Search PubMed⌕ Search

Biomedical subjects

G Nikiforidis

Publications and source records attributed to G Nikiforidis.

35 records · Page 2Linked to original sources
PubMed1997

Mechanical behaviour of scalp hair in premature and full-term neonates.

Using a new computerized methodological procedure a separate analysis and a quantitative determination of the viscous and elastic parameters of the scalp hair shaft were performed in 37 neonates of both sexes with a gestational age of 28-29 weeks (n = 16) and 39-40 weeks (n = 21), respectively. A statistically significant (p < 0.001) decrease in the values of modulus of elasticity (E alpha) was found in the hair shaft of premature neonates, as compared to the full-term ones, whereas the values of post yield slope (E beta) and of SDIS/SSTOR (viscous parameter) did not significantly differ in the two groups. The decrease in modulus of elasticity in the hair shaft of premature neonates may be interpreted in terms of an insufficient number of disulphide bonds between the alpha-helical keratin units of the hair cortex or of a disordered arrangement of microfibrils within the matrix. Further studies are now warranted to determine the pattern of mechanical parameters of the scalp hair shaft in large numbers of newborn infants of different gestational ages and to answer the question as to whether this pattern might be useful in the accurate postnatal assessment of fetal maturation.

Biomechanical Phenomena↗
PubMed1996

Brittle and sparse hair with normal cystine content caused by methionine deficiency?

The unusual case of an 8-year-old girl with a hair disorder is presented, characterized by brittle, short and sparse hair. On polarizing microscopy the latter reveals a "tiger tail" pattern, whereas severe cuticular defects are detected on scanning electron microscopy. The patient's hair has a normal cystine content but is completely devoid of methionine and reveals distinct changes of its visoelastic parameters. It is presently unknown whether the lack of methionine may be implicated in the pathogenesis of this hair disorder, which to the best of our knowledge has not been previously described.

Child↗
PubMed1995

Reduced variance of latencies in pudendal evoked potentials after normalization for body height.

The value of the Somatosensory Evoked Potentials (SEP) in the assessment and detection of neurological disorders could be considerably enhanced if the normative standards of (SEP) characteristic parameters were normalized taking into account all other systematic sources of variance. The present study examines the influence of body height on the peak and interpeak latencies of the pudendal somatosensory evoked potentials. We examined the peak latency (L1) of the evoked potential recorded at the L1 vertebra and the onset latency (ONc) of the cortical evoked potentials, after stimulation of the pudendal nerve, as a function of body height in 40 normal male subjects (age 20-40 years). Significant positive correlation was found between both (ONc) latency and ONc-L1 interpeak latency and body height (H). Assuming that the latter is proportional to the length of the neural pathways, the experimental data were fitted using a theoretical model representing the conduction in the sensory neuraxis as a function of body height. Using the estimated fitting functions, we normalized our data with regard to a typical value of body height. The normalized values of the aforementioned latencies reveal a significantly reduced variance, as compared to the original ones, and consequently their diagnostic importance is significantly increased. Similar procedures applied to the L1 (spinal) latencies and the latencies of the bulbocavernosus reflex (BCR) reveal no correlation with body height and this is discussed on the basis of neuroanatomical considerations.

Adult↗
PubMed1995

In vivo estimation of radiation dose in renal pelvis and parenchyma during renography.

A method is presented for the determination of the spatio-temporal distribution of the radionuclide in the kidney and estimation of the dose in the renal pelvis wall and parenchyma, during renograms, on the basis of real data. A protocol was formulated by means of which the processing of the frames acquired in the various stages of the renogram enables the determination of the mass of the renal pelvis and the parenchyma as well as the time distribution of radioactivity in these compartments. The proposed methodology was applied to 30 normal subjects and 35 patients with obstructive nephropathy, acute and chronic obstructive uropathy and hydronephrosis. Our results, when compared with the MIRD dose estimations for the entire kidney showed slight deviations in normals, whereas very significant deviations were observed in the cases with pathology. This is due to the fact that the mass of the 'source' and 'target' organs as well as the biodistribution of the radiopharmaceuticals are essential in dose determination and were completely different in our calculations from those used in the MIRD estimations. Comparing the absorbed dose in renal parenchyma and pelvis wall with that estimated in vivo for the kidney considered as a system of one compartment, we found large differences only in abnormal cases. Differences were also noted between the absorbed dose in the aforementioned renal compartments depending on the considered abnormal renal states.

Adult↗
PubMed1995

Anatomical shape of the airways in two different European populations. A radio-anatomical study of the airways.

Lateral radiographs of the airways were taken in 20 men and 24 women lying supine with the neck in the normal position. The mean configuration of the airways for men and women is presented in a standard coordinate system. The results (contours of the airways) are compared to those of a Swedish study since the same method was applied in order to find out, if the established model is valid for other populations. Significant differences were found between the two population groups as well as between males and females. This indicates both inter-racial and inter-sexual modification of the anatomical shape of the airways.

Adult↗
PubMed1994

Trichothiodystrophic hair reveals an abnormal pattern of viscoelastic parameters.

