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Biomedical subjects

S E Rittgers

Publications and source records attributed to S E Rittgers.

At least 37 records · Page 2Linked to original sources
PubMed1983

Evaluation of transplant renal artery blood flow by Doppler sound-spectrum analysis.

Doppler ultrasonography sound-spectrum analysis (SSA) was used to evaluate blood flow in the transplanted kidney and its renal artery. Seven patients with posttransplant hypertension and a bruit over the transplanted kidney were screened for renal artery stenosis (RAS). In five patients, RAS was diagnosed by SSA, and in two it was not. These findings were confirmed by subsequent angiography in all patients. Three patients studied after surgical correction of their RAS had improvement in their SSA patterns. Fourteen hypertensive patients with a cause other than RAS were evaluated by SSA. None of them had SSA findings suggestive of RAS. Doppler ultrasonography with SSA is an effective, noninvasive technique of monitoring transplant renal blood flow, especially in the screening of hypertensive transplant recipients for transplant RAS.

Auscultation↗
PubMed1982

Real-time Doppler spectrum analysis: predictive value in defining operable carotid artery disease.

A prospective study compared the sensitivity, specificity, and predictive value of indirect periorbital Doppler screening and direct carotid Doppler interrogation using real-time sound spectrum analysis to detect operable extracranial carotid occlusive disease. The results of noninvasive studies were compared with independently assessed contrast arteriograms of carotid arteries of patients studied for symptomatic cerebrovascular disease. Periorbital Doppler ultrasound was insensitive to carotid stenosis of less than 75% and did not distinguish operable stenosis from inoperable occlusion of the internal carotid artery. Carotid Doppler spectrum analysis was sensitive to 98% of hemodynamically significant disease and correctly discriminated 77% of carotid occlusions, 96% of stenoses larger than 50%, and 70% of stenoses of less than 50%. The predictive value for direct carotid interrogation in identifying carotid occlusion or operable stenosis was 94% and 86%, respectively. Real-time spectrum analysis of direct carotid Doppler signals substantially improves the diagnostic accuracy of noninvasive identification of operable carotid artery disease.

Arterial Occlusive Diseases↗
PubMed1981

Prediction of amputation wound healing. Roles of Doppler ultrasound and digit photoplethysmography.

Segmental limb blood pressures (BPs) measured by Doppler ultrasound and digit photoplethysmography were used to define hemodynamic correlates of wound healing in 122 lower-extremity amputations for ischemia. Healing of digit or transmetatarsal amputations were influenced by the presence of diabetes and correlated better with digit pulsation and BP than with ankle pressure. Healing of below-knee amputation did not correlate with segmental limb BPs. In the absence of an absolute threshold to predict wound healing or failure, caution is urged in using hemodynamic indices to select the level of amputation of arterial insufficiency.

Aged↗
PubMed1981

Audible interpretation of carotid Doppler signals. An improved technique to define carotid artery disease.

Direct interrogation of the common, internal, and external carotid arteries with a bidirectional Doppler detector was performed on 199 vessels in 101 patients. Audible interpretations of normal, disturbed (stenotic), or absent (occluded) flow signals were made by vascular technologists and the results were compared with independently assessed carotid arteriograms. The sensitivity in detecting severe (greater than or equal to 50%) stenosis or occlusion was 9.2%, with correct differentiation of these two conditions in 84% of vessels. Nonobstructive (less than 50%) stenoses were detected in 30% of cases. The specificity in identifying normal carotid arteries was 91%. The predictive values of normal, abnormal, and absent flow signals were 95%, 90%, and 90%, respectively. Direct carotid Doppler signal analysis is more accurate than indirect periorbital Doppler screening in defining carotid stenosis or occlusion.

Adult↗
PubMed1981

Linear relationship between electrical systole, mechanical systole, and heart rate.

The relationship between the duration of electrical systole (QT) and heart rate (HR) and the relationship between the QT interval and total electromechanical systole (QS2) were studied in the resting state in 200 patients (100 males and 100 females) without evidence of cardiovascular disease. A linear relationship was found between the QT and HR in males and females (males, QT = 521 msec - 2.0 HR, r = .91; females, QT = 511 msec - 1.8 HR, r = .90). In 20 male and 20 female subjects, the relationship between QT and QS2 was studied. The QT was slightly shorter but paralleled the QS2 (males QT = 529 msec - 2.1 HR, QS2 = 541 msec - 2.2 HR; females QT = 511 msec - 1.9 HR, QS2 = 540 msec - 2.0 HR). Thus, over the physiologic range of resting HR, a linear relationship exists between QT and HR. The QT interval is slightly shorter but parallels the QS2 in patients without heart disease. These linear relationships permit a direct comparison of the duration of electrical and mechanical systole.

