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At least 235 records · Page 13Linked to original sources

PubMed2006

Air-flow sensitive hairs: boundary layers in oscillatory flows around arthropod appendages.

The aim of this work is to characterize the boundary layer over small appendages in insects in longitudinal and transverse oscillatory flows. The problem of immediate interest is the early warning system in crickets perceiving flying predators using air-flow-sensitive hairs on cerci, two long appendages at their rear. We studied both types of oscillatory flows around small cylinders using stroboscopic micro-particle image velocimetry as a function of flow velocity and frequency. Theoretical predictions are well fulfilled for both longitudinal and transverse flows. Transverse flow leads to higher velocities than longitudinal flow in the boundary layer over a large range of angles between flow and cylinder. The strong spatial heterogeneity of flow velocities around filiform-shaped appendages is a rich source of information for different flow-sensing animals. Our results suggest that crickets could perceive the direction of incoming danger by having air-flow-sensitive hairs positioned around their entire cerci. Implications for biomimetic flow-sensing MEMS are also presented.

Air Movements↗

PubMed1990

Beneficial effects of low-flow perfusion resumed early after zero-flow ischemia on myocardial energy metabolism and mechanical function: 31P-NMR study in the isolated perfused rat heart.

Effects of low-flow perfusion after zero-flow ischemia on myocardial mechanical function and energy metabolism were studied with 31P nuclear magnetic resonance spectroscopy, using isolated perfused rat hearts. After control perfusion, hearts were randomly divided into five experimental groups: Groups I and II were subjected to zero-flow ischemia of 40 and 60 min, respectively. In groups III-V the perfusion was resumed at a rate of 0.1 ml/min after 40 (group III), 30 (group IV) and 20 (group V)-min of zero-flow ischemia in order to compare the effects of low-flow perfusion with those of persistent zero-flow. After these interventions all the hearts were perfused for 40 min at a normal flow rate. Compared with the hearts exposed to total ischemia of 60 min, the preservation of high energy phosphate compounds (HEP) was better in groups with early low-flow perfusion; Creatine phosphate (CrP) levels, which had decreased rapidly after induction of zero-flow ischemia, increased gradually after initiation of the low-flow perfusion and reached significantly higher levels at the end of ischemic period in groups IV and V than in group II (p less than 0.05). The decrease in adenosine triphosphate (ATP) was likewise significantly suppressed by low-flow perfusion (groups IV and V greater than group II). Restoration of CrP levels after complete reperfusion was also significantly greater in group V than in group II. The recovery of ATP after complete reperfusion was also much better in group V being comparable to those in group I, although the total duration of ischemia was longer in group V than in group I. These results indicate the beneficial effects of low-flow perfusion on the preservation during ischemia and recovery after reperfusion of myocardial HEP.

Adenosine Triphosphate↗

PubMed1999

[Estimation of left internal thoracic artery flow reserve after coronary artery bypass grafting using Doppler flow wire].

The usefulness of the left internal thoracic artery (LITA) for aortocoronary bypass grafting is now established. Reports of variation in LITA graft function are rare. Graft flow was measured using a Doppler flow wire to estimate graft function in 27 patients (24 males, 3 females) who underwent LITA grafting to the left anterior descending artery. Patients were classified into the following 3 groups: Group A consisted of 9 patients with normal left ventricular function and no native flow; Group B consisted of 11 patients with normal ventricular function and good native flow; Group C consisted of 7 patients with abnormal left ventricular function and no native flow. LITA graft function was also estimated 1 year after operation in 12 of these 27 patients (4 in each group). Diastolic/systolic velocity ratio (DSVR) and flow reserve were determined in the proximal, middle, and distal portions of the LITA graft and native left anterior descending artery before and after papaverine administration (8-10 mg). DSVR was significantly higher in the distal portion than in the proximal portion (p < 0.01), but this value did not change after papaverine administration. After 1 year, DSVR in the proximal portion was significantly higher in Group C than in Groups A or B (p < 0.05 for both). Four weeks after operation, the flow reserve of the distal portion was significantly higher in Group A than in Group C (p < 0.001). After 1 year, this value was significantly higher in Group A than in either Groups B or C (p < 0.01, p < 0.001, respectively). The rate of increase in flow reserve in the distal portion was significantly greater in Group A (23.4%) than in groups B (2.53%) or C (1.94%; p < 0.05 for both). The distal portion of the LITA was the best measurement site, since the flow pattern in the LITA graft varied throughout all portions. Diastolic flow velocity in the LITA graft was dominant in patients with myocardial damage. The results indicate that flow reserve of the LITA graft depends on antegrade native coronary flow and distal myocardial damage.

