Management of intracranial meningeal hemangiopericytomas: outcome and experience.

Hemangiopericytomas represent rare intracranial tumors that have a tendency to recur locally and have the unique characteristic of giving extracranial metastases. Our current communication reviews a series of patients diagnosed with hemangiopericytoma who were treated in our facility. Eleven patients with a mean age of 51.2 years underwent follow-up for a mean time of 7.1 years. Their neuroimaging preoperative evaluation included plain skull X-rays, head CT scans, brain MRI, angiograms, and (1)HMRS. Preoperative embolization of the tumor was employed in 6/11 patients. All patients underwent craniotomy for tumor resection and postoperative radiation treatment was employed on all but one. Grade I resection was accomplished in 6/11 (54.5%), grade III in 4/11 (36.4%), and grade IV in 1/11 (9.1%). Local recurrence was detected in 3/11 (27.3%) at a mean period of 5 (range 2-7.5) years. Extracranial metastatic disease was documented in 4/11 (36.4%) patients at a mean of 4.9 (range 2.5-7) years after the initial diagnosis. The GOS score was: 7/11 (63.6%) scored 5, while 4/11 (36.4%) died at a mean time of 5.5 (range 3-8) years after the initial diagnosis. Intracranial hemangiopericytomas management requires aggressive surgical resection, postoperative radiation treatment, and extensive follow-up to rule out local recurrences and delayed extracranial metastases.

C1-C2 transarticular screw fixation for atlantoaxial instability.

OBJECTIVES: The atlantoaxial segment of the cervical spine is commonly destabilized in a variety of disorders. Transarticular screw fixation of the C1-C2 joint has been proposed as a biomechanically superior therapeutic modality. The authors present their experience with this technique. METHODS: A retrospective analysis of 23 patients treated with this technique was performed. The mean follow-up period was 39.5 +/- 0.1 months. RESULTS: Mean duration of hospitalization was 3.4 +/- 0.1 days (range, 2 to 11 days). No intraoperative or early postoperative complications were detected. Four patients (17.4%) had postoperative complications unrelated to the primary procedure. The position of the screw was judged as satisfactory in 21 patients (91.3%). Two patients (8.7%) with suboptimal positioning of the screws were neurologically intact but needed no reoperation. Solid osseous fusion was detected in 19 patients (82.6%). CONCLUSIONS: Transarticular C1-C2 screw fixation appears to be a safe and surgically reliable technique. Criteria for its application and refinements in its technical considerations continue to advance its clinically versatile therapeutic potential.

The development and evaluation of the UK national telepathology network.

AIMS: As technology advances and costs fall, it may be anticipated that soon every histopathologist will expect to be able to exchange electronic images with colleagues. Arguing that the value of a network increases as more people are connected, we sought to install a simple, low-cost telepathology system into any histopathology laboratory which requested it within the UK. METHODS AND RESULTS: We assumed that laboratories had microscopes, computers and internet access. We offered low-cost video cameras, video input cards, software and training to any histopathology department requesting installation, limited only by resources supplied by the UK government. We also established central servers and a website with 'help' files. After 1 year we studied system use and pathologists' opinions by circulating a questionnaire. Installations were completed in 35 laboratories; there are currently 66 registered users of the system, with 16 identified 'experts' covering most organ systems. Serious difficulties were caused by institutional firewalls and reluctance of local information technology (IT) staff to make changes to facilitate the installation or to help resolve subsequent network problems. After installation, many of the telepathology systems remain unused. Concerns were expressed about image quality, though mainly by pathologists who had not used the system for diagnostic work. The system remains available, but the level of use is low. CONCLUSIONS: This project has not achieved its aims. The reasons are complex, but mainly relate to human attitudes. Pathologists with excessive workloads were reluctant to use time to learn new skills which were not directed to reducing workload. IT staff did not perceive the project as part of their routine work. There were also numerous technological problems, but although image quality was cited by many, it was not a complaint of those who actively used the system. These problems have not been encountered by previous projects which involved small groups of committed enthusiasts.

