Associated parameter measuring and/or monitoring such as in the evaluation of pressure differences

• US 6,526,357 B1
• Filed: 08/01/2000
• Issued: 02/25/2003
• Est. Priority Date: 08/09/1999
• Status: Expired due to Term

• Current Assignee: Gambro Renal Products, Inc. (Baxter International Inc.)
• Original Assignee: Gambro, Inc. (DaVita Incorporated)
• Inventors: Miller, Douglas P., Soussan, Daniel A.
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): Sun, Xiuqin
• Application Number:
  US09/631,204
• Time in Patent Office: 938 Days
• Field of Search: 604/65, 364/509, 702/45, 733/04, 222/15
• US Class Current: 702/45
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1609 after use, i.e. downstream of dialyser
• CPC Class Codes: A61M 1/3496 Plasmapheresis; Leucopheresis; Lymphopheresis A61M1/3472 takes precedence
• CPC Class Codes: A61M 1/3639 Blood pressure control, pressure transducers specially adapted therefor
• CPC Class Codes: A61M 1/3641 Pressure isolators
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2205/705 Testing of filters for leaks
• CPC Class Codes: G01L 27/002 Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination

Abstract

Correction quantities are generated for yielding closer approximations of actual parameters. These are obtained by preliminarily subjecting parametric transducers to pre-selected parametric values and recording the measured values for each transducer in a data table for later use as or in correction quantities. An embodiment includes interpolation relative to data table values closest to the operationally measured parametric value and using the resulting interpolated value as a corrected parametric value. Such interpolations may be performed for two parametric transducers relative to two substances. The resulting corrected parametric values may then be subtracted to obtain a parametric difference. A further embodiment may include using correction quantities of a reference parametric transducer in interpolation calculations for the actual parametric transducers. Similarly, other data table correction recordations such as differences between two measured parameters can be used to modify an operationally measured parametric differential. Reference transducer corrections can be used here as well.

Claims

1. A method for determining a parametric difference between first and second fluids in a fluid system, said fluid system having a first and a second fluid container each containing one of the respective first and second fluids, the first fluid container having a first parametric transducer operatively associated therewith, the second fluid container having a second parametric transducer operatively associated therewith, the method comprising the steps of:

a) subjecting the first and second transducers to a pre-selected parametric value;

b) recording in a data table the respective first and second parametric measurements measured by the first and second transducers as a result of being subjected to said pre-selected parametric value, and calling these parametric measurements recorded correction quantities;

c) repeating the above steps a) and b) for a set of pre-selected parametric values;

d) exposing the respective first and second transducers to the respective first and second fluids in the first and second fluid containers in operation; and

e) calculating the operational parametric difference as follows;

1) measuring the first and second operational parametric values;

2) locating in the data table the recorded correction quantities closest to the first and second operationally measured parametric values;

3) converting the operationally measured parametric values into first and second corrected parametric values to find the parametric difference according to;

parametric difference=first corrected parametric value−

second corrected parametric value.

2. A method according to claim 1 wherein the substep of converting the operationally measured parametric values includes using single point interpolation in which the first corrected parametric value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest recorded correction quantities, hereafter called F_a1, F_m1, thereto, by the relation:

$F_{\mathrm{ax}}=F_{\mathrm{mx}}·<br><br>\frac{\left(F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m1}}\right)};<br><br>$

and, the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the closest recorded correction quantities, hereafter called W_a2, W_m2, thereto, by the relation;

$W_{\mathrm{ay}}=W_{\mathrm{my}}·<br><br>\frac{\left(W_{\mathrm{a2}}\right)}{\left(W_{\mathrm{m2}}\right)}.$

3. A method according to claim 1 wherein the substep of converting the operationally measured parametric values includes using two point interpolation in which the first corrected parametric value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest sets of recorded correction quantities, hereafter called F_a1, F_m1, and F_a2, F_m2, thereto, by the relation:

$F_{\mathrm{ax}}=F_{\mathrm{mx}}·<br><br>\frac{\left(F_{\mathrm{a2}}-F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)};<br><br>$

and, the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest sets of recorded correction quantities, hereafter called W_a3, W_m3, and W_a4, W_m4, thereto, by the relation;

$W_{\mathrm{ay}}=W_{\mathrm{my}}·<br><br>\frac{\left(W_{\mathrm{a4}}-W_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}.$

4. A method according to claim 1 wherein the substep of converting the operationally measured parametric values includes using two point interpolation in which the first corrected parametric value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest sets of recorded correction quantities, hereafter called F_a1, F_m1, and F_a2, F_m2, thereto, by the relation:

