Pressure oscillations in anesthetized dogs and its conversion into quasi-periodic orbits.

Using a basic representation of dynamic systems, arterial blood pressure pulsation is converted into quasi-periodic orbits with the purpose of transforming a periodic phenomena into a cyclical one by plotting the pressure p(t) versus its first derivative dp/dt. This elementary mathematical procedure made it possible to evaluate the variability of the systemic arterial pressure pulsations, both systolic and diastolic, as well as the slope variability of the anachrotic and catachrotic phases. Two periods, which can be used to estimate different sources of variability, can be distinguished in the catachrotic phase. One corresponds to the open aortic valves, and the other is associated with the closed valves. Furthermore, through the first derivative of pressure oscillations we were able to identify small changes in arterial pressure, which appeared when the sampling rate was at least 150 samples per second. Since the time variable was converted into a parameter, the result was a synoptic or holistic approach, which is a considerable improvement for the visual analysis of cardiovascular phenomena. This simplified mathematical procedure can be easily implemented on a personal computer in real time and applied to all rhythmic phenomena in Physiology and Pathology.     

Time-frequency analysis of phonocardiogram signals using wavelet transform: a comparative study

Analysis of phonocardiogram (PCG) signals provides a non-invasive means to determine the abnormalities caused by cardiovascular system pathology. In general, time-frequency representation (TFR) methods are used to study the PCG signal because it is one of the non-stationary bio-signals. The continuous wavelet transform (CWT) is especially suitable for the analysis of non-stationary signals and to obtain the TFR, due to its high resolution, both in time and in frequency and has recently become a favourite tool. It decomposes a signal in terms of elementary contributions called wavelets, which are shifted and dilated copies of a fixed mother wavelet function, and yields a joint TFR. Although the basic characteristics of the wavelets are similar, each type of the wavelets produces a different TFR. In this study, eight real types of the most known wavelets are examined on typical PCG signals indicating heart abnormalities in order to determine the best wavelet to obtain a reliable TFR. For this purpose, the wavelet energy and frequency spectrum estimations based on the CWT and the spectra of the chosen wavelets were compared with the energy distribution and the autoregressive frequency spectra in order to determine the most suitable wavelet. The results show that Morlet wavelet is the most reliable wavelet for the time-frequency analysis of PCG signals.     

Dynamic behavior of CO2 uptake as affected by light: system identification based on spectral analysis

Summary The dynamic behavior of CO₂ uptake in sunflower plants was measured in a computer controlled apparatus and identified systematically using spectral analysis.To obtain impulse responses of net CO₂ uptake, power spectra were estimated by the Fast Fourier Transform (FFT) method. FFT was done by computing 512 separate data points sampled at one minute intervals. From examination of coherency, it was determined that dynamic behavior of CO₂ uptake could be estimated by linear filtering based on impulse response as affected by the light in changes slower than 0.08 cycle min^-1. This suggests that other dynamic phenomena in physiological ecology could be estimated effectively by using advanced system theory involving many algorithms.     

High resolution electrocardiography in healthy dogs: time domain parameters and comparison of the non-stationary (Wigner distribution) versus standard stationary frequency domain analysis methods

Fractionated heart activation can be detected as late potentials from surface recordings of signal-averaged electrocardiograms (SA ECG) which are considered as a marker of sustained ventricular tachycardia. For animal studies, reference values in time and frequency domain analyses are essentially missing. In the present study, we have established reference values in SA ECG time domain analysis and time-frequency representation of heart activation in healthy dogs. A group of 25 healthy mongrel dogs (body weight 12-15 kg) was investigated. Wigner distribution and our modification of Fast Fourier transform (FFT), gliding window FFT, was applied in SA ECG frequency domain analysis. Reference values in time domain SA ECG were established. Time and voltage criteria were adapted to short duration of heart cycle and fast voltage decrement of the QRS complex in dogs. Wigner distribution and gliding window FFT were applied in order to describe mean heart activation in the frequency domain. Contribution of higher frequencies (30-80 Hz) was detected by both frequency analysis methods in the second third of ventricular activation in healthy animals. Presented results could offer a basis for further experimental arrhythmologic studies.     

