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Background: Haemodynamic responses to exercise are related to physical impairment and worse prognosis in patients with pulmonary arterial hypertension (PAH). It is clinically relevant, therefore, to investigate the practical usefulness of non-invasive methods of monitoring exercise haemodynamics in this patient population., Methods: Using a novel impedance cardiography (ICG) approach that does not require basal impedance estimations and relies on a morphological analysis of the impedance signal (Signal-Morphology-ICG(™)), stroke volume (SV) and cardiac index (CI) were evaluated in 50 patients and 21 age-matched controls during a ramp-incremental cardiopulmonary exercise testing., Results: Technically unacceptable readings were found in 12 of 50 (24%) patients. In the remaining subjects, early decrease (N = 9) or a 'plateau' in SV (N = 8) and Δ (peak-unloaded exercise) SV <10 ml were markers of more advanced PAH (P<0.05). ΔCI ≤ 1.5-fold and early estimated lactate threshold were the only independent predictors of a severely reduced peak oxygen uptake (VO(2)) in patients (R(2) = 0.71, P<0.001). The finding of ΔCI ≤ 1.5-fold plus peak VO(2) < 50% predicted was associated with a number of clinical and functional markers of disease severity (P<0.001). In addition, abnormal SV responses and ΔCI ≤ 1.5-fold were significantly related to 1-year frequency of PAH-related adverse events (death and balloon atrial septostomy, N = 8; P<0.05)., Conclusions: 'Qualitative' and 'semi-quantitative' signal-morphology impedance cardiography(™) (PhysioFlow(™)) during incremental exercise provided clinically useful information to estimate disease severity and short-term prognosis in patients with PAH in whom acceptable impedance signals could be obtained., (© 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine.)