Decrease In Blood Flow Velocity Research Articles

Cerebral blood flow in relation to contralateral carotid disease, an MRA and TCD study.

to describe redistribution of cerebral blood flow in patients with severe internal carotid artery (ICA) stenoses in relation to contralateral ICA disease. sixty-six patients scheduled for carotid endarterectomy (CEA) were grouped according to severity of contralateral stenosis (<30% [group I]; 30-69% [group II]; 70-99% [group III]; occlusion [group IV]. Transcranial Doppler (TCD) and magnetic resonance angiography (MRA) investigations were performed preoperatively. TCD demonstrated a reversed flow in the contralateral anterior cerebral artery (A(1)segment) and ophthalmic artery in three-quarters of group IV patients (p <0.0001). Group IV patients also exhibited decreased blood flow velocity in the contralateral middle cerebral artery (p =0.001). MRA showed increased ipsilateral ICA and basilar artery (BA) blood flow volumes (Q-flows) in group IV patients when compared to the other groups (p <0.001). No changes in total Q-flow (ICAs+BA) were found. in patients considered for CEA, the severity of the contralateral ICA disease is an important determinant of the pattern of blood flow redistribution through the anterior communicating pathway and ophthalmic artery. Significant flow redistribution through the posterior communicating pathway occurs especially in patients with contralateral ICA occlusion.

Mechanisms of cerebral autoregulation, assessment and interpretation by means of transcranial doppler sonography

Cerebrovascular autoregulation assures constancy of cerebral perfusion despite blood pressure changes, as long as mean blood pressure remains in a range between 50-170 mmHg. Static and dynamic myogenic mechanisms dampen sudden blood pressure changes. Neurogenic influences of sympathetic, noradrenergic fibers modulate primarily proximal, large diameter segments of cerebral arteries, but also small 15-20 microns diameter vessels. Parasympathetic, vasodilating impulses are of less influence. Monoaminergic brainstem centers such as the dorsal raphe nucleus, locus coeruleus or nucleus reticularis pontis oralis also influence vessel tone. Metabolic, local parenchymal and endothelial substances have major impact on cerebral vessel tone. Particularly important are nitric oxide, calcitonin gene related peptide, substance P, endothelin, potassium channels and autocoids such as histamine, bradykinin, arachidonic acid, prostanoids, leucotrienes, free radicals or serotonin. The clinical examination of autoregulation is mostly based on brief blood pressure changes induced by drugs such as angiotensin, phenylephrine or sodium nitroprusside, or by challenge maneuvers. Frequently, blood pressure is challenged by a tilt-table maneuver, the "leg-cuff"-method according to Aaslid, or a Valsalva maneuver. The analysis of coherence and phase relation between spontaneous or metronomic breathing modulation of blood pressure and brain perfusion also assesses autoregulatory function. Cerebral blood flow is determined by means of transcranial Doppler sonography, mostly of the proximal segment of the mid-cerebral artery. There is some controversy whether a decrease of cerebral blood flow velocity measured at this segment indicates vasodilatation at the insonated segment or reflects blood flow reduction due to decreased perfusion of down-stream vessel segments. Various clinical and animal studies are presented demonstrating diameter constancy of the insonated mid-cerebral artery segment and thus indicating that slowing of mid cerebral artery blood flow velocity as assessed by transcranial Doppler sonography is due to a decrease of down-stream perfusion. Direct, intraoperative measurements of vessel diameter confirm this conclusion.

Aminophylline influences cerebral hyperperfusion after severe birth hypoxia.

Doppler sonographic investigations have presented cerebral hyperperfusion in neonates after severe asphyxia. Neonates with disturbed cerebral blood flow velocity (CBFV) tend to have poor outcomes. The purpose of this clinical study was to examine the influence of aminophylline on cerebral hyperperfusion. An intravenous bolus of 4 mg/kg aminophylline was given to nine neonates with Doppler sonographic signs of cerebral hyperperfusion. CBFV was determined before, 5 min, 60 min and 120 min after aminophylline administration and on the following day. After aminophylline the mean systolic (56.5 vs. 41.6 cm/s) and end diastolic (21.0 vs. 12.3 cm/s) blood flow velocity decreased and the mean pulsatility index (0.83 vs. 1.1) increased significantly. Repeated measurements showed a decrease in blood flow velocities and an increase in pulsatility index on the following days. Heart rate, mean arterial blood pressure and pCO2 were not significantly changed. We conclude that aminophylline influences cerebral hyperperfusion in neonates with disturbed autoregulation.

