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Biomedical subjects

C Hartung

Publications and source records attributed to C Hartung.

At least 19 recordsLinked to original sources
PubMed2001

Biomechanical comparison of different fixations of femur-interlocking-nails.

OBJECTIVE: A new design of intra-medullary nailing fixation is investigated in this study. The strength properties of the new design are compared to the standard fixation method. DESIGN: The bone-implant-compound is examined by using experimental methods. BACKGROUND: Failure of bone substance in the region of the interlocking screws is a complication in particular in treating fractures of osteoporotic bone. A new additional implant is investigated, which should improve the fracture fixation of the bone-implant-compound. METHODS: The experiments were performed by using an universal testing machine. The bone-implant-compound was loaded by different compressive forces and the stiffness of the bone-implant-compound was measured. The maximum force to failure was also determined by a destructive test. RESULTS: The experimental results indicate that the additional implant increases the stiffness of the bone-implant-compound. The highest stress concentrations occur at the drill holes of the interlocking screws. Failure of the bone-implant-compound occurs at higher maximum forces by using the additional implant. CONCLUSIONS: The additional implant improves the strength of the bone-implant-compound. In the case of osteoporotic bone, the use of the additional implant is recommended. RELEVANCE: In surgical treatment of fractured femurs, the fracture is bridged by a medullary nail fixed with interlocking screws. Failure of bone substance in the region of the interlocking screws is the most common complication in the treatment of osteporotic bone. With the aim of preventing this complication, a new additional implant is developed and investigated.

Biomechanical Phenomena↗
PubMed2001

In vitro susceptibility of 137 Candida sp. isolates from HIV positive patients to several antifungal drugs.

Oropharyngeal candidiasis caused by various species of Candida is one of the most common infections in HIV seropositive or AIDS patients. Drug resistance among these yeasts is an increasing problem. We studied the frequency of resistance profile to fluconazole, itraconazole, ketoconazole, amphotericin B and terbinafine of 137 isolates of Candida sp. From HIV positive or AIDS patients with oropharyngeal candidiasis at Instituto de Inmunología, U.C.V. and the Hospital "Jose Ignacio Baldó", Caracas Venezuela, using the well diffusion susceptibility test (Magaldi et al.). We found that nearly 10% of C. albicans isolates were primarily fluconazole resistant, 45% of C. albicans isolates from patients with previous treatment were resistant to fluconazole, of which 93% showed cross-resistance to itraconazole, and even about 30% of C. tropicalis (n = 13) were resistant to fluconazole and/or itraconazole. To this respect, several recent reports have been described antifungal cross-resistance among azoles. Therefore, we consider that C. tropicalis should be added to the growing list of yeast in which antifungal drug resistance is common. This report could be useful for therapeutic aspect in AIDS patients with oral candidiasis.

AIDS-Related Opportunistic Infections↗
PubMed2001

Quantitative evaluation of the performance of different electrical tomography devices.

Two widely used electrical tomography systems, the Sheffield Mark I and the DAS-01P, were quantitatively evaluated and compared to the newly developed Goe-MF system. The performance was quantified using a hardware phantom which closely matches the real input and transfer impedances of the human thorax and allows measurements equivalent to different states of lung inflation. Our results demonstrate that adequate averaging is necessary for noise reduction for the Mark I and especially for the DAS-01P system to get meaningful results even in visualizing maximal respiratory manoeuvres. The Goe-MF system showed a notably improved signal-to-noise ratio which allows also dynamic measurements at low levels of lung volume changes, e.g., in intensive care lung injury patients.

Calibration↗
PubMed2000

Computerized classification of corpus cavernosum electromyogram signals by the use of discriminant analysis and artificial neural networks to support diagnosis of erectile dysfunction.

