Pulmonary Physiology |

Use of Transcutaneous Measurement of PaCO2 in Determining Dead Space Ventilation During Exercise in Patients with COPD; a Pilot Study FREE TO VIEW

Robert Cao, MD; William Stringer, MD; Janos Porszasz, PhD
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LABioMed, Torrance, CA

Chest. 2015;148(4_MeetingAbstracts):901A. doi:10.1378/chest.2258702
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SESSION TITLE: Pulmonary Physiology Posters

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 28, 2015 at 01:30 PM - 02:30 PM

PURPOSE: Cardiopulmonary exercise testing equipment estimates VD/VT based on PETCO2.In emphysema the A-a gradient for pCO2 is widening leading to false determination of PaCO2. The purpose of this pilot study was to test whether using tcPCO2 (TOSCA500, Radiometer) as surrogate to PaCO2 leads to a better estimation of dead space ventilation.

METHODS: Ten moderate to severe COPD patients (age:68 ± 10yrs, FEV1:34 ± 12%predicted,range 20-58% and FEV1/FVC:0.30 ± 0.07, range 0.23-0.42) completed a 5W/min incremental exercise test to the limit of tolerance on a cycle-ergometer. Respiratory gas exchange (VE, VO2 and VCO2) was measured breath-by-breath (Vmax Spectra,Carefusion) and the ventilatory equivalent for CO2 (VE/VCO2) was calculated. Arterialized capillary pCO2 was determined by heated combined electrode (TOSCA500,Radiometer) capable also measuring sPO2 (Masimo, SET) from earlobe and adequate time (about 10 minnutes) was allowed for the signals to stabilize. The estimated (VD/VTest using PETCO2) and the calculated VD/VT (VD/VTcalc using tcPCO2, Eq.1) was averaged at rest, unloaded cycling, at the lactate threshold and at peak exercise. VD/VT=1-863/(PaCO2*VE/VCO2) (Eq.1)

RESULTS: PETCO2 rose significantly during exercise, but the difference between PETCO2 and tcPCO2 remained significant. The VE/VCO2 was high at rest and did not fall below 30 even at peak exercise. Both the estimated and calculated VD/VT decreased during exercise; however VD/VTcalc was consistently and significantly higher at all levels of exercise. Six out of ten subjects decreased spO2 below 89% at peak exercise. Work Rate(Watts) VO2(L/min) VE(L/min) PETCO2(mmHg) tcPCO2(mmHg) VE/VCO2 VD/VTET(%) VD/VTtc(%) Rest n/a 0.32 ± 0.09 14 ± 2 34.7 ± 6.0 47.2 ± 9.3 52 ± 11 41 ± 5 61 ± 10 UL n/a 0.50 ± 0.12 19 ± 4 36.4 ± 5.4 47.1 ± 8.5 44 ± 8 37 ± 4 56 ± 9 LT 19 ± 10 0.65 ± 0.11 23 ± 5 38.1 ± 6.3 46.9 ± 7.9 39 ± 7 34 ± 2 54 ± 7 Peak 46 ± 22 0.93 ± 0.3 30 ± 7 41.2 ± 8.0 46.8 ± 7.0 35 ± 7 31 ± 4 47 ± 13

CONCLUSIONS: Using transcutaneously determined pCO2 as surrogate to PaCO2 in the calculation of VD/VT resulted in a remarkably higher VD/VT throughout rest and exercise.

CLINICAL IMPLICATIONS: Nonivasive estimation of VD/VT using tcPCO2 might serve a better diagnosis of the gas exchange inefficiency during exercise in COPD. However, confirmation is needed by direct arterial blood gas measurements.

DISCLOSURE: The following authors have nothing to disclose: Robert Cao, William Stringer, Janos Porszasz

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