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At least 19 recordsLinked to original sources
PubMed1982

[Measurement of blood flow velocity, blood volume flow and arterial cross section using the integral Doppler ultrasonic method--comparison and synthesis of two solutions].

Starting with a short comparison of the space resolving, pulsed Doppler method with the integral Doppler techniques for blood flow measurement, the formula is derived, after which the profile independent cross-sectional mean velocity v is to be measured using the integral method. When evaluating the Doppler signal power, moreover, volume flow Q can be measured. Two versions of the integral method for volume flow Q, one with (WAVUD) and the other without (WUVUD), and the need for a separate determination of the angle of incidence are explained and compared. Combination of the two results in a new method for measuring the mean velocity v and cross-sectional area F of blood flow from one single sound direction, without the need for determining the angle of sound incidence into the artery. The main problems of the integral method are addressed and in vitro test results are reported, showing that 20% measurement accuracy should be practical in vivo.

Arteries↗
PubMed1982

[Measuring blood flow velocity, blood volume flow and arterial diameter using integral Doppler ultrasound--comparison and synthesis of 2 solutions].

Starting with a short comparison of the space resolving, pulsed Doppler method with the integral Doppler techniques for blood flow measurement, the formula is derived, after which the profile independent cross-sectional mean velocity v is to be measured using the integral method. When evaluating the Doppler signal power, moreover, volume flow Q can be measured. Two versions of the integral method for volume flow Q, one with (WAVUD) and the other without (WUVUD), and the need for a separate determination of the angle of incidence are explained and compared. Combination of the two results in a new method for measuring the mean velocity v and cross-sectional area F of blood flow from one single sound direction, without the need for determining the angle of sound incidence into the artery. The main problems of the integral method are addressed and in vitro test results are reported, showing that 20% measurement accuracy should be practical in vivo.

Arteries↗
PubMed1991

Effects of intrauterine growth retardation on postnatal visceral and cerebral blood flow velocity.

Blood flow velocity and pulsatility index were measured with Doppler ultrasound in the superior mesenteric artery, coeliac axis, and anterior cerebral artery in 18 very low birth weight, small for gestational age infants, and compared with findings from 18 weight matched, and 18 gestation matched, appropriate for gestational age controls. Mean velocity in the superior mesenteric artery was lower in the small for gestational age infants (15 cm/s) than in the gestation matched control group (20.4 cm/s). In those small for gestational age infants who had evidence of fetal hypoxia the mean velocity in the superior mesenteric artery was even lower (11.5 cm/s). There were no differences in velocity in the cerebral artery among the groups. Infants who were small for gestational age still had significantly lower superior mesenteric artery velocity than gestation matched controls at 1 week of age. The results suggest a specific reduction in visceral perfusion in infants who are small for gestational age and who have experienced fetal hypoxia, and this could predispose these infants to necrotising enterocolitis.

Aging↗
PubMed1992

[A multichannel telemetry system for autonomic neural signals, blood flow velocity, blood pressure, and ECG measurements].

A radio multichannel telemetry system has been developed for use with chronically instrumented, unrestrained, small animals. The system can simultaneously record autonomic neural signals, blood flow velocity, blood pressure, and ECG. The system is time-multiplexed and pulse width modulation (PWM)/FM device, which employs two sampling frequencies. The system is designed with 10 standard low power integrated circuits, a 3 terminal voltage regulator, and a transistor. The size is 53 x 42 x 20 mm, and the weight, including two batteries is 40 grams. The system is powered by two lithium cells, which provide 60 hours of continuous operation.

Action Potentials↗
PubMed1992

[The effect of halothane, alfentanil and propofol on blood flow velocity, blood vessel cross section and blood volume flow in the middle cerebral artery].

