Search results for "Velocimetry"
showing 10 items of 94 documents
Blood flow velocity waveforms of the fetal middle cerebral artery in a normal population: reference values from 18 weeks to 42 weeks of gestation
2002
The aim of this prospective cross-sectional study was to establish new Doppler reference curves for peak blood flow velocities (Vmax, Vmean, Vmin) and impedance indices (PI, RI) of the middle cerebral artery at 18-42 weeks of gestation by an automatic wave form analysis integrated into the ultrasound device. In 962 low-risk pregnancies, blood flow velocities were derived from the middle cerebral artery with pulsed color Doppler ultrasonography. Reference curves were constructed for the individual parameters based on a growth function from a four-parameter class of monotonic continuous functions according to the smallest square principle for maximum blood flow velocities, as well as on a pol…
Imaging photoplethysmography for clinical assessment of cutaneous microcirculation at two different depths
2016
The feasibility of bispectral imaging photoplethysmography (iPPG) system for clinical assessment of cutaneous microcirculation at two different depths is proposed. The iPPG system has been developed and evaluated for in vivo conditions during various tests: (1) topical application of vasodilatory liniment on the skin, (2) skin local heating, (3) arterial occlusion, and (4) regional anesthesia. The device has been validated by the measurements of a laser Doppler imager (LDI) as a reference. The hardware comprises four bispectral light sources (530 and 810 nm) for uniform illumination of skin, video camera, and the control unit for triggering of the system. The PPG signals were calculated and…
Autonomic regulation of nasal vessels during changes in body position
1994
The effects of postural changes on nasal airflow and nasal capillary blood flow were investigated in 15 healthy volunteers. Measurements were performed following nasal application of saline solution (control), the alpha-1 receptor antagonist prazosin, the alpha-2 receptor antagonist yohimbine, and after application of both prazosin and yohimbine. Nasal airflow in the control experiments did not significantly differ in the upright (362 +/- 166 ml/s), dorsally recumbent (350 +/- 167 ml/s) and 70 degrees head down position (311 +/- 167 ml/s). Following application of prazosin, nasal airflow was reduced to 223 +/- 121 ml/s in the upright position. Prazosin treatment significantly reduced nasal …
Sympathetic Vasomotor Response of the Radial Artery in Patients With Diabetic Foot Syndrome
2003
OBJECTIVE—Neurophysiological assessment of the peripheral autonomic system is characterized by various limitations. An alternative approach to laser Doppler and venous plethymography is the assessment of the sympathetic vasomotor response of the radial artery obtained by continuous wave Doppler sonography. Nomogram data have been established and demonstrate the temporary disappearance of diastolic flow after coughing or deep inspiration. RESEARCH DESIGN AND METHODS—We assessed the sympathetic vasomotor response in 25 patients (mean age 64 years, range 43–76) with diabetic foot syndrome. The Doppler data were correlated with nerve conduction studies of the median and peroneal nerve, the exte…
Uterine effects of clomiphene citrate in women with polycystic ovary syndrome: a prospective controlled study
2006
Background Previous data on the efficacy of clomiphene citrate, the most commonly used drug for treating anovulatory infertility in patients with polycystic ovary syndrome (PCOS), have shown a discrepancy between ovulation and pregnancy rates. In the present subanalysis (of a larger previously published randomized controlled trial), the effect of clomiphene citrate on several ultrasonographic markers of uterine receptivity in PCOS patients who ovulated under treatment was studied. Methods Thirty-three PCOS women who ovulated under 150 mg daily clomiphene citrate and 33 healthy controls were studied. Uterine, subendometrial and endometrial blood flows, endometrial thickness and pattern were …
Laboratory Measurements of Flow and Turbulence in Discontinuous Distributions of Ligulate Seagrass
2007
Turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies. The reliability of velocity measurements obtained using an acoustic Doppler velocimeter within the canopy was shown using specifically designed experiments. In relatively fast flow (mean velocity 5.5 cm s−1), the mean flow profile was logarithmic above the canopy, had an inflection point near its top, and uniformly low values within it. Within the gap, a recirculation cell formed. Reynolds stress maxima were approximately coincident with the mean flow inflection point. Quadrant analysis revealed an ejection-d…
Delayed filling of retinal and ciliary circulation after central retinal artery occlusion
1988
The filling times of the retinal and choroidal circulation were evaluated in 17 patients with central retinal artery occlusion by means of fluorescein angiography. A correlation between the filling times of the two circulations was found. However, two filling patterns were seen: first, both fillings delayed; second, both fillings normal. It is probable that in the former case an obstructive disease of the carotid arteries exists, while in the latter case an important pathology of the carotid arteries is lacking, favouring a rapid restoration of the retinal circulation. This hypothesis seems to be confirmed by the results of the Doppler velocimetry of the carotid arteries.
Microcirculation after cerebral venous occlusions as assessed by laser Doppler scanning.
1997
✓ Research on cerebral venous circulation disturbances (CVCDs) has been limited partly by the paucity of animal models that produce consistent venous infarction. Occlusion of two adjacent cortical veins in rats by means of a photochemical thrombotic technique provides a minimally invasive, clinically relevant, and reproducible model suited to study the pathophysiology of CVCDs. In this study, the effects of venous occlusion on regional cortical blood flow and the brain damage that ensues were evaluated. Cortical vein occlusion was induced by photoactivation of rose bengal via 100-µm fiberoptic illumination. The cerebral venous flow pattern was examined using fluorescence angiography until 9…
On the measurement of bubble size distribution in gas–liquid contactors via light sheet and image analysis
2010
Abstract Particle image velocimetry techniques coupled with advanced image processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas–liquid mechanically agitated vessels. When trying to analyze image information the problem arises that bubble sizes are generally underestimated, due to the fact that the laser sheet used for lighting the system randomly cuts bubbles over non-diametrical planes, leading to an apparent bubble size distribution even in the ideal case of single sized bubbles. Clearly in the case of bubbles with a size distribution the experimental information obtained is affected by the superposition of effects.…
Mobile phone based laser speckle contrast imager for assessment of skin blood flow
2014
Assessment of skin blood flow is of interest for evaluation of skin viability as well as for reflection of the overall condition of the circulatory system. Laser Doppler perfusion imaging (LDPI) and laser speckle contrast imaging (LASCI) are optical techniques used for assessment of skin perfusion. However, these systems are still too expensive and bulky to be widely available. Implementation of such techniques as connection kits for mobile phones have a potential for primary diagnostics. In this work we demonstrate simple and low cost LASCI connection kit for mobile phone and its comparison to laser Doppler perfusion imager. Post-occlusive hyperemia and local thermal hyperemia tests are us…