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Biomedical subjects

R G Ackerstaff

Publications and source records attributed to R G Ackerstaff.

At least 19 recordsLinked to original sources
PubMed2001

Different behavior of sequential versus single left internal mammary artery to left anterior descending area grafts(1).

To study echo Doppler characteristics of sequential versus single left internal mammary artery (LIMA) to left anterior descending (LAD) area grafts transthoracic echo Doppler at the LIMA origin and angiography were performed pre- and postoperatively. In 17 patients single LIMA to LAD (group I) and in 45 patients sequential LIMA to LAD area (group II) bypass grafting was performed. All patients show an early postoperative shift towards diastolic coronary Doppler velocity spectra. Only group II shows a further significant late increase in diastolic, velocity time integral and some systolic echo Doppler parameters at rest. Diastolic peak and diastolic as well as total mean and velocity time integral maximal values are significantly higher in group II in late postoperative hyperemic response. Preoperative and late control angiography showed no significant differences in overall grading of native LAD stenosis between both groups. The large coronary reserve in LIMA sequential grafts may contribute to an improved long-term patency.

Aged↗
PubMed2001

Differences in LIMA Doppler characteristics for different LAD perfusion areas.

OBJECTIVES: To correlate supraclavicular left internal mammary artery (LIMA) to left anterior descending artery (LAD) area Doppler characteristics with angiographically perfused area. METHODS: Sixty patients (50 male, mean age 62+/-7.3 years) with LIMA to LAD area grafting were prospectively entered in a follow up study. Supraclavicular echo Doppler of the LIMA was studied at the LIMA origin preoperatively, and at 4.8+/-3.8 months and 1.8+/-0.9 years postoperatively. The potential area to be revascularized judged from preoperative angiography was called the 'target' area. Control angiography (native and LIMA) was done at 1.5+/-0.9 years. The perfused area % was classified into group I < or =17.0% (n=16), group II >17.0% and <22.50% (n=17), and group III > or =22.50% (n=18) and related to LIMA Doppler characteristics. Multivariate linear regression analyses (MLRA) were performed to assess the relations between Doppler variables and the perfused area, target area and ratio of perfused/target area. RESULTS: At MLRA perfused area was significantly related to the natural logarithm of diastolic peak velocity (DPV) (P=0.013) and diastolic mean velocity (P=0.048) and the ratio only to the degree of LAD stenosis (P=0.004). In hyperaemic response maximal DPV (DPV max) showed significant correlation to the perfused area (P=0.005) as well as to the ratio (P=0.017). When analyzing the additive power of both investigations, only DPV max (P=0.005) correlated significantly to the perfused area and for the ratio only the degree of stenosis of the LAD emerged as significant (P=0.004). CONCLUSIONS: At MLRA the diastolic flow pattern at rest and the maximal DPV in hyperaemic response correlated significantly with the LIMA run-off area whereas the last variable is the strongest predictor of the LIMA run-off area.

Coronary Angiography↗
PubMed2001

SonoVue in transcranial Doppler investigations of the cerebral arteries.

