GB2084321A

GB2084321A - Apparatus for Measuring Respiratory Replacement

Info

Publication number: GB2084321A
Application number: GB8128104A
Authority: GB
Original assignee: Fuji Electric Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 1980-09-18
Filing date: 1981-09-17
Publication date: 1982-04-07
Also published as: GB2084321B; DE3137258A1; JPS5755133A

Abstract

Instead of sampling only the exhaled gases a collector 30 is positioned adjacent to but spaced from the patient's mouth and nose and draws in at a constant rate ambient atmosphere. Exhalation gives rise to collection of expired gases also. The collected gases are analysed at 37, 38 for carbon dioxide and oxygen concentrations and the results used with the value of the constant flow rate in arithmetic units 35, 36. The constant flow rate can be ensured by means of a flow control valve (32) or by using a constant volume pump. A flowmeter 31 is optional. <IMAGE>

Description

SPECIFICATION Apparatus for Measuring Respiratory Replacement The present invention relates to apparatus for measuring respiratory replacement as is necessary when examining and diagnosing physiological functions of lungs, and more particularly the apparatus is for measuring amounts of certain constituents of an expired gas to monitor respiratory replacement of patients and premature babies.

Conventional measuring apparatus of this type includes a mask for intimate contact with the mouth and nose of a patient or a nose grip and a mouthpiece for preventing respiration through the nose thereby to allow effective collection only of a gas exhaled by the patient.

Two examples of prior art apparatus will now be described with reference to the accompanying drawings in which~ Figs. 1 and 2 are schematic diagrams of respective different prior art apparatus for measuring respiratory replacement; Fig. 3 is a schematic diagram of apparatus for measuring respiratory replacement and embodying this invention; and Fig. 4 is a set of graphs illustrating the operation of the apparatus shown in Fig. 3.

Referring to Figs. 1 and 2, mouthpieces 15 are connected to a directional control valve 11 and a flowmeter 21, respectively. A patient, while being examined, uses such a mouthpiece 15 and a nose grip 14 for effective collection of expired gas only.

In Fig. 1, the expired gas collected from the patient is introduced for a determinate period of time into a collector bell 12 through the directional control valve 11 so as to enable the measurement of the amounts and concentrations of constituents of the exhaled gas in the collector bell 12. From this can be found the amount of carbon dioxide discharged and the amount of oxygen taken in the determinate period of time.

Referring now to Fig. 2, the rate of flow of expired gas is measured by the flowmeter 21, and the concentrations of oxygen and carbon dioxide are continuously measured by analyzers 22, 23, respectively, which give the results of the measurement to an arithmetic unit (not shown) for computation. More specifically, the results of the measurement given by the oxygen concentration analyzer 23 and the carbon dioxide concentration analyzer 22 are multiplied by the rate of flow measured by the flow meter 21.

Consecutive results of this multiplication are summed to find the amount of carbon dioxide discharged by the patient and the amount of oxygen taken by the patient within a determinate interval of time.

These known arrangements are disadvantageous, however, in that the expired gas collectors such as the mouthpiece and nose grip have to be worn by the patient who is consequently subjected to discomfort, and hence do not lend themselves to continuous measuring operation. The prior art arrangements are not very useful particularly for premature babies and serious illness cases.

With the Fig. 2 arrangement, it is necessary to measure the rate of flow of the expired gas and the concentration of the expired gas at the same time since the measurement of the rate of flow of the expired gas by the flowmeter has to be multiplied by the measurements of the concentrations of constituents of the expired gas by the analyzers. However, the device tends to produce errors due to a difference in time between such measurements and hence is susceptible to incorrect measurements. Provision must therefore be made to compensate for such errors.

It is an object of the present invention to provide apparatus capable of measuring respiratory replacement continuously over a long period of time without causing the patient pain and discomfort and with enhanced accuracy of measurement.

According to this invention there is provided apparatus for measuring respiratory replacement and comprising a collector, locatable adjacent, but spaced from, the mouth and/or nose of a patient being examined, for taking in gases from the vicinity of the patient's mouth and/or nose, said gases including ambient atmospheric air and, at least during exhalationby the patient, gas expired by the patient means for drawing in said gases at a constant flow rate at all times, means for measuring the concentrations of carbon dioxide and/or oxygen in the expired gas based on said gases drawn at the constant rate via said collector, and means for computing the amount of carbon dioxide expired and/or the amount of oxygen taken by the patient in a predetermined period of time based on the results of the measurements in the measuring means and on the constant rate of flow of the gases.

The means for controlling the mixture so as to flow at a constant rate may comprise a constant volume pump or a flow control valve.

An embodiment of the present invention will now be described, by way of example, with reference to Figs. 3 and 4 of the accompanying drawings.

Referring to Fig. 3 an atmosphere and expired gas collector 30 is located adjacent, but spaced from, the mouth and nose of a patient 13 being examined (rather than being held in intimate contact with the mouth and nose of the patient 13) so as to collect ambient atmospheric air as well as exhaled gas. A mixture of the expired gas and ambient air is introduced via a flowmeter 31, a needle valve 32, a pump 33 and a T-branch 34 into a carbon dioxide analyzer 37 and an oxygen analyzer 38. The needle valve 32 serves as a flow control valve for controlling the gas mixture so as to flow through the flowmeter 31 at a constant rate, and the pump 33 draws, mixes, and supplies the mixture to the analyzers 37, 38.The amount of expired gas exhaled by the patient varies with time over a cycle from the time at which the expired gas starts being exhaled to the time at which the expired gas ceases to be exhaled. The needle valve 32 is adjusted such that the pump 33 draws a constant amount of the gas mixture which is greater than the maximum amount of gas exhaled in one cycle, thus taking into consideration a quantity of ambient air to be introduced.