Duplicated popliteal and superficial femoral veins: incidence and potential significance.

Duplication of the popliteal and superficial femoral veins (PV, SFV) is a normal variant previously reported in up to 25% of limbs. Little clinical significance, however, has been attributed to this apparently common anomaly. The present study was designed to determine the incidence of duplications in individuals presenting for venous incompetence studies, and whether their presence could, in theory, act as a predisposing factor to deep venous thrombosis (DVT) formation. Duplex ultrasound examinations were performed in which venous duplications were actively searched for and recorded. The diameters of both limbs of any duplicated system and the single vessel immediately distal to it were recorded. Using these measurements, the changes in total cross-sectional area (CSA) associated with these anomalies were calculated. In addition, with the knowledge that the volume flow rate must remain constant, the velocity changes associated with such systems were calculated. A total of 248 limbs from 177 patients was scanned. Duplications were found in 39 (15.7%) of these limbs. Of these, 30 limbs (77%) involved only the SFV, seven (18%) involved both the SFV and PV, and two (5%) involved only the PV. Short-segment SFV duplications were used to calculate the percentage change in total CSA and therefore blood flow velocities. Of the 13 (33%) suitable for such calculations, and calculating for each individual duplicated system, a mean increase in the vessel's total CSA of 42%, which corresponded to a theoretical decrease in blood flow velocity of 36%, was found. The present study confirms the significantly high incidence of duplications of the PV and SFV and raises the possibility of the potential for DVT formation secondary to changes in flow velocities.

Influence of the ultrasound contrast agent Levovist on human nailfold capillary microcirculation.

Little is known about the behavior of ultrasound contrast microbubbles in human capillaries. The evaluation of circulatory effects of echo contrast media may bring valuable information for the interpretation of echo contrast phenomena in the human myocardium. In 12 healthy volunteers (aged 31 +/- 6.7 years; five women), nailfold capillaries were examined by means of TV microscopy. The authors investigated acral microcirculation at rest and after local cold application with and without saccharide-based microbubbles (10 mL Levovist 300 mg/mL IV). The mean blood flow velocity at rest was 1.18 +/- 0.18 mm/s (mean value +/-1 SD) and 1.11 +/- 0.11 mm/s (mean value +/- 1 SD) after the injection of Levovist (ns). One minute after local cold exposure a decrease of the blood flow velocity by 61% before and by 75% after intravenous Levovist was found. In both groups the cold-induced decrease of blood flow velocity was statistically significant (p<0.01), whereas there was no significant difference in flow reaction between the two groups. No wall adhesion of blood cells or extravasation of contrast into the surrounding tissue was detected. After intravenous injection of a regular dose of saccharide-based microbubbles Levovist, no change of blood cell flow velocity and no wall adhesion or extravasation could be found at rest and after cold application in human nailfold capillaries. Since microcirculatory flow characteristics in the finger nailfold capillaries are not influenced by Levovist, it might be assumed also that myocardial blood flow behavior remains unchanged, so that this contrast agent may be used as a flow tracer for cardiac investigation.

Cerebral blood flow during vasovagal syncope induced by active standing or head up tilt

BACKGROUNDVasovagal syncope is usually associated with a sudden drop of blood pressure and/or heart rate. However, occasionally the symptoms of syncope induced by orthostatic stress testing are not associated with...

Middle Cerebral Artery Circulation During Carotid Surgery: A Transcranial Doppler Study

Objective - Perioperative carotid cross-clamping might induce low stump pressures as well as hypoperfusion of the middle cerebral artery. In this study blood flow velocities in the middle cerebral artery were compared with intraoperative measurements of the poststenotic carotid blood pressure. Design - Forty-one patients with internal carotid artery stenosis were operated on without shunting, under general anesthesia. Poststenotic carotid pressures and middle cerebral artery flow velocities were measured before and during cross-clamping. The hemodynamic responses to preoperative carotid compressions and intraoperative cross-clamping were evaluated. Results - In seven patients the poststenotic carotid blood pressure decreased on clamping despite unchanged or even increased middle cerebral artery blood flow velocities. In all other patients, pressure changes were significantly correlated to the decrease in middle cerebral artery blood flow velocities. Autoregulatory blood flow velocity responses after preoperative common carotid artery compression were not reproducible by cross-clamping. Conclusions - Stump blood pressure measurements may not reflect middle cerebral artery perfusion in about 20% of thrombendarterectomies performed under general anesthesia. A possible explanation might be dimished cerebral autoregulation and changes in collateral flow distributions.

