PubMed Health⌕ Search

Biomedical subjects

C Ludvigsen

Publications and source records attributed to C Ludvigsen.

At least 19 recordsLinked to original sources
PubMed1996

Carbohydrate-deficient transferrin evaluation in dry blood spots.

The aim of this study was to assess the performance of the isoelectric focusing/immunoblotting/laser densitometry (IEF/IB/LD) procedure to evaluate carbohydrate-deficient transferrin (CDT) derived from dry blood spots. Serum specimens obtained from insurance applicants were analyzed for CDT by IEF/IB/LD. Dry blood spots derived from 50 serum specimens were analyzed by IEF/IB/LD. A comparative analysis of these serum specimens and the paired dry blood spots by IEF/IB/LD shows a highly significant correlation of the CDT values (r = 0.94, p < 0.0001). Stability studies indicate that, under proper storage conditions (2-3 days at room temperature, 2 weeks at 4 degrees C, or frozen at or below -20 degrees C indefinitely), dry blood spots can be used as a source of CDT for analysis by IEF/IB/LD, thus simplifying sampling, storage, and transportation of specimens to the testing site.

Alcoholism↗
PubMed1994

Hearing aid measurements with speech and noise signals.

An increasing number of hearing aid types include one or more features which are intentionally non-linear. In such devices measurement of frequency response and distortion using sweep tone measurements are typically of little relevance. Five different non-linear hearing aid types were used to evaluate three different broad-band measuring methods. The results revealed that these methods were meaningful in estimating average frequency response obtained with a specific input signal, but none of the three methods used in the study was able to evaluate separately the effects of the most important signal modifications: memoryless non-linearity like peak clipping, time-varying gain from AGC and additive internal noise.

Equipment Design↗
PubMed1993

The design and testing of a noise reduction algorithm based on spectral subtraction.

Three noise reduction algorithms based on amplitude subtraction were designed and used to process speech mixed with babble noise in two signal-to-noise ratios. The estimation of the noise-magnitude spectrum was performed with a novel synchro method, which exploits specific characteristics of the speech signal. The unprocessed and processed signals were evaluated psychoacoustically by means of a four-alternative-forced choice test with monosyllabic words (minimal pairs) in carrier phrases. The testing was carried out on groups of normally hearing and hearing-impaired subjects and the long-term power spectra of the processed signals were shaped to be essentially identical with those from the corresponding unprocessed signals. For the hearing-impaired subjects all signals were spectrally shaped according to the POGO-fitting rule. None of the algorithms improved speech intelligibility for any group of listeners and no change in the overall pattern of confusion was observed.

Acoustic Stimulation↗
PubMed1993

Evaluation of a noise reduction method--comparison between observed scores and scores predicted from STI.

Speech was mixed with different noise signals and then processed according to the well-known noise reduction method of 'spectral subtraction'. Three different algorithms were examined. The speech signals were subjected to a four alternative forced choice (4AFC) test. Both the processed and unprocessed signals were evaluated psycho-acoustically and objectively. Speech intelligibility was measured with the 4AFC test by presenting the signals via headphones to a group of normal-hearing and to a group of hearing-impaired listeners. The intelligibility scores were compared with the intelligibility scores predicted from a modified version of the Speech Transmission Index (STI). It appeared that although the noise reduction algorithms reduced the noise level, they did not improve the measured speech intelligibility, either for normal-hearing or for hearing-impaired listeners. This, however, was inconsistent with the scores estimated from STI, which erroneously predicted a significant improvement in intelligibility due to the noise reduction processing.

Acoustic Stimulation↗
PubMed1992

Comparison of certain measures of speech and noise level.

Four different methods of measuring speech and noise level in speech audiometry are compared. The methods differ with regard to the temporal characteristic of the integrator used for determining the level. The four methods are characterized by their so-called detector/indicator characteristics, being 'fast', 'slow', 'impulse', and long-term integration. It is concluded that the method using long-term integration is preferable. If the speech material consists of short speech segments such as isolated words separated by pauses, the long-term rms level should be measured without integrating over the pauses between the speech segments.

Audiometry↗
PubMed1990

Prediction of intelligibility of non-linearly processed speech.

Speech in various noise backgrounds was processed through four different non-linear devices and the intelligibility of the processed signals was predicted from the Speech Transmission Index (STI). A novel calculation method was applied in order to avoid artifacts. Running speech was used as input signal and STI was calculated from the envelopes of the squared, noise-free speech signal and of the processed, squared, noisy signal in 23 critical bands. In situations with linearly processed speech and a stationary background noise, this calculation method gives results identical with the procedure described by Steeneken & Houtgast (6). However, in a number of situations with non-linearly processed speech, or a time varying background noise level, the calculation method used here is preferable. The predictions were evaluated in a psycho-acoustic listening test and the predictions agreed well with the listening test results.

Hearing Aids↗
PubMed1989

DANTALE: a new Danish speech material.

A new Danish speech material (DANTALE) for clinical and experimental speech audiometry is digitally recorded on compact disc (CD). The speech material is designed to meet present audiological requirements at Danish hearing centres. One channel of the CD contains the speech signals and the other a masking noise. The CD also contains various calibration signals recorded on both channels at the end of the CD. The speech material compromises: 1) Digit triplets for the measurement of speech reception threshold (SRT). 2) Lists of monosyllabic words for the measurement of discrimination score (DS) for adults, children and small children. The word lists for the adults are equalized with regard to important phonetic and "visual" elements and the word lists for the children consist of minimal pairs. 3) Continuous speech for the measurement of the most comfortable loudness level (MCL), assessment of hearing aid fitting and the like. The masking noise is an amplitude-modulated, speech-shaped noise signal, which is designed to simulate a 4-person speech babble in order to assess both the frequency selectivity and the temporal resolution. The speech material is described and the long-term power spectra and modulation spectra are given.

Audiometry, Speech↗
PubMed1987

Prediction of speech intelligibility for normal-hearing and cochlearly hearing-impaired listeners.

The word recognition ability of 4 normal-hearing and 13 cochlearly hearing-impaired listeners was evaluated. Filtered and unfiltered speech in quiet and in noise were presented monaurally through headphones. The noise varied over listening situations with regard to spectrum, level, and temporal envelope. Articulation index theory was applied to predict the results. Two calculation methods were used, both based on the ANSI S3.5-1969 20-band method [S3.5-1969 (American National Standards Institute, New York)]. Method I was almost identical to the ANSI method. Method II included a level- and hearing-loss-dependent calculation of masking of stationary and on-off gated noise signals and of self-masking of speech. Method II provided the best prediction capability, and it is concluded that speech intelligibility of cochlearly hearing-impaired listeners may also, to a first approximation, be predicted from articulation index theory.

Adult↗
PubMed1986

Testing for antibodies to AIDS-associated retrovirus (HTLV-III/LAV) by indirect fixed cell immunofluorescence: specificity, sensitivity, and applications.

Seropositivity to the AIDS-associated retrovirus, HTLV-III/LAV, has profound implications. Simple and reliable tests are needed to detect such antibodies. A rapid, sensitive indirect immunofluorescence assay (IFA) on acetone-fixed virus-producing CEM/LAV-N1 cells was adapted for detection of human antibodies to HTLV-III/LAV. Specific and nonspecific patterns of of immunofluorescent reactivity were easily distinguished, and results paralleled those obtained by Western blotting and radioimmunoprecipitation (RIP), indicating that there is no need to confirm IFA positivity. In contrast, the commercial enzyme-linked immunosorbent assay (ELISA) was less reliable. False positives occurred with sera from seven hemophiliacs that were negative on Western blots, and false-negative reactions were observed on two occasions. These involved low-titer AIDS-patients' sera that were positive on Western blots, and from one of which virus was successfully isolated. Our results emphasize the requirement for confirmatory assays when the ELISA test is used for primary screening of sera for antibodies to HTLV-III/LAV. The IFA method is especially well-suited to quantitative analysis of serum antibody levels. Our data suggest that serum antibody titers rise as disease progression occurs, ultimately falling as severe complications ensue. It is suggested that in laboratories where the demand for HTLV-III/LAV antibody testing is not excessive (1,000-2,000 sera/month), IFA could serve as the only serological assay for both screening and epidemiological purposes.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Effect of leukocyte antibodies and HLA matching on the intravascular recovery, survival, and tissue localization of 111-indium granulocytes.

The effect of leukocyte antibodies detected under different conditions on the fate in vivo of granulocytes was studied using 111-indium-labeled granulocytes. Sera from patients were tested by granulocyte agglutination (GA), granulocytotoxicity (GC), granulocyte immunofluorescence (GIF), lymphocytotoxicity (LC), and antibody-dependent lymphocyte-mediated granulocytotoxicity. Granulocytes from donors to be studied were labeled with 111-indium and injected. Then the intravascular recovery and survival or tissue localization was determined in 93 studies. Antibodies detected by granulocyte agglutination were associated with a significant reduction in recovery (6.7% v 30.8% in controls; P less than .001) and t1/2 (0.3 hours v 5.6 hours in controls; P = .002). When all possible combinations of serum reactivity were considered, reactivity in the GA plus GIF assays had the best correlation with decreased recovery (R2 = .49; P less than .001) and t1/2 (R2 = .73; P less than .001). When the relationship between the strength of antibody reactivity and the recovery and t1/2 were analyzed, the best relationship was between the combination of LC and GIF with recovery (R2 = .62; P = .001). Because of the general availability of the HLA (LC) testing, the role of LC reactivity was investigated in other ways. There was a strong relationship between sera highly reactive by LC and those reactive by GIF. These highly reactive sera were also associated with reduced recovery and t1/2. The influence of specific HLA antigen mismatches was also studied. When donor and recipient were mismatched for the HLA-A2, B8, or BW44 antigens, there was a significant reduction in either recovery, t1/2, or both. Tissue localization was studied by body scans in patients with and without known sites of inflammation. Antibodies detected by a combination of GA and GIF caused abnormal pulmonary sequestration of granulocytes (three cases) and failure of granulocytes to localize at known sites of inflammation (three cases). HLA (LC) antibodies did not alter tissue localization despite the presence of the corresponding HLA antigens on granulocytes. It appears that GA, GIF, or a combination of these tests is the most effective predictor of altered in vivo fate of granulocytes. However, sera highly reactive by LC and GIF probably define a group of highly immunized patients in whom granulocyte recovery and t1/2 are also reduced. Mismatching for certain HLA antigens is also associated with reduced granulocyte recovery and survival. At present, GA, with or without the immunofluorescence assay, is the most effective predictor of altered in vivo granulocyte activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies↗
PubMed1985

Relations among some psychoacoustic parameters in normal and cochlearly impaired listeners.

Frequency resolution (viz., masking by low-pass-filtered noise and broadband noise) and temporal resolution (viz., masking by interrupted noise) were compared with hearing thresholds and acoustic reflex thresholds for four normally hearing and 13 cochlearly impaired subjects. Two models, one for frequency resolution (model I) and one for temporal resolution (model II), were introduced, and these provided a means of predicting individual frequency and temporal resolution from hearing thresholds for both normal-hearing and hearing-impaired listeners. Model I is based on the assumption that the upward spread of masking increases in cochlearly impaired hearing with an amount proportional to the hearing threshold in dB HL. Model II is based on the assumption that the poststimulatory masked thresholds return to the level of the hearing threshold within a duration of 200 ms, independent of the level of the masker and the amount of cochlear hearing loss. Model parameters were determined from results from other studies. Although some discrepancies between measured and predicted values were observed, the model predictions generally agree with measurements. Thus, to a first-order approximation, it seems possible to predict individual frequency and temporal resolution of cochlearly hearing-impaired listeners solely on the basis of their hearing thresholds.

Acoustic Stimulation↗
PubMed1983

Experiences with computer-aided hearing and fitting.

Computer-aided hearing aid fitting has recently been introduced in the clinical routine at the Audiological Department of Bispebjerg Hospital. Denmark. The rationale for the programme is described and the experience from the first 6 months of use is presented. This experience includes the reactions from the hearing impaired patients as well as the personnel of the department.

Audiometry↗
PubMed1982

Similarities between insulin, hydrogen peroxide, concanavalin A, and anti-insulin receptor antibody stimulated glucose transport: increase in the number of transport sites.

Plasma membranes from insulin or insulin mimicker (hydrogen peroxide, anti-insulin receptor antibody, and concanavalin A) treated adipocytes showed an increase in glucose transport compared to control cells due to an increase in Vmax and not due to alteration in Km. Arrhenius plots showed no difference in the energy of activation between control and insulin or insulin mimicker stimulated glucose transport states. Glucose transport by plasma membranes from control or treated adipocytes was equally (percentage) inhibited by N-ethylmaleimide, reduced glutathione, or cytochalasin B. The data indicate that the increased transport resulted from addition of new transport sites similar to the sites existing in the basal state.

Adipose Tissue↗
PubMed1980

A comparison of basal and insulin-stimulated glucose transport in rat adipocyte plasma membranes.

Specific D-glucose transport in plasma membranes prepared from control and insulin-treated rat adipocytes was measured using a recently developed dual isotope ([3H]-D-glucose and [14C]-L-glucose), rapid filtration assay which allowed measurements of initial rates at 1 s and 37 degrees. Plasma membranes from insulin-treated adipocytes showed an increase in glucose transport compared with control cells. Saturation kinetic data revealed that the plasma membranes from insulin-treated and control cells had the same Km (26 mM) for glucose transport, whereas insulin treatment increased the Vmax from 4433 pmol/mg protein/s to 9465 pmol/mg proteins/s. Arrhenius plots showed no difference in the energy of activation between control and insulin-stimulated glucose transport states. The optimum pH of both control and insulin-stimulated glucose transport was 7.4. Lower or higher pHs progressively decreased both control and insulin-stimulated glucose transport proportionately. Calcium in the transport assay media did not affect basal or insulin-stimulated glucose transport. However, omission of calcium from the adipocyte incubation media significantly lowered the insulin stimulation by 24% while basal levels were not significantly affected. Insulin specifically bound to the plasma membrane was carried through the fractionation procedure, but removal of this insulin did not alter the stimulated glucose transport. Glucose transport by plasma membranes from control or insulin-treated adipocytes was equally (percentage) inhibited by N-ethylmaleimide, dithiothreitol, reduced glutathione, or cytochalasin B. No inhibition of control or insulin-stimulated transport was seen with cytochalasin D or oxidized glutathione. The data presented are consistent with insulin causing the formation of new transport sites similar to the existing basal sites.

Adipose Tissue↗
PubMed1980

Acoustic aspects of auditory training with and without hearing aid.

Language stimulation of hearing impaired children is discussed from an acoustic point of view in two situations, 1) when the child is wearing a hearing aid, 2) when the child is not wearing a hearing aid but is spoken to directly at the ear (ad concham). Particularly the long-term spectrum of speech at the place of the eardrum is calculated in the two situations. Some factors of importance for the perception are discussed, viz. speech to noise ratio, distortion, the possibility of auditory and visual feedback etc. Psychological and pedagogical aspects are not treated.

Child↗
PubMed1979

A kinetic analysis of D-glucose transport by adipocyte plasma membranes.

The measurement of the initial rate of glucose uptake is of critical importance for the kinetic analysis of the effects of temperature, ions, or hormones on the uptake process. Presented here is a highly reproducible double isotope assay system which for the first time allowed the measurement of the initial rates of glucose uptake into isolated adipocyte plasma membrane vesicles by having time points as early as 1/2 s. Measurement of the initial rates of uptake at 1 s allowed the calculation of a Km of 9.0 mM and a Vmax of 3209 pmol/mg of protein/s for specific D-glucose transport (D-glucose minus L-glucose). The time course of specific D-glucose uptake is extremely rapid, reaching an equilibrium value in approximately 20 s with a half-time of 4 s. This uptake process is markedly inhibited by cytochalasin B. The similarity of these findings to those for intact adipocytes indicates that the plasma membrane preparation and the assay conditions used have retained the structural and functional integrity of the glucose transport system from the intact cell.

Adipose Tissue↗