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K W Beach

Publications and source records attributed to K W Beach.

At least 19 recordsLinked to original sources
PubMed1992

Vector Doppler: accurate measurement of blood velocity in two dimensions.

An ultrasound Doppler system capable of determining both the magnitude and direction of complex blood velocities has been developed and demonstrated. This system uses a single transmitter and two receivers to resolve orthogonal velocity vector components. The system has been tested on a moving string phantom and on a carotid artery. The method may improve the detection of early vascular diseases and improve the accuracy of volumetric blood flow measurements in peripheral arteries.

Blood Flow Velocity↗
PubMed1992

1975-2000: a quarter century of ultrasound technology.

The most popular forms of ultrasonic diagnostic technology experienced a major transition around 1975 with the introduction of real-time B-mode imaging and the combination of real-time imaging with pulsed Doppler in the Ultrasonic Duplex Scanner. At about the same time, the superposition of Doppler data as color on the gray-scale B-mode image was conceived and demonstrated. Since that time, the instruments have been commercialized and distributed broadly. Except for advancements in scanhead design, the introduction of dynamic focussing on echo receive, and conversion of the instruments from analog to digital processing, little has changed in ultrasound instruments; their size, price, features, and portability have been constant. A fully trained examiner using the most modern instrument made in 1978 can easily adapt the same examination methods to instruments made in 1990. The major change in ultrasound technology has been the increased application of ultrasound examination, specifically Doppler examinations to new organ systems. These trends will change in this final decade of the century. The comments here are from a perspective of noninvasive vascular diagnosis. Each of the advancements in ultrasound technology have resulted from the combined efforts and cooperation of many people. I will not attempt to credit those people here.

Forecasting↗
PubMed1990

Testing ultrasonic pulsed Doppler instruments with a physiologic string phantom.

The spatial, temporal, and frequency resolution of conventional ultrasonic Doppler instruments and the time/space distortions in two-dimensional color Doppler imaging systems can be measured using a pulsatile moving string target. The diameter of the string is small compared with the Doppler sample volume, the velocity (speed and direction), acceleration and timing of the string motions are precisely known with reference to the R wave timing mark, and the spatial location of the string is known. A loop of surgical thread or monofilament fishline running between pulleys is driven by a motor that provides constant string speeds from 0.05 to 150 cm/s and variable string speeds programmed to mimic arterial velocity waveforms from the carotid, aortic, and femoral arteries. Constant string speeds are used to evaluate the Doppler sensitivity, frequency processing, and sample volume size; pulsatile movement of the string provides a physiologic model to evaluate the temporal performance of conventional Doppler systems and the temporal and spatial performance of two-dimensional color Doppler imaging scanners.

Blood Flow Velocity↗
PubMed1989

Should results of ultrasound Doppler studies be reported in units of frequency or velocity?

There is a current tendency to report the results of ultrasound Doppler studies in units of velocity instead of Doppler frequency. This is probably motivated by the intuitive feeling that blood flow studies should naturally be reported in cm/s and the notion that "velocity" is a normalizing factor for Doppler ultrasound studies. In order to determine velocity, the Doppler angle theta or angle formed by the ultrasound beam and flow velocity vector, must be known. It is not possible, using currently available systems, to obtain an accurate estimate of this angle. The physics related to the Doppler equation are reviewed in this paper along with examples to illustrate the origin and magnitude of errors that could arise when reporting in units of velocity. Guidelines are provided for thinking about and reporting results of Doppler studies in units of velocity. An understanding of the Doppler equation and its use in clinical studies are promoted in this paper to enhance the diagnostic usefulness of Doppler ultrasound studies and to reduce serious errors which could lead to faulty information dictating patient management.

Blood Flow Velocity↗
PubMed1989

An ultrasonic measurement of superficial femoral artery wall thickness.

An ultrasonic measurement of the superficial femoral artery wall thickness was performed on 16 volunteers. The measurement included all echogenic tissue between the lumen of the superficial femoral artery and the lumen of the superficial femoral vein. The average arterial wall plus vein wall thickness in volunteers with peripheral arterial disease was 2.13 +/- 0.87 mm, significantly greater than the 1.27 +/- 0.50 mm found in those without detectable peripheral arterial disease.

Aged↗
PubMed1989

Diagnosis of deep venous thrombosis. A prospective study comparing duplex scanning to contrast venography.

