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PubMed1981

Validity of impedance measurements and referral criteria in school hearing screening programmes.

The increasing use of impedance methods in screening programmes for auditory dysfunction requires that the techniques and validity of the referral criteria be continually monitored. This research report describes one such study carried out as part of the normal school hearing test procedure. Comparative measurements were made using conventional pure tone sweep audiometry and with the 'Tympanometer' (American Electromedics 85 AR). Results are based on 423 ears from 9-year old juniors and 298 ears from 5-year old infants. Agreement between the two methods was obtained with 81% of the juniors and 74% of the infants. The majority of the disagreement resulted from the high sensitivity of the impedance system in detecting middle-ear disorders which did not result in a hearing loss detectable by a 20-dB sweep. Significantly, the Tympanometer missed two infants with moderate sensorineural losses. These false negatives relate directly to the Tympanometer reflex system which proved to be unreliable. The need for care in the selection of instrumentation is stressed.

Acoustic Impedance Tests↗
PubMed1991

Eliminating diathermy-induced artifacts during intraoperative monitoring of somatosensory-evoked potentials: a hardware solution.

Somatosensory-evoked potentials (SEPs) recorded intraoperatively are often contaminated by artifacts arising from unipolar diathermy. This increases variability in serial SEP recordings and decreases the reliability of SEPs for intraoperative monitoring. Rejection of single sweeps on the basis of a voltage criterion can only partially prevent the inclusion of sweeps containing artifacts. We describe a low-cost hardware system that will halt SEP acquisition automatically before diathermy becomes active. Activation of the diathermy switch will halt SEP acquisition by sending a digital inhibit signal to the evoked potential machine via a fiberoptic cable. A timer delays the activation of the diathermy until the last sweep has been completed. To allow the electroencephalographic amplifiers to recover from any overload condition resulting from the high-voltage/high-frequency input during diathermy, acquisition is resumed only after a user-selectable time interval. The system was evaluated in 50 patients. It effectively interrupted SEP acquisition each time diathermy was used. By eliminating diathermy noise from the averaged waveforms, the system will allow evoked potential monitoring even during periods of intensive use of diathermy.

Artifacts↗
PubMed2001

Bioanalytical utility of sonovoltammetry.

Dopamine dissolved within egg homogenate was used as a model system to study the effects of electrode contamination and its subsequent reactivation through ultrasonically mediated in situ cleaning effects. The merits in conducting electroanalytical investigations under the influence of the ultrasonic field were also appraised. Maintaining the ultrasound field during oxidative measurements was found to yield hydrodynamic profiles that were linear over the concentration range 2-20 microM dopamine. The resulting sonolinear sweep voltammograms were compared with conventional rotating disk measurements, with the former found to provide significantly increased limiting currents that were attenuable through the manipulation of the field intensity. The problem of retaining selectivity in the presence of high concentrations of ascorbate was also assessed with the addition of cupric ion prior to commencing the measurements found to efficiently negate an otherwise substantive interference.

Dopamine↗
PubMed2006

Signal-to-noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials.

In this study, a frequency domain formulation of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials is developed and applied for the extraction of transient responses from recordings obtained at high stimulation rates. This formulation allows for a faster execution of CLAD by using fast Fourier transform algorithms. The frequency characteristics of the deconvolution filter depends exclusively on the stimulus sequence and determines whether the noncoherent noise is amplified or attenuated in different frequencies. A formula for calculating the signal-to-noise ratio (SNR) achieved by the deconvolution process is developed. The newly developed theory and the methodology is applied to the extraction of the auditory brainstem and middle latency responses using various sequences. The effects of the sequence used and the number of sweeps averaged in ongoing acquisition on SNR are examined by using single sweep recordings. The results verify the deconvolution theory and the methodology and show its limitations. Depending on the frequency characteristics of the sequence, the deconvolution process can amplify or attenuate the EEG noise. Proper selection of the stimulus sequence can increase the SNR enhancement obtained with conventional averaging.

Acoustic Stimulation↗
PubMed1977

Receptive field characteristics of neurons in a visual area of the rabbit temporal cortex.

