PDZK1IP1 and pulmonary arterial hypertension: However, Fisher et al. (5) and D'Alto et al. (6) limited the interval between invasive and non-invasive measurements to 1 h, while Rich et al. (7) carried out their study in 23 PAH patients and performed simultaneous RHC and D-ECHO measurements of sPAP and demonstrated that estimated sPAP by D-ECHO was inaccurate.