Effect of acute exposure to hypergravity (GX vs. GZ) on dynamic cerebral autoregulation.

We examined the effects of 30 min of exposure to either +3GX (front-to-back) or +GZ (head-to-foot) centrifugation on cerebrovascular responses to 80 degrees head-up tilt (HUT) in 14 healthy individuals. Both before and after +3 GX or +3 GZ centrifugation, eye-level blood pressure (BP(eye)), end tidal PCO2 (PET(CO2)), mean cerebral flow velocity (CFV) in the middle cerebral artery (transcranial Doppler ultrasound), cerebral vascular resistance (CVR), and dynamic cerebral autoregulatory gain (GAIN) were measured with subjects in the supine position and during subsequent 80 degrees HUT for 30 min. Mean BP(eye) decreased with HUT in both the GX (n = 7) and GZ (n = 7) groups (P < 0.001), with the decrease being greater after centrifugation only in the GZ group (P < 0.05). PET(CO2) also decreased with HUT in both groups (P < 0.01), but the absolute level of decrease was unaffected by centrifugation. CFV decreased during HUT more significantly after centrifugation than before centrifugation in both groups (P < 0.02). However, these greater decreases were not associated with greater increases in CVR. In the supine position after centrifugation compared with before centrifugation, GAIN increased in both groups (P < 0.05, suggesting an autoregulatory deficit), with the change being correlated to a measure of otolith function (the linear vestibulo-ocular reflex) in the GX group (r = 0.76, P < 0.05) but not in the GZ group (r = 0.24, P = 0.60). However, GAIN was subsequently restored to precentrifugation levels during postcentrifugation HUT (i.e., as BP(eye) decreased), suggesting that both types of centrifugation resulted in a leftward shift of the cerebral autoregulation curve. We speculate that this leftward shift may have been due to vestibular activation (especially during +GX) or potentially to an adaptation to reduced cerebral perfusion pressure during +GZ.

Cerebral vasoconstriction precedes orthostatic intolerance after parabolic flight.

The effects of brief but repeated bouts of micro- and hypergravity on cerebrovascular responses to head-up tilt (HUT) were examined in 13 individuals after (compared to before) parabolic flight. Middle cerebral artery mean flow velocity (MCA MFV; transcranial Doppler ultrasound), eye level blood pressure (BP) and end tidal CO(2) (P(ET)CO(2)) were measured while supine and during 80 degrees HUT for 30 min or until presyncope. In the postflight tests subjects were classified as being orthostatically tolerant (OT) (n = 7) or intolerant (OI) (n = 6). BP was diminished with HUT in the OT group in both tests (p < 0.05) whereas postflight BP was not different from supine in the OI group. Postflight compared to preflight, the reduction in P(ET)CO(2) with HUT (p < 0.05) increased in both groups, although significantly so only in the OI group (p < 0.05). The OI group also had a significant decrease in supine MCA MFV postflight (p < 0.05) that was unaccompanied by a change in supine P(ET)CO(2). The decrease in MCA MFV that occurred during HUT in both groups preflight (p < 0.05) was accentuated only in the OI group postflight, particularly during the final 30 s of HUT (p < 0.05). However, this accentuated decrease in MCA MFV was not correlated to the greater decrease in P(ET)CO(2) during the same period (R = 0.20, p = 0.42). Although cerebral vascular resistance (CVR) also increased in the OI group during the last 30 s of HUT postflight (p < 0.05), the dynamic autoregulatory gain was not simultaneously changed. Therefore, we conclude that in the OI individuals, parabolic flight was associated with cerebral hypoperfusion following a paradoxical augmentation of CVR by a mechanism that was not related to changes in autoregulation nor strictly to changes in P(ET)CO(2).

Vertical shift in cerebral autoregulation curve: a graded head-up tilt study.

