size of aerodynamic resistance (R) is calculated on a formula:
R = (P A - P 1 ) / V,
where P A — size of alveolar pressure, P 1 — pressure necessary for overcoming resistance, V — rate of volume flow of an air flow at breath.
The method of the forced oscillations provides creation of low-amplitude pulsations of pressure in a pnevmotakhografichesky tube with a frequency apprx. 10 Hz. A lack of these methods — dependence of the received result on time of equalization of pressure, time of overlapping and frequency of oscillations; with increase in resistance of respiratory tracts time of equalization of pressure increases that demands to extend overlapping and to reduce the frequency of oscillation, but at the same time errors increase. More exact results are yielded by the general pletizmografiya (see).
At express diagnosis apply the pneumotachometers containing, e.g., the converter of air consumption in pressure difference and the mechanical or differential manometer to measurement of the maximum speed of the forced exhalation (breath). Such pneumotachometers have an electric exit to the chart recorder for record of a pnevmotakhogramma.
Bibliography: Zilber A. P. Clinical physiology for the anesthesiologist, page 13, M., 1977; Komro Dzh., Etc. Lungs, the lane with English, M., 1961; M and r it about in and I. S. The errors of converters of air consumption connected with the accuracy of their production, the Medical technician, L'1-3, page 17, 1976; H av hosts of l of M., To and d l of e of c To. and D and at S. Patofiziologiya's m of breath, the lane from Czeches., M. — Prague, 1967; With about m of about e J. H. Physiology of respiration, Chicago, 1975.
M. I. Anokhin; I. S. Mironova (tekhn.).