[Cortical auditory evoked potentials in congenital hearing impaired children with cochlear implants].

OBJECTIVE: By investigating the auditory cortical evoked potential in congenital hearing impaired children with cochlear implants, the association between central auditory development and the age of implantation was studied. METHODS: P1-N1-P2 were recorded in 110 profound hearing impaired children, aged from 12 to 80 months old and being implanted with cochlear implants before the age of 5 years. Their implant using time ranged from just at the switch-on to 48 months. The stimuli were /m/, /t/, /g/, presented at 65 dB SPL in sound field. The presence rate of each wave was obtained and the relationship between P1 latency and implant age, the time of speech processor switch-on were analyzed. RESULTS: The presence rate of P1, N1 and P2 was 66.4%, 15.5% and 12.7%, respectively. The presence of P1 was significantly higher than that of N1(χ(2)=228.542, P=0.00)and P2(χ(2)=257.438, P=0.00). There was no significant difference of P1 presence rate elicited by /m/, /t/ and /g/(64.1%, 66.9% and 68.3%, χ(2)=0.589, P=0.75). There existed no significant difference either among P1 latency(P=0.22)or amplitude(P=0.09) elicited by /m/, /t/ and /g/. There was significant difference between the implant age before and after 42-month-old regarding the proportion that entered the age-appropriate normal P1 latency range(P=0.02). No significant difference was found among groups of implant using time of 1, 2, 3 and 4 years in aspect of the proportion that entered the age-appropriate normal P1 latency range(P=1.00). CONCLUSIONS: Compared with implanted after the age of 42-month-old children with prelingual hearing impairment younger than 5 years old, the ones implanted before 42-month-old have more chance for normal development for central auditory system. Once implanted before 42-month-old, the cortical auditory system restored its normal development as early as 1 year after implantation.

A wave transmission model of the umbilicoplacental circulation based on hemodynamic measurements in sheep.

Electrical analog models of the umbilical circulation were developed based on hemodynamic measurements in fetal sheep. The umbilical artery was represented by a transmission line and the placenta by a resistive load. Model predictions of input impedance and pressure and flow waveforms agreed with in vivo measurements under baseline conditions, following placental embolization, and during angiotensin II infusion. A unique positive impedance phase observed at the heart rate frequency under baseline conditions was best explained by the unusual viscoelastic properties of the umbilical arterial wall and small load reflections. Furthermore, a short, less vasoactive segment of the umbilical artery in the retroperitoneal space had a large impact on the input impedance of the umbilical circulation, which was particularly apparent when the artery was constricted during angiotensin II infusion. The model indicated that reflections arising near the approximate location where the first arterial branches leave the main umbilical artery have a measurable impact on impedance spectra when load reflections are low.

Ultrasound scattering from blood with hematocrits up to 100%.

The backscattering coefficient of saline suspensions of porcine red blood cells was measured for hematocrits up to about 90%. It was found that the coefficient peaks at approximately 15%, but then, contrary to what a simple "gap theory" might suggest, it decays smoothly to zero, without showing another peak at high hematocrits. A one-dimensional (1-D) slab scattering model, in which the number of slabs per unit length represents the hematocrit and whose thickness and acoustical properties are similar to red cells/plasma, was also used to investigate the relation between the backscattered power and hematocrit. Monte-Carlo simulations performed for randomized boundary conditions show a similar relation to that of the 3-D system. The experimental data is compared to the Percus-Yevick theory for the packing of hard spheres, and the simulated data is compared to the Percus-Yevick theory for infinite slabs.

Aggregation effects in whole blood: influence of time and shear rate measured using ultrasound.