Adult↗
PubMed1979

Changes in diastolic time with various pharmacologic agents: implication for myocardial perfusion.

Diastolic time (DT) is calculated as the cycle length (RR) minus electromechanical systole (QS2). The ratio of DT (RR-QS2) to RR interval times 100, or the percent diastole (%D), varies nonlinearly with heart rate (HR), increasing rapidly with decreasing HR. The effect of commonly used cardioactive agents on %D was studied in five groups of normal subjects. In group 1 (n = 12), propranolol (160 mg daily) increased %D from 55.9 +/- 1.7 to 64.7 +/- 1.3 (p less than 0.001) by slowing HR. In group 2 (n = 12), dobutamine (2.5 micrograms/kg/min) increased %D from 56.4 +/- 1.4 to 61.8 +/- 1.3 (p less than 0.005) by shortening the QS2. In group 3 (n = 10), Cedilanid-D (1.6 mg i.v.) increased %D from 55.5 +/- 1 to 63.2 +/- 0.7 (p less than 0.001), both by slowing the HR and shortening the QS2. In group 4 (n = 12), isoproterenol (2 micrograms/min) increased HR and shortened the QS2 significantly. The net result was a significant reduction of %D from 56.1 +/- 1.4 to 53.5 +/- 1.1, (p less than 0.05). In group 5 (n = 15), a 100-mg bolus of i.v. lidocaine did not have a significant effect on %D. This study indicates that cardiovascular drugs may have significant effects on the relative duration of diastole either by affecting HR or the duration of systole. This may have clinical implications for patients with coronary artery disease and patients with left ventricular hypertrophy, since in both cases coronary flow in mostly diastolic.

Administration, Oral↗
PubMed1979

Noninvasive determination of carotid artery operability by Doppler ultrasound.

Indirect periorbital screening techniques may detect obstruction of the extracranial internal carotid artery, but they do not distinguish operable stenosis from inoperable occlusion. In an attempt to overcome this limitation, direct interrogation of carotid artery flow velocity by Doppler ultrasound was added to periorbital screening of 97 arteries in 53 patients. Analysis of results suggests that this assessment can improve diagnostic accuracy and distinguish stenosis from occlusion of the internal carotid arteries in stroke-prone patients.

Aged↗
PubMedDate not supplied

Quantitative analysis of carotid artery Doppler spectral waveforms: diagnostic value of parameters.

Continuous-wave ultrasonic Doppler recordings made at the carotid bifurcation have been processed by spectrum analysis and off-line microprocessor software. Data reduction algorithms were defined and tested prior to incorporation in an integrated, hard-wired device. Subsequent analysis of waveforms in real-time provided measures of peak and mode frequencies and degree of spectral broadening. Correlation of results with 123 angiographically visualized internal carotid arteries showed that peak and mode frequencies generally increased with degree of stenosis while the systolic window decreased. Ratios of peak and mode frequencies in the proximal to the distal internal carotid artery and the systolic window at the distal internal carotid artery were retrospectively found to have diagnostic value with a combination of these three parameters providing the best overall accuracy.

Adult↗
PubMedDate not supplied

Detection of renal artery stenosis: experimental and clinical analysis of velocity waveforms.

Mass screening of hypertensive patients by a noninvasive method could uncover the 10% of those cases where renal artery stenosis is the primary etiology. Treatment by transluminal angioplasty or surgery could replace a long-term medical regimen. To investigate an ultrasonic technique, normal velocity waveforms were obtained from the abdominal aorta, celiac artery and renal arteries in seven mongrel dogs using a 5 MHz, continuous-wave Doppler detector. Renal artery pressure gradients, volume flow rates and velocity recordings were subsequently made during induced proximal renal artery stenoses. The ratio of peak renal artery frequency to peak aortic frequency was 88% sensitive to stenoses of greater than 20 mm Hg pressure gradient, while the renal artery systolic frequency window was 79% sensitive to the same obstructions. Ninety-five hypertensive and vascular surgical patients were examined using a 3 MHz duplex scanner with 175 of the 190 (92%) renal arteries adequately detected (clear signal with high diastolic component). Analysis of velocity waveforms based on peak frequency, proximal to distal peak frequency changes, evidence of flow disturbances and associated bruit were compared to contrast arteriograms in 84 vessels. Of the 76 (90%) arteries adequately examined by duplex scanning, 59 of 61 (97%) with 0-59% diameter reduction, 10 of 12 (83%) with 60-99% diameter reduction and 1 of 3 (33%) occlusions were correctly identified. Velocity waveform analysis can accurately detect renal artery stenosis and may prove effective in mass screening of hypertensive patients for renovascular disease.

