Forward and backward transmission of pressure waves in the pulmonary vascular bed of the dog

Can the Pulmonary Artery Wedge Pressure be Used Reliably as a Surrogate for the Left Atrial Mean Pressure in Pre-Fontan Evaluation?

The correlation between mean pulmonary artery wedge pressure (PAWP) and left atrial mean pressure (LAMP) has been poorly studied in patients with single ventricle (SV) physiology (Bernstein et al. in Pediatr Cardiol 33: 15-20 2012). The aim of this study is to determine if the PAWP can be used safely as a surrogate to the LAMP to calculate the pulmonary vascular resistance (PVR) during the pre-Fontan evaluation. Also, we aimed to understand if the presence of significant systemic-to-pulmonary collaterals (SPCs) is a confounding factor for accurate estimation of the LAMP. From February 2007 to February 2017, forty-one patients were eligible for inclusion in the study. These patients were varied in terms of underlying cardiac malformation. Sex distribution was equal with 20 males and 21 females. Median weight was 11.8 kg, median body surface area was 0.51 m², median age at catheterization was 2 years, and the median age at Glenn surgery was 5 months. We found the left and right PAWP and LAMP correlated strongly and the differences in the measurements were negligible. Similar findings were observed when calculating PVRs using PAWP and LAMP. These findings were more pronounced in the absence of significant SPCs. PAWP and LAMP correlation was still valid in the presence of significant SPCs; however, the correlation among the calculated PVRs was more attenuated.

Determinants and prognostic implications of the negative diastolic pulmonary pressure gradient in patients with pulmonary hypertension due to left heart disease

AIMS

The diastolic pulmonary pressure gradient (DPG) has recently been introduced as a specific marker of combined pre-capillary pulmonary hypertension (Cpc-PH) in left heart disease (LHD). However, its diagnostic and prognostic superiority compared with traditional haemodynamic indices has been challenged lately. Current recommendations explicitly denote that in the normal heart, DPG values are greater than zero, with DPG ≥7 mmHg indicating Cpc-PH. However, clinicians are perplexed by the frequent observation of DPG <0 mmHg (DPG_NEG ), as its physiological explanation and clinical impact are unclear to date. We hypothesized that large V-waves in the pulmonary artery wedge pressure (PAWP) curve yielding asymmetric pressure transmission might account for DPG_NEG and undertook this study to clarify the physiological and prognostic implications of DPG_NEG .

METHODS AND RESULTS

Right heart catheterization and echocardiography were performed in 316 patients with LHD due to primary myocardial dysfunction or valvular disease. A total of 256 patients had PH-LHD, of whom 48% demonstrated DPG_NEG . The V-wave amplitude inversely correlated with DPG (r = -0.45, P < 0.001) in patients with low pulmonary vascular resistance (PVR), but not in those with elevated PVR (P > 0.05). Patients with large V-waves had negative and lower DPG than those without augmented V-waves (P < 0.001) despite similar PVR (P >0.05). Positive, but normal DPG (0-6 mmHg) carried a worse 2-year prognosis for death and/or heart transplantation than DPG_NEG (hazard ratio 2.97; P < 0.05).

CONCLUSION

Our results advocate against DPG_NEG constituting a measurement error. We propose that DPG_NEG can partially be ascribed to large V-waves and carries a better prognosis than DPG within the normal positive range.

The pulmonary capillary wedge pressure accurately reflects both normal and elevated left atrial pressure

BACKGROUND

Pulmonary capillary wedge pressure (PCWP) is routinely used as an indirect measure of the left atrial pressure (LAP), although the accuracy of this estimate, especially under pathological hemodynamic conditions, remains controversial.

OBJECTIVES

The aim of this prospective study was to investigate the reliability of PCWP for the evaluation of LAP under different hemodynamic conditions.

METHODS

Simultaneous left and right heart catheterization data of 117 patients with pure mitral stenosis, obtained before and immediately after percutaneous mitral comissurotomy, were analyzed.

RESULTS

A strong correlation and agreement between PCWP and LAP measurements was demonstrated (correlation coefficient = 0.97, mean bias ± CI, 0.3 ± -3.7 to 4.2 mm Hg). Comparison of measurements performed within a 5-minute interval and those performed simultaneously revealed that simultaneous pressure acquisition yielded better agreement between the 2 methods (bias ± CI, 1.82 ± 1.98 mm Hg). In contrast to previous observations, the discrepancy between the 2 measures did not increase with elevated PCWP. Multiple regression analysis failed to identify hemodynamic confounders of the discrepancy between the 2 pressures. The ability of PCWP to distinguish between normal and elevated LAP (cutoff set at 12 and 15 mm Hg, respectively), as tested by receiver operating characteristics analysis, demonstrated a remarkably high diagnostic accuracy (area under the curve: 0.989 and 0.996, respectively).

CONCLUSIONS

Although the described limits of agreement may not allow the interchangeability of PCWP and LAP, especially at lower pressure ranges, our data support the clinical use of PCWP as a robust and accurate estimate of LAP.

