Effect of systolic flow rate on the prediction of effective prosthetic valve orifice area

The Gorlin equation for the hemodynamic assessment of valve area is commonly used in cardiac catheterization laboratories. A study was performed to test the prediction capabilities of the Gorlin formula as well as the Aaslid and Gabbay formula for the effective orifice area of prosthetic heart valves. Pressure gradient, flow, and valve opening area measurements were performed on four 27 mm valve prostheses (two mechanical bileaflet designs, St. Jude and Edwards-Duromedics, an Edwards pericardial tissue valve, and a trileaflet polyurethane valve) each mounted in the aortic position of an in vitro pulse duplicator. With the known valve orifice area, a different discharge coefficient was computed for each of the four valves and three orifice area formulas. After some theoretical considerations, it was proposed that the discharge coefficient would be a function of the flow rate through the valve. All discharge coefficients were observed to increase with increasing systolic flow rate. An empirical relationship of discharge coefficient as a linear function of systolic flow rate was determined through a regression analysis, with a different relationship for each valve and each orifice area formula. Using this relationship in the orifice area formulas improved the accuracy of the prediction of the effective orifice area with all three formulas performing equally well.     

A Nitrogen Pressure-Shearing Apparatus for Preparing Distinct Populations of Chromatin Fractions

A method for preparing reproducible chromatin fractions is described. Fragmentation is accomplished by expelling whole chromatin from an enclosed stainless-steel chamber through a restricted orifice utilizing low nