Analysis Of Pressure Signals Research Articles

The mixing layer over a deep cavity at high-subsonic speed

The flow over a cavity at a Mach number 0.8 is considered. The cavity is deep with an aspect ratio (length over depth) L/D = 0.42. This deep cavity flow exhibits several features that makes it different from shallower cavities. It is subjected to very regular self-sustained oscillations with a highly two-dimensional and periodic organization of the mixing layer over the cavity. This is revealed by means of a high-speed schlieren technique. Analysis of pressure signals shows that the first tone mode is the strongest, the others being close to harmonics. This departs from shallower cavity flows where the tones are usually predicted well by the standard Rossiter’s model. A two-component laser-Doppler velocimetry system is also used to characterize the phase-averaged properties of the flow. It is shown that the formation of coherent vortices in the region close to the boundary layer separation has some resemblance to the ‘collective interaction mechanism’ introduced by Ho & Huang (1982) to describe mixing layers subjected to strong sub-harmonic forcing. Otherwise, the conditional statistics show close similarities with those found in classical forced mixing layers except for the production of random perturbations, which reaches a maximum in the structure centres, not in the hyperbolic regions with which turbulence production is usually associated. An attempt is made to relate this difference to the elliptic instability that may be observed here thanks to the particularly well-organized nature of the flow.

The cavitation instability induced by the development of a re-entrant jet

The instability of a partial cavity induced by the development of a re-entrant jet is investigated on the basis of experiments conducted on a diverging step. Detailed visualizations of the cavity behaviour allowed us to identify the domain of the re-entrant jet instability which leads to classical cloud cavitation. The surrounding regimes are also investigated, in particular the special case of thin cavities which do not oscillate in length but surprisingly exhibit a re-entrant jet of periodical behaviour. The velocity of the re-entrant jet is measured from visualizations, in the case of both cloud cavitation and thin cavities. The limits of the domain of the re-entrant jet instability are corroborated by velocity fluctuation measurements. By varying the divergence and the confinement of the channel, it is shown that the extent of the auto-oscillation domain primarily depends upon the average adverse pressure gradient in the channel. This conclusion is corroborated by the determination of the pressure gradient on the basis of LDV measurements which shows a good correlation between the domain of the cloud cavitation instability and the region of high adverse pressure gradient. A simple phenomenological model of the development of the re-entrant jet in an adverse pressure gradient confirms the strong influence of the pressure gradient on the development of the re-entrant jet and particularly on its thickness. An ultrasonic technique is developed to measure the re-entrant jet thickness, which allowed us to compare it with the cavity thickness. By considering an estimate of the characteristic height of the perturbations developing on the interface of the cavity and of the re-entrant jet, it is shown that cloud cavitation requires negligible interaction between both interfaces, i.e. a thick enough cavity. In the case of thin cavities, this interaction becomes predominant; the cavity interface breaks at many points, giving birth to small-scale vapour structures unlike the large-scale clouds which are periodically shed in the case of cloud cavitation. The low-frequency content of the cloud cavitation instability is investigated using spectral analysis of wall pressure signals. It is shown that the characteristic frequency of cloud cavitation corresponds to a Strouhal number of about 0.2 whatever the operating conditions and the cavity length may be, provided the Strouhal number is computed on the basis of the maximum cavity length. For long enough cavities, another peak is observed in the spectra, at lower frequency, which is interpreted as a surge-type instability. The present investigations give insight into the instabilities that a partial cavity may undergo, and particularly the re-entrant jet instability. Two parameters are shown to be of most importance in the analysis of the re-entrant jet instability: the adverse pressure gradient and the cavity thickness compared to the re-entrant jet thickness. The present results allowed us to conduct a qualitative phenomenological analysis of the stability of partial cavities on cavitating hydrofoils. It is conjectured that cloud cavitation should occur for short enough cavities, of the order of half the chordlength, whereas the instability often observed at the limit between partial cavitation and super-cavitation is here interpreted as a cavitation surge-type instability.

