JPH06311979A - Functional residual capacity measurement method - Google Patents

Abstract

(57) [Summary] [Purpose] By improving the known nitrogen flushing method,
(EN) A method for easily measuring a functional residual capacity of a patient while reducing the burden on the patient while reducing the measurement error while maintaining the breathing mode necessary for treating the patient. [Taru-nari] All the exhaled gas of the patient after switching the inspiratory gas to pure oxygen is captured and as a flow with one-way fluctuation,
The flow rate measuring unit 6 and the nitrogen concentration meter 7 are arranged there, and the functional residual air amount is calculated from the time integrated amount of the product of both signals.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the method for measuring functional residual capacity, which is one of the influential numerical values for diagnosing respiratory function in patients with respiratory diseases. is there. 2. Description of the Related Art Functional residual value (Functional)
It is well known that the Residual Capacity (hereinafter abbreviated as FRC) is effective as a numerical value indicating whether the alveoli are optimally opened and ventilation is effective as a numerical value effective for diagnosing respiratory function in patients with respiratory diseases. ， Measurement was not so easy, and the patient went to the laboratory and it was an expensive and large machine that could only be performed by a specialized technician. In the case of infants, it was almost impossible because the amount of measurement was so small that the patient could not cooperate. However, in recent years, the treatment technology for respiratory failure in infants has improved, and more objective respiratory function data have been required for infants, and the need for FRC is increasing. Typical methods for measuring FRC include a closed circuit method using helium gas, a method in which nitrogen contained in air is washed out with pure oxygen, and a plethysmograph method in which a patient is placed in a sealed box and the change in pressure and flow rate due to breathing is performed. is there. When measuring FRC in infants, the closed circuit method using helium is difficult to use because of leaks, and the nitrogen flushing method is small in measuring the amount of nitrogen discharged per breath and it is also difficult to correct dead space. Therefore, this is also not practically accurate.
The plethysmograph method requires large measuring equipment and cannot be easily implemented. Gerhardt is a method to easily measure the FRC of infants using the principle of the nitrogen flushing method.
It has been announced by Mr. (Reference A Simp
le Method for Measuring fu
nctional residual Capacit
y by N2 washout in Small
Animals and Newborn Infan
ts: A simple method for measuring functional residual capacity by nitrogen flushing in small animals and newborns Pedeatrick Research vol. 19, No. 11 19851165
To summarize this method, patients who spontaneously breathe inspiratory gas containing nitrogen are switched to breathe at a single point in a closed tube through which a known flow of pure oxygen inspiratory gas is breathed at the end timing of expiration, and the patient is breathed. A chamber with a capacity for suppressing fluctuations in flow rate due to respiration and making the concentration uniform is provided downstream of, and a highly sensitive nitrogen concentration meter is placed at its outlet, and the concentration signal is integrated until it becomes zero after switching. . Since the flow rate is known and constant, the integral value is multiplied by an appropriate coefficient to determine the total nitrogen excretion, and thus the end-expiratory lung volume or FRC of the patient. This method is an excellent method that can be easily measured with a simple configuration if the flow rate at the measurement point of the nitrogen concentration meter is considered to be constant or average. However, in reality, it is surprisingly difficult to sufficiently suppress the flow rate fluctuation in the downstream due to the patient's respiration, and there is an actual nitrogen concentration meter time delay, and the response time cannot be ignored, and matching with the flow rate fluctuation is difficult. ， Accuracy can be expected only under the condition of very limited respiratory rate and volume. In addition, this method can measure only spontaneous breathing, and not in patients who require more critical artificial respiration. SUMMARY OF THE INVENTION The present invention improves the FRC measurement accuracy of the above-mentioned simple nitrogen flushing method, especially for infants,
It is intended to provide a method capable of accurately and easily measuring FRC in both spontaneous and artificial respiration. Configuration Example of the Invention FIG. 1 shows a configuration example of the present invention. The ventilator part 1 is capable of supplying inspiratory gas containing a known concentration of nitrogen such as air, while the ventilator part 2 is capable of supplying inspiratory gas of pure oxygen. Specifically, two commercial ventilators, each of which may be used alone, may be prepared. However, the ventilator part 2 is used at the time of measurement, as will be described later, and it is known that pure oxygen or high oxygen concentration can be stably supplied and that all gas discharged on the expiratory side can be captured and sent to the closed pipe system. It is necessary. The respective patient mouths are inputs 3-1 and 3-2 of the circuit switching device 3.
