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PubMed1982

Phase locking, period doubling bifurcations and chaos in a mathematical model of a periodically driven oscillator: a theory for the entrainment of biological oscillators and the generation of cardiac dysrhythmias.

A mathematical model for the perturbation of a biological oscillator by single and periodic impulses is analyzed. In response to a single stimulus the phase of the oscillator is changed. If the new phase following a stimulus is plotted against the old phase the resulting curve is called the phase transition curve or PTC (Pavlidis, 1973). There are two qualitatively different types of phase resetting. Using the terminology of Winfree (1977, 1980), large perturbations give a type 0 PTC (average slope of the PTC equals zero), whereas small perturbations give a type 1 PTC. The effects of periodic inputs can be analyzed by using the PTC to construct the Poincaré or phase advance map. Over a limited range of stimulation frequency and amplitude, the Poincaré map can be reduced to an interval map possessing a single maximum. Over this range there are period doubling bifurcations as well as chaotic dynamics. Numerical and analytical studies of the Poincaré map show that both phase locked and non-phase locked dynamics occur. We propose that cardiac dysrhythmias may arise from desynchronization of two or more spontaneously oscillating regions of the heart. This hypothesis serves to account for the various forms of atrioventricular (AV) block clinically observed. In particular 2:2 and 4:2 AV block can arise by period doubling bifurcations, and intermittent or variable AV block may be due to the complex irregular behavior associated with chaotic dynamics.

Arrhythmias, Cardiac↗
PubMed1987

Atrioventricular Wenckebach periodicity in athletes: influence of increased vagal tone on the occurrence of atypical periods.

In 37 athletes with atrioventricular (AV) Wenckebach periodicity, the relationship between PP and RR intervals was investigated. In most athletes, when PP intervals gradually lengthened, RR as well as PR intervals usually also gradually lengthened until a blocked P wave occurred, resulting in the occurrence of an atypical Wenckebach period with prolongation of the last RR interval (variant I). In 20 athletes, sudden marked prolongation of a PR interval occasionally occurred, which was usually followed by a blocked P wave (variant II). In five athletes, once sudden marked prolongation of a PR interval occurred, markedly long PR intervals were maintained for some time, and then a PR interval suddenly shortened without a blocked P wave (variant III). It appeared that the above findings were caused by spontaneous variations in vagal tone. It was suggested that longitudinal dissociation and concealed reentry in the AV node occurred in atypical Wenckebach periods of variants II and III, but not in the other periods.

Adolescent↗
PubMed1996

Periodic K-alpha sleep EEG activity and periodic limb movements during sleep: comparisons of clinical features and sleep parameters.

The K-alpha sleep electroencephalographic (EEG) phenomenon is characterized by periodic (approximately 20-40 seconds) K-complexes, immediately followed by alpha-EEG activity (7.5-11 Hz) of 0.5- to 5.0-second duration. A group of 14 subjects with the periodic K-alpha anomaly was found to have a similar distribution pattern of interevent intervals as compared with previously published data for sleep-related periodic limb movements during sleep (PLMS). Sleep parameters and somatic symptoms of 30 patients with K-alpha were compared with 30 patients with PLMS. The periodic K-alpha group was predominantly female, younger, exhibiting more slow-wave sleep, gastrointestinal symptoms and muscular complaints and fewer movement arousals on overnight polysomnography. The K-alpha group presented uniformly with complaints of unrefreshing sleep, often associated with fibromyalgia and chronic fatigue syndrome. The PLMS group was predominantly male, showed greater sleep disruption and presented with a variety of sleep-related symptoms.

Adult↗
PubMed1981

Phase locking, period-doubling bifurcations, and irregular dynamics in periodically stimulated cardiac cells.

The spontaneous rhythmic activity of aggregates of embryonic chick heart cells was perturbed by the injection of single current pulses and periodic trains of current pulses. The regular and irregular dynamics produced by periodic stimulation were predicted theoretically from a mathematical analysis of the response to single pulses. Period-doubling bifurcations, in which the period of a regular oscillation doubles, were predicted theoretically and observed experimentally.

Animals↗
PubMed1998

Microfilarial periodicity of Wuchereria bancrofti and man landing periodicity of the vector Culex quinquefasciatus say in Matara, Sri Lanka.

