Conjecture on reflectionlessness of blood-vascular system as a wave-conducting medium (original) (raw)
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Quantification of wave reflection in the human aorta from pressure alone: a proof of principle
…, 2006
Wave reflections affect the proximal aortic pressure and flow waves and play a role in systolic hypertension. A measure of wave reflection, receiving much attention, is the augmentation index (AI), the ratio of the secondary rise in pressure and pulse pressure. AI can be limiting, because it depends not only on the magnitude of wave reflection but also on wave shapes and timing of incident and reflected waves. More accurate measures are obtainable after separation of pressure in its forward (P f ) and reflected (P b ) components. However, this calculation requires measurement of aortic flow. We explore the possibility of replacing the unknown flow by a triangular wave, with duration equal to ejection time, and peak flow at the inflection point of pressure (F tIP ) and, for a second analysis, at 30% of ejection time (F t30 ). Wave form analysis gave forward and backward pressure waves. Reflection magnitude (RM) and reflection index (RI) were defined as RMϭP b /P f and RIϭP b /(P f ϩP b ), respectively. Healthy subjects, including interventions such as exercise and Valsalva maneuvers, and patients with ischemic heart disease and failure were analyzed. RMs and RIs using F tIP and F t30 were compared with those using measured flow (F m ). Pressure and flow were recorded with high fidelity pressure and velocity sensors. Relations are: RM tIP ϭ0.82RM mf ϩ0.06 (R 2 ϭ0.79; nϭ24), RM t30 ϭ0.79RM mf ϩ0.08 (R 2 ϭ0.85; nϭ29) and RI tIP ϭ0.89RI mf ϩ0.02 (R 2 ϭ0.81; nϭ24), RI t30 ϭ0.83RI mf ϩ0.05 (R 2 ϭ0.88; nϭ29). We suggest that wave reflection can be derived from uncalibrated aortic pressure alone, even when no clear inflection point is distinguishable and AI cannot be obtained. Epidemiological studies should establish its clinical value. (Hypertension. 2006;48:1-7.) Key Words: aorta Ⅲ blood flow Ⅲ blood flow velocity Ⅲ blood pressure Ⅲ pulse
New Simple Phenomenological Model for Laser Doppler Measurements of Blood Flow in Tissue
Proceedings of the 10th International Joint Conference on Biomedical Engineering Systems and Technologies, 2017
Laser Doppler flowmetry (LDF) for measurements of tissue blood flow is well-known today. The basic theory of forming the registered optical signal in LDF is the model developed by R.Bonner and R. Nossal. However, claiming to be a detailed and comprehensive analysis of the interaction of light with tissues, it does not describe many phenomena. Multiple simplifications and assumptions in the model diminish the efforts on the analysis of peculiarities of light scattering inside the tissue, resulting in a very approximate output. In this our study, a qualitatively similar result was obtained with the use of more simple and general approach. It was shown, that the power spectra of analyzed signals in the form of the exponential decay, similar to a fractal noise (1/f noise), is a consequence mainly of the Maxwell's distribution of moving particles' velocities. Moreover, in contrast to the classic model, our model shows that the first moment of the frequency is linearly proportional not only to the velocity of red blood cells, but also is inversely proportional to the wavelength of illuminating radiation, that is more physically grounded.
Model for laser Doppler measurements of blood flow in tissue
Applied Optics, 1981
A theory is developed which relates quasi-elastic light scattering measurements to blood flow in tissue microvasculature. We assume that the tissue matrix surrounding the blood cells is a strong diffuser of light and that moving erythrocytes, therefore, are illuminated by a spatially distributed source. Because the surrounding tissue is considered to be stationary, Doppler shifts in the frequency of the scattered light arise only from photon interactions with the moving blood cells. The theory implies that the time decay of the photon autocorrelation function scales proportionally with cell size and inversely with mean translational speed. Analysis of multiple interactions of photons with moving cells indicates the manner in which spectral measurements additionally are sensitive to changes in blood volume. Predictions are verified by measurements of particle flow in model tissues.
