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  • 1
    Online Resource
    Online Resource
    Measurement of hemodynamics in human carotid artery using ultrasound and computational fluid dynamics
    American Physiological Society ; 2002
    In:  Journal of Applied Physiology Vol. 92, No. 3 ( 2002-03-01), p. 957-961
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 92, No. 3 ( 2002-03-01), p. 957-961
    Abstract: The objective of the study was to investigate the feasibility of using computational fluid dynamic modeling (CFD) with noninvasive ultrasound measurements to determine time-variant three-dimensional (3D) carotid arterial hemodynamics in humans in vivo. The effects of hyperoxia and hypoxic hypercapnia on carotid artery local hemodynamics were examined by use of this approach. Six normotensive volunteers followed a double-blind randomized crossover design. Blood pressure, heart rate, and carotid blood flow were measured while subjects breathed normal air, a mixture of 5% CO 2 and 15% O 2 (hypoxic hypercapnia), and 100% O 2 (hyperoxia). Carotid artery geometry was reconstructed on the basis of B-mode ultrasound images by using purpose-built image processing software. Time-variant 3D carotid hemodynamics were estimated by using finite volume-based CFD. Systemic blood pressure was not significantly affected by hyperoxia or hypoxic hypercapnia, but heart rate decreased significantly with hyperoxia. There was an increase in diastolic flow velocity in the external carotid artery after hypoxic hypercapnia, but otherwise carotid blood flow velocities did not change significantly. Compared with normal air, hyperoxic conditions were associated with a decrease in the width of the region of flow separation in the external carotid artery. During hyperoxia, there was also an increase in the minimum and a decrease in maximum shear stress in the bifurcation and hence a reduction in cyclic variation in shear stress. Hypoxic hypercapnia was associated with a reduced duration of flow separation in the external carotid artery and an increase in the minimum shear stress without affecting the cyclic variation in shear stress. This study demonstrates the feasibility of using noninvasive ultrasound techniques in conjunction with CFD to describe time-variant 3D hemodynamics in the human carotid arterial bifurcation in vivo.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00171.2001
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2002
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 2
    Online Resource
    Online Resource
    Effects of transmural pressure and wall shear stress on LDL accumulation in the arterial wall: a numerical study using a multilayered model
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 292, No. 6 ( 2007-06), p. H3148-H3157
    Details
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 292, No. 6 ( 2007-06), p. H3148-H3157
    Abstract: The accumulation of low-density lipoprotein (LDL) is recognized as one of the main contributors in atherogenesis. Mathematical models have been constructed to simulate mass transport in large arteries and the consequent lipid accumulation in the arterial wall. The objective of this study was to investigate the influences of wall shear stress and transmural pressure on LDL accumulation in the arterial wall by a multilayered, coupled lumen-wall model. The model employs the Navier-Stokes equations and Darcy's Law for fluid dynamics, convection-diffusion-reaction equations for mass balance, and Kedem-Katchalsky equations for interfacial coupling. To determine physiologically realistic model parameters, an optimization approach that searches optimal parameters based on experimental data was developed. Two sets of model parameters corresponding to different transmural pressures were found by the optimization approach using experimental data in the literature. Furthermore, a shear-dependent hydraulic conductivity relation reported previously was adopted. The integrated multilayered model was applied to an axisymmetric stenosis simulating an idealized, mildly stenosed coronary artery. The results show that low wall shear stress leads to focal LDL accumulation by weakening the convective clearance effect of transmural flow, whereas high transmural pressure, associated with hypertension, leads to global elevation of LDL concentration in the arterial wall by facilitating the passage of LDL through wall layers.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    URL: Article
    DOI: 10.1152/ajpheart.01281.2006
    RVK:
    WA 15000
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
    detail.hit.zdb_id: 1477308-9
    SSG: 12
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  • 3
    Online Resource
    Online Resource
    Effects of elastic compression stockings on wall shear stress in deep and superficial veins of the calf
    American Physiological Society ; 2008
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 294, No. 5 ( 2008-05), p. H2112-H2120
    Details
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 294, No. 5 ( 2008-05), p. H2112-H2120
    Abstract: The purpose of this study was to estimate wall shear stress (WSS) in individual vessels of the venous circulation of the calf and quantify the effects of elastic compression based on change of vessel geometry and velocity waveform. The great saphenous vein and either a peroneal or posterior tibial vein have been imaged in four healthy subjects using magnetic resonance imaging, with and without the presence of a grade 1 medical stocking. Flow through image-based reconstructed geometries was numerically simulated for both a range of steady flow rates and ultrasound-derived transient velocity waveforms, scaled to give a standardized time averaged flow rate. For steady flow, the stocking produced an average percentage increase in mean WSS of ∼100% in the great saphenous vein across a range of 0.125–1.25 ml/s. The percentage increase in the peroneal/posterior tibial veins varied from 490 to 650% across a range of 0.5–5 ml/s. In addition, application of the stocking eliminated periods of very low or zero flow from the transient waveforms. The average minimum value of WSS in all vessels without the stocking was 〈 0.1 Pa. With the stocking, this was increased to 0.7 Pa in the great saphenous and 0.9 Pa in the peroneal/posterior tibial veins. The pathophysiological effects of these changes are discussed. In conclusion, the flight stocking was effective in raising venous WSS levels in prone subjects, and this effect was much more pronounced in the deep vessels. The stocking also tended to prevent cessation of flow during periods of increased downstream pressure produced by respiration.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    URL: Article