Increase in kinins on post-exercise hypotension in normotensive and hypertensive volunteers

Post-exercise hypotension is an important event for blood pressure regulation, especially in hypertensive individuals. Although post-exercise hypotension is a well-known phenomenon, the mechanism responsible is still unclear. The kallikrein-kinin system is involved in blood pressure control, but its role in post-exercise hypotension has not yet been investigated. Thus, the purpose of this study was to investigate the involvement of the vasodilators bradykinin and des-Arg(9)-BK and kallikrein activity in post-exercise hypotension promoted by 35 min of cycle ergometer (CE) or circuit weight-training (CWT) bouts in normotensive and hypertensive individuals. A significant decrease in mean arterial pressure at 45 and 60 min after CE and 45 min after CWT was observed in normotensive individuals. Hypertensive values of mean arterial pressure were significantly reduced at 45 and 60 min after CE and at 60 min after CWT. Before exercise, plasma bradykinin concentrations and kallikrein activity were higher in hypertensive compared to normotensive volunteers. Kinin levels increased in the groups evaluated at the end of the training period and 60 min post-exercise. These data suggest that the kallikrein-kinin system may be involved in post-exercise hypotension in normotensive and hypertensive individuals subjected to CE and CWT bouts.     

Baroreflex modulation of ultradian oscillations of blood pressure and heart rate in unanesthetized dogs

Telemetered, free-running dogs were studied to determine the role of cardiovascular control systems in modulation of ultradian oscillations of arterial pressure (MAP) and heart rate (HR). Data, aquired (2 Hz) by a stable telemetry system, was stored on a digital computer and analyzed for its harmonic content by a Fast Fourier Transform (FFT) algorithm. Both AP and HR consistently demonstrated rhythms having a period of from 0.6 to 1.0 h. Modulation of these rhythms by arterial pressure control systems was assessed in dogs studied before and carotid sinus baroreceptor denervation, before and after denervation of the aortic arch baroreceptors and before and after a combination of both these procedures. The data indicate the power spectral density (PSD) of MAP, but not HR, is increased (p less than 0.05) after denervation of the carotid sinuses alone, while the primary frequency of the oscillations was unchanged. On the other hand, denervation of the aortic arch baroreceptors alone was without effect on either the frequency or PSD of these oscillations. A combination of both carotid sinus and aortic arch denervation resulted in an increased (p less than 0.05) PSD of MAP oscillations but not in their frequency. These data indicate that the carotid sinuses modulate rhythmic behavior of MAP by buffering the magnitude, but not frequency, of the oscillations. Moreover, since oscillations were present in dogs after denervation of both the carotid sinus and aortic arch baroreceptors, these ultradian oscillations are not a result of a non-linear negative feedback mechanisms arising from these pressure sensitive regions.     

Dynamic processes in the human EEG

The possible mechanisms which determine the temporal dynamics of discrete narrow-band spectral components of human EEG recorded by a single electrode in the state of rest were analyzed. The dynamics of short-segment spectra was observed by application of Fast Fourier Transform (FFT) to 5-s EEG epochs successively shifted by 0.32 s. For each subject the matrices were formed and presented in a graphic mode. Matrix rows represented the number of points in each short-segment spectrum, and the columns represented the number of short-segment spectra. The columns reflect the amplitude dynamics of a given frequency, and power transition between the columns reflects the frequency dynamics. The most common type of the amplitude dynamics consisted in short (2-8 s) periods of stable activity of the discrete spectral components replaced by symmetrical bifurcation or confluence of spectral peaks. The obtained results suggest by the presence of both additive and multiplicative mechanisms of oscillatory interactions in the EEG. More detailed analysis of the amplitude-modulated EEG processes is provided by application of some additive features of the FFT to both EEG and computer-simulated signals.     

Frequency response of arterial bioelastomers

This work aims at estimating the quality of arterial bioelasticity. The non invasive employed method consists to obtain phase spectrum of blood flow velocity and arterial pressure. An original transducer allows us to obtain these signals at the same point of a superficial artery then to record them on magnetic tape. A mathematical model binds the phase spectrum and rheological parameters.     

