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Differences of cardiac output measurements by open-circuit acetylene uptake in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension: a cohort study

Martin Schwaiblmair*, Christian Faul, Wolfgang von Scheidt and Thomas M Berghaus

Author Affiliations

1. Department of Internal Medicine, Klinikum Augsburg, Ludwig-Maximilians-University Munich, Stenglinstrasse 2, D-86156 Augsburg, Germany

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Respiratory Research 2012, 13:18  doi:10.1186/1465-9921-13-18

Published: 12 March 2012



As differences in gas exchange between pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) have been demonstrated, we asked if cardiac output measurements determined by acetylene (C2H2) uptake significantly differed in these diseases when compared to the thermodilution technique.


Single-breath open-circuit C2H2 uptake, thermodilution, and cardiopulmonary exercise testing were performed in 72 PAH and 32 CTEPH patients.


In PAH patients the results for cardiac output obtained by the two methods showed an acceptable agreement with a mean difference of -0.16 L/min (95% CI -2.64 to 2.32 L/min). In contrast, the agreement was poorer in the CTEPH group with the difference being -0.56 L/min (95% CI -4.96 to 3.84 L/min). Functional dead space ventilation (44.5 ± 1.6 vs. 32.2 ± 1.4%, p < 0.001) and the mean arterial to end-tidal CO2 gradient (9.9 ± 0.8 vs. 4.1 ± 0.5 mmHg, p < 0.001) were significantly elevated among CTEPH patients.


Cardiac output evaluation by the C2H2 technique should be interpreted with caution in CTEPH, as ventilation to perfusion mismatching might be more relevant than in PAH.

Pulmonary arterial hypertension; Chronic thromboembolic pulmonary hypertension; Cardiac output; Single-breath open-circuit acetylene uptake; Thermodilution