$F_{\mathrm{ax}}=\frac{\left(F_{\mathrm{a2}}-F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)}·<br><br>\left(F_{\mathrm{mx}}-F_{\mathrm{m1}}\right)+F_{\mathrm{a1}};<br><br>$

and, the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest sets of recorded correction quantities, hereafter called W_a3, W_m3, and W_a4, W_m4, thereto, by the relation;

$W_{\mathrm{ay}}=\frac{\left(W_{\mathrm{a4}}-W_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}·<br><br>\left(W_{\mathrm{my}}-W_{\mathrm{m3}}\right)+W_{\mathrm{a3}}.$

5. A method according to claim 1 wherein a third parametric transducer is disposed in operative position relative to one of the first and second fluid compartments, wherein the substep of subjecting the first and second transducers to a pre-selected parametric value also includes subjecting the third transducer to said pre-selected parametric value, and said substep of recording in a data table the respective first and second parametric measurements further includes recording the parametric measurement of said third transducer as a result of being subjected to said pre-selected parametric value, and said sub-step of repeating further includes repeating for the first two steps for a set of pre-selected parametric values for the third transducer as well;

wherein the measurements of the third parametric transducer are used as reference correction quantities; and

wherein the substep of converting the operationally measured parametric values includes using two point interpolation in which the first corrected value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest sets of recorded correction quantities, hereafter called R_a1, F_m1, and R_a2, F_m2, thereto (R_a1 and R_a2 being the reference correction quantities from the third transducer), by the relation;

$F_{\mathrm{ax}}=\frac{\left(R_{\mathrm{a2}}-R_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)}·<br><br>\left(F_{\mathrm{mx}}-F_{\mathrm{m1}}\right)+R_{\mathrm{a1}};<br><br>$

and, the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest sets of recorded correction quantities, hereafter called R_a3, W_m3, and R_a4, W_m4, thereto (R_a3 and R_a4 being the reference correction quantities from the third transducer), by the relation;

$W_{\mathrm{ay}}=\frac{\left(R_{\mathrm{a4}}-R_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}·<br><br>\left(W_{\mathrm{my}}-W_{\mathrm{m3}}\right)+R_{\mathrm{a3}}.$

6. A method according to claim 1 wherein the substep of converting the operationally measured parametric values includes using an added correction element, hereafter called C_s1, in which the first corrected parametric value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest set of recorded correction quantities, hereafter called F_m1 and W_m1, thereto, by the relation:

7. A method according to claim 6 wherein the substep of converting the operationally measured parametric values further includes using a second added correction element, hereafter called C_s2, in which the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the closest recorded correction quantities, hereafter called F_m2 and W_m2, thereto, by the relation:

8. A method according to claim 1 wherein a third parametric transducer is disposed in operative position relative to one of the first and second fluid containers, wherein the substep of subjecting the first and second transducers to a pre-selected parametric value also includes subjecting the third transducer to said pre-selected parametric value, and said substep of recording in a data table the respective first and second parametric measurements further includes recording the parametric measurement of said third transducer as a result of being subjected to said pre-selected parametric value, and said sub-step of repeating these first two steps further includes repeating for the first two steps for a set of pre-selected parametric values for the third transducer as well;

wherein the measurements of the third parametric transducer are used as reference correction quantities; and

wherein the substep of converting the operationally measured parametric values includes using an added correction quantity in which the first corrected parametric value, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest recorded correction quantities, hereafter, R_a1, F_m1, thereto (R_a1=R_m1, being the reference correction quantities from the third transducer), by the relation;

9. A method according to claim 8 wherein the second corrected parametric value, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the closest recorded correction quantities, hereafter called R_a3, W_m3, thereto (R_a3=R_m3 being the reference correction quantities from the third transducer), by the relation:

10. A method for measuring a parametric difference in a fluid system which has a first and a second flow channel separated by a semi-permeable membrane, the first fluid channel having a first parametric transducer operatively associated therewith, the second fluid channel having a second parametric transducer operatively associated therewith, the method comprising the steps of:

preliminary to actual use;

a) subjecting the first and second transducers to a pre-selected parametric value;

b) recording in a data table the pre-selected parametric value and the corresponding first and second parametric measurements measured by the respective first and second transducers and calling the recorded parametric value and at least one of the corresponding parametric measurements a set of correction quantities;

c) repeating the above steps a) and b) for a set of pre-selected parametric values; and

, during actual use;

d) exposing the respective first and second transducers to respective first and second fluids in the first and second fluid channels; and

e) calculating the parametric difference as follows;