According to the classical theory of cerebral autoregulation, cerebral blood flow (CBF) will be maintained at a near-constant level for cerebral perfusion pressure (CPP) within the range of 60-150 mmHg. In recent years, however, studies with contradicting results have demonstrated a change in CBF when the level of CPP had not changed significantly. It is suggested that a shift in the autoregulation curve may have taken place along the horizontal axis or along the vertical axis. This paper describes previously unreported findings of a graded head-up tilt (HUT) study which was designed as a preliminary experiment to test the protocol for possible use on astronauts upon returning from space-flight. Data from this study tend to support the findings of previous studies regarding possible shifts in the cerebral autoregulation curve. Five female and four male healthy volunteers were exposed to HUT for 5 minutes at each angle of 30 degrees, 60 degrees, and 90 degrees. Throughout the test, cerebrovascular and cardiovascular responses were evaluated by use of continuous acquisition of mean flow velocity (MFV) from the right middle cerebral artery with transcranial Doppler sonograhy, mean arterial blood pressure (MABP, Finapres) and heart rate (HR, ECG). Based on the last 60 seconds of data at each tilt angle and baseline, the percentage changes in MFV from baseline were found to be similar to those in MABP at the level of the brain (MABPbrain), and both were significant (p<0.05) at the 60 degrees (-9.1 +/- 7% for MABP brain, -9.8 +/- 5% for MFV) and 90 degrees (-13 degrees +/- 8%, -12.0 +/- 6%) positions. Heart rate (HR) increased significantly (p<0.05) from the baseline at 30 degrees (6.3 +/- 5%) through 90 degrees (23.3 +/- 8%). The trend toward decreasing MFV in normal subjects, even while MABP brain remained within the normal limits of cerebral autoregulation, may suggest a downward shift of the cerebral blood flow plateau in the classic cerebral autoregulation curve.

Complexity of middle cerebral artery blood flow velocity: effects of tilt and autonomic failure.

We examined spectral fractal characteristics of middle cerebral artery (MCA) mean blood flow velocity (MFV) and mean arterial blood pressure adjusted to the level of the brain (MAPbrain) during graded tilt (5 min supine, -10 degrees, 10 degrees, 30 degrees, 60 degrees, -10 degrees, supine) in eight autonomic failure patients and age- and sex-matched controls. From supine to 60 degrees, patients had a larger drop in MAPbrain (62 +/- 4.7 vs. 23 +/- 4.5 mmHg, P < 0.001; means +/- SE) and MFV (16.4 +/- 3.8 vs. 7.0 +/- 2.5 cm/s, P < 0.001) than in controls. From supine to 60 degrees, there was a trend toward a decrease in the slope of the fractal component (beta) of MFV (MFV-beta) in both the patients and the controls, but only the patients had a significant decrease in MFV-beta (supine: patient = 2.21 +/- 0.18, control = 1.99 +/- 0.60; 60 degrees: patient = 1.46 +/- 0.24, control = 1.62 +/- 0.19). The beta value of MAPbrain (MAPbrain-beta; 2.19 +/- 0.05) was not significantly different between patients and controls and did not change with tilt. High and low degrees of regulatory complexity are indicated by values of beta close to 1.0 and 2.0, respectively. The increase in fractal complexity of cerebral MFV in the patients with tilt suggests an increase in the degree of autoregulation in the patients. This may be related to the drop in MAPbrain. The different response of MFV-beta compared with that of MAPbrain-beta also indicates that MFV-beta is related to the regulation of cerebral vascular resistance and not systemic blood pressure.

Cerebrovascular and cardiovascular responses to graded tilt in patients with autonomic failure.

