Variation of PetCO 2 during incremental exercise and severity of IPAH and CTEPH

Background and objective End-tidal PCO 2 (PetCO 2 ) patterns during exercise testing as well as ventilatory equivalents for CO 2 have been reported for different pulmonary vascular diseases but seldomly for the significant differences in exercise response depending on the etiology of pulmonary hypertension. We aimed to compare PetCO 2 change pattern in IPAH and CTEPH with varying severity during incremental cardiopulmonary exercise testing (CPET). Methods 164 IPAH patients and 135 CTEPH patients referred to Shanghai Pulmonary Hospital between 2012 and 2019 were retrospectively recruited into the study. All patients performed CPET and also underwent right-heart catheterization (RHC). Forty-four healthy subjects also performed CPET and were included as controls. Results PetCO 2 was significantly lower in IPAH and CTEPH patients as compared to normal subjects. Moreover, the PetCO 2 did not rise, in fact fell from rest to anaerobic threshold (AT), then further decreased until peak in both IPAH and CTEPH. PetCO 2 value at rest, unloaded, AT and peak were proportionately reduced as the World Health Organization functional class (WHO-Fc) increased in both IPAH and CTEPH patients. The PETCO 2 in IPAH patients had significant differences during all phases of exercise between WHO-Fc I-II and III-IV subgroup. CTEPH also demonstrated significant difference except for PetCO 2 at peak. PetCO 2 values were significantly higher in IPAH during all phases of exercise as compared to CTEPH patients (all P < 0.001). PeakVO 2 %pred correlated significantly with PetCO 2 at rest (r = 0.477, P < 0.001), AT (r = 0.609, P < 0.001) and peak exercise (r = 0.576, P < 0.001) in IPAH. N-terminal natriuretic peptide type-B (NT-proBNP) also correlated markedly with PetCO 2 , with a correlation coefficient of − 0.326 to − 0.427 (all P < 0.001). Additionally, PetCO 2 at rest, at AT and at peak correlated positively with peakVO 2 %pred and showed an inverse correlation with NT-proBNP in CTEPH patients (all P < 0.05). Conclusions PetCO 2 during exercise in IPAH and CTEPH patients was significantly different from normal subjects. Moreover, PetCO 2 values were significantly higher in IPAH during all phases of exercise as compared to CTEPH patients (all P < 0.001). PetCO 2 was progressively more abnormal with increasing disease severity according to peakVO 2 %pred and WHO-Fc.