Gas Exchange Score with VE/VCO2 and ETCO2 Reliably Predicts Pulmonary Vascular Disease in Suspected Pulmonary Hypertension

Abstract

Introduction Non-invasive methods to identify phenotype of pulmonary hypertension (PH) remains a topic of interest. Cardiopulmonary exercise test (CPET) provides gas exchange (GX) parameters including end-tidal carbon dioxide (ETCO2) and ventilation of minute ventilation to carbon dioxide ventilation ratio (VE/VCO2). A direct correlation of these GX parameters with invasive hemodynamics can provide further insight into the ability of GX parameters to predict PH phenotype. Hypothesis Using a direct correlation of gas exchange parameters with invasive hemodynamics, we propose that in subjects with suspected PH, rest gas exchange parameters can reliably predict pulmonary vascular disease. Methods We reviewed clinical, echocardiographic and invasive CPET (iCPET) data for 41 patients. We then analyzed the data with receiver operator curve (ROC) to help estimate the area under the curve (AUC) of different gas exchange parameters to help define the hemodynamics of different PH groups and derive the most appropriate parameters to define PH. *p Results Among the overall cohort, mean age (± SD) was 63.9±11.35 years, and 20 subjects were female (49 %). The distribution of WHO groups of PH based on the final diagnosis among the overall cohort was: 8 patients WHO group I (19.5%), 21 patients WHO group II (51.2%), 3 patients WHO group III (7.3%), 1 patient WHO group IV (2.4%), and 8 patients had no evidence of rest or exercise PH (19.5%). For the purpose of analysis, we created three groups: 1) pulmonary vascular disease (PVD): combination of WHO group I, III and IV, 2) pulmonary venous hypertension (PVH): WHO group II, 3) Control: no PH group. On ROC analysis, rest and exercise ETCO2 and VE/VCO2 had equally high predictive ability to predict exercise PVR > 3 WU (rest ETCO2=0.806, exercise ETCO2=0.880, rest VE/VCO2=0.794, exercise VE/VCO2=0.820). Similar pattern of ETCO2 and VE/VCO2 was identified with prediction of rest PVR >3WU and WHO group I PAH. Based on the ROC analysis, we found that the ideal cutoffs (to predict rest PVR>3WU or exercise PVR>3WU or PVD group) were ≤30 mmHg for ETCO2 and ≥42 for VE/VECO2.Using these cutoffs, we created a scoring system of “rest-only” GX parameters (+1 for ETCO2 ≤30 and VE/VCO2 ≥42; and -1 for vice versa). Each patient would have a total score of -2, 0 or +2. The AUC for this rest-only scoring system to predict exercise PVR >3WU was 0.841. When applied to the whole cohort, score of -2 (n=14) included: 8 PVH and 5 with no PH, score of +2 (n=11) included 6 PVD (percentages shown in figure). Conclusions Among individuals with suspected PH, a composite gas exchange score with VE/VCO2 (≥42) and ETCO2 (≤30 mmHg) reliably predicts PVD.