A critical appraisal of transpulmonary and diastolic pressure gradients

Pulmonary hypertension (PH) resulting from left heart failure is an increasingly recognized clinical entity. To distinguish isolated postcapillary PH from combined post‐ and precapillary PH, the use of a diastolic pressure gradient (DPG = diastolic Pulmonary Artery Pressure − Pulmonary Arterial Wedge Pressure, dPAP − PAWP) has been advocated over the transpulmonary pressure gradient (TPG = mean Pulmonary Artery Pressure − PAWP, mPAP − PAWP) since DPG was suggested to be independent of cardiac output (CO) and only slightly related to PAWP, while TPG depends on both. We quantitatively derived and compared the DPG and TPG. Using right heart catheterization data (n = 1054), we determined systolic pulmonary artery pressure (sPAP), dPAP and mPAP, PAWP, and CO. From this data, we derived TPG and DPG and tested their dependence on PAWP and CO. We found that dPAP and sPAP are proportional with mPAP over a wide range of PAWP (1–31 mmHg), with dPAP = 0.62mPAP and sPAP = 1.61mPAP. As a consequence, TPG and DPG are equally dependent on PAWP: TPG = mPAP − PAWP, and DPG = 0.62mPAP − PAWP. Furthermore, we showed that both TPG and DPG depend on CO. The absolute increase in DPG with CO is 62% of the TPG increase with CO, but the relative dependence is the same. Both TPG and DPG depend on PAWP and CO. Thus, in principle, there are no major advantages for using DPG to distinguish postcapillary pulmonary hypertension from combined post‐ and precapillary pulmonary hypertension. The proportionality of diastolic and systolic with mean pulmonary artery pressure is maintained for a very wide range of pulmonary artery wedge pressures (PAWP), which implies that both transpulmonary (TPG) and diastolic pressure gradient (DPG) depend on PAWP and cardiac output. Thus, in principle there are no major advantages for using DPG to distinguish postcapillary pulmonary hypertension from combined post‐ and precapillary pulmonary hypertension.