Transcranial Doppler sonography (TCD) has gained in relevance for noninvasive monitoring of the cerebral circulation during the perioperative period. As long as the diameters of the investigated vessels remain unknown, however, flow velocities alone are not really informative. Exact vessel diameter determination in humans under the influence of different anesthetic drugs has not yet been performed due to ethical and methodological restrictions. A new modification of TCD allows analysis of the reflected "Doppler power", which is proportional to the cross-sectional area of the insonated vessel. METHODS. Three groups of 15-16 patients each (ASA I) were investigated after informed consent. Anesthesia was induced with droperidol, alfentanil, thiopental, and vecuronium bromide. After intubation patients were normoventilated with N2O:O2 = 3:2 and additional doses of alfentanil were injected until the transcranial ultrasound probe was fixed to the temporal bone and focused on the middle cerebral artery. Baseline values of heart rate (HR), mean arterial pressure (MAP), expiratory minute volume (EMV), end-expiratory CO2 (FeCO2), and TCD were measured. Then 1.5 vol% halothane, 25-50 micrograms/kg alfentanil, or propofol (1.5 mg/kg iv., 10 mg/kg.min) was administered. Further measurements (HR, MAP, EMV, FeCO2 and TCD) were performed at 3, 6, 10, and 20 min after the start in the halothane and propofol groups and after 3 and 6 min in the alfentanil group. The following transcranial parameters were derived from the TCD device: mean maximal flow velocity (vmmax), pulsatility index, time-averaged mean velocity (vmmen), "vessel area (VA)", and "volume flow (VF)". The mean +/- standard deviation of each parameter was calculated. Statistical evaluation was performed by paired t-tests (level of significance P less than 0.05). RESULTS. HR showed a tendency to increase after halothane and to decline after alfentanil. Alfentanil induced a short-term decline in MAP. End-expiratory minute volume and FeCO2 showed only minor alterations in all three groups. The vmmax was nearly doubled by halothane. Alfentanil induced a transitory decline in vmmax while Propofol decreased it markedly. The pulsatility index showed a decrease after halothane; alfentanil caused a short-term increase. Propofol induced a strong increase after 3 min; in the following period a return to baseline values was observed. The vmmean was increased by halothane and reduced by 32% propofol. VA was found to be unaltered by alfentanil and propofol but was more than doubled by halothane. Accordingly, the relative value for VF increased by 148% under halothane. VF appeared to decline after propofol. DISCUSSION. The described method allows only the determination of relative values: it is not possible to quantify exactly how much the VA changed. Halothane caused significant increases of VA measured in the middle cerebral artery, whereas alfentanil and propofol did not influence this parameter. This is in accordance with previous experiments in dogs in which halothane decreased the resistance of large basal cerebral arteries (LAR). LAR remained unaltered after alfentanil administration. The site of action of some anesthetic agents on cerebral vessels does not seem to be restricted to cerebral arterioles: at least for halothane, a vasodilating effect on large cerebral arteries could be demonstrated. This should be kept in mind when transcranial Doppler is applied during the perioperative period.

Alfentanil↗
PubMed2002

Effects of temperature and haematocrit on the relationships between blood flow velocity and blood flow in a vessel of fixed diameter.

BACKGROUND: To determine whether temperature and haematocrit (Hct) alter the relationship between blood flow (BF) and blood flow velocity (BFV). METHODS: Using a transcranial Doppler apparatus, we measured the peak velocity of whole blood cells pumped by a cardiopulmonary bypass (CPB) circuit, through a 0.15-cm internal diameter segment of rigid tubing. BF and BFV relationships were obtained at temperatures of 19, 28, and 37 degrees C and at Hct of 0.05, 0.22, 0.39, and 0.54, by altering CPB flow over a range from 10 to 100 cc/min. Linear regression analysis was performed. RESULTS: The relationship between velocity and flow for the pooled Hct data was y=(0.43)x+0.86, r2=0.998 and 95% CI (0.999-1) whereas the association for the temperature data was y=(0.42)x+0.02, r2=0.9998 and 95% CI (0.999-0.9997). Changes of blood viscosity had no effect on velocity at a given flow rate. The combined effect of Hct and temperature on velocity for the relationship with flow is expressed by: y=1.3+2.4x. CONCLUSION: In fixed diameter vessels with laminar flow, the linear relationship between flow and velocity is not affected by changes in temperature and Hct in clinical ranges. These results are explained by the Fahraeus-Lindquist effect. They support the use of transcranial Doppler sonography to estimate cerebral blood flow in infants who may have large variations of Hct and/or temperature during bypass.

