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Biomedical subjects

J Nielsen

Publications and source records attributed to J Nielsen.

At least 289 records · Page 16Linked to original sources
PubMed1992

Syntheses, resolution, and structure-activity relationships of potent acetylcholinesterase inhibitors: 8-carbaphysostigmine analogues.

The synthesis of a series of 1,2,3,3a,8,8a-hexahydroindeno[2,1-b]pyrrole 5-alkylcarbamates and their resolution are reported. These compounds are structurally related to physostigmine with substitution of a methylene group in place of the NMe group at position 8 of physostigmine. Many of these 8-carbaphysostigmine analogues are more potent acetylcholinesterase inhibitors in vitro and less toxic in vivo than physostigmine. The (-)-enantiomer (e.g., 1d and 1g) possessing the same absolute configuration at C3a and C8a as that of physostigmine, is about 6 to 12-fold more potent at inhibiting acetylcholinesterase than the corresponding (+)-enantiomer (e.g., 1e and 1h).

Animals↗
PubMed1992

Central facilitation of Ia inhibition during tonic ankle dorsiflexion revealed after blockade of peripheral feedback.

Recent studies have reported that no increase of the disynaptic reciprocal inhibition can be observed during tonic voluntary dorsiflexion of the foot as compared to rest, when the size of the control H-reflex is kept constant. Other studies have, however, shown that a voluntary contraction evokes a strong and long-lasting depression of the synaptic transmission from Ia afferents to motoneurones, most likely secondary to activation of these afferents during the contraction (post-activation depression). It was thought that this effect could also interfere with the demonstration of a central facilitation of the reciprocal inhibition during movement. The amount of disynaptic Ia reciprocal inhibition from the pretibial flexors to the soleus H-reflex was therefore estimated in normal human subjects at rest and during voluntary tonic dorsiflexion before, during and after blocking the peripheral feedback from the investigated muscles. It was observed that the reciprocal inhibition measured during dorsiflexion increased during occlusion of the blood supply to the leg, reaching a maximum of inhibition after 30 min of ischaemia. After release of the ischaemia the inhibition gradually decreased to its pre-ischaemic level. It is therefore suggested that the brain facilitates transmission in the Ia disynaptic reciprocal pathway during tonic voluntary dorsiflexion of the foot, but that this facilitation is normally not observed due to a post-activation depression following the peripheral feedback activation during the movement.

Adult↗
PubMed1992

Methods to produce calibration mixtures for anesthetic gas monitors and how to perform volumetric calculations on anesthetic gases.

A simple procedure for making calibration mixtures of oxygen and the anesthetic gases isoflurane, enflurane, and halothane is described. One to ten grams of the anesthetic substance is evaporated in a closed, 11,361-cc glass bottle filled with oxygen gas at atmospheric pressure. The carefully mixed gas is used to calibrate anesthetic gas monitors. By comparison of calculated and measured volumetric results it is shown that at atmospheric conditions the volumetric behavior of anesthetic gas mixtures can be described with reasonable accuracy using the ideal gas law. A procedure is described for calculating the deviation from ideal gas behavior in cases in which this is needed.

Anesthesia, Inhalation↗
PubMed1992

Modelling the growth of filamentous fungi.

Despite the considerable industrial importance of filamentous fungi there have been very few attempts to model the complex growth process of these microorganisms. With a new generation of high performance, computerized bioreactors and new analytical techniques it is possible to obtain the necessary experimental data for setting up reliable structured models describing the growth process of filamentous fungi. It is therefore interesting to review the mathematical models described previously in the literature and the experimental data on which these models are built. Only structured models are considered due to the complex metabolism of filamentous fungi and to the natural cellular structuring of the biomass, i.e. the biomass can be divided into different cell types. In order to set up good structured models it is strictly necessary to have a detailed knowledge of the mechanisms underlying the growth process. This involves both biochemical insight and understanding of the interactions between different macromolecules and cytological organelles.

Biotechnology↗
PubMed1992

Clomipramine in autism: preliminary evidence of efficacy.

This report provides preliminary evidence for the efficacy of clomipramine in the treatment of young adults with autistic disorder. Four of five outpatients with autistic disorder showed significant improvement in social relatedness, obsessive compulsive symptoms, and aggressive and impulsive behavior with clomipramine treatment. These findings are consistent with previous evidence, suggesting that serotonin neurotransmission may be relevant to the treatment, and possibly the pathophysiology, of some symptoms of autistic disorder.

Adolescent↗
PubMed1992

Aeroallergen analyses and their clinical relevance. II. Sampling by high-volume airsampler with immunochemical quantification versus Burkard pollen trap sampling with morphologic quantification.

