Cardiovascular regulation during sleep quantified by symbolic coupling traces

Sleep is a complex regulated process with short periods of wakefulness and different sleep stages. These sleep stages modulate autonomous functions such as blood pressure and heart rate. The method of symbolic coupling traces (SCT) is used to analyze and quantify time-delayed coupling of these measurements during different sleep stages. The symbolic coupling traces, defined as the symmetric and diametric traces of the bivariate word distribution matrix, allow the quantification of time-delayed coupling. In this paper, the method is applied to heart rate and systolic blood pressure time series during different sleep stages for healthy controls as well as for normotensive and hypertensive patients with sleep apneas. Using the SCT, significant different cardiovascular mechanisms not only between the deep sleep and the other sleep stages but also between healthy subjects and patients can be revealed. The SCT method is applied to model systems, compared with established methods, such as cross correlation, mutual information, and cross recurrence analysis and demonstrates its advantages especially for nonstationary physiological data. As a result, SCT proves to be more specific in detecting delays of directional interactions than standard coupling analysis methods and yields additional information which cannot be measured by standard parameters of heart rate and blood pressure variability. The proposed method may help to indicate the pathological changes in cardiovascular regulation and also the effects of continuous positive airway pressure therapy on the cardiovascular system.     

Evidence of chaotic dynamics of brain activity during the sleep cycle

Recent progress in nonlinear dynamics provides the means for the characterisation of the behavior of natural systems from time series. The analysis of electroencephalogram data from the human brain during the sleep cycle reveals the existence of chaotic attractors for sleep stages two and four. The onset of sleep is followed by increasing “coherence” towards deterministic dynamics involving a limited set of variables.     

Articulatory dynamics of loud and normal speech

A comparison was made between normal and loud productions of bilabial stops and stressed vowels. Simultaneous recordings of lip and jaw movement and the accompanying audio signal were made for four native speakers of Swedish. The stimuli consisted of 12 Swedish vowels appearing in an /i'b_b/ frame and were produced with both normal and increased vocal effort. The displacement, velocity, and relative timing associated with the individual articulators as well as their coarticulatory interactions were studied together with changes in acoustic segmental duration. It is shown that the production of loud as compared with normal speech is characterized by amplification of normal movement patterns that are predictable for the above articulatory parameters. In addition, it was observed that the acoustic durations of bilabial stops were shortened, whereas stressed vowels were lengthened during loud speech production. Two interpretations of the data are offered, viewing loud articulatory behavior as a response to production demands and perceptual constraints, respectively.     

Nonlinear time series analysis of normal and pathological human walking

Characterizing locomotor dynamics is essential for understanding the neuromuscular control of locomotion. In particular, quantifying dynamic stability during walking is important for assessing people who have a greater risk of falling. However, traditional biomechanical methods of defining stability have not quantified the resistance of the neuromuscular system to perturbations, suggesting that more precise definitions are required. For the present study, average maximum finite-time Lyapunov exponents were estimated to quantify the local dynamic stability of human walking kinematics. Local scaling exponents, defined as the local slopes of the correlation sum curves, were also calculated to quantify the local scaling structure of each embedded time series. Comparisons were made between overground and motorized treadmill walking in young healthy subjects and between diabetic neuropathic (NP) patients and healthy controls (CO) during overground walking. A modification of the method of surrogate data was developed to examine the stochastic nature of the fluctuations overlying the nominally periodic patterns in these data sets. Results demonstrated that having subjects walk on a motorized treadmill artificially stabilized their natural locomotor kinematics by small but statistically significant amounts. Furthermore, a paradox previously present in the biomechanical literature that resulted from mistakenly equating variability with dynamic stability was resolved. By slowing their self-selected walking speeds, NP patients adopted more locally stable gait patterns, even though they simultaneously exhibited greater kinematic variability than CO subjects. Additionally, the loss of peripheral sensation in NP patients was associated with statistically significant differences in the local scaling structure of their walking kinematics at those length scales where it was anticipated that sensory feedback would play the greatest role. Lastly, stride-to-stride fluctuations in the walking patterns of all three subject groups were clearly distinguishable from linearly autocorrelated Gaussian noise. As a collateral benefit of the methodological approach taken in this study, some of the first steps at characterizing the underlying structure of human locomotor dynamics have been taken. Implications for understanding the neuromuscular control of locomotion are discussed. (c) 2000 American Institute of Physics.     