In a program of surveying the characteristics of visual receptive fields of neurons in rabbit brain, we have explored cortical sectors beyond the striate and occipital cortices and found cells in a part of the temporal lobe that were responsive to visual stimulation. Using evoked potential and unit-cluster methods, this temporal visual area was mapped to be roughly oval-shaped, 3 mm x 2mm in size, and at about the level posterior to the apex region of auditory area 1. It is located ventral to and continuous with visual area 11, at about the caudal half of M. Rose's temporal cortices 1 and 2 (T1 and T2). Only about two-thirds of 96 units studied responded to some sort of moving light stimulation. These motion-sensitive cells were divided into four groups. Cells in the first group (22) responded best to a large light spot or shadow sweeping quickly across the field. Cells in the second group (29) responded to slow moving, jerking spot. Nine cells responded to a narrow, dark bar thrusting into a lighted field. Four cells are "direction-selective," responding to light stimulus moving in one direction and showing either no response or decreased background discharges in the opposite direction. In addition, three cells required unusual stimulus features. Of the 38 cells tested, nine of them were found to be binocularly driven. These receptive field characteristics are quite different from those described for other visual centers of the rabbit. The significance of these results together with data on the anatomical connections of this cortical area as reported in the following paper were discussed.

Animals↗
PubMed1994

Chirp evoked otoacoustic emissions.

The principles of short frequency sweeps (chirps) and their application to evoke transiently evoked otoacoustic emissions (TEOAE) are developed in comparison to using standard click stimuli. In contrast to click stimuli, chirp signals have the advantage of stimulating a freely selectable frequency range. In addition, chirp signals contain more energy than a click stimulus with the same maximum amplitude. The effects of different stimuli on TEOAE were investigated in normal hearing and hearing-impaired subjects. Using wide-band chirp signals yields a better signal-to-noise ratio compared to click stimulation. In addition, the stimulation of selected regions of the basilar membrane with frequency-limited chirps evokes TEOAE with frequency components that lie within the stimulated frequency range. The characteristic fine structure of this spectrum was found to be independent of the stimulus applied. The utilization of chirp stimuli appears to be useful for evoking TEOAE in, e.g., clinical applications.

Acoustic Stimulation↗
PubMed1999

Effects of beta2-adrenergic stimulation on single-channel gating of rat cardiac L-type Ca2+ channels.

Cardiac L-type Ca2+ channels can be stimulated by activation of beta2-adrenoceptors. We intended to determine how the gating behavior at the single-channel level (cell-attached configuration) is affected after selective stimulation of beta2-adrenoceptors. Rat cardiomyocytes were exposed to zinterol, a beta2-agonist (n = 7), isoproterenol (n = 6), a nonselective agonist, 8-bromo-cAMP (n = 6), and a combination of isoproterenol and ICI-118551 (n = 8), a selective beta2-receptor antagonist, or isoproterenol and CGP-20712A, a beta1-selective antagonist (n = 7). In all groups the ensemble-average current and the availability of the channels to open on depolarization were increased in a similar fashion. In addition, the open probability (Po) within active sweeps was elevated. However, zinterol exerted this effect in a unique manner. It elevated Po not by shortening closed times but solely by reducing active sweeps with very low Po and a short burst duration. All zinterol effects were abolished by ICI-118551 (n = 5) and mimicked by isoproterenol plus CGP-20712A (n = 7). We conclude that beta2-adrenoceptor activation of L-type channels differs qualitatively from the classical cAMP-dependent mechanism.

Adrenergic beta-Agonists↗
PubMed2001

Effectiveness of HVAC duct cleaning procedures in improving indoor air quality.

Indoor air quality has become one of the most serious environmental concerns as an average person spends about 22 hr indoors on a daily basis. The study reported in this article, was conducted to determine the effectiveness of three commercial HVAC (Heating Ventilation Air Conditioning) duct cleaning processes in reducing the level of airborne particulate matter and viable bioaerosols. The three HVAC sanitation processes were: (1) Contact method (use of conventional vacuum cleaning of interior duct surfaces); (2) Air sweep method (use of compressed air to dislodging dirt and debris); (3) Rotary brush method (insertion of a rotary brush into the ductwork to agitate and dislodge the debris). Effectiveness of these sanitation processes was evaluated in terms of airborne particulate and viable bioaerosol concentrations in residential homes. Eight identical homes were selected in the same neighborhood. Two homes were cleaned using each procedure and two were used as controls. It was found that both particle count readings and bioaerosol concentrations were higher when cleaning was being performed than before or after cleaning, which suggests that dirt, debris and other pollutants may become airborne as a result of disturbances caused by the cleaning processes. Particle count readings at 0.3 micron size were found to have increased due to cigarette smoking. Particle counts at 1.0 micron size were reduced due to HVAC duct cleaning. Post-level bioaerosol concentrations, taken two days after cleaning, were found to be lower than the pre-level concentrations suggesting that the cleaning procedures were effective to some extent. Homes cleaned with the Air Sweep procedure showed the highest degree of reduction in bioaerosol concentration among the three procedures investigated.

Aerosols↗
PubMed2002

The influence of long emersion on biota, ammonium fluxes and nitrification in intertidal sediments of Marennes-Oléron Bay, France.

A comparative study between waterlogged and reflooded intertidal sediments was undertaken in March and June 1999 through statistical analysis of selected sediment parameters (biota, salinity, O2, Eh), pool sizes and benthic fluxes of nutrients (NH4+, NO2-, NO3-) and nitrification rates. In March samples, absence of polychaetes and oligochaetes from upper sediment horizons were due to erosional events sweeping away surface sediments. Presence of richer annelid assemblages in June samples indicated more stable hydrodynamic conditions that favoured the development of benthic microalgae biofilms. Dewatering of sediments during a 3-day emersion period promoted a salinity rise on top layers, migration of pore water ions towards the sediment surface, and created sediment fissures that accelerated water exchange on reflooding. Reflooded and waterlogged sediment systems were comparable with respect to the release of NH4+ to overlying water but were different with respect to nitrification rates. Sediment-water NH4+ fluxes were higher (P = 0.011) in March (3.3 mmol m(-2) day(-1) compared to June (1.4 mmol m(-2) day(-1) due to higher macrofauna biomasses and lower benthic microalgae concentrations in March samples. Potential nitrification rates (range from 19 to 60 mmol NO3- (-2) day(-1)) were not statistically different between March and June. A thinner oxic layer in reflooded compared with waterlogged systems reflects a decrease of O2 diffusion into sediment at high salinities which resulted in the fall of the actual nitrification rates (P < 0.05). Our data suggest that long term dessication of intertidal sediments may depress the nitrification process at the ecosystem level.

Analysis of Variance↗
PubMed1984

Application of phase spectral analysis for brain stem auditory evoked potential detection in normal subjects and patients with posterior fossa tumors.

A statistical test of the brain stem auditory-evoked potential (BAEP) detection is presented. The data were collected by averaging groups of 200 sweeps in order to obtain a set of group averages. The synchrony measure (SM), which represents the degree of reproducibility for group averages, is used as a statistical measure and is calculated from the phase variance for selected Fourier components of the group averages. The sensitivity of the test was demonstrated on 375 normal BAEPs with different stimulus intensities (45, 60, 75 dB SL) from both the ipsilateral and contralateral recordings, and on 82 BAEP recordings in the absence of stimulus. In all 375 cases of normal BAEPs the SM exceeds the threshold level while in the absence of stimulation the SM was below the threshold level. The clinical usefulness of the test was demonstrated on 22 patients with tumors of the posterior fossa. The absence of the BAEP was detected in 21 patients. In 12 out of 13 patients with lateralized tumors (acoustic neuromas), absence of the BAEP was noted for stimulation of the affected ear.

Adolescent↗
PubMed2002

Development of a rheometric technique to measure the mucoadhesive capacity of a dry powder formulation.

