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Biomedical subjects

M Frenz

Publications and source records attributed to M Frenz.

32 records · Page 2Linked to original sources
PubMed1995

Bioelectrical impedance analysis as a predictor of survival in patients with human immunodeficiency virus infection.

In patients with AIDS, short-term survival has been related to body weight, body composition, and serum nutritional parameters, but their prognostic impact at earlier stages of the HIV infection is not known. With an individual follow-up period of 1,000 days, we investigated the prognostic relevance of electrical tissue conductivity [resistance R, reactance Xc, phase angle alpha, extracellular mass (ECM), body cell mass (BCM)] measured by bioelectrical impedance analysis, of the CD4+ cell count, and of serum parameters indicating malnutrition in 75 HIV-infected male patients at Walter Reed stages 3-5. After initial recording, 29 patients (38.7%) died from AIDS during this period. Among 12 parameters estimated with a semiparametric Cox regression model adjusted for therapy (pentamidine, azidothymidine), the phase angle alpha (parameter estimate: -1.043, 95% confidence interval of -0.61 to -1.47; p < or = 0.0001), the ECM/BCM ratio, Xc, BCM, serum cholesterol, number of CD4+ cells, and serum albumin had significant prognostic influence on survival, whereas age, body weight, body mass index, resistance, serum protein, and serum triglycerides did not. In a model with four covariates (CD4+ cells, phase angle, pentamidine, azidothymidine), the prognostic impact of the CD4+ cell count (parameter estimate: -0.549) was lower compared with the phase angle alpha (parameter estimate: -0.799; p < or = 0.0001) and did not gain statistical significance (p = 0.0626). The phase angle alpha was the best single predictive factor for survival among all 12 parameters (comparison of the respective Cox models with the likelihood ratio test).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Plastic hollow waveguides: properties and possibilities as a flexible radiation delivery system for CO2-laser radiation.

BACKGROUND AND OBJECTIVES: One significant inconvenience of the CO2 laser is the lack of flexible fibers essential for endoscopic applications. The goal of this study is to test the feasibility of hollow waveguides in view of a practical use in medicine. STUDY DESIGN/MATERIALS AND METHODS: Various types of plastic hollow waveguides for flexible delivery of CO2 laser radiation were examined. The transmission losses, divergence angle, damage threshold, and input and output beam profiles were determined. The interaction process between radiation transmitted through these guides with soft as well as hard tissues was studied. RESULTS: Plastic hollow waveguides can transmit high power (up to 50 W) with low losses (straight guide 1 dB/m) even through bendings. The divergence angle is < 13 degrees. Cutting quality and extent of thermal damage are comparable to incisions performed with a free laser beam. CONCLUSION: The results of this study show good cutting quality and durability of these flexible plastic hollow waveguides, which render possible to deliver CO2 radiation in the power range needed for most surgical applications with affordable transmission losses. Plastic hollow waveguides are, therefore, a real alternative to replace the mirror arms.

Animals↗
PubMed1994

Effects of various laser types and beam transmission methods on female organ tissue in the pig: an in vitro study.

The purpose of this in vitro study was to investigate and compare effects of various laser types (CO2, Argon, Erbium:YAG, Erbium:YSGG, and Holmium:YAG) and laser beam transmission methods (optical lens and flexible fiber) on ovarian and uterine tissue of the pig. The Erbium laser radiation was transmitted through Zirconium fluoride fibers (ZrF4). To circumvent the low mechanical stability of these fibers, we developed a special microlens system, which refocuses the radiation and protects the distal end from damage. Tissue lesions were performed with 1 and 5 joule. Histologic analysis of acute Er:YAG laser lesions reveal precise cutting effects with a minimal thermal damage zone of 40 microns and a high damage resistance of the fiber microlens systems. The extent of thermal damage caused by the Erbium:YSGG and CO2 laser is about two times larger, whereas the Argon and Holmium laser tissue lesions show a damage of the surrounding tissue of 200-300 microns. This study suggests that for precise cutting and coagulation, Erbium and Holmium lasers transmitted via our modified fiber tip may render the use of these lasers possible in a wide range of laparoscopic surgery applications.