A portion of the gas mixture supplied by the pump 33 is fed via the T-branch 34 to the analyzers 37, 38 for the measurement of carbon dioxide concentration (volume %) and oxygen concentration (volume %).

Fig. 4 comprises two graphs illustrative of waveforms of output signals from the analyzers, respectively, the graphs each having an abscissa axis indicative of time and respectively, having an ordinate axis indicative of the output of the carbon dioxide analyzer CO2 and the output of the oxygen gas analyzer 02.

Designated in Fig. 4, at C1 is a cycle of exhalation by the patient and at C2 is a cycle of inhalation. During the cycle of inhalation C2, the graph shows a concentration of carbon dioxide A2 and a concentration of oxygen B2 in the ambient air. During the cycle of exhalation C1, the graph illustrates a concentration of carbon dioxide A1, and a concentration of oxygen B1 in a mixture of ambient air and expired gas.

Concentrations of carbon dioxide and oxygen at a given point in time are given by A1 minus A2 and B2 minus B,. Such instantaneous concentration values are multiplied by the constant rate of flow of the mixture through the flowmeter 31. Consecutive results of the multiplication are added together to find an amount of carbon dioxide exhaled and an amount of oxygen taken in a determinate period of time.

Stated otherwise, the amount of carbon dioxideexhaled and the amount of oxygen taken can be obtained by multiplying the hatched areas in the graph by the constant rate of flow, and by adding consecutive products.

The concentration of carbon dioxide in air (corresponding to A2in Fig. 4) and the concentration of oxygen in air (corresponding to B2 in Fig. 4) are known in advance by measurement. The concentration of carbon dioxide in expired gas (corresponding to A1 in Fig.

4) and the concentration of oxygen in the expired gas (corresponding to B1 in Fig. 4) are given by the analyzers 37, 38, respectively. An arithmetical unit 35 finds the increase (during exhalation) in the concentration of carbon dioxide, that is, A1 minus A2, and an arithmetical unit 36 finds the reduction (during exhalation) in the concentration of oxygen that is, B2 minus B1. Values thus formed are multiplied by the constant rate of flow given by the flow meter 31 and are integrated to find the amounts of carbon dioxide and oxygen respectively exhaled and taken by the patient within a determinate interval of time.

With this arrangement, no grip or mouthpiece need be worn by a person under test, and it is only necessaryfora collector to be located adjacent the mouth and/or nose of the patient who is therefore not consequently subject to discomfort, thus enabling continuous measurement over a long period of time.

Since the gas mixture flows through the flowmeter at a constant rate, no error is produced due to difference in time between measurement of the flow rate and measurement of gas concentration, so enabling precise measurement.

Instead of the flow control valve, a constant volume pump may be used to provide constant flow rate. The flowmeter can be dispensed with because the constant-volume pump or flow control valve keeps the rate of flow constant. In such a case the arithmetical unit could be supplied in advance with a value indicative of the rate of flow of the gas mixture predetermined by the constant-volume pump or flow control valve.

With an expired gas mixed with ambient air, the mixture can be arranged to have a low degree of humidity so as to help avoid the inner walls of connector pipes from becoming dewed with water droplets.

Clearly, if required, the apparatus may be arranged to measure the concentration of only one of the gases, carbon dioxide or oxygen.

Claims

1. Apparatus for measuring respiratory replacement and comprising a collector, locatable adjacent, but spaced from, the mouth and/or nose of a patient being examined, for taking in gases from the vicinity of the patient's mouth and/or nose, said gases including ambient atmospheric air and, at least during exhalation by the patient, gas expired by the patient means for drawing in said gases at a constant flow rate at all times, means for measuring the concentrations of carbon dioxide and/or oxygen in the expired gas based on said gases drawn at the constant rate via said collector, and means for computing the amount of carbon dioxide expired and/or the amount of oxygen taken by the patient in a predetermined period of time based on the results of the measurements in the measuring means and on the constant rate of flow of the gases.

2. Apparatus according to claim 1 wherein said constant flow rate drawing means comprises a constant-volume pump.

3. Apparatus according to claim 1 wherein said constant flow rate drawing means comprises a constant flow control valve and a pump.

4. Apparatus according to any one of the preceding claims wherein said measuring means comprise a carbon dioxide measurement analyzer and an oxygen measurement analyzer connected in parallel to the supply of gas collected.

5. Apparatus according to claim 4 wherein said computing means comprises a respective arithmetic unit connected to each of the analyzers.

6. Apparatus according to claim 5 wherein each arithmetic unit is pre-programmed with the value of the constant flow rate.

7. Apparatus according to any one of claims 1 to 5 wherein a flowmeter is arranged to indicate the constant flow rate.

8. Apparatus for measuring respiratory replacement and substantially as described herein with reference to Figs. 3 and 4 of the accompanying drawings.