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Biomedical subjects

G Lidén

Publications and source records attributed to G Lidén.

At least 19 recordsLinked to original sources
PubMed1996

Dynamics of ammonia uptake in nitrogen limited anaerobic cultures of Saccharomyces cerevisiae.

Dynamics of the ammonia uptake by Saccharomyces cerevisiae under anaerobic conditions was studied in ammonia limited continuous cultures. A large number of pulse additions of ammonia (25-100 mg 1(-1)) were made at different dilution rates (0.05-0.20 h-1). The response was followed by on-line monitoring of the carbon dioxide evolution rate (CER), optical density, and by frequent analysis of extra- and intracellular metabolites. The uptake of a pulse of ammonia proceeded in a qualitatively highly reproducible pattern. Initially, a rapid and growth rate dependent uptake of ammonia was observed (lasting for about 10-15 min). Next followed a phase with little uptake (approx. 5 min). Finally, the rest of the ammonia pulse was taken up at a somewhat smaller rate which also depended on the growth rate. The first phase coincided with an increase in CER caused by mobilization of the intracellular carbohydrate trehalose and subsequently of glycogen. Regardless of dilution rate and the amount of ammonia added, the initial high uptake rate of ammonia was maintained until approximately the same amount of ammonia had been taken up. Transition from the first to the second uptake phase was associated with an increased glycerol production, indicating an elevated anabolic activity.

Ammonia↗
PubMed1996

Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae.

The effects of nitrogen starvation on the anaerobic physiology of Saccharomyces cerevisiae were studied in cells cultivated in a bioreactor. The composition of the mineral medium was designed such that the nitrogen source became depleted while there was still ample glucose left in the medium. The culture was characterized by acoustic gas analysis, flow injection analysis and HPLC analysis of extracellular substrates and metabolites. During the cultivation, the macromolecular composition of the cells was analysed with respect to the cellular content of RNA, protein, trehalose and glycogen. During exponential growth under anaerobic conditions, the maximum specific growth rate conditions. Depletion of ammonium in the medium led to an abrupt decrease (mumax) of S. cerevisiae CBS 8066 (0.46 h-1) was identical to the mumax determined under aerobic in the flux through glycolysis. Subsequently, a continuous decrease in the carbon dioxide evolution rate, caused by catabolite inactivation of the hexose-transport system, was observed. The apparent half-life of the transport system under nitrogen starvation was 13 h. During the exponential growth phase, the cellular content of RNA and protein was 15% (w/w) and 60% (w/w), respectively. At the end of the cultivation where the cells had been starved of nitrogen for 18 h, the cellular content of RNA and protein had decreased to 4% (w/w) and 22% (w/w), respectively. The intracellular carbohydrate content increased dramatically as trehalose and glycogen accumulated to final concentrations of 7% (w/w) and 25% (w/w), respectively. Glycerol formation during nitrogen starvation was higher than that accounted for by the formation of organic acids, suggesting a protein turnover of approximately 6% h-1. The growth energetics of S. cerevisiae CBS 8066 also changed as a result of nitrogen starvation, and YxATP was observed to increase from 80 mmol g-1 during the exponential growth phase to more than 130 mmol g-1 towards the end of the cultivation. The presented results illustrate the effect of nitrogen starvation on glycerol formation, protein turnover, catabolite inactivation of the sugar-transport system, the cellular composition, the cell cycle and growth energetics.

Ammonia↗
PubMed1996

A glycerol-3-phosphate dehydrogenase-deficient mutant of Saccharomyces cerevisiae expressing the heterologous XYL1 gene.

The gene XYL1, encoding a xylose reductase, from Pichia stipitis was transformed into a mutant of Saccharomyces cerevisiae incapable of glycerol production because of deletion of the genes GPD1 and GPD2. The transformed strain was capable of anaerobic glucose conversion in the presence of added xylose, indicating that the xylose reductase reaction can fulfill the role of the glycerol-3-phosphate dehydrogenase reaction as a redox sink. The specific xylitol production rate obtained was 0.38 g g-1 h-1.

Aldehyde Reductase↗
PubMed1996

Influence of the nitrogen source on Saccharomyces cerevisiae anaerobic growth and product formation.

