RU2185087C2 - Method for evaluating functional state of lungs - Google Patents

Abstract

FIELD: medicine. SUBSTANCE: method involves recording temperature changes in inhaled and exhaled gas mixture by means of temperature pickups set on the way of gas flow during the whole respiratory cycle, its duration and exhaled air volume. Heat quantity released in breathing is calculated by means of formula

where Q_E is the mean quantity of released heat in cal, C is the mean heat capacity of air in temperature interval from 20 to 40 C in cal/g/K, ρ is the mean air density in g/cm³, V is the exhale air volume in ml, t₁-t₂ is the respiratory cycle duration in s and T is the respiratory mixture temperature in C. EFFECT: high accuracy of noninvasive method; enabled quantitative estimation.

Description

 The invention relates to medicine, in particular to methods for studying the functional state of the lungs.

 A known method of recording an electropneumogram that allows you to determine the frequency and rhythm of breathing (see VV Kravtsov. Using an electric thermometer to register external respiration. Bull. Expert. Biol. Honey., 1971, 9, p.227). The listed indicators are recorded using a Temp-1 electric thermometer, the sensor of which is fixed at the inlet of the breathing mask. A semiconductor thermistor is used as a heat-sensitive element in the device, the signal of which is amplified and fed to the recorder.

 The disadvantage of this method is that it does not allow registration of changes in the temperature of exhaled air and determine the amount of heat generated, but only makes it possible to determine the presence or absence of respiratory cycles and register their frequency per unit time.

 The closest in technical essence to the claimed is a method of studying the function of external respiration of a person, consisting in the fact that a hollow pyroelectric trap is installed in the exhaled air flow, the energy flows of each indicator are modeled according to a certain law and the pyroelectric resistance of each face is recorded (see A. S. of the USSR , 693197, publ. 28.10.79). This method allows you to indirectly study the gas composition, air flow rate, radiation and convective components of the heat balance, frequency and minute volume of respiration.

 The disadvantage of the method chosen as a prototype is the impossibility of directly recording the temperature of the inhaled and exhaled air, and therefore the heat generated by breathing, since the electrical signal received in the pyroelectric sensors is proportional not to the temperature, but to the rate of its change. That is, the application of this method does not allow you to determine the amount of heat generated during breathing, which in turn does not make it possible to comprehensively evaluate the function of external respiration. For its implementation, a sensor is required, made in the form of a hollow pyramid, the base of which must be installed on a plane normal to the velocity vector of the air flow under study, and the characteristic dimensions of the pyramid base and the profile of the cross section of the air flow must be equal. The pyramid must be made of a dielectric material having pyroelectric properties. In addition, a modulator of the energy flow of each of the indicators of the function of external respiration is required, and to decrypt the indicated data, a demodulator of each of the energy flows is needed.

 The objective of the invention is to quantify pulmonary heat exchange while simplifying measurements.

 This object is achieved by the fact that in the method for assessing the functional state of the lungs using temperature sensors placed in the path of the gas stream, temperature changes of the inhaled and exhaled gas mixture are recorded simultaneously throughout the respiratory cycle, its duration and the volume of exhaled air.

где Q_Е - среднее количество выделяемого тепла, кал;
С - средняя теплоемкость воздуха в температурном интервале 20-40^oС, кал/г/К;
ρ - средняя плотность воздуха в температурном интервале 20-40^oС, г/см³;
V - объем выдыхаемого воздуха, мл;
t₁-t₂ - длительность дыхательного цикла, с;
Т - температура дыхательной смеси, ^oС.Another difference of the proposed method is that the amount of heat generated during breathing is calculated taking into account the average temperature of the respiratory cycle and heat capacity, density and volume of the gas mixture according to the formula

where Q _E is the average amount of heat generated, feces;
C is the average heat capacity of air in the temperature range of 20-40 ^o C, cal / g / K;
ρ is the average density of air in the temperature range of 20-40 ^o C, g / cm ³ ;
V is the volume of exhaled air, ml;
t ₁ -t ₂ - the duration of the respiratory cycle, s;
T is the temperature of the respiratory mixture, ^o C.

 The amount of heat released during breathing is an important indicator characterizing the heat transfer function of the lungs and allowing us to judge their functional state, since it has a close correlation with many indicators of gas exchange.

 When comparing the amount of heat released during respiration (an indicator of the heat transfer function of the lungs) and oxygen consumption by the lungs (an indicator of the function of external respiration), a direct correlation dependence was obtained, indicating a close relationship between the two main pulmonary functions, gas exchange and heat exchange (r = 0.73, p <0 , 05).

 The implementation of the proposed method is not associated with the operation of complex and expensive equipment, as for a parametric evaluation, any device consisting of a sensitive temperature sensor, analog-to-digital converter and a personal computer, as well as a device for determining the volume of exhaled air can be used.

 Example. Patient E., 26 years old, East. bol. N1546, entered the Research Institute of Emergency Medicine. I.I. Janelidze with a diagnosis of Closed skull injury, severe brain contusion, closed chest injury, multiple rib fractures, hip fracture, shock III tbsp. Shortly after admission, the patient measured the respiratory volume of the pulmonary heat transfer function and determined the average temperature of exhaled air. The amount of heat generated during breathing was calculated based on the specific heat of the air, the density and volume of exhaled air. In this example, the amount of heat generated was 0.8 cal per respiratory cycle, respectively, in 1 min (at a frequency of 20 breaths), its value was 16 cal. Thus, the result indicates a decrease in the amount of heat by more than 2 times in comparison with the data of the control group, which means a reduction in the area of the functioning surface of the lungs and a decrease in gas exchange in them. This is confirmed by gas analysis of arterial and mixed venous blood.

 After complex anti-shock therapy, the amount of heat generated during breathing, measured in a similar way, increased to 32 cal / min, which indicated an increase in the area of the functioning surface of the lungs, and, therefore, the restoration of effective pulmonary gas exchange.

 Thus, dynamic control of the amount of heat generated during breathing during the treatment of patients with traumatic shock allows us to judge the effectiveness of anti-shock therapy.

 This method can be used in intensive care and intensive care for the diagnosis of respiratory disorders and cellular metabolism in patients with chocogenic trauma.

 It is fundamentally important that the method is bloodless (non-invasive), that is, it does not require opening the lumen of the vessel and introducing sensors into the circulatory system. It is also important that the proposed method can be used to quantify the functional state of the lungs and the effectiveness of therapeutic measures, both with preserved independent breathing and with various modes of mechanical ventilation.

Claims (1)

A method for assessing the functional state of the lungs using temperature sensors placed in the path of the gas stream, characterized in that the temperature of the inhaled and exhaled gas mixture is simultaneously recorded during the entire respiratory cycle, its duration and volume of exhaled air, and the amount of heat released during breathing is calculated according to the formula

where Q _E is the average amount of heat generated, feces;
C is the average heat capacity of air in the temperature range of 20 - 40 ^o C, cal / g / K;
ρ is the average density of air in the temperature range of 20 - 40 ^o C, g / cm ³ ;
V is the volume of exhaled air, ml;
t ₁ - t ₂ - the duration of the respiratory cycle, s;
T is the temperature of the respiratory mixture, ^o C.