A comparison was made between the amount of airborne pollen collected by Burkard airsampler and the allergenic activity of particles trapped on glass fibre filters in an Accu-Vol high-volume airsampler. The comparison was made throughout the pollen seasons 1986 to 1989. Both airsamplers were operated 24 h a day. They were placed less than 5 m apart, and estimation of the pollen amount was made on a day-to-day basis during the pollen seasons, and on a weekly basis outside the seasons. The occurrence of the 3 clinically most important allergenic types of pollen, birch, grass, and mugwort, was analysed, and close correlations between the 2 sampling techniques were found (rs 0.5-0.8, p < 0.001). The detected range of counted pollens/m3 was: birch 0-1075, grass 0-156, and mugwort 0-44. By immunochemical analysis we found the corresponding amounts to be 0-80, 0-8, and 0-1 SQ-U/m3, respectively. Pollen counts and immunochemical estimation were compared with the symptom score recordings of allergic persons for birch season 1989 and for grass seasons 1986, 1988, and 1989. A close correlation was found for both sampling techniques for the grass seasons in 1986 and 1989 (rs 0.51-0.61, p < 0.001-0.0001), but a less significant correlation was found for the 1988 grass season, and for birch in 1989 (rs 0.24-0.34, p < 0.001-0.05).

Air Pollutants↗
PubMed1992

Alfentanil infusion in total intravenous anaesthesia (TIVA). Population pharmacokinetics fails to predict plasma concentration of alfentanil.

In order to evaluate the ability to predict plasma concentrations from population-corrected pharmacokinetics, a prospective study comprising 14 women admitted for elective hysterectomy was done. Alfentanil was given in combination with propofol in a total intravenous anaesthesia technique. The predicted median alfentanil concentration (289(256-363) ng ml-1) was significantly lower than the measured median plasma concentration of 368(168-666) ng ml-1). In conclusion, population-based pharmacokinetics were found not to be accurate as they underestimate plasma concentrations of alfentanil.

Alfentanil↗
PubMed1992

The regulation of disynaptic reciprocal Ia inhibition during co-contraction of antagonistic muscles in man.

1. The disynaptic reciprocal inhibition from ankle dorsiflexors to ankle plantarflexors was investigated at rest, during tonic plantar- and dorsiflexion and during co-contraction. In relation to rest, it was found to be decreased during plantarflexion and co-contraction, but unchanged during dorsiflexion. 2. When increasing the strength of plantarflexion the amount of inhibition became progressively smaller. Already during weak co-contraction, the amount of inhibition was very small and it did not become smaller during stronger contraction. The decrease of inhibition during co-contraction could not be explained by an addition of the changes of inhibition observed during plantar- and dorsiflexion individually. 3. The disynaptic reciprocal inhibition was also found to be decreased when the peripheral feedback from the muscles was blocked by inducing ischaemia in the leg and at the beginning of a dynamic co-contraction before sensory feedback could interfere. This implies that the observed decrease is caused by a central inhibition of the transmission in the pathway. 4. The amount of disynaptic reciprocal inhibition was also investigated during standing. No significant difference in the amount of inhibition was found when the subjects were standing up at rest as compared to sitting down at rest. When the subjects were forced to make a co-contraction in order to maintain balance, i.e. when they were standing on one leg, leaning backwards or standing on an unstable platform, a decrease of disynaptic reciprocal inhibition was seen. When the subjects leaned forward, thus forcing a contraction of the soleus muscle, a decrease was also seen, but it was smaller than in the co-contraction tasks. Finally, when the subjects lifted the examined leg, thus contracting the tibialis anterior muscle, either no change or a small increase of inhibition was seen. 5. A similar control of the disynaptic reciprocal inhibition as described for the pathway from ankle dorsiflexors to ankle plantarflexors was also observed for the pathway from ankle plantarflexors to dorsiflexors and from wrist extensors to wrist flexors. 6. It is concluded that when co-contraction is used in order to stabilize a joint, i.e. to maintain posture, a specific co-contraction motor programme is activated that depresses the transmission in the disynaptic reciprocal pathway thereby ensuring a high excitability level in the motoneurones of both antagonistic muscles.

Adult↗
PubMed1992

Allergy to methyltetrahydrophthalic anhydride in epoxy resin workers.