To prevent the loss of raw material in ethanol production by anaerobic yeast cultures, glycerol formation has to be reduced. In theory, this may be done by providing the yeast with amino acids, since the de novo cell synthesis of amino acids from glucose and ammonia gives rise to a surplus of NADH, which has to be reoxidized by the formation of glycerol. An industrial strain of Saccharomyces cerevisiae was cultivated in batch cultures with different nitrogen sources, i.e., ammonium salt, glutamic acid, and a mixture of amino acids, with 20 g of glucose per liter as the carbon and energy source. The effects of the nitrogen source on metabolite formation, growth, and cell composition were measured. The glycerol yields obtained with glutamic acid (0.17 mol/mol of glucose) or with the mixture of amino acids (0.10 mol/mol) as a nitrogen source were clearly lower than those for ammonium-grown cultures (0.21 mol/mol). In addition, the ethanol yield increased for growth on both glutamic acid (by 9%) and the mixture of amino acids (by 14%). Glutamic acid has a large influence on the formation of products; the production of, for example, alpha-ketoglutaric acid, succinic acid, and acetic acid, increased compared with their production with the other nitrogen sources. Cultures grown on amino acids have a higher specific growth rate (0.52 h-1) than cultures of both ammonium-grown (0.45 h-1) and glutamic acid-grown (0.33 h-1) cells. Although the product yields differed, similar compositions of the cells were attained. The NADH produced in the amino acid, RNA, and extracellular metabolite syntheses was calculated together with the corresponding glycerol formation. The lower-range values of the theoretically calculated yields of glycerol were in good agreement with the experimental yields, which may indicate that the regulation of metabolism succeeds in the most efficient balancing of the redox potential.

Amino Acids↗
PubMed1995

Energetics and product formation by Saccharomyces cerevisiae grown in anaerobic chemostats under nitrogen limitation.

Anaerobic fermentation of glucose (20 g/l) by Saccharomyces cerevisiae CBS 8066 was studied in a chemostat (dilution rate = 0.05-0.25 h-1) at different concentrations of the nitrogen source (5.00 g/l or 0.36 g/l ammonium sulphate). The ethanol yield (g ethanol produced/g glucose consumed) was found to be higher and the glycerol yield (g glycerol formed/g glucose consumed) lower during nitrogen limitation than under carbon limitation. The biomass yield on ATP (g dry weight biomass produced/mol ATP consumed), was consequently found to be lower during nitrogen-limited conditions.

Adenosine Triphosphate↗
PubMed1994

The bone-anchored hearing aid: principal design and audiometric results.

The principle of the bone-anchored hearing aid (BAHA) is simple: sound vibrations are directly transmitted to the skull bone via a skin-penetrating titanium implant, and then are further transmitted to the cochlea, bypassing the middle ear. The present paper summarized the audiometric results from 122 patients with an average follow-up time of 5.6 years. When herein-suggested indications for treatment with the bone-anchored sound processor HC 300 are followed, the success rate is very high. The improved quality of life reported by the patients is a combination of improved quality of sound (warble tone threshold, speech reception threshold, and discrimination in noise), improved comfort, and relief from middle ear and ear canal disease occasioned by conventional hearing aids.

Audiometry↗
PubMed1991

Comparison of measured respirable dust sampler penetration curves with sampling conventions.

Measured sampler penetration curves are presented for British personal cyclone samplers and the MRE 113A static horizontal elutriator in calm air. These curves are compared with previous results for these instruments, and with theoretical models of sampler behaviour. The sampling efficiency of the elutriator when facing a moderate wind is discussed. The penetration curves are assessed by comparison with standard sampling conventions for respirable dust.

Air Pollutants, Occupational↗
PubMed1990

Ten years of experience with the Swedish bone-anchored hearing system.

In 1977, a new phase began in hearing rehabilitation of patients with chronic middle and external diseases and atresias. Thus far, these patients have had to rely on conventional bone conduction and air conduction devices that for various reasons give poor rehabilitation. The principle of the new treatment, made possible by the Swedish bone-anchored hearing system, is simple: sound vibrations are directly transmitted to the skull bone via a skin-penetrating titanium implant and then are further transmitted to the cochlea, bypassing the middle ear. The present paper summarizes our results in 147 patients over 10 years, including a total of 6,334 follow-up months. No significant rate of skin infections was observed. In over 93% of the observations, no sign of adverse skin reaction was seen. When herein-suggested indications for treatment with the bone-anchored sound processor HC-200 are followed, the success rate is over 90%. The improved quality of life reported by the patients is a combination of improved quality of sound, improved comfort, and relief from middle ear and ear canal disease occasioned by conventional hearing aids.

Adolescent↗
PubMed1989

The application of performance standards to personal airborne dust samplers.

This paper summarizes current proposals for the specification and testing of personal sampler performance, and discusses their implications for the precision of dust concentration estimates. A method of specifying the performance of a sampling instrument in terms of the range of masses it would collect from various dust clouds is proposed. Some of the practical difficulties which are likely to arise in the process of testing real samplers with respect to performance standards are discussed.

Aerosols↗
PubMed1984

Perinatal risk factors in the aetiology of hearing loss in preschool children.

In order to assess the importance of pertinent perinatal risk factors in causing hearing loss (HI), a retrospective evaluation was made of the records of 146 affected children born in the city of Göteborg between 1970 and 1979. The incidence among six-year-olds born between 1970 and 1974 was 3.8 per 1000 newborns. If only HI of more severe degree was taken into account (above 40dB in the best ear), the remaining incidence was 1.4/1000. Sensorineural HI (SNHI) accounted for 87 per cent of the cases. A positive hereditary tendency for HI was found in 55 per cent. In 61 per cent the origin of the HI was presumably prenatal, either positive heredity alone or in the form of facio-auricular anomalies, syndromes and toxic influences (infection and alcohol) during early pregnancy. Postnatal infections (meningitis, parotitis and secretory otitis media) could be ascertained as causes in about 20 per cent of the cases. For 12 per cent no aetiology could be determined. Perinatal aetiology was probable or possible in about 10 per cent of the children. The frequency of SNHI was found to be increased among survivors of neonatal intensive care, VLBW, LBW and SFD infants. Caesarean section, ventouse and breech delivery were not associated with increased rates, nor were hyperbilirubinaemia, exchange transfusion or birth asphyxia. No cases could be traced to aminoglycoside treatment. Neonatal sepsis/meningitis may have been the cause in two of the 146 cases. Hypoxia as a consequence of apnoea and respiratory distress syndrome necessitating mechanical ventilation appeared to be the major risk-factor in the neonatal period. However, in comparison with genetic predisposition, potentially damaging perinatal factors appeared to be of minor importance.

Child, Preschool↗
PubMed1984

Hearing aid prescription rules using insertion gain measurements.

Many of the decisions regarding hearing aid selection and use are based mainly upon clinical impressions. It was therefore decided to investigate whether the old fitting of 25 aided subjects with moderate hearing loss could be improved by using more precise prescription rules and a real ear measuring technique. The rules formulated should give a frequency response of moderate low and pronounced high frequency gain. The application of these rules resulted in improved high frequency gain and better speech discrimination for consonants in noise. As a result of the investigation, the routine procedure of hearing aid fitting has been revised. Earmold modifications of different types should be used more often and real ear canal measurements are recommended for incorporation in the routine examination of hearing aid performance.

Audiometry↗
PubMed1984

Ipsilateral acoustic reflex thresholds in neonates and in normal-hearing and hearing-impaired pre-school children.

Acoustic reflex thresholds (ART) were measured ipsilaterally in 20 neonates, 220 children with normal hearing and 56 children with sensorineural hearing loss, using a probe-tone frequency of 660 Hz. Middle-ear function was assessed with tympanometry (220 Hz probe tone) in all children. All the neonates had normal tympanograms and middle- ear pressure better than -- 1kPa, even a few hours after birth. The mean acoustic reflex threshold (ART) averaged over the frequency range 0.5-4 kHz was 85 dB HL, with standard deviations (SD) varying between 5 and 9 dB. With broad-band noise (BBN), the mean ART average was 57 dB HL with SD +/- 10 dB. Measurements of the ART on the children with normal-hearing and at an age of 1 month up to 5 years showed that the ARTs increased in relation to age. At 4 kHz the ARTs increased from an age of 2 months. At an age of one year 28% of 40 ears failed to manifest a reflex at the maximum testing level (90 dB HL). At frequencies 1.0 and 2.0 kHz the mean ART increased from 85 dB HL in neonates to 90 and 92 dB HL at an age of 5 years. The standard deviations in the different age groups varied between 4 and 9 dB for pure tones and 6-8 dB for BBN. Twenty (9%) of the 220 children with normal hearing had elevated ARTs by puretone stimuli and 19 by BBN. No reflexes could be elicited at 0.5 kHz and at 1.0 and 2.0 kHz the ARTs were abnormally elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry, Pure-Tone↗
PubMed1984

Analysis of hearing aid fittings using insertion gain measurements.

Insertion gain was measured in 166 persons after they were fitted with a hearing aid according to the Swedish prescription guidelines. Fitting was considered inadequate (1) when the levels of the long-term RMS speech spectrum were not amplified above the tone threshold at 1.0, 1.5 and 2.0 kHz, or (2) when the speech peak levels did not exceed the tone thresholds at 3.0 and 4.0 kHz. At least 40% of the subjects were found to have inadequate amplification according to these criteria. This number increased further when the measured insertion gain was compared with the gain recommended by other investigators. Our results indicate that real ear insertion gain measurements should be introduced as a routine clinical procedure in the fitting of hearing aids.

Aged↗
PubMed1982

Spontaneous improvement in ears with middle ear disease.

The 'healthy-baby-clinics' in Göteborg, as in all Sweden, test all 4-year-olds with pure tone screening (failure criterion greater than 20 dB). Those who fail are referred to an oto-audiological health center. In an effort to prevent over-referrals of false positives as well as under-referrals of false negatives all referred children in this study have been tested with pure tone audiometry supplemented by tympanometry. At the oto-audiological health center a test program including 3 tests with intervals of 6 weeks was initiated. Failure criteria were middle ear pressure less than - 150 mm H2O and hearing loss (HL) in the frequency range 0.125-8 kHz greater than 20 dB. In Göteborg (430,000 inhabitants) 5928 4-year-olds were tested at the 'healthy-baby-clinics' during 1980. Of these 498 (8.4%) failed in pure tone screening, 248 of which are included in the present study. At the first check in our test program, which was performed 3-8 weeks after referral, only 45% of the children were abnormal. Of these 60% normalized during the test program. Thus of the ears referred following the pure tone screening at the 'healthy-baby-clinics' only 18% remained after 15-20 weeks for referral to an ENT-doctor.

Acoustic Impedance Tests↗
PubMed1981

Factors influencing hearing after stapedectomy.

Surgical results of stapes surgery have been evaluated postoperatively after 3 years, in 834 subjects with otosclerosis. The following audiological tests were used: (1) the air-bone gap; (2) pre- and postoperative speech reception thresholds (SRT); (3) postoperative SRT related to the air-bone gap; (4) the BC loss at 4000 Hz.

Bone Conduction↗
PubMed1980

Impedance and tone screening of school children.

Impedance screening has supplemented tone screening on 5 886 seven-year-olds (11 772 ears) in five separate investigations carried out between 1972 and 1978. In the last and most conclusive study, 1 027 seven-year-olds were investigated with impedance and tone screening. Those children who failed had a repeat test at school after 4-6 weeks. Only those who failed the second screening test were referred for a final clinical control. At this investigation the otologist found 5.8% pathological ears. The stapedius reflex threshold testing (ipsilateral stimulation), criterion level greater than or equal to 110 dB SPL, rated 7.6% of the ears as abnormal. Tympanometry resulted in 6.4% pathological ears. Tone screening showed pathological values at 0.5 kHz in 1.9%, at 3.0 kHz in 1.5% and at 4.0 kHz in 2.1%. On the basis of our findings in the above-mentioned studies the following screening procedures are recommended: Tone screening at 0.5 and 4.0 kHz supplemented by tympanometry. A middle ear pressure of less than or equal to -150 mmH2O or a flat tympanogram and/or hearing threshold levels > 20 dB HL at 0.5 kHz and or 4.0 kHz are considered as indicative of ear pathology. Children failing the screening test should have a repeat test after 4-6 weeks at school and only those who do not pass on this occasion should be referred to an ENT department.

Acoustic Impedance Tests↗