Cardiovascular Engineering (dordrecht, Netherlands)最新文献

The brain is most sensitively dependent on oxygen to maintain its normal function. Methods to assess the degree of its oxygenation have generally been invasive and indirect. Rapid assessment of brain oxygenation is particularly vital during cerebrospinal ischemia and hypoxia. We have developed a noninvasive electro-optical method using pulsed near-infrared (NIR) light to quantify brain oxygenation during ischemia and hypoxia in anesthetized rabbits. Cerebral ischemia was induced through 30-40 s of bi-lateral carotid artery occlusion. Cerebral hypoxia was induced by varying inspired oxygen levels. The NIR light response to the interventions was expressed in terms of relative absorption (RA). Results showed that our pulsed NIR system could rapidly detect sudden alterations in oxygenation and blood flow to the brain. The response patterns during cerebral ischemia and hypoxia were significantly different, although both decreased brain oxygenation. The overall RA response to ischemia was much faster (in seconds) than during hypoxia (in minutes). These different response patterns can serve as early warning signal of low brain oxygenation and to discriminate the cause of the diminished oxygenation. The present pulsed NIR system is capable to provide a rapid, noninvasive and continuous monitoring of such decreases in brain oxygenation.

The aim of this study is to describe a robust unified framework for segmentation of the phonocardiogram (PCG) signal sounds based on the false-alarm probability (FAP) bounded segmentation of a properly calculated detection measure. To this end, first the original PCG signal is appropriately pre-processed and then, a fixed sample size sliding window is moved on the pre-processed signal. In each slid, the area under the excerpted segment is multiplied by its curve-length to generate the Area Curve Length (ACL) metric to be used as the segmentation decision statistic (DS). Afterwards, histogram parameters of the nonlinearly enhanced DS metric are used for regulation of the α-level Neyman-Pearson classifier for FAP-bounded delineation of the PCG events. The proposed method was applied to all 85 records of Nursing Student Heart Sounds database (NSHSDB) including stenosis, insufficiency, regurgitation, gallop, septal defect, split sound, rumble, murmur, clicks, friction rub and snap disorders with different sampling frequencies. Also, the method was applied to the records obtained from an electronic stethoscope board designed for fulfillment of this study in the presence of high-level power-line noise and external disturbing sounds and as the results, no false positive (FP) or false negative (FN) errors were detected. High noise robustness, acceptable detection-segmentation accuracy of PCG events in various cardiac system conditions, and having no parameters dependency to the acquisition sampling frequency can be mentioned as the principal virtues and abilities of the proposed ACL-based PCG events detection-segmentation algorithm.

Several works have separated the pressure waveform p in systemic arteries into reservoir p(r) and excess p(exc) components, p = p(r) + p(exc), to improve pulse wave analysis, using windkessel models to calculate the reservoir pressure. However, the mechanics underlying this separation and the physical meaning of p(r) and p(exc) have not yet been established. They are studied here using the time-domain, inviscid and linear one-dimensional (1-D) equations of blood flow in elastic vessels. Solution of these equations in a distributed model of the 55 larger human arteries shows that p(r) calculated using a two-element windkessel model is space-independent and well approximated by the compliance-weighted space-average pressure of the arterial network. When arterial junctions are well-matched for the propagation of forward-travelling waves, p(r) calculated using a three-element windkessel model is space-dependent in systole and early diastole and is made of all the reflected waves originated at the terminal (peripheral) reflection sites, whereas p(exc) is the sum of the rest of the waves, which are obtained by propagating the left ventricular flow ejection without any peripheral reflection. In addition, new definitions of the reservoir and excess pressures from simultaneous pressure and flow measurements at an arbitrary location are proposed here. They provide valuable information for pulse wave analysis and overcome the limitations of the current two- and three-element windkessel models to calculate p(r).