BACKGROUND AND PURPOSE: The authors investigated the safety and diagnostic potential of a new ultrasound contrast agent (SonoVue) using transcranial color-coded duplex sonography (TCCS). METHODS: Forty patients were enrolled in a multicenter, open-label (on-site), blind (off-site), randomized, dose-ranging crossover study. SonoVue was administered as an intravenous bolus injection of 4 different dosages (0.3, 0.6, 1.2, and 2.4 mL). Efficacy was evaluated as (1) off-site assessment of global quality of the Doppler investigation (based on color or power Doppler images and spectral analysis) at baseline and following each dose of SonoVue according to a 4-point scale (from very poor to excellent imaging of blood flow) and (2) duration of clinically useful signal enhancement and color or power Doppler visualization of blood flow. Additional on-site efficacy assessments performed following each dose of SonoVue included confidence in diagnosis and global consequences of contrast enhancement on diagnosis. Safety evaluations included clinical laboratory tests, neurological examination, injection site tolerability, and incidence of adverse events and their relationship to the study agent. RESULTS: All doses of SonoVue significantly improved the global quality of Doppler examinations (P < .05). The median duration of clinically useful enhancement was dose related (P < .001) and ranged from 2 to 6 minutes at the highest dose. The administration of the contrast agent changed a nondiagnostic study to a diagnostic one in 66% of patients and increased the confidence in diagnosis in 74% of cases. No serious adverse events were recorded following SonoVue administration. The observed adverse reactions were all transient and mild in intensity. CONCLUSIONS: The results obtained from this multicenter study demonstrate that the administration of SonoVue to patients with ischemic cerebrovascular disease who undergo TCCS examination of cerebral vessels improves the visualization of intracranial arteries, providing a dose-dependent contrast enhancement and a clinically useful duration of signal enhancement related to the dose. During this multicenter study, SonoVue proved to be a safe and well-tolerated compound.

Analysis of Variance↗
PubMed2000

A new algorithm for off-line automated emboli detection based on the pseudo-wigner power distribution and the dual gate TCD technique.

Research on microembolic signals (MES) using the dual-gate technique has shown promising results, when the time difference (Deltat) of a MES in two sample volumes (SVs) placed serially has been measured manually. On the other hand, the computerized discrimination of MES and artefacts has been reported not to be superior to algorithms based on a single SV. Therefore, a dataset containing MES as well as four types of artefacts was made to test a preliminary version of a new algorithm for automated emboli detection. We monitored 20 patients during carotid endarterectomy (n = 17) and heart surgery (n = 3). Two transcranial Doppler (TCD) signals with a partial overlap of the SVs were recorded online and analysed off-line with an algorithm based on three consecutive steps: 1. Is there an intensity increase in both channels (64-point FFT; 50% overlap)? 2. What is the expected time difference (Deltat), with the velocity measured in channel 1 as the calculation basis? 3. What is the 'exact' Deltat (pseudo-Wigner power function)? Two human experts decided whether a signal was a MES or belonged to one of the four artefact groups. Of a total of 97 MES, 28% (n = 27) could not be detected in the distal channel. Thus, 72% (n = 70) of the MES were present in both channels and could be analysed based on the abovementioned criteria. Of these 70 MES, 87% (n = 61) were correctly identified off-line. We assessed artefact rejection for four different types of artefacts: changes of TCD settings, probe movement, low flow artefacts and electrocautery. The reliability of artefact rejection was 98% for setting changes (n = 382), 96% for probe movement (n = 477) and 98% for low flow artefacts (n = 91), but only 68% for electrocautery (n = 264). These preliminary results are promising, but need careful interpretation: 28% of the MES were not detectable in the distal SV, probably due to a poor signal-to-noise ratio (SNR) and anatomical restrictions. Electrocautery signals were insufficiently rejected. However, even an artefact rejection of 96% can be insufficient if the number of MES is very small compared to the number of artefacts.

Algorithms↗
PubMed2000

Association of intraoperative transcranial doppler monitoring variables with stroke from carotid endarterectomy.