Corpus cavernosum electromyogram (CC-EMG) provides diagnostic information on cavernous autonomic innervation and a measure of the degree to which the cavernous smooth muscle cells are intact. The complicated CC-EMG is evaluated and used in the diagnosis of patients suffering from erectile dysfunction. The evaluation procedure has been simplified by applying digital signal processing techniques. Since mathematically-based interpretations require quantitative data, spectral analysis was performed. The derived biosignals were analyzed by fast Fourier transform (FFT). Besides various other spectral parameters, specific frequency bands were determined in the power spectrum using factor analysis. The parameters were used for the computerized classification of normal and pathological CC-EMG data and the classification was performed using two independent methods: discriminant analysis (DA) and artificial neural networks (ANN). A medical expert analyzed a total of 200 CC-EMG recordings from patients with and without erectile dysfunction and separated these into normal (136) and pathological (64) cases. Although each independent method had already resulted in a relatively high number of correct classifications, the classification success rate could be slightly improved by using a combination of both classification methods. A total of 72.79% and 77.94% were successfully classified using DA and ANN, respectively. The combination of both methods increased the classification success to 80.15%. The results of this study enabled impartial evaluation of the CC-EMG signals for clinical diagnostic purposes of erectile dysfunction. This method provided an objective and easy way to analyze the CC-EMG. Furthermore, this results in patient diagnosis becoming an easier task for less experienced doctors, since little knowledge of the raw signal is needed.

Algorithms↗
PubMed2000

Erysipelas and tinea pedis.

During a 2-year period 30 adults were selected out of a group of patients diagnosed with erysipelas, who, except for tinea pedis, were apparently otherwise healthy patients. Clinical and epidemiological studies were performed to establish how tinea pedis and erysipelas are related. Thirteen of 30 patients with a diagnosis of erysipelas were found to have tinea pedis due to Trichophyton mentagrophytes and Trichophyton rubrum. In seven of the patients (23%) tinea pedis was found to be the unique predisposing factor for erysipelas. Tinea pedis may be a risk factor for streptococcal infections such as erysipelas, mainly in tropical countries, where tinea pedis is a frequent disease.

Erysipelas↗
PubMed2000

Card Perseveration Task performance and post-task feeling states: relationship to drug use in adolescents.

This study examined whether performance on the Card Perseveration Task (Card Task) and self-report of feeling state after the task are related to self-report of drug use. The evaluation was of 64 adolescents from an adolescent psychiatric outpatient clinic (40 males, aged 15.5 years, SD = 1.6; 24 females aged 16.9 years, SD = 1.5). Drug use histories were obtained using a substance dependence symptom checklist based on DSM-III-R. The Card Task was administered, and after completion, a Post-Task Self-Report (PTSR) was administered. A factor analysis with varimax rotation grouped the 28 items of the PTSR into Distress, Happy, Satisfied, and Wanting to Win subscales. Correlations of drug use with performance on the Card Task and the PTSR subscales were obtained. Cards Played on the Card Task were correlated with alcohol (cc = .31, p < or = .01); marijuana (cc = .35, p < or = .01) and polydrug (cc = .26, p < or = .05) dependence symptoms. Money Won on the Card Task was correlated negatively with nicotine (cc = -.26, p < or = .05) and marijuana (cc = -.27, p < or = .05) dependence symptoms. The PTSR Distress subscale correlated with nicotine (cc = .49, p < or = .001), alcohol (cc = .37, p < or = .01), marijuana (cc = .39, p < or = .01), and polydrug (cc = .49, p < or = .001) dependence symptoms. These findings provide evidence that both the Card Task and feeling states associated with task performance are related to self-reports of drug use.

Adolescent↗
PubMed2000

[Finite element analysis of an additional implant for intramedullary nailing].

In the surgical treatment of fractured femurs, the fracture is bridged by a medullary nail fixed in the bone with interlocking screws. Failure of bone substance in the region of the interlocking screws is the most common complication in the treatment of osteoporotic bone. With the aim of preventing this complication, an additional implant was developed. A finite element analysis of an ideal bone/implant system was carried out to investigate the role of the additional implant. Three defined finite element models were generated, and the associated stress situations compared. The first model is a standard fixation without the additional implant. In the second model, the additional implant is integrated within the bone/implant system. The third model uses a modified form of the additional implant. The results show that both additional implants reduce the stresses occurring, both in the bone substance and at the screws. The modified form of the additional implant proved to be the most favorable version. In the case of the original additional implant, the negative effect of the sharp edges of the thread was demonstrable.

Biomechanical Phenomena↗
PubMed1998

High affinity regulation of cardiac Cl- and Ca2+ conductances by (13R)-spiroforskolin.