Modulation of human muscle spindle discharge by arterial pulsations--functional effects and consequences

Arterial pulsations are known to modulate muscle spindle firing; however, the physiological significance of such synchronised modulation has not been investigated. Unitary recordings were made from 75 human muscle spindle afferents innervating the pretibial muscles. The modulation of muscle spindle discharge by arterial pulsations was evaluated by R-wave triggered averaging and power spectral analysis. We describe various effects arterial pulsations may have on muscle spindle afferent discharge. Afferents could be "driven" by arterial pulsations, e.g., showing no other spontaneous activity than spikes generated with cardiac rhythmicity. Among afferents showing ongoing discharge that was not primarily related to cardiac rhythmicity we illustrate several mechanisms by which individual spikes may become phase-locked. However, in the majority of afferents the discharge rate was modulated by the pulse wave without spikes being phase locked. Then we assessed whether these influences changed in two physiological conditions in which a sustained increase in muscle sympathetic nerve activity was observed without activation of fusimotor neurones: a maximal inspiratory breath-hold, which causes a fall in systolic pressure, and acute muscle pain, which causes an increase in systolic pressure. The majority of primary muscle spindle afferents displayed pulse-wave modulation, but neither apnoea nor pain had any significant effect on the strength of this modulation, suggesting that the physiological noise injected by the arterial pulsations is robust and relatively insensitive to fluctuations in blood pressure. Within the afferent population there was a similar number of muscle spindles that were inhibited and that were excited by the arterial pulse wave, indicating that after signal integration at the population level, arterial pulsations of opposite polarity would cancel each other out. We speculate that with close-to-threshold stimuli the arterial pulsations may serve as an endogenous noise source that may synchronise the sporadic discharge within the afferent population and thus facilitate the detection of weak stimuli.     

延髓头端腹外侧区神经元电活动与心血管活动相干性的研究

本文分析了大鼠延头端腹外侧区（ＲＶＬＭ）神经元单位活动与心血管活动的相干性,观察了ＲＶＬＭ区神经元电 对电刺激中脑防御反应区的诱发反应,以及对压力感受性反射的反应,并用ＦＦＴ对ＲＶＬＭ区神经元自发单位放电和血压波进行频域的相干性分析,以判断是具有心节律。还分析了ＲＶＬＭ区单位放电变异性与心率变异性的相干性。结果显示：ＲＶＬＭ区大多数神经元对电刺激中脑防御反应区呈兴奋反应（６７％）,７０％神经元放电     

Correlations between short-time Fourier- and continuous wavelet transforms in the analysis of localized back and hip muscle fatigue during isometric contractions.

The aims of the current study were to examine the stationarities of surface electromyographic (EMG) signals obtained from eight bilateral back and hip muscles during a modified Biering-Sørensen test, and to investigate whether short-time Fourier (STFT) and continuous wavelet transforms (CWT) provided similar information with regard to EMG spectral parameters in the analysis of localized muscle fatigue. Twenty healthy subjects participated in the study after giving their informed consent. Reverse arrangement tests showed that 91.6% of the EMG signal epochs demonstrated no significant trends (all p > 0.05), meaning 91.6% of the EMG signal epochs could be considered as stationary signals. Pearson correlation coefficients showed that STFT and CWT in general provide similar information with respect to the EMG spectral variables during isometric back extensions, and as a consequence STFT can still be used.     

On the transmission of external pressure fluctuations to the cerebrospinal fluid

A theory has been formulated to explain the manner in which external pressure fluctuations are transmitted to the cerebrospinal fluid (CSF). The theory is based upon a three-compartment model which consists of the cerebral ventricles, the basal cisterns and spinal subarachnoid space, and the cortical subarachnoid space. The external pressure disturbance is represented by a Fourier series summed over the frequency ω. The mathematical analysis leads to a time constant τ which depends upon the compliances of the spinal region and sources of external pressure fluctuations, the rate of CSF absorption and the rate of fluid transfer between compartments. For arterial pulsations where ωτ ? 1, the theory is in accord with the experimental observations that (i) the arterial and CSF pulse waves are nearly identical in shape, and (ii) the amplitude of the CSF pulse wave increases with intracranial pressure. Moreover, it predicts that the amplitude of the wave will be larger in the spinal region than in the ventricles. The theory also accounts for the observation of one per minute pulse waves observed in hydrocephalic patients with decreased absorption rates.     