Separate analysis and quantitative determination of the viscous and elastic parameters of hair performed in 5 patients with trichothiodystrophy and in 20 sex- and age-matched control subjects revealed an abnormal pattern of the mechanical behavior of trichothiodystrophic hair. The change of the viscous parameter is probably associated with the profound alterations in the high-sulfur proteins of the interfilamentary matrix; the changes in the elastic parameters may be related to the reduced stability of the irregularly arranged microfibrils of trichothiodystrophic hair caused by the marked reduction of the disulfide cross-links.

Adolescent↗
PubMed1994

Effects of oral isotretinoin on human auditory brainstem response.

BACKGROUND: Accumulating evidence suggests that synthetic retinoids may be capable of affecting the differentiation and growth of nervous tissue in vivo and in vitro. On the other hand, adverse reactions concomitant with brainstem involvement definitely or probably related to oral retinoid therapy have been reported in a small number of patients. OBJECTIVE: The purpose of the present study was to substantiate the possible effects of oral isotretinoin on the synaptic activity and propagation of action potentials along the nerve fibers. METHODS: The auditory brainstem response of 33 patients with severe nodulocystic acne before and 3 weeks after the onset of oral isotretinoin administration was investigated using auditory evoked potentials. RESULTS: The paired analysis of the response variables before and after treatment failed to reveal any statistically significant differences. However, a marked increase in latencies and interpeak latencies and a decrease in amplitudes for both ears were found in 3 patients after therapy. CONCLUSIONS: It seems reasonable to suggest that these subclinical changes may be due to an isotretinoin-induced synaptic malfunction or to a conduction defect in the auditory nerve fibers.

Acne Vulgaris↗
PubMed1993

In vivo determination of radiation dose in kidneys and bladder during renogram: a new approach.

The radiation dose absorbed by a patient from a radiopharmaceutical is usually calculated with the help of the equations published by the Society's Medical Internal Radiation Dose (MIRD) Committee and the use of a Reference Man. However, the (MIRD) estimations are based on the assumption that the patient is a normal subject with the characteristics of the Reference Man. This is not always true particularly in some pathological situations which present large deviations from normal. The purpose of this paper is to determine the dose in kidneys and bladder, during renograms, on the basis of real data. A protocol is formulated by means of which the processing of the frames acquired in the various stages of the renogram enables the determination of the kidney and bladder mass as well as the time distribution of radioactivity in these organs. Our results are in accordance with MIRD estimations for normal cases, whereas very significant deviations are observed in pathological ones. This is due to the fact that the mass of the 'source' and 'target' organs as well as the biodistribution of the radiopharmaceuticals are essential in the dose determination and large deviations are expected between estimated and real doses when in some pathological cases the mass of kidney is particularly reduced or its clearance retarded.

Adolescent↗
PubMed1993

A method for the determination of viscoelastic parameters of human hair in relation to its structure.

An analytical model and the corresponding experimental procedure are presented, which make it possible to separately analyze the viscous and elastic components of human hair. Moreover, a computerized experimental system is described with which a standardized quantitative determination of the most important mechanical parameters of human hair can be performed. Comparative investigations of the mechanical behavior of hair specimens obtained from the frontoparietal and occipital scalp regions of 10 healthy human subjects showed no statistically significant differences with regard to their mechanical parameters. Nevertheless, the paired analysis of the mechanical parameters of thin and thick hair specimens revealed that the values of two of these parameters are significantly higher in thin than in thick hair specimens. These findings suggest that there are mechanical parameters of human hair related to gross hair morphology, whereas others depend on hair microstructure.

Adolescent↗
PubMed1992

Viscoelastic response of human hair cortex.

The present study describes a new methodological approach which allows the separate analysis and quantitative determination of the viscous and elastic components of human hair using a computerised experimental system. In a first series of experiments subsequent to the estimation of the cross-sectional surface area of the cuticle, the cortex and the medulla, the viscoelastic response of hair (considered as a homogeneous material) and of its cortex were determined in ten hair specimens derived from the same human subject. Statistically significant differences were found between hair and its cortex with regard to the values of the modulus of elasticity, limit of linearity and post-yield slope. In a second series of experiments the viscoelastic parameters of hair and its cortex were separately determined in 100 hair specimens derived from ten healthy human subjects (ten specimens from each subject). It was found that the dispersion of the values of modulus of elasticity, limit of linearity and post-yield slope of the cortex was significantly reduced compared with that of the hair. Our results indicate that the pattern of the viscoelastic parameters of human hair cortex, which strongly depends on its microstructural features, may be regarded as a more reliable and sensitive diagnostic marker than that of hair in various structural and functional hair disorders.

Biomechanical Phenomena↗
PubMed1992

Mechanical parameters of human hair: possible application in the diagnosis and follow-up of hair disorders.