Ultrasound B-mode imaging (7 MHz) was used to measure blood echogenicity and velocity profiles simultaneously as they developed with axial distance for a steady flow of 28% hematocrit whole blood flowing in a long (> 60 D) large diameter (D = 2.54 cm) tube. At selected sites along the flow axis, velocity profiles were measured using block matching (cross correlation) between successive digitized images with a known time separation; from these shear rate profiles were calculated. The corresponding echogenicity profiles were also determined by averaging the digitized images. It was found that over a range of low shear rates, the echogenicity is enhanced in a manner similar to the previously reported influence on aggregation. Evidence is presented confirming the important role of aggregation in controlling the echogenicity. The transient effects of abrupt flow stoppage were studied and shown to provide useful insights into aggregation kinetics. Based on the above results, a detailed explanation is provided of the echogenicity variations seen in B-mode ultrasound images of slow-moving blood.

[The isolation of vestibular hair cells in guinea pig crista ampullaris].

Young guinea pigs (250-300 g) were rapidly decapitated and the temporal bones were immediately removed. Under dissecting microscope, the crista ampullaris was removed and incubated in Hank's balanced salt solution containing 0.125 mg/ml collagenase (Sigma IV) at 37 degrees C for 50-60 min. After mechanical dissociation, the isolated cells were transferred onto the coverslips coated with poly-lysine. The cells were left 10-15 min to settle down on the coverslips. Afterward, the collagenase containing solution was replaced by Hank's solution. Observations were made under converted phase-contrast microscope. The results were as follows: 1. Vestibular hair cells are classified into two types. Type I cell was flask-shaped with sensory hairs, a cuticular plate, a long neck and a round bottom containing a large nucleus. The length of type I cell was 18.10 +/- 2.05 microns (mean +/- s n = 32). Type II cells were round shaped or cylindrically shaped without neck but with sensory hairs, a cuticular plate. The longitudinal axis of cylindrically shaped cell was 14.00 +/- 3.16 microns and horizontal axis 9.88 +/- 2.01 microns (mean +/- s n = 29). The diameter of the round cell was 10.31 +/- 1.98 microns (mean +/- s n = 10). 2. The proportion of type I and type II cells was 61/39. 3. An average of 500-700 vestibular hair cells were obtained from each ampulla. 4. Generally, vestibular hair cells could live in Hank's solution for 7-8 hours. The earliest sign of viability degression was the appearance of granules in the cytoplasm.

A unified approach to modeling the backscattered Doppler ultrasound from blood.

A unified approach to modeling the backscattered Doppler ultrasound signal from blood is presented. The approach consists of summing the contributions from elemental acoustic voxels each containing many red blood cells (RBC's). For an insonified region that is large compared to a wavelength, it is shown that the Doppler signal is a Gaussian random process that arises from fluctuation scattering, which implies that the backscattered power is proportional to the variance of local RBC concentrations. As a result, some common misconceptions about the relationship between the backscattering coefficient and hematocrit can be readily resolved. The unified approach was also used to derive a Doppler signal simulation model which shows that, regardless of flow condition, the power in the Doppler frequency spectrum is governed by the exponential distribution. For finite beamwidth and paraxial flow, it is further shown that the digitized Doppler signal can be modeled by a moving average random process whose order is determined by the signal sampling rate as well as the flow velocity profile.

Role of models in understanding and interpreting clinical Doppler ultrasound.

Mathematical and physical models are essential tools in both fundamental and clinically applied Doppler ultrasound research. In this paper we illustrate a variety of models and show how they can be used to understand and interpret clinical Doppler ultrasound signals, particularly from stenosed arteries. The physical models discussed include both steady and pulsatile flow systems, and also a flow visualization technique that can be used to interpret the Doppler signals at a fundamental hemodynamic level. The mathematical models deal with three different aspects of the Doppler signal: models that describe the mechanism of ultrasound scattering by blood, a model to stimulate the returned Doppler signal and a model that may be used to aid in the analysis of clinical recordings. Each of these models provides a more complete understanding of blood flow through normal and stenosed vessels and contributes to the interpretation of clinical Doppler signals.

Effect of placental resistance, arterial diameter, and blood pressure on the uterine arterial velocity waveform: a computer modeling approach.

