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40 records · Page 3Linked to original sources
PubMed2000

Heart rate signal decomposition.

This paper proposes a method for decomposing heart rate fluctuations into background, respiratory and blood pressure oriented fluctuations. A signal cancellation scheme using the adaptive RLS algorithm has been introduced for cancelling respiration and blood pressure oriented changes in the heart rate fluctuations. The computer simulation confirmed the validity of the proposed method. Then, heart rate fluctuations, instantaneous lung volume and blood pressure changes are simultaneously recorded from eight normal subjects aged 20-24 years. It was shown that after signal decomposition, the power spectrum of the heart rate showed a consistent monotonic 1/fa type pattern. The proposed method enables a clear interpretation of heart rate spectrum removing uncertain large individual variations due to the respiration and blood pressure change.

Adult↗
PubMedDate not supplied

[Vector systems and rhythms in movements and orientation of elk (Alces alces L.) and other wild animals (Mammalia)].

The orientation of elk and other mammals studied in fields with visual and instrumental tracing has obviously hierarchical organization. Animals usually choose general direction headed for distant markers and then select short-distance landmarks. Movements of animals to distant and close landmarks is characterized by almost constant or regularly changing angles between main direction and movement vector. Fragments of trajectories represent left-side or right-side spirals with decreasing or increasing curvature according to the main direction. Three types of spirals differed by average values of initial angles are considered. Orientation to distant landmarks or along direction of movement possesses discrete reaction on the given landmarks and has some characters of iteration process. Special rhythms of activity (rhythms of orientation changing) participate in regulation of changing of movement directions and orientation reactions. They take part in formation of sinusoid, spiral and other trajectories. Rhythmic regulation involves great statistical variability of parameters (lengths, angles, time periods between consecutive orientations) that can be adaptive meaning. Lengths of orientation vectors and trajectory fragments are similar to some linear elements of landscape. Angular parameters of orientation are more variable. The main ones are similar to the angular parameters of Earth rotation. It looks, that orientation parameters evolved under the influence of Sun-Earth compass in inertial field of Earth rotation.

Animals↗
PubMedDate not supplied

Plasma renin activity, aldosterone and cortisol in relation with postural changes in dogs.

Experiments were carried out in six dogs anesthetized with chloralose, fixed on a tilting table and moved from the supine to the vertical posture. In one dog this postural change was done after cutting both Hering nerves, and in another one after bilateral nephrectomy (BN), these experiments being orientative. Changing the supine to the vertical posture was followed by increase in plasma renin activity (PRA) and in aldosterone and cortisol plasma concentration (p.c.) Between PRA and aldosterone p.c., there was a slight correlation, but between aldosterone and cortisol this was evident. Therefore it may be supposed that aldosterone hypersecretion is produced by ACTH hypersecretion, a common stimulatory pathway for both hormones. This stimulatory mechanism is sustained by the orientative experiment on dogs, with BN, in which supine to vertical changed posture was followed by an important aldosterone hypersecretion despite minimal values of PRA.

Aldosterone↗
PubMed1987

Surface organization of orientation and direction selectivity in cat area 18.

Two-dimensional maps of orientation and direction preference were made in area 18 of the cat's visual cortex using multiple electrode penetrations 150-300 micron apart. The maps were then analyzed by autocorrelation and Fourier transformation. The power spectrum of the orientation map was sharply peaked below the theoretical cutoff frequency for the sampling function (the pattern of electrode penetrations) used to obtain the map. This suggested that it would be possible to interpolate orientation values between the sample points in the cortex. This was done and the resulting fine-grain maps of orientation preference were studied. Empirical testing showed that the interpolated orientation values were accurate to within +/- 30 degrees. Study of the fine-grain maps showed that iso-orientation domains for broad orientation ranges (0 degrees-90 degrees) were branching bands running from an anterolateral to a posteromedial direction across the surface of the cortex with a periodicity of 1.25 +/- 0.13 mm. Domains for smaller orientation ranges (0 degrees-30 degrees) were periodically spaced, but somewhat irregularly shaped patches. The orientation maps contained numerous point singularities where orientation changed discontinuously. These were spaced about 750 micron apart and most were surrounded by a single 180 degrees cycle of orientations. Autocorrelation analysis of the maps of preferred direction revealed local clustering that extended over a distance of 250-300 micron, but spectral analysis failed to reveal any evidence of periodicity. The absence of periodicity was probably due to a relatively large number of 180 degrees reversals in the map of direction preference, which do not affect the continuity of the orientation map and are not sufficiently numerous to destroy local continuity in the direction map. It is shown that the direction map, if it is to be as continuous as possible, must nevertheless contain lines across which direction preference reverses by 180 degrees. These lines run from one orientation singularity to another. Evidence that the direction map approaches this degree of continuity is presented.

Action Potentials↗