Duplex scanning has been proposed as a safe alternative to contrast venography for diagnosing deep venous thrombosis, but its accuracy has not been proved. In this prospective, double-blind study of 47 patients, the sensitivity and specificity of duplex scan criteria were determined relative to contrast venography for lower extremity deep venous thrombosis. Criteria considered to show the presence of deep venous thrombosis included visualization of thrombus (T), absence of spontaneous flow by Doppler ultrasonography (F), absence of phasicity of flow with respiration (P), and incompressibility of the vein with probe pressure (VC). When analyzed individually, the variables T and F had low sensitivities (50% and 76%) but high specificities (92% and 100%). VC had low values for both (79% and 67%, respectively). The best single variable was P (sensitivity and specificity = 92%). The best combinations of variables were T+P (sensitivity = 95%, specificity = 83%), T+F+P (sensitivity = 95%, specificity = 83%), F+P (sensitivity and specificity = 92%), and F+T (sensitivity = 92%, specificity = 87%). The low specificity of vein incompressibility was secondary to cases in which normal veins were difficult to compress in the thigh. All false-negative cases were from isolated calf vein thrombi. We conclude that isolated criteria from duplex scanning should not be used to diagnose deep venous thrombosis. In cases of suspected calf vein thrombosis, repeat duplex examination should be obtained in 3-4 days to determine the most appropriate therapy. In equivocal cases of proximal vein thrombosis, a contrast venogram should be obtained.

Adult↗
PubMed1989

Spontaneous lysis of deep venous thrombi: rate and outcome.

Ultrasonic duplex scanning was used to study the rates at which lysis of thrombi, valvular incompetence, and symptoms of the postthrombotic syndrome (edema) developed in 21 patients after deep venous thrombosis (DVT). Lysis of thrombi occurred rapidly in most patients. In 11 of 21 patients (53%), recanalization occurred in all segments by 90 days after presentation. In four patients, extension of the initial DVT occurred between 30 and 180 days, despite treatment with warfarin. Valvular incompetence developed in 13 patients during the study period. The number of patent venous segments with incompetent valves increased from the initial presentation to 180 days, at which time 25% of patent segments contained incompetent valves. Valvular incompetence developed in previously thrombosed segments that were initially competent after recanalization and in segments not previously thrombosed. This suggested that although incompetence may occur as a result of a direct effect of the thrombus on the valve, other mechanisms must also be involved. Patients with edema early after DVT (from 7 to 30 days) were more likely to have residual occlusion than valvular incompetence. The late development of edema (from 90 to 270 days) was more closely correlated with valvular incompetence.

Humans↗
PubMed1988

Progression of lower-extremity arterial occlusive disease in type II diabetes mellitus.

The prevalence of lower-extremity arterial occlusive disease (LEAOD), the progression of LEAOD, and the incidence of new LEAOD were determined by noninvasive method in 410 volunteers between the ages of 50 and 70 yr; 252 individuals had type II (non-insulin-dependent) diabetes, 158 were control subjects. LEAOD was monitored with the ankle/arm systolic blood pressure index in combination with Doppler arterial velocity waveform analysis. LEAOD was much more prevalent in the type II patients (22%, 55 of 252) than in the control subjects (3%, 4 of 158) (P less than .00001). The prevalence of risk factors for LEAOD was much higher in the type II patients, including elevated triglyceride, depressed high-density lipoprotein (HDL) cholesterol, hypertension, smoking, and elevated systolic blood pressure. In type II diabetic patients the incidence of new LEAOD over a 2-yr period (14%, 28 of 197) was lower than the incidence of LEAOD progression (87%, 45 of 52). Type II patients with LEAOD also had a high incidence of mortality (22%, 12 of 55) compared with those without LEAOD (4%, 8 of 197) (P less than .0005). A risk score including smoking history, duration of diabetes, depressed HDL cholesterol, total cholesterol, elevated systolic blood pressure, and low obesity index is related to LEAOD. After accounting for the effect of all of the risk factors, we suggest that type II diabetes contributes additional risk for LEAOD.

Aged↗
PubMed1988

Duplex ultrasound scanning in the diagnosis of renal artery stenosis: a prospective evaluation.

Since ultrasonic energy can be used to interrogate vessels at great depth, it is only natural that it should be applied to deeply placed arteries in the abdomen. Early studies suggested that high-grade stenoses of the renal artery could be detected by this approach as long as the peak systolic velocity in the renal artery was normalized by that measured in the abdominal aorta. A retrospective study comparing the peak velocity in the renal artery to that from the adjacent abdominal aorta (the renal aortic ratio) showed that if this value exceeded 3.5, it is likely to be associated with a greater than 60% diameter-reducing stenosis. To test this hypothesis, we used duplex scanning to prospectively evaluate 58 renal arteries in 29 patients in whom arteriograms were available. There were 39 renal arteries with 0% to 59% stenosis, 14 with 60% to 99% stenosis, and five occlusions by angiography. Renal duplex scanning accurately diagnosed 38 of 39, 11 of 14, and four of five of these, respectively, giving a sensitivity of 84%, a specificity of 97%, and a positive predictive value of 94% for the detection of a greater than 60% diameter-reducing stenosis. The overall agreement with angiography was 93%. These data show that renal duplex scanning can be used to diagnose renal artery stenosis in patients with hypertension or renal dysfunction, thus providing a rational basis for the selection of patients for angiography.