Blood Flow Velocity↗
PubMed1989

Acute and protracted effects of intratracheal surfactant application on internal carotid blood flow velocity, blood pressure and carbondioxide tension in very low birth weight infants.

As a part of a multicentre clinical trial of prophylactic treatment with bovine surfactant (SF-RI 1) given to immature infants below 31 gestational weeks, short term and protracted effects on cerebral haemodynamics were assessed by Dopplersonographic measurements of the right internal carotid artery. Measurements were performed every 10 min for 1 h after intratracheal application of the surfactant in ten treated infants. The results of additional measurements every 12 h up to the age of 100 h were compared with a control group. In single cases there were changes of time averaged mean maximum velocity (Vmax) of as much as 100% immediately after intratracheal surfactant application, although the mean short term and protracted variability of Vmax was the same as the protracted variability in the control group. Variability of mean arterial blood pressure and transcutaneous carbondioxide tension (tcpCO2) was even less. With proper adjustment of ventilatory settings intratracheal treatment with surfactant does not affect variability or absolute values of internal carotid Vmax, mean arterial blood pressure and transcutaneous pCO2 in low birth weight infants within 100 h after application.

Blood Flow Velocity↗
PubMed1996

Relationships between cerebral regional blood flow velocities and volumetric blood flows and their respective reactivities to acetazolamide.

BACKGROUND AND PURPOSE: The technique of transcranial Doppler ultrasonography (TCD) is widely used for assessment of cerebral blood flow velocity. Whether measurement of changes in TCD velocity can be used for studying volumetric cerebral blood flow variations remains a matter of debate. We therefore investigated the relationship between flow velocity and volumetric cerebral blood flow before and during acetazolamide-induced vasodilation. METHODS: The middle cerebral artery mean blood flow velocity (MV) measured by TCD and the corresponding regional and hemispheric cerebral blood flows assessed with 133Xe single-photon emission CT were measured in 52 unselected patients. Absolute values of flow and velocity before and after stimulation and their reactivity to acetazolamide were compared. When the correlation was statistically significant, the linearity of the relationship was tested. RESULTS: Absolute values of hemispheric cerebral blood flow were correlated with MV both before (r = .315, P = .02) and after acetazolamide (r = .436, P = .001), whereas regional cerebral blood flow was correlated with MV only after acetazolamide (before, r = .262, P = .06; after, r = .446, P = .001). All these relationships fitted a linear model. In contrast, there was no correlation between acetazolamide-induced relative increments of flow and velocity. CONCLUSIONS: Our results support a linear model describing the relationship between absolute values of flow and velocity when arterial section is the slope and anastomotic blood flow is the intercept. In contrast, relative increments in volumetric flow and velocity may be proportional only if anastomotic flow is negligible, ie, in subjects without cerebrovascular disease. We conclude that, for patients with cerebrovascular disease, TCD does not satisfactorily model cerebral vasoreactivity in terms of volumetric cerebral blood flow.

Acetazolamide↗
PubMed1988

Intracranial arterial blood flow velocity and brain blood flow during hypocarbia and hypercarbia in newborn lambs: a validation of range-gated Doppler ultrasound flow velocimetry.

A transfontanellar range-gated ultrasound Doppler technique for recording blood flow velocity in an artery on the base of the skull was validated in eight anesthetized newborn lambs during hypo-, normo-, and hypercarbia. Blood flow velocity was linearly related to PaCO2 from 20 to 80 mm Hg; mean blood flow velocity (Vmean) (r = 0.86, p less than 0.001), peak systolic blood flow velocity (r = 0.83, p less than 0.001), and end-diastolic blood flow velocity (r = 0.87, p less than 0.001). Vmean changed 2.0% per mm Hg of PaCO2. A linear relationship was demonstrated between brain blood flow (BBF), as determined by the microsphere method, and PaCO2 (r = 0.91, p less than 0.001), with BBF changing 3.6%/mm Hg of PaCO2. Blood flow velocity was linearly related to BBF in the PaCO2 range studied; Vmean (r = 0.89, p less than 0.001), peak systolic blood flow velocity (r = 0.87, p less than 0.001), and end-diastolic blood flow velocity (r = 0.87, p less than 0.001). However, Vmean predicted only approximately 55% of the change in BBF, which suggests a concomitant change in the cross-sectional area of the artery being studied. Despite this limitation, these data suggest that blood flow velocity, recorded by a transfontanellar range-gated Doppler technique from one of the two main arteries perfusing the brain, provides qualitative information on changes in BBF.