    DOI: 10.1152/ajpheart.01302.2007
    RVK:
    WA 15000
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2008
    detail.hit.zdb_id: 1477308-9
    SSG: 12
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    High dietary salt intake increases carotid blood pressure and wave reflection in normotensive healthy young men
    American Physiological Society ; 2011
    In:  Journal of Applied Physiology Vol. 110, No. 2 ( 2011-02), p. 468-471
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 110, No. 2 ( 2011-02), p. 468-471
    Abstract: Dietary salt intake is associated with high brachial blood pressure (BP) and increased risk of cardiovascular disease. We investigated whether changes in dietary salt intake are associated with changes in central BP and wave reflection in healthy volunteers. Ten healthy normotensive male volunteers (22–40 yr) participated in a 6-wk double-blind randomized crossover study to compare a low-dietary salt intake (60–80 mmol sodium/day) with a high-salt intake (low salt intake supplemented with 128 mmol sodium/day) on central BP and wave reflection. Brachial and carotid BP, carotid blood flow velocity, forward (P f ) and backward (P b ) pressure, wave intensity, body weight, and urinary electrolyte excretion were measured at the end of each crossover period. High salt intake significantly increased carotid systolic BP [98 (SD 11) vs. 91 mmHg (SD 13), P 〈 0.01] and increased wave reflection [ratio of backward to forward pressure (P b /P f ) 0.13 (SD 0.02) vs. 0.11 (SD 0.03), P = 0.04] despite only small effects on brachial BP [114 (SD 9) vs. 112 mmHg (SD 6), P = 0.1] . Urinary sodium excretion and body weight were also increased following high salt intake. High salt intake disproportionately increases central BP compared with brachial BP as a result of enhanced wave reflection. These effects may contribute to the adverse effect of high dietary salt intake on the risk of cardiovascular disease.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00917.2010
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2011
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
    Location Call Number Limitation Availability
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  • 5
    Online Resource
    Online Resource
    Stress phase angle depicts differences in coronary artery hemodynamics due to changes in flow and geometry after percutaneous coronary intervention
    American Physiological Society ; 2009
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 296, No. 3 ( 2009-03), p. H765-H776
    Details
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 296, No. 3 ( 2009-03), p. H765-H776
    Abstract: The effects of changes in flow velocity waveform and arterial geometry before and after percutaneous coronary intervention (PCI) in the right coronary artery (RCA) were investigated using computational fluid dynamics. An RCA from a patient with a stenosis was reconstructed based on multislice computerized tomography images. A nonstenosed model, simulating the same RCA after PCI, was also constructed. The blood flows in the RCA models were simulated using pulsatile flow waveforms acquired with an intravascular ultrasound-Doppler probe in the RCA of a patient undergoing PCI. It was found that differences in the waveforms before and after PCI did not affect the time-averaged wall shear stress and oscillatory shear index, but the phase angle between pressure and wall shear stress on the endothelium, stress phase angle (SPA), differed markedly. The median SPA was −63.9° (range, −204° to −10.0°) for the pre-PCI state, whereas it was 10.4° (range, −71.1° to 25.4°) in the post-PCI state, i.e., more asynchronous in the pre-PCI state. SPA has been reported to influence the secretion of vasoactive molecules (e.g., nitric oxide, PGI 2 , and endothelin-1), and asynchronous SPA (≈−180°) is proposed to be proatherogenic. Our results suggest that differences in the pulsatile flow waveform may have an important influence on atherogenesis, although associated with only minor changes in the time-averaged wall shear stress and oscillatory shear index. SPA may be a useful indicator in predicting sites prone to atherosclerosis.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    URL: Article
    DOI: 10.1152/ajpheart.01166.2007
    RVK:
    WA 15000
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2009
    detail.hit.zdb_id: 1477308-9
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 6
    Online Resource
    Online Resource
    Reduced systolic wave generation and increased peripheral wave reflection in chronic heart failure
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 293, No. 1 ( 2007-07), p. H557-H562
    Details
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 293, No. 1 ( 2007-07), p. H557-H562
    Abstract: In human heart failure the role of wave generation by the ventricle and wave reflection by the vasculature is contentious. The aim of this study was to compare wave generation and reflection in normal subjects with patients with stable compensated heart failure. Twenty-nine normal subjects and 67 patients with heart failure (New York Heart Association class II or III) were studied by noninvasive techniques applied to the common carotid artery. Data were analyzed by wave intensity analysis to determine the nature and direction of waves during the cardiac cycle. The energy carried by an early systolic forward compression wave (S wave) generated by the left ventricle and responsible for acceleration of flow in systole was significantly reduced in subjects with heart failure ( P 〈 0.001), and the timing of the peak of this wave was delayed. In contrast, reflection of this wave was increased in subjects with heart failure ( P 〈 0.001), but the timing of reflections with respect to the S wave was unchanged. The energy of an expansion wave generated by the heart in protodiastole was unaffected by heart failure. The carotid artery wave speed and the augmentation index did not significantly differ between subjects with heart failure compared with normal individuals. The ability of the left ventricle to generate a forward compression wave is markedly impaired in heart failure. Increased wave reflection serves to maintain systolic blood pressure but also places an additional load on cardiac function in heart failure.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    URL: Article
    DOI: 10.1152/ajpheart.01095.2006
    RVK:
    WA 15000
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
    detail.hit.zdb_id: 1477308-9
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
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