Biomedical subjects

R Michalak

Publications and source records attributed to R Michalak.

3 recordsLinked to original sources

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↗