Animals↗
PubMed1993

[The effect of nicardipine on internal carotid artery blood flow velocity, local cerebral blood flow and carbon dioxide reactivity].

To study the effect of nicardipine on the blood flow velocity of the internal carotid artery, on local cerebral blood flow (LCBF), and on carbon dioxide reactivity, an initial dose of 0.5 microgram/kg/min of nicardipine was administered in patients for scheduled craniotomy for cerebral aneurysm clipping under isoflurane anesthesia. This agent was administered until the mean arterial blood pressure decreased and could be maintained at about 75% of the initial value until the completion of aneurysm clipping. The measurements of hemodynamics and LCBF were performed after the exposure of the internal carotid artery (T0), and 10 min, 30 min after the starting of nicardipine (n = 13), (T1, T2 respectively), before aneurysm clipping (T3) and 30 min after its discontinuation (T4). Local cerebral blood flow was measured by the thermal gradient blood flow meter. The blood flow velocity of the internal carotid artery was measured at T0 and T3 by a 20MHz pulsed ultrasound Doppler Flow-meter under surgical microscope. Carbon dioxide reactivity was evaluated with % delta LCBF/delta PaCO2 (%/mmHg) at T0, T3 and T4. Mean arterial blood pressure decreased after nicardipine infusion. Local cerebral blood flow did not change during nicardipine infusion, but blood velocity increased significantly after nicardipine infusion from 43 +/-12 to 55 +/- 12 cm/sec (p = 0.024). Carbon dioxide reactivity did not change after nicardipine infusion but had a close correlation with LCBF before (rs = 0.64, p < 0.05), during (rs = 0.84, p < 0.01) and after hypotension (rs = 0.65, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

The effect of nicardipine on carotid blood flow velocity, local cerebral blood flow, and carbon dioxide reactivity during cerebral aneurysm surgery.

We studied the effects of nicardipine (initial infusion rate 0.5 micrograms.kg-1 x min-1) on blood flow velocity in the internal carotid artery, local cerebral blood flow (LCBF), and carbon dioxide reactivity in 20 patients undergoing craniotomy for cerebral aneurysm clipping under isoflurane anesthesia. The blood flow velocity in the internal carotid artery was measured at T0 and T3 by a 20-MHz pulsed ultrasound Doppler flowmeter. LCBF was measured by the thermal gradient blood flow meter. Group A consisted of 10 patients with a good neurologic status (Hunt and Kosnik Grade I); Group B consisted of 10 patients with a poor status (Grades II-IV). Nicardipine was infused until the mean arterial blood pressure decreased to about 75% of the initial value and was maintained at this level until the completion of aneurysm clipping. The measurements of hemodynamics and LCBF were performed after the exposure of the internal carotid artery (T0), and 10 and 30 min after the start of nicardipine (T1 and T2, respectively), before aneurysm clipping (T3), and 30 min after its discontinuation (T4). Carbon dioxide reactivity [% ALCBF/APaCO2 (%/mm Hg)] was evaluated at T0, T3, and T4. Mean arterial blood pressure decreased after nicardipine infusion in both groups. LCBF did not change during nicardipine infusion in either group. Blood flow velocity increased significantly in Group A after nicardipine infusion from 45.1 +/- 6.9 to 51.5 +/- 6.4 cm/s (P < 0.05), but in Group B flow velocity did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Comparison of anterior cerebral artery blood flow velocity and cerebral blood flow during hypoxia.

Measurement of anterior cerebral artery blood flow velocity with a continuous wave bidirectional Doppler was compared with cerebral blood flow (CBF) measured with radioactive microspheres in 11 paralyzed newborn lambs during hypoxic hypoxia. The Doppler probe was maintained in a fixed position during each experiment. The objectives of the study were to validate this noninvasive technique that is being used widely in the clinical setting to qualitatively assess changes in CBF, and to evaluate which of the velocity parameters measured provide the most information. Diastolic velocity (DV), peak systolic velocity (PSV), area under the velocity curve (AUC), and pulsatility index (PI) were examined under conditions of varied arterial oxygen content and compared to microsphere CBF. DV (r = 0.72, p less than 0.001), AUC (r = 0.72, p less than 0.001), and PSV (r = 0.63, p less than 0.001) demonstrated stronger correlations with changes in CBF than did the PI (r = -0.41, p less than 0.05). DV (r = 0.81, p less than 0.001), AUC (r = 0.80, p less than 0.001), and PSV (r = 0.75, p less than 0.001) also exhibited stronger relationships with changes in arterial oxygen content than did the PI (r = -0.36, p less than 0.05). These data demonstrate that changes in cerebral blood flow velocity are useful qualitative measures of changes in cerebral blood flow. However, the utility of this technique is dependent upon a stable probe position, and assessment of the actual velocity measurements (DV, PSV, AUC) rather than simply the pulsatility index.

Animals↗
PubMed2003

A comparison of propofol and sevoflurane anaesthesia: effects on aortic blood flow velocity and middle cerebral artery blood flow velocity.

We compared systemic (aortic) blood flow and cerebral blood flow velocity in 30 patients randomly allocated to receive either propofol or sevoflurane anaesthesia. Cerebral blood flow velocity (CBFv) was measured in the middle cerebral artery using transcranial Doppler. Systemic blood flow velocity (SBFv) was measured in the aorta using transthoracic Doppler sonography at the level of the aortic valve. Bispectral index (BIS) was used to measure the depth of anaesthesia. Measurements were made in the awake patient and repeated during propofol or sevoflurane anaesthesia, with BIS measurements of 40-50. The effects of SBFv on CBFv were estimated by calculating the cerebral/systemic blood flow velocity-index (CsvI). A CsvI value of 100 indicating a 1 : 1 relationship between CBFv and SBFv. The results demonstrated that propofol anaesthesia produced a significantly greater reduction in CsvI than did sevoflurane anaesthesia [propofol: 60 (19); sevoflurane: 83 (16), p = 0.009, t-test]. This suggests a direct reduction in CBFv independent of SBFv during propofol anaesthesia. The greater reduction of CBFv occurring during propofol anaesthesia may be due to lower cerebral metabolic demand compared with sevoflurane anaesthesia at comparable depths of anaesthesia.

Adult↗
PubMed1983

Validity of Doppler measurements of anterior cerebral artery blood flow velocity: correlation with brain blood flow in piglets.

Continuous wave Doppler ultrasonography through the anterior fontanel has recently been used to assess changes in cerebral blood flow in human neonates. There has been controversy concerning whether measurements of Doppler blood flow velocity indeed correlate with brain blood flow. An in vivo correlation was performed between brain blood flow as measured by the microsphere method and Doppler flow velocity measurements of the cerebral arteries via an artificial fontanel in young piglets. The peak systolic velocity (r = .76, P less than .001), end diastolic velocity (r = .72, P less than .001) and area under the velocity curve (r = .86, P less than .001) all showed significant positive correlations with brain blood flow. The pulsatility index did not correlate with brain blood flow. Although continuous wave Doppler flow velocity measurements of the anterior cerebral artery cannot quantitatively assess cerebral blood flow, this methodology can be used to correlate changes in cerebral blood flow and provide a meaningful trend analysis following physiologic or pharmacologic perturbation of the cerebral circulation.

Animals↗
PubMed2001

Influence of aortic blood flow velocity on changes of middle cerebral artery blood flow velocity during isoflurane and sevoflurane anaesthesia.

BACKGROUND AND OBJECTIVE: We studied the influence of systemic (aortic) blood flow velocity on changes of cerebral blood flow velocity under isoflurane or sevoflurane anaesthesia. METHODS: Forty patients (age: isoflurane 24-62 years; sevoflurane 24-61 years; ASA I-III) requiring general anaesthesia undergoing routine spinal surgery were randomly assigned to either group. Cerebral blood flow velocity was measured in the middle cerebral artery by transcranial Doppler sonography (depth: 50-60 mm). Systemic blood flow velocity was determined by transthoracic Doppler sonography at the aortic valve. Heart rate, arterial pressure, arterial oxygen saturation and body temperature were monitored. After standardized anaesthesia induction (propofol, remifentanil, vecuronium) sevoflurane or isoflurane were used as single agent anaesthetics. Cerebral blood flow velocity and systemic blood flow velocity were measured in the awake patient (baseline) and repeated 5 min after reaching a steady state of inspiratory and end-expiratory concentrations of 0.75, 1.00, and 1.25 mean alveolar concentrations of either anaesthetic. To calculate the influence of systemic blood flow velocity on cerebral blood flow velocity, we defined the cerebral-systemic blood flow velocity index (CSvI). CSvI of 100% indicates a 1:1 relationship of changes of cerebral blood flow velocity and systemic blood flow velocity. RESULTS: Isoflurane and sevoflurane reduced both cerebral blood flow velocity and systemic blood flow velocity. The CSvI decreased significantly at all three concentrations vs. 100% (isoflurane/sevoflurane: 0.75 MAC: 85 +/- 25%/81 +/- 23%, 1.0 MAC: 79 +/- 19%/74 +/- 16%, 1.25 MAC: 71 +/- 16%/79 +/- 21%; [mean +/- SD] P = 0.0001). CONCLUSIONS: The reduction of the CSvI vs. 100% indicates a direct reduction of cerebral blood flow velocity caused by isoflurane/sevoflurane, independently of systemic blood flow velocity.

Adult↗
PubMed1993

[The effect of carotid endarterectomy on the reserve capacity of cerebral blood flow velocity].

Cerebral blood flow velocity was measured by transcranial Doppler sonography at rest and during cerebral vasodilatation evoked with acetazolamide in 14 patients before and after carotid endarterectomy. Before surgery the vasoreactivity in the affected middle cerebral artery territories was reduced and abnormal (asymptomatic side: 35.9 +/- 25.6% [mean +/- SD; n = 14]; symptomatic side: 25.6 +/- 10.7%), but the difference between the two hemispheres was not significant however, vasoreactivity was normalized 5 days after surgery (asymptomatic side: 46.9 +/- 22.3% symptomatic side: 58.9 +/- 23%) (p < 0.001). The increase in cerebral reserve capacity and changes in Gosling's index of pulsatility correlated significantly in both hemispheres (p < 0.02). This findings indicate an improved perfusion reserve on the fifth day following carotid endarterectomy in patients with an internal carotid artery diameter reduction of at least 70%.

Blood Flow Velocity↗
PubMed1984

Can perinatal asphyxia cause cerebral edema and affect cerebral blood flow velocity?

Cerebral blood flow velocity (C.B.F.V.) was estimated in 49 newborn babies by calculating the pulsatility-index (P.I.) of the anterior cerebral arteries (A.C.A.) using Doppler ultrasound. We studied the changes in P.I. of the A.C.A. in relation to the clinical condition in three full-term babies with evidence of cerebral edema (in one patient proved by autopsy) due to perinatal asphyxia. There was a relation between the level of consciousness and the P.I.; a low P.I. (a sign of arterial vasodilatation) occurred with a low level of consciousness, while higher P.I. values (reduced vasodilatation) were detected when improvement of consciousness occurred. The following explanation is given: cerebral edema causes an increase of intracranial pressure and venous obstruction. The cerebral perfusion decreases and cerebral function changes; stupor and coma occur. By vasodilatation the resistance of the cerebral arteries is lowered; the C.B.F.V. increases in an attempt to restore cerebral perfusion. The vasodilation is reflected in the low P.I. values, as we found in our three patients.

Adult↗