BACKGROUND AND PURPOSE: The outcomes of carotid endarterectomy (CEA) are, in addition to patient baseline characteristics, highly dependent on the safety of the surgical procedure. During the successive stages of the operation, transcranial Doppler (TCD) monitoring of the middle cerebral artery (MCA) was used to assess the association of cerebral microembolism and hemodynamic changes with stroke and stroke-related death. METHODS: By use of data pooled from 2 hospitals in the United States and the Netherlands, including 1058 patients who underwent CEA, the association of various TCD emboli and velocity variables with operative stroke and stroke-related death was evaluated by univariable and multivariable logistic regression analyses in combination with receiver operating characteristic (ROC) curve analyses. The impact of basic patient characteristics, such as age, sex, preoperative cerebral symptoms, and ipsilateral and contralateral internal carotid artery stenosis, on the prediction of operative stroke was also evaluated. RESULTS: We observed 31 patients with ischemic and 8 patients with hemorrhagic operative strokes. Four of these patients died. Emboli during dissection (odds ratio [OR] 1.5, 95% CI 0.8 to 2.9) and wound closure (OR 2.3, 95% CI 1.2 to 4.4) as well as > or =90% decrease of MCA peak systolic velocity at cross-clamping (OR 3.3, 95% CI 1.3 to 8.5) and > or =100% increase of the pulsatility index of the Doppler signal at clamp release (OR 7.1, 95% CI 1.4 to 35.7) were independently associated with stroke. The ROC area of this model was 0.69. Of the patient characteristics, only preoperative cerebral ischemia (OR 1.9, 95% CI 1.0 to 3.7) and > or =70% ipsilateral internal carotid artery stenosis (OR 0.5, 95% CI 0.2 to 0.9) were associated with stroke. Adding these patient characteristics to the model, the area under the ROC curve increased to 0.73. CONCLUSIONS: In CEA, TCD-detected microemboli during dissection and wound closure, > or =90% MCA velocity decrease at cross-clamping, and > or =100% pulsatility index increase at clamp release are associated with operative stroke. In combination with the presence of preoperative cerebral symptoms and > or =70% ipsilateral internal carotid artery stenosis, these 4 TCD monitoring variables reasonably discriminate between patients with and without operative stroke. This supports the use of TCD as a potential intraoperative monitoring modality to alter the surgical technique by enhancing a decrease of the risk of stroke during or immediately after the operation.

Aged↗
PubMed1999

Cerebral ischemic disease and morphometric analyses of carotid plaques.

Atherosclerotic carotid plaque morphology and especially, intraplaque hemorrhage are assumed to be related to neurological symptoms. Most researchers have only investigated the incidence of intraplaque hemorrhage in symptomatic and asymptomatic patients. In the present study, the amount of intraplaque hemorrhage is determined in carotid endarterectomy specimens from 33 symptomatic and 14 asymptomatic patients that caused >70% luminal stenosis. The plaque components (fibrosis, lipids, intraplaque hemorrhage, calcification, and intraluminal thrombosis) were quantified as a percentage of the total plaque volume. A high incidence of intraplaque hemorrhage was found in both the symptomatic (94%, 31/33) and asymptomatic (71%, 10/14) patients. The amount of intraplaque hemorrhage was very small within the plaques of the symptomatic (0.39% +/- 0.70%) and asymptomatic (0.37% +/- 1.12%) patients. The plaques of the symptomatic patients contained more fibrosis than lipids (45.62% +/- 14.99% and 20.45% +/- 21.45%, respectively), as did the plaques of the asymptomatic patients (42. 51% +/- 15.28% and 15.46% +/- 15.22%, respectively). Finally, intraluminal thrombosis and calcification were rare. We conclude that the amount of intraplaque hemorrhage was very small and therefore question its direct role in the development of neurological symptoms. In general, the "unstable" plaque contained more fibrosis than lipids.

Adult↗
PubMed1999

An in vivo evaluation of the reproducibility of intima-media thickness measurements of the carotid artery segments using B-mode ultrasound.

B-mode ultrasound may be used to measure the intima-media thickness (IMT) in subjects with a history of atherosclerosis. The variability between measurements depends on the subjective interpretation of ultrasonographers and readers. The two carotid arteries, subdivided in common (CCA), bulbus (BUL) and internal (ICA) of 10 men with proven coronary disease, were scanned twice by two ultrasonographers with a 1-week interval. The IMTs were measured off-line by two readers. The number of IMT measurements was 75 (94%) of 80 in the CCA, 61 (76%) of 80 in the BUL and 43 (54%) of 80 in the ICA segment. In the CCA segment, the agreement between readers (mean = 0.02 mm; limits: -0.26 to +0.3 mm) and between visits for each reader separately (reader 1: mean = 0.01 mm; limits: -0.33 to +0.35 mm and, reader 2: mean = 0.04 mm; limits: -0.36 to +0.44 mm) was better than in the more distal segments. Therefore, it is concluded that IMT measurements are best performed in the CCA segment.