Analysis of Unsteady Pressure Signals on a Pitching Delta Wing

Results from wind-tunnel tests conducted on a pitching 60-deg delta wing in ramp-up motion are presented and described. The wing was instrumented with 192 miniature pressure transducers, which, in conjunction with a powerful multichannel data-logging system, allowed the distribution of time-varying surface pressures to be measured at high temporal resolution for a range of pitching cases. In addition to allowing the forward progression of vortex breakdown with incidence to be tracked, it has been possible to isolate dominant postbreakdown buffet frequencies in both the static and pitching cases. It is demonstrated that, during pitch up, these frequencies differ significantly from those of the static case, indicating that alterations in flow structure may be taking place

SPECTRAL CHANGES IN SYSTEMIC ARTERIAL PRESSURE SIGNALS DURING ACUTE MEVINPHOS INTOXICATION IN THE RAT

We investigated the cardiovascular consequences of acute intoxication by the organophosphate poison, mevinphos (Mev), and delineated the underlying mechanism. Based on on-line power spectral analysis of systemic arterial pressure (SAP) signals in rats anesthetized and maintained by propofol, we identified two distinct phases after intravenous administration of Mev (160 or 320 microg/kg). Phase I was characterized by transient hypertension and mild tachycardia, concurrent with an increase in the very high-frequency (BVHF; 5-9 Hz), high-frequency (BHF; 0.8-2.4 Hz), low-frequency (BLF; 0.25-0.8 Hz),and very low-frequency (BVLF; 0-0.25 Hz) components of SAP signals. Phase II exhibited significant hypotension, a reversal of the BVHF and BVLF power to control levels, and further reduction in the power density of both BHF and BLF components to below baseline. Microinjection of Mev (2 microg) into the bilateral nucleus reticularis ventrolateralis (NRVL), the medullary origin of sympathetic neurogenic vasomotor tone, essentially duplicated those phasic cardiovascular changes. Similarly, sympathoexcitatory NRVL neurons exhibited respectively an elevation and a decline in their spontaneous activities during Phase I and Phase II Mev intoxication. We conclude that the progressive accumulation of acetylcholine over time induced by a direct inhibition of Mev on cholinesterase in the NRVL may be responsible for the phasic changes in cardiovascular events over the course of acute Mev intoxication. Whereas the initial amount of acetylcholine is excitatory to NRVL neurons, overstimulation by the amassed acetylcholine results instead of an inhibitory action.

Analysis of unsteady pressure signals on a pitching delta wing

Analysis of unsteady pressure signals on a pitching delta wing

Evaluation of Stress on the Autonomic Nervous System of Patients on Mechanical Circulatory Assist

The power density values of high (HF; 0.15 to 0.4 Hz) and low frequency (LF; 0.04 to 0.15 Hz) components of arterial pressure were adopted for evaluation of stress on the autonomic nervous system of patients supported by mechanical circulatory assist. Power spectral analysis (PSA) of arterial pressure signals was carried out, and trends in changes in the spectral components were observed in 12 patients on mechanical circulatory support (IABP and/or PCPS) and without the support (n=10). The normalized LF was depressed initially and increased gradually in both groups of patients except for four patients on mechanical circulatory assist. Three patients among them consequently died. Depressed LF represented marked stress on ANS and prolongation of the depression was related to poor outcome of patients. PSA of systemic blood pressure offers a reasonable tool for evaluation of stress on the ANS and for prediction of the prognosis of patients with circulatory assist devices.

Leak detection in pipelines through spectral analysis of pressure signals

The development and test of a technique for leak detection in pipelines is presented. The technique is based on the spectral analysis of pressure signals measured in pipeline sections where the formation of stationary waves is favoured, allowing leakage detection during the start/stop of pumps. Experimental tests were performed in a 1250 m long pipeline for various operational conditions of the pipeline (liquid flow rate and leakage configuration). Pressure transients were obtained by four transducers connected to a PC computer. The obtained results show that the spectral analysis of pressure transients, together with the knowledge of reflection points provide a simple and efficient way of identifying leaks during the start/stop of pumps in pipelines.

Spectral analysis of systemic arterial pressure and heart rate signals of patients with acute respiratory failure induced by severe organophosphate poisoning.