BACKGROUND AND PURPOSE: Patients with autonomic nervous system failure often experience symptoms of orthostatic intolerance while standing. It is not known whether these episodes are caused primarily by a reduced ability to regulate arterial blood pressure or whether changes in cerebral autoregulation may also be implicated. METHODS: Eleven patients and eight healthy age- and sex-matched control subjects were studied during a graded-tilt protocol. Changes in their steady state middle cerebral artery mean flow velocities (MFV), measured by transcranial Doppler, brain-level mean arterial blood pressures (MABPbrain), and the relationship between the two were assessed. RESULTS: Significant differences between patients and control subjects (P < .05) were found in both their MFV and MABPbrain responses to tilt. Patients' MFV dropped from 60 +/- 10.2 cm/s in the supine position to 44 +/- 14.0 cm/s at 60 degrees head-up tilt, whereas MABPbrain fell from 109 +/- 11.7 to 42 +/- 16.9 mm Hg. By comparison, controls' MFV dropped from 54 +/- 7.8 cm/s supine to 51 +/- 8.8 cm/s at 60 degrees, whereas MABPbrain went from 90 +/- 11.2 to 67 +/- 8.2 mm Hg. Linear regression showed no significant difference in the MFV-MABPbrain relationship between patients and control subjects, with slopes of 0.228 +/- 0.09 cm.s-1.mm Hg-1 for patients and 0.136 +/- 0.16 cm.s-1.mm Hg-1 for control subjects. CONCLUSIONS: The present study found significant differences between patients and control subjects in their MFV and MABPbrain responses to tilt but no difference in the autoregulatory MFV-MABPbrain relationship. These results suggest that patients' decreased orthostatic tolerance may primarily be the result of impaired blood pressure regulation rather than a deficiency in cerebral autoregulation.

Transfer function analysis of cerebral autoregulation dynamics in autonomic failure patients.

BACKGROUND AND PURPOSE: Autonomic nervous system diseases affect systemic blood pressure regulation. Patients with autonomic nervous system diseases have consistently larger drops in blood pressure associated with standing than the normal population. Autonomic dysfunction and/or these changes in blood pressure may affect dynamic cerebral autoregulation. METHODS: Heart rate, mean blood flow velocity (MBFV) of the middle cerebral artery via transcranial Doppler ultrasound, mean arterial blood pressure adjusted to brain level (MABPbrain) via Finapres, and end tidal CO2 were measured continuously during graded tilt (after 5 minutes in supine position as baseline, -10 degrees, +10 degrees, +30 degrees, +60 degrees, -10 degrees, and supine recovery) in autonomic failure patients and their age- and sex-matched control subjects. The dynamic response of MBFV to spontaneous variations in MABPbrain was investigated by cross-spectral analysis. The transfer gain and phase relationships between MBFV and MABPbrain were determined from the final 256 beats of each 5-minute-tilt segment. The transfer gain was normalized to mean MABPbrain and MBFV and then converted to decibels (dB). RESULTS: MBFV variation (0.03 to 0.14 Hz) preceded MABPbrain by similar phase angles in patients and control subjects and in all tilt conditions (patients: 31 +/- 5 degrees; control subjects: 30 +/- 5 degrees; mean +/- SEM). Patients had a higher supine gain than control subjects (P < .05). Both patients and control subjects showed a significant decrease in gain with tilt and by 60 degrees the patients were not different from the control subjects (supine to 60 degrees: patients = 5.23 +/- 0.77 to -1.65 +/- 0.89 dB; control subjects = 1.74 +/- 0.82 to -1.80 +/- 0.62 dB). CONCLUSIONS: These data indicate an altered, yet present, autoregulatory response with autonomic failure.

Simultaneous cerebrovascular and cardiovascular responses during presyncope.