It is connected to the. The patient 4 is connected to the output port 3-3 of the circuit switching device 3 through a mask or endotracheal intubation, and initially 3-1 and 3-3 are connected depending on the operating state of the circuit switching device 3 and the ventilator part 1 Breathing inspiratory gas containing nitrogen.
In general, a ventilator can generate a steady flow for spontaneous breathing, positive pressure intermittent breathing, or mixed mode (so-called IMV), so in this case as well, the patient's condition and later As described below, the measurement can be started by breathing from the ventilator unit 1 in any mode. On the other hand, the ventilator part 2 sets the breathing mode under the same conditions as the ventilator part 1 except the inspiratory gas as much as possible. Then, the exhaled gas is discharged through the measurement system described below. The expiratory side circuit 5 including the expiratory valve of the ventilator unit 2 has a structure capable of collecting all gas flows including the exhaled gas of the patient 4, and the collected gas is soft and elastic such as a rubber bag downstream thereof. The flow rate measuring unit 6 and the nitrogen concentration meter 7 are arranged further downstream of the reservoir unit 8 having the above. As the nitrogen concentration meter 7, the one using the nitrogen concentration dependence of the vacuum glow discharge brightness is widely used, and the required sample gas amount is as small as several mL / min, and it has a delay and response of about 0.1 seconds. ing. In the actual device configuration, the measurement control unit 9 uses a microcomputer. Before the measurement, the flow rate measuring unit 6 and the nitrogen concentration meter 7 can be calibrated and the results can be stored. Further, if a flow rate measuring unit 10 using a pneumotachogram or the like is placed at the mouth of the patient 4 for the purpose of monitoring the patient's breathing, the microcomputer monitors the signal and switches the time of measurement by recognizing the end-expiration. The operation of the vessel 3 can be automatically performed. [Measurement of Measurement Operation] The measurement is performed by operating the circuit switching device 3 at the timing of the expiration of the patient 4 and breathing the patient from the next inspiration to the insufflation from the ventilator unit 2, that is, pure oxygen. Start. The nitrogen gas contained in the portion corresponding to the FRC of the patient 4 is mixed with the exhaled air toward the expiratory side circuit 5 by pure oxygen breathing and flows out. The outflow gas has a unidirectional fluctuating flow rate, and the flow rate is measured by a flow rate measuring unit 6 using a flow sensor with a small pressure loss such as a pneumotachography graph, and the nitrogen concentration of the flowing gas is measured by a nitrogen concentration meter 7 and measurement control is performed. Sent to department 9. The instantaneous flow rate of the outflow gas increases or decreases depending on the phase of the inspiratory expiration in the patient's spontaneous breathing or artificial respiration mode. However, since the reservoir 8 is provided, the flow tray does not become zero even if positive pressure intermittent artificial respiration is performed, and the flow is smoothed and supplied to the flow measuring unit 7. After the start of measurement, the measurement control unit 9 multiplies the flow rate signal and the nitrogen concentration signal to obtain an instantaneous nitrogen gas amount, and integrates this until the concentration signal becomes zero. The integrated amount represents the total amount of nitrogen washed out from the patient 4, and the FRC is obtained by dividing by the nitrogen concentration of the inspiratory gas before the start of measurement. In order to maintain the accuracy under various respiratory conditions, it is desirable to consider the delay time of the nitrogen gas concentration signal. In order to correct the delay, the delay time may be accurately obtained separately, the value may be given to the measurement control unit 9, and integration may be performed using the flow rate signal that is old by that time. When the concentration signal becomes zero, the patient 4 should be quickly returned to the original ventilator unit 1 by operating the circuit switch 3. From the viewpoint of examination, the ventilator unit 1 may be the ventilator originally used to treat the patient 4. After the start of measurement, the washout flow downstream of the expiratory circuit 5 varies, but its flow rate is measured at an instant and multiplied by the concentration at that instant. Therefore, even if the breathing mode of the patient is spontaneous breathing under a steady flow, even if the flow rate at the time downstream of inspiration becomes zero due to positive pressure intermittent breathing, there is an effect that it is possible to cope with the state. In the illustrated example, the reservoir 8 is provided downstream of the exhalation, but for this reason, the reservoir 8 does not necessarily have to be used. However, as in the case of the positive pressure intermittent respiration, the flow signal has an intermittent waveform. It is better to smooth the flow signal with a filter element such as a reservoir as in the simple method cited above. Since the responsiveness of 6 and the nitrogen concentration meter 7 easily causes an error due to an artifact with respect to a rapid change in a rectangular wave shape, it is desirable in the sense of avoiding it.