Aged↗
PubMed1999

Middle cerebral artery anatomy and characteristics of embolic signals: a dual gate computer simulation study.

In terms of microembolic signal (MES) detection, the anatomy of the middle cerebral artery (MCA) mainstem has only scarcely been considered. The vessel itself, however, could be at least partly responsible for the enormous variation when calculating the essential time difference (deltat) values of MES using the dual-gate technique. Therefore, we studied the time characteristics of MES in a computer simulation applying an anatomically realistic vessel and a dual-gate TCD approach. Three different MCA anatomies and two MES to blood intensities were simulated as well as two different sample volume settings. The MES length (proximal sample volume t1; distal sample volume t2) and deltat were calculated for different angles of insonation and sample volume depths. The calculations of the time characteristics of MES showed extreme variation, with only modest changes of the insonation angle (t1 4-34 ms; deltat 9-27 ms) or the sample volume depth (t1 7-27 ms; deltat 6-32 ms). The variation could be considerably reduced with modified TCD settings i.e., a shorter gate separation combined with a shorter receiver gate time in the distal sample volume (deltat with changing insonation angles 6-19 ms; deltat with changing insonation depths 13-17 ms). These results not only urge us to a cautious interpretation of the properties of single MES, but also contribute to an understanding of the marked deltat variation using the dual-gate technique.

Cerebral Arteries↗
PubMed1999

Transcranial Doppler monitoring during carotid endarterectomy helps to identify patients at risk of postoperative hyperperfusion.

OBJECTIVES: to investigate whether transcranial Doppler (TCD) monitoring can identify patients at risk of hyperperfusion, and whether active postoperative treatment of selected patients decreases the risk of intracerebral haemorrhage (ICH). DESIGN: a case cohort study of 688 patients undergoing carotid endarterectomy (CEA) with intraoperative TCD monitoring. METHODS: sixty-two patients (9%) fulfilled the TCD criteria for hyperperfusion, i.e. >100% increase of peak blood flow velocity or pulsatility index of the middle cerebral artery, compared to preclamp baseline values. In these patients, blood pressure was closely monitored and controlled postoperatively. RESULTS: postoperatively, seven of these patients (11%) exhibited clinical signs or symptoms of hyperperfusion but no cerebral haemorrhage (ICH). This is a significantly better outcome (p <0.005) compared to a 2% incidence of ICH after CEA in previous years in our hospital. CONCLUSIONS: patients at risk of hyperperfusion syndrome after CEA can be identified intraoperatively by TCD monitoring. In these selected patients, immediate and adequate postoperative treatment of hypertension results in a decreased risk of intracerebral haemorrhage.

Aged↗
PubMed1998

Ultrasonographic characterization of carotid plaques.

The composition of atherosclerotic plaques in the carotid artery is assumed to be related to the development of neurological symptoms. The echo patterns produced by B-mode ultrasound may be of use in the assessment of the plaques' composition. It is suggested that fibrotic and "stable" plaques are more echogenic than lipid/hemorrhagic and echolucent or "unstable" plaques. B-mode ultrasound procedures were performed 1 day prior to surgery on 46 consecutive endarterectomies. Two observers assessed the plaques according to their echo pattern and echogenicity and sorted them into three categories: 1) predominantly echolucent, 2) heterogeneous, and 3) predominantly echogenic. The intraobserver agreement was moderate (kappa = 0.44) and the interobserver agreement low (kappa = 0.38). Furthermore, subjective categorization of plaque types resulted in type 1 plaques being as fibrotic as type 2 or 3 plaques. We conclude that B-mode ultrasound and subsequent subjective categorization of atherosclerotic plaques cannot adequately determine the volume of fibrosis or lipids within the plaque.