1) measuring the first and second operational parametric values;

2) locating in the data table the respective sets of correction quantities closest to the respective operationally measured parametric values;

3) using interpolation to convert the operationally measured parametric values into first and second corrected parametric quantities to find the parametric difference according to;

11. A method according to claim 10 wherein the substep of using interpolation to convert the operationally measured parametric values includes using single point interpolation in which the first corrected quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest recorded set of correction quantities, hereafter called F_a1, F_m1, thereto, by the relation:

$F_{\mathrm{ax}}=F_{\mathrm{mx}}·<br><br>\frac{\left(F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m1}}\right)};<br><br>$

and, the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the closest recorded set of correction quantities, hereafter called W_a2, W_m2, thereto, by the relation;

$W_{\mathrm{ay}}=W_{\mathrm{my}}·<br><br>\frac{\left(W_{\mathrm{a2}}\right)}{\left(W_{\mathrm{m2}}\right)}.$

12. A method according to claim 10 wherein the substep of using interpolation to convert the operationally measured parametric values includes using two point interpolation in which the first corrected parametric quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest recorded sets of correction quantities, hereafter called F_a1, F_m1, and F_a2, F_m2, thereto, by the relation:

$F_{\mathrm{ax}}=F_{\mathrm{mx}}·<br><br>\frac{\left(F_{\mathrm{a2}}-F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)};<br><br>$

and, the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest recorded sets of correction quantities, hereafter called W_a3, W_m3, and W_a4, W_m4, thereto, by the relation;

$W_{\mathrm{ay}}=W_{\mathrm{my}}·<br><br>\frac{\left(W_{\mathrm{a4}}-W_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}.$

13. A method according to claim 10 wherein the substep of using interpolation to convert the operationally measured parametric values includes using two point interpolation in which the first corrected parametric quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest recorded sets of correction quantities, hereafter called F_a1, F_m1, and F_a2, F_m2, thereto, by the relation:

$F_{\mathrm{ax}}=\frac{\left(F_{\mathrm{a2}}-F_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)}·<br><br>\left(F_{\mathrm{mx}}-F_{\mathrm{m1}}\right)+F_{\mathrm{a1}};<br><br>$

and, the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest recorded sets of correction quantities, hereafter called W_a3, W_m3, and W_a4, W_m4, thereto, by the relation;

$W_{\mathrm{ay}}=\frac{\left(W_{\mathrm{a4}}-W_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}·<br><br>\left(W_{\mathrm{my}}-W_{\mathrm{m3}}\right)+W_{\mathrm{a3}}.$

14. A method according to claim 10 wherein a third parametric transducer is disposed in operative position relative to one of the first and second fluid channels, wherein the substep of subjecting the first and second transducers to a pre-selected parametric value also includes subjecting the third transducer to said pre-selected parametric value, and said substep of recording in a data table the respective first and second parametric measurements further includes recording the parametric measurement of said third transducer as a result of being subjected to said pre-selected parametric value, and said sub-step of repeating the first two steps further includes repeating the first two steps of subjecting and recording for the set of pre-selected parametric values for the third transducer as well;

wherein the measurements of the third parametric transducer are used as reference correction quantities; and

wherein the substep of using interpolation to convert the operationally measured parametric values includes using two point interpolation in which the first corrected quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the two closest sets of recorded correction quantities, hereafter called R_a1, F_m1, and R_a2, F_m2, thereto (R_a1 and R_a2 being the reference correction quantities from the third transducer), by the relation;

$F_{\mathrm{ax}}=\frac{\left(R_{\mathrm{a2}}-R_{\mathrm{a1}}\right)}{\left(F_{\mathrm{m2}}-F_{\mathrm{m1}}\right)}·<br><br>\left(F_{\mathrm{mx}}-F_{\mathrm{m1}}\right)+R_{\mathrm{a1}};<br><br>$

and, the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest sets of recorded correction quantities, hereafter called R_a3, W_m3, and R_a4, W_m4, thereto (R_a3 and R_a4 being the reference correction quantities from the third transducer), by the relation;

$W_{\mathrm{ay}}=\frac{\left(R_{\mathrm{a4}}-R_{\mathrm{a3}}\right)}{\left(W_{\mathrm{m4}}-W_{\mathrm{m3}}\right)}·<br><br>\left(W_{\mathrm{my}}-W_{\mathrm{m3}}\right)+R_{\mathrm{a3}}.$

15. A method according to claim 14 wherein the substep of using interpolation includes using the third transducer measurements as reference correction quantities in a two point interpolation such that:

F_m1=the closest lower correction quantity associated with F_mx;

F_m2=the closest upper correction quantity associated with F_mx;

R_m1=the third transducer correction quantity that corresponds to F_m1;

R_m2=the third transducer correction quantity that corresponds to F_m2; and

by linear interpolation, $F_{\mathrm{ax}}=\frac{R_{\mathrm{m2}}-R_{\mathrm{m1}}}{F_{\mathrm{m2}}-F_{\mathrm{m1}}}·<br><br>\left(F_{\mathrm{mx}}-F_{\mathrm{m1}}\right)+R_{\mathrm{m1}};<br><br>\text{\hspace{1em}<br><br>}<br><br>\text{and},$

 

W_m3=the closest lower correction quantity associated with W_my;

W_m4=the closest upper correction quantity associated with W_my;

R_m3=the third transducer correction quantity that corresponds to W_m3;

R_m4=the third transducer correction quantity that corresponds to W_m4; and

by linear interpolation, $W_{\mathrm{ay}}=\frac{R_{\mathrm{m4}}-R_{\mathrm{m3}}}{W_{\mathrm{m4}}-W_{\mathrm{m3}}}·<br><br>\left(W_{\mathrm{my}}-W_{\mathrm{m3}}\right)+R_{\mathrm{m3}}.$

16. A method for measuring a parametric difference in a fluid system which has a first and a second flow channel separated by a semi-permeable membrane, the first fluid channel having a first parametric transducer operatively associated therewith, the second fluid channel having a second parametric transducer operatively associated therewith, the method comprising the steps of:

preliminary to actual use;

a) subjecting the first and second transducers to a pre-selected parametric value;

b) recording in a data table the respective first and second parametric measurements measured by the first and second transducers and calling these parametric measurements a set of correction quantities;

c) repeating the above steps a) and b) for a set of pre-selected parametric values; and

, during actual use;

d) exposing the respective first and second transducers to respective first and second fluids in the first and second fluid channels; and

e) calculating the parametric difference as follows;

1) measuring the first and second operational parametric values;

2) locating in the data table the first and second sets of correction quantities closest to the respective operationally measured parametric values;

3) using the located first and second sets of correction quantities to convert the operationally measured parametric values into first and second corrected parametric quantities to find the parametric difference according to;

17. A method according to claim 16 wherein the substep of converting the operationally measured parametric values includes using an added correction element, hereafter called C_s1, in which the first corrected parametric quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest set of recorded correction quantities, hereafter called F_m1 and W_m1, thereto, by the relation:

18. A method according to claim 17 wherein the substep of converting the operationally measured parametric values further includes using a second added correction element, hereafter called C_s2, in which the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the closest recorded set of correction quantities, hereafter called F_m2, and W_m2, thereto, by the relation:

19. A method according to claim 16 wherein a third parametric transducer is disposed in operative position relative to one of the first and second fluid channels, wherein the substep of subjecting the first and second transducers to a pre-selected parametric value also includes subjecting the third transducer to said pre-selected parametric value, and said substep of recording in a data table the respective first and second parametric measurements further includes recording the parametric measurement of said third transducer as a result of being subjected to said pre-selected parametric value, and said sub-step of repeating these first two steps further includes repeating for the first two steps for a set of pre-selected parametric values for the third transducer as well;

wherein the measurements of the third parametric transducer are used as reference correction quantities; and

wherein the substep of converting the operationally measured parametric values includes using an added correction element in which the first corrected parametric quantity, hereafter called F_ax, is related to the first operationally measured parametric value, hereafter called F_mx, relative to the closest recorded correction quantities, hereafter, R_a1, F_m1, thereto (R_a1=R_m1 being the reference correction quantities from the third transducer), by the relation;

20. A method according to claim 19 wherein the second corrected parametric quantity, hereafter called W_ay, is related to the second operationally measured parametric value, hereafter called W_my, relative to the two closest sets of recorded correction quantities, hereafter called R_a3, W_m3, thereto (R_a3=R_m3 being the reference correction quantities from the third transducer), by the relation:

21. A method for measuring a trans-membrane pressure (TMP) in a system which has a first and a second flow channel separated by a semi-permeable membrane, the first flow channel having a filter pressure transducer operatively associated therewith on the upstream side of the first flow channel and a return pressure transducer operatively associated therewith on the downstream side of the first flow channel, the second flow channel having an effluent pressure transducer operatively associated therewith, the filter, effluent and return pressure transducers each having a transducer side and an opposing fluid side, the transducer sides being adapted to be exposed to controlled pressurizations through connection to a compressed fluid circuit which includes a compressed fluid source, the method comprising the steps of:

a) opening exposure of the filter, effluent, and return transducers to communication with the compressed fluid circuit;

b) using the return transducer as the standard, applying a controlled pressurization to the transducer sides of the filter, effluent and return transducers to minus 50 mmHg.;

c) allowing the applied pressurization to stabilize;

d) recording in a data table the measured filter pressure value, measured effluent pressure value, and measured return pressure value;

calling these pressure values correction pressure quantities;

e) repeating the above steps a) through d) for applied pressurizations of 0, +50, +100, +150, +200, +250, +300, +350, +400, +450 mmHg.;

f) closing off communication of the transducers with the compressed fluid circuit;

the g) exposing the respective transducers to respective first and second fluid flows in the first and second fluid flow channels; and

h) calculating the trans-membrane pressure, hereafter referred to as the TMP, as follows;

1) measuring an operational filter pressure value;

2) locating in the data table the two filter correction pressure quantities closest to the measured operational filter pressure value;

3) using interpolation to convert the measured operational filter pressure value into a Corrected Filter Pressure according to;

F_lx the closest recorded lower filter correction pressure quantity;

F_u=the closest recorded upper filter correction pressure quantity;

F_Fl=the return correction pressure quantity that corresponds to the lower filter correction pressure quantity;

R_Fu=the return correction pressure quantity that corresponds to the upper filter correction pressure quantity; and

, $\text{Corrected Filter Pressure}=\frac{R_{\mathrm{Fu}}-R_{\mathrm{F1}}}{F_u-F_1}·<br><br>\left(\text{Measured Filter Pressure}-F_1\right)+R_{\mathrm{F1}};<br><br>$

and

4) measuring an operational effluent pressure value;

5) locating in the data table the two effluent correction pressure quantities closest to the measured operational effluent pressure value;

6) using interpolation to convert the measured operational effluent pressure value into a Corrected Effluent Pressure according to;

E_l=the closest recorded lower effluent correction pressure quantity;

E_u=the closest recorded upper effluent correction pressure quantity;

R_El=the return correction pressure quantity that corresponds to the lower effluent correction pressure quantity;

R_Eu=the return correction pressure quantity that corresponds to the upper effluent correction pressure quantity; and

, $\text{Corrected Effluent Pressure}=\frac{R_{\mathrm{Eu}}-R_{\mathrm{E1}}}{E_u-E_1}·<br><br>\left(\text{Measured Effluent Pressure}-E_1\right)+R_{\mathrm{E1}};<br><br>$

and

7) using the Corrected Filter Pressure and the Corrected Effluent Pressure to calculate the TMP as follows;

22. A method for measuring a trans-membrane pressure (TMP) in a system which has a first and a second flow channel separated by a semipermeable membrane, the first flow channel having a filter pressure transducer operatively associated therewith on the upstream side of the first flow channel and a return pressure transducer operatively associated therewith on the downstream side of the first flow channel, the second flow channel having an effluent pressure transducer operatively associated therewith, the filter, effluent and return pressure transducers each having an air side and an opposing measured fluid side, the air sides being adapted to be exposed to controlled pressurizations through connection to a compressed air circuit which includes a compressed air source, the method comprising the steps of:

a) opening exposure of the filter, effluent, and return transducers to communication with the compressed air circuit;

b) using the return transducer as the standard, applying a pressurization to the air sides of the filter, effluent and return transducers to minus 50 mmHg.;

c) allowing the applied pressurization to stabilize;

d) recording in a data table the measured filter pressure value, measured effluent pressure value, and measured return pressure value;

calling these pressure values correction pressure quantities;

e) repeating the above steps a) through d) for air pressures of 0, +50, +100, +150, +200, +250, +300, +350, +400, +450 mmHg.;

f) closing off communication of the transducers with the compressed fluid circuit;

g) exposing the transducers to respective first and second fluid flows in the first and second fluid flow channels; and

h) calculating the trans-membrane pressure, hereafter the TMP, as follows;

1) measuring an operational filter pressure value;

2) locating in the data table the filter correction quantities closest to the operationally measured filter pressure value;

3) using an added correction element to convert the measured filter pressure value into a Corrected Filter Pressure according to;

F_mx=the operationally measured filter pressure value;

F_m1=the closest recorded filter correction pressure quantity;

R_mx=the return pressure value that corresponds to the operationally measured filter pressure value;

R_m1=the return pressure correction quantity that corresponds to the closest recorded filter correction pressure quantity; and

,

Corrected Filter Pressure=; and