Julius Melbin

Bio: Julius Melbin is an academic researcher from University of Pennsylvania. The author has contributed to research in topics: Deformation (engineering) & Korotkoff sounds. The author has an hindex of 13, co-authored 29 publications receiving 777 citations.

Reduced Models of Arterial Systems

Abstract: Simple models that manifest input impedances of arterial systems are compared. An improvement upon documented two-, three-, and five-element models is presented. The classical two-element model (the windkessel) accounts for the lowest frequency components, and the three-element model (the modified windkessel) accounts for both low-and high-frequency components of the spectrum of interest. Five-element models, however, by allowing for reflection, can account for principal features over the entire frequency range of interest.

Hereditary defects of the conotruncal septum in Keeshond dogs: pathologic and genetic studies.

Abstract: Pathologic studies of a hereditary cardiovascular defect in Keeshond dogs demonstrated a spectrum of malformations, primarily involving the ventricular outflow tracts. Lesions ranged from subclinicai defects of the crista supraventricularis to end-stage tetralogy of Fallot and included isolated ventricular septal defects and pulmonic stenosis. The spectrum can be explained by assuming that the anatomic variations represent different thresholds along a continuum of maldevelopment producing hypoplasia and malpositioning of the conotruncal septum. The results of breeding experiments conducted in a colony of Keeshond dogs with conotruncal septal defects confirmed the hereditary nature of the abnormality but were not consistent with any simple genetic hypothesis. Both the incidence and the severity of the conotruncal lesions increased with the severity of the parental defect. The results are shown to fit a polygenic model with three developmental thresholds, in which multiple genes act additively to produce a continuous distribution of maldevelopment involving the conotruncal septum. Lesions of increasing severity occur with an increasing “dose” of genes predisposing to conotruncal septal defects.

The Krotkoff sound

Abstract: As the auscultatory method of blood pressure measurement relies fundamentally on the generation of the Korotkoff sound, identification of the responsible mechanisms has been of interest ever since the introduction of the method, around the turn of the century. In this article, a theory is proposed that identifies the cause of sound generation with the nonlinear properties of the pressure-flow relationship in, and of the volume compliance of the collapsible segment of brachial artery under the cuff. The rising portion of a normal incoming brachial pressure pulse is distorted due to these characteristics, and energy contained in the normal pulse is shifted to the audible range. The pressure transient produced is transmitted to the skin surface and stethoscope through deflection of the arterial wall. A mathematical model is formulated to represent the structures involved and to computer the Korotkoff sound. The model is able to predict quantitatively a range of features of the Korotkoff sound reported in the literature. Several earlier theories are summarized and evaluated.

Reducing stress at vascular graft anastomoses

Abstract: Methods for attaching prostheses to natural vessels are disclosed. Prosthetic vessels having improved resistance to occlusion by tissue reaction upon implantation by reducing transmural stresses are also disclosed. Prostheses having elliptical cross-sections governed by the maximum strain expected in the natural vessel and possessing a higher bulk compliance than previous designs are provided. Additionally, novel methods are presented for implanting improved prostheses by using angled bias cuts to produce an elliptical cross-section at each end of the natural vessel section receiving the prosthesis. In accordance with preferred embodiments, vessels are provided where the cross-sectional geometry is approximated by the equations: a=r.sub.0 [1+2e(2+e)].sup.1/2 and b=r.sub.0.

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals Part 1: Blood Pressure Measurement in Humans: A Statement for Professionals From the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research

Abstract: Accurate measurement of blood pressure is essential to classify individuals, to ascertain blood pressure-related risk, and to guide management. The auscultatory technique with a trained observer and mercury sphygmomanometer continues to be the method of choice for measurement in the office, using the first and fifth phases of the Korotkoff sounds, including in pregnant women. The use of mercury is declining, and alternatives are needed. Aneroid devices are suitable, but they require frequent calibration. Hybrid devices that use electronic transducers instead of mercury have promise. The oscillometric method can be used for office measurement, but only devices independently validated according to standard protocols should be used, and individual calibration is recommended. They have the advantage of being able to take multiple measurements. Proper training of observers, positioning of the patient, and selection of cuff size are all essential. It is increasingly recognized that office measurements correlate poorly with blood pressure measured in other settings, and that they can be supplemented by self-measured readings taken with validated devices at home. There is increasing evidence that home readings predict cardiovascular events and are particularly useful for monitoring the effects of treatment. Twenty-four-hour ambulatory monitoring gives a better prediction of risk than office measurements and is useful for diagnosing white-coat hypertension. There is increasing evidence that a failure of blood pressure to fall during the night may be associated with increased risk. In obese patients and children, the use of an appropriate cuff size is of paramount importance.

