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Biomedical subjects

F T Nichols

Publications and source records attributed to F T Nichols.

At least 19 recordsLinked to original sources
PubMed2006

Transcranial Doppler ultrasonography in adults with sickle cell disease.

BACKGROUND: Transcranial Doppler (TCD) is used to select children with sickle cell disease (SCD) for primary stroke prevention using regular blood transfusion. Whether it can also identify high stroke risk in adults with SCD is not known. METHODS: The authors examined 112 adult patients from two convenience population samples with SCD and 53 healthy control subjects to compare velocities in adults to those reported in children with SCD and to evaluate the influence of age and hematocrit on TCD. RESULTS: Adults with SCD had a higher mean time-averaged maximum mean velocity (110.9 +/- 25.7 cm/s) compared with healthy controls (71.1 +/- 12.0 cm/s), and the difference is approximately proportional to their anemia. No cases with velocities >/=200 cm/s (the threshold used in children for prophylactic treatment) were found in this sample. CONCLUSIONS: Transcranial Doppler velocities in adults with sickle cell disease (SCD) are lower than those in children with SCD. Velocity criteria used in children cannot be used to stratify risk of stroke in adults.

Adult↗
PubMed2001

Comparison of transcranial color Doppler imaging (TCDI) and transcranial Doppler (TCD) in children with sickle-cell anemia.

BACKGROUND: Transcranial Doppler (TCD) has been demonstrated to identify those at highest risk of stroke among children with sickle-cell disease. Based on a randomized clinical trial [Stroke Prevention in Sickle-Cell Anemia Trial (STOP)], which ended in 1997, the National Heart Lung and Blood Division of NIH has recommended TCD screening and chronic blood transfusion based on Nicolet TC 2000 dedicated Doppler (TCD). Studies performed using TCD imaging modalities need to be correlated to that used in the clinical trial to provide information for treatment decisions when screening with TCDI. OBJECTIVE: To correlate transcranial arterial time-averaged mean velocities obtained from an Acuson Transcranial Doppler Imaging to those obtained using the TCD as the gold standard for treatment decisions based on STOP. MATERIALS AND METHODS: A total of 29 children with sickle-cell disease, age 3-16 years, were studied at one of two scanning sessions using both techniques and a scanning protocol based on that used in STOP performed and read independently. The average difference in the measured velocities for each arterial segment was tested to determine difference from zero. Differences were compared before and after modifications to the TCDI technique were made to mimic the STOP protocol more closely. RESULTS: TCDI velocities were generally lower than TCD velocities for the same segment, but the difference was reduced (from 15 % to 10% for the middle cerebral artery) by modifications to the TCDI protocol. CONCLUSIONS: Measurements using the Acuson system are modestly lower than those obtained with dedicated Doppler using the Nicolet TCD.

Adolescent↗
PubMed2001

Stroke prevention in sickle cell disease (STOP) study guidelines for transcranial Doppler testing.

The Stroke Prevention in Sickle Cell Disease (STOP) trial used transcranial Doppler (TCD) to screen children with sickle cell disease with no history of stroke. Children (who consented) who had time-averaged mean of the maximum (TAMM) velocities in the middle cerebral artery and/or distal internal carotid artery were randomized to transfusion or standard. Over a slightly more than 20-month average follow-up, there were 11 strokes in the standard care arm and 1 stroke in the transfusion arm. This study has caused a great deal of interest in using TCD to screen children with sickle cell disease. For the STOP TCD data to be applied appropriately, it is necessary for users of TCD to understand how the STOP TCD examinations were performed, how the TCD velocities were measured, and which velocities were used. This article will review the STOP TCD scanning protocol and the reading protocol and review the TAMM velocity and how it differs from other velocity measurements.

Adolescent↗
PubMed1998

Prevention of a first stroke by transfusions in children with sickle cell anemia and abnormal results on transcranial Doppler ultrasonography.