In vitro spectroscopic study of normal and pathological blood denaturation

By means of a systematic spectroscopic study of an in vitro blood clot model, iron compounds involved in blood denaturation have been identified and evaluated at each stage of blood denaturation. So, a blood denaturation pattern is available for normal blood, but also for some pathological bloods (polyglobulic, -thalassemic and drepanocytic). Normal blood denaturation stands for a reference that will be used for several purposes. Thus, this study compares normal and pathological blood denaturation rates. Polyglobulic and -thalassemic blood denaturations are quite similar to normal blood denaturation. On the opposite, drepanocytic blood denaturation is really different (some hemochromes are not observed) and is a lot slower. This delay can be attributed to deoxyhemoglobin S fiber formation that could protect trapped compounds from oxidization.     

An analysis of psychophysical tuning curves in normal and pathological ears

Simultaneous psychophysical tuning curves were obtained from normal-hearing and hearing-impaired listeners, using probe tones that were either at similar sound pressure levels or at similar sensation levels for the two types of listeners. Tuning curves from the hearing-impaired listeners were flat, erratic, broad, and/or inverted, depending upon the frequency region of the probe tone and the frequency characteristics of the hearing loss. Tuning curves from the normal-hearing listeners at low-SPL's were sharp as expected; tuning curves at high-SPL's were discontinuous. An analysis of high-SPL tuning curves suggests that tuning curves from normal-hearing listeners reflect low-pass filter characteristics instead of the sharp bandpass filter characteristics seen with low-SPL probe tones. Tuning curves from hearing-impaired listeners at high-SPL probe levels appear to reflect similar low-pass filter characteristics, but with much more gradual high-frequency slopes than in the normal ear. This appeared as abnormal downward spread of masking. Relatively good temporal resolution and broader tuning mechanisms were proposed to explain inverted tuning curves in the hearing-impaired listeners.     

Non-Newtonian thin films with normal stresses: dynamics and spreading

The dynamics of a thin film on a horizontal solid substrate is investigated in the case of non-Newtonian fluids exhibiting normal stress differences, the rheology of which is strongly non-linear. Two coupled equations of evolution for the thickness of the film and the shear rate are proposed within the lubrication approximation. This framework is applied to the motion of an advancing contact line. The apparent dynamic contact angle is found to depend logarithmically on a lengthscale determined solely by the rheological properties of the fluid and the velocity of the contact line.     

Nonlinear oscillation of pathological vocal folds during vocalization

The extended two-mass model is adopted to analyze the nonlinear oscillation of pathological vocal folds during vocalization. Redundant tissue or area in laryngeal patients is modeled as a massless rigid connected to the upper mass of the vocal folds, and a parameter Q is introduced to represent the change of glottal configurations and tension imbalance between the left and right sides of vocal folds. Numerical simulations demonstrate that the pathological vocal-fold decreases the threshold of Q to generate nonlinear vocal oscillation, indicating the improvement of the sensitivity of vocal folds to asymmetries and enhancing the coupling between two sides. Furthermore, the pathological vocal-fold can lower the fundamental frequency and eliminate high-order harmonics, For example, the fundamental frequency decreases from 119.94 Hz to 84.95 Hz when Q=0.58 and the sub-glottal pressure 1450 Pa. However, there are no prominent effects on the amplitudes of sub-harmonic and low-order harmonics.     