Adolescent↗
PubMed1987

Variability in measurement of specific parameters for carotid duplex examination.

The variability of four carotid artery frequency parameters used for classifying disease with duplex scanning was prospectively studied. Forty-eight patients (94 patent carotid arteries) were each examined by two technologists. Measured parameters were the peak systolic frequency (PSF) and the first zero slope from the common carotid artery, and the PSF and end diastolic frequency (EDF) from the internal carotid artery. Measurements from all the examinations were made twice by each technologist. Interobserver, intraobserver, and interpatient variability in measurement of the first zero slope was so great that we have abandoned its use. Measurement of variability for PSF and EDF was much less (correlation coefficients 0.68 to 0.92). These parameters were measured with sufficient precision to warrant their continued use for important decision steps in classifying carotid artery disease. Interpatient differences in PSF sufficient to cause disagreement regarding the hemodynamic significance of carotid disease occurred in only three instances. In each of these cases the differences were due to examination technique (failure to identify a very distal internal carotid artery stenosis, difficulty distinguishing between a kink and a stenosis, and failure to recognize an improper Doppler angle). We conclude that the variability of PSF and EDF is within clinically acceptable levels and is mainly due to examination technique rather than measurement of waveform parameters or changes in patient hemodynamics.

Arterial Occlusive Diseases↗
PubMed1987

Noninvasive assessment of normal carotid bifurcation hemodynamics with color-flow ultrasound imaging.

The combination of a B-mode imaging system and a single range-gate pulsed Doppler flow velocity detector (duplex scanner) has become the standard noninvasive method for assessing the extracranial carotid artery. However, a significant limitation of this approach is the small area of vessel lumen that can be evaluated at any one time. This report describes a new duplex instrument that displays blood flow as colors superimposed on a real-time B-mode image. Returning echoes from a linear array of transducers are continuously processed for amplitude and phase. Changes in phase are produced by tissue motion and are used to calculate Doppler shift frequency. This results in a color assignment: red and blue indicate direction of flow with respect to the ultrasound beam, and lighter shades represent higher velocities. The carotid bifurcations of 10 normal subjects were studied. Changes in flow velocities across the arterial lumen were clearly visualized as varying shades of red or blue during the cardiac cycle. A region of flow separation was observed in all proximal internal carotids as a blue area located along the outer wall of the bulb. Thus, it is possible to detect the localized flow patterns that characterize normal carotid arteries. Other advantages of color-flow imaging include the ability to rapidly identify the carotid bifurcation branches and any associated anatomic variations.

Adult↗
PubMed1987

Assessment of pressure gradient by Doppler ultrasound: experimental and clinical observations.

Three methods for estimating peripheral artery pressure gradients from ultrasound data were assessed by means of an acute canine aortic coarctation with a variable stenosis and retrospective data from 18 patients with iliac stenoses who had duplex scanning studies and pressure measurements at the time of angiography. The measured pressure difference was correlated with end-diastolic velocity, the presence or absence of reverse flow in diastole, and a pressure difference calculated with the modified Bernoulli equation. Although the calculated pressure gradients correlated well with measured values in animal studies (11 animals, r = 0.78, n = 224, SD = 8.1), they did not in the clinical studies (r = 0.54, n = 33, SD = 28). In both cases, pressure gradients were consistently overestimated for mild stenoses. There was a strong correlation between end-diastolic velocity and pressure gradient (r = 0.71, n = 94, SD = 5.2 for animal studies; r = 0.81, n = 36, SD = 23 for clinical studies), but the data were too variable to provide useful pressure estimates. In clinical studies the absence of reverse flow in diastole at the site of the stenosis was the best indicator of a resting pressure gradient of greater than 15 mm Hg. We conclude that the modified Bernoulli equation and end-diastolic velocity correlate highly with the pressure gradient but are not clinically useful because the variability is too great. The absence of reverse flow in diastole is a more reliable indicator of hemodynamically significant stenosis.

Animals↗
PubMed1986

Calcium homeostasis. III: The bone membrane potential and mineral dissolution.

Active ionic transport through the bone membrane appears to be involved in the regulation of calcium level in the bloodstream. This transport process can be monitored by the transmembrane electrical potential difference, which increases in the presence of parathyroid hormone. The present work is an evaluation of the constraints placed on the system by the solubility limit of the mineral phase. A thermodynamic analysis demonstrates that control of mineral dissolution can only occur when the transported species is one of the mineral phase constituents. A combination of previous experimental results with the present development limits the possible active transport mechanism responsible for the adjustment of mineral dissolution/deposition to: an outward-directed pump for hydroxyl ion, an outward-directed pump for phosphate ion, or an inward-directed pump for hydrogen ion.