Coronary Artery Bypass↗

PubMed1986

[Visualization of coronary blood flow by transesophageal Doppler color flow mapping].

For noninvasive evaluation of coronary blood flow, 22 patients were examined with transesophageal Doppler color flow mapping within six hours after cardiovascular surgery. The anatomical structure of the left main coronary trunk (LMT) was observed by conventional two-dimensional echocardiography (2-DE) in 20 patients (91%), and color flow of the LMT was visualized in 18 of 21 patients (86%) (one patient had total occlusion). The blood flow in the LMT began in mid-systole, but the flow was observed mainly in diastole. The peak of the flow was observed mainly in late diastole and the range of the peak velocity was 35 to 163 cm/sec (average = 76.9 +/- 31.4 cm/sec). The proximal portion of the right coronary artery (RCA) was observed in 13 patients (59%), and its color flow was visualized in only two patients (9%). In two patients intra-aortic balloon pumping (IABP) assist was performed postoperatively, and the direct effect of the assist on the coronary blood flow was clearly observed by transesophageal Doppler color flow mapping. The peak blood flow velocity of the LMT increased by 32% during the assist. In conclusion, human coronary blood flow can be visualized and evaluated noninvasively using transesophageal Doppler color flow mapping. This technique can be used for future investigation of coronary circulation.

Adult↗

PubMed1993

Cerebral blood flow velocity patterns during cardiac surgery utilizing profound hypothermia with low-flow cardiopulmonary bypass or circulatory arrest in neonates and infants.

To examine the effects of low-flow cardiopulmonary bypass (CPB) and circulatory arrest (PHCA) on cerebral pressure-flow velocity relationships, we studied 32 patients (< 9 mo of age) undergoing corrective cardiac procedures. Pressure-flow velocity relationships were studied during profound hypothermia (nasopharyngeal temperature < 20 degrees C). Cerebral blood-flow velocity (CBFV) was measured in the middle cerebral artery using transcranial Doppler sonography. The anterior fontanel pressure (AFP) was measured using an intracranial pressure monitor. Cerebral perfusion pressure (CPP) was calculated (mmHg) as mean arterial pressure (MAP) minus AFP. Nasopharyngeal temperature, PaCO2 and haematocrit were controlled during the study period. Alpha-stat acid-base management was employed. The CBFV measurements were made continuously over a range of CPP as pump flow (Q) was decreased to low-flow or to circulatory arrest and again during the subsequent increase in Q and CPP to normal. As Q and CPP were increased after a period of low-flow CPB during which period detectable CBFV was present, the CBFV was greater at any given CPP than prior to the low-flow state (P < 0.05). However, after PHCA a higher CPP (P < 0.05) was necessary to re-establish detectable CBFV and at any given CPP the CBFV was less than prior to PHCA (P < 0.05). Seventeen patients underwent low-flow CPB during which CBFV became non-detectable (7 +/- 1 cm.sec-1). In 12 of these patients the pattern of recovery of CBFV was the same as that observed after low-flow CPB whereas the remaining five (29%) demonstrated a pattern of recovery identical to the ones recorded after PHCA. We conclude that after PHCA a higher CPP is necessary to re-establish and maintain detectable CBFV. Furthermore, during low-flow CPB, patients where CBFV becomes non-detectable and show a pattern of CBFV recovery similar to PHCA, cessation of cerebral perfusion must be considered.