Adult↗
PubMedDate not supplied

MR imaging of model fluid velocity profiles.

A projection MR technique for imaging the velocity profiles of moving fluids has been applied to various steady flow models designed to simulate a variety of flow conditions. From such profiles can be readily deduced peak velocities, volume flow rates, information concerning the degree of flow development, features such as flow separation, and estimates shear stresses at the vessel wall.

Blood Flow Velocity↗
PubMedDate not supplied

Computational simulation of biomechanics in e-PTFE and venous Miller's cuffs: implications for intimal hyperplasia.

A computational distal end-to-side Miller's cuff anastomotic model was used to analyse the possible difference in intimal hyperplasia (IH) formed between e-PTFE and venous cuffs. A large strain FEA model was used to compute the strain after physiological loading and the deformed geometries used as wall boundaries for CFD analysis. Regression analysis was performed to investigate relationships between mechanical factors and prior IH. The results showed that the venous Miller's cuff anastomosis deformed twice as much as the e-PTFE cuff and that the expansion of both cuffs generated elevated strains in the artery floor while the fluid shear indices were qualitatively similar in each case. In the e-PTFE cuff, the strain and OSI correlated with IH in a proportional and equivalent manner; however, these regressions grossly over-estimated the predicted IH in the vein cuff. Thus, biomechanical effects may be important in synthetically cuffed anastomoses, but do not account for the reduced IH in venous cuffed anastomoses.

Anastomosis, Surgical↗
PubMedDate not supplied

Particle motion within in vitro models of stenosed internal carotid and left anterior descending coronary arteries.

Asymmetric 75% and 95% area reduction, transparent Sylgard stenotic models were operated under internal carotid artery (ICA) [Womersley parameter, alpha=5.36, Re(mean) =213 and 180, respectively, and Re(peak)=734 and 410, respectively] and left anterior descending coronary artery (LAD) flow wave forms (alpha=2.65, Re(mean)=59 and 57, respectively, and Re(peak)= 137 and 94, respectively) to evaluate the effect of these conditions on particle residence times downstream of the stenoses. Amberlite particles (1.05 g/cm3, 400 microm) were added to the fluid to simulate platelets and their motion through the stenotic region and were traced using a laser light sheet flow visualization method with pseudo-color display. Two-dimensional (2D) particle motions were recorded and particle washout in the stenotic throat and downstream section were computed for all cases. All four model cases demonstrated jetting through the stenosis which followed an arching pattern around a large separation zone downstream. Considerable mixing was observed within these vortex regions during high flow phases. Particle washout profiles showed no clear trend between the degrees of stenosis although particles downstream of the stenoses tended to remain longer for LAD conditions. The critical washout cycle (1% of particles remaining downstream of the stenosis), however, was longer for the 95% stenoses cases under each flow condition due to the larger protected region immediately downstream and maximal for the LAD 95% case. Results of this study suggest that particle residence times downstream of 75% and 95% stenoses (approximately 3-6 s for ICA and approximately 8-10 s for LAD) exceed the minimum time for platelet adhesion (approximately 1 s) for at least 1% of cells and, thus, may be sufficient to initiate thrombus formation under resting conditions.

Biomedical Engineering↗
PubMedDate not supplied

Determination of the prime electrostatic endothelial cell transplantation procedure for e-PTFE vascular prostheses.

The purpose of this study was to evaluate the extent of cellular adhesion (density and morphological maturation), cellular membrane damage, and cellular viability after an electrostatic transplantation of human umbilical vein endothelial cells (HUVECs) onto 6-cm segments of 4-mm I.D. e-PTFE (GORE-TEX) vascular prostheses using a prototype electrostatic endothelial cell transplantation device (EECTD). The electrostatic transplantation parameters evaluated were the apparatus-applied voltage and transplantation time. By our definition, the combination of applied voltage and transplantation time that met the a priori criteria of: 1) maximum transplanted cellular viability, 2) maximum transplantation density, 3) maximum morphological maturation (degree of cellular flattening), and 4) minimal cellular membrane damage would be the prime transplantation procedure. The results of the experimentation indicated that the prime conditions for HUVEC transplantation were obtained when +1.0 V was applied for a transplantation time of 16 min. These conditions achieved an average viable graft surface coverage of 97.4+/-1.6% with an average transplantation density of 73,540+/-8.514 HUVECs/cm2. Furthermore, the transplanted HUVECs were morphologically mature (flattened) with minimal apparent cellular membrane damage (lysis or pitting). The overall clinical significance of this study is that viable endothelial cell transplantation to synthetic vascular grafts can be accomplished at high cellular densities and morphological maturation in 16 min using the EECTD. With the promising in vitro transplantation results, the next logical investigations will include additional in vitro evaluations (cellular retention upon shear stress exposure and biochemical assays) followed by in vivo evaluations to examine thromboresistance and influence on intimal/anastomotic hyperplasia.

