fig1 schematically shows a high - end evaluation apparatus co - ts . the co - ts ( co - transfer simulator ) comprises a compartment 4 coupled to a conditioning unit 13 via an input connection tube 6 and an output connection tube 7 . conditioning unit 13 comprise a canister 1 , a sensor 12 , a pump 2 , a flow transducer 8 and a flow controller 9 . canister 1 , sensor 12 , flow transducer 8 and pump 2 are coupled in series between input connection tube 6 and an output connection tube 7 . canister 1 contains a material that dries the gas ( if necessary ) and eliminates all the co from the gas flowing through canister 1 . the co removing material may be moleculite ™ 403 for example and the drying material may be calcium chloride for example . in operation a gas - flow is sucked out of compartment 4 through connection tube 6 . this gas - flow is led through a canister 1 where the gas is dried ( if necessary ) and substantially all co from the gas is eliminated ( e . g . to less than 2 % of its original partial pressure ). the gas passes to co - sensor 12 , which is optionally provided to measure concentration of co - gas still remaining in the gas coming out of canister 1 . the sensor only functions to test the effectiveness of the material in canister 1 . when the co - ts is functioning properly the concentration value of co should be substantially zero . if not the material in canister 1 has lost its effectiveness after some time , this is indicated by sensor 12 , so that the material can be replaced . pump 2 provides flow through conditioning unit 13 . this flow is measured by means of a flow transducer 8 . the measured flow is used as input for flow controller 9 . flow controller regulates the flow of pump 2 to a pre - set value . a control input 10 may be provided to set this value by hand or by means of software in a control computer ( not shown ). from pump 2 , the gas is led back into the compartment 4 through output connection tube 7 . inside compartment 4 a fan 3 is provided to ensure of a proper mixing of the gas inside compartment 4 . an embodiment is shown wherein the compartment 4 is of type of which the volume can be changed . in the example shown in the figure , the volume can be changed by means of a servo - controlled piston , but alternatively compartment 4 may be partly or completely in the form of a bellows . the use of a compartment 4 with adjustable volume simulates breathing in and breathing out . in an embodiment a control computer ( not shown ) is provided to control the change of volume as a function of time . a sinusoidal volume cycle may be used for example , or any other volume as a function of time . by using a computer controlled patterns of changes these patterns of changes can be repeated accurately . the change of volume ( indicated by arrows 5 ) can also be performed by hand if the quality of the desired pattern is less important . trough a port 11 the co - ts is connected to the device under evaluation 14 . a control computer ( not shown ) may be configured to control the flow through the canister in relation to the value of the volume space in order to mimic the dependency of dlco of alveolar volume . if necessary flow controller 9 can be integrated in the control computer . the apparatus of fig1 simulates a co diffusion capacity of the lung that is equal to the flow rate realized by pump 2 . the simulated dlco equals v ′/( r * t ), wherein v ′ is the flow rate , r is the gas constant and t is absolute temperature . with flow rates of 3 - 30 liters per minute dlco &# 39 ; s from those for babies to those of athletes can be simulated . the dlco value can be set by setting flow rate , which makes it easy to calibrate dlco measurements of the measurement apparatus for different dlco values . there is no effect of inhalation and residue volumes and no reference gas supply is needed . it should be appreciated that this form of simulation enables reliable evaluation of all types of co diffusion measurement , including not only single breath measurement , but also the known multiple breath measurements , re - breathing and steady state methods to be used on patients breathing themselves or artificially ventilated . preferably , a plurality of measurements is performed at different flow rates to obtain verification of the measurement for different diffusion capacity values . this can be realized by adjusting the flow rate in different measurements , using flow controller 9 . in general , diffusion capacity in the natural lung increases when the volume of the lung increases , because lung surface area increases . therefore , it may be desirable to simulate a normalized diffusion capacity , which corresponds to a defined pattern of variation of diffusion capacity in correlation with volume of the lung . simulation of measurements of such a normalized diffusion capacity can be realized by making flow controller 9 increase the flow rate when the volume of compartment 4 increases and vice versa . at each point in time a flow rate that is a predetermined function ( e . g . a linear function ) of the volume at that point of time may be set for example . alternatively , both the volume changes and the flow rate may be controlled as predetermined functions of time . in this way , a more accurate evaluation of measurements of normalized diffusion capacity under natural breathing circumstances can be realized . fig2 shows a low - end solution for use in testing a single - breath ( sb ) measurement device . the normal procedure for the sb - measurement is as follows : a patient breaths normally ( phase i ), and