Blood Flow Velocity↗

PubMed2003

Betamethasone associated changes in umbilical artery flow velocity waveforms in multiple pregnancies with umbilical artery absent end diastolic flow.

OBJECTIVES: It has been previously shown that glucocorticoids alter umbilical artery flow velocity waveforms in singleton pregnancies complicated by umbilical artery absent end diastolic flow. Whether similar effects are evident in multiple pregnancies where one fetus has umbilical artery absent end diastolic flow is not known. METHODS: Women with a twin or triplet pregnancy complicated by umbilical artery absent end diastolic flow in one fetus were admitted to hospital for intensive fetal surveillance including daily umbilical artery flow velocity waveform studies, as per hospital protocol. All women received prophylactic betamethasone (11.4 mg x 2, 24 h apart) in anticipation of preterm delivery. RESULTS: Between October 1996 and February 2002, 24 women with a multiple pregnancy complicated by umbilical artery absent end diastolic flow were cared for. Of these, six had a pregnancy with feto-fetal transfusion and excluded from further analysis. Of the remaining 18 women, eight had monochorionic diamniotic twins, eight had dichorionic twins, and two had trichorionic, triamniotic triplets. The median (range) gestation at diagnosis of umbilical artery absent end diastolic flow was 210.5 days (173-241). In nine (50%) of the 18 pregnancies the administration of betamethasone was associated with return of umbilical artery end diastolic flow for a median of 5 days. There was no association between this effect and chorionicity. The median (range) interval from diagnosis of umbilical artery absent end diastolic flow to delivery was 11 days (1-46). CONCLUSIONS: As previously reported in singleton pregnancies, the maternal administration of betamethasone in multiple pregnancies with umbilical artery absent end diastolic flow is associated with a transient return of end diastolic flow.

Betamethasone↗

PubMed1966

The effects of adrenaline and noradrenaline on venous return and regional blood flows in the anaesthetized cat with special reference to intestinal blood flow.

1. In cats, a venous long-circuit technique was used to measure the blood flows in the superior vena cava and the hepatic, renal and iliac segments of the inferior vena cava. The sum of these flows gave the venous return (minus coronary and bronchial flows). In further experiments using an electromagnetic flowmeter, flow in the portal vein and in the superior mesenteric and coeliac arteries was measured.2. Approximately two-thirds of the hepatic blood flow is derived from the portal vein.3. After block of conduction in the cervical region of the spinal cord, the proportions of the venous return coming from each region during the control periods were not significantly altered although the arterial pressure and total venous return were decreased.4. Intravenous infusions of adrenaline caused an increase in venous return which was associated with a marked increase in hepatic blood flow. The increase in hepatic blood flow was due to an increase in flow in the superior mesenteric artery and portal vein. Flow in the coeliac artery remained unchanged. This response was unaffected by block of the cervical region of the spinal cord and by atropine or pentolinium.5. Intravenous infusions of noradrenaline caused little change in venous return or regional blood flows. Small increases in superior mesenteric artery flow were occasionally seen and on cessation of the infusion a large but brief increase occurred. These facts suggest that noradrenaline has a similar action to adrenaline but this is masked by concomitant vasoconstriction.

Animals↗

PubMed1982

Significance of intraindividual changes in maximum expiratory flow volume and peak expiratory flow measurements.