Blood Vessel Prosthesis↗
PubMedDate not supplied

Electrostatic endothelial cell seeding technique for small-diameter (<6 mm) vascular prostheses: feasibility testing.

Multiple studies have indicated the importance of surface charge in the adhesion of multiple cardiovascular cell lines including platelets and endothelial cells on the substrate materials (1,4,7-10,12-15). It is the purpose of this article to report a feasibility study conducted using an electrostatic endothelial cell seeding technique. The feasibility study was conducted using human umbilical vein endothelial cells (HUVEC), a static pool apparatus, a voltage source, and a parallel plate capacitor. The HUVEC concentration and seeding times were constant at 560,000 HUVEC/ml and 30 min, respectively. Scanning electron microscopy examination of the endothelial cell adhesion indicated that an induced temporary positive surface charge on e-PTFE graft material enhances the number and the maturation (flattening) of HUVECs adhered. The results indicated that the total number of endothelial cells adhered (70.9 mm2) was increased from 9198 +/- 1194 HUVECs on the control (no induced surface charge) e-PTFE to 22,482 +/- 4814 HUVECs (2.4 x control) on the maximum induced positive surface charge. The total number of cells in the flattened phase of adhesion increased from 837 +/- 275 to 6785 +/- 1012 HUVECs (8.1x) under identical conditions. Thus, the results of the feasibility study support the premise that electrostatic interaction is an important factor in both the endothelial cell adhesion and spreading processes and suggest that the electrostatic seeding technique may lead to an increased patency of small diameter (<6 mm) vascular prostheses.

Blood Vessel Prosthesis↗
PubMedDate not supplied

Electrostatic endothelial cell transplantation within small-diameter (<6 mm) vascular prostheses: a prototype apparatus and procedure.

This article presents a novel, clinically relevant electrostatic endothelial cell transplantation (seeding/sodding) device (U.S. & Foreign Patent Protections Pending) for small-diameter (<6 mm) vascular prostheses. The prototype apparatus was designed and built to tissue engineer 4.0 mm, I.D. GORE-TEX (W.L. Gore & Associates, Inc.) standard wall graft segments varying in length from 4 to 12 cm. The prototype electrostatic endothelial cell transplantation apparatus is composed of an external and internal conductor, aluminum base, end supports, pillow blocks, filling apparatus, electric motor drive system, and a voltage source. The cylindrical capacitor arrangement of the device along with an electrical potential applied across the internal and external conductors creates the unique feature of this endothelial cell transplantation technique, an electric field within the cylindrical capacitor (within the graft lumen) which in turn induces a temporary positive surface charge on the graft (dielectric material) luminal surface. Multiple studies have shown that a positively charged substrate is more conducive to endothelial cell adhesion and morphological maturation (flattening) (1,2, 7,8,10,13-15). This induced positive surface charge dissipates immediately upon removal from the electrostatic endothelial cell transplantation device. Thus, after endothelial cell adhesion the graft luminal surface reverts back to its natural (nonthrombogenic) negative surface charge.

Blood Vessel Prosthesis↗
PubMedDate not supplied

Non-invasive measurement of blood flow-rate in expanded polytetrafluoroethylene grafts.

Four 6 mm e-PTFE grafts were placed subcutaneously into four dogs between the carotid artery and jugular vein to model shunt flow through an access graft. Flow-rates were varied from 120 to 2000 ml/min (N = 42) by use of a cardiac stimulant (Aramine) and external constrictor. Measures of graft flow were made simultaneously by electromagnetic flowmeter (EMF) and Doppler ultrasound based on a known graft diameter, use of a flat-head probe providing a fixed beam-to-vessel angle and derivation of the mean Doppler-shift frequency from first moment computation of the frequency spectra. Correlation coefficients between the Doppler ultrasound and EMF recordings were 0.54, 0.96 and 0.92 at measurement sites just beyond the arterial/graft anastomosis, at the graft loop and just proximal to the graft/venous anastomosis, respectively. Availability of a simple and accurate non-invasive flowmeter for superficially placed e-PTFE grafts may be valuable for evaluating the systemic effects of vascular shunts, for monitoring the patency of access grafts and for assessing the function of bypass grafts for limb ischaemia.

Animals↗