Arteriosclerosis↗
PubMed1998

Variance components analysis of carotid and femoral intima-media thickness measurements. REGRESS Study Group, Interuniversity Cardiology Institute of The Netherlands, Utrecht, The Netherlands. Regression Growth Evaluation Statin Study.

B-mode ultrasound intima-media thickness (IMT) measurements of carotid and femoral arterial walls are used in atherosclerosis studies. In this study, the components contributing to IMT measurement variability in males with coronary artery disease were investigated by means of repeated B-mode ultrasound scans and repeated off-line video image analyses. For statistical analysis, a mixed-model analysis of variance was used. From sonographer data, it was shown that human subjects and their arterial wall segments contributed 75% of the total IMT measurement variability in this population. Inter-sonographer variance contributed 25%. The intra-sonographer variance was negligible (<1%). In off-line image analysis, variance components due to subjects and segments, inter-analyst variance, and residual fluctuation were 88%, < 1% and 11%, respectively. Intra-analyst variance was negligible (<1%). The major source of B-mode ultrasound IMT measurement variability finds its origin in subjects and their arterial walls. Although sonographers proved a lesser source of variability, in comparative studies they should enter a study well trained and should be randomly assigned to subjects. Follow-up examinations should preferably be done by the same sonographer. Off-line image analysis contributed little to IMT measurement variability.

Adult↗
PubMed1998

B-mode ultrasound assessment of pravastatin treatment effect on carotid and femoral artery walls and its correlations with coronary arteriographic findings: a report of the Regression Growth Evaluation Statin Study (REGRESS).

OBJECTIVES: In this B-mode ultrasound study we assessed pravastatin treatment effects on carotid and femoral artery walls and investigated the correlations between the state and evolution of peripheral and coronary atherosclerosis. BACKGROUND: The Regression Growth Evaluation Statin Study (REGRESS) was an 11-center, 2-year, double-blind, placebo-controlled, prospective study of 885 men with coronary artery disease (CAD) (total cholesterol 4 to 8 mmol/liter). The study primarily investigated pravastatin treatment effects on the coronary lumen. This report focuses on the 255 patients who participated in the REGRESS ultrasound study. METHODS: Carotid and femoral artery walls were imaged at baseline and at 6, 12, 18 and 24 months. Pravastatin treatment effect was defined as the difference in progression of the combined intima-media thicknesses (IMT) between treatment groups. RESULTS: Pravastatin treatment effects were highly significant (combined IMT: p = 0.0085; combined far wall IMT: p < 0.0001; common femoral artery far wall IMT: p = 0.004). Correlations between the IMTs of the arterial wall segments ranged from -0.17 to 0.81. Baseline correlations between IMT and percent coronary lumen stenoses ranged from 0.23 to 0.36. Baseline IMT correlated with the mean coronary segment diameter (r = -0.32, p = 0.001) and minimal coronary obstruction diameter (r = -0.27, p = 0.005). There were no individual correlations between IMT and coronary lumen variables (p > 0.30). CONCLUSIONS: Pravastatin treatment effects on carotid and femoral artery walls were observed. B-mode ultrasound imaging studies of peripheral arterial walls could not describe the state and evolution of the coronary lumen in the individual patient, but proved to be a highly suitable tool for the assessment of antiatherosclerotic properties of agents.

Anticholesteremic Agents↗
PubMed1998

Near-infrared reflected spectroscopy and electroencephalography during carotid endarterectomy--in search of a new shunt criterion.