To examine criteria to assess significant changes of measurements derived from the forced expiratory vital capacity (FVC), and to examine changes in the peak expiratory flow (PEF) maneuvers, ten subjects were tested on approximately 30 occasions. Since mini Wright peak flow meters are increasingly used for clinical and research purposes, peak flow intraindividual variability and relations to FVC peak flow were examined, each set of tests consisting of five FVC maneuvers and one peak flow. Measurements on a pneumotachograph included FVC, (FEV1), maximum mid-expiratory flow (MMF or FEF25-75%), and instantaneous maximum expiratory flow after 50 and 75 percent expiration of the FVC. PEF measurements were derived using the mini Wright peak flow meter and the pneumotachograph. The coefficients of variation for the FVC measurements were greatest for maximum expiratory flow measurements and least for the FVC and FEV1. Maximum values from each set of tests reduced the variability. From these values, criteria and estimates were derived to evaluate significant intraindividual change. The PEF measurements were evaluated also to determine intraindividual changes. The coefficients of variation were only 2 percent to 14 percent. The peak flows obtained were shown to correlate well with the PVC peak flow.

Adult↗

PubMed1989

Measuring bovine mammary gland blood flow using a transit time ultrasonic flow probe.

Lactating cattle were used to validate a transit time ultrasonic blood flow metering system for measuring mammary gland arterial blood flow. Blood flow probes were surgically placed around the right external pudic artery. An electromagnetic flow probe was implanted in tandem with the ultrasonic probe in two cows for comparative measurements. The absolute accuracy of the implanted flow probes was assessed in vivo by mechanical means on anesthetized cows after 2 to 3 wk of implantation. The zero offset of the ultrasonic probes ranged from -12 to 8 ml/min. When the ultrasonic probe was properly implanted, the slopes of the calibration curves were linear and ranged from .92 to .95, tracking absolute flow to within 8%. The transit time instrument's performance was examined under a variety of physiological conditions. These included milking and hormone injections. The transit time ultrasonic flow meter accurately measured physiological changes in mammary arterial blood flow in chronically prepared conscious cattle. Blood flow increased 29% during milking. Epinephrine decreased mammary blood flow by 90 to 95%. Oxytocin doses increased mammary blood flow by 15 to 24%.

Animals↗

PubMed1975

Discrepancies in the measurement of changes in blood flow using flow- and velocity-sensitive electromagnetic probes.

Blood flow was measured in the descending thoracic aorta of the anaesthetised dog using a perivascular flow probe and electromagnetic flowmeter. Blood velocity was measured in the same vessel with an intravascular velocity probe and electromagnetic flowmeter. Changes in blood pressure, flow and velocity, were induced by intravenous administration of noradrenaline, angiotensin, isoprenaline and aminophylline. If the velocity probe was within the cuff of the flow probe, percentage changes in flow and velocity were comparable, but if the velocity probe was "upstream" or "downstream" from the cuff, discrepancies between percentage drug-induced changes in flow and velocity were of the order of 30% and, in 12 out of 80 observations, in opposite directions. Measuring absolute flow with the velocity-sensitive device produced variable results showing a systematic underestimate of flow estimated from velocity, compared with flow measured with the perivascular probe. It is concluded that the measurement of blood flow and changes in blood flow, with the intravascular velocity probe, is liable to produce inaccurate data.

Aminophylline↗

PubMed1999

Using flow relaxography to elucidate flow relaxivity.

We have investigated the theoretical and experimental linear dependence of the reciprocal of the apparent longitudinal relaxation time [(T*1)-1] of the NMR signal from spins in a flowing fluid on the volume flow rate, Fv, the so-called inflow effect. We refer to the coefficient of this dependence as the longitudinal flow relaxivity, r1F. A very simple model predicts that, under a range of conditions pertinent to modern flow studies and perfusion imaging experiments, r1F is controlled by the volume of the fluid in which the magnetization is perturbed by pulsed RF inversion or saturation, not the detection volume, and that it can be approximated as the reciprocal of half of the inversion volume. Phantom sample experiments, using a new, quantitative approach that we call flow relaxography, confirm the general predictions of this simple model. There are two intriguing implications of these findings for general NMR flow studies as well as for medical applications. It should be possible to vary the value of r1F by simply (noninvasively) adjusting the inversion slice thickness, and thus measure the value of (blood 1H2O, for example) Fv in a vessel without changing Fv, from the resultant varying T*1 values. Also, it should be possible to extrapolate to the intrinsic T1 value of the fluid signal (as if it were stationary), without altering or stopping the flow. Again, these are quite successful in phantom sample studies. Imaging versions of the flow relaxographic experiments are also possible. The twin goals of flow studies in medical MRI are the quantitative discrimination of the signals from flowing and nonflowing spins, and the accurate measurement of the flow rate of the former.