BACKGROUND: Blood transfusions prevent recurrent stroke in children with sickle cell anemia, but the value of transfusions in preventing a first stroke is unknown. We used transcranial Doppler ultrasonography to identify children with sickle cell anemia who were at high risk for stroke and then randomly assigned them to receive standard care or transfusions to prevent a first stroke. METHODS: To enter the study, children with sickle cell anemia and no history of stroke had to have undergone two transcranial Doppler studies that showed that the time-averaged mean blood-flow velocity in the internal carotid or middle cerebral artery was 200 cm per second or higher. The patients were randomly assigned to receive standard care or transfusions to reduce the hemoglobin S concentration to less than 30 percent of the total hemoglobin concentration. The incidence of stroke (cerebral infarction or intracranial hemorrhage) was compared between the two groups. RESULTS: A total of 130 children (mean [+/-SD] age, 8.3+/-3.3 years) were enrolled; 63 were randomly assigned to receive transfusions and 67 to receive standard care. At base line, the transfusion group had a slightly lower mean hemoglobin concentration (7.2 vs. 7.6 g per deciliter, P=0.001) and hematocrit (20.4 vs. 21.7 percent, P=0.002). Ten patients dropped out of the transfusion group, and two patients crossed over from the standard-care group to the transfusion group. There were 10 cerebral infarctions and 1 intracerebral hematoma in the standard-care group, as compared with 1 infarction in the transfusion group -- a 92 percent difference in the risk of stroke (P<0.001). This result led to the early termination of the trial. CONCLUSIONS: Transfusion greatly reduces the risk of a first stroke in children with sickle cell anemia who have abnormal results on transcranial Doppler ultrasonography.

Adolescent↗
PubMed1998

Stroke prevention trial in sickle cell anemia.

Stroke occurs in 7-8% of children with Sickle Cell Disease (Hb SS) and is a major cause of morbidity. Rates of recurrence have been reduced from 46-90% to less than 10% through chronic blood transfusions. Prevention of first stroke, however, would be preferable because even one stroke can cause irreversible brain injury. Transcranial Doppler (TCD) ultrasound can detect arterial blood flow rates associated with subsequent stroke risk. By combining TCD screening and a potentially effective treatment, first stroke may be prevented. The Stroke Prevention Trial in Sickle Cell Anemia (STOP) is the first stroke prevention trial in Hb SS and the first randomized, controlled use of transfusion in Hb SS. This multi-center trial is designed to test whether reducing sickle hemoglobin to 30% or less with periodic blood transfusions will reduce first-time stroke by at least 70% compared to standard care. Primary endpoints will be clinically evident symptoms of cerebral infarction with consistent findings on Magnetic Resonance Imaging and Angiography (MRI/MRA) or symptomatic intracranial hemorrhage. Secondary endpoints will be asymptomatic brain lesions detected by MRI in brain areas not involved in primary endpoints. The design calls for a 6-month start-up interval, 18 months of TCD screening and randomization, and observation for stroke from entry through month 54. Key features of the trial are standardized TCD and MRI/MRA protocols interpreted blindly, and blinded adjudication of endpoints. The sample size (60 per treatment group) is based on prospective data relating TCD velocity to risk of stroke. A time-averaged mean velocity of > or = 200 cm/sec is associated with a 46% risk of cerebral infarction over 39 months. The sample size is sufficient to detect 70% reduction in the primary endpoint at 90% power. This trial will determine if transfusion is effective in the primary prevention of stroke. Secondary aims may further the understanding of the effects of transfusion on the brain and guide future research into cerebrovascular disease in Hb SS.

Adolescent↗
PubMed1997

Long-term stroke risk in children with sickle cell disease screened with transcranial Doppler.

Stroke is an important complication of sickle cell disease. Stroke prediction is clinically important because it offers the possibility of primary prevention. In 1992, transcranial Doppler (TCD) evidence of elevated intracranial internal carotid or middle cerebral artery velocity was demonstrated to be associated strongly with an increased risk of ischemic stroke. This study extends the original study and includes 125 more children, longer follow-up, and intracranial hemorrhage in the stroke-risk model. Elevated time averaged mean maximum blood flow velocity, especially when velocity is 200 cm/sec or greater by TCD, was associated strongly with stroke risk. The cases not predicted by TCD point to the need for more information on the optimal timing of TCD surveillance for stroke risk.

Adolescent↗
PubMed1996

A computer-based statistical pattern recognition for Doppler spectral waveforms of intracranial blood flow.