Physics Linkages Between Arterial Morphology, Pulse Wave Reflection and Peripheral Flow
Artery Research
Background Previous physics-based analyses of arterial morphology in relation to pulsatile pressure and flow, with pulse wave reflection, focused on the large arteries and required assumptions about the relative thicknesses of arterial walls and the velocities of pulse waves in the arteries. A primary objective of this study was to analyze arterial morphology and pulse wave reflection, using physics-based wave propagation, which explicitly includes arterial stiffness, with potential autonomic flow regulation, for both large and small arteries. Methods Pulse wave reflections that occur at arterial bifurcations, and their impact on macrocirculation and microcirculation pulse pressures and flows, are analyzed using the physics of wave propagation and impedance matching. Results The optimum combinations of arterial dimensions and stiffnesses which minimize pulsatile reflections at arterial bifurcations are identified for both macrocirculation and microcirculation. The optimum ratio of a...
Quantification of Wave Reflection in the Human Aorta From Pressure Alone
Hypertension, 2006
Wave reflections affect the proximal aortic pressure and flow waves and play a role in systolic hypertension. A measure of wave reflection, receiving much attention, is the augmentation index (AI), the ratio of the secondary rise in pressure and pulse pressure. AI can be limiting, because it depends not only on the magnitude of wave reflection but also on wave shapes and timing of incident and reflected waves. More accurate measures are obtainable after separation of pressure in its forward (P f ) and reflected (P b ) components. However, this calculation requires measurement of aortic flow. We explore the possibility of replacing the unknown flow by a triangular wave, with duration equal to ejection time, and peak flow at the inflection point of pressure (F tIP ) and, for a second analysis, at 30% of ejection time (F t30 ). Wave form analysis gave forward and backward pressure waves. Reflection magnitude (RM) and reflection index (RI) were defined as RM=P b /P f and RI=P b /(P f +P...
2009
Wave intensity (WI) is a hemodynamic index, which can evaluate the working condition of the heart interacting with the arterial system. It can be defined at any site in the circulatory system and provides a great deal of information. However, we need simultaneous measurements of blood pressure and velocity to obtain wave intensity, which has limited the clinical application of wave intensity, in spite of its potential. To expand the application of wave intensity in the clinical setting, we developed a real-time non-invasive measurement system for wave intensity based on a combined color Doppler and echo-tracking system. We measured carotid arterial WI in normal subjects and patients with various cardiovascular diseases. In the coronary artery disease group, the magnitude of the first peak of carotid arterial WI (W 1 ) increased with LV max. dP/dt (r = 0.74, P \ 0.001), and the amplitude of the second peak (W 2 ) decreased with an increase in the time constant of LV pressure decay (r = -0.77, P \ 0.001). In the dilated cardiomyopathy group, the values of W 1 were much lower than those in the normal group (P \ 0.0001). In the hypertrophic cardiomyopathy group, the values of W 2 were much smaller than those in the normal group (P \ 0.0001). In mitral regurgitation before surgery, W 2 decreased or disappeared, but after surgery W 2 appeared clearly. In the hypertension group, the magnitude of reflection from the head was considerably greater than that in the normal group (P \ 0.0001). We also evaluated hemodynamic effects of sublingual nitroglycerin in normal subjects. Nitroglycerin increased W 1 significantly (P \ 0.001). WI can be obtained non-invasively using an echo-Doppler system in the clinical setting. This method will increase the clinical usefulness of wave intensity.
2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vols 1-8, 2008
Pressure waveforms measured at different locations in the cardiovascular system present a very similar diastolic decay. Previous work has shown the cardiovascular system can be modelled as a Windkessel and wave system. This concept has been extended to any arbitrary location in the cardiovascular system. We suggest that it is possible to calculate a time-varying reservoir pressureP (t) and a distance-and time-varying wave pressure p(x, t) by fitting an exponential function to the diastolic decay of the measured pressure P ; defining that the measured pressure P (x, t)=P (t)+p(x, t). Velocity waveforms U can also be separated into its reservoir,Ū , and wave, u,