Spectral analysis of systemic arterial pressure (BP) and heart rate (HR) signals may be an alternative prognostic tool for predicting patient outcome in the intensive care unit (ICU). We evaluated the applicability of the same analysis in the emergency department for predicting mortality in patients with acute respiratory failure induced by severe organophosphate poisoning. Prospective collection of data from 14 emergency service patients. Emergency service at a large, university-affiliated medical center. Consecutive patients who, after attempting suicide by ingesting organophosphates, were admitted to the ICU of the emergency service with acute respiratory failure and remained for > or =2 days None. Demographic and survival data and day 1 Acute Physiology and Chronic Health Evaluation (APACHE) II and Glasgow Coma Scale scores were recorded. Continuous, on-line, real-time spectral analysis of BP and HR signals was carried out during the first 12 hrs after admission. We then computed the total sum of power density during this period of the low-frequency (0.04-0.15 Hz) and very low-frequency (0.004-0.04 Hz) components in the BP and HR spectra, along with the averaged values of mean BP and HR. Eight patients who recovered exhibited vigorous power in the low-frequency and very low-frequency components of their BP and HR signals. There was a significant reduction in the power density of those four spectral components in three patients who eventually died. Three patients discharged in a vegetative state manifested significantly reduced power in the low-frequency component in their BP spectra, with maintained power in the other three spectral components. APACHE II and Glasgow Coma Scale scores of the recovered patients were discernibly different from those of patients who eventually died or who became vegetative. None of the 14 patients showed appreciable differences in mean BP, mean HR, erythrocyte or plasma cholinesterase concentration, or atropine requirement during the first 24 hrs. The low-frequency and very low-frequency components of BP and HR signals may be a sensitive alternative index for early prediction of mortality in patients with acute respiratory failure induced by severe organophosphate poisoning.

SYMPATHOINHIBITION IN CRITICAL ILLNESS DURING MECHANICAL CIRCULATORY SUPPORT

In variability of systemic blood pressure, the power spectral component with high frequency (0.15 to 0.4 Hz) is usually regarded as a marker of the para-sympathetic activity, and the component with low frequency (0.04 to 0.15 Hz) has been related to the sympathetic activity. Purpose: To evaluate the applicability of power spectral analysis of systemic blood pressure in estimating the state of patients after cardiac surgery. Methods: Hemodynamic data were sampled every 2 hours at 100 Hz for 6 minitutes in patients undergone cardiac surgery. Power spectral analysis of systemic arterial pressure signals was carried out. A trend of changes in the spectral components of systemic arterial pressure were obsereved in the patients with mechanical circulatory support (group M; n=9) for low cardiac output syndrome (LOS) and in control patients without mechanical circulatory support (group N; n=9). Results: The power spectral component with low frequency have the tendency to increase in both groups except 3 patients in group M, and the increment of group M is behind that of group N. Sustained low values in the low frequency component of systemic arterial pressure signals in the 3 patients were related to prolonged mechanical circulatory support, and 2 patients among them were expired consequently. Conclusion: Recovery from the postoperative sympathoinhibitory state in patients with mechanical circulatory support significantly delayed comparing with that in patients without the support. Power spectral analysis of systemic arterial pressure provides a reasonable tool to evaluate the severity of patients' condition regarding the activity of autonomic nervous system which regulates the heart and blood vessels.

163 Analysis of Pressure Signal in a Gas-Solid Two-Phase flow Based on Discrete Wavelet Transform

The discrete wavelet transform was applied to experimental pressure-time signals in this paper, in order to analyze the characteristics of the gas-solid two-phase flow in both Fourier and physical spaces. From randomlike pressure fluctuations, the fluctuating pressure components due to dispersed suspension flow and dune flow can be extracted over a time-scale plane based on the wavelet multiresolution analysis. It was found that the dominant scale of the heterogeneous suspension flow over the dunes increases along flow direction and reaches 0.017s in the fully developed region of dune flow.

