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Biomedical subjects

A Fronek

Publications and source records attributed to A Fronek.

At least 37 records · Page 2Linked to original sources
PubMed1991

Determination of in vitro simulated blood cell velocity by laser-Doppler with state space methods.

In this paper a signal processing method based on an important tool of numerical analysis, the singular value decomposition (SVD), is used. This method is applied to the unprocessed output of a Laser-Doppler fluxmeter to obtain parameters that are more sensitive to blood velocity than to hematocrit. The SVD-based method utilizes the exponential shape of the frequency spectrum of the laser light scattered from the moving red blood cells and demonstrates an inverse relationship between the damping constant beta associated with the exponential shape and the blood velocity. This method was applied to samples of rat blood of several known hematocrit values that were rotated at different velocities on a turntable. The method extracted one dominant singular value from the spectra, indicating that the spectra can be modeled as a single exponential dominated by scatterings with a single moving red blood cell. A 68% change in inverse velocity resulted in a 50% change in the damping constant (hematocrit 29.5% vol). On the other hand, a 37% change in hematocrit resulted in a far smaller change in the damping constant beta of only 17%. Analysis of the extracted parameters shows that the damping constants are far more influenced by blood velocity than by blood hematocrit.

Animals↗
PubMed1991

Coronary disease and stroke in patients with large-vessel peripheral arterial disease.

Previous reports have indicated an excess of mortality from coronary heart disease (CHD), cardiovascular disease (CVD), and all causes in subjects with large-vessel peripheral arterial disease (LV-PAD). However, there is little information available concerning the risk of nonfatal events (morbidity) in this patient group. In a population-based study of 67 patients with LV-PAD and 408 control subjects without this condition, nonfatal CHD and stroke, and total CVD events, morbidity and mortality were evaluated in both men and women. Those with LV-PAD had a 3-fold excess of CVD morbidity at baseline compared with control subjects of the same sex. However, the absolute CVD rates were greater in men than women. During the 10 years of follow-up, women with LV-PAD had more nonfatal CVD events than men, resulting in comparable overall morbidity rates. In logistic regression models adjusted for other CVD risk factors, total CVD morbidity and mortality combined with 2.5 times as great in men and 5 times as great in women with LV-PAD as in those without peripheral arterial disease. These results suggest that the total morbidity and mortality burden are dramatically increased in both men and women with LV-PAD.

Adult↗
PubMed1991

[D-SGP Duo--a new plethysmography for acral, arterial and venous blood pressure measurement].

This is to present a new portable plethysmograph using modern microprocessor technology, a two-channel digital strain gauge plethysmograph (D-SGP Duo). This system contains two strain gauges and a pressure gauge and has measuring programmes for thrombosis screening (venous occlusion test) and for the acral blood pressure measurement. For the first time it is possible to determine not only the acral systolic arterial pressure but also the acral venous blood pressure. Examples of application are given.

Blood Pressure↗
PubMed1991

Real-time color duplex scanning after sclerotherapy of the greater saphenous vein.

A color real-time duplex scanner was used to scan the greater saphenous vein in 89 limbs of 55 patients to study the efficacy of prior greater saphenous vein sclerotherapy. The greater saphenous vein was insonated from the saphenofemoral junction to the knee to evaluate both reflux to a standardized 30 mm Hg Valsalva maneuver and evidence of greater saphenous vein obliteration by sclerotherapy. These data were correlated with the number of sclerosing injections used (mean, 1.8; range, 1 to 6), time from the last injection (mean, 27.5 mo.; range, 3 to 55 mo), and concentration of injectant used (0.5% to 3% sodium tetradecyl sulfate). Fifty-one of 89 injected limbs (57%) demonstrated reflux through the saphenofemoral junction, and reflux down the more distal greater saphenous vein was found in 67 of 89 injected limbs (75%). Greater saphenous vein obliteration was noted in only 18 of 89 injected limbs (20%); two were totally obliterated, and 16 were partially obliterated. The greater saphenous vein was obliterated in 6% below a refluxing saphenofemoral junction and in 40% below a nonrefluxing junction. A greater saphenous vein obliteration rate of 9% was found with a refluxing greater saphenous vein, and 50% in a nonrefluxing greater saphenous vein. Femoral vein reflux was identified in 11 of the 110 limbs (10%) and in every case was associated with both saphenofemoral junction and greater saphenous vein reflux. We noted a trend toward more successful results with more concentrated injectate (3% sodium tetradecyl sulfate). Fifty percent of patients reported improvement in symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Determination of volume of vortices in poststenotic pulsatile flow by ultrasonic Doppler power ratio and spectrum analysis.

Based on the principle of ultrasonic Doppler flowmetry, a power ratio was derived from independent forward and reverse flow Doppler shift signals to measure a ratio of the volume of vortices to the total vessel volume in poststenotic separated flow. The ratio was also proportional to the ratio of the cross-sectional areas of vortices to the vessel lumen. In vitro pulsatile flow experiments were performed to test the methodology and to study flow separation and vortex shedding downstream from model stenoses. The averaged flow cross-sectional area ratio linearly correlated (r = 0.91) with the actual area reduction of the stenosis.