BACKGROUND AND PURPOSE: Presyncope, characterized by symptoms and signs indicative of imminent syncope, can be aborted in many situations before loss of consciousness occurs. The plasticity of cerebral autoregulation in healthy humans and its behavior during this syncopal prodrome are unclear, although systemic hemodynamic instability has been suggested as a key factor in the precipitation of syncope. Using lower body negative pressure (LBNP) to simulate central hypovolemia, we previously observed falling mean flow velocities (MFVs) with maintained mean arterial blood pressure (MABP). These findings, and recent reports suggesting increased vascular tone within the cerebral vasculature at presyncope, cannot be explained by the classic static cerebral autoregulation curve; neither can they be totally explained by a recent suggestion of a rightward shift in this curve. METHODS: Four male and five female healthy volunteers were exposed to presyncopal LBNP to evaluate their cerebrovascular and cardiovascular responses by use of continuous acquisition of MFV from the right middle cerebral artery with transcranial Doppler sonography, MABP (Finapres), and heart rate (ECG). RESULTS: At presyncope, MFV dropped on average by 27.3 +/- 14% of its baseline value (P < .05), while MABP remained at 2.0 +/- 27% above its baseline level. Estimated cerebrovascular resistance increased during LBNP. The percentage change from baseline to presyncope in MFV and MABP revealed consistent decreases in MFV before MABP. CONCLUSIONS: Increased estimated cerebrovascular resistance, falling MFV, and constant MABP are evidence of an increase in cerebral vascular tone with falling flow, suggesting a downward shift in the cerebral autoregulation curve. Cerebral vessels may have a differential sensitivity to sympathetic drive or more than one type of sympathetic innervation. Future work to induce dynamic changes in MABP during LBNP may help in assessing the plasticity of the cerebral autoregulation mechanism.

Determination of appropriate clomipramine dosage among depressed African outpatients in Dar es Salaam, Tanzania.

In an open clomipramine dose finding study, 33 depressed indigenous African outpatients were randomly assigned to two regimens of treatment with 125 mg and 75 mg oral medications daily. At the end of eight weeks of treatment, 16 patients (48.5 pc) were on the 75 mg regime, and 17 (54.8 pc) were on 125 mg. Analysis of depression scores on the Beck-Rafaelsen scale indicated improvements of depression in both regimes of equal magnitude. Analysis of variance showed no statistically significant difference on dose response between the two regimes. The higher doses, however, were associated with more drowsiness and tremulousness. It is suggested that Black African patients respond to tricyclic antidepressants in much lower doses than those recommended in Western textbooks. It is also apparent that side effects of tricyclic antidepressants, which have been implicated in non-compliance to medication, could be avoided without compromising treatment outcome.

Simultaneous transcranial Doppler and arterial blood pressure response to lower body negative pressure.

Microgravity induces fluid shifts which can alter the cardiovascular responses of astronauts both during space flight and on return to Earth. The decrease in orthostatic tolerance in astronauts returning from a weightless environment can be modelled in ground-based studies using lower body negative pressure (LBNP). This study examined the physiological changes induced by LBNP and determined a reliable method of predicting the onset of presyncope to enable evaluation of countermeasures for loss of orthostatic tolerance, such as glycerol-induced hyperhydration. Six healthy male subjects, aged 18 to 45 years, were each subjected to two LBNP tests, with or without glycerol ingestion. Continuous, non-invasive measurements of middle cerebral artery blood flow velocities (CBF) by transcranial Doppler, arterial blood pressure (Finapres ABP), ECG and LBNP box pressures were recorded during each test. Negative pressure was increased in three minute intervals until symptoms of presyncope were observed. An increase in heart rate (HR), a relatively constant mean ABP and a steady decline in mean CBF were consistently observed as the box pressure was decreased. The continuous on-line measurements clearly showed consistent dynamic changes in both CBF and ABP waveforms in response to changes in LBNP. At the onset of presyncope, sudden drops in mean ABP, HR and mean CBF were typically noted, the latter providing the earliest indication of presyncope. The time required to re-establish original baseline values of CBF and ABP after release of box pressure varied widely from six to over ten minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow velocities by transcranial Doppler during parabolic flight.

