Unsteady Fluid Dynamics of Several Mechanical Prosthetic Heart Valves Using a Two Component Laser Doppler Anemometer System

Abstract: Five typical mechanical heart valves (Starr-Edwards, Björk-Shiley convexo-concave (c-c), Björk-Shiley monostrut, Bicer-Val, and St. Jude Medical) were tested in the mitral position under the pulsatile flow condition. The test program included measurements of velocity and turbulent stresses at 5 downstream locations. The study was carried out using a sophisticated cardiac simulator in conjunction with a highly sensitive 2 component laser Doppler anemometer (LDA) system. The continuous monitoring of parametric time histories revealed useful details about the complex flow and helped to establish the locations and times of the peak parameter values. Based upon the nondimensional presentation of data, the following general conclusions can be made. First, all the 5 valve designs created elevated turbulent stresses during the accelerating and peak flow phases, presenting the possibility of thromboembolism and perhaps hemolysis. Second, the difference in valve configuration seemed to affect the flow characteristics; third, the bileaflet design of the St. Jude valve appeared to create a lower turbulence stress level.     

Hyperaemia prior to acute cerebral swelling in severe head injuries: The role of transcranial doppler monitoring

Summary Acute cerebrovascular congestion after a closed head injury is significantly related to intracranial hypertension. As an indirect method of cerebral blood flow measurement, transcranial doppler sonography (TCD) provides a rapid and noninvasive assessment of cerebral haemodynamics, including hyperaemic conditions.TCD examinations was serially performed in 35 patients with severe head injury with intact cerebral circulation; i.e. the mean flow velocity (MFV) patterns of the middle cerebral artery (MCA) did not show signs of cerebral circulatory arrest such as systolic spike, to and fro, or no flow. The results showed that the MFV of the MCAs and ipsilateral extracranial internal carotid arteries (ICAs) in 9 of these patients increased sharply and pulsatility index (PI) decreased during 48–96 hours after the injury. This was soon followed by patterns of high intracranial resistance, consistent with elevated intracranial pressure (ICP) in monitored patients and acute brain swelling on repeated computed tomographic (CT) scans. The correlation between increased MFVs, decreased PIs, and cerebral haemodynamic changes leading to acute brain swelling is discussed.The number of patients who ended with severe disability, vegetative state, or death was 66% in this group of 9 patients, compared to only 34% for the 35 patients overall with severe head injury. Though the morbidity and mortality rates largely depend on the primary injury, the presence of acute cerebral swelling aggravate the grave course in these patients. And the ability of TCD to monitor the hyperaemic state prior to oedema should lead us to adjust the therapy in order to minimize the secondary insult related to intracranial hypertension.     

Value of Doppler ultrasound for the diagnosis of renal artery stenosis in children

To evaluate the reliability of Doppler ultrasonography (US) in identifying children with renal artery stenosis (RAS) among those with hypertension, we compared Doppler US results in 22 hypertensive children (mean age 8.9±4.3 years), with (13 cases) and without RAS at angiography, and in 33 normotensive children (mean age 8.8±4.7 years). We observed 2 false-negatives and 2 false-positives with Doppler US. Of the 2 false-negative diagnoses, 1 had RAS on an accessory renal artery located behind a normal upper polar artery and the other was observed in a patient with bilateral multiple stenosis of the very distal segments of renal arteries. The 2 false-positive diagnoses were due to sinuous left renal artery and to technical reasons, respectively. In another patient, Doppler US showed a tight RAS, while arteriography was normal. RAS was subsequently confirmed by a second arteriography. Peak systolic velocity values of Doppler US were significantly higher in patients with proven angiographic RAS (3.44±0.66 m/s) than in hypertensive patients with normal renal arteries at angiography (0.99±0.35 m/s, P <0.0001) and normotensive healthy children (1.04±0.23 m/s, P <0.0001). With the use of multiple views, and the experience acquired with practice, false-negatives or false-positives due to the geometry of the renal artery can be avoided. Nevertheless, very distal stenosis can be missed by Doppler US. Received October 30, 1995; received in revised form April 16, 1996; accepted May 14, 1996     

经颅彩色多普勒对大脑血流动力学的研究

目的 :探讨认知过程中脑血流动力学的变化。方法 :应用经颅彩色多普勒对不同生理情况下大脑半球血流速度的变化进行监测。结果 :每项试验前后比较 ,血流速度的增加有显著差异 (P <0 0 1) ,语言试验血流速度增加偏侧在左半球 ,面视试验偏侧在右半球 ,光刺激试验时枕区血流速度最快。结论 :经颅多普勒能监测认知过程中半球血液动力学变化的差异     

眼动脉彩色多普勒血流频谱检测在甲亢诊断中的应用

采用ＣＤＦＩ对３４例初诊甲亢患者的眼动脉进行检测，３４例患者根据Ｔ３结果分为两组，同时１０位患者治疗前后的眼动脉血流速度对照。结果表明，甲亢患者的眼动脉血流速度高于正常人，但与Ｔ３值无相关。１０例患者的眼动脉血流速度随着Ｔ３、Ｔ４下降而恢复正常。结论：ＣＤＦＩ测定眼动脉血流频谱可用于甲亢的诊断和治疗观察。     

Reduction in Internal Carotid Arterial Blood Flow Velocity in Children During Antiepileptic Drug Therapy with Clinical Dosages

Summary: We studied the effect of antiepileptic drugs (AEDs) on internal carotid artery (ICA) blood flow velocity, as an index of total cerebral blood flow (CBF). The subjects were 45 newly diagnosed children with febrile convulsion or epilepsy who were seizure-free for a period long enough not to affect the results. They had no neurologic deficit, received fixed monotherapy, and were examined by a noninvasive Doppler ultrasound method, in comparisonwith 13 age-matched normal volunteers with no AED. In 30 patients, the measurements were performed before and after AED administration [10 with phenobarbital (PB), 10 with carbamazepine (CBZ), and 10 with valproate (VPA)], and performed before and after AED discontinuation in the remaining 15 patients (all with PB). Normal volunteers underwent the two consecutive examinations with a mean interval equal to that of the entire patient group, and there was no difference in velocity values between the measurements. In patients receiving CBZ or VPA, a significant reduction was noted in blood flow velocity after drug administration. Although velocity values in the patients receiving PB did not change after drug administration, they were significantly increased after complete discontinuation. In the present study, a slight but significant reduction in CBF caused by AED administration at therapeutic doses in children was suggested.     

Primary and secondary malignancies of the penis: ultrasound features

Cancer of the penis is a rare neoplasm in developed countries but worldwide represents a significant health problem. In this study, the ultrasonographic features of primary and secondary malignant lesions of the penis are described. Squamous cell carcinoma usually presents as a hypoechoic lesion with heterogeneous appearance. Invasions of the corpora cavernosa and the corpus spongiosum are appreciable. B-cell lymphoma presents as a well-vascularized mass, a plaque, or ulcers in the penile skin. Penile metastases result from hematogenous or lymphatic spreading of distant tumors or, more frequently, as penile infiltration by tumors from adjacent organs. Diffuse corporeal or nodular involvement can result. 1Award-winning poster at the 10th European Symposium on Urogenital Radiology; Uppsala, Sweden, September 4•7, 2003.     

使用电力载波技术实现中央控制电子钟

本文应用电力载波技术，实现远端时钟的中央控制。系统通过电力载波芯片从电力线上收发控制信号，中央控制端发送的时钟校准信号到电力线网络，接人网络的远端时钟接收到校准信号后，由微处理器解析数据调整受控端时钟显示，从而实现时钟的中央控制。