Search PubMed⌕ Search

Biomedical subjects

L Pourcelot

Publications and source records attributed to L Pourcelot.

At least 37 records · Page 2Linked to original sources
PubMed1992

[The role of ultrasound technique in blood group typing].

The work presented here concerns the study and fabrication of a robot. This tool allows one to bring out the enormous potential represented by the interaction of ultrasounds with globular suspension. The traditional hemagglutination techniques employ the systematic use of a centrifuge and mechanical suspension. The advantage of these processes is the acceleration of reactions, however, the major inconvenience remains in the difficulty of automating these tests completely, especially when microplaques are used. Our study demonstrates that the force of the ultrasonic radiation created in an atmosphere of suspension is susceptible to replacing all mechanical movements. In a stationary ultrasonic field the erythrocytes in suspension assemble towards the pressure points. This phenomenon is characterized by a faster rate of sedimentation favoring agglutination as well. Under certain conditions the ultrasonic bundle produces small whirlwinds in the bowl. The result of this process is the homogenization of the suspension which permits the differentiation between the positive and negative reactions. With these observations in mind we developed a programmable robot prototype, the goal of which was to provide us with a means of greater investigation. The originality of this technique necessitated the realization of a high frequency ultrasound captor with large range and power. For supplying the necessary energy to the transducer we developed an electronic force based on the principle of commutation. The automation is controlled by a programmable microsequensor. This instrument will allow a standardization of a protocol primarily for tests of the group ABO. The results obtained are very encouraging; the next step is to further advance experimentation in more delicate tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Grouping and Crossmatching↗
PubMed1992

[Demonstration of cerebral lateralisation disorder in autistic children: study of auditory reactivity by transcranial pulsed Doppler].

Transcranial Doppler Ultrasonographic recordings of the middle cerebral arteries were performed on children with autistic behavior (AUT), compared to retarded children without autistic behavior (NON-AUT) and normal children (NOR). Blood flow measurements (resistance index) were performed at rest and during auditory stimulations. Compared to NOR and NON-AUT, significant differences of the resistance index were found in AUT on the left side, thus suggesting differences in metabolic mechanisms evoked by auditory stimulations. This result confirms the hypothesis of abnormal development of cerebral lateralization in autism.

Autistic Disorder↗
PubMed1992

Results of a 4-week head-down tilt with and without LBNP countermeasure: II. Cardiac and peripheral hemodynamics--comparison with a 25-day spaceflight.

Cardiovascular hemodynamics were assessed by ultrasound echography and Doppler during a 28-d head-down tilt "CNES HDT: 87-88," and during the 25-d French-Soviet spaceflight "Aragatz 88." For both studies we used the same ultrasound methodology. The main hemodynamic parameters of the left heart function and of the peripheral arterial system (cerebral, renal, femoral arteries) were measured four times during the HDT (day 7, 14, 21, 28) and twice post-HDT. The same measurements were performed six times during the flight (day 4, 5, 15, 18, 20, 24) and five times postflight. During the HDT, two groups were studied: six subjects no countermeasures and six subjects with repeated lower body negative pressure (LBNP). In the first group the cardiac volumes and the cardiac output were significantly decreased, whereas in the group with LBNP these parameters were superior to the basal value. In the group without LBNP the cerebral flow was maintained because of a decrease of the brain vascular resistance. In this group the renal vascular resistance was decreased as inflight. In the lower limbs we observed a loss of the vasomotor control. The vascular resistance was decreased after the end of the HDT and the subjects suffered orthostatic intolerance. In the population with LBNP, we did not observe the same decrease of vascular resistance during the HDT, and after the HDT no sign of orthostatic intolerance was observed. During the flight, the left ventricular volume was significantly decreased. The carotid flow was maintained owing to a decrease of the cerebral vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Increment of brain temporal perfusion during auditory stimulation. Preliminary study with technetium-99m HMPAO SPET.

A study on the dynamic exploration of the auditory pathway is presented, in which technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPET) was used in volunteers with normal hearing. Changes in 99mTc-HMPAO distribution were calculated using a region of interest/whole-brain count ratio. The results showed a temporal perfusion increment of 17% (right) and 19% (left) during tonal supraliminar stimulation, which was significantly different from the control ROI. Sensitivity tests for the method were requested before any clinical application.

Acoustic Stimulation↗
PubMed1991

Intraoperative measurements of cerebral haemodynamics during ductus arteriosus ligation in preterm infants.