In the present study, the use of an in vitro technique applying oscillatory shear rheology to determine the interaction between a dry polymer powder and mucin is investigated. The polymers examined are Carbopol 974P, Noveon AA1 and a polymer mixture containing Carbopol 974P and Drum Dried Waxy Maize Starch. The degree of interaction is assessed by analysing the variation of the elastic and viscous modulus as a function of oscillation stress. Both moduli are used to calculate a mucoadhesive index at a selected single stress/frequency combination. The contribution of physical entanglements and secondary bond formation to the interaction can be derived from the mathematical analysis of the relation between the moduli and the oscillation frequency. When considering the stress sweep data, the interaction between mucin and the various polymers investigated seems very similar. This similarity is also observed when calculating the mucoadhesive indexes. On the contrary, the mathematical analysis of the frequency sweep data clearly indicates that the secondary bond formation between the polymer powder particles and mucin can be obtained only in the case of Carbopol 974 P.

Acrylic Resins↗
PubMed1992

Responses of visual single cells in the superior colliculus of the albino rat to bright bars.

We studied the responses of 57 visual cells of the superior colliculus of the albino rat to bright sweeping and stationary flashing bright bars to determine the properties of their receptive fields. We observed that 9% (8% in superficial and 11% in deep layers) of the studied cells presented orientation preference and 16% showed direction selectivity (13% in superficial and 22% in deep layers). According to their responses to a flashed bright bar they were classified in OFF-type (19%) and ON-OFF-type (81%). No ON-type cells were found. All cells were driven by the contralateral eye, and only in three cases was single cell activation from the ipsilateral eye possible. Twenty-one per cent (22% in superficial and 18% in deep layers) showed end-stopping when they were tested with bright bars of several lengths.

Action Potentials↗
PubMed2003

Design of the Jacky dragon visual display: signal and noise characteristics in a complex moving environment.

Visual systems are typically selective in their response to movement. This attribute facilitates the identification of functionally important motion events. Here we show that the complex push-up display produced by male Jacky dragons ( Amphibolurus muricatus) is likely to have been shaped by an interaction between typical signalling conditions and the sensory properties of receivers. We use novel techniques to define the structure of the signal and of a range of typical moving backgrounds in terms of direction, speed, acceleration and sweep area. Results allow us to estimate the relative conspicuousness of each motor pattern in the stereotyped sequence of which displays are composed. The introductory tail-flick sweeps a large region of the visual field, is sustained for much longer than other components, and has velocity characteristics that ensure it will not be filtered in the same way as wind-blown vegetation. These findings are consistent with the idea that the tail-flick has an alerting function. Quantitative analyses of movement-based signals can hence provide insights into sensory processes, which should facilitate identification of the selective forces responsible for structure. Results will complement the detailed models now available to account for the design of static visual signals.

Animals↗
PubMed1996

Selective determination of chloride and bromide ions in serum by cyclic voltammetry.

Voltammetric determination of chloride and bromide ions in serum was made using a one-body type Ag electrode, whose surface was covered with a dialysis membrane for preventing interference from proteins. This determination was based on measurement of the charge of the reduction wave of silver halide formed on the Ag electrode surface in a halide ion solution during a cathodic potential sweep. In this method, depending on the potential sweep range, the charge of the reduction wave of AgI, AgI + AgBr, or AgI + AgBr + AgCl can be measured. Here, the method was used to determine the chloride and bromide ions in artificial serum. Linear concentration ranges were 1.0 x 10(-2)-2.4 x 10(-1) M for chloride ions and 5.0 x 10(-3)-1.8 x 10(-2) M for bromide ions. The correlation coefficient was 0.999 in each case. The relative standard deviation for chloride ion (1.0 x 10(-1) M) was 1.9% (n = 10), and that for bromide ion (1.5 x 10(-2) M) was 2.5% (n = 10). Bromide ions at a relatively high concentration as the component of serum had no effect on the determination of the chloride ion in the serum. This method is thus useful for the selective determination of chloride and bromide ions in serum.

Blood Substitutes↗
PubMed2004

Protecting haploid polymorphisms in temporally variable environments.

