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Biomedical subjects

J Juhasz

Publications and source records attributed to J Juhasz.

At least 19 recordsLinked to original sources
PubMed2004

Influence of proportional assist ventilation on diaphragmatic activity in normal subjects.

In six awake healthy adults we studied the physiological effects of mechanical unloading of the respiratory muscles during increased ventilatory demand. We were interested in whether respiratory muscle activity is down regulated and if this is mainly a consequence of chemical factors, i.e. CO2-reduction, or non-chemical neuromuscular inhibition. With 33 mmHg inspiratory CO2 we induced modest hyperpnea of 24.4 +/- 3.9 L/min. Proportional assist ventilation (PAV) was applied with flow-related assist of 2.5 cm H2O/L/s and volume-related assist of 6 cm H2O/L. Respiratory muscle activity was measured by transdiaphragmatic pressure. Unloading caused a 57 percent reduction of the inspiratory transdiaphragmatic pressure-time product (p<0.05), while tidal volume, breathing frequency, and breathing pattern did not significantly change. These observations suggest that during increased ventilatory requirements, PAV results in down regulation of respiratory muscle activity and that this effect is mainly a consequence of neuromechanical inhibition.

Adult↗
PubMed2000

Multistep production of bioengineered skin substitutes: sequential modulation of culture conditions.

Many studies are being conducted to define the role of growth factors in cutaneous physiology in order to add cytokines in a timely fashion for optimal tissue engineering of skin. This study is aimed at developing a multistep approach for the production of bioengineered skin substitutes, taking into account the effects of various growth factors according to the culture time. The use of a serum-supplemented medium throughout the whole culture period of skin substitutes was compared to the sequential use of specific additives at defined culture steps. Histological analysis revealed that serum was necessary for keratinocyte proliferation and migration on dermal substitutes during the first 2 d after their seeding. However, the serum-free medium presented some advantages when supplemented with different additives at specific culture steps. Interestingly, ascorbic acid added to the dermal substitutes before and after keratinocyte seeding maintained their cuboidal morphology in the basal epidermal layer. In the absence of serum, collagen matrix degradation slowed down, and a better multilayered epidermal organization was obtained, notably with retinoic acid. Stratum corneum formation was also enhanced by fatty acids. Thus, sequential addition of exogenous factors to the medium used to produce skin substitutes can improve their structural features and functional properties in vitro.

Animals↗
PubMed1999

Physical characterization of the stratum corneum of an in vitro human skin equivalent produced by tissue engineering and its comparison with normal human skin by ATR-FTIR spectroscopy and thermal analysis (DSC).

An in vitro human skin equivalent may be obtained by culturing human keratinocytes on a collagen gel containing fibroblasts. The anchored skin equivalent cultured at the air-liquid interface closely resembles human skin and is acceptable for in vitro percutaneous absorption. However, it is still more permeable than human skin. Since intercellular lipids have been recognized to play an important role in skin permeability, infrared spectroscopy and differential scanning calorimetry were performed on the stratum corneum of bovine or human skin equivalents grown at different days of air-liquid culture. The symmetric and asymmetric CH(2) stretching vibrations suggested that for all days observed, the intercellular lipids were less organized than those in human skin, irrespective of whether bovine or human collagen was used. Different culture conditions were also tested and the medium without serum and no epidermal growth factor at the air-liquid culture showed results significantly more comparable to human skin. Actually, the thermal behavior of in vitro stratum corneum showed transitions at lower temperatures than human skin. The transition around 80 degrees C, in the form of a lipid-protein complex, was absent. These results showed that the structural arrangement of intercellular lipids and their thermodynamic properties hold a crucial role in the barrier function of the stratum corneum.

Animals↗
PubMed1999

Clinical significance of sleep-related breathing disorders in patients with implantable cardioverter defibrillators.

The prevalence and clinical significance of sleep-related breathing disorders (SRBDs) in patients with cardiac disease and a history of life-threatening ventricular tachyarrhythmias is unclear. Forty consecutive recipients of implantable cardioverter defibrillators (ICDs) with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full night polysomnography. SRBDs were diagnosed if the apnea/hypopnea index was > 10. SRBD were diagnosed in 16 of 40 patients (40%): central sleep apnea (CSA) was present in 9 of these 16 patients (56%), 8 of whom had associated Cheyne-Stoke respiration. Seven of the 16 patients with SRBD (44%) had obstructive sleep apnea (OSA). Patients with and without SRBDs were comparable with respect to left ventricular ejection fraction, NYHA classification, underlying heart disease, ICD indications, and concomitant antiarrhythmic drug and beta-blocker therapy. Patients were followed prospectively for 2 years. ICD-treated ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA (NS). The numbers and circadian distributions of episodes recorded during follow-up in patients without SRBD versus with CSA or OSA were not significantly different (14 +/- 25, median = 4 vs 4 +/- 5, median = 2.5 vs 15 +/- 15, median = 7, respectively). The 2-year mortality, which was entirely attributable to nonsudden cardiac events, was highest in patients with CSA (4/9 [44%], vs 0/7 [0%] with OSA, vs 3/24 patients (12.5%) without SRBD; P < 0.05).

