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Biomedical subjects

J Petzold

Publications and source records attributed to J Petzold.

At least 19 recordsLinked to original sources
PubMed2001

Spatial integration in polarization-sensitive interneurones of crickets: a survey of evidence, mechanisms and benefits.

Many insects exploit the polarization pattern of the sky for compass orientation in navigation or cruising-course control. Polarization-sensitive neurones (POL1-neurones) in the polarization vision pathway of the cricket visual system have wide visual fields of approximately 60 degrees diameter, i.e. these neurones integrate information over a large area of the sky. This results from two different mechanisms. (i) Optical integration; polarization vision is mediated by a group of specialized ommatidia at the dorsal rim of the eye. These ommatidia lack screening pigment, contain a wide rhabdom and have poor lens optics. As a result, the angular sensitivity of the polarization-sensitive photoreceptors is very wide (median approximately 20 degrees ). (ii) Neural integration; each POL1-neurone receives input from a large number of dorsal rim photoreceptors with diverging optical axes. Spatial integration in POL1-neurones acts as a spatial low-pass filter. It improves the quality of the celestial polarization signal by filtering out cloud-induced local disturbances in the polarization pattern and increases sensitivity.

Animals↗
PubMed2000

Succinylcholine metabolite succinic acid alters steady state activation in muscle sodium channels.

BACKGROUND: Animal experiments revealed that succinylcholine produced masseter muscle rigidity and activated myotonic discharges despite neuromuscular blockade with a nondepolarizing blocker. These results suggest that either succinylcholine or its metabolites might interfere directly with voltage-operated ion channels of the sarcolemma. The aim of this study was to examine effects of one product of succinylcholine hydrolysis, succinic acid, on voltage-gated muscle sodium (Na+) channels. METHODS: Alpha subunits of human muscle sodium channels were heterologously expressed in HEK293 cells. Activation of Na+ currents was examined applying standard whole-cell voltage-clamp protocols in the absence (control and washout) and presence of succinic acid in different concentrations (0.05-10 mm). RESULTS: Succinic acid shifted the midpoints of steady state activation plots in the direction of more negative test potentials, indicating that channels open during smaller depolarizations in the presence of the drug. The maximum amount of the negative shift in 10 mm succinic acid was -6.3 +/- 1.7 mV; the EC50 for this effect was 0.39 mm. In addition, succinic acid (10 mm) significantly enhanced maximum currents after depolarizations with respect to a series of control experiments. CONCLUSION: Succinic acid facilitates voltage-dependent activation in muscle sodium channels in vitro. This might lead to muscle hyperexcitability in vivo.

Anti-Ulcer Agents↗
PubMed1989

A new method for the classification of subvigil stages, using the Fourier transform, and its application to sleep apnea.

An online classification for two-second segments of the EEG is developed. Based on the calculation of a norm and three characteristic frequencies the automatic classification shows satisfactory agreement with visual classification. The influence of the Fourier phase spectra is discussed. Trajectories in the parameter space are introduced. The automatic classification was applied to patients with a pronounced sleep-wake disorder and proved to be valuable in the diagnosis of a disturbed sleep structure.

Electroencephalography↗
PubMed1989

[Relation of uteroplacental hemodynamics and fetal respiratory behavior in pregnancy with threatened premature labor or intrauterine retardation].

The results of uteroplacental hemodynamics obtained by nuclear medicine were correlated with the corresponding antepartal and intrapartal cardiotocographic findings in 52 patients with preterm labor and in 53 patients with intrauterine-growth-retarded fetuses. With the existence of continued disturbance in pregnancy the relationship between primary maternal hemodynamic disorders and decreased fetal respiratory performance is already evident antepartum and unambiguously intrapartum. The dependence of the antepartal cardiotocographic findings on therapeutical improvements in perfusion is of clinical relevance.

Cardiotocography↗
PubMed1987

[Premature labor in gestosis].