Intraoperative Doppler sonographic examinations were carried out on seven preterm neonates to measure cerebral blood flow velocity changes in the anterior cerebral arteries during ductus arteriosus ligation. Age at surgery was 12 +/- 6 days. Continuous recordings during the operative procedure showed a rapid increase in diastolic blood pressure (P less than 0.01), whereas systolic blood pressure was not significantly higher compared with pre-occlusion values. In the anterior cerebral arteries, ductal closure led to a decrease in resistance index of Pourcelot (mean = 1.02 +/- 0.08 vs 0.65 +/- 0.07 (P less than 0.001)) and to an increase in area under the velocity curve (mean = 3.64 +/- 0.38 vs 8.16 +/- 1.07 (P less than 0.001)). These changes were associated with a corresponding increase of the end diastolic flow velocity (P less than 0.001) but no change in the peak systolic velocity. The heart rate did not change significantly during ductal closure. TcPO2, TcPCO2 remained normal during the study period. These data indicate that changes in cerebral blood flow velocity during surgical ligation are principally determined by changes in systemic diastolic pressure. Systolic blood pressure and peak systolic flow velocity remain unchanged or slightly higher than preligation values, thereby restoring normal cerebral blood flow velocity pattern without increasing the stress on the wall of cerebral vessels and thus the risk of peri-intraventricular haemorrhage.

Blood Flow Velocity↗
PubMed1991

Evaluation of cerebral blood flow in rabbits with transcranial Doppler sonography: first results.

A transcranial Doppler sonographic system with a special 2-MHz probe for prolonged experimentation has been developed for Doppler waveform recordings from the basilar artery on rabbits. Measurements were made from the maximum velocity wave form, and Pourcelot's resistance index was used to express the results. The diastolic flow, similar to that observed in humans in physiological conditions, decreases with increased intracranial pressure during chronic intracranial hypertension. This Doppler model may be valuable for assessing rapid changes of cerebral blood flow in conscious animals during prolonged or acute experimental procedures.

Animals↗
PubMed1991

Influence of the measurement location on the resistance index in the umbilical arteries: a hemodynamic approach.

A computer model was used to study the primary factors generating the reduction in resistance index, (S-D)/S, values observed by ultrasonic Doppler measurements in the umbilical artery, from the fetal insertion to the placental insertion (S represents the amplitude of the systolic peak and D the amplitude of the diastolic peak). This hemodynamic approach shows that the placental resistance is the primary factor, the viscosity and the cord length playing secondary roles. Clinically, the position of the measurement along the cord is an important factor. To increase the sensitivity of the index, the Doppler measurement must be performed near the fetal insertion, whereas a measurement near the placental insertion will make the Doppler examination more specific.

Blood Flow Velocity↗
PubMed1991

[HMPAO radionuclide of temporal cortex in the study of deafness].

A new method of dynamic exploration of central auditory pathway is presented, using measurement of cortical temporal perfusion variations, during auditory stimulation (tonal stimulation in normal hearing patients, electrical stimulation with promontory test in profoundly deaf patients). This study shows a perfusion increment in normal hearing and deaf patients with positive promontory test, which doesn't exist in a patient with negative promontory test. Further development of this study could help for optimization of post implantation auditory results.

Acoustic Stimulation↗
PubMed1990

[125I]MIBG uptake and release in different regions of the rat brain.

Radioiodinated m-iodobenzylguanidine [( 125I]MIBG) and tritiated norepinephrine [( 3H]NE]) uptake and release were compared, in different regions of the brain of the rat. The classification of the regions according to uptake was the same for both tracers:striatum greater than hypothalamus greater than hippocampus greater than cortex greater than brainstem. Tetrabenazine (TBZ), a granular monoamine uptake inhibitor reduced the uptake in the different regions. The inhibition rate was higher for [3H]NE uptake than for [125I]MIBG. The spontaneous release was the same for [125I]MIBG and [3H]NE and was the lowest in the striatum. The K+ stimulated release of [3H]NE was more complete than the release of [125I]MIBG and was the most important in the striatum. From these results, it is inferred that MIBG enters the brain tissue via NE uptake mechanisms. It appears that MIBG is stored in the chromaffin granules, as NE, but also in the cytoplasm. A modified molecule derived from MIBG which would cross the blood-brain barrier, would then appear as a potential scintigraphic marker of monoamine uptake, storage and release.

3-Iodobenzylguanidine↗
PubMed1990

[The contribution of color-coded Doppler in early vascular complications of kidney transplantation].

Ultrasound techniques and radionuclide studies are very often used to assess vascularization of renal transplants. Although, in acute tubular necrosis or acute rejection, it is difficult to choose between these two techniques, in 3 recent cases of renal artery thrombosis, we conclude that color coded Doppler is preferable to nuclear medicine or duplex system to diagnose this form of thrombosis.