基于独立元分析和联合小波熵检测多导联ECG信号的QRS

QRS波群的准确定位是ECG信号自动分析的基础。为提高QRS检测率,提出一种基于独立元分析（ICA）和联合小波熵（CWS）检测多导联ECG信号QRS的算法。ICA算法从滤波后的多导联ECG信号中分离出对应心室活动的独立元;然后对各独立元进行连续小波变换（CWT）,重构小波系数的相空间,结合相空间中的QRS信息对独立元排序;最后检测排序后独立元的CWS得到QRS信息。实验对St.Petersburg12导联心率失常数据库及64导联犬心外膜数据库测试,比较本文算法与单导联QRS检测算法和双导联QRS检测算法的性能。结果表明,该文算法的性能最好,检测准确率分别为99.98%和100%。     

Passive aortic counterpulsation: Biomechanical rationale and bench validation

Aortic counterpulsation (IABP) consists in an ECG-controlled forced deflation and inflation of a balloon positioned in the aorta. The device is designed to decrease the ventricular afterload during systole and to increase the coronary driving pressure during diastole. In biomechanical terms, the IABP improves the mechanical matching between the pump and the load, facilitating the transfer of ventricular energy. This paper describes a completely passive aortic counterpulsation solution, with an intra-aortic balloon without a pumping system, designed to improve the mechanical matching between the ventricle and the artery at very low cost and complexity. The only requirement is an external reservoir to amplify the balloon pulsations due to physiologic arterial pressure pulse.     

Concerning the amplitude modulation of the human EEG

Amplitude-modulated processes can be formally presented as a product of two or more sinusoids. This makes it possible to study them by means of analysis of multiplicative phenomena using the Fast Fourier Transform (FFT). To assess the contribution of amplitude EEG modulation to the dynamic of electrical activity of the human brain, the results of the FFT of simulated signals obtained by multiplication of oscillatory processes with different parameters were compared with the results of the FFT of a single EEG recording from a subject at rest. We studied the temporal dynamics of spectral components calculated with different spectral resolution under similar conditions for real and simulated signals. An attempt was made to analyze and interpret the amplitude-modulated EEG processes using the additive properties of the FTT. It was shown that processes of amplitude modulation are present in electrical brain activity and determine the synchronism of changes in time in the majority of frequency components of the EEG spectrum. The presence of the amplitude modulation in bioelectrical processes is of a fundamental nature, since it is a direct reflection of the control, synchronization, regulation, and intersystem interaction in the nervous and other body systems. The study of this modulation gives a clue to the mechanisms of these processes.     

Arterial baroreflex function and cardiovascular variability: interactions and implications

The arterial baroreflex contributes importantly to the short-term regulation of blood pressure and cardiovascular variability. A number of factors (including reflex, humoral, behavioral, and environmental) may influence gain and effectiveness of the baroreflex, as well as cardiovascular variability. Many central neural structures are also involved in the regulation of the cardiovascular system and contribute to the integrity of the baroreflex. Consequently, brain injuries or ischemia may induce baroreflex impairment and deranged cardiovascular variability. Baroreflex dysfunction and deranged cardiovascular variability are also common findings in cardiovascular disease. A blunted baroreflex gain and impaired heart rate variability are predictive of poor outcome in patients with heart failure and myocardial infarction and may represent an early index of autonomic activation in left ventricular dysfunction. The mechanisms mediating these relationships are not well understood and may in part be the result of cardiac structural changes and/or altered central neural processing of baroreflex signals.     

A coupled hydrodynamic model of the cardiovascular and cerebrospinal fluid system

Coupling of the cardiovascular and cerebrospinal fluid (CSF) system is considered to be important to understand the pathophysiology of cerebrovascular and craniospinal disease and intrathecal drug delivery. A coupled cardiovascular and CSF system model was designed to examine the relation of spinal cord (SC) blood flow (SCBF) and CSF pulsations along the spinal subarachnoid space (SSS). A one-dimensional (1-D) cardiovascular tree model was constructed including a simplified SC arterial network. Connection between the cardiovascular and CSF system was accomplished by a transfer function based on in vivo measurements of CSF and cerebral blood flow. A 1-D tube model of the SSS was constructed based on in vivo measurements in the literature. Pressure and flow throughout the cardiovascular and CSF system were determined for different values of craniospinal compliance. SCBF results indicated that the cervical, thoracic, and lumbar SC each had a signature waveform shape. The cerebral blood flow to CSF transfer function reproduced an in vivo-like CSF flow waveform. The 1-D tube model of the SSS resulted in a distribution of CSF pressure and flow and a wave speed that were similar to those in vivo. The SCBF to CSF pulse delay was found to vary a great degree along the spine depending on craniospinal compliance and vascular anatomy. The properties and anatomy of the SC arterial network and SSS were found to have an important impact on pressure and flow and perivascular fluid movement to the SC. Overall, the coupled model provides predictions about the flow and pressure environment in the SC and SSS. More detailed measurements are needed to fully validate the model.     