796 pregnancies complicated by preeclampsia and 1,299 pregnancies without toxemia of the years 1981 to 1985 have been compared with regard to prematurity. Prematurity rates were 12.4 respectively 13.8 per cent, hypotrophy rates were 20 resp. 13 per cent, acidosis morbidity was 75 resp. 20 per cent and Apgar values below 8 were 63 resp. 24 per cent. Morbidity rate of respiratory distress syndrome was 8 resp. 12 per cent, of sepsis 2 resp. 7 per cent, intrauterine death rate 5 resp. 2 per cent, but survival rate overall was 93 resp. 90 per cent. Prematurity was influenced by severity of preeclampsia, time of onset and prenatal care. Prolongation of pregnancy by tocolysis is possible principally, but influenced in its effect by maternal and fetal symptoms and the necessity of termination of pregnancy by these factors.

Birth Weight↗
PubMed1987

[Therapy of suspected intrauterine fetal retardation].

In a randomized prospective study, performed on 45 pregnancies with clinical and sonographic suspicion for intrauterine fetal growth retardation, examinations were done to evaluate the therapeutic effect of bed rest and of additional daily administered glucose infusions or oral galactose applications respectively on the fetal growth, the hemodynamic, respiratory and endocrine insufficiency of the materno-feto-placental unit as well as selected biochemical parameters of the umbilical blood. There is no positive therapeutic effect, either on the impaired endocrine partial function nor on the reduced respiratory function of the feto-placental unit. It is obvious, that despite the improvement of the nutritional supply of the fetus and the revival of the regular fetal growth, the previous lack of fetal growth can not be altered. This can be demonstrated in all three therapeutic groups due to the fact of a resulting high hypotrophy-rate of the newborns. The results prove that the additional supply of the fetus with glucose or galactose does not remarkably improve the therapeutic effectivity as opposed by strict bed rest alone.

Bed Rest↗
PubMed1986

[Hemodynamic placental insufficiency and its therapeutic modification in threatened premature labor].

The authors are involved in a study in the field of nuclear medicine aimed at further clarifying the connection between premature delivery and placental insufficiency. They are particularly concerned with uteroplacental perfusion at the time when a trend is emerging toward premature birth, and with ways of treating this by exclusive therapy using betamimetics and/or additional maternal oxygen inhalation/additional maternal transcutaneous dorsal nerve stimulation (TNS). The significantly longer half-life periods of activity increase found at the time of hospitalization similar to pregnancies with intra-uterine fetal retardation, as compared with a normal control group, are interpreted as expressing a hemodynamic placental insufficiency and a risk of premature delivery. In contrast to exclusive betamimetic therapy, additional O2 inhalation/additional TNS significantly shorten the half-life period both in short-time and long-time tests. The better therapeutic effect on uteroplacental perfusion in cases of imminent premature delivery which is thus demonstrated can be seen also in an improved respiratory condition of the fetus as shown in a cardiotocogram. From a clinical point of view, the authors call attention to the clearly prolonged pregnancy periods regardless of the duration of gestation, at the time when a trend is emerging toward premature birth, as compared with exclusive betamimetic therapy, the duration of tocolysis/amount of betamimetic applied being the same.

Combined Modality Therapy↗
PubMed1985

[Therapeutic efforts and prenatal modification of selected disordered fetomaternal relations].

Based on the current view about disturbances of the feto-materno-placental unit we examined 37 women with suspected intrauterine fetal growth retardation and 12 women with threatened premature labor and looked for possibilities of antenatal therapeutic influence of nutritive, respiratory, endocrine and hemodynamic insufficiency. In a randomized study we can prove a normal increase of the distance between symphysis pubis and fundus as well, as the biparietal diameter not only following bedrest but also following bedrest with additional intravenous infusion of glucose respectively oral application of galactose. The high rate of hypotrophic babies is no argument against a positive influence on nutritive insufficiency, but the acquired retardation can not be compensated totally. Neither a positive influence on the endocrine insufficiency nor the moderate respiratory one could be found. As well by maternal transcutaneous nerval stimulation as by maternal oxygen inhalation an oral long-term tocolysis we can demonstrate a considerable improvement of the uteroplacental perfusion measured with isotopes. These positive aspects are basis for further investigations. An important supposition to a successful therapy remains an early diagnosis.

Bed Rest↗