In the present invention, pure oxygen only flows through the flow rate measuring unit 6 before the start of measurement and the nitrogen concentration meter 7. Even if the ventilator unit 2 does not use pure oxygen and contains some nitrogen, if the nitrogen concentration signal of the measurement control unit 9 is biased to zero at this concentration before the start, the patient will start measuring after the start of measurement. Since the input concentration signal becomes zero when the additional nitrogen in the
RC can be calculated. This point is effective when it is not desired to inhale pure oxygen even for a short time depending on the condition of the patient 4. Further, as described above, the oxygen concentration of the inspiratory gas of the ventilator unit 1, that is, (100-nitrogen concentration) is not always equal to that of air.
It need not be 0.6% as long as an accurate number is known. Actually, if the nitrogen concentration is too low, the measurement error is large and it is not practical, but this point is also effective when the oxygen concentration cannot be lowered so much in the treatment of the patient 4. The nitrogen flushing method according to the present invention described so far has been described on the assumption of an infant, but this method can be applied to an adult as it is, only by changing the size of each component used, and the effect can be utilized. By using the computer for the measurement system, not only the calculation process of the data during the measurement but also the monitoring of the nitrogen concentration zero and the detection of the end of the measurement are detected and the patient 4 is automatically placed in the original therapeutic ventilator unit 1. The patient can be kept safe by quickly returning the device so that the amount of pure oxygen breathing accompanying the measurement can be minimized. Also, the measurement operation as a whole is simplified and a highly accurate result can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural example of an FRC measurement method according to the present invention. [Description of reference numerals] 1 is a ventilator part 1, 2 is a ventilator part 2, 3 is a circuit switch, 4 Is the patient, 5 is the expiratory circuit of the ventilator 2, and 6
Is a flow rate measurement unit, 7 is a nitrogen concentration meter, 8 is a reservoir, 9 is a measurement control unit, and 10 is a flow rate measurement unit.

Claims (1)

Claims: 1. An artificial respirator part (1) for supplying an aspirate gas containing nitrogen and an artificial respirator part (2) for supplying an aspirate gas having a pure oxygen concentration, both of which are instantaneous. The patient 4 is made to breathe through the circuit switching device 3 which can be switched to and used, and the expiratory gas in the expiratory side circuit 5 of the artificial respirator unit 2 is connected to the flow rate measuring unit 6 and nitrogen downstream of all the collected gas flow. A method for measuring functional residual air amount by a nitrogen flushing method in which a densitometer 7 is arranged. 2. A switching device which has an artificial respirator part 1 for supplying an aspirate gas containing nitrogen and an artificial respirator part 2 for supplying an aspirate gas having a pure oxygen concentration, any of which can be instantly switched for use. The patient 4 is made to breathe through the ventilator 3, and the expiratory side circuit 5 of the ventilator part 2 inserts a conservative reservoir 8 downstream of all the collected gas flow and further downstream thereof. A method for measuring a functional residual air amount by a nitrogen flushing method in which a flow rate measuring unit 6 and a nitrogen concentration meter 7 are arranged. 3. The method according to claim 1 or 2, wherein the switching device 3 is switched from the artificial respiration unit 1 to 2 at the end of the expiration of the patient 4 and at the same time the signal of the flow rate measurement unit 6 and nitrogen. Start the integration of the two signals obtained from the densitometer 7 with time and start the nitrogen densitometer 7
Measurement method to calculate the functional residual capacity from the integrated value obtained until the signal of becomes zero.