Animals↗
PubMed1994

[High caloric parenteral nutrition in patients with mouth and oropharyngeal cancers--a clinical study].

Patients with carcinomas of the oral cavity and oropharynx often show signs of malnutrition. This is caused by reduced intake in patients due to chronic alcoholism resulting in suppressed appetite and disturbed gastrointestinal functions. Also the growth of the tumor can cause painful swallowing. The effects of chronic malnutrition reduce patients tolerance regarding surgical treatment, chemotherapy and radiation. A pretherapeutic parenteral balanced nutrition should achieve an anabolic metabolism. Changes in body cell mass (bcm) as a parameter of total protein synthesis can be estimated by bioelectrical impedance analysis in order to prove the success of this management. Twenty-eight patients participated in this study, divided into three groups: group 1 = 18 male subjects and group 3 = 3 female subjects, all able to be operated upon, and group 2 = 7 male subjects, not able to be operated. High caloric nutrition in group 1 lead to a higher increase of bcm than in group 2. The review of single cases showed that in both groups one part of the patients failed increasing bcm despite nutrition. The therapeutic response was correlated to survival by means of a Kaplan-Meier analysis and a Cox-model. Survival probability could positively be correlated to an increased bcm.

Adult↗
PubMed1993

Lasers in endoscopic surgery.

Lasers provide the endoscopic surgeon with a sophisticated tool for high precision cutting, destruction of tissue and coagulation. The laser allows efficient and time-saving operating techniques. Various laser systems emitting at different wavelengths are available. The absorption of the laser is determined by the tissue properties, such as water content or pigmentation, and varies strongly with the wavelength. Each laser offers advantages for the treatment of specific disorders. Further data from clinical studies are required to evaluate whether the advantages found in experimental studies are of significance in clinical use.

Female↗
PubMed1993

Proposal for a modified T-classification for oral cancer. The DOSAK.

The UICC plans to publish a modification of the TNM system. A proposal for a T category is calculated out of the data from the DOSAK tumour registry containing more than 3000 cases of primary squamous cell carcinomas of the oral cavity & oropharynx. By adding tumour thickness as a factor of the T component, the prognostic relevance of the classification is enhanced.

Carcinoma, Squamous Cell↗
PubMed1990

Lateral thermal damage along pulsed laser incisions.

The damage adjacent to incisions created in dorsal mouse skin by overlapping Er3+ and CO2 laser pulses of a duration of 250 microseconds is investigated histologically. It is compared to injuries induced by long-term heating. We demonstrate how the lateral thermal damage near the laser cuts can be explained by heat conduction. We show that it is necessary to introduce as a heat reservoir a layer of tissue that has been liquified during the cutting process. The width of the thermally damaged region depends mainly on the extension of the liquid material that remains in the cut after the laser-tissue interaction.

Animals↗
PubMed1988

Transport of biologically active material in laser cutting.

The transport of biologically active material during laser cutting with CO2 and Er lasers is demonstrated. This transport mechanism removes particles from the surface of gelatin, agar, and liver samples into the depth of the laser-formed craters. The transport phenomenon is explained by a contraction and condensation of enclosed hot water vapor. We show by cultivating transported bacteria in agar that biological particles can survive the shock of the transport. Determination of the numbers of active cells evidences a more pronounced activity of the cultivated bacteria after impact with an Er laser than with a CO2 laser.

Agar↗
PubMed1986

Time-resolved fluorescence of conifers exposed to environmental pollutants.

With regard to an early diagnosis of defects within the photosynthetic system of conifers by air pollutants, we measured the chlorophyll fluorescence from microscopic parts of individual pine and spruce needles. In particular, different spruces had been exposed before to well-defined doses and concentrations of ozone and SO2. In addition to spectral distributions and time courses of fluorescence intensity, fluorescence lifetimes were detected after picosecond laser pulse excitation. Time constants of tau 1 = (0.10 +/- 0.02) ns and tau 2 = (0.50 +/- 0.10) ns were measured for intact photosynthesis; an increase of tau 2 and a further time constant tau 3 = (2.5 +/- 0.5) ns were found, if defects within the photosynthetic system occurred. Most significant defects were so far measured after exposition to high ozone doses during longer time periods.

Air Pollutants↗