OBJECTIVE: To compare the microfilarial periodicity of Wuchereria bancrofti, with the man landing periodicity of the vector Culex quinquefasciatus in Matara, Sri Lanka. DESIGN: Periodicity was estimated using a statistical method. 60 microliters finger prick (FP) blood was smeared from a single subject every 2 hours for 24 hours of the day to make 12 samples. Smears were stained with Giemsa and the microfilariae (mff) counted. Man landing catches of mosquitoes were made inside a bedroom of a house in the same area on a sleeping volunteer during the night, between 18.00 and 06.00 hours. Each hourly catch was placed in separate paper cups. Hourly C. quinquefasciatus taken were counted. SUBJECTS: 10 asymptomatic microfilaria (mf) carriers. RESULTS: The individual mf peaks in the 10 carriers varied from 22.00 to 04.00 hours. Using the statistical method the parameter k showing the mf peak hour was 1.19 estimating the peak mf density at 01.11 hours. The influence of different times of blood collection on false negatives among the very low density carriers was estimated by the periodicity curve. It would be desirable to collect blood during the estimated time interval when the mf count was 80% of the peak count, between 21.55 and 04.27 hours in Matara. The results of 25 all-night mosquito landing catches gave a peak activity hours of k as 7.78, corresponding to 01.47 hours. CONCLUSION: The close agreement in the peak hours of mf density and vector activity suggests a perfect adaptation between parasite and vector for optimum transmission.

Animals↗
PubMed2000

Developmental changes in heart period and high-frequency heart period variability from 4 months to 4 years of age.

Cardiac measures of heart period and high-frequency heart period variability are increasingly employed as dependent variables in studies of social and emotional development in infancy and childhood. This study describes significant developmental increases in these measures in a longitudinal sample assessed at 4, 9, 14, 24, and 48 months of age. In addition, developmental changes in the characteristics of the heart period power spectra are described. These changes have implications for the quantification of high-frequency heart period variability in infancy and childhood. First, shorter analysis epoch lengths may be used for younger infants. Second, the commonly used high-frequency band for infants (0.24-1.04 Hz) appears to reach its practical limit at an age of around four years. Findings are discussed in relation to the design of developmental psychophysiological studies.

Age Factors↗
PubMed2002

Effect of a short period of desiccation during the patent period on cercarial shedding of Schistosoma haematobium from Planorbarius metidjensis.

Planorbarius metidjensis infected with Schistosoma haematobium were subjected, from the first day of shedding, to a 5- or 10-day period of desiccation in order to study its effect on the cercarial release occurring after reactivation of snails in water. These results were compared to those of infected controls that were not subjected to desiccation. Compared to controls, the duration of shedding following reactivation was shorter and the total number of cercariae shed by each infected snail was smaller in the 5- and 10-day groups. The rhythm occurring in the daily cercarial production of the 5-day group was shorter (11 days only) at the beginning of the shedding period and lengthened to 17-18 days at the end of the patent period. In the 10-day group, no rhythm was found. These results could be explained by the length of the desiccation period and its consequences on the development of S. haematobiumsporocysts in the body of snails.

Animals↗
PubMed1992

Comparison of autoregression and fast Fourier transform techniques for power spectral analysis of heart period variability of persons with sudden cardiac arrest before and after therapy to increase heart period variability.

Clinical studies have used two types of analysis of the power spectral estimates of heart period variability: autoregressive and fast Fourier transform techniques. Controversy exists regarding which method is the most valid. The specific aims of this study are: (1) to describe the power spectra of heart period variability before and after an intervention designed to increase heart period variability in persons after sudden cardiac arrest; (2) to compare the integral of power spectral density between autoregressive and fast Fourier transform techniques within low and high-frequency bands; (3) to compare the magnitude of the spectral peak values determined by autoregressive and fast Fourier transform techniques approaches within low and high-frequency bands; and (4) to compare the aforementioned parameters using 4-minute, 1-hour, and 24-hour blocks of heart period data. Results indicated high correlations between spectral estimations by autoregressive and fast Fourier transform techniques using integrals or peak values within either the low or high-frequency ranges. The autoregressive technique demonstrated better resolution of sharp peaks than the fast Fourier transform technique, and makes a smoother, more interpretable curve. Lastly, people can cognitively change their heart rate variability.

Biofeedback, Psychology↗
PubMed1995

The effect of amygdaloid kindling on heart period and heart period variability.

Two studies were conducted on rats to assess the effects of amygdaloid kindling on baseline measures of heart period and heart period variance. The results indicate that seizure activity was associated with increased vagal influence on heart period marked by sinus bradycardia and decreased beat-to-beat variability. The resultant bradycardia was enhanced following each seizure and persisted for at least a one-week period of time. The results are discussed in terms of the role of vagal tone in influencing abnormal cardiac patterns which could result in sudden unexplained death in some epileptic patients.

Amygdala↗
PubMed2004

Rational reduction of periodic propagators for off-period observations.

