Transcript CPET
What is the difference between - EQCO2 - VE/VCO2 – slope Dr. Hermann Eschenbacher Sr. Product Manager Marketing Department RDx March 11, 2015 © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Important parameter definitions BF - Breathing frequency VT - Tidal volume VE - Minute ventilation (expiratory) VI - Minute ventilation (inspiratory) VO2 - Oxygen uptake EQO2 - Breathing or ventilatory equivalent O2 VCO2 - Carbon dioxide production (ml/min) EQCO2 - Breathing or ventilatory equivalent CO2 VDf - Functional dead space VDs - System dead space © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Breathing Equivalents (1) VO2 ~ VI * FIO2 – VE * FEO2 VCO2 ~ VE * FECO2 – VI * FICO2 The effectiveness of the gas exchange can be estimated via the breathing equivalents: EQO2 = VE – BF * VDs VO2 EQCO2 = VE – BF * VDs VCO2 Note 1: The correction (BF*VDs) eliminates the system dependency of these parameters from the used apparatus dead space Note 2: “~” due to the fact, that VI and VE are in [BTPS], VO2 and VCO2 in [STPD] © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Breathing Equivalents (2) In a lot of publications the graphs are indicated as VE/VCO2, and also the values are the mentioned as VE/VCO2-ratio. However mathematically this is not correct, as EQO2 EQCO2 VE VO2 VE VCO2 My recommendation: Do not use VE/VCO2, use EQCO2 !! Comment: Several times a year I get the following complaint: “If I calculate VE/VCO2 directly, I do not get the same result as “your” EQCO2 – so there seems to be a bug in your software!” – see above !! © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Breathing Equivalents (3) Two examples for the EQO2 / EQCO2: Normal Increased © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. VDf & Gas exchange VO2, VCO2 ~ VE But: VE = VAlv + Gas exchange VDf no gas exchange That means, both cases – an increased dead space or a reduced diffusion – will lead to higher ventilations and therefore to increased EQO2 and EQCO2. For a further differentiation blood gases may help: With blood gases (PaO2, PaCO2): VDf and VDf / VT: => Dead space P(A-a)O2: => Diffusion © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Ventilatory Demand (1) The question is: Can we get further info from the CPET - data without blood gases, e.g. what is the difference between Panel 4 and © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Panel 6 Ventilatory Demand (2) As VE is normally driven by VCO2, we can assume that VE increases proportional with VCO2 plus an additional component to overcome the functional dead space VDf: VE = m * VCO2 + VDf * BF VE = m * VCO2 + c or (assuming VDf*Bf is almost constant): m VE = m * VCO2 + c which leads to a linear dependency in panel 4 c © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Ventilatory Demand (3) It was VE = m * VCO2 + c Dividing both sides by VCO2 leads to the EQCO2: EQCO2 = m + c / VCO2 which means, that • the offset c is mainly representing the dead space ventilation • EQCO2 is not directly representing the slope • EQCO2 ≈ m only for high VCO2 and small VDf © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Ventilatory Demand (4) Converting from panel 4 to panel 6: 15 0.5 10 0.2 23 1.0 32 1.5 41,5 2.0 50.5 2.5 59.5 3.0 68 3.5 m © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Ventilatory Demand (5) Converting two different cases from panel 4 to panel 6: m m Both EQCO2 have similar shapes and similar values at end of the test, however completely different slopes and offsets !! © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Ventilatory Demand (6) VO2, VCO2 ~ VE But: VE = Valv + VD gas exchange EQCO2 Slope = no gas exchange VE VCO2 = Valv + VD VCO2 VE VCO2 = Valv + VD VCO2 Assumption: VD = k That means: The slope mainly describes the influence of the gas exchange, while the offset is related more to dead space ventilation! © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Model calculation 100 120,0 EQCO2 90 P4 100,0 80,0 P6 80 70 Low diffusion 60 m = 25 60,0 50 VA+VD 40 40,0 30 20 20,0 10 0,0 0 0 0,5 1 1,5 2 2,5 3 0 0,4 0,8 1,2 1,6 2 2,4 2,8 1 Increased slope 100 120,0 EQCO2 90 100,0 P4 80 P6 70 80,0 High dead space 60 m = 25 60,0 VA+VD 50 40 40,0 30 20 20,0 10 0,0 0 0,5 1 1,5 2 2,5 3 0 0,8 1,2 1,6 2 Increased offset © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. 2,4 2,8 1,2 Summary • Do not use “VE/VCO2 – ratio”, use EQCO2 • The nadir (minimum) of EQCO2 does not exactly represent the VE/VCO2-slope • You always should consider all 3 values: • EQCO2 • VE/VCO2 – slope • VE/VCO2 – offset Final comment: Even I made these calculations already in 1999 and mentioned this in the VIASYS-Info (2002) as well, it took more then 10 years until the first poster in this respect was presented on the ERS in 2014. It also was mentioned by Agostoni in our last CPET-AG-meeting 2015 © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Questions? © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Thank you © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved. Vyntus, CareFusion and the CareFusion logo are trademarks or registered trademarks of CareFusion Corporation or one of its subsidiaries. All other trademarks are the property of their respective owners. © 2015 CareFusion Corporation or one of its subsidiaries. All rights reserved.