Sildenafil in Patients with Severe Group 3 Pulmonary Hypertension - Price,L; Kempny,A; Mccabe,C; Dimopoulos,K; Kotecha,J; Harries,C; Barbosa,J; Hopkinson,N; Simonds,A; Wells,A; Wort,J (EUROPEAN RESPIRATORY SOC JOURNALS LTD, 2018)