Relationship of pulmonary artery wedge pressure to left atrial pressure and pulmonary vascular resistance in preoperative Fontan patients

Pulmonary artery wedge pressure (PAWp) as a surrogate for left atrial pressure (LAp) has been validated in patients with fully pulsatile two-ventricle circulations. This study was to validate PAWp as an accurate estimate of LAp for calculating pulmonary vascular resistance in single-ventricle patients after the bidirectional Glenn operation. A prospective study measuring direct branch pulmonary artery pressures, ipsilateral PAWp, and direct LAp to calculate pulmonary and systemic blood flows was conducted. Pulmonary vascular resistance (PVR) was calculated for each patient using the PAWp and compared to the PVR calculated by direct LAp measurements. Twenty-eight patients were enrolled; 27 were eligible for study inclusion. Ages ranged from 21 to 60 months and weights ranged from 9.5 to 20.8 kg. Underlying congenital heart defect diagnoses varied, with all patients either functionally or anatomically univentricular. Left mPAWp measured 4.4 ± 2.6, statistically different from simultaneous direct mLAp of 2.5 ± 2.4 mmHg (P < 0.001. Right mPAWp measured 4.3 ± 3.2 mmHg, statistically different from simultaneous direct mLAp of 2.8 ± 2.6 mmHg (P < 0.001. The PVR calculated using mPAWp was 1.2 ± 0.7 W.U., statistically different to 1.8 ± 0.95 W.U. using mLAp (P < 0.001). The average PVR measurement calculated using mPAWp underestimated the PVR calculated using mLAp by 0.6 W.U. It can be extrapolated that a PVR of 2.3 W.U. calculated using wedge measurements would estimate a PVR of 3 W.U. calculated using direct LA measurements. In this study, the PVR calculated using PAWp as a surrogate for LAp either equaled or underestimated the true PVR, up to 33% different. This difference is important in patients with univentricular physiology who rely on low PVR for cardiac output. Thus, based on this study, a PVR measurement of greater than 2.3 W.U. by the mPAWp method should prompt a direct LA pressure measurement, in order to more appropriately determine true surgical risk.

Pulmonary capillary wedge pressure in mitral stenosis accurately reflects mean left atrial pressure but overestimates transmitral gradient

Current opinion varies as to whether pulmonary capillary wedge pressure assessment of transmitral gradient in mitral stenosis is accurate; we therefore compared transmitral gradient in 36 patients awaiting balloon valvuloplasty using both pulmonary capillary wedge pressure and direct left atrial pressure. Mean pulmonary capillary wedge pressure correlated well with mean left atrial pressure (limits of agreement -1.5 to +3.7 mm Hg), but mean diastolic mitral gradient calculated using pulmonary capillary wedge pressure differed significantly from that calculated using left atrial pressure (limits of agreement -1.2 to +9.8 mm Hg): wedge pressure-assessed transmitral gradient is therefore misleading, routinely overestimating stenosis severity.

Regulation of the pulmonary circulation

Factors regulating pressure and flow in the lungs are reviewed with particular emphasis on their role in regulating blood flow velocity and distribution within the lung capillaries. The behaviour of the pulmonary arterial, system, alveolar capillaries, and pulmonary venous system are considered individually. The effect of heart disease on lung capillary blood flow is examined.

The cite of action of nerves in the pulmonary vascular bed in the dog

1. The effects of stimulation of the thoracic vagosympathetic nerve or upper thoracic sympathetic chain on the pulmonary vascular resistance have been studied in atropinized, isolated, ventilated lung lobes under various conditions of pulmonary circulation perfusion. Throughout the nerve-stimulation tests bronchial circulation perfusion was maintained or temporarily interrupted.2. The pulmonary vascular resistance increase evoked by nerve stimulation (a) occurred in the absence of tidal air changes; (b) did not consistently differ during predominantly ;sluice' and ;non-sluice' conditions of pulmonary circulation perfusion; (c) was approximately one and a half times greater during constant pressure than during constant volume inflow perfusion of the pulmonary circulation; and (d) was greater during reverse than during forward perfusion.3. In lung lobes perfused in either direction at constant volume inflow nerve stimulation produced an increase in inflow pressure and a diminution in total lung blood volume reflected by a temporary increase in blood outflow.4. In lung lobes in which neither the pulmonary nor the bronchial circulations were perfused and the capillaries were completely blocked by high intratracheal pressures, thus isolating the pulmonary arterial system from the venous system, nerve stimulation produced a diminution in the blood volume of both systems.5. Nerve stimulation produced a rise in bronchial arterial pressure in the absence of pulmonary circulation perfusion.6. Further evidence is adduced that pulmonary vasomotor nerve responses do not depend upon the transfer of transmitter substances from the bronchial to the pulmonary circulation.7. The possible significance of these observations in relation to the site of action of pulmonary vasomotor nerves is discussed.