Carotid Artery Diseases↗
PubMed1990

Detection of moving flow separation in pulsatile flow and the degree of stenosis by power of Doppler shift signals.

Power ratios were derived from the principle of ultrasonic Doppler velocimetry to determine a ratio of the volume of vortices to the total vessel volume under the ultrasonic beam. This ratio also equals the ratio of the cross-sectional area of vortices to the vessel lumen. In vitro pulsatile flow experiments were performed in a Reynolds number range of 1,230-4,320 with axisymmetric constrictions with area reductions of 55%, 65%, 70%, and 85% to model carotid stenosis. Flow separation downstream from the model stenoses was detected, and the power ratio fluctuated when vortices with the forward- and reverse-flow velocity components passed by the measurement position. The power ratio estimated the degree of stenosis within 10% of error. Ensemble average of the power ratio was computed to obtain the statistically averaged separated flow region. The moving flow reattachment point was revealed downstream from the 85% stenosis at a Reynolds number of 900.

Blood Circulation↗
PubMed1989

Peripheral arterial disease in large vessels is epidemiologically distinct from small vessel disease. An analysis of risk factors.

The authors used noninvasive techniques, including flow velocity by Doppler ultrasound, to accurately assess and distinguish between large and small vessel peripheral arterial disease in a population study in southern California, 1978-1981. In 565 men and women aged 38-82 years, there were 69 cases of large vessel peripheral arterial disease, 19 of which were severe, and 90 cases of isolated small vessel peripheral arterial disease. In cross-sectional multivariate analysis in men, large vessel peripheral arterial disease was significantly associated with age, pack-years of cigarettes smoked, systolic blood pressure, fasting plasma glucose, and marginally with obesity. Similar analysis in women revealed significant associations only for age and systolic blood pressure, although the associations for pack-years of cigarettes, obesity, and low density lipoprotein cholesterol were suggestive. By contrast, isolated small vessel peripheral arterial disease was not significantly associated with any of the major cardiovascular disease risk factors, including two measures of carbohydrate metabolism, fasting plasma glucose and glycosylated hemoglobin. These findings, coupled with our earlier report that large vessel peripheral arterial disease but not isolated small vessel peripheral arterial disease was independently predictive of subsequent mortality, suggest that large vessel peripheral arterial disease and isolated small vessel peripheral arterial disease are epidemiologically, as well as pathophysiologically, distinct entities.

Adult↗
PubMed1989

Anatomy and pathophysiology of varicose veins.

The venous anatomy of the leg is described with special reference to the superficial venous system. The histologic and histochemical differences between varicose and normal veins are presented. The pathophysiology of varicose veins is related to congential or acquired abnormalities of the deep venous system, venous valves, and/or fascial or vein wall weakness. Increased deep venous pressure may be both proximal and distal in etiology, arising from arteriovenous anastomoses, incompetent communicating veins, or venous obstruction. Primary valvular incompetence arises from venous obstruction (thrombosis), thrombophlebitis, or valvular agenesis. Secondary valvular incompetence occurs from deep venous obstruction or increased venous distensibility (usually secondary to circulating estrogens). Finally, fascial weakness of the vein wall or supporting fascia provided a genetic basis for the pathophysiology of varicose veins. Understanding the anatomy and pathophysiology of varicose veins should lead to a more rational and efficacious treatment.

Elastic Tissue↗
PubMed1988

Effects of vibration on steady flow downstream of a stenosis.

A physical model was used to test the effects of vibrations on the position of transition to turbulence (zt) downstream of a constriction. Constrictions were inserted in a length of clear plastic (Tygon) tubing and vibrated. Water was the fluid medium and flow was visualized with India ink. The frequency and velocity of vibration were monitored. For a given constriction and flow velocity, there was a band of frequencies which caused zt to move upstream. This band corresponded to frequencies of flow disturbances as measured with a hot-film anemometer without vibration. Both flow-visualization and hot-film frequencies were correlated via a Strouhal number to the Reynolds number and contraction ratio of the flow. Values of zt decreased with increasing vibration amplitude. The critical Reynolds number for turbulence was also decreased by vibration. These results are of importance in the diagnosis of vascular disease and the design of physical models of stenotic flows.

Arterial Occlusive Diseases↗
PubMed1988

New method for ultrasonic Doppler probe angle determination.

A new method is described to determine the Doppler probe angle using a standard pulsed Doppler; the technique is based on the determination of vessel position with respect to the skin surface. The transit times of ultrasound waves toward the vessel from multiple probe positions on the skin, the distance between probe positions, and the probe-skin angle are measured. Using the probe-skin angle and the slope of the regression curve, the vessel-skin angle is determined trigonometrically. Experimental results show high accuracy within a vessel-skin angle range of 5-40 degrees.

Mathematics↗
PubMed1988

Shear-layer detection in poststenotic flow by spectrum analysis of Doppler signals.

