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Biomedical subjects

V Ball

Publications and source records attributed to V Ball.

At least 19 recordsLinked to original sources
PubMed2005

Mechanically responsive films of variable hydrophobicity made of polyelectrolyte multilayers.

Mechanically responsive surfaces that allow to switch reversibly from a hydrophobic to a hydrophilic substrate are reported. The surfaces are constituted of polyelectrolyte multilayers deposited on modified charged silicone sheets. n bilayers of poly(allylamine)-Nafion (PAH-Naf) and m bilayers of poly(allylamine)-poly(acrylic acid) (PAH-PAA) composed the multilayers. A (PAH-Naf)(n) film possesses a water contact angle of around 105 degrees, whereas the contact angle of a (PAH-Naf)(4)-(PAH-PAA)(m) multilayer is around 50 degrees. When such a film with m < 5 and terminated by PAA is stretched out, its water contact angle increases up to around 100 degrees. Successive elongation/retraction cycles allow the water contact angle to alternate reversibly between 100 and 57 degrees indicating the reversible mechanical responsive nature of the film.

Letter↗
PubMed2005

Layer by layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles obtained by spraying: integrity of the vesicles.

In a previous paper (Michel, M.; Vautier, D.; Voegel, J.-C.; Schaaf, P.; Ball, V. Langmuir 2004, 20, 4835), we showed that phospholipid vesicles can be incorporated into poly(glutamic-acid)/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films built by the alternated dipping of a surface in polyanion and polycation solutions. AFM imaging, quartz crystal microbalance, and ellipsometry suggested that the vesicles remain intact when adhering on the surface. In the present paper, we show that such films can also be realized by spraying both the polyelectrolyte solutions and the vesicles onto the surface. Using such vesicles filled with ferrocyanide ions, we prove by cyclic voltammetry that the sprayed vesicles remain intact when embedded in the multilayers. We show that multilayers containing two distinct layers of intact vesicles separated by several polyanion/polycation bilayers can also be constructed. Polyelectrolyte multilayers containing layers of phospholipid vesicles could act as reservoirs for drug or other biologically active molecules in controlled release bioactive coatings.

Electrochemistry↗
PubMed2005

Multivalent ion/polyelectrolyte exchange processes in exponentially growing multilayers.

We show, in this paper that multivalent ferrocyanide anions can penetrate into exponentially growing (PGA/PAH)n multilayer films whatever the nature of the last deposited layer. These ions are not able to diffuse out of the film when it is brought in contact with a pure buffer solution. However, the contact of this film with a poly(allylamine) (PAH) or a poly(L-glutamic acid) (PGA) solution leads to the release of ferrocyanide ions from the multilayer. It is shown that the release of ferrocyanide anions, when the film is in contact with a PGA solution, is due to the diffusion of the PGA chains into the film so that an exchange between ferrocyanide ions and PGA chains takes place inside the film. On the other hand, PAH chains do not diffuse into PGA/PAH multilayers. When the film is then brought in contact with a PAH solution, the PAH chains from the solution are expected to strongly interact with the ferrocyanide ions and thus induce a diffusion mechanism of the multivalent anions out of the film, the film/solution interface playing the role of a sink for these ions. This work thus shows that interactions between multivalent ions and exponentially growing films are much more complex than expected at first sight and that polyelectrolyte multilayers must be seen as dynamic entities in which diffusion and exchange processes can take place.

Adsorption↗
PubMed2005

The pregnancies of women with Type 2 diabetes: poor outcomes but opportunities for improvement.

AIM: To compare the outcomes of Type 1 and Type 2 diabetic pregnancies and identify risk factors for poor outcome of Type 2 pregnancies METHODS: The data from all (389 Type 1 and 146 Type 2) pre-gestational diabetic pregnancies from 10 UK hospitals were collected prospectively. RESULTS: The Type 2 mothers were less likely to have documented pre-pregnancy counselling (28.7 vs. 40.5%; P<0.05) or be taking folic acid at conception (21.9 vs. 36.4%; P<0.001) than Type 1 mothers. The percentage of pregnancies having a serious adverse outcome was higher in Type 2 patients (16.4 vs. 6.4%; P=0.002). Congenital abnormalities (12.3% in Type 2 vs. 4.4% in Type 1; P=0.002) accounted for most of this difference. The HbA1c of the Type 2 patients was similar to that of the Type 1 with mean first trimester HbA1c of 7.22 and 7.35%, respectively (P=0.5). Treatment with oral hypoglycaemic agents [odds ratio (OR), 1.8; 95% confidence interval (CI), 1.0-3.3; P=0.04], body mass index (OR, 1.09; 95% CI, 1.01-1.18; P=0.02) and folic acid supplementation (OR, 0.3; 95% CI, 0.09-1.0; P=0.04) were all independently associated with congenital malformation. CONCLUSION: Type 2 diabetic pregnancies are characterized by poor pre-pregnancy planning, inadequate folic acid supplementation and treatment with oral hypoglycaemic agents, all of which may contribute to the serious adverse outcomes affecting one in six Type 2 diabetic pregnancies. These remediable aspects of the pre-pregnancy care of women with Type 2 diabetes provide opportunities for improving the outcome towards that of women with Type 1 diabetes.

Adult↗
PubMed2001

Protein-calixarene interactions: complexation of Bovine Serum Albumin by sulfonatocalix[n]arenes.

The complexation of Bovine Serum Albumin with sulfonatocalix[n]arenes has been demonstrated by means of electrospray mass spectrometry, dynamic light scattering and atomic force microscopy; with sulfonatocalix[4]arene one strong and two weaker binding sites are detected; the effects on the structure of thin films formed by surface deposition of BSA show that the sulfonatocalix[n]arenes act to reticulate the films and produce essentially planar systems.

Animals↗
PubMed2001

p-Sulfonatocalix[6]arene is an effective coacervator of poly(allylamine hydrochloride).

p-Sulfonatocalix[6]arene is shown to form insoluble complexes with poly(allylamine hydrochloride) when the charge balance between the negative calixarene sulfonate groups matches the positive charge carried by the polyelectrolyte, this makes this glycosylaminoglycan analog an interesting candidate for controlled release systems in the case of proteins encapsulated in mesoscopic complexes with polyelectrolytes.

Journal Article↗
PubMed2001

Mass spectrometry as a novel approach to probe cooperativity in multimeric enzymatic systems.

Investigating cooperativity in multimeric enzymes is of utmost interest to improve our understanding of the mechanism of enzymatic regulation. In the present article, we propose a novel approach based on mass spectrometry to probe cooperativity in the binding of a ligand to a multisubunit enzyme. This approach presents the selective advantage of giving a direct insight into all the subsequent ligation states that are formed in solution as the ligand is added to the enzyme. A quantitative interpretation of the electrospray ionization (ESI) mass spectra gives the relative abundance of all the distinct enzymatic species, which allows one to directly deduce the cooperativity of the system. The overall method is described for the addition of the oxidized cofactor nicotinamide adenine dinucleotide (NAD(+)) to a dimeric mutant of Bacillus stearothermophilus glyceraldehyde-3-phosphate dehydrogenase (GPDH). It is then applied to four tetrameric enzymes: sturgeon muscle GPDH, wild type and S48G mutant of GPDH from B. stearothermophilus, and alcohol dehydrogenase (ADH) from Bakers yeast. The results illustrate the possibilities offered by this new technique. First, mass spectrometry allows a control of the enzymes before the addition of NAD(+). Second, the cooperative behavior can be drawn from one single ESI mass spectrum, which makes the method highly attractive in terms of the amount of biological material required. Above all, the major benefit lies in the direct visualization of all the enzymatic species that are in equilibrium in solution. The direct measurement of cooperativity readily resolve the inconvenience of the classical approaches employed in this field, which all need to model the experimental data in order to get the cooperative behavior of the system.

Animals↗
PubMed1998

The value of ultrasound with ultrasound-guided fine-needle aspiration biopsy compared to computed tomography in the detection of regional metastases in the clinically negative neck.

PURPOSE: Head and neck oncologists have not reached consensus regarding the role of contemporary imaging techniques in the evaluation of the clinically negative neck in patients with head and neck squamous cell carcinoma (HNSCC). The purpose of the present study was to compare the accuracy of ultrasound with guided fine-needle aspiration biopsy (UGFNAB) and computed tomography (CT) in detecting lymph node metastasis in the clinically negative neck. METHODS AND MATERIALS: Sixty-four neck sides of patients with HNSCC were examined preoperatively by ultrasound/UGFNAB and CT at one of five participating tertiary care medical centers. The findings were correlated with the results of histopathologic examination of the neck specimen. RESULTS: Ultrasound with guided fine-needle aspiration biopsy was characterized by a sensitivity of 48%, specificity of 100%, and overall accuracy of 79%. Three cases had nondiagnostic aspirations using UGFNAB and were excluded. CT demonstrated a sensitivity of 54%, specificity of 92%, and overall accuracy of 77%. UGFNAB detected two additional metastases not visualized on CT, whereas CT detected no metastases not seen on UGFNAB. The results of UGFNAB were similar between the participating centers. CONCLUSIONS: Approximately one half of the clinically occult nodal metastases in our patient group were identified by both CT and UGFNAB. Overall, UGFNAB and CT demonstrated comparable accuracy. The sensitivity of CT was slightly better than UGFNAB, but the latter remained characterized by a superior specificity. The results of CT and UGFNAB did not appear to be supplementary. The choice of imaging modality for staging of the clinically negative neck depends on tumor site, T-stage, and experience and preference of the head and neck oncologist. If CT is required for staging of the primary tumor, additional staging of the neck by UGFNAB does not provide significant additional value.

Biopsy, Needle↗
PubMed1997

Pediatric residency as preparation for primary care practice.

OBJECTIVES: To assess the effectiveness of pediatric residency training as preparation for primary care and make recommendations for improving residency training. METHOD: Two surveys were sent to graduate of the pediatric residency at the University of Colorado from 1984 to 1991. The first survey requested information about practice patterns and ratings of preparedness in 45 areas important for primary care. The second survey requested ratings of importance for increasing training time in 25 areas judged as inadequate in the first survey. RESULTS: Of 147 surveys mailed, 103 graduates responded and rated themselves as less than adequately trained in 25 of 45 areas selected for relevance to primary care. Graduates of the primary care track rated themselves as significantly better trained than graduates of nonprimary care tracks in 10 of 45 areas; nonprimary care graduates had higher ratings in 2 of 45 areas. The second survey (completed by 70 of the 103 initial responders) indicated that the top 5 areas needing increased time in residency training were, in descending order, orthopedics, developmental and behavioral problems, learning disability, attention-deficit hyperactivity disorder, and school difficulty. Graduates of the primary care track rated themselves as adequately trained in developmental and behavioral problems and attention-deficit hyperactivity disorder, but they and nonprimary care graduates felt inadequately prepared in the other 3 areas. CONCLUSION: Implications of these results change with different content areas, suggesting the need to improve training for all residents in some areas and extending to all residents some of the curriculum already implemented in the primary care track.

Colorado↗
PubMed1994

Kinetics of exchange processes in the adsorption of proteins on solid surfaces.

The homogeneous exchange process whereby IgG molecules adsorbed onto latex particles are replaced by IgG molecules from the bulk solution was studied by means of 125I radiolabeling. The exchange mechanism was investigated on surfaces saturated with either labeled or unlabeled proteins in the presence of a solution of the opposite species in two sets of independent experiments. After rinsing of the surface by pure buffer followed by supplementary IgG adsorption, the exchange process followed a kinetic law of first order with respect to the IgG molecules from the bulk solution, and the apparent exchange rate constant was (2.3 +/- 0.4) x 10(-5) cm.hr-1.

Adsorption↗
PubMed1993

Lip-reading the BKB sentence lists: corrections for list and practice effects.

Two groups of 21 adult subjects with normal hearing viewed the video recordings of the Bamford-Kowal-Bench standard sentence lists issued by the EPI Group in 1986. Each subject viewed all of the 21 lists and attempted to write down the words contained in each sentence. One group lip-read the lists with no sound (the LR:alone condition). The other group also heard a sequence of acoustic pulses which were synchronized to the moments when the talker's vocal folds closed (the LR&Lx condition). Performance was assessed both by loose (KW(L)) and by tight (KW(T)) keyword scoring methods. Both scoring methods produced the same pattern of results: performance was better in the LR&Lx condition; performance in both conditions improved linearly with the logarithm of the list presentation order number; subjects who produced higher overall scores also improved more with experience of the lists. The data were described well by a logistic regression model which provided a formula which can be used to compensate for practice effects and for differences in difficulty between lists. Two simpler, but less accurate, methods for compensating for variation in inter-list difficulty are also described. A figure is provided which can be used to assess the significance of the difference between a pair of scores obtained from a single subject in any pair of presentation conditions.

Adolescent↗
PubMed1993

New developments in speech pattern element hearing aids for the profoundly deaf.

Two new developments in speech pattern processing hearing aids will be described. The first development is the use of compound speech pattern coding. Speech information which is invisible to the lipreader was encoded in terms of three acoustic speech factors; the voice fundamental frequency pattern, coded as a sinusoid, the presence of aperiodic excitation, coded as a low-frequency noise, and the wide-band amplitude envelope, coded by amplitude modulation of the sinusoid and noise signals. Each element of the compound stimulus was individually matched in frequency and intensity to the listener's receptive range. Audio-visual speech receptive assessments in five profoundly hearing-impaired listeners were performed to examine the contributions of adding voiceless and amplitude information to the voice fundamental frequency pattern, and to compare these codings to amplified speech. In both consonant recognition and connected discourse tracking (CDT), all five subjects showed an advantage from the addition of amplitude information to the fundamental frequency pattern. In consonant identification, all five subjects showed further improvements in performance when voiceless speech excitation was additionally encoded together with amplitude information, but this effect was not found in CDT. The addition of voiceless information to voice fundamental frequency information did not improve performance in the absence of amplitude information. Three of the subjects performed significantly better in at least one of the compound speech pattern conditions than with amplified speech, while the other two performed similarly with amplified speech and the best compound speech pattern condition. The three speech pattern elements encoded here may represent a near-optimal basis for an acoustic aid to lipreading for this group of listeners. The second development is the use of a trained multi-layer-perceptron (MLP) pattern classification algorithm as the basis for a robust real-time voice fundamental frequency extractor. This algorithm runs on a low-power digital signal processor which can be incorporated in a wearable hearing aid. Aided lipreading for speech in noise was assessed in the same five profoundly hearing-impaired listeners to compare the benefits of conventional hearing aids with those of an aid which provided MLP-based fundamental frequency information together with speech+noise amplitude information. The MLP-based pattern element aid gave significantly better performance in the reception of consonantal voicing contrasts from speech in pink noise than that achieved with conventional amplification and consequently, it also gave better overall performance in audio-visual consonant identification.(ABSTRACT TRUNCATED AT 400 WORDS)

Algorithms↗
PubMed1992

Speech pattern hearing aids for the profoundly hearing impaired: speech perception and auditory abilities.

A family of prototype speech pattern hearing aids for the profoundly hearing impaired has been compared to amplification. These aids are designed to extract acoustic speech patterns that convey essential phonetic contrasts, and to match this information to residual receptive abilities. In the first study, the presentation of voice fundamental frequency information from a wearable SiVo (sinusoidal voice) aid was compared to amplification in 11 profoundly deafened adults. Intonation reception was often better, and never worse, with fundamental frequency information. Four subjects scored more highly in audio-visual consonant identification with fundamental frequency information, five performed better with amplified speech, and two performed similarly under these two conditions. Five of the 11 subjects continued use of the SiVo aid after the tests were complete. A second study examined a laboratory prototype compound speech pattern aid, which encoded voice fundamental frequency, amplitude envelope, and the presence of voiceless excitation. In five profoundly deafened adults, performance was better in consonant identification when additional speech patterns were present than with fundamental frequency alone; the main advantage was derived from amplitude information. In both consonant identification and connected discourse tracking, performance with appropriately matched compound speech pattern signals was better than with amplified speech in three subjects, and similar to performance with amplified speech in the other two. In nine subjects, frequency discrimination, gap detection, and frequency selectivity were measured, and were compared to speech receptive abilities with both amplification and fundamental frequency presentation. The subjects who showed the greatest advantage from fundamental frequency presentation showed the greatest average hearing losses, and the least degree of frequency selectivity. Compound speech pattern aids appear to be more effective for some profoundly hearing-impaired listeners than conventional amplifying aids, and may be a valuable alternative to cochlear implants.

Adult↗
PubMed1991

Computer-based tools for assessment and remediation of speech.

The electrolaryngograph (ELG), first conceived in the 1970s, has been used extensively as a tool in both research and clinical practice. Recent software developments have extended its clinical utility for both quantitative assessment of voice production and as an interactive visual display for remediation and teaching. In this paper, we discuss applications of the electrolaryngograph, highlighting general principles of computer-based assessment and remediation.

Audiovisual Aids↗
PubMed1990

The effects of two different speech-coding strategies on voice fundamental frequency control in deafened adults.

Control of voice fundamental frequency (Fx) during reading of a standard passage was assessed for four profoundly deafened adults receiving auditory feedback in one of two conditions: (i) with an extended low-frequency response amplifying aid; (ii) with the SiVo aid, which provided only Fx information. A third condition, where the subjects were unaided, was also included. For each feedback condition, quantitative analyses of laryngograph recordings were used to provide measures of Fx mode, 90% Fx range and the regularity of vocal fold vibration. In baseline unaided recordings, three subjects (S1, S2 and S4) showed some aspects of Fx control outside the normal range, while the other (S3) had appropriate Fx control. In the three subjects with impaired control, simplified Fx feedback led to better control than feedback from amplified speech. In two of these subjects, these differences were statistically significant. S3, who showed unimpaired Fx control, did not show any changes in Fx control under the different feedback conditions. Although the patterns of data were different in the individual subjects, simplified Fx feedback led to either improved or unimpaired control of Fx relative to speech feedback or to not feedback. These findings have important implications for speech-processing strategies implemented in hearing aids and cochlear implants, where the effects of different speech-coding strategies on production have been largely ignored.

Adult↗
PubMed1989

Effect of text complexity on connected discourse tracking rate.

The effect of three levels of text complexity upon connected discourse tracking rates was investigated in normal listeners who tracked by lipreading alone and by lipreading with auditorily presented voice pitch. Text complexity affected connected discourse tracking under both lipreading conditions, with tracking rates decreasing as the level of text complexity increased. The improvement in tracking rate with the addition of voice pitch information was found to be invariant over changes in text complexity when expressed as a simple difference between the two tracking rates.

Female↗