Bruit

Abstract: Real time signal processing technique for ultrasonic imaging of tissue vibrations for localizing source of a bruit in 2D image with respect to anatomy and/or for obtaining simultaneous information about vibrations and underlying blood flow. The bruit can be quantitatively assessed using an ensemble of ultrasound echoes. Signal processing enables estimation of wall displacement and display of time-resolved vibration spectrum. Vibrations are detected and color-coded according to amplitude and frequency and overlaid on the B-mode and/or color-flow image in real time. Proposed vibration imaging algorithms use data acquired during conventional ultrasonic color-flow imaging and the clutter signal, normally suppressed in color-flow imaging, to detect and characterize tissue vibrations. Three vibration imaging algorithms based on parametric modeling of vibrations and other criteria distinguish between clutter, blood flow, and vibrations. The techniques are usable to detect, locate, image, and quantitatively grade stenoses in blood vessels.

Abstract: The sound generated by blood flow in stenosed arteries is investigated for a model that consists of a channel with a one-sided constriction. The blood flow-induced arterial "bruits" are computed directly using a hybrid approach wherein the hemodynamic flow field is solved by an immersed boundary, incompressible flow solver, and the sound generation is modeled by a first-principles approach that employs the linearized compressible perturbation equations. The transmission and propagation of the sound through the surrounding biological tissues is also modeled with a simplified, linear structural wave equation. The flow field inside the artery and the bruit sound signal at the epidermal surface are examined to delineate the precise source of the arterial bruit and the correlation between the bruit and the arterial wall pressure fluctuations. It is found that the bruits are related primarily to the time-derivative of the integrated pressure force on the post-stenotic segment of arterial wall. The current study provides a clear perspective on the generation of bruits from stenosed arteries and enables an assessment of the conjectures of previous researchers regarding the source of arterial bruits.

Abstract: Annoyance due to environmental noise from various sources constitutes an important public health problem. Extensive work has been performed to obtain a basis for dose response curves, which can later be used for regulation purposes. Using such data, limits for noise exposure have been suggested or enforced for noise from aircraft, trains and road traffic. The estimation of the noise exposure for environmental noise is usually performed using the dB(A) unit. This is based upon early experiments where equal loudness curves were constructed by exposing test subjects to mainly pure tones of various frequencies for short exposure periods (e.g. Fletcher and Munson 1933, Churcher et al1937, Robinson and Dadson 1956). Experience from practical public health work demonstrates that this concept for judging annoyance can be questioned. Complaints to Local Health Authorities are frequently raised concerning low frequency sounds, and annoyance is reported, although dB(A) levels fall well below current limits. Sources oflow frequency noise, such as heavy vehicles, ventilation installations and compressors have increased in number in urban areas. In Sweden a recent source of low frequency noise is the use of heat pumps which extract heat from the air. There has been a rapid rise in the number of heat pumps owing to their ability to reduce heating costs. The pumps and compressors used, radiate low frequency noise, usually dominated by frequencies in the range 63-125 Hz. This is not a high noise level according to current noise limits, seldom exceeding 40 dB(A) outdoors. Despite this, many heat pumps have been reported as sources of annoyance to people living in the vicinity as shown by complaints received by Local Health Authorities (Persson and Rylander 1986). To further study annoyance from low frequency noise, we have performed studies in a laboratory environment. Subjects were exposed to two different noises of the same dB(A) levelbut where one of the noises contained a higher proportion oflow frequencies. The annoyance experienced by the subjects was assessed after a 30 minute exposure.

Abstract: Influence des caracteristiques geometriques sur le bruit d'un ventilateur centrifuge a ailettes incurvees vers l'avant