Dynamical systems analysis of arterial blood pressure signals in relation to heart rate fluctuations in chick embryos

We attempted a new approach based on a modern dynamical system theory to reconstruct the arterial blood pressure signals in relation to heart rate fluctuations of developing chick embryos. The dynamical systems approach in general is to model a phenomenon that is presented by a single time series record and approximate the dynamical property (e.g. heart rate fluctuations) of a system based only on information contained in a single-variable (arterial blood pressure) of the system. The time–series data of the arterial blood pressure was reconstructed in 3-dimensional space to draw characteristic orbits. Since the reconstructed orbits of the blood pressure should retain information contained in the pressure signals, we attempted to derive instantaneous heart rate (IHR) from the reconstructed orbits. The derived IHR presenting HR fluctuations coincided well with the IHR obtained conventionally from the peak-to-peak time intervals of the maximum blood pressure. Movements of the reconstructed orbits of the arterial blood pressure in 3-dimensional space reflected HR fluctuations (i.e. transient decelerations and accelerations).

Multiscale analysis of blood pressure signals.

We describe the multiresolution wavelet analysis of blood pressure waves in vasovagal syncope-affected patients compared with those in healthy people, using Haar and Gaussian bases. A comparison between scale-dependent and scale-independent measures discriminating the two classes of subjects is made. What emerges is a sort of equivalence between these two methodological approaches, that is, both methods reach the same statistical significance of separation between the two classes.

How to assess sympathetic activity in humans.

Sympathetic factors play a central role not only in cardiovascular homeostatic control but also in the pathogenesis and/or in the progression of several cardiovascular diseases, such as essential hypertension, myocardial infarction, cardiac arrhythmias and congestive heart failure. This explains why assessment of adrenergic neural function in humans has been, and certainly still remains, one of the major fields in cardiovascular research. The present paper will review in detail the haemodynamic, pharmacological, biochemical, neurophysiological, neurochemical and neural imaging techniques by which sympathetic activity is assessed in humans, highlighting the main advantages and limitations of each of them. Although plasma noradrenaline measurement represents a useful guide to assess sympathetic neural function, direct recording of sympathetic nerve traffic via microneurography and noradrenaline radiotracer methods have in recent years largely supplanted the plasma noradrenaline approach. This is because they allow (1) discrimination between the central or peripheral nature of increased plasma noradrenaline levels, and (2) precise estimation of the behaviour of regional sympathetic neural function both under physiological and pathological conditions. In contrast, the approach based on spectral analysis of heart rate and blood pressure signals has been shown to have important limitations which prevent the method from faithfully reflecting sympathetic cardiovascular drive. Neural imaging techniques, which require expensive technical support, allow direct visualization of sympathetic enervation of human organs, thus providing information on the 'in vivo' metabolism of noradrenaline in different cardiovascular districts. Although technical improvements have allowed a more precise assessment of human adrenergic function, no technique so far available can be viewed as a 'gold standard' with which the others might be compared. Limitations and disadvantages of the various techniques may be reduced if these methods are seen as being complementary and employed in combination, allowing more reliable information to be achieved on the sympathetic abnormalities characterizing cardiovascular diseases, and thus hopefully providing a stronger rationale for newer therapeutic approaches involving pharmacological modification of the sympathetic nervous system and adrenoreceptors.

Time-frequency analysis of transient pressure signals for a mechanical heart valve cavitation study.

A series of transient pressure signals (TPSs) can be measured using a miniature pressure transducer mounted near the tip of the inflow side of a mechanical heart valve (MHV) occluder during closure. A relationship appears to exist between the intensity and pattern of the TPS and the cavitation potential of a MHV. To study the relationship between MHV cavitation and the TPSs, we installed an MHV in a valve testing chamber of a digitally controlled burst test loop. A charge coupled device (CCD) camera and a personal computer based image grabbing program was used to visualize cavitation bubbles appearing on or near the occluder surface. One bileaflet MHV was used as the model for this study. Cavitation bubbles were observed within 300 microsec of the leaflet/housing impact. The valve was tested at various driving pressures between 100 and 1,300 mmHg. MHV cavitation bubble intensities were qualitatively classified into three categories: 1) strong, 2) weak, and 3) none. Digital images of the MHV occluder inflow surface were recorded simultaneously with the TPSs. TPSs were studied by the time-frequency analysis method (spectrogram) and correlated to MHV cavitation potential. The intensity of the cavitation bubbles was found to be associated with burst test loop driving pressures during leaflet closure.