Animals↗
PubMed1986

Noninvasive diagnosis of renal artery stenosis by ultrasonic duplex scanning.

We retrospectively studied the results of duplex scanning for evaluation of renal artery disease in 158 patients. Satisfactory examinations were achieved in 144 patients (90%). Arteriograms were available for 43 renal arteries. We used the ratio of the peak velocities in the renal artery and the aorta (RAR) to separate nonstenotic arteries (less than 60% diameter reduction) from stenotic arteries (greater than 60% diameter reduction). With an RAR of greater than 3.5 to indicate stenotic lesions, duplex scanning had a sensitivity of 91% (20 of 22 diseased arteries correctly identified) and specificity of 95% (20 of 21 normal or insignificantly diseased arteries correctly identified). One of four occluded arteries was incorrectly interpreted as patent because of misidentification of a collateral vessel. Prospective studies will be necessary to validate this test and establish other criteria for a more detailed classification of renal artery stenosis. The ratio of the end-diastolic to peak systolic velocities in the renal artery (EDR) tended to decrease with increasing serum creatinine levels, presumably because renal vascular resistance increases with end-stage parenchymal disease. EDR may prove useful in the detection of advanced parenchymal disease before renal artery revascularization is attempted.

Aorta, Abdominal↗
PubMed1985

An objective assessment of the physiologic changes in the postthrombotic syndrome.

To determine what physiologic changes might contribute to the development of the postthrombotic syndrome, venous outflow, venous refilling time, and valvular competence were assessed in 32 patients (39 limbs) with documented deep venous thrombosis. The follow-up ranged from nine to 144 months (mean, 41 months) after the acute deep venous thrombosis. Pain was noted by 49% of the patients, but more objective end points occurred less frequently (edema, 21%; pigmentation, 26%; ulceration, 3%). Venous outflow was lower in the affected limbs but was not a good indicator of those patients with or without symptoms. Venous refilling time after calf compression was markedly reduced in limbs with incompetent valves (mean +/- SD, 8.4 +/- 3.8 s v 25.3 +/- 12.1 s), as well as in those with edema, pigmentation, and ulceration. It appears that most of the sequelae of the postthrombotic syndrome can be attributed to the loss of valvular function.

Adult↗
PubMed1985

Calcium homeostasis: the effect of parathyroid hormone on bone membrane electrical potential difference.

Although it is generally accepted that calcium ion homeostasis is performed primarily by bone, the mechanism by which this regulation is accomplished remains unclear. The recent demonstration of a metabolism-related electrical potential difference across bone membrane implies an active transport process within this layer of cells lining bone surfaces. This work presents a determination of the effect of parathyroid hormone on the measured potential difference to demonstrate whether this potential is involved in the homeostatic mechanism. A thermodynamic evaluation is performed based on a measurement of the distribution of charged and uncharged tracers between bone extra-cellular fluid and the bathing medium. For embryonic chick calvaria whose viability was assured by the measurement of oxygen consumption, parathyroid hormone at dosage levels up to pharmacological caused an increase in the measured potential difference and thus in the inferred activity level of ionic transport through the membrane. This result is shown to be consistent with an indirect regulation of Ca++ ion through a variable active transport of K+ ion into the interior of bone and thus provides support for the argument that the membrane potential is part of the calcium homeostatic mechanism.

Animals↗
PubMed1985

Carotid endarterectomy. Relationship of outcome to early restenosis.

The results following carotid endarterectomy were prospectively evaluated in 134 patients (145 sides) by repeat ultrasonic duplex scanning and clinical evaluation extending for a period of 4 years. There were 107 men and 27 women in the study group. The perioperative stroke rate was 1.3% and the mortality rate, 0.7%. There were 9 late deaths, of which two were stroke related (1.4%). Focal symptoms occurred in 12 patients on the ipsilateral side, six of which were strokes (one lacunar). The remaining symptoms developed in the presence of moderate degrees of carotid stenosis (less than 50%). There were seven patients who had transient ischemic attacks (TIAs) referable to the operated side, but only two of these were associated with a recurrent high-grade stenosis. During follow-up 32 (22%) patients had recurrent high-grade stenosis. Restenosis regressed in seven, giving a persistent rate of 17.1%. The incidence of restenosis was significantly higher in women (p less than 0.01). By life-table analysis, restenosis occurred early, the majority within 24 months. There was no consistent association between the development of symptoms and the occurrence of restenosis. Therefore, it is concluded that there is no justification for reoperation based on the degree of narrowing observed to prevent subsequent TIAs and strokes.

Aged↗