The aim of this clinical study was to evaluate cerebral oximetry with near-infrared reflected spectroscopy (NIRS) as a monitoring system during carotid endarterectomy. The cross-clamping changes of cerebrovascular hemoglobin oxygen saturation (cereb. O2 satn.) were compared with data from a processed EEG analysis. Using the EEG as the gold standard we try to define a new shunt criterion based on near-infrared spectroscopy. 102 patients were studied. During cross-clamping the percentual decrease of cereb. O2 satn. was calculated. The relation between EEG and cereb. O2 satn. is described in terms of sensitivity and specificity, and is graphically shown in a Receiver Operator Characteristic (ROC) curve. At a cut-off value of 5% decrease or more for the cereb. O2 satn., a sensitivity of 100% was found. However, the specificity was only 44%. Higher cut-off values resulted in a gradual increase of the specificity at the expense of a significant decrease of the sensitivity. In conclusion, improved validation and calibration techniques are necessary before this technique may be used for relevant assessment of cerebral oxygenation during carotid surgery. In particular, in order to define a new shunt criterion, the focal aspect of this new technique is probably one of the limitations.

Arteriovenous Shunt, Surgical↗
PubMed1998

Preliminary report of detecting microembolic signals in transcranial Doppler time series with nonlinear forecasting.

BACKGROUND AND PURPOSE: Most algorithms used for automatic detection of microembolic signals (MES) are based on power spectral analysis of the Doppler shift. However, controversies exist as to whether these algorithms can replace the human expert. Therefore, a different algorithm was applied that takes advantage of the periodicity of the MES. This so-called nonlinear forecasting (NLF) is able to detect periodicity in a time series, and it is hypothesized that this technique has the potential to detect MES. Moreover, because of the lack of prominent periodicity in both the normal Doppler signals (DS) and movement artifacts (MA), the NLF has a potential to differentiate MES from normal blood flow variations and MA. METHODS: Twenty single MES and 100 MA were selected by 2 human experts. NLF was applied to MES and MA and compared with 200 randomly chosen DS. NLF resulted in a so-called prediction value that ranges from + 1 in signals with prominent periodicity to 0 in signals that lack periodicity. RESULTS: NLF revealed that MES are more predictable than the normal Doppler signals (prediction [MES]=0.829+/-0.084 versus prediction [DS]= -0.060+/-0.228; P<0.0001). Moreover, MES are more predictable than the MA (prediction [MA]=-0.034+/-0.223; P<0.0001). No difference in prediction could be found between DS and MA. CONCLUSIONS: This preliminary report shows that MES can be separated from DS and MA by NLF. Research is needed as to whether this technology can be further developed for automatic detection of MES.

Artifacts↗
PubMed1996

An in vitro evaluation of the line pattern of the near and far walls of carotid arteries using B-mode ultrasound.

This in vitro study was executed to evaluate the double line pattern generated at both near and far walls of human carotid arteries using B-mode ultrasound. Therefore, extravascular (7.5 MHz) and intravascular (30 MHz) ultrasound imaging were performed at the same locations of the carotid artery. The thickness of the double line pattern of the extravascular image (7.5 MHz) was compared to the thickness of the intima-media complex seen on the corresponding intravascular image (30 MHz) and on the histologic section. At the far wall of the extravascular image, the measurements were executed at the leading edge of the echo. The data showed high correlation and agreement with the intravascular (r = 0.91, p < 0.001; mean(diff) = -0.01 and SDdiff = 0.12) and the histologic measurements (r = 0.87, p < 0.001; mean(diff) = -0.12 and SDdiff = 0.13). In addition, the results of the measurements of the intravascular image showed high correlations and agreement with the histologic data (r(near) = 0.86, p < 0.001; mean(diff) = -0.08 and SDdiff = 0.15, respectively, r(far) = 0.92, p < 0.001; mean(diff) = -0.12 and SDdiff = 0.12). For comparison with other studies, near wall measurements were also included. These had to be performed at the trailing edge of the echoes to be compatible with these studies. The results of the measurements of the extravascular image showed poor correlations and lack of agreement with those of the intravascular (r = 0.49, p = 0.03; mean(diff) = 0.09 and SDdiff = 0.25) and of the histologic (r = 0.37, p = 0.03; mean(diff) = 0.04 and SDdiff = 0.23) measurements. These results can easily be explained from the physical limitations of measuring at the trailing edges. We conclude that the double line pattern seen at the far wall of the extravascular image is representative of the intima-media complex.

Adult↗