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Biomedical subjects

R Michalak

Publications and source records attributed to R Michalak.

9 recordsLinked to original sources
PubMed1999

Laser-Spectroscopic Investigation of Higher Excited Electronic States of the KAr Molecule.

Higher excited electronic states of the van der Waals molecule 39KAr have been investigated using a supersonic beam and a two-step excitation. Four hundred seventy Doppler-free lines have been observed in the second step leading to the electronic states 5d2Sigma, 5d2Pi, 5d2Delta, and 7s2Sigma. The spectroscopic parameters of rotation, of spin-orbit splitting, of spin-rotation coupling, and of lambda-type doubling have been determined for altogether 19 vibrational levels of these electronic states. The molecular spin-orbit splitting turns out to be -0.42 cm-1 for 5d2Delta and -0.15 cm-1 for 5d2Pi, which is in fair agreement with the theoretical prediction for a Hund's coupling case a. The vibrational numbering was deduced from theoretical calculations of the interatomic potential. Six vibrational levels have been assigned to the 5d2Delta and the 5d2Sigma state, respectively, allowing a determination of the Dunham coefficients in these two states. For the equilibrium parameters of the 5d2Delta state, we obtain Re = 3.22(15) Å, De = 900(80) cm-1. Copyright 1999 Academic Press.

Journal Article↗
PubMed1993

Results of a low-altitude flight noise study in Germany: acute extraaural effects.

This paper begins by outlining the aims which our study into the acute effects of low-altitude flight noise set out to achieve. The key question here concerns the relationship between noise parameters (maximum sound level and sound level rise rate) and specific reactions by the individuals affected. The subjects, healthy volunteers, were exposed via earphones to digitally recorded MLAF noise, using sophisticated recording technology. Their reactions were studied on various levels ranging from the subjective experience of negative effects through startle reactions to changes in the cardiovascular and endocrine systems. It emerged that a high sound level rise rate is a physical parameter which leads not only to more physical symptoms being cited by the subjects, but also to more pronounced myokinetic effects of an objectively measurable nature. Studies of circulation physiology were also conducted to throw light on the haemodynamic mechanism of the startle reaction. The findings suggest that increases in cardiac output per minute in a startled subject with a healthy circulation need not necessarily lead to protracted increases in blood pressure. A counter-regulation occurs by means of vasculomotory responses in the muscle. Should this regulatory system be impaired, as may be the case with elderly people, for example, blood pressure increases of up to 45 mm Hg over the initial value may ensure. A sensitization is observed after repeated exposure, with the startle reaction intensifying or else being triggered off by lower sound levels. The sensitization of startle reactions is neuro-physiologically associated with unpleasant or fear-inducing environmental stimuli. Together with the observed increases in plasma hydrocortisone and changes in magnesium metabolism of a type characteristic of stress, this phenomenon of sensitization enables us to establish the hypothetical link between specific acute reactions to MLAF noise and long-term health effects.

Adult↗
PubMed1990

Acute circulatory effects of military low-altitude flight noise.

Volunteers aged 70 to 89 years living in a senior citizen's home in Haifa were exposed to flight noise via earphones while watching video films. Their blood pressure and heart rates were measured simultaneously. A high-quality recording and reproduction technique was employed. They were exposed to the noise of two to three overflights with Lmax = 99-114 dB(A) and slow sound pressure level increase (aircraft take off) or with Lmax = 95-112 dB(A) and a fast sound pressure level increase (low-altitude flight at high subsonic speed) at intervals of 10 to 15 min. The systolic and diastolic blood pressure was raised at Lmax = 112 dB(A) and high speed level increase at the average of 23 and 13 mmHg, respectively with individual maximal values of about 40 mm Hg (systolic). In order to prevent risks to the subjects' health, the noise exposure was not raised to levels above 112 dB(A) and fast level increase, although Lmax = 125 dB(A) has been measured in 75 m-low-altitude flight areas. The blood pressure response to a repeated single exposure increased in proportion to the preceding noise exposure. At high intensities and fast level increase an up to fourfold reaction intensification was detected in the majority of subjects. This change in reactivity is regarded as the result of sensitization toward the special type of noise and the implications of these observations for the long-term effects of chronic exposure to low-altitude flight noise are considered. On the basis of these results, proposals are made for limiting values for Lmax and for the speed of sound pressure level increase, the implementation of which would lead to a marked reduction in health risks from low-altitude flight noise.

Aged↗
PubMed1985

Periodic and nonperiodic burst responses of frog (Rana pipiens) retinal ganglion cells.

