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K W Beach

Publications and source records attributed to K W Beach.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1984

Sex differences in the effect of diabetes mellitus on lipoprotein triglyceride and cholesterol concentrations.

We studied sex differences in the serum lipid abnormalities associated with diabetes mellitus in 111 patients with insulin-dependent diabetes and 270 patients with non-insulin-dependent diabetes, who were compared with 586 nondiabetic controls. Relative to control levels, the increases in triglycerides were 17 to 34 mg per deciliter greater in diabetic women than in diabetic men. The median low-density-lipoprotein cholesterol concentration in non-insulin-dependent diabetics was 1 to 4 mg per deciliter lower than the control level in women and 16 to 22 mg per deciliter lower in men, and was 30 mg per deciliter higher than control in insulin-dependent diabetic women and similar to control in insulin-dependent diabetic men. The decrease in median high-density-lipoprotein cholesterol in non-insulin-dependent diabetics was 2 to 7 mg per deciliter greater in women than in men, and the increase in high-density-lipoprotein cholesterol in insulin-dependent diabetics was 3 mg per deciliter less in women than in men. We conclude that diabetes has a greater adverse effect on triglyceride and lipoprotein cholesterol concentrations in diabetic women than in diabetic men, and that this may explain the greater increase in risk of arteriosclerosis in diabetic women.

Adult↗
PubMed1984

Pathophysiology of venous claudication.

Patients with chronic iliofemoral venous obstruction may develop severe thigh pain and a sensation of tightness with vigorous exercise (venous claudication). The discomfort requires 15 to 20 minutes to subside. In the seven patients studied the venous capacitance (VC) and venous outflow (VO) are lower than those of the unaffected limb even at rest. With exercise to the point of pain, the VO was unchanged but the VC decreased even further. The problem appears to rest with the venous collaterals, which have a high and fixed resistance. Because of this high outflow resistance, venous volume increases to near maximum during exercise. With this rise in venous volume, the amount the VC can increase during the period immediately following exercise is further reduced.

Adult↗
PubMed1982

Evaluation of extracranial carotid artery disease by ultrasonic duplex scanning: a clinical perspective.

The development of noninvasive methods of extracranial carotid artery evaluation over the past decade has led to questions as to their usefulness in daily clinical practice. They have generally been proposed for use in screening asymptomatic patients with bruits or those about to undergo major operative procedures. Since patients with focal symptoms are considered candidates for arteriography, noninvasive tests in this situation may be redundant. However, as the accuracy of the imaging and pulsed Doppler methods has improved, it is appropriate to re-examine this question. Based upon our experience, it is our current feeling that initial screening using ultrasonic Duplex scanning does have a place in symptomatic patients and can be shown to be cost effective.

Angiography↗
PubMed1981

Spectral analysis of Doppler velocity patterns in normals and patients with carotid artery stenosis.

A computerized pattern recognition program was utilized to assess the predictive ability of various parameters obtained from the spectra of ultrasonic pulsed Doppler signals from the carotid arteries. The most accurate features selected by linear regression analysis were the natural log (ln) of the ratio of the mean velocity in the internal carotid artery compared to that in the common carotid artery, and the ln of the maximum velocity, the ln of the maximum frequency, and the square of the fractional broadening term, all of which were measured at peak systole in the internal carotid artery. Using the combination of the velocity ratio and the fractional broadening term, the average difference in the estimated percentage stenosis, as compared to that obtained by arteriography, was 12.8%.

Arteriosclerosis↗
PubMed1980

Electrical potential difference across bone membrane.

The control of ion fluxes to and from bone has important implications to mineralization and calcium homeostasis. Since ionic transport frequently results in an electrical potential difference across the layer of cells lining bone surfaces, knowledge of this potential is critical to understanding the means of regulation of ionic concentrations in the interior bone fluid phase. This work presents a determination of a metabolism-related electrical potential difference by a thermodynamic argument based on the distribution of charged and uncharged tracers between the bone extracellular fluid compartment and the bathing medium. For embryonic chick calvaria whose viability was assured by oxygen consumption measurements, an electrical potential of 4 mV was determined, positive with respect to the bone fluid compartment. This measurement is shown to be consistent with the active transport of K+ ion into the interior of bone; the potential developed by this transport process will then exclude from the interior phase a passively leaked Ca2+ ion.

Animals↗
PubMed1980

Arteriosclerosis obliterans and associated risk factors in insulin-dependent and non-insulin-dependent diabetes.

The prevalence of arteriosclerosis obliterans (ASO) of the legs was determined by a battery of noninvasive tests in 141 insulin-dependent and 289 non-insulin-dependent diabetic subjects and in 64 other subjects. The prevalence of detectable ASO ranges from 18% in the younger IDDM group to 41% in the diet-treated NIDDM group. The prevalence of ASO increases 7.5% per decade, appears to increase 6.5% in the age-adjusted IDDM group, 9% in males, 19% in those with hypertension, and 12% in smokers. No consistently significant correlations with fasting glucose, glycosylated hemoglobin, or obesity were found. After accounting for the effect of smoking, the increased risk for ASO in males becomes nonsignificant.

Adolescent↗
PubMed1979

Noninvasive testing vs clinical evaluation of arterial disease. A prospective study.

In a prospective clinical study involving 458 diabetic patients, the results of noninvasive testing procedures were compared with the findings obtained by clinical evaluation. The results of the study showed that nearly one third of the patients who gave no history of intermittent claudication were found to have arterial disease when tested. One fifth of the patients with what were considered normal physical examination results had abnormal results by noninvasive testing. When history and physical examination prove ineffective for obtaining a diagnosis of arterial disease, the use of noninvasive devices effectively rules out or confirms the presence of hemodynamically significant arterial obstruction. Not only can simple, noninvasive testing methods greatly increase the accuracy of clinical diagnosis for the presence of arterial disease, but the baseline data obtained can serve as objective indexes to follow the natural history of the disease.

Adolescent↗