A computer-based statistical pattern recognition system has been developed for the analysis of transcranial Doppler (TCD) spectral waveforms of the intracranial middle cerebral artery with varying degrees of increased intracranial pressure. This system extracts multidimensional features from TCD waveforms and performs a cluster analysis of those features. The system can automatically recognize the pattern of spectral waveform and classify it as a normal, abnormal, or borderline subclass of TCD spectral waveform. An optimum decision function was generated based on the Bayes Gaussian classifier. The accuracy of the Bayes Gaussian model the spectral waveforms reaches 100% by estimating posterior probability and using the resubstituting method of estimating misclassification in the training TCD data.

Artificial Intelligence↗
PubMed1994

Alpha thalassemia and stroke risk in sickle cell anemia.

In an effort to identify possible risk factors for stroke in Sickle Cell Anemia (Hb SS), we analyzed the distribution of alpha-globin gene deletions in a group of Hb SS patients with and without stroke. The group with stroke consisted of 44 patients, (27 male, 17 female) with a mean of 7.5 years at time of stroke. The control group (non-stroke) had 256 Hb SS patients (126 male, 130 female) with a mean age of 7.7 years. There were 9 patients with heterozygous alpha-thalassemia in the stroke group (20.5%). In the control group, there were 93 patients with heterozygous alpha-thalassemia and 5 with homozygous alpha-thalassemia. The incidence of alpha-thalassemia in Hb SS patients without stroke (38%) was comparable to that reported for the African-American population in general. The incidence in the stroke population (20.5%) was significantly lower (P = 0.02) These results indicate that alpha-thalassemia is associated with a lower risk of stroke in Hb SS. This observation should be confirmed in studies involving larger numbers of patients. Possible protective effects of alpha-thalassemia are unknown but may be related to decreased hemolysis and more favorable rheologic properties of red blood cells.

Adolescent↗
PubMed1994

Transcranial Doppler correlation with angiography in detection of intracranial stenosis.

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate the use of velocity criteria applied to transcranial Doppler (TCD) signals in the detection of stenosis of the middle cerebral (MCA), distal vertebral, and basilar arteries. METHODS: Sixty-five patients who underwent both cerebral angiography and transcranial Doppler examinations in the workup of acute cerebral ischemia were reviewed. Angiography was performed a mean of 7 +/- 5 days (range, 1 to 28 days) after TCD. Interpretation of the angiogram was performed without input regarding the TCD findings. TCD interpretation was performed according to standard criteria. RESULTS: When we used a mean velocity (MV) cutoff of > or = 80 cm/s in the MCA as the criterion for stenosis, 10 of 12 stenoses of any degree were detected by TCD, with 11 of 87 false-positives. Nine of 12 MCA stem (M1) stenoses were detected when a cutoff of > or = 90 cm/s was used, with 7 of 87 false-positives. When we used an MV cutoff of > or = 70 cm/s as the criterion for > or = 50% stenosis of the vertebrobasilar system, 5 of 6 stenoses were detected, with 15 of 85 false-positives. The most important confounding factor was the presence of > or = 75% stenosis of the extracranial internal carotid artery, resulting in both false-positive (from collateral flow) and false-negative (decreased volume flow from the proximal stenosis without adequate collateral flow) errors in TCD interpretation. When patients with > or = 75% stenosis of the cervical internal carotid artery were excluded from analysis, a TCD MV cutoff of > or = 80 cm/s identified 9 of 10 M1 lesions with 7 of 61 false-positives, and an MV of > or = 70 cm/s identified 3 of 4 vertebrobasilar lesions causing > or = 50% stenosis with 7 of 56 false-positives. CONCLUSIONS: TCD may be an effective screening test for M1 stenosis when velocity criteria alone are used. TCD may less reliably detect intracranial vertebral and basilar artery stenosis.

Adult↗
PubMed1993

Carotid plaque associations among hypertensive patients.