Analysis of a continuous-time model shows that a protected polymorphism can arise in a haploid population subject to temporal fluctuations in selection. The requirements are that population size is regulated in a density-dependent manner and that an allele's arithmetic mean relative growth rate is greater than one when rare and that its harmonic mean relative growth rate is less than one when common. There is no requirement that relative growth rate be frequency dependent. Comparisons with discrete-time models show that the standard formalism used by population genetics ignores forced changes in generation time as rare advantageous alleles sweep into a population. In temporally variable environments, frequency-dependent changes in generation times tend to counteract these invasions. Such changes can prevent fixation and protect polymorphisms.

Alleles↗
PubMed2003

Determination of 5-aminosalicylic acid in pharmaceutical formulation by differential pulse voltammetry.

The oxidative behaviour of 5-aminosalicylic acid (5-ASA) has been investigated by differential pulse voltammetry using a glassy carbon electrode in different buffer systems. Linear sweep voltammetry was used to study the influence of pH on the peak current and peak potential. The solution conditions and instrumental parameters were optimized to obtain a good sensitivity. The Britton-Robinson buffer of pH 1.81 was selected as a suitable analytical medium in which 5-ASA exhibited a sensitive diffusion controlled oxidative peak at 0.564 V (vs. Ag/AgCl). The peak current varied linearly with drug concentration in the range between 1 x 10(-4) and 2 x 10(-6) M. The proposed voltammetric method has been applied to the determination of the drug in commercial delayed-release tablet forms. A mean recovery of 101.23% with a relative standard deviation of 1.35% was obtained.

Calibration↗
PubMed1998

A biophysical model for the developmental time course of retinal orientation selectivity.

A quantitative study of the time course of development of the percentage of orientationally selective and isotropic ganglion cells in turtle retina has recently been performed. This study revealed that as soon as ganglion cells start responding to light, a large percentage of them are selective to the orientations of moving visual stimuli. This percentage decreases with age to reach a minimum around hatching, increases dramatically after birth and finally, decreases again following the first month of life to reach adult level. Concomitantly, the percentage of cells responding isotropically to the orientation of elongated stimuli increases monotonically until about 30 days after birth, stabilizing afterwards. To account for both time courses, we propose a biophysical model implementing features ubiquitous to developing vertebrate retinas. These features include early dendritic and synaptic spatial polarization, dendritic growth, and waves of activity generated spontaneously or by visual stimulation sweeping across the inner plexiform layer (IPL). The model also assumes a physiologically plausible Hebbian rule, which includes long-term potentiation and depression. Computer simulations of this model yield good fits of the data. The quality of these fits confirms and extends results from an earlier model using computationally-simple mechanisms, which suggested that early dendritic polarization might be the seed for mature orientation selectivity.

Animals↗
PubMedDate not supplied

Primary health care is viable.

'Selective primary health care' and other recent vertical health strategies have been justified on the grounds that the broad primary health care (PHC) approach cannot be afforded by developing countries in the present constrained economic circumstances. This judgement is too sweeping. A simulated case example is presented, starting with baseline health expenditure data that are representative of the situation in many developing countries. It is assumed that real economic growth occurs and that government funding of health care is allowed to grow in parallel. Two annual growth rates are considered: 2 and 5 per cent. Two restrictive conditions are applied: none of the main health services is subjected to absolute cuts; and, additional funds from existing or new sources of finance are not considered. It is shown that, even with slow growth rates, substantial increases in the funding of priority (rural and PHC) services can be achieved if the growth in expenditures of lower-priority services is curtailed. Also, savings from improved health service efficiency can be channelled to priority services. The message is that the PHC approach is viable even with slow economic growth. What is required is the technical capacity to identify and plan resource flows in the health sector, and the political will to effect resource allocations according to PHC priorities. A strategic policy like PHC should not be 'adjusted' out of effective existence because of reversible economic problems. Rather, actions should be taken to reverse the adverse economic environment. International health-related agencies should continue to support countries to develop national health systems based on PHC, and should campaign for reforms in the world economy to create at least the minimum economic conditions necessary for PHC implementation.

Data Collection↗