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Figure 3 Time course of pulmonary vascular resistance index (PVRI) in response to iloprost and sildenafil treatment. Values for PVRI are presented as the mean and SEM. Open squares represent pre-iloprost values, assessed in the morning after an overnight break of prostanoid inhalation. Closed squares represent PVRI values subsequent to iloprost inhalation. Data pairs (pre- and post-inhalation) were obtained after three months of inhaled iloprost therapy (Ilo 3 months), after a mean interval of 18 ± 4 months on clinical deterioration (Pre-Sil), and after another three months of adjunct sildenafil therapy while leaving the iloprost regimen unchanged (Sil-Ilo). Plus signs with vertical bars on either side demonstrate significant differences (assessed by Wilcoxon test, two-sided p values given) for the impact of adjunct sildenafil treatment.