OBJECTIVE: To assess the relationship between cardiovascular risk factors and carotid plaque. DESIGN: Hypertensive patients were screened for randomization into the Multicenter Isradipine Diuretic Atherosclerosis Study, a trial intended to determine if blood pressure control by isradipine as compared with hydrochlorothiazide will blunt the progression of carotid plaque (intima plus media thickness, 1.3 to 3.5 mm) in patients with serum cholesterol levels of less than 6.85 mmol/L (265 mg/dL) without insulin-dependent diabetes mellitus or estrogen therapy. Demographics of those who underwent B-mode ultrasound evaluations at common, bifurcation, and internal carotid artery sites to detect plaque were assessed from a southern and a northern site. SETTING: Participants were from ambulatory outpatient clinics associated with medical schools. PATIENTS: The initial screening included 1823 hypertensive volunteer patients who were between 40 and 83 years of age who had a diastolic pressure of 90 to 114 mm Hg (or < 90 mm Hg with treatment). OUTCOME MEASURES: Complete data were collected on the variables of age, cholesterol, cigarette smoking, race, gender, and the presence of carotid plaque in 1126 patients. RESULTS: All variables were significantly associated with carotid plaque (intima plus media thickness, > or = 1.3 mm). The adjusted percentage with plaque was 66.4% +/- 3.4% for blacks and 70.1% +/- 2.3% for whites at the southern site and 42.7% +/- 4.5% for blacks and 61.3% +/- 3.2% for whites at the northern site. The rate of plaque was 75.8% among cigarette smokers, despite a mildly elevated cholesterol level. CONCLUSIONS: Although these 1126 cases do not constitute a random sample of patients, these data suggest that there may be regional differences in racial tendencies toward plaque among blacks.

Aged↗
PubMed1993

Focal headache during balloon inflation in the vertebral and basilar arteries.

BACKGROUND AND PURPOSE: Headache may be seen in acute cerebrovascular disease. The significance of localized headache in association with vertebrobasilar disease has not been recognized. SUMMARY OF REPORT: We describe a patient with a cerebellar arteriovenous malformation who underwent intravascular balloon occlusion of the vertebral and basilar artery. He developed reproducible patterns of referred pain with balloon inflation at specific sites. CONCLUSIONS: Well localized head pain in the setting of acute stroke should alert physicians to the possibility of localized arterial injury. The pattern seen in this patient has been documented in experimental situations, and should be of use in the setting of acute stroke.

Basilar Artery↗
PubMed1993

Coronary artery disease, myocardial infarction, and brain embolism.

The incidence of in-hospital stroke complicating acute myocardial infarction is approximately 1%. This rate is largely unaffected by thrombolytic therapy. Large myocardial infarctions, anterior wall involvement, prior stroke, and increasing age are risk factors for ischemic stroke. Left ventricular thrombi commonly occur with anterior wall infarctions. There is some evidence that anticoagulation reduces their incidence and uncontrolled studies suggest that anticoagulation may reduce the risk of embolization. Left ventricular aneurysms have a low rate of embolization and do not require systemic anticoagulation. Treatment of acute myocardial infarction with t-PA and anisoylated plasminogen streptokinase activator complex are associated with a higher risk of stroke than treatment with streptokinase; this excess risk is attributable to an increased rate of cerebral hemorrhages.

Brain↗
PubMed1992

Transcranial Doppler correlation with cerebral angiography in sickle cell disease.

BACKGROUND AND PURPOSE: Cerebral infarction in sickle cell disease is associated with arterial narrowing or occlusions of intracranial arteries. Primary stroke prevention would be feasible if a noninvasive screening test could be developed to detect intracranial disease in patients before symptoms develop. METHODS: To determine the sensitivity and specificity of transcranial Doppler in detecting significant (greater than or equal to 50% lumen diameter reduction) intracranial arterial lesions, we compared transcranial Doppler and cerebral angiography in a primarily young, symptomatic group of 33 patients (18 males and 15 females) with sickle cell disease. RESULTS: From a total of 34 examinations, transcranial Doppler detected significant abnormalities in 26 of 29 (sensitivity 90%, specificity 100%). Five were normal by both techniques. The transorbital examination detected abnormalities in two patients whose studies were otherwise unremarkable. CONCLUSIONS: Transcranial Doppler is sensitive and specific for the detection of arterial vasculopathy of sickle cell disease. Screening should include a transorbital examination of the distal internal carotid artery as well as examination using the transtemporal approach.

Adolescent↗