Mechanical analysis of human hair may provide the dermatologists with several markers of considerable diagnostic importance. In the present paper, using a new computerised experimental system, attempts were made firstly to interpret the curves of the elastic and viscous components of the mechanical behavior of human hair and secondly to determine characteristic parameters which correlate well with its structural features. In order to overcome methodological problems due to the inhomogeneous structure of human hair, mechanical parameters were defined which either depend on the cortical microstructure or correlate well with the size of hair medulla.

Adolescent↗
PubMed1992

[Curling and kinking of hair caused by etretinate].

In two female psoriasis patients, curling and kinking of the scalp hair developed subsequent to a long-term etretinate therapy. Scanning electron microscopic examination of kinking hair revealed twists with sharp-edged defects and splitting of the cuticle cells in several hairshafts. The quantitative determination of the mechanical parameters of these hairs using a computerized system revealed statistically significant changes from the pattern in the scalp hair of untreated psoriasis patients. This finding suggests etretinate-induced alteration of the expression of the psoriatic phenotype in the keratin composition of hair in psoriasis patients.

Adult↗
PubMed1990

Monitoring of fracture healing by lateral and axial vibration analysis.

The ability to monitor the healing of bone fractures is crucially important in their treatment. The aim of the present study was to develop and validate an objective method for monitoring fracture healing based on bone vibrational response. An analytic model was formulated, with which the mechanical parameters at the fracture site could be studied in relation to both lateral and axial bone vibration. Non-uniformities in the stiffness of the bone at the fracture site can be detected since they produce shifting of the vibration and the phase spectrum and result in strong coupling between the lateral and axial vibration response spectra. The validity of the model was tested in experiments using fresh cadaver tibiae with transverse osteotomy and materials simulating fracture callus. The results of the study of vibration amplitude and phase angle and the coupling of axial and lateral vibration in these experiments confirm our analytic projection. Preliminary results of in vivo investigations using the described method are encouraging.

Adolescent↗
PubMedDate not supplied

[Adaptation of the viscoelastic behavior of bone cement to bone as a stabilizing factor in endoprostheses].

Incompatibility of viscoelastic properties is a major factor contributing to the development and enlargement of microscopic cracks between bone and bone cement. In the study reported here the viscoelastic characteristics of fresh long bones were studied in vitro and compared with those of bone cement. Using strain gauges, creep elongation was measured over time spans ranging from 10(-2) to 10(3) seconds with an applied stress of 10 MPa. On the basis of these measurements creep compliance and permanent elongation at two points on a sheep femur were calculated by means of a rheologic Kelvin model with three parameters. The possibility of obtaining an optimal bone/cement bond was studied in the light of these results and of data published in the literature on bone cement creep related to cement composition factors.

Biomechanical Phenomena↗
PubMedDate not supplied

Computer-based grading of haematoxylin-eosin stained tissue sections of urinary bladder carcinomas.

PURPOSE: A computer-based image analysis system was developed for assessing the malignancy of urinary bladder carcinomas in a more objective manner. Tumours characterized in accordance with the WHO grading system were classified into low-risk (grades I and II) and high-risk (grades III and IV). MATERIALS AND METHODS: Images from 92 haematoxylin-eosin stained sections of urinary bladder carcinomas were digitized and analysed. An adequate number of nuclei were segmented from each image for morphologic and textural analysis. Image segmentation was performed by an efficient algorithm, which used pattern recognition methods to automatically characterize image pixels as nucleus or background. Image classification into low-risk or high-risk tumours was performed by means of the quadratic non-linear Bayesian classifier, which was designed employing 36 textural and morphological features of the nucleus. RESULTS: Automatic segmentation of nuclei on all images was about 90% on average. Overall system accuracy in correctly classifying tumours into low-risk or high-risk was 88%, employing the leave-one-out method and the best combination of three textural and one morphological feature. Classification accuracy for low-risk tumours was 88.8% and for high-risk tumours 86.2%. CONCLUSION: The proposed image analysis system may be of value to the objective assessment of the malignancy of urine bladder carcinomas, since it relies on nuclear parameters that are employed in visual grading and their prognostic value has been proved.

Algorithms↗
PubMedDate not supplied

A prospective cohort study of the outcome of acute whiplash injury in Greece.

OBJECTIVE: An earlier pilot study suggested that the late whiplash syndrome is uncommon in Greece. The purpose of the present study is to extend the evaluation to a larger sample, and include the prevalence of specific symptoms in the evaluation. METHODS: In a prospective, cohort study, a total of 180 accident victims were consecutively recruited following Emergency ward presentation. A standard questionnaire asked about neck pain, headache, shoulder pain, limb numbness or pain, and dizziness. Accident victims were followed for 6 months. RESULTS: In the initial 4 weeks after the accident, accident victims reported neck pain, headache, shoulder pain, arm numbness or pain, and dizziness, but at 4 weeks more than 90% had recovered from these, the remainder of the subjects having minor symptoms (not requiring therapy), and returning to their pre-accident state of health (which included minor symptoms). There were no cases of chronic disability. CONCLUSION: In Greece, symptoms after an acute whiplash injury are self-limiting, brief, and do not appear to evolve into the so-called late whiplash syndrome.

Acute Disease↗