Spectrum analysis of the Doppler signals was performed 0.5 tube diameters downstream from an axisymmetric constriction with an area reduction of 80 percent in steady flow at a jet Reynolds number of 2840. Both pulsed and continuous wave (CW) Doppler spectra showed significant reverse flow components in the separated flow. The pulsed Doppler spectra exhibited sudden changes when the sample volume crossed the shear layer between the center jet and the separated flow. A power spectrum equation was theoretically derived from continuity of flow to define the Doppler shift frequency for the shear layer velocity. The CW Doppler spectrum showed a minimum spectrum density at a frequency which equalled the shear layer Doppler shift frequency derived from the equation. The pulsed spectra exhibited the sudden changes at the same frequency as well.

Blood Flow Velocity↗
PubMed1988

The role of non-invasive vascular studies in determining levels of amputation.

Various non-invasive vascular studies have been reported to provide valuable data for selection of the optimum level of amputation in limbs in patients who have vascular disease. We evaluated three such methods: (1) measurement of the change in the transcutaneous PO2 after inhalation of oxygen; (2) determination, by the Doppler method, of segmental blood pressure; and (3) measurement of the temperature of the skin. The records of eighty patients (ninety amputations) were retrospectively reviewed for correlations between the results of the vascular studies and the outcome of the amputation. Measurement of transcutaneous PO2 was found to be the most accurate predictor of successful healing of an amputation; the other two measurements were less reliable. The values for transcutaneous PO2 both at rest and after inhalation of oxygen were significantly different (p less than 0.001) for the patients who had a healed amputation compared with those who had a failed amputation. Regardless of the initial value, if, after inhalation of oxygen, the transcutaneous PO2 reached ten millimeters of mercury or more, it predicted healing of the amputation stump with a sensitivity of 98 per cent. When the level of amputation was selected on the basis of clinical judgment at the time of operation, the sensitivity was only 90 per cent.

Adult↗
PubMed1987

Analysis of break frequencies downstream of a constriction in a cylindrical tube.

Experiments were performed to correlate steady-flow power spectra downstream of a stenosis in a cylindrical tube with the flow geometry and velocity. The experiments were motivated by the need to improve quantitative phonoangiography. An objective break frequency (fb) was computed from spectra of velocity fluctuations, as measured with a hot film anemometer. Least squares fits with two independent variables were used to find an empirical relationship between a Strouhal number (S2), the contraction ratio (ds/D) and the Reynolds number (Re). The variables D and ds, are, respectively, the unobstructed tubing diameter and the inner diameter of the stenosis. The relationship found was S2 = Re 0.72(ds/D)0.26 The contraction ratio ds/D, can be found from the empirical relation in terms of known parameters. For the hot wire data the average error between the computed value of ds/D and the known value was 2.3%.

Arterial Occlusive Diseases↗
PubMed1987

The value of power frequency spectrum analysis in the identification of aortoiliac artery disease.

Prediction and localization of significant proximal occlusive disease in the lower extremities, whether in isolation or in combination with significant distal disease, still represent major problems to the noninvasive vascular laboratory. Power frequency spectrum analysis (PFSA) was done on continuous-wave Doppler signals in the common femoral artery of 86 limbs in 50 patients before and after postocclusive reactive hyperemia testing in an effort to differentiate hemodynamically significant from insignificant proximal occlusive disease, whether in isolation or in combination with hemodynamically significant distal disease. Limbs were assigned to four different categories according to their angiographic findings. With the use of a bandwidth at 50% peak amplitude (f50%) of 2000 Hz as the cut-off point between a positive and a negative examination, the test was 93% sensitive, 90% specific, and 92% accurate in distinguishing hemodynamically significant proximal lesions from hemodynamically insignificant lesions, regardless of distal disease. In addition, there exists a small group with significant disease at or close to the site of Doppler sampling, which produces f50% values of more than 3000 Hz. Diagnosis in this subgroup was much like that in carotid disorders. Finally, the predictive accuracy of standard noninvasive Doppler/segmental pressure measurement was compared with results of PFSA. In most patients, standard measurements were comparable; however, in the subgroup with hemodynamically significant proximal and distal disease, the PFSA technique accurately predicted hemodynamically significant proximal diseases in 93% of patients, where combined pressure/Doppler testing had an accuracy of only 61%. In all, spectrum analysis of common femoral artery velocity signals can greatly aid in determining the presence or absence of significant proximal disease in all situations.

Aorta, Abdominal↗
PubMed1986

Photoplethysmographic evaluation of the relationship between skin reflectance and skin blood volume.

Although photoplethysmography can be used successfully to determine venous recovery time, it cannot be used in tests which rely on a determination of the blood volume change (e.g. maximum venous outflow). In seeking an explanation for this inadequacy it was shown that although the photoplethysmograph is able to indicate changes in reflectance, it is incapable of measuring reflectance, per se; information which is essential for an accurate calculation of venous volume decrease. A minor modification of the system enables relative reflectance measurements to be made. Measurements were performed under in vitro conditions to establish the skin-reflectance/skin-blood volume relationship; photon diffusion theory is then used to describe the skin-reflectance/skin-blood volume relationship and to determine the scattering and absorption coefficients of skin and whole blood.

Blood Volume↗