Pulmonary venous flow evaluated by Doppler echocardiography

Pulmonary venous flow from fetal to neonatal period

There are few reports about the effect of fetal or transitional circulation on the pulmonary venous flow. The purposes of this study were to investigate flow patterns of the pulmonary vein serially from fetal to neonatal period and to determine the relationship between pulmonary venous flow and other parameters from aortic and mitral valve. Pulmonary venous flow velocity was analyzed in 21 normal term human fetuses. Postnatal follow-up studies were performed at 1, 6, 24 h, 3 days, 1 week and 1 month. In each time point, pulsed Doppler echocardiography was used to interrogate right upper pulmonary vein, mitral and aortic valve. The measured parameters of pulmonary vein were heart rate, velocity time integral (VTI), and velocities at systolic peak (S), at diastolic peak (D), at nadir between S and D (O), and at nadir between D and the next S (X). E/A ratio and VTI were measured for mitral valve and peak systolic velocity and VTI for aortic valve. Pulmonary venous flow in fetus was phasic and continuous with low velocity. One hour after birth, without a change of flow pattern, all velocities increased dramatically. These high velocities showed a significant decrease during 24 h after birth. Three days after birth, the velocity decreased slightly and flow pattern changed from continuous to interrupted pattern with or without atrial reversal. No Doppler parameters from aortic or mitral valve showed any correlation with parameters from pulmonary vein. In conclusion, the flow pattern of the pulmonary vein in fetus may result from low pulmonary flow and decreased capacitance of the pulmonary venous system. Sudden increase in the pulmonary flow after birth is likely to be responsible for the highest velocities recorded immediately after birth. Left to right shunt through the ductus arteriosus may also contribute to the flow pattern observed in the first several days, as do changes in reservoir function of the pulmonary vein.

Hemodynamic determinants of Doppler pulmonary venous flow velocity components: new insights from studies in lightly sedated normal dogs

OBJECTIVES

We sought to define the hemodynamic determinants of pulmonary venous (PV) flow velocities to assess how these are affected by respiration, heart rate and loading conditions.

BACKGROUND

Pulmonary venous flow velocity (PVFV) recorded with pulsed wave Doppler technique is currently used in the noninvasive evaluation of left ventricular (LV) diastolic function and filling pressures. Although previous studies in both animals and humans have shown that PV flow is pulsatile, the hemodynamic determinants of the individual components of this flow remain controversial. Understanding the physiologic mechanisms should help to better define the clinical utility of these Doppler techniques.

METHODS

PV flow velocities obtained with transesophageal pulsed wave Doppler imaging were recorded together with PV, left atrial (LA) and LV pressures in 10 sedated, spontaneously breathing normal dogs. PVFV and hemodynamic data were analyzed during apnea, inspiration and expiration, at atrial paced heart rates of 60, 80, 100 and 120 beats/min and mean LA pressures of 6, 12, 18 and 24 mm Hg.

RESULTS

The data showed that 1) PV pressure varied depending on recording site, resembling pulmonary artery pressure closer to the pulmonary capillary bed and LA pressure closer to the venoatrial junction; 2) PVFV qualitatively followed changes in the PV-LA pressure gradient; 3) four PVFV components exist under normal conditions-three of which follow phasic changes in LA pressure and one of which (the late systolic component) is more influenced by RV stroke volume and the compliance of the pulmonary veins and left atrium; 4) normal respiration and changes in heart rate significantly alter PVFV variables--in particular, reverse flow velocity at atrial contraction; and 5) increasing LA pressure results in larger PV A wave and PV early systolic flow velocities, as well as an earlier peak in PV late systolic flow velocity and a more prominent velocity minimum before PV diastolic flow.

CONCLUSIONS

Using transesophageal pulsed wave Doppler technique, four PVFV components are identifiable and determined by PV-LA hemodynamic pressure gradients. These gradients appear to be influenced by a combination of physiologic events that include RV stroke volume, the compliance of the pulmonary vasculature and left atrium and phasic changes in LA pressure. PV flow velocity components are significantly influenced by heart rate, respiration and LA pressure. These findings have implications for the interpretation of LV diastolic function and filling pressures by current Doppler echocardiographic techniques but require further clinical investigation.