Blood Flow Velocity↗

PubMed1998

Cerebrospinal fluid flow waveforms: effect of altered cranial venous outflow. A phase-contrast MR flow imaging study.

Our purpose was to assess the effect of alterations in the cranial venous outflow on cerebrospinal fluid (CSF) flow waveforms using phase-contrast MRI. Thirteen healthy subjects were assessed for CSF flow and cerebral vascular flow at the C2-3 level, both before and after jugular venous compression (JVC). The flow waveforms were assessed both as an aggregate, and after dividing subjects in two groups based on percent jugular venous flow (PJVF) i.e. jugular outflow expressed as percent of cerebral arterial inflow. Group 1:7 subjects with PJVF more than and including median (predominantly jugular outflow); Group 2:6 subjects with PJVF less than median (predominantly extra-jugular outflow). CSF waveforms: JVC produced rounding of contours and flattening of dicrotic waves, with the effect being greater in group 1 than group 2. In group 1, systolic upslopes of the waveforms increased. No significant aggregate amplitude changes were noted; amplitudes increased in group 1 (P = 0.001), and decreased in group 2 (P = 0.03). Temporal interval to the maximum CSF systolic flow significantly increased in group 1. Vascular flow: Arterial flow significantly decreased in group 1. Jugular flow significantly decreased in both groups. The results suggest that CSF flow waveforms are sensitive to alterations in the cranial venous outflow. Changes in group 1 are most likely because of an elevation in intracranial pressure. Analysis of CSF flow waveforms appears a promising noninvasive tool for assessment of cranial compartment.

Adult↗

PubMed1993

Computer-assisted modeling of blood-flow: theoretical evidence for the existence of optimal flow wave patterns.

The purpose of this study was to model blood-flow waveforms in order to examine the relationship between various waveform shapes and input impedance spectra. Twenty distinct single cardiac cycle flow waveforms having the same mean flow and heart rate were created based on clinical and published observations. The "best" waveform was one with a steep flow upstroke, a high peak flow value, swift deceleration following peak flow, and flow reversal during diastole. Each flow waveform was paired with 20 computer-generated pressure waveforms to calculate input impedance spectra by discrete Fourier transformation. "Favorable" flow waveforms were associated consistently with a lower characteristic impedance (average of 4th-10th harmonics, Zav) irrespective of the shape or magnitude of the input pressure wave. Zav corresponds to the degree of compliance of the vascular bed and could be expected to be lower under favorable outflow conditions and in non-diseased vessels. In conclusion, this study provides theoretical evidence for the existence of optimal flow wave patterns and supports the notion of flow waveform assessment for diagnostic purposes.

Blood Circulation↗

PubMed1994

Organ blood flow following cardiac arrest in a swine low-flow cardiopulmonary bypass model.