Characterization of regimes and regime transitions in bubble columns by chaos analysis of pressure signals

In this study it is shown that the transition from the homogeneous to the heterogeneous flow regime in bubble columns can be quantitatively found with high accuracy by analysing the chaotic characteristics of the pressure fluctuation signal (PFS). In previous work (van den Bleek and Schouten, 1993; Schouten et al., 1996), the authors have already applied this technique to time series from gas-solid fluid beds. Also, it was shown (Krishna et al., 1993, Ellenberger and Krishna, 1994) that hydrodynamics of bubble columns and fluid beds can be described in an analogous manner. Therefore in this work, the method of chaos analysis is applied to bubble columns. A distinctive feature of the pressure signal from bubble columns is that it is composed of two different parts: a low frequency part resulting from the motion of the large bubbles and a high frequency part resulting from all other processes (coalescence, collapse, breakup) that take place in the column. From the phase of the cross spectrum of two pressure probes, placed at different axial positions, it was possible to identify the bands in the spectrum of the PFS that show a significant time delay. This time delay is of the order of the passage time of bubbles between the measurement locations. This band in the spectrum of the PFS was used to estimate the Kolmogorov entropy to quantify the chaotic dynamics in the bubble column. The Kolmogorov entropy as a function of gas velocity indicates a sharp transition from the homogeneous to the churn-turbulent flow regime. From other methods considered (e.g. holdup and other properties of the signal such as variance), this transition was less clear. Therefore chaos analysis of PFSs is believed to be a powerful technique for on-line identification of flow regimes.

Diminished vasomotor component of systemic arterial pressure signals and baroreflex in brain death.

We compared the cardiovascular autonomic regulatory mechanisms between patients with brain death or under a persistent vegetative state and healthy volunteers, based on auto- and cross-spectral analysis of systolic blood pressure (SBP) and interpulse interval (PPI) signals. Brain-dead patients exhibited a significant reduction in the absolute and relative power of the low-frequency (LF; 0.04-0.15 Hz) component in both SBP and PPI spectra, along with appreciable decrease in the very low frequency (VLF; 0.004-0.04 Hz), LF, and high-frequency (HF; 0.15-0.4 Hz) power of the PPI signals. Patients in a persistent vegetative state exhibited a power of the VLF and LF component in the SBP spectrum that was comparable to that in healthy subjects, although a discernible reduction in the VLF, LF, and HF power of the PPI spectrum was manifested by the former group. Assessments with the magnitude of SBP-PPI transfer function and linear regression analysis of beat-to-beat fluctuations in SBP and PPI revealed a progressive decline in spontaneous baroreflex sensitivity from healthy subjects to patients in a persistent vegetative state or with brain death. We conclude that the vasomotor component of systemic arterial pressure signals and spontaneous baroreflex are highly correlated with the functional integrity of the brain stem.

A technique for measurement of the jet penetration height in fluidized beds by pressure signal analysis

Pressure fluctuations induced by gas discharge through an upward nozzle in a fluidized bed have been studied with the objective of setting up a new experimental technique for evaluating a characteristic length of the jetting region. Pairs of pressure signals were recorded simultaneously on the jet axis and at the bed side wall at the same distance from the distributor. The statistical analysis of the signals allowed the fluidized bed operating conditions to be associated with the characteristics of the signals in the frequency domain, and the characteristic height of the jet to be determined. The analysis also supported the evaluation of the jet height by means of direct comparison between the fluctuations of static pressure on the axis and at the wall. The features of the technique are discussed and compared with those of previously proposed techniques for measurement of the jet penetration length. It was found that the characteristic height conforms with the definition of penetration length based on the concept of jet momentum dissipation.