The effects of a new forskolin derivative, (13R)-spiroforskolin, on the ventricular cAMP-activated chloride current (I(Cl(cAMP))) and the atrial L-type calcium current (I(Ca,L)) were measured by means of whole-cell recording from isolated guinea-pig cardiac myocytes at 30 degrees C and 20-22 degrees C, respectively. In contrast to forskolin, the derivative contains a tetrahydrofuran rather than a tetrahydropyran moiety. (13R)-spiroforskolin activated I(Cl(CAMP)) in 58% of the ventricular myocytes studied. The concentration required for the half maximal effect (EC50 value) amounted to 9.6x10(-11) M and was lower than the EC50 value for forskolin (2.4x10(-8) M). (13R)-spiroforskolin evoked a smaller maximal I(Cl(cAMP)) amplitude than forskolin. The rundown of the (13R)-spiroforskolin-activated I(Cl(cAMP)) was faster than that of the forskolin-induced current. Neither forskolin nor (13R)-spiroforskolin in maximally effective concentrations increased I(Cl(cAMP)) in cells containing high concentrations of cAMP. Furthermore, as an activator of atrial I(Ca,L) (13R)-spiroforskolin displayed a smaller activation and a lower EC50 value (5.8x10(-10) M) than forskolin (EC50 value: 3.7x10(-7) M). The effect of (13R)-spiroforskolin was observed in only 30% of the atrial cells studied. None of the drugs exerted a stimulatory effect in atrial cells containing a high [cAMP]. The washout of the drug effect was significantly faster in (13R)-spiroforskolin- than in forskolin-treated atrial myocytes. We conclude that (13R)-spiroforskolin as a forskolin derivative displays unique characteristics. It is a more potent but less efficacious activator of cardiac ionic conductances than the parent compound. The results suggest that (13R)-spiroforskolin, like forskolin, most probably exerts its effects via stimulation of the adenylyl cyclase.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1997

Computer-assisted interpretation of electromyograms of corpora cavernosa using fuzzy logic.

An electromyogram of the corpora cavernosa (CC-EMG) imparts information on the autonomic cavernous innervation and/or the cavernous smooth muscles. The CC-EMG is interpreted mainly by evaluation of signal patterns of higher activity. The time required for interpretation is reduced by the implementation of a computer-assisted diagnosis program with a Microsoft Windows user interface. The program offers four levels of diagnosis: on the first level, recordings can be edited; on the second and third levels, signal patterns can be searched or evaluated; and on the last level the final diagnosis is provided. The computer-assisted interpretation is based on digital measurement data. These data have been obtained through a 170.6-Hz sampling frequency and a quantization of 10 V/12 Bit of the amplified signal. The first task of this diagnosis program is to discover and extract signal patterns of higher activity from data stored on the hard disk of a personal computer (PC). For a mathematic description of these patterns the following features were defined: relative time position, relative reproducibility, part of normal phases, and part of whip phases. Syntactic pattern recognition was introduced to identify the characteristic signal forms. An evaluation of the patterns could be derived from these features using fuzzy logic. For a summary of the evaluated patterns the variable global normality was established. The global normality forms an important evaluation basis along with the global synchronism, which represents an investigator's first impression of a recording. The final diagnosis is completed using fuzzy logic. The program was tested by comparison of expert and computer diagnoses. A total of 30 records were independently evaluated by an expert team and the computer program. With reference to the four classified levels of diagnosis a correspondence of 70% could be found. Furthermore, the rate in each of the classified levels was higher than 50%. The discrimination between normal and abnormal evaluation was 80% for clinical routine. Our results show that a computer-assisted interpretation of the CC-EMG can be achieved using mathematically based software. Within the last 7 months this computer-assisted CC-EMG program proved to be of great help in routine diagnosis. Furthermore, it demonstrated results comparable with a blinded-expert interpretation. This approach should bring about dramatic improvements in the diagnosis of erectile dysfunction.

Electromyography↗
PubMed1997

Computer-assisted evaluation of the smooth-muscle electromyogram of the corpora cavernosa by fast Fourier transformation.