A computer model was used to simulate velocity waveforms that can be visualized in the human uterine artery using Doppler ultrasound. It was found that increasing uteroplacental vascular resistance from normal caused an increase in the systolic/diastolic velocity ratio (S/D) and pulsatility index (PI) of the waveform. Increasing uteroplacental resistance also caused the appearance of a dicrotic notch. Reducing the uterine artery radius increased the S/D and PI and this effect was accentuated at high placental resistance. In contrast, increasing mean arterial pressure in the uterine artery had little effect on S/D and PI. Results suggest that waveform shape abnormalities observed in obstetric patients with pregnancy-induced hypertension are primarily caused by high uteroplacental vascular resistance and a reduced uterine arterial diameter.

Uterine artery flow velocity waveforms in normal and growth-retarded pregnancies.

Uterine artery flow velocity waveforms were measured by continuous-wave Doppler ultrasound in 15 normal pregnant women studied from midgestation until term. Results were analyzed by calculation of the pulsatility index and the systolic/diastolic blood velocity [corrected] ratio. Both indices decreased from 16 to 20 weeks (indicating a lowering of resistance) and thereafter remained stable until term. Resistance was lower when waveforms were recorded directly over the placenta or from the uterine artery close to the placenta. A group of women with severe intrauterine growth retardation were also studied. In preeclampsia, uterine artery resistance was increased in almost all patients. In pregnancies complicated by intrauterine growth retardation of non preeclamptic origin, a wide range of results was obtained.

Comparison of four digital maximum frequency estimators for Doppler ultrasound.

The performance of four methods for digitally estimating the maximum frequency waveform from the Doppler ultrasound spectrum, are described. The methods investigated are: a percentile method, D'Alessio's threshold crossing method [D'Alessio T. (1985) "Objective" algorithm for maximum frequency estimation in Doppler spectral analysers. Med. Biol. Engng and Comput. 23, 63-68.], a modified threshold crossing method, and a new hybrid algorithm. Evaluations of the variance and bias were performed using stationary simulated continuous wave (CW) Doppler signals of different bandwidths and signal/noise ratios (SNR) of 9 and 17 dB. Furthermore, a simulated nonstationary Doppler signal, similar to that from a normal internal carotid artery, was also used to compare the various methods. Overall, it was found that the modified threshold method and the new hybrid method have the best performance over a wide range of signal and noise hybrid method have the best performance over a wide range of signal and noise conditions; however, D'Alessio's method also performs well for low SNR's.

A transmission line modelling approach to the interpretation of uterine Doppler waveforms.

An electrical analogue model of an artery that terminates into a vascular bed is presented. The model consists of an uniform transmission line that represents the artery and a load impedance that represents the vascular bed. The transmission line parameters are based on a well-established first-order approximation of the Navier-Stokes equations for fluid flow in distensible tubes. The model can be used to predict the incident and reflected components of both the arterial pressure and flow waveforms. In addition, it can predict the vessel diameter change and the mean blood velocity waveforms. In this study, the model was applied to the uterine artery so that the characteristics of the utero-placental circulation can be related to Doppler ultrasound recordings. It was found that the presence of the dicrotic notch in the uterine artery time-velocity waveform is the result of wave reflection and that a persistent notch past 20 weeks' gestation may be indicative of an abnormally high placental bed resistance. It is shown that the simulation results are consistent with the known physiological data and the clinically recorded uterine Doppler waveforms.

Early diagnosis of scoliosis based on school-screening.

A total of 8165 schoolchildren were screened for scoliosis by two teams of orthopaedic surgeons using the same procedures and criteria. Of 790 children who had positive physical signs, 689 were examined roentgenographically. Using 5 and 10 degrees as cut-off points, the prevalence of scoliosis was 6.58 and 2.4 per cent, respectively. A follow-up study of children who had been reported to have scoliosis at the age of eleven months showed that only half of them actually had scoliosis.