Evaluation of the jet penetration depth in gas-fluidized beds by pressure signal analysis

The interaction between a single jet and a bed of fluidized solids was investigated with the aim of evaluating a characteristic height of the jetting region corresponding to the distance from the nozzle at which the dispersion of jet momentum is practically complete. A new experimental technique, based on simultaneous measurements of the static pressure at the bed side wall and on the jet axis and on their elaboration, was used. Various experimental configurations, based on the combination of two fluidization columns (0.35 and 0.20 m, i.d.) and four jet nozzles (6, 10, 19 and 25 mm, i.d.), were employed. Glass ballotini of 800–1200 μm were used as bed material. The influence of the nozzle gas velocity, of the fluidization velocity, and of the nozzle and the column sizes on the characteristic height of the jet was investigated. This height increases as nozzle gas velocity and nozzle size increase. In contrast, the influence of the fluidization velocity appears more complex and, in particular, cannot be separated from that of the nozzle diameter. The effect of the column diameter was negligible. Experimental results were compared with predictions of jet penetration length from literature correlations since the characteristic height shows up evident similarities with the jet penetration length based on momentum dissipation.

Power spectral analysis of arterial pressure signals: physiologic principles and clinical applications.

Acta Anaesthesiologica ScandinavicaVolume 41, Issue S110 p. 119-120 Power spectral analysis of arterial pressure signals: Physiologic principles and clinical applications Samuel Chan, Samuel Chan Center for Neuroscience National Yang-Ming University Taipei, Taiwan, Republic of ChinaSearch for more papers by this author Samuel Chan, Samuel Chan Center for Neuroscience National Yang-Ming University Taipei, Taiwan, Republic of ChinaSearch for more papers by this author First published: 02 February 2011 https://doi.org/10.1111/j.1399-6576.1997.tb05525.xCitations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume41, IssueS110June 1997Pages 119-120 RelatedInformation

Spectral analysis of systemic arterial pressure and heart rate signals as a prognostic tool for the prediction of patient outcome in the intensive care unit

To evaluate the applicability of changes in spectra of systemic arterial pressure and heart rate signals in the prediction of patient outcome in an adult intensive care unit (ICU). To compare the prognostic predictability of this method with the Acute Physiology and Chronic Health Evaluation II (APACHE II) scoring system. Prospective data collection from 52 ICU patients. Adult ICU at a large, university-affiliated, medical center. Consecutive patients who were admitted to the adult ICU due to noncardiac emergencies, and who remained for at least 2 days. None. The demographic data, diagnosis, and survival data were recorded for each patient enrolled in this study. For the period between admission and 24 hrs before discharge, the APACHE II score was tabulated daily. Likewise, continuous, on-line, and real-time spectral analysis of systemic arterial pressure and heart rate signals was carried out every day for at least 30 mins at 2200 to 2400 hrs. The averaged power density values during this 30-min recording period of the high-frequency (0.15 to 0.4 Hz), low-frequency (0.08 to 0.15 Hz), and very low-frequency (0.016 to 0.08 Hz) components of systemic arterial pressure and heart rate signals were subsequently computed. Systemic vascular resistance index and cardiac index were also determined daily. We observed a trend of changes in the spectral components of systemic arterial pressure and heart rate signals in patients who eventually survived (n = 25) or died (n = 27). Progressive increases in the power density values of both the low-frequency and very low-frequency components of systemic arterial pressure and heart rate signals appeared to be related to recovery. Conversely, progressive decreases in the power density values of these spectral components was indicative of deterioration and fatality. The predicted outcome based on the trend of changes in the low-frequency and very low-frequency components of systemic arterial pressure and heart rate signals correlated positively with daily APACHE II scores. No direct correlation, however, was indicated by mean systemic arterial pressure, heart rate, systemic vascular resistance index, and cardiac index. We also confirmed that the differential trend of spectral changes in patients who survived or died was not due to circadian rhythm, nor alterations in the responsiveness of the blood vessels to intravenous infusion of dopamine. Power spectral analysis of systemic arterial pressure and heart rate signals offers a reasonable means of monitoring acute, critically ill patients, and may be used as an alternative prognostic tool for the prediction of patient outcome in the ICU.