Aged↗
PubMed1998

[Clinical significance of sleep apnea disorders after implantation of a cardioverter-defibrillator in patients with cardiac disease and sustained ventricular tachyarrhythmia].

The purpose of our study was to determine the prevalence of sleep related breathing disorders (SRBD) in patients with an implantable cardioverter-defibrillator (ICD) and to evaluate prospectively the possible influence of SRBD on arrhythmia recurrence and circadian arrhythmia variation as well as on cardiac mortality during long-term follow-up. Forty consecutive ICD recipients with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full-night polysomnography and were followed for 2 years. In 16 of 40 patients (40%), SRBD were diagnosed (Apnea/Hypopnea Index (AHI) > 10); in 9 of these 16 patients (56%) central sleep apneas (CSA) occurred (in 8 of these 9 patients in combination with Cheyne-Stokes respiration). Seven of the 16 patients with SRBD (44%) revealed obstructive sleep apneas (OSA). AHI was 32 +/- 15 (12-60) in patients with CSA and 32 +/- 27 (11-86) in patients with OSA. Patients with and without SRBD were comparable concerning left ventricular ejection fraction, NYHA classification, cardiac disease, ICD indication, and concomitant medication. ICD registered ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA. The numbers and circadian variation of episodes registered during follow-up in patients without SRBD, with OSA or CSA were comparable (14 +/- 25, median 4 vs 15 +/- 15, median 7 vs 4 +/- 5, median 2.5). The 2-year cardiac mortality was highest in patients with CSA (4/9 (44%) vs. 0/7 patients (0%) with OSA vs 3/24 patients (12.5%) without SRBD. Thus, the prevalence of SRBD in patients with chronic heart failure and a history of malignant ventricular tachyarrhythmias is high (40%) and the occurrence of CSA seems to be predictive for cardiac mortality in these patients. An influence of moderate SRBD on arrhythmia recurrence and circadian variation of spontaneous sustained tachyarrhythmic events could not be demonstrated.

Aged↗
PubMed1998

Influence of endothelial cells on structure, biochemistry and functionality of epidermis reconstructed on synthetic porous membrane.

The model of keratinocytes cultured on a synthetic porous membrane at the air-liquid interface leads to the formation of a pluristratified and cornified epidermis with histological and biochemical characteristics near those observed in vivo. In the present study, we evaluated the effect of proliferative endothelial cells on epidermalization. Keratinocytes were grown in three culture conditions: in defined medium (DM; control), in medium previously conditioned by proliferative endothelial cells (CM) and in medium with proliferative endothelial cells (pEC). The structures of reconstructed epidermis were analyzed by electron microscopy, their biochemistry by DNA, protein and cytokine analyses and finally their functionality was evaluated by estradiol and water absorption testing. Ultrastructural analysis showed a well-developed and cornified epidermis for each culture condition. In addition, living epidermis was thinner in the presence of endothelial cells, revealing faster epidermal differentiation. DNA and protein analyses were in accordance with these results. Secreted soluble factors varied according to culture conditions. At 37 degreesC, the permeability of reconstructed epidermis in DM, in CM or with pEC was 5- to 10-fold higher than that of native human epidermis with both tracers. Laminin coating of the inserts led to similar absorption results except for the DM where the barrier function to estradiol was decreased 2-fold. At 32 degreesC, reconstructed and native epidermis were, respectively, 1.5- and 2-fold less permeable to estradiol compared to 37 degreesC. In conclusion, this model is adequate for fundamental and pharmacological studies since it allows the study of interactions between two cell types without their direct contact as well as percutaneous absorption tests directly performed in the modified culture chamber.

Cell Differentiation↗
PubMed1997

Study of the Gelation Process of Polyethylene Oxidea -Polypropylene Oxideb -Polyethylene Oxidea Copolymer (Poloxamer 407) Aqueous Solutions

The gelation process of polyethylene oxidea -polypropylene oxideb -polyethylene oxidea copolymer (poloxamer 407) aqueous solutions is studied by means of FTIR spectroscopy, rheology, and differential scanning calorimetry (DSC). The C-O-C stretching bands of infrared spectra were found to shift toward higher wavenumbers with sol-gel transition, indicating that hydrogen bonding is not the driving force for gelation. Linear viscoelastic data provide an alternative method for gel point determination of these thermoreversible gels. The results obtained with this method are found to coincide with those obtained using DSC. Gel point temperatures determined by these methods are close to 14 degrees C for 25% (w/w) poloxamer 407 solutions and 10 degrees C for 30% (w/w) solutions. In gel state, the elastic modulus (G ') and dynamic viscosity (eta*) are found to be concentration and temperature independent for temperatures ranging from 20 to 35 degrees C. In light of our results, we suggest a mechanism of gelation based on micelles packing and entanglements.