Microgravity is produced for 20 to 30 seconds in NASA's KC-135 aircraft at the end of a 2 G pullup for each of 40 parabolas per flight. Continuous transcranial Doppler ultrasound, arterial blood pressure, and acceleration levels were recorded for 12 male and 8 female healthy subjects without known cardiovascular or cerebrovascular disease. Recordings were made throughout 10 parabolas per subject in each of the supine, sitting, and standing postures. The data were digitized for off-line analysis using Fast Fourier Transform and other signal processing methods. A phase lag in changes to transcranial Doppler waveforms from the onset of acceleration was more pronounced in the standing position than in the sitting position. There was less of a phase lag in the supine position. These ultrasound changes preceded the more delayed variations in arterial blood pressure. The KC-135 provides a unique short-term environment that allows measurement of the human response to variations in acceleration but limits physiological monitoring of responses to a steady state of microgravity.

Development of methods to analyse transcranial Doppler ultrasound signals recorded in microgravity.

During space flights, several clinical syndromes may be the result of changes in cerebral circulation. The purpose of the paper is to describe the development and initial evaluation of a system for recording, processing and displaying transcranial Doppler ultrasound (TCD) waveforms from the middle cerebral artery (MCA) in microgravity. Volunteers were repeatedly subjected to 15-20 s intervals of microgravity ('near zero gravity') during flights on the KC-135 military aircraft. Continuous TCD recordings from the MCA were stored on magnetic tape. The paper describes the system that was developed to digitise the Doppler ultrasound data and markers that corresponded to the various levels of microgravity, obtain the maximum and mean Doppler waveforms, identify the waveforms and quantify them. The results demonstrate the feasibility of making TCD recordings in a microgravity environment and illustrate excellent performance of the system and its ease of operation. Quantitative waveform analysis of the recordings from the first subject studied in the supine position showed statistically significant changes in MCA velocity waveforms during microgravity.

Comparison of CW Doppler ultrasound spectra with the spectra derived from a flow visualization model.

The methods and results of a study to determine the accuracy of continuous wave (CW) Doppler spectral recordings by comparison to the spectra derived from the flow profiles photographed simultaneously in a pulsatile flow visualization model are reported in this paper. A pulsatile pump produced a flow velocity waveform, similar to that seen in the human femoral artery, in a quartz glass tube. The velocity profiles, which were made visible by using a photochromic dye/laser technique, were photographed, and at the same time the instantaneous Doppler spectra were recorded. A comparison of the Doppler data and the photographed profiles gave the following results. The Doppler spectrograms and those reconstructed from the flow visualization data were quite similar. Excellent agreement was observed between the instantaneous maximum and mean Doppler waveforms. Individual spectra showed some differences and these differences were quantified by the novel application of certain statistical shape descriptor coefficients that are based on the estimation of the higher order moments of the spectra. The Doppler spectra are generally more skewed towards higher frequencies, narrower, and more peaked than the flow visualization spectra. Analysis of the assumptions and various sources of error lead to the conclusion that the differences were probably caused by ultrasound beam nonuniformity and the effects of refraction, causing a reduction of the beam field response at the tube edges. It is concluded that provided certain precautions are taken in the measurement technique, the CW Doppler ultrasound spectra fairly accurately represent the true velocity profile.

A new pulsatile flow visualization method using a photochromic dye with application to Doppler ultrasound.

A nonintrusive method for the visualization of pulsatile flow velocity profiles is described. The method is based on the use of a photochromic dye that is added to the fluid being studied and a nitrogen laser which excites the dye producing a marker "line" whose movement can be photographed. A microcomputer is used as a system controller, to coordinate the system timing and to manage the data transfer. The method used for analysis of the photographs to determine the velocity profiles is described. Examples are presented of instantaneous velocity profiles obtained from velocity waveforms that are similar to those of the femoral artery. In addition, application of the system for studying the relationship between Doppler ultrasound spectral recordings and flow velocity profiles is discussed.

Quantitative estimation of spectral broadening for the diagnosis of carotid arterial disease: method and in vitro results.