Many common solid-state nuclear magnetic resonance problems take advantage of the periodicity of the underlying Hamiltonian to simplify the computation of an observation. Most of the time-domain methods used, however, require the time step between observations to be some integer or reciprocal-integer multiple of the period, thereby restricting the observation bandwidth. Calculations of off-period observations are usually reduced to brute force direct methods resulting in many demanding matrix multiplications. For large spin systems, the matrix multiplication becomes the limiting step. A simple method that can dramatically reduce the number of matrix multiplications required to calculate the time evolution when the observation time step is some rational fraction of the period of the Hamiltonian is presented. The algorithm implements two different optimization routines. One uses pattern matching and additional memory storage, while the other recursively generates the propagators via time shifting. The net result is a significant speed improvement for some types of time-domain calculations.

Algorithms↗
PubMed2002

Periodic arousals or periodic limb movements during sleep?

Periodic limb movements during sleep (PLMS), frequently found in polysomnograms, are often accompanied by arousals. The relationship is not clear, however, because PLMS can occur before, after or simultaneous to the electromyographic (EMG) activation. We describe the case of a patient who presents PLMS during two of three consecutive recording nights, and periodic arousals without motor activation on the other night. We conclude that, at least in some patients with a periodic limb movement disorder, there exists an underlying arousal disorder that produces periodic activation and deactivation of the cerebral cortex.

Journal Article↗
PubMed1976

[Substitution of protein animal feed through lysine-supplemented high-protein wheat during the breeding and laying periods of hens. 5. Influence of graded lysine supplements fed during the laying period on the production characteristics of hens].

A large-scale trial was performed with 1500 laying hens which were kept under conditions of industrial egg production. The trial was carried out to investigate whether supplements of L-lysine would increase the food value of high-protein wheat and in which way a proportional decrease of dietary protein by 50% would affect the egg production of the hens. Additionally, studies were made to investigate whether the egg production of the hens was influenced by changes in the plane of feeding of the young hens during their rearing period. Both the young hens and the laying hens received isonitrogenous and isocaloric rations containing 4 graded levels of lysine. All of the 16 groups of the hens received a different diet. This was achieved by suitable combinations within the feeding regime. The control animals received, at all periods of age, food prepared on the basis of government-controlled standard rations. No significant differences in the level of food consumption were observed between the experimental groups whereas the control birds consumed more food (124 g per bird/day) than the experimental hens (120 g per bird/day; alpha less than 0.05). The levels of production were in all groups associated with the lysine content of the ration. The lysine-deficient birds produced the smallest eggs, layed the smallest number of eggs and consumed the largest quantity of food per 100 g of egg weight. The egg production of the hens in groups 11 and 12 (receiving a fish meal ration during the rearing period and a fish meal or wheat ration + 0.15% L-lysine during the laying period) was 70% of that of the birds in the control groups. The results of the present trial suggest that lysine-supplemented high-protein wheat rations for laying hens could be used but care should be taken that the plane of feeding for the young hens will not be too much restricted.

Animal Feed↗
PubMed1999

A TEM study of long-period mica polytypes: determination of the stacking sequence of oxybiotite by means of atomic resolution images and Periodic Intensity Distribution (PID).

In this study it is shown that the stacking sequences in long-period mica polytypes (including a rare example of a mixed-rotation polytype, with a 36-layer long periodicity) can be unambiguously determined using atomic resolution images recorded down two zone axes separated by 30 degrees (e.g. [100] and [31;0]) at the same area. Uniformity of these stacking sequences in a large area is further confirmed by the correspondence between computed and observed Periodic Intensity Distributions (PIDs) in electron diffraction patterns. The appearance of long-period polytypes containing layers with different orientation parity may be explained by the coalescence of two small crystals during crystal growth.

Journal Article↗
PubMed2004

Regional cerebral blood flow correlates with heart period and high-frequency heart period variability during working-memory tasks: Implications for the cortical and subcortical regulation of cardiac autonomic activity.

The aim of the present study was to characterize the functional relationships between behaviorally evoked regional brain activation and cardiac autonomic activity in humans. Concurrent estimates of regional cerebral blood flow (rCBF; obtained by positron emission tomography), heart period, and high-frequency heart period variability (HF-HPV; an indicator of cardiac parasympathetic activity) were examined in 93 adults (aged 50-70 years) who performed a series of increasingly difficult working-memory tasks. Increased task difficulty resulted in decreased heart period (indicating cardioacceleration) and decreased HF-HPV (indicating decreased cardiac parasympathetic activity). Task-induced decreases in heart period and HF-HPV were associated with concurrent increases and decreases in rCBF to cortical and subcortical brain regions that are speculated to regulate cardiac autonomic activity during behavioral processes: the medial-prefrontal, insular, and anterior cingulate cortices, the amygdala-hippocampal complex, and the cerebellum. These findings replicate and extend a small number of functional neuroimaging studies that suggest an important role for both cortical and subcortical brain systems in human cardiac autonomic regulation.

