Background--The usual positioning of the Doppler sample volume to assess fetal pulmonary vein flow is in the distal portion of the vein, where the vessel diameter is maximal. This study was performed to test the association of the pulmonary vein pulsatility index (PVPI) with the vessel diameter.

Methods and Results--Twenty-three normal fetuses (mean gestational age, 28.6±5.3 weeks) were studied by Doppler echocardiography. Pulmonary right upper vein flow was assessed adjacent to the venoatrial junction ("distal" position) and in the middle of the vein ("proximal" position). The vessel diameter was measured by 2D echocardiography with power Doppler, and the PVPI was obtained by the ratio (maximal velocity [systolic or diastolic peak]-minimal velocity [presystolic peak])/mean velocity. The statistical analysis used t test and exponential correlation studies. Mean distal diameter was 0.33±0.10 cm (0.11 to 0.57 cm), and mean proximal diameter was 0.16±0.08 cm (0.11 to 0.25 cm) (P<0.0001). Mean distal PVPI was 0.84±0.21 (0.59 to 1.38), and mean proximal PVPI was 2.09±0.59 (1.23 to 3.11) (P<0.0001). Exponential inverse correlation between pulmonary vein diameter and pulsatility index was highly significant (P<0.0001), with a determination coefficient of 0.439.

Conclusions--In the normal fetus, the pulmonary venous flow pulsatility decreases from the lung to the heart, and this parameter is inversely correlated to the diameter of the pulmonary vein, which increases from its proximal to its distal portion. This study emphasizes the importance of the correct positioning of the Doppler sample volume, adjacent to the venoatrial junction, to assess pulmonary venous flow dynamics.