Hemodialysis causes severe orthostatic reduction in cerebral blood flow velocity in diabetic patients.

Orthostatic hypotension is a serious problem in patients with diabetes mellitus (DM) undergoing hemodialysis (HD). To evaluate cerebral circulation during orthostasis in patients with DM, we examined changes in mean blood flow velocity in the middle cerebral artery (VMCA) during 60 degrees head-up tilt for 5 minutes in patients with DM (six men, two women; age, 57 +/- 3 years [mean +/- SEM]; HD duration, 47 +/- 27 months) before and after bicarbonate HD by using transcranial Doppler sonography. The findings were compared with those in HD patients without diabetes (non-DM; 12 men, 5 women; age, 47 +/- 3 years; HD duration, 82 +/- 23 months). Mean blood pressure (MBP) in the supine position, hematocrit (Hct), plasma fibrinogen, and volume of fluid removed by HD were not significantly different between the two groups (MBP, 106 +/- 6 versus 103 +/- 4 mm Hg; Hct, 26% +/- 1% versus 28% +/- 1%; fibrinogen, 355 +/- 37 versus 357 +/- 27 mg/dL; fluid, 2.5 +/- 0.2 versus 2.3 +/- 0.2 L). Percentage of change in VMCA (% VMCA) during tilt was compared between the groups before and after HD. Before HD, MBP decreased significantly to 93 +/- 5 mm Hg during tilt only in patients with DM. The degree of MBP reduction was -13 +/- 2 mm Hg in DM and -2 +/- 2 mm Hg in non-DM patients (P < 0.01). % VMCA equally decreased during tilt; DM, -12% +/- 3%, and non-DM, -12% +/- 2%. After HD; MBP decreased by 36 +/- 7 mm Hg in patients with DM, which was significantly greater than before HD. VMCA also decreased in both groups after HD, and % VMCA in DM (-32% +/- 5%) was significantly greater than before HD (P < 0.01) and in non-DM patients (-13% +/- 2%; P < 0.01). % VMCA positively correlated with the percentage of change ratio of MBP during tilt in both groups after HD (DM, r = 0. 87, P < 0.01; non-DM, r = 0.61, P < 0.01). Our results showed a significant decrease in cerebral blood flow velocity during tilt of equal magnitude in both groups before HD despite differences in the level of hypotension, whereas reduction in cerebral blood flow velocity and decrease in MBP were more marked in DM after HD. Orthostasis could thus cause hemodynamically mediated brain damage after HD, especially in patients with DM.

Interactions between the right ventricle and pulmonary vasculature in the fetus.

A midsystolic plateau differentiates the pattern of fetal pulmonary trunk blood flow from aortic flow. To determine whether this plateau arises from interactions between the left (LV) and right ventricle (RV) via the ductus arteriosus or from interactions between the RV and the lung vasculature, we measured blood flows and pressures in the pulmonary trunk and aorta of eight anesthetized (ketamine and alpha-chloralose) fetal lambs. Wave-intensity analysis revealed waves of energy traveling forward, away from the LV and the RV early in systole. During midsystole, a wave of energy traveling back toward the RV decreased blood flow velocity from the RV and produced the plateau in blood flow. Calculations revealed that this backward-traveling wave originated as a forward-traveling wave generated by the RV that was reflected from the lung vasculature back toward the heart and not as a forward-traveling wave generated by the LV that crossed the ductus arteriosus. Elimination of this backward-traveling wave and its associated effect on RV flow may be an important component of the increase in RV output that accompanies birth.

The decreased blood flow velocity in the vertebral and internal carotid arteries in hypertensives.

The decreased blood flow velocity in the vertebral and internal carotid arteries in hypertensives.

Infarctus ischémique cérébral du nouveau-né. Diagnostic par doppler puisé et couleur

In newborn infant, cerebral infarction is often difficult to distinguish from cerebral hemorrhage, both pathologies being moreover frequently associated. We report a left anterior stroke in a fullterm newborn who had seizures on the third day of life. Ultrasound scanning showed a hyperechogenic zone in the territory of the left anterior cerebral artery. Pulsed and color Doppler imaging showed a decreased blood flow velocity in comparison to the opposite side, thus enabling the diagnosis.

In vivo blood flow abnormalities in the transgenic knockout sickle cell mouse.

