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As important as having mature lungs at birth are to the baby, in the last 25 years ultrasound professionals have only proposed two methods of judging their maturity, neither of which have been effective. Neither echo texture of the lungs in comparison to the liver, or placental maturity have correlated as closely with lung maturity as was once hoped.
November 4, 1998, Edinburgh, Scotland
As important as having mature lungs at birth are to the baby, in the last 25 years ultrasound professionals have only proposed two methods of judging their maturity, neither of which have been effective. Neither echo texture of the lungs in comparison to the liver, or placental maturity have correlated as closely with lung maturity as was once hoped. Now, in the last year or so several new ways of evaluating lung maturity sonographically are being studied and are showing promise. I am fairly sure the important question of predicting fetal lung maturity non-invasively will be solved… perhaps before the end of this millenium.
Chair: Professor Arduini, Italy
Professor Arduini began with a brief history of the fetal lung going back to the Mesopotamians, and overview of the current state of sonography of the fetal lung.
Tracheal Flow new possibilities in evaluating fetal lung function
Kalache is researching the measurement of fluid volume exchange as an indicator of lung maturity. He showed several beautiful color Doppler images and video of the fluid ebb and flow in the fetal upper respiratory passages as first demonstrated by Timor-Trich. The research has demonstrated that the volume of flow increases with fetal age, and that non-surviving neonates with congenital diaphragmatic hernias have a reduced "tidal volumes" before birth. Several different patterns of "breathing" patterns have been shown using spectral Doppler, this promising research continues.
Doppler of fetal lungs in IUGR
Wladimiroff is approaching fetal lung maturity by using color Doppler guided spectral analysis of blood flow in the pulmonary arteries and veins. He and associates have sampled the flow in several locations: the central, mid, and peripheral pulmonary vascularity. They have shown that an increase in lung perfusion occurs around 15-16 weeks, and that peak diastolic velocity increases with age. The research is also studying the venous flow, pulsatility indexes, and changes in blood flow in various states of fetal activity. The research continues.
Is it possible to detect fetal lung hypoxia by 3D ultrasound prenatally?
Pohls, et al have performed research using the very new 3D sonographic methods to estimate lung volumes. These methods are similar to those currently used by echocardiographers to measure changes in cardiac ventricular volumes, and intuitively seems to be a good approach. Greater volume has been shown in the right versus left lungs, as expected. In eight cases with reduced lung volume, six were fatal, and two survived. Pohls concluded that better and faster 3D sonographic machines, and more useful and flexible volume acquisitions methods are needed to achieve success with this method.
Ultrasound study of fetal lungs in pulmonary hypoplasia
Roberts and associates have spent the most time studying the important question of lung maturity. They have also been using the approach of Doppler evaluation of lung perfusion. They have also demonstrated some changes in plural blood flow in surviving and non-surviving fetuses. In addition they have found that in pulmonary hypoplastic conditions due to asymmetric compression, as in congenital diaphragmatic hernia, there appears to be compensatory growth in the less affected lung. This is similar to the affect observed in kidneys, but to this reviewers knowledge this is the first time this important piece of knowledge has been demonstrated.
The concluding Round Table discussion agreed that more research is required and more time to accumulate more abnormal cases for comparisons. During the discussion it was suggested that perhaps the lung volume in ratio to the fetal head volume might be useful… however, no mention was made of how the head volume would be estimated; a topic in which this reviewer has much interest (see: www.io.com/~dubose, Fetal Head Volume). It was also noted that the use of newer sonographic methods such as harmonic imaging to revisit the older evaluations of lung/liver/bowel echo textures were not presented here. All these methods appear to hold some promise to answering this important question of predicting fetal lung maturity. Those who finally find an effective non-invasive method will, no doubt, win the whole set of dishes.
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Photographs by: Roberta Speyer