STUDY OBJECTIVE: To determine organ blood flow changes, relative to baseline, following cardiac arrest and resuscitation in a closed-chest cardiac arrest swine model using cardiopulmonary bypass to achieve reproducible return of spontaneous circulation (ROSC). INTERVENTIONS: Following 10 min of ventricular fibrillation (VF), animals (n = 10) received low-flow cardiopulmonary bypass at 10 ml/kg/min from 10-15 min. At 15 min of VF, norepinephrine (0.12 mg/kg) was given and bypass flow increased to 50 ml/kg/min, followed by countershocks at 16 min. Following ROSC, cardiopulmonary bypass was immediately weaned off with norepinephrine support. Organ blood flows were determined during normal sinus rhythm, during reperfusion of VF and during the early post-ROSC period while off cardiopulmonary bypass support. Organ blood flows during the early ROSC period were compared with organ blood flow at baseline and during VF. RESULTS: During early reperfusion of VF prior to any drug therapy, myocardial, cerebral and abdominal organ blood flows were all low. All animals achieved ROSC at 16.9 +/- 0.7 min and were weaned from bypass in < 5 min following ROSC. During the early post-ROSC period, blood flow to the myocardial, cerebral and adrenal vascular beds was significantly elevated relative to baseline. Simultaneously, blood flow to the kidneys, liver, spleen and lungs was reduced relative to baseline. CONCLUSIONS: This low-flow bypass model produces reproducible high resuscitation rates and ROSC times. Early post-resuscitation organ blood flow is characterized by a selective hyperemia involving the cerebral, myocardial and adrenal vascular beds, in contrast to hypoperfusion of the pulmonary and mesenteric vascular beds.

Animals↗

PubMed1988

Doppler echocardiographic flow characteristics of isolated patent ductus arteriosus: better delineation by Doppler color flow mapping.

Eighteen infants and children with isolated ductus arteriosus and various hemodynamic states were examined with the Doppler color flow mapping technique to study the flow patterns of the patent ductus and its adjacent structures. Direct visualization of the ductus was achieved in all patients. All ductal flow was shunting left to right from the descending aorta to the pulmonary artery even in the presence of significant elevation of pulmonary artery pressure. However, transient bidirectional shunting was observed in two patients on serial studies. Disturbed systolic and diastolic flows were demonstrated within the ductus in each case. The blood flows in the main pulmonary artery consisted of three distinguishable areas: 1) a characteristic high velocity turbulent retrograde ductal jet throughout the entire cardiac cycle, located in the anterolateral aspect of the main pulmonary artery; 2) nonspecific low velocity retrograde late systolic and early diastolic flow, located in the posteromedial aspect of the main pulmonary artery; and 3) low velocity forward systolic and diastolic flow, occupying the remaining area of the pulmonary artery. The blood flows in the descending aorta near the ductal orifice consisted of disturbed systolic and diastolic flows in a reversed direction. By providing detailed real time blood flow information with simultaneous imaging of the ductus, Doppler color flow mapping greatly facilitates the detection of a small ductal shunt. This technique also allows detection of a bidirectional or right to left ductal shunt.

Aorta↗

PubMed2006

Relationship between uterine blood flow and endometrial and subendometrial blood flows during stimulated and natural cycles.

OBJECTIVE: To evaluate the relationship between uterine Doppler flow and endometrial and subendometrial blood flows during stimulated and natural cycles. DESIGN: A prospective observational study. SETTING: A tertiary-assisted reproduction unit. PATIENT(S): Infertile patients undergoing IVF treatment. INTERVENTIONS: A three-dimensional ultrasound examination with power Doppler was performed on the day of egg retrieval in stimulated cycles and the day after the LH surge in natural cycles. MAIN OUTCOME MEASURE(S): Pulsatility and resistance indices of uterine vessels, and the vascularization, flow, and vascularization flow indices of endometrial and subendometrial regions. RESULT(S): Uterine pulsatility and resistance indices were negatively correlated with subendometrial vascularization, flow, and vascularization flow indices in both stimulated and natural cycles, whereas uterine resistance index was negatively correlated with endometrial vascularization and flow indices in natural cycles only. Subendometrial vascularization and vascularization flow indices were significantly lower in patients with an uterine resistance index > or =0.95 than those with an uterine resistance index <0.95. CONCLUSION(S): Uterine blood flow is a poor reflection of subendometrial blood flow during stimulated and natural cycles, and its measurement cannot reflect endometrial blood flow during stimulated cycles.

