A critical appraisal of transpulmonary and diastolic pressure gradients

Abstract

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.

Keywords: Cardiac output; heart failure; physiology; pulmonary hypertension; pulmonary wedge pressure.

Figure 1

The relation between diastolic pulmonary artery pressure (dPAP) and pulmonary arterial wedge pressure (PAWP): dPAP = 0.37PAWP + 18 mmHg; 95% confidence interval slope: 0.24–0.49, R ² = 0.03, n = 1054.

Figure 2

(A) The relation of systolic (sPAP) and dPAP with mean pulmonary arterial pressure (mPAP), n = 1054. The relations with intercept (lighter dashed lines) and without intercept (continuous lines) nearly completely overlap, and are visually nearly indistinguishable. (B–D) The relation of sPAP and dPAP with mPAP for the three subgroups of patients are consistent between subgroups. Group A: mPAP < 25 and PAWP ≤ 15 mmHg, n = 333; Group B: mPAP ≥ 25 and PAWP ≤ 15 mmHg, n = 578; Group C: mPAP ≥ 25 and PAWP > 15 mmHg, n = 143. For visual reasons only, the data point of one patient with mPAP > 100 mmHg was not plotted.

Figure 3

(A–B) The relation of sPAP and dPAP with mPAP in patients with a PAWP of 10 mmHg (n = 115) and of 24 ± 1 mmHg (n = 24). The relations with intercept (lighter dashed lines) and without intercept (continuous lines) nearly completely overlap. (C) The ratio of sPAP and dPAP relative to mPAP, as function of PAWP; standard errors are indicated.

Figure 4

(A–B). Relations between transpulmonary pressure gradient (TPG) and diastolic pressure gradient (DPG) as a function of PAWP, for a low (A, n = 77) and high (B, n = 38) value of mPAP. All slopes do not differ from the predicted slope‐1. (C–D) Relations between TPG and DPG and cardiac output (CO), for two different values of pulmonary vascular resistance (PVR): (C) Average PVR = 1.2 Wood units (WU). TPG, n = 106; DPG and PAWP 10 mmHg, n = 16; DPG and PAWP 24 ± 4 mmHg, n = 9; (D) Average PVR =6.5WU. TPG, n = 67; DPG and PAWP 10 ± 1 mmHg, n = 18 DPG and PAWP 22 ± 2 mmHg, n = 9. Slopes of TPG are equal to PVR. Slopes of DPG are not different from the predicted 0.62PVR. The intercepts with the vertical axis do not differ from the predicted −0.38PAWP.

Figure 5

Schematic representation of the dependence of TPG and DPG on (A) PAWP and (B) on CO.

Figure A1

The relation between the predicted DPG (DPG _predicted = 0.62 PVR*CO − 0.38 PAWP) and the actual measured DPG (R ² = 0.89, P < 0.001). For clarity, three data points were left out because they were out of range (but included in the statistical analysis).

Figure A2

In a subgroup of patients, a fluid‐challenge was performed for diagnostic reasons (n = 28). The dPAP/mPAP and sPAP/mPAP ratio remained constant despite increase in PAWP during fluid challenge. The dotted lines mark the overall dPAP/mPAP and sPAP/mPAP ratios that were found for the whole group.