subsequently a technician ask the patient to take a deep breath in until total lung capacity is reached ( phase ii ). thereafter during 10 seconds the breath is held ( phase iii ), after which an expiration follows ( phase iv ). in this case a much simpler embodiment of the co - ts can be used . the basics of this co - ts are the same but a much simpler conditioning is used . in this set - up there are a first , second and third valve 19 , 20 , 21 . the compartment 4 with piston can be connected to the device under test , output connection tube 7 or input connection tube 6 via first valve 19 , second valve 20 and third valve 21 , respectively . in most situations valve 19 is already incorporated in the device under test . during phase i and phase ii , the volume is connected to the device under test ( first valve 19 open and second and third valves 20 and 21 closed ). at the end of a simulated deep breath - in , first valve 19 is closed and third valve 21 is opened . then a predefined amount of gas is squeezed out of the compartment 4 , through the canister 1 into the volume space inside a bellows 17 by moving the piston in ( phase iii - a ). thereafter , the third valve 21 is closed and second valve 20 is opened , and the same amount of air is sucked out from the space inside bellows 17 back into the volume space ( number 4 ) by pulling the piston with the same amount ( phase iii - b ). then again second valve 20 is closed . thereafter first valve 19 is opened , where after expiration follows ( phase iv ). this procedure must be performed within the time - window between closing and opening of first valve 19 , e . g ., by performing phases iiia an iiib during ten seconds , which corresponds to the duration that the air remains breathed in a sb experiment . the amount of gas that is led through the canister is again a measure for the dlco . the inner volume of gas space of the cannister 1 and the connecting tubes 6 and 7 is preferably as small as possible . the volume of space inside bellows 17 is constructed such that it is as low as possible before phase iii - a is started . first valve 19 will be under control of the device under test . second and third valves 20 and 21 can be one - way valves that open in response to a small pressure differential in one direction . in the embodiment of fig2 the simulated dlco value depends on the volumes of compartment 4 and bellows 17 . if the initial volume of compartment 4 equals v 0 and the volume with simulated inhaled air v 1 (= v 0 + vi ). the volume change of bellows 17 is designated by vp . in this case the co concentration in exhaled air is reduced by a factor rco = vi / v 1 *( v 1 − vp )/ v 1 and the inert gas concentration is reduced by a factor rig = vi / v 1 . these factors are substituted in eq ( 1 ) of the sb - method . hence the simulated dlco value is different dlco values can be set by selecting different values of v 1 and vp , for example by varying the extent to which bellows 17 is extended , or by selecting the initial position of the piston . as will be appreciated the results of the measurements of both apparatus can be used to decide whether the apparatus functions properly . in a further embodiment the results of such evaluation measurements can be compiled into a calibration factor or a calibration table to calibrate operating parameters of the apparatus for measuring dlco . for example , output signals of a gas analyser in the apparatus for measuring dlco could be calibrated directly , or as part of the overall apparatus for measuring dlco , by determining calibration values that are needed to obtain a predicted dlco value given a simulated diffusion capacity value realized with a flow rate used during calibration . this may be repeated for different flow rates in order to obtain a calibration table in the case of a non - linear response ; but in some cases a single measurement may suffice to define a calibration factor . such calibration data may be programmed into the dlco measurement apparatus for conversion of measurement results during subsequent use with one or more persons , for example during a predetermined time period ( such as a day or a week ). alternatively , a written table for use by an operator may be generated for example . in a further embodiment calibration data may be gathered for a variety of breathing conditions , so that breathing condition dependent corrections to computed dlco values can be provided . in this way , no conditions need to be imposed on the way of breathing of the person under investigation . thus for example , measurements are possible on a person that is unconscious or otherwise incapable of following instructions . in a further alternative , the calibration may be performed for a single person at a time , the pattern of volume changes , setting flow rates , flow rate changes in correlation volume changes etc . until they correspond to those of the person under investigation .
a method of evaluating a measuring device for measuring , in normal operation , a diffusion capacity of a person &# 39 ; s lungs by measuring a change of concentration of a gas species in a mixture , when the mixture is inhaled and subsequently exhaled by the person or imposed by an artificial ventilator , the method comprising the steps of : receiving the mixture in a compartment ; circulating gas from the compartment back to the compartment through a circulation circuit ; and selectively reducing partial pressure of the gas species in the circulation circuit to a predetermined level . a device for implementing the evaluation method is also disclosed .