Estimation of Central Aortic Pressure Waveform by Mathematical Transformation of Radial Tonometry Pressure Validation of Generalized Transfer Function

Abstract: Background Central aortic pressures and waveform convey important information about cardiovascular status, but direct measurements are invasive. Peripheral pressures can be measured noninvasively, and although they often differ substantially from central pressures, they may be mathematically transformed to approximate the latter. We tested this approach, examining intersubject and intrasubject variability and the validity of using a single averaged transformation, which would enhance its applicability. Methods and Results Invasive central aortic pressure by micromanometer and radial pressure by automated tonometry were measured in 20 patients at steady state and during hemodynamic transients (Valsalva maneuver, abdominal compression, nitroglycerin, or vena caval obstruction). For each patient, transfer functions (TFs) between aortic and radial pressures were calculated by parametric model and results averaged to yield individual TFs. A generalized TF was the average of individual functions. TFs varied among patients, with coefficients of variation for peak amplitude and frequency at peak amplitude of 24.9% and 16.9%, respectively. Intrapatient TF variance with altered loading (>20% variation in peak amplitude) was observed in 28.5% of patients. Despite this, the generalized TF estimated central arterial pressures to ≤0.2±3.8 mm Hg error, arterial compliance to 6±7% accuracy, and augmentation index to within −7% points (30±45% accuracy). Individual TFs were only marginally superior to the generalized TF for reconstructing central pressures. Conclusions Central aortic pressures can be accurately estimated from radial tonometry with the use of a generalized TF. The reconstructed waveform can provide arterial compliance estimates but may underestimate the augmentation index because the latter requires greater fidelity reproduction of the wave contour.

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals: Part 1: Blood Pressure Measurement in Humans: A Statement for Professionals From the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research

Abstract: In experimental animals, as in humans, techniques for measuring blood pressure (BP) have improved considerably over the past decade. In this document, we present recommendations for measuring BP in experimental animals with the goal of helping investigators select optimal methods for BP monitoring in the research laboratory. The advantages and disadvantages of various BP measurement methods are discussed and specific recommendations are provided for selecting the optimal technique depending on the study objective. Although indirect techniques that permit only sporadic measurements of BP may be suitable for some purposes, methods for directly measuring BP are generally preferred because of their ability to monitor the highly dynamic nature of BP in a comprehensive fashion. Selection of the methods to be used should ultimately be guided by the study objectives to insure that the techniques chosen are appropriate for the experimental questions being explored.

Heart Disease: A Textbook of Cardiovascular Medicine

Abstract: This third edition of what has now become a well-established textbook in cardiovascular medicine is again edited by Dr Eugene Braunwald with the assistance of 65 other authors who read like a Who's Who of American Cardiology. Since the second edition, 12 new chapters have been added or substituted and others have been significantly revised. The first volume includes Part I on "Examination of the Patient" and Part II on "Normal and Abnormal Circulatory Function." The second volume deals with specific diseases. Part III, "Diseases of the Heart, Pericardium and Vascular System," includes new sections on "Risk Factors for Coronary Artery Disease," "The Pathogenesis of Atherosclerosis," and "Interventional Catheterization Techniques." Part IV, "Broader Perspectives on Heart Disease and Cardiologic Practice," includes new chapters on "Genetics and Cardiovascular Disease," "Aging in Cardiac Disease," and "Cost Effective Strategies in Cardiology." The last 200 pages of the book (Part V) are devoted to

Artificial graft and implantation method

Abstract: An intraluminal grafting system includes a hollow graft which has a proximal staple positioned proximate its proximal end and a distal staple adapted proximate its distal end. The system includes a capsule for transporting the graft through the lumen and for positioning the proximal end of the graft upstream in a lumen which may be a blood vessel or artery. A tube is connected to the capsule and extends to exterior the vessel for manipulation by the user. A catheter is positioned within the tube to extend from the cavity and through the graft to exterior the body. The catheter has an inflatable membrane or balloon proximate the distal end thereof which is in communication via a channel with inflation and deflation means located exterior the vessel. With the inflatable membrane deflated, the capsule is positioned in the lumen and manipulated to a desired location. The inflatable membrane is manipulated by the rod away from the graft. The force exerted by the inflatable membrane and the structure of the staples urges the staples in the vessel wall, retaining the graft in position. The remainder of the intraluminal grafting system is then removed from the corporeal vessel.