Neural activity of class 3 retinal ganglion cells was recorded in frog optic tectum, using extracellular microelectrodes. The stimuli were rectangular patches of contrast (light-on-dark or dark-on-light), applied within the previously determined receptive fields, for periods ranging from a few milliseconds to several seconds. ON and OFF responses were recorded for as long as 1 s following stimulation. Poststimulus time histograms revealed two types of responses, labeled periodic and nonperiodic bursters. The periodic bursters were characterized by periods of high activity separated by silent or near-silent intervals. The bursts occurred rhythmically with frequencies roughly between 15 and 50 Hz. Nonperiodic bursters generally showed both broad and sharp peaks in activity, but no regular periodicities. Activity profiles were flat initially, with silent periods appearing after the first few stimulus presentations, suggesting an inhibitory nature of the bursting process. The records were shown to combine the activities of several neurons. Analysis of the waveforms in real time made possible isolation of some units. In these cases, neurons exhibited a high degree of selective synchrony, i.e., the sharing of a portion of the activity profile, and notable differences at other times. These data have implications for the processing of visual information.

Action Potentials↗
PubMed1979

The Alopex process: visual receptive fields by response feedback.

The determination of trigger features of single neurons in afferent pathways has been one of the central problems in sensory physiology. A novel method, called Alopex, has been developed, in which response feedback is used to construct visual patterns that optimize the responses. Data are presented which show the emergence of trigger features of cells monitored in frog visual tectum. The method id checked against results obtained by scanning the visual field with a small spot. Correlations between Alopex pattern and scann patterns are generally between 0.3 and 0.5 but may be as high as 0.9 when smoothing and/or averaging procedures are applied to the Alopex patterns. The dynamics of the Alopex process are discussed and details of the algorithms are presented. The series of experiments presented here has established the validity of the method and suggests that this approach should find wide application in receptive field studies. For that purpose data on the instrumentation and software are also presented.

Afferent Pathways↗
PubMedDate not supplied

Stress effects of noise in a field experiment in comparison to reactions to short term noise exposure in the laboratory.

Reactions to noise-induced communication disturbance of 42 men during a seminar were investigated. Stress reactions with or without road traffic noise (Lm = 60 dBA) were compared. Traffic noise was played back via loudspeakers during one day in the seminar room. The following parameters were measured: Fatigue and mental tension by questionnaire; blood pressure and heart rate; excretion of adrenaline, noradrenaline and cAMP from the collected urine. The same subjects participated in a laboratory test where the blood pressure was measured during 5 minutes of rest and after 5 minutes of exposure to intermittent white noise (Lm=97 dBA). It was found that the noise in the field experiment caused psychological and physiological stress effects in half of the subjects. Increased mental tension was correlated to increases as well as decreases of the blood pressure. Systolic blood pressure reactions were stronger than the reactions of diastolic blood pressure. Noise sensitive subjects reacted stronger than the others. In the short-term laboratory test, systolic blood pressure increases were smaller than the diastolic increases. At the end of the 5 minutes noise exposure only the diastolic blood pressure increases were significant. There was no correlation between the blood pressure reactions in the two different noise exposure experiments. There existed a positive correlation between noise sensitivity and the systolic blood pressure increases during the seminar, whilst the correlation, between noise sensitivity and systolic blood pressure increases in the laboratory exposure, was negative. From these results we conclude that short-term noise exposure experiments do not provide information about the effects of long-term real life exposure to environmental noise. Potential health effects of chronic noise-induced disturbances of activities are discussed.

Adaptation, Physiological↗
PubMedDate not supplied

IA induction by gut and epidermal cells of nude mice following administration of human lymphocytes.

Expression of class II molecules by epidermal cells of BALB/c nude mice following an adoptive transfer of lymphoid cells from normal semisyngeneic mice has been previously observed. The purpose of the present study was to determine whether similar expression might be observed after injection of human lymphocytes and to utilize this model to determine whether there would be expression of class II molecules by mucosal and epidermal cells following administration of lymphocytes from young and old donors. In order to address this question, a group of nude mice received a single i.v. injection of human T lymphocytes obtained from aged subjects, and a second group received i.v. injection of lymphocytes from young volunteers. Evaluation of I-A and I-E molecules expression of murine cells were performed by indirect immunoperoxidase staining. More prominent and diffuse staining of class II was observed in the mucosal cells as compared with the keratinocytes. Diffuse and intense staining of intestinal cells was observed mainly in mice treated with lymphocytes from young donors.

Adoptive Transfer↗