Mental stress induces sustained elevation of blood pressure and lipid peroxidation in postmenopausal women

Mental stress is thought to underlie cardiovascular events, but there is information on oxidative stress induced by mental stress in association with cardiovascular responses in women. Using a sensitive assay for plasma 4-hydroxy-2-nonenal (HNE), as a marker for oxidative stress, we addressed the relation between pressor responses and oxidative stress induced by mental or physical stress in premenopausal and postmenopausal women. Healthy subjects (7 postmenopausal and 8 premenopausal women, in early and late follicular phases) were subjected to mental and physical stress evoked by a Color Word Test (CWT) and isometric handgrip, respectively. The CWT induced a rapid elevation of diastolic blood pressure (DBP), at a higher level in the postmenopausal than in the premenopausal women (p<0.01), and this higher DBP was sustained during the CWT and recovery (p<0.01). The CWT induced a significant elevation in plasma noradrenaline in premenopausal women in the early follicular phase and in postmenopausal women (p<0.05). Plasma nitric oxide metabolites were higher in postmenopausal than in the premenopausal women in the late follicular phase (p<0.05), but did not change during exposure to the two types of stress in either group. Plasma HNE was increased during recovery from the CWT, but not the handgrip, in postmenopausal women (2.4 times, p<0.05). There was a significant difference in the time course of the CWT-induced HNE response between the postmenopausal and premenopausal women (p<0.05). These findings suggest that mental, but not physical, stress causes sustained diastolic blood pressure elevation in postmenopausal women, accompanied by heightened oxidative stress.     

Arterial pulsation-driven cerebrospinal fluid flow in the perivascular space: a computational model

This study was conducted to determine whether local arterial pulsations are sufficient to cause cerebrospinal fluid (CSF) flow along perivascular spaces (PVS) within the spinal cord. A theoretical model of the perivascular space surrounding a "typical" small artery was analysed using computational fluid dynamics. Systolic pulsations were modelled as travelling waves on the arterial wall. The effects of wave geometry and variable pressure conditions on fluid flow were investigated. Arterial pulsations induce fluid movement in the PVS in the direction of arterial wave travel. Perivascular flow continues even in the presence of adverse pressure gradients of a few kilopascals. Flow rates are greater with increasing pulse wave velocities and arterial deformation, as both an absolute amplitude and as a proportion of the PVS. The model suggests that arterial pulsations are sufficient to cause fluid flow in the perivascular space even against modest adverse pressure gradients. Local increases in flow in this perivascular pumping mechanism or reduction in outflow may be important in the etiology of syringomyelia.     

Arterial Pulsation-driven Cerebrospinal Fluid Flow in the Perivascular Space: A Computational Model

This study was conducted to determine whether local arterial pulsations are sufficient to cause cerebrospinal fluid (CSF) flow along perivascular spaces (PVS) within the spinal cord. A theoretical model of the perivascular space surrounding a "typical" small artery was analysed using computational fluid dynamics. Systolic pulsations were modelled as travelling waves on the arterial wall. The effects of wave geometry and variable pressure conditions on fluid flow were investigated. Arterial pulsations induce fluid movement in the PVS in the direction of arterial wave travel. Perivascular flow continues even in the presence of adverse pressure gradients of a few kilopascals. Flow rates are greater with increasing pulse wave velocities and arterial deformation, as both an absolute amplitude and as a proportion of the PVS. The model suggests that arterial pulsations are sufficient to cause fluid flow in the perivascular space even against modest adverse pressure gradients. Local increases in flow in this perivascular pumping mechanism or reduction in outflow may be important in the etiology of syringomyelia.