For the quantitative assessment of carotid arterial disease using continuous wave Doppler ultrasound, the choice of an index to describe the degree of spectral broadening is important. It is shown that a spectral broadening index (SBI) given by 100(1 - fmean/fmax) and evaluated over a 25 msec period around peak systole is relatively insensitive to artifacts and has potential for achieving good clinical sensitivity. Furthermore, it can be implemented very simply on a microcomputer for on-line display. A description of a microcomputer based system, together with the results obtained using an in vitro flow model that closely approximates the carotid flow velocity waveform, are presented. Results relating the SBI to the degree of stenosis, recording site, and angle of insonation, are given. In addition, the results obtained with a commercial system that computes SBI based on the power spectrum, are presented for comparison.

Determination of the hemodynamic factors which influence the carotid Doppler spectral broadening.

In the diagnosis of extracranial carotid arterial disease, quantitative measurements from the continuous wave (CW) Doppler spectrum have the potential for detecting stenoses and occlusions. The measurement of maximum peak Doppler frequency at the site of stenosis has been shown to detect severe, but not minor or moderate, stenoses. Diagnosis of minor or moderate stenoses may be possible by assessing the degree of flow disturbance beyond the stenosis. Such flow disturbances cause the Doppler spectrum at peak systole to be broadened, and it has been suggested that the measurement of spectral broadening may be of diagnostic value. This paper describes the results of an in vitro study aimed at determining the hemodynamic factors that influence the severity of the Doppler spectral broadening. The spectral broadening index (SBI) at peak systole, defined as SBI = 1 - Fmean/Fmax, was used to quantify the instantaneous spectrum. In a pulsatile flow in vitro model that produced spectral waveforms virtually identical to those recorded in the human carotid, we observed a direct linear relationship between SBI and the severity of stenosis, at least for those stenoses having greater than 40% cross-sectional area (R = 0.82 to 0.93). The SBI was found to be maximum when recorded immediately beyond the stenosis and returned to normal 4-5 cm downstream from the stenosis. The SBI was higher for nonsymmetrically shaped stenoses than for symmetrical stenoses for lesions greater than 60%, but not for stenoses less than 60%. In this model, the SBI recorded from both normal or abnormal waveforms was not affected by the flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro comparison of alternative methods for quantifying the severity of Doppler spectral broadening for the diagnosis of carotid arterial occlusive disease.

Quantitative analysis of continuous wave Doppler recordings is of clinical value in the noninvasive diagnosis of carotid arterial disease. Peak frequency measurements are useful and accurately detect severe stenoses but do not reliably diagnose minor or moderate stenoses because the measurement is dependent upon the probe to vessel angle, which cannot be measured accurately. Recent investigations have focused on efforts to overcome this limitation by quantifying the degree of spectral broadening that occurs as the result of flow disturbances downstream from a stenosis. In this study, an in vitro model was used to determine the optimum method for quantifying the instantaneous Doppler spectrum. The model generates blood flow velocity waveforms that are virtually identical to those found in the human internal carotid artery. Doppler recordings were made from normal tubes and distal to stenoses (39-87% cross-sectional area reduction). The spectra were quantified by the following angle-independent measurements: spectral broadening index and three standard statistical shape descriptors, namely the coefficients of variation, skewedness and kurtosis. Using this model, the results demonstrate an excellent relationship between the severity of the stenosis and each of spectral broadening index (r = 0.99), coefficient of variation (r = 0.96), and coefficient of skewedness (r = 0.99). The calculation of each of the measurements can be implemented quite easily, and a prospective trial is warranted to evaluate their clinical diagnostic accuracy.

Spectral analysis of Doppler flow velocity signals: assessment of objectives, methods, and interpretation.

The objective of this paper is to review the theoretical basis and clinical application of electrical impedance plethysmography in the noninvasive evaluation of peripheral arterial and venous disease. Theoretical, experimental and clinical studies have not demonstrated a direct relationship between electrical impedance changes and limb volume changes. Potential sources of error have also been identified. This has led to the development of clinical tests based on impedance plethysmography for the detection of peripheral arterial disease, venous insufficiency and venous outflow obstruction. Impedance plethysmography, using the method of venous occlusion, is presently the most commonly employed noninvasive method for the detection of deep venous thrombosis.