Adult↗
PubMed1989

Visualization of the fetal circle of Willis and intra-cerebral arteries by color-coded Doppler.

We report here the visualization of the intra-cerebral vessels in a normal fetus of 28 weeks gestational age, by color-coded Doppler. The color-flow mapping method makes it possible to identify very small vessels that up to date could not be detected on B-mode imaging, and will permit new clinical and physiological studies of the circulation in specific areas of the fetal brain.

Cerebral Arteries↗
PubMed1989

Very high frequency pulsed Doppler apparatus.

A study of a method for exploration of microvessels is presented. Theoretical considerations taking into account the backscattering of ultrasound wave from a red cell and the attenuation versus frequency (up to 180 MHz) show that a frequency in the range of 80 to 120 MHz is most favorable for small depths of exploration (300 microns). The characteristics of the 113 MHz Doppler system which was built are described. The minimum detectable signal is 3 microV, the lateral resolution around 20 microns and the minimum length of the Doppler sample volume about 80 microns. The Doppler data are displayed in the form of a frequency spectrum. The first encouraging tests carried out using 20 microns rectangular glass capillary tubes and 50 to 150 microns microvessels of the mesentery of rat have demonstrated the resolution and the sensitivity of the system. A discussion illustrates the difficult problem of motion artefacts and the improvements which have to be made. From a technical point of view the authors think that it is possible to work with such a high frequency but there are two main difficulties: the processing of a very low frequency Doppler spectrum and the optimization of the probe (dimensions and shape).

Animals↗
PubMed1989

Doppler assessment of the intracerebral circulation of the fetus.

Fetal cerebral arteries have been explored during normal pregnancies (n = 40). The index of cerebral resistance (Rc) as defined by Pourcelot (Rc = (S-D)/S where S is the systolic amplitude and D is the diastolic amplitude) shows variations similar to the placental index (Rp). During normal pregnancy, the cerebral index is higher than the placental index and the cerebro-placental ratio (Rc/Rp) is greater than one. This preliminary study of the umbilical and cerebral circulation during 21 pathological pregnancies with hypertension seems to demonstrate that when fetal growth retardation is also present (n = 6) either or both of the indices Rc and Rp may be outside the normal range but the cerebro-placental ratio (CPR) is always less than one. However, a larger number of patients needs to be explored in order to evaluate the clinical usefulness of such an observation.

Adult↗
PubMed1989

Effect of caffeine on cerebral blood flow velocity in preterm infants.

A continuous-wave form Doppler monitor was used to examine the effect of caffeine on cerebral blood flow velocity (CBFV) in 7 clinically stable preterm neonates suffering from apnea. Caffeine, in the form of caffeine citrate, or saline were given intravenously at loading doses of 20 mg/kg. Every subject was his own control. Placebo (saline) was systematically injected prior to caffeine citrate. Simultaneous recording of heart rate, arterial blood pressure, respiratory rate, TcPO2, TcPCO2 were made before, then at the end of the injection, and 30, 60 and 120 min after the end of each administration of either placebo or caffeine. Compared with placebo, caffeine injection was not associated with significant changes in CBFV. An increase was found in both heart-rate and respiratory rate (p less than 0.05). Mean arterial blood pressure, TcPCO2 and TcPO2 did not change significantly. Our data suggest that a caffeine citrate loading dose of 20 mg/kg as currently used at the beginning of treatment of apnea in preterm neonates has no effect on CBFV.

Blood Flow Velocity↗
PubMed1989

Caffeine and cerebral blood flow velocity in preterm infants.

Continuous wave Doppler monitor was used to examine the effect on cerebral blood flow velocity (CBFV) of caffeine in 7 clinically stable preterm neonates suffering from apnea. Caffeine, as caffeine citrate at a loading dose of 20 mg.kg-1 BW, or saline were given intravenously. Every subject was his own control. Placebo (saline) was systematically injected prior to caffeine citrate. Simultaneous recording of heart rate, arterial blood pressure, respiratory rate, Tc PO2, and Tc PCO2 were made before, at the end of the injection, and 30, 60 and 120 min after the end of each administration of either placebo or caffeine. Compared with placebo, caffeine injection was not associated with significant changes in CBFV. An increase was found in both heart rate and respiratory rate (p less than 0.05). Mean arterial blood pressure, Tc PCO2 and Tc PO2 did not change significantly. Our data suggest that a caffeine citrate loading dose of 20 mg.kg-1 BW as currently used at the beginning of treatment of apnea in preterm neonates has no effect on CBFV.

Blood Pressure↗