One hundred and forty four current and 26 former workers in a plant producing barrels for rocket guns from an epoxy resin containing methyltetrahydrophthalic anhydride (MTHPA; time weighted average air concentration up to 150 micrograms/m3) were studied. They showed higher frequencies of work related symptoms from the eyes (31 v 0%; p < 0.001), nose (53 v 9%; p < 0.001), pharynx (26 v 6%; p < 0.01), and asthma (11 v 0%; p < 0.05) than 33 controls. Also they had higher rates of positive skin prick test to a conjugate of MTHPA and human serum albumin (16 v 0%; p < 0.01), and more had specific IgE and IgG serum antibodies (18 v 0%; p < 0.01 and 12 v 0%; p < 0.05 respectively). There were statistically significant exposure-response relations between exposure and symptoms from eyes and upper airways, dry cough, positive skin prick test, and specific IgE and IgG antibodies. There was a non-significant difference in reaction to metacholine between exposed workers and non-smoking controls. In workers with and without specific IgE antibodies, differences existed in frequency of nasal secretion (54 v 23%; p < 0.05) and dry cough (38 v 12%; p < 0.05). Workers with specific IgG had more dry cough (38 v 12%; p < 0.05), but less symptoms of non-specific bronchial hyperreactivity (0 v 26%; p < 0.05). Atopic workers sneezed more than non-atopic workers (65 v 30%; p < 0.01). In a prospective study five sensitised workers who left the factory became less reactive to metacholine, and became symptom free. In 41 workers who stayed, there was no improvement, despite a 10-fold reduction in exposure. The results show the extreme sensitising properties of MTHPA.

Adolescent↗
PubMed1992

Hormonal and menstrual changes after laparoscopic sterilization by Falope-rings or Filshie-clips.

OBJECTIVE: To evaluate the influence of laparoscopic sterilization by Falope-rings (Cabot Medical Corp., Langhorne, PA) or Filshie-clips (Femcare, Nottingham, United Kingdom) on menstrual pattern and ovulatory function. DESIGN: A prospective, nonrandomized study of women sterilized by Falope-rings (n = 6) or Filshie-clips (n = 5). Menstrual charts were kept. Serum follicle-stimulating hormone (FSH), estradiol (E2) and progesterone (P) were measured by means of radioimmunoassay in one cycle before and 3, 6, and 12 months after the sterilization. Blood samples were drawn on day -6, -2, 0, +6, +10 of the menstrual cycle, ovulation corresponding to day 0. The women sterilized by Filshie-clips had abdominal ultrasonography of the ovaries measuring the leading follicle on day -6, -2, 0, +6 of the menstrual cycle. PATIENTS: Twelve women, 25 to 38 years old, with regular menstrual cycles and no use of oral contraceptives or intrauterine contraceptive device at least 6 months before sterilization. One woman was excluded. RESULTS: After the sterilization, all women reported unchanged menstrual pattern. The follicular rise in E2 unchanged, and FSH levels fell accordingly. Progesterone levels were ovulatory, but the midluteal P peak 3 months poststerilization was significantly decreased. Serial abdominal ultrasonography in women sterilized by Filshie-clips confirmed ovulation in all cycles except in one woman, who had an unruptured follicle in one cycle before and in the sixth cycle after sterilization. CONCLUSION: Laparoscopic sterilization by Falope-rings or Filshie-clips does not seem to interfere with menstrual pattern or ovulatory function.

Adult↗
PubMed1991

Serum IgE and lung function in workers exposed to phthalic anhydride.

A total of 23 phthalic anhydride (PA)-exposed workers (air levels up to 17 mg/m3) showed significantly (P less than 0.01) more workrelated symptoms in their eyes (48% vs 6%) and nose (39% vs 0) than did 18 unexposed control subjects. Two of the exposed workers had PA-associated asthma. Surprisingly, the control group exhibited significantly (P less than 0.05) more symptoms of nonspecific bronchial hyperreactivity (44% vs 13%). The exposed workers showed significantly higher levels of total serum IgE (medians, 32 vs 15 kIU/l, P less than 0.05), although values for specific IgE against PA did not differ. This may indicate that such exposure can facilitate the entry of common allergens. There was a significant difference in PA-specific IgG [enzyme-linked immunosorbent assay (ELISA) ratios 0.21 vs 0.12; P less than 0.01]. There were no differences in lung function with regard to vital capacity (VC) and forced expiratory volume (FEV1), closing volume expressed as a percentage of VC (CV%), volume of trapped gas (VTG) before and after inhalation of metacholine, or carbon monoxide transfer factor (TLCO), whereas exposed workers displayed significantly higher late expiratory flow rates (MEF50 and MEF25). In a [99mTc]-diethylenetriamine penta-acetate (DTPA) clearance test, there was no difference between exposed subjects and controls. In summary, exposure to PA did not cause subclinical effects of the lungs. Subjects with lower-airway symptoms showed lower FEV1, MEF50, and MEF25 values and higher VTG (after metacholine) than did those without symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