Correlated and uncorrelated regions in heart-rate fluctuations during sleep

Healthy sleep consists of several stages: deep sleep, light sleep, and rapid eye movement (REM) sleep. Here we show that these sleep stages can be characterized and distinguished by correlations of heart rates separated by n beats. Using the detrended fluctuation analysis (DFA) up to fourth order we find that long-range correlations reminiscent to the wake phase are present only in the REM phase. In the non-REM phases, the heart rates are uncorrelated above the typical breathing cycle time, pointing to a random regulation of the heartbeat during non-REM sleep.     

Structural variations of collagen in normal and pathological tissues: role of electron microscopy

The spectrum of ultrastructural appearances assumed by collagen in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal fibrillar collagen types are described in order to provide a basis for comparing other normal and abnormal forms. In normal tissues, the anchoring fibril and basal lamina (basement membrane) represent tissue structures largely containing collagen but differing significantly in organisation from normal types I to III fibrillar collagen. In pathological tissue, deviations from normal fine structure are reflected in abnormal aggregates of collagen fibrils (amianthoid and skeinoid fibres) and abnormalities in fibril diameter and cross-sectional profile. Fibrous and segment long-spacing collagen represent two further organisational variants of collagen, the former found widely in pathological tissues, the latter very rarely. Much remains to be discovered about these abnormal collagen variants-their mode of formation, the cells that produce them, and their roles. They also present a challenge for the collagen biologist formulating hypotheses of collagen fibril assembly and molecular organisation.     

Phosphorus-31 MR spectroscopic imaging (MRSI) of normal and pathological human brains.

The goals of this study were to evaluate 31P MR spectroscopic imaging (MRSI) for clinical studies and to survey potentially significant spatial variations of 31P metabolite signals in normal and pathological human brains. In normal brains, chemical shifts and metabolite ratios corrected for saturation were similar to previous studies using single-volume localization techniques (n = 10; pH = 7.01 +/- 0.02; PCr/Pi = 2.0 +/- 0.4; PCr/ATP = 1.4 +/- 0.2; ATP/Pi = 1.6 +/- 0.2; PCr/PDE = 0.52 +/- 0.06; PCr/PME = 1.3 +/- 0.2; [Mg2+]free = 0.26 +/- 0.02 mM.) In 17 pathological case studies, ratios of 31P metabolite signals between the pathological regions and normal-appearing (usually homologous contralateral) regions were obtained. First, in subacute and chronic infarctions (n = 9) decreased Pi (65 +/- 12%), PCr (38 +/- 6%), ATP (55 +/- 6%), PDE (47 +/- 9%), and total 31P metabolite signals (50 +/- 8%) were observed. Second, regions of decreased total 31P metabolite signals were observed in normal pressure hydrocephalus (NPH, n = 2), glioblastoma (n = 2), temporal lobe epilepsy (n = 2), and transient ischemic attacks (TIAs, n = 2). Third, alkalosis was detected in the NPH periventricular tissue, glioblastoma, epilepsy ipsilateral ictal foci, and chronic infarction regions; acidosis was detected in subacute infarction regions. Fourth, in TIAs with no MRI-detected infarction, regions consistent with transient neurological deficits were detected with decreased Pi, ATP, and total 31P metabolite signals. These results demonstrate an advantage of 31P MRSI over single-volume 31P MRS techniques in that metabolite information is derived simultaneously from multiple regions of brain, including those outside the primary pathological region of interest. These preliminary findings also suggest that abnormal metabolite distributions may be detected in regions that appear normal on MR images.     

Comparison between train noise and road noise annoyance during sleep

Sleep disturbance by train and road noises was studied through in situ physiological recordings on two groups of people submitted to both types of exposure. At different sites acoustical parameters do not influence sleep in the same way. In a quiet place, emergence is an important factor of disturbance, but in a noisy place, noise duration and peak level are acting with interaction to disturb sleep.     

