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Biomedical subjects

H Janssens

Publications and source records attributed to H Janssens.

12 recordsLinked to original sources
PubMed2004

Neutron field measurements for alara purposes around a Van de Graaff accelerator building.

The Institute for Reference Materials and Measurements operates a 7.0 MV Van de Graaff accelerator to generate monoenergetic neutron radiation for experimental applications. Owing to increased intensities of generated neutron fields and the more stringent regulation related to the maximum dose for the public, a concrete shielding wall surrounding the experimental building was constructed. This paper presents a study aiming at evaluating the effect of the shielding on the neutron field outside the wall. For this purpose, the following measurements were carried out around the building: (1) cartography of the neutron field for different experimental conditions; (2) measurement of neutron spectra using multiple Bonner spheres; (3) activation measurements using gold discs followed by low-level gamma spectrometry. From the measurements, it can be concluded that the wall fulfils its purpose to reduce the neutron dose rate to the surrounding area to an acceptable level.

Air Pollution, Indoor↗
PubMed2000

Endocrinological aspects of aging in men: is hormone replacement of benefit?

Age-related decreases of serum testosterone (total, free and bioavailable), DHEA, DHEA-S, growth hormone (GH) and IGF-I are well established in elderly healthy men. Although substantial, the decrease of these hormones is small compared to the estrogen changes observed in postmenopausal women. Elderly men also loose bone and muscle, gain fat and have less sexual appetite. Therefore, the assumption that hormonal therapy is a potential 'fountain of youth' appears logical. At present, however, the effects of replacement of testosterone, DHEA and GH in healthy elderly men have been studied in only a few randomised placebo-controlled trials. These studies were small and of short duration. Although some significant overall effects of either androgen or GH replacement on body composition (less fat and more muscle) were found, the effects of such therapy on muscle strength, on metabolic and sexual function and on skeletal homeostasis have been less consistent. Also, the safety of such therapy should be better documented. Moreover, data obtained in healthy elderly men cannot be transposed to non-healthy elderly men. In conclusion, more scientific work is needed before general replacement of the 'falling hormones' should be regarded as beneficial for elderly men.

Aging↗
PubMed1999

Isolation and characterization of drosocrystallin, a lens crystallin gene of Drosophila melanogaster.

We have cloned the drosocrystallin gene (dcy) of Drosophila melanogaster, which encodes a major protein of the corneal lens, previously described in part by Komori et al. (1992, J. Cell Sci. 102, 191-201). Synthesis of the DCY protein starts weakly in 2-day-old pupae, reaches a peak at day 3 and day 4 of pupal development, and decreases very fast in young adults. The dcy mRNA is detected in the compound eyes as well as in the ocelli. The presence of a putative signal peptide and the extracellular location of DCY suggest that DCY is a secreted protein. Interestingly, the dcy gene shows sequence similarities to some insect cuticular proteins and is detected as well in two closely related Drosophila species, D. sechellia and D. simulans, and in one more distantly related species, D. virilis. This finding supports the hypothesis that Drosophila used the same strategy as vertebrates and mollusks, namely, recruiting a multifunctional protein for refraction in the lens, by a gene-sharing mechanism. Furthermore, it supports our intercalary evolution hypothesis, which suggests that the development of an elaborate structure (for example, a compound eye) from an original primitive form (an ancestral photoreceptor organ) can be achieved by recruiting novel genes into the original developmental pathway.

Amino Acid Sequence↗
PubMed1998

A protocol for extraocular muscle surgery after orbital floor fracture ("blow-out")

PURPOSE: If, after primary repair of an orbital fracture by maxillo-facial surgeons, diplopia persists, extraocular muscle surgery may be necessary. It was the purpose of this study to examine proposed surgical treatment in these cases to determine their efficacy. SUBJECTS AND METHODS: We analyzed, retrospectively, the files of 14 patients who were treated in our strabismological department for persistent diplopia caused by injury to the extraocular muscles and/or to the surrounding structures. The aim of our treatment protocol was to restore comfortable binocular single vision in primary position and downgaze. The selection of the surgical procedure depended on the deviation in primary position and on the degree of ocular muscle imbalance. Surgery consisted of recession of the inferior rectus muscle of the affected eye in 4 cases, resection of the inferior rectus muscle of the affected eye in 4 other cases, and large recessions of the vertical muscles of the contralateral normal eye in 6 cases. RESULTS: In all 14 patients, we obtained the desired comfortable field of binocular single vision, considered "good" (20 degrees up to 30 degrees downgaze) or "satisfactory" (a useful field). In 11 cases this was achieved in one procedure. Two patients needed a reintervention because of initial overcorrection, and one patient for an initial undercorrection. All 14 patients had a "good" or "satisfactory" final result (useful binocular single vision). CONCLUSIONS: When extraocular muscle surgery is necessary, we recommend in patients with limited forced elevation, recession of the taut rectus inferior muscle; in patients with the clinical characteristics of an inferior rectus palsy, a resection of this muscle; and in cases with a normal or only slightly limited forced duction test, weakening the contralateral synergists.

Diplopia↗
PubMed1996

Colour contrast thresholds are normal in functional amblyopia.

We evaluated colour contrast thresholds in patients with unilateral functional amblyopia. A computer-controlled colour vision test was used to determine colour contrast thresholds along a blue-yellow tritan axis. Prior to the threshold measurement, a heterochromatic flicker brightness test was performed to ensure isoluminance between the test stimulus and the background for every subject individually. Luminance contrast thresholds were also measured using the same computer-based system. Twenty amblyopic patients were tested. All showed normal tritan colour contrast thresholds both for their amblyopic eye and non-amblyopic fellow eye. Luminance contrast thresholds were elevated in all 6 refractive amblyopic eyes, in 4 of 9 strabismic eyes and in 2 of 5 mixed amblyopic eyes. Colour contrast thresholds are normal in functional amblyopia (with central fixation). Whenever elevated tritan colour contrast thresholds are found in patients with a decreased visual acuity, other causes of visual impairment are to be evaluated.

Adolescent↗
PubMed1992

Surgery on the extra-ocular muscles after orbital fracture.

We analyzed the files of 61 patients presenting with diplopia due to orbital fractures. Thirty-four patients needed a primary orbital reconstruction and this diminished the complaints of diplopia in most cases. In only 5 cases additional ocular surgery on the extra-ocular muscles was indicated. Of the 27 patients who did not require orbital surgery, 5 underwent extra-ocular muscle surgery to diminish diplopia. We present our guidelines for treatment, based on forced duction testing, ocular motility, primary position and field of binocular single vision.

Diplopia↗
PubMed1989

Postoperative diplopia, also in children.

Permanent diplopia caused by strabismus surgery can also occur in children. In certain cases we see an analogy with the feared and well known persistent diplopia that can occur after anti-suppressive therapy. This article discusses some of these cases and their treatment.

Adolescent↗
PubMed1989

Primary exodeviations. Surgical results of 94 patients operated since 1983.

Surgical results of 94 patients with primary exodeviation operated since 1983 are presented. Seventy-five patients where treated bilateral rectus externus muscle recession and 19 patients with recession of rectus externus combined with resection of rectus internus muscle. Both techniques have equal results.

Adolescent↗
PubMed1982

Experimental human exposure to n-Hexane. Study of the respiratory uptake and elimination, and of n-Hexane concentrations in peripheral venous blood.

The respiratory uptake rate of n-hexane showed considerable differences in six healthy male persons, exposed at rest to 360 mg/m3 and 720 mg/m3 of n-hexane in inspired air and to 360 mg/m3 under different levels of physical exercise. These differences could partly be explained by a positive correlation with the amount of body fat. At rest also a strong influence of the respiratory minute volume and respiratory frequency on the uptake rate could be proven. The average uptake rate remained virtually constant over a range of 20 to 60 W of continuous external physical load, indicating that under these circumstances the inspired n-hexane concentration alone predominantly determines the uptake rate. The respiratory elimination during the first hours after an exposure was also subject to important inter- and intraindividual fluctuations. The pulmonary ventilation rate at the moment of breath sampling had a pronounced influence on the measured exhaled concentration. On the other hand, there was no apparent effect of the amount of body fat. Generally, the correlation between the amount of n-hexane taken up and breath concentrations at different time intervals was rather poor. n-Hexane concentrations in peripheral venous blood reacted rapidly to changes in exposure conditions, but not in the same proportion as the uptake rate. The blood concentration proved more closely related to respiratory n-hexane retention than to the uptake rate, reflecting the state of saturation of different body tissues. At rest this parameter was clearly influenced by the amount of body fat. A decrease in relative blood perfusion of fatty tissue could explain why such relation was not found during exposure combined with physical effort.

Adult↗