Adult↗

PubMed1997

Magnetic resonance imaging quantitation of superior sagittal sinus flow: correlation to cerebral blood flow measured by xenon-enhanced computed tomography.

We compared measurements of venous blood flow velocity in the superior sagittal sinus (SSS) obtained by magnetic resonance imaging (MRI) and quantitative measurements of cerebral blood flow (CBF) obtained by xenon-enhanced CT, in neurosurgical patients and normal volunteers, to assess the clinical usefulness of MRI for determination of CBF. Flow measurements were obtained in 15 neurosurgical patients and 3 normal volunteers. SSS velocimetry was performed using the direct bolus imaging technique with a 1.5-tesla MRI system near the point of lambda on a sagittal MR image. Quantitative CBF was measured by xenon-enhanced CT and correlated with SSS flow velocity. We also examined the effect of surgical evacuation of a hematoma or cranioplasty in 3 patients, mannitol in 5 patients and acetazolamide in 4 patients by performing SSS velocimetry. The peak SSS flow velocity during the entire cardiac cycle was 27.2 +/- 6.3 cm sec-1 (mean +/- SD) in normal volunteers and 23.5 +/- 8.9 cm sec-1 in patients. The SSS flow velocity increased after surgery. Mean SSS peak flow velocity increased by 24% and 48% at 10 min after administration of mannitol and acetazolamide, respectively. SSS peak flow velocity showed significant linear correlations with both cerebral cortical (r = 0.74) and hemispheric flows (r = 0.73). Our results suggest that SSS flow velocity reflects CBF and that MRI assessment of SSS flow provides a simple method for assessing and monitoring global changes in cerebral hemodynamics.

Acetazolamide↗

PubMed2002

Ophthalmic artery flow direction on color flow duplex imaging is highly specific for severe carotid stenosis.

BACKGROUND/PURPOSE: Collateral flow patterns are important risk factors for brain ischemia in the presence of internal carotid artery (ICA) stenosis or occlusion. Ophthalmic artery (OA) flow reversal, routinely studied by transcranial Doppler sonography, is an important marker for high-grade ICA stenosis or occlusion. The authors sought to define the value of assessing OA flow direction with color flow duplex ultrasonography (CDUS) in the setting of significant ICA disease. METHODS: Of all patients having routine carotid ultrasound in the neurosonology laboratory between July 1995 and November 2000, 152 had both carotid and orbital (OA flow direction by reduced power orbital CDUS) examinations as well as angiographic confirmation of stenosis to which North American Symptomatic Carotid Endarterectomy Trial criteria could be applied. Degree of angiographic stenosis in these 152 patients (304 arteries) was correlated with OA flow direction. RESULTS: Of 304 arteries, 101 had greater than 80% stenosis by angiogram. In 56 of these 101 arteries with high-grade stenosis or occlusion, the ipsilateral OA was reversed; however, OA flow direction was never reversed ipsilateral to arteries with less than 80% stenosis (sensitivity 55%, specificity 100%, negative predictive value 82%, and positive predictive value 100% for OA flow reversal as a marker of high-grade carotid lesions). DISCUSSION/CONCLUSIONS: OA flow direction is easily studied with CDUS. Reversed OA flow direction is highly specific (100%) for severe ipsilateral ICA stenosis or occlusion, with excellent positive predictive value, moderate negative predictive value, and limited sensitivity. OA flow reversal is not only quite specific for severe ICA disease, which may be helpful if the carotid CDUS is difficult or inadequate, but may also provide additional hemodynamic insights (i.e., the inadequacy of other collateral channels such as the anterior communicating artery). OA evaluation can provide important hemodynamic information and should be included as part of carotid CDUS if there is any evidence of ICA stenosis or occlusion.

Blood Flow Velocity↗