OBJECTIVE: The aim of our study was to investigate analogous and digital recording of corpus cavernosum EMGs (CC-EMGs) in normal men according to criteria that were recently agreed upon in an international consensus workshop. METHODS: CC-EMGs were analogously and digitally registered from 37 normal subjects. Power spectra in the frequency domain were determined via fast Fourier transformation (FFT). RESULTS: Thirty-one of men showed identical or at least very similar electrical activity patterns in the analogous and digital registration. Needle penetration artifacts (investigated in 18 subjects) were found in 17/18 CC-EMGs during the first 20 min. Power spectra show a maximum of power at a frequency of 0.3 Hz with more than 90% of the power located between 0 and 5 Hz. CONCLUSIONS: Registration of CC-EMGs in normal men resulted in interindividually reproducible recordings. Age hardly affected CC-EMGs. Computer-assisted evaluation by FFT after elimination of artifacts was feasible. Thus, interpretation of the CC-EMG signals by a computer-aided expert system seems to be promising for clinical routine, in particular with respect to an increase in objectivity and a decrease in time needed for interpretation.

Adolescent↗
PubMed1997

[Electromyograms in erectile dysfunction and computer-assisted interpretation].

The electromyogram of the corpora cavernosa (CC-EMG) provides information on the autonomic innervation and/or smooth musculature. The interpretation of the CC-EMG, usually by evaluating signal patterns of higher activity, is time-consuming. To improve this situation, a computer-aided diagnosis employing a Microsoft Windows user interface was developed. The computer-aided interpretation is based on digital measurement data obtained using a 170.6 Hz sampling frequency and quantization of 10 V/12 bits of the signal. The first task of the program is to extract signal patterns of higher activity from stored data. To describe these patterns in mathematical terms, the features "relative time position", "relative reproducibility", "portion of normal phases", and "portion of whip phases" are calculated. Characteristic signal forms (normal and whip phases) are identified by means of syntactic pattern recognition. Using fuzzy logic, the features are used to effect pattern evaluation. To summarize the evaluated patterns, the variable "global normality" has been established, and linked to the "global synchronicity" at a second fuzzy logic level, to produce the final diagnosis. Finally, 30 records were evaluated independently by a team of experts and by the computer program. In relation to four established diagnostic classes, a correspondence of 70% was found. Furthermore, the accuracy achieved in each of the individual classes was better than 50%. Discrimination between normal and abnormal evaluation, which is of particular interest, reached 80%.

Autonomic Nervous System↗
PubMed1996

Application of factor analysis for the determination of specific frequency bands in corpus cavernosum EMG power density spectra.

Corpus cavernosum electromyogram (CC-EMG) recording provides diagnostic information on cavernous autonomic innervation and the intact state of cavernous smooth muscle cells. Evaluation of these signals is time consuming and complex. Therefore, we attempted to facilitate their interpretation and to increase their objectivity by using computer-based digital signal processing. Spectral parameters were used as a starting point for this analysis, which were calculated from the Fourier-transformed time domain CC-EMGs. Factor analysis was applied to determine specific frequency bands in the CC-EMG power density. Two hundred power spectra, taken from normal subjects (n = 66) and from patients suffering from erectile dysfunction (n = 134), constituted the basic data. As a result of applying factor analysis, four specific frequency bands were depicted: 0.0-0.3, 0.3-3.5, 3.5-6.0 and 6.0-10.0 Hz. The results of this study form the basis for further mathematical evaluation and calculation of the CC-EMG for clinical and diagnostic purposes.

Adult↗
PubMed1996

Mechanical testing of isolated senile human eye lens nuclei.

Phacoemulsification is a cataract surgery technique during which the eye lens nucleus is carefully dissected by an oscillating hollow needle simultaneously serving as a suction line for lens fragments. As the success of this procedure depends greatly on the mechanical properties of the nucleus, the basic mechanical properties of extracted senile human eye lens nuclei were studied. For this purpose a novel measuring system had to be developed enabling the study of the biomaterial's responses to any chosen excitation function. Either force- or displacement-controlled testing signals can be selected serving as a one-dimensional input. The resultant quantity can be recorded in the time or frequency domain. An almost linear viscoelastic behavior of lens nuclei is observed. Typical phenomena such as hysteresis, creep, relaxation, and a frequency-dependent compliance are evaluated. The ultimate strength of the specimen is studied by penetration tests. Finally the possible correlation between mechanical and optical parameters of lens nuclei is discussed. If correlated, a surgeon could use this information when deciding whether an extracapsular extraction or a phacoemulsification should be the preferred approach.

Aged↗