Submaximal exercise gas analysis may be a useful method to assess and track pulmonary arterial hypertension (PAH) severity. The aim of the present study was to develop an algorithm, using exercise gas exchange data, to assess and monitor PAH severity. Forty patients with PAH participated in the study, completing a range of clinical tests and a novel submaximal exercise step test, which lasted 6 minutes and incorporated rest (2 minutes), exercise (3 minutes), and recovery (1 minute) ventilatory gas analysis. Using gas exchange data, including breathing efficiency, end-tidal carbon dioxide, oxygen saturation, and oxygen pulse, a pulmonary hypertension gas exchange severity (PH-GXS) score was developed. Patients were retested after about 6 months. There was significant separation between healthy controls and patients with moderate PAH (World Health Organization [WHO] class I/II) and those with more severe PAH (WHO class III/IV) for breathing efficiency, end-tidal carbon dioxide, oxygen saturation, and oxygen pulse. The PH-GXS score was significantly correlated with WHO class (r = 0.51), 6-minute walking distance (r = -0.59), right ventricular systolic pressure (r = 0.49), log N-terminal pro-B-type natriuretic peptide (r = 0.54), and pulmonary vascular resistance (r = 0.71). The PH-GXS score remained unchanged in 22 patients retested (1.50 ± 0.92 vs 1.48 ± 0.94), as did WHO class (2.3 ± 0.8 vs 2.3 ± 0.8) and 6-minute walking distance (455 ± 120 vs 456 ± 103 m). Small individual changes were observed in the PH-GXS score, with 8 patients improving and 8 deteriorating. In conclusion, the PH-GXS score differentiated between patients with PAH and was correlated with traditional clinical measures. The PH-GXS score was unchanged in our cohort after 6 months, consistent with traditional clinical metrics, but individual differences were evident. A PH-GXS score may be a useful way to track patient responses to therapy.
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