Aged↗
PubMed1975

Quantitative determination of immunoglobulins, lysozyme, and certain electrolytes in breast milk during the entire period of lactation, during a 24-hour period, and in milk from the individual mammary gland.

During a period commencing at birth and lasting for up to 27 months 193 milk samples have been collected from 29 mothers. The IgA globulin content was high immediately after birth, averaging 2.7 arb.U, decreasing to 0.3 arb.U within the first 2 to 3 weeks after birth, then remaining almost constant for the rest of the lactational period. In the case of IgG globulin, similar results were obtained, but the quantity was much smaller. IgM globulin was demonstrated in small quantities during the first 3 weeks of lactation. The lysozyme content varied considerably during the whole lactational period. Individual variations were found for all the immunoglobulins, while the concentration in the individual woman varied only slightly from day to day following in other respects the pattern described above. In 19 mothers IgA, IgG, IgM, lysozyme and electrolyte content were determined in serum and in milk from the right and the left breast on the same day. No difference in content was found between milk from the left and the right mammary gland. A positive correlation was found between the concentrations of IgA and sodium chloride in milk, between those of IgG in milk and serum, and between those of lysozyme in milk and serum. No variations were registered during the individual breast feeding, nor for the 24-hour period as a whole.

Adult↗
PubMed1998

A period-extender gene, pex, that extends the period of the circadian clock in the cyanobacterium Synechococcus sp. strain PCC 7942.

We cloned the pS1K1 plasmid in the process of apparently "complementing" a circadian clock mutant of cyanobacterium Synechococcus sp. strain PCC 7942, SP22, which has a 22-h period (T. Kondo, N. F. Tsinoremas, S. S. Golden, C. H. Johnson, S. Kutsuna, and M. Ishiura, Science 266:1233-1236, 1994). Sequence analysis revealed that SP22 did not have a mutation in the genomic DNA segment carried on pS1K1, and the sp22 mutation was later found in a recently cloned new clock gene, kaiC. Therefore, the period-extender gene pex that was carried on pS1K1 was a suppressor gene for the sp22 mutation. The pex gene encoded a protein of 148 amino acid residues. No meaningful homologs were found in DNA or protein databases including the Synechocystis genome database. The pex gene was transcribed from 129 and 164 bp upstream of the translation initiation codon as 0.6-kb transcripts. The Pex protein was detected as a fusion protein with a molecular mass of 15 kDa by the epitope tag fusion method using a c-Myc epitope tag. Disruption of the pex gene in wild-type cells shortened the period of the rhythms by 1 h, although it did not affect other properties of the rhythms, whereas its overexpression extended the period by 3 h with a concomitant reduction in the amplitude of the rhythms. In various clock mutants examined, overexpression caused arrhythmicity. Thus, Pex is likely to function as a modifier of the circadian clock in Synechococcus.

Amino Acid Sequence↗
PubMed2002

Omnidirectional reflection from finite periodic and Fibonacci quasi-periodic multilayers of alternating isotropic and birefringent thin films.

Omnidirectional reflection from periodic and Fibonacci quasi-periodic multilayers that are embedded in an isotropic medium is further analyzed. Besides the isotropic structures, birefringent structures are considered that comprise uniaxial layers in the principal-axis system, alternating with isotropic layers so that the refractive index of isotropic layers is equal to the principal extraordinary refractive index of the uniaxial layers. The transfer-matrix method is applied, and the same formalism is used forboth the isotropic and the uniaxial media in the principal-axis system. Simple and original relations are obtained for the invariant of the one-dimensional Fibonacci sequences at oblique incidence. Numerical examples are given comparatively for the isotropic and the birefringent structures in the case of periodic and Fibonacci quasi-periodic sequences at different values of the refractive indices.

Journal Article↗
PubMed2004

Scattering of light by a periodic structure in the presence of randomness. III. Limit of the extended matched filtering method for the detection of weak periodicities.

It is known that, for scattering of light by a rough grating, the periodically occurring intensity maxima that are characteristic of the periodic part of the scattering medium get smeared off and hence become undetectable if coherence length r0 of the randomness is much smaller than wavelength A of the periodic part of the grating. It is also known that by conventional intensity measurements the detectability region is r0/lambda > or = 0.33, which can be extended to lower regions by intensity interferometry. It is established here that an extended matched filtering method enables one to detect the periodic part of the medium, even in the presence of higher roughness (i.e., lower r0), and the limit is placed at r0/lambda approximately 0.11 by our numerical experiments.

Journal Article↗