The pulmonary vein Doppler flow velocity waveform: feature analysis by comparison of in vivo pressures and flows with those in a computerized fetal physiological model

Objectives Doppler flow velocity waveforms (FVW) in fetal veins that discha rge into the atria show fluctuations related to atrial events. Pulmonary ve ins are of particular interest because both ends (atrial and collecting ven ule) are within the intrathoracic pressure environment reducing fetal breat hing artifacts. Indices, such as pulsatility index for veins (PIV), have be en suggested to classify FVWs and relate them to fetal well being. We wished to examine the relationship between function and FVW in circumsta nces which cannot ethically be examined in vivo, by studying the mechanisms which produced altered 'flows' in a detailed fetal computer model. We then related these findings to current flow indices. Methods A computer model of the fete-placental unit, responding to changes in organ oxygenation and regional pew is briefly described. In vivo intraca rdiac pressures and FVWs obtained from other studies were used to extend de tail in the model until matching 'pressures' and 'flows' resulted. The effe cts of flow redistribution in the hypoxic fetus on pulmonary vein 'Doppler' flow, velocity wave-forms were then studied. Results and conclusions Flow reversal in pulmonary veins during atrial cont raction indicates hypoxia, but change of shape of the FVW envelope reflects the changes in the pressure waveform of the left atrium. Of the major vein s the pulmonary vein Doppler FVW gave the truest representation of atrial p ressure response to both intracardiac and systemic vascular status. Althoug h current indices indicate general fetal condition, more specific indices a re needed if pulmonary venous pow is to be used as an end-point. A pulmonar y vein pressure gradient index is suggested.