Journal Article↗
PubMed1990

Mucoadhesion of hydroxypropylmethacrylate nanoparticles to rat intestinal ileal segments in vitro.

The purpose of this study was to evaluate the adhesion of HPMA nanoparticles to mucus using a perfused rat ileum test system. Radiolabeled nanoparticles were prepared and deposited onto rat ileal segments in vitro. The segments were perfused and the perfusate was collected in fractions and assayed for radioactivity. Between 10 and 50% of the radioactivity was eliminated over the first 120-sec perfusion, whereas the remaining activity was firmly attached to the ileum. Among the variables tested, the time interval between nanoparticle deposition and perfusion played the major role, indicating that the mucus-nanoparticle interaction is likely to result from the diffusion of polymers into the mucus and of mucin into the polymeric matrix.

Acrylates↗
PubMed1989

New method for the preparation of cyanoacrylic nanoparticles with improved colloidal properties.

The purpose of this study was to prepare nanoparticles with a size significantly smaller than 0.1 micron. It was shown that when sulphur dioxide was dissolved in the cyanoacrylic monomer at a high concentration, subsequent anionic polymerization in an aqueous phase produced particles as small as 10 nm. Moreover, the obtained particles displayed an important negative charge which improve their stability against aggregation. Finally, nanoparticles were successfully prepared in double-distilled water, thereby avoiding the use of dextran which can induce anaphylactoid reactions.

Chemistry, Pharmaceutical↗
PubMed1989

Diffusion of rat atrial natriuretic factor in thermoreversible poloxamer gels.

Concentrated poloxamer 407 solutions display a negative thermorheological behaviour, resulting in a higher viscosity at body temperature than below. This could be exploited for various controlled delivery applications including the nasal delivery of peptides. The rheology of the gel and the diffusion of ANF were studied as a function of temperature. A theory is proposed, according to which a temperature rise creates an intermicellar network resulting in a viscosity increase. The diffusion of the drug appears limited only by the presence of micelles which lengthens the diffusion pathways and is not significantly influenced by the formation of this network.

Atrial Natriuretic Factor↗
PubMed1987

Ambroxol and simple chronic bronchitis. Effects on subjective symptoms and ventilatory function.

In a double-blind, randomized, controlled trial using parallel groups, we evaluated the effects of two dose levels of ambroxol (60 and 120 mg daily) versus placebo by means of pulmonary function tests, patients' diary cards, interviews on current airway symptoms and subjective drug effects in 92 subjects with simple hypersecretory chronic bronchitis. The treatment period was 2 weeks. Subjects in the 120-mg group compared to the placebo group reported improvement in respiratory symptoms (p less than 0.05), particularly in phlegm loosening (p less than 0.05) and tended to prefer the treatment period when compared to placebo (p = 0.056). Lung function values and diary cards did not indicate significant changes.

Adult↗
PubMed1976

The effect of intracranial hypertension on cerebrovascular resistance--an experimental study.

Pulse transmission through cortex between a vein and artery in the middle cerebral distribution has been used as an index of vascular resistance in the middle cerebral field in baboons. Following catheterisation of these small vessels, the skull has been reconstituted and the effect of intracranial hypertension produced by cisternal infusion has been studied. An earlier linear relaxation of resistance in relation to rising intracranial pressure has been succeeded by a second phase in which pulse transmission increases quite profoundly despite minimal further increase in intracranial pressure. This appears to represent the exhaustion of the compliance of the vascular compartment, and corresponds closely to levels of intracranial pressure at which failure of autoregulation to increased intracranial pressure has been observed in previous experiments. Spontaneous bursts of transient increased pressure made their appearance in a number of animals at this level of pressure. The possible significance of increased pulse transmission following exhaustion of compliance in relation to breakdown of the blood brain barrier and potential spreading oedema is discussed.

Animals↗
PubMed1976

Measurements of oxygen tension in the cerebral cortex of baboons.