Our institution is in development of a low frequency, non-invasive Diastolic Timed Vibrator (DTV) for use in emergency treatment of ST Elevation Myocardial Infarction (STEMI). It is preferable to avoid vibration emissions during the IsoVolumetric Contraction Period (IVCP) and at least the majority of mechanical systole thereafter, as systolic vibration may cause a negative inotropic effect in the ischemic heart. Furthermore diastolic vibration should preferably include the IsoVolumetric Relaxation Period (IVRP) which has been shown in clinical studies to improve cardiac performance and enhance coronary flow. Electrocardiographic (ECG) monitoring can be used to enable diastolic tracking, however, the timing of the phases of the cardiac cycle in relation to the ECG waveform must first be verified. The objective of this study was therefore to determine timing of onset of mechanical systole and diastole in reference to the QRS-T Complex. One hundred and twenty-three adult echocardiographic studies were assessed for the point of mitral and aortic valve closure in relation to the QRS complex and T wave in a representative population. We found that onset of mechanical systole occurred on and usually shortly after the peak of a first dominant QRS complex deflection, and onset of diastole occurred at the earliest on and most commonly beyond the peak or midpoint of the T wave. A DTV should ideally be able to stop vibrating on or before the peak of the first dominant deflection of a QRS complex, and begin vibrating near the peak of the T wave. Given early detection of ventricular depolarization can occur 10-20 ms prior to R wave peak, it is proposed that a DTV should preferably be able to stop vibrating within 10 ms of a triggered stop command. Onset of vibration during peak of T wave could be approximated by a rate adapted Q-T interval regression equation, and then fine tuned by manual adjustment during therapy.

Tortuous or twisted veins are often seen in the retina, cerebrum, and legs (varicose veins) of one-third of the aged population, but the underlying mechanisms are poorly understood. While the collapse of veins under external pressure has been well documented, the bent buckling of long vein segments has not been studied. The objectives of this study were to develop a biomechanical model of vein buckling under internal pressure and to predict the critical pressure. Veins were modeled as thin-walled nonlinear elastic tubes with the Fung exponential strain energy function. Our results demonstrated that veins buckle due to high blood pressure or low axial tension. High axial tension stabilized veins under internal pressure. Our buckling model estimated the critical pressure accurately compared to the experimental measurements. The buckling equation provides a useful tool for studying the development of tortuous veins.

A clinical comparison, of two methods of afterload assessment, has been made. The first method, systemic vascular resistance index (SVR(i)), is based upon the traditional formula for afterload which utilizes central venous pressure (CVP), as well as cardiac index (C(i)), and mean arterial blood pressure (MAP). The second method, total systemic vascular resistance index (TSVR(i)), also uses MAP and C(i). However, TSVR(i) ignores the contribution of CVP. This preliminary examination, of 10 randomly-selected ICU patients, has shown a high degree of correlation (ranging from 90 to 100%) between SVR(i) and TSVR(i) (P < 0.0001). Furthermore, there was also a high degree of correlation (ranging from 94 to 100%) noted between the hour-to-hour change in SVR(i) with the hour-to-hour change in TSVR(i) (P < 0.0001). The results, of this pilot study, support the premise that the use of CVP may not always be necessary for afterload evaluation in the clinical setting. Minimally-invasive means of measuring both C(i) and MAP, without CVP, may be adequate for use in assessing afterload.

The problem of heart failure with preserved ejection fraction (HFpEF) has recently received much attention. In this study we discuss some relations that connect ejection fraction EF to the parameters describing the end-systolic pressure-volume relation (ESPVR). It is shown that the study of the relation between EF and ESPVR can give some understanding of the problem of HFpEF. An important feature of the present approach is the introduction of the active force of the myocardium (also called isovolumic pressure) in the formalism describing the ESPVR.

T-wave abnormalities are gaining significance in the realm of electrocardiogram diagnostics. In particular, T-wave alternans are proving to be powerful predictive indicators of potentially fatal arrhythmias. T-wave morphology monitoring and analysis are the means by which alternans and other abnormalities are detected. We have presented a preliminary design of an analog T-wave monitor to provide a characteristic description of the beat-to-beat T-wave morphology in terms of its maximum leading edge and trailing edge slopes, and its area. Experimental results showed that data from the analog T-wave monitor compared well with those predicted theoretically. Current design of the T-wave monitor, once improved, can find use in the screening, diagnosis, and early detection of T-wave abnormalities in clinical settings.