Temporal and spatial assessment of normal cerebrospinal fluid dynamics with MR imaging

The purpose of this study was to measure normal cerebrospinal fluid (CSF) pulsations within the intracranial and upper cervical subarachnoid spaces and the ventricular system. Phase contrast cine MR sequences were performed in sagittal and axial planes on 13 volunteers with flow encoding in the craniocaudal direction. CSF pulsations displayed considerable variations in healthy subjects, depending both on measurements localization and subjects, with CSF peak velocities ranging from 0 to 7 cm/s. In the subarachnoid spaces, the highest velocities occurred in the anterior location and increased from the cerebellar pontine angle cisterns towards the lower cervical spaces. In the ventricular system, the highest velocities occurred through the aqueduct of Sylvius. CSF flow within the third ventricle seemed to reflect a circular motion. There was a caudal net CSF flow in the aqueduct whereas in the upper cervical spaces net CSF flow was caudal anteriorly and cranial laterally. Velocity profiles of CSF pulsations demonstrated arterial morphology. After the R wave, caudal systolic motion was first observed in the posterior subarachnoid spaces, soon after in the anterior subarachnoid spaces and later in the ventricular system. Considering the morphology of CSF pathways, three successively initiated phenomena may explain the temporal course of CSF motion: the systolic expansion of the main arteries at the base of the brain, the systolic expansion of the cerebrospinal axis and, finally, the systolic expansion of the choroid plexuses.     

Laryngeal and respiratory activity during vocalization in macaque monkeys

The present study describes the laryngeal and respiratory muscle activity associated with vocalizations in macaque monkeys. During the bark vocalization, a short, aperiodic call, the cricothyroid, thyroarytenoid, rectus abdominis, and intercostals were active while the posterior cricoarytenoid and diaphragm were quiet. During the coo vocalization, a longer, clear call, the cricothyroid, thyroarytenoid, intercostals, rectus abdominis, and diaphragm were active. In one monkey, the posterior cricoarytenoid was also active during the call, while in another monkey it was not. Laryngeal muscle activity was correlated with the amplitude and duration of the coo call. Results suggest that the amplitude and duration differences between calls are determined primarily by laryngeal modification of the airflow, and that the differences in posterior cricoarytenoid activity may be due to differences in voice intensity.     

Nonlinear dynamics of fermions during preheating

We study the role of dynamical fermions during preheating after inflation. We compute the nonequilibrium dynamics of Dirac fermions coupled to a scalar (inflaton) field at next-to-next-to-leading order in a coupling expansion of the 2PI effective action. Besides the well-known parametric production of bosons and fermions and their back-reaction on the background inflaton field, this includes direct interactions between produced particles, which have been neglected in previous studies. We present preliminary numerical results in 3+1 dimensions which indicates that, for intermediate Yukawa couplings, the latter can dramatically affect the usual picture of preheating.     

Spin dynamics of the muon in muonium in normal metals

The question of the charge state of the proton (the positive muon) in metals is of fundamental importance for the theory of metal hydrides. The theory developed here permits determination of the charge state of μ ⁺ in normal metals. The experimental possibilities of the observation of Mu atoms in metals at various strengths of the external magnetic field and various temperatures are analyzed. Zh. éksp. Teor. Fiz. 111, 730–736 (February 1997)     

Surrogate analysis for detecting nonlinear dynamics in normal vowels.

Normal vowels are known to have irregularities in the pitch-to-pitch variation which is quite important for speech signals to be perceived as natural human sound. Such pitch-to-pitch variation of vowels is studied in the light of nonlinear dynamics. For the analysis, five normal vowels recorded from three male and two female subjects are exploited, where the vowel signals are shown to have normal levels of the pitch-to-pitch variation. First, by the false nearest-neighbor analysis, nonlinear dynamics of the vowels are shown to be well analyzed by using a relatively low-dimensional reconstructing dimension of 4 < or = d < or = 7. Then, we further studied nonlinear dynamics of the vowels by spike-and-wave surrogate analysis. The results imply that there exists nonlinear dynamical correlation between one pitch-waveform pattern to another in the vowel signals. On the basis of the analysis results, applicability of the nonlinear prediction technique to vowel synthesis is discussed.