The accepted importance of circulatory impairment to sickle cell anemia remains to be verified by in vivo experimentation. Intravital microscopy studies of blood flow in patients are limited to circulations that can be viewed noninvasively and are restricted from deliberate perturbations of the circulation. Further knowledge of sickle blood flow abnormalities has awaited an animal model of human sickle cell disease. We compared blood flow in the mucosal-intestinal microvessels of normal mice with that in transgenic knockout sickle cell mice that have erythrocytes containing only human hemoglobin S and that exhibit a degree of hemolytic anemia and pathological complications similar to the human disease. In sickle cell mice, in addition to seeing blood flow abnormalities such as sludging in all microvessels, we detected decreased blood flow velocity in venules of all diameters. Flow responses to hyperoxia in both normal and sickle cell mice were dramatic, but opposite: Hyperoxia promptly slowed or halted flow in normal mice but markedly enhanced flow in sickle cell mice. Intravital microscopic studies of this murine model provide important insights into sickle cell blood flow abnormalities and suggest that this model can be used to evaluate the causes of abnormal flow and new approaches to therapy of sickle cell disease.

Transcranial color Doppler sonography of basal cerebral arteries in 182 healthy subjects: age and sex variability and normal reference values for blood flow parameters.

Only a limited number of transcranial color-coded Doppler studies have provided ranges for the normal reference values of cerebral hemodynamic parameters. These reports are not fully convergent in relation to the range of values or to the age and sex dependence of blood flow parameters. The aim of the present study was to provide data regarding normal reference ranges. We examined 182 healthy volunteers (79 men and 103 women; age range, 20-86 years old) with color-coded Doppler sonography via a temporal acoustic window with a 2.5-MHz transcranial probe. The subjects were divided into three age groups: 20-40 years old (group 1), 41-60 years old (group 2), and more than 60 years old (group 3). Angle-corrected peak systolic, end-diastolic, and mean velocities as well as impedance indexes were determined in anterior, middle, and posterior cerebral arteries. Mean velocity values for middle, anterior, and posterior cerebral arteries in age group 1 were 81+/-20, 56+/-14, and 52+/-12 cm/sec (mean +/- SD), respectively. In group 2, the values were 73+/-19, 53+/-16, and 51+/-12 cm/sec (mean +/- SD), and in group 3, the values were 59+/-11, 44+/-11, and 40+/-9 cm/sec (mean +/- SD). Decrease in blood flow velocities and a concomitant increase in impedance indexes were found in all vessels with advancing age-findings that were most pronounced in subjects who were more than 40 years old. In the 20- to 40-year-old group, mean velocities for all vessels were higher in women than in men, whereas impedance indexes were not significantly different. Flow velocities in basal cerebral arteries range widely and are significantly age dependent. Age and sex matching of Doppler sonographic data is a prerequisite for clinically valuable conclusions.

Assessment of intracranial venous hemodynamics in normal individuals and patients with cerebral venous thrombosis.

Despite ongoing improvements in noninvasive imaging techniques, transcranial color-coded duplex sonography (TCCS) has so far been used only on a limited basis in patients with cerebral venous thrombosis. We evaluated the diagnostic value of both noncontrast and contrast-enhanced TCCS by comparing normal volunteers and patients with acute cerebral venous thrombosis. In 75 healthy volunteers (aged 45.8+/-17.4 years), normal values for the deep cerebral veins (DCVs) and the posterior fossa sinuses were established by transtemporal insonation. Eight patients with cerebral venous thrombosis were assessed by TCCS, through which the hemodynamics of the DCVs were measured, and the patients were followed-up over a period of between 33 and 387 days after examination. MR angiography served as the "gold standard" technique for confirming the venous status in all 8 patients. No side differences in flow velocities were detected in the paired venous structures in normal volunteers. As indirect signs of (and diagnostic criteria for) cerebral venous thrombosis, pathologically increased flow velocities or significant side differences in the DCVs were registered in 5 of the 8 patients; the other patients showed nonsignificant increases in flow velocity which decreased over time. During follow-up, the status of the posterior fossa sinuses could be diagnosed correctly in seven patients after contrast enhancement when these results were compared with those of venous MR angiography. In 1 patient, a partial recanalization was mistakenly diagnosed as an occlusion. TCCS allows a reliable evaluation of the major DCVs and posterior fossa sinuses. The anterior and mid portions of the superior sagittal sinus and cortical veins cannot be assessed. Increased venous blood flow velocity can be used as an indirect criterion for indicating a cerebral venous thrombosis. Clinical recovery coincided with decreases in blood flow velocity in the series of patients investigated in this study.

Cerebral effects of a single dose of intravenous vinpocetine in chronic stroke patients: a PET study.

The effects of vinpocetine (Cavinton) on the cerebral glucose metabolism of chronic stroke patients are studied with positron emission tomography. The regional and global cerebral metabolic rates of glucose (CMRglu) and the kinetic constants related to them are quantified before and after single-dose intravenous vinpocetine treatment. These measurements are completed with transcranial Doppler sonography and single photon emission computed tomography to explore the possible mechanisms underlying the resulting changes in glucose uptake and metabolism in the brain. The authors' findings indicate that a single-dose vinpocetine treatment, although it does not affect significantly the regional or global metabolic rates of glucose, improves significantly the transport of glucose (both uptake and release) through the blood-brain barrier in the whole brain, the entire contralateral hemisphere, and in the brain tissue around the infarct area of the symptomatic hemisphere. These changes are in accord with increased blood flow in the entire contralateral hemisphere as well as decreased blood flow velocity and increased peripheral vessel resistance in the entire symptomatic hemisphere.

Factors affecting assessment of cerebral autoregulation using the transient hyperaemic response test

The transient hyperaemic response in the middle cerebral artery blood flow velocity on the release of brief compression of the ipsilateral common carotid artery has been validated as an indicator of cerebral autoregulation. We evaluated, in three stages, the effect of experimental factors such as duration of compression of the common carotid artery and magnitude of the decrease in blood flow velocity during common carotid artery compression on the transient hyperaemic response. In stage 1, 13 healthy volunteers underwent six transient hyperaemic response tests each; two tests each for either 3, 6 or 10 s duration of compression of the common carotid artery. In stage 2, 10 volunteers underwent four transient hyperaemic response tests each; two tests each for either 10 or 15 s duration of compression of the common carotid artery. In stage 3, data from the transient hyperaemic response tests using 10 s compression from the 23 volunteers who participated in stages 1 and 2 were analysed to evaluate the relationship between magnitude of decrease in blood flow velocity at the onset of compression and the transient hyperaemic response. The transient hyperaemic response ratio (blood flow velocity after the release of compression/baseline blood flow velocity) increased significantly when the duration of common carotid artery compression increased from 3 to 6 s, or from 6 to 10 s (stage 1); increase in the duration from 10 to 15 s did not have any significant effect (stage 2). The transient hyperaemic response ratio correlated significantly with the magnitude of decrease in blood flow velocity after compression, up to the values of the compression ratio (percent decrease in blood flow velocity at the onset of compression) of 40% but not more (stage 3). We conclude that experimental factors such as duration of common carotid artery compression and magnitude of the decrease in blood flow velocity during common carotid artery compression can significantly influence the transient hyperaemic response. These factors should be controlled if the transient hyperaemic response test is used for a comparison between repeated measurements. A compression time of 10 s and a compression ratio of 40% or more, allow maximum expression of the hyperaemic response in healthy volunteers.

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<h3>BACKGROUND</h3> Vasovagal syncope is usually associated with a sudden drop of blood pressure and/or heart rate. However, occasionally the symptoms of syncope induced by orthostatic stress testing are not associated with obvious haemodynamic changes. The mechanisms of syncope in these patients are not clear. <h3>AIM</h3> To evaluate changes in cerebral blood flow velocities during orthostatic stress testing in children and adolescents with vasovagal syncope. <h3>METHODS</h3> Electrocardiogram, instantaneous arterial blood pressure, and right middle cerebral artery blood flow velocity were recorded at rest, during active standing, and 80° head up tilt. 32 children and adolescents aged between 7 and 18 years with a history of repeated vasovagal syncope and 23 healthy control subjects were studied. <h3>RESULTS</h3> Presyncope occurred in 10 patients during standing, and 13 patients during head up tilt. None of the controls had symptoms during the test. The transcranial Doppler study showed that the symptoms were associated with significant decreases of diastolic cerebral blood flow velocity and an increase of pulsatility. There was no significant change of the systolic cerebral blood flow velocity. The changes of cerebral blood flow velocities occurred in all episodes of presyncope, including those not associated with severe drop of blood pressure or heart rate. <h3>CONCLUSIONS</h3> Diastolic cerebral blood flow velocity decreased significantly during episodes of presyncope induced by orthostatic stress. Impairment of autoregulation of cerebral blood flow might play an important role in the pathophysiology of syncope.

Hemodynamic changes in hepatic artery after glucose ingestion in healthy subjects and patients with cirrhosis

Purpose The purpose of this study was to investigate hemodynamic changes in the hepatic artery after glucose ingestion. Methods We used color Doppler sonography to measure hemodynamic changes in the right hepatic artery and the right portal vein in response to glucose ingestion (225 ml, 300 kcal) in 25 healthy subjects and 25 patients with cirrhosis. Results In healthy subjects, the peak systolic and end-diastolic velocities in the right hepatic artery decreased (33 ± 3% and 53 ± 3%) from baseline velocities measured in the fasting state. The resistance index of the right hepatic artery and the velocity in the right portal vein in these subjects significantly (p < 0.01) increased (14 ± 2% and 32 ± 2%) from baseline values after glucose ingestion. Glucose ingestion produced significantly (p < 0.01) smaller changes in cirrhotic patients. The maximum decreases in the peak systolic and end-diastolic velocities in the right hepatic artery were 13 ± 2% and 25 ± 3% from baseline velocities, and the maximum increases in the resistance index of the right hepatic artery and the velocity in the right portal vein were 6 ± 1% and 10 ± 3% from baseline values. Conclusions The decrease in blood flow velocity in the right hepatic artery after glucose ingestion is presumably a homeostatic mechanism to maintain constant hepatic perfusion. This reciprocal response was reduced in cirrhotic patients. © 1998 John Wiley & Sons, Inc. J Clin Ultrasound26:137–142, 1998.

Hemodynamic changes in hepatic artery after glucose ingestion in healthy subjects and patients with cirrhosis.

The purpose of this study was to investigate hemodynamic changes in the hepatic artery after glucose ingestion. We used color Doppler sonography to measure hemodynamic changes in the right hepatic artery and the right portal vein in response to glucose ingestion (225 ml, 300 kcal) in 25 healthy subjects and 25 patients with cirrhosis. In healthy subjects, the peak systolic and end-diastolic velocities in the right hepatic artery decreased (33 +/- 3% and 53 +/- 3%) from baseline velocities measured in the fasting state. The resistance index of the right hepatic artery and the velocity in the right portal vein in these subjects significantly (p < 0.01) increased (14 +/- 2% and 32 +/- 2%) from baseline values after glucose ingestion. Glucose ingestion produced significantly (p < 0.01) smaller changes in cirrhotic patients. The maximum decrease in the peak systolic and end-diastolic velocities in the right hepatic artery were 13 +/- 2% and 25 +/- 3% from baseline velocities, and the maximum increases in the resistance index of the right hepatic artery and the velocity in the right portal vein were 6 +/- 1% and 10 +/- 3% from baseline values. The decrease in blood flow velocity in the right hepatic artery after glucose ingestion is presumably a homeostatic mechanism to maintain constant hepatic perfusion. This reciprocal response was reduced in cirrhotic patients.

Relationships between cerebral blood flow velocities and arterial pressures during intra-aortic counterpulsation

Objective: To determine the effects of intra-aortic counter-pulsation (IABP) on cerebral blood flow velocity. Design: Prospective self-controlled study. Setting: University hospital surgical intensive care unit. Participants: Nineteen cardiac surgical patients requiring perioperative IABP assistance. Interventions: Simultaneous recording of transcranial Doppler middle cerebral artery blood flow velocity and arterial pressure in response to changes in the magnitude of augmentation and trigger ratio. Measurements and Main Results: Instantaneous cerebral blood flow velocities correlated with arterial pressures during IABP ( r = 0.650) at different magnitudes of augmentation and trigger ratios. The increase in arterial pressure during balloon inflation was associated with an increase in cerebral blood flow velocity, and the decrease in arterial pressure in response to balloon deflation was associated with a decrease in cerebral blood flow velocity that was dependent on the magnitude of augmentation. Different magnitudes of augmentation or trigger ratios had no effect on peak systolic cerebral blood flow velocity, mean cerebral blood flow velocity, mean arterial pressure, or the mean velocity-to-pressure ratio. Instantaneous cerebral blood flow velocity to arterial pressure ratios were lowest in response to balloon deflation at the time of pre-ejection. Conclusions: IABP modified the phasic profile of cerebral blood flow to reflect the arterial pressure waveform without affecting mean cerebral blood flow velocity. Peak systolic cerebral blood flow velocity was maintained in augmented beats despite the decreased systolic arterial pressure associated with afterload reduction. The acute decrease in cerebral blood flow velocity at pre-ejection was balanced by increased cerebral blood flow velocity during balloon inflation in diastole.