Bias and variance in the estimate of the Doppler frequency induced by a wall motion filter.

In pulsed Doppler flowmeters, processing of the Doppler signals is often done digitally. The first step in the analysis of the echoes is the filtering which is needed to remove stationary components and low frequency shifts induced by wall motion. This preliminary step is of utmost importance. The influence of uncorrelated noise on the measurement of Doppler signals at the input of this filter is analysed. The frequencies of the Doppler signals are extracted by an algorithm based on correlation techniques. We observed that the filter induces a correlated noise term, which results in an overestimation of the frequency. An effect similar to frequency aliasing may appear. The level of the bias is dependent on filter characteristics and noise level. Our study was carried out on simulated Doppler signals using first and second order filters. An especially desirable solution in flow mapping is proposed in order to decrease this error.

[Quantitative measure of the output of the deep abdominal vessels with a new device Duplex. Preliminary results]. / Mesure quantitative du débit de vaisseaux abdominaux profonds par un nouvel appareil Duplex. Résultats préliminaires.

Deep abdominal vessels blood flow can be measured noninvasively with the relation Q = V x A, where Q = flow, V = blood velocity and A = area of the considered vessel. In most Duplex devices, V is only calculated as a mean by the Doppler effect and A estimated by an echograph. Our newly developed multi-gated pulsed Doppler provides the velocity profile across the vessel, so minimizing errors in flow determination. On fifty healthy volunteers, we found flow of 717 +/- 238 ml/min for the portal vein, 1594 +/- 293 ml/min for the upper abdominal aorta and 794 +/- 168 ml/min for the lower aorta. These results are obtained through many technical and practical problems, but are feasible, even if still subject to errors. Further investigation will determine if the technique is also suitable for patients. Better assessment of deep abdominal vessels hemodynamics may be expected.

[Measuring fetal ischemia using multichannel pulsed Doppler sonography of the aorta and umbilical vein. Preliminary results in normal pregnancy]. / Débimétrie foetale au moyen d'un Doppler pulsé multicanaux dans l'aorte et la veine ombilicale. Résultats préliminaires dans la grossesse normale.

The recent development of ultrasound techniques linked to a continuous or pulsed Doppler system allows an immediate and atraumatic study of fetal blood flow to be performed. Using pulsed Doppler techniques, blood velocity waves can be analyzed and blood flow can then be calculated using ultrasound to determine the diameter of the fetal vessel; the result is expressed in milliliters per minute. A study of aortic and umbilical venous blood flow has been carried out with a prototype pulsed Doppler system with 128 gates. The same probe was used to obtain pictures by B mode ultrasound as well as to generate Doppler waves. The study group consisted of 90 normal pregnancies between 32 and 41 weeks of gestation. The umbilical venous blood flow has been measured in 50 subjects and the aortic blood flow in 79 subjects. The average aortic blood flow varied from 345 to 618 ml/min. In the umbilical vein, the flow was between 240 and 420 ml/min. It was noticed that as pregnancy advanced, blood flow slightly increased. The paper discusses the results obtained and the problems encountered with this method.

[Measuring bronchial obstruction in intensive care]. / Mesure de l'obstruction bronchique en soins intensifs.

The nature and degree of bronchial obstruction is not easy to assess in the intensive care unit. The classic airway resistance measurement technique cannot be performed without heavy equipment and the patient's cooperation. On the basis of the forced oscillations technique, measurement of acoustical respiratory impedance is an extension, in a higher frequency range, of earlier dynamic compliance measurements, which are known to be sensitive to peripheral airway obstruction but unsuitable for critically ill patients. The main advantage of respiratory impedance measurement is simplicity, since the patient simply breathes freely for a minute in the apparatus. This method contributes an effective means of quantifying evolution and treatment during an asthmatic attack. It can also be used to monitor left heart failure.