A polystyrene-covered platinum electrode (100-150 mum diameter) has been used to measure cortical tissue oxygen tension in baboon brains. The method of preparation, calibration, and the importance of small residual current (less than 40 nA) as an attribute of a reliable electrode, are described. With electrodes of this size, there was a large (16 +/- 12nA/torr) and linear current output with pO2 changes. The effect of avrious gases in addition to oxygen is described; halothane inhalation increases the apparent pO2 and hydrogen, used for blood flow estimations, reduces the recorded pO2. In 48 separate electrode placements in 13 baboons, the mean cortical qo2 was 23.8 +/- 12 mm Hg, with a range from 1-79 mm Hg; following occlusion of one middle cerebral artery, 37 electrodes recorded a pO2 of less then 5 mm Hg pO2 Oscillations were invariably noted in control conditions, independent of blood pressure; these waves disappeared during MCA occlusion and appeared to be augmented following release of the clip. Blood pressure "spikes" produce immediate and synchronous changes in all electrodes entirely different from the spontaneous waves. Such blood pressure changes may mask the true effect of hypercapnia on tissue pO2 and, if ignored, may lead to erroneous assumptions regarding local neural control of the circulation, the increased pO2 secondary to hypertension being regarded as evidence of regional vasodilation. A SUdden change in inspired pO2-the "air test"-was performed in control conditions and following the ischaemic insult, and the rate of change of cortical pO2 compared. The gradient was significantly greater (P less than 0.05) following ischaemia, suggesting a changed ratio in the tissue's flow to oxygen requirements and/or a persisting vasodilatation.

Animals↗
PubMed1976

Changes in regional cortical tissue oxygen tension and cerebral blood flow during temporary middle cerebral artery occlusion in baboons.

Cortical tissue oxygen measured by a platinum cathode, and cerebral blood flow recorded by a hydrogen clearance technique, were measured in 13 baboons before, during and after temporary occlusion of the middle cerebral artery. Mean control pO2 was 23.8 +/- 14 mm Hg and mean flow 51.3 +/- 12 ml/100g/min. During the occlusion, there was a gradation in pO2 from values in the opercular area of 3.6 +/- 5.9 mm Hg, to values in the high parietal area of 11.9 +/- 11.7, these being statistically different (P less than 0.05) from each other. The corresponding flow values were 5.5 +/- 7.5 (opercular) and 22.3 +/- 21.7 ml/100 g/min parietal (P less than 0.01). Following removal of the MCA clip, between 20% and 30% of the electrodes registered an early hyperoxia and hyperaemia, which lasted up to 5 min. A late and prolonged hyperoxia, with less evidence of hyperaemia, was also noted in about 20%. The mean tissue pO2, however, at 5-min intervals up to 40 min following the removal of the clip only reached 60-80% of control values in the most ischaemic areas. Only the parietal region showed a mean pO2 above control levels. The mean flow data were uniformly reduced in all regions to about 80% of control values. During and after a second occlusion in 6 animals, similar changes were noted but with even fewer instances of hyperoxia. The mean oxygen and flow results were lower than with the first occlusion, but the reduction was not significant. There was no overall effect of hypercapnia on cortical tissue pO2 during the control period, but there was a significant (P less than 0.05) reduction during the same procedure after the period of ischaemia. An increase in pO2 during hypercapnia could be observed if there were arousal responses of blood pressure "spikes".

Animals↗
PubMedDate not supplied

Local cerebral blood flow and vascular reactivity in a chronic stable stroke in baboons.

Blood flow in the hemispheres of baboons three years after middle cerebral artery occlusion has been assessed by the hydrogen clearance technique. Blood flow in the infarct itself varied from very low (8 ml/100 gm per minute) to very high (89 ml/100 gm per minute) values and, averaging the values for the infarct as a whole, it was impossible to distinguish average flows in the infarct from those of the normal hemisphere. Flow values in surrounding zones of the infarct remained significantly lower than those of comparable normal hemispheres, and, excluding the infarct, the mean average hemispheral blood flow was 35.2 ml/100 gm per minute. This indicates a significant reduction in flow in the cortex, subsequently shown histologically to be normal, compared with normal blood flow values for the baboon hemisphere. Autoregulation was lost in the infarct and impaired in surrounding tissue. CO2 reactivity was grossly reduced in the hemisphere as a whole but was present in all areas, even occasionally in electrode placements within the infarct itself. After perfusion fixation of the head, pathological study of the area of infarction showed a fairly consistent distribution, the infarct itself consisting of many dilated blood vessels of non-capillary nature scattered among fibrous tissue in what was virtually a glial scar.

Animals↗
PubMedDate not supplied

Early surgery for ruptured cerebral aneurysm.

Preliminary experience with 150 consecutive cases of ruptured cerebral aneurysms operated on within 48 hours is reported. The rationale of this emergency procedure is to prevent early rerupture and also to prevent neurological ischaemic consequences of the subarachnoid haemorrhage likely to develop in the first week after a rupture. The acceptable outcome of the surgically treated cases (87% excellent and good outcome) has been favourably matched to those of a group of equal number of consecutive cases seen in suitable condition for surgery within 48 hours by medical personnel but that remained unoperated for various reasons. The incidence of delayed neurological ischaemia as the definite cause of death is lower in the group operated on in the acute stage than those with delayed surgery, although the overall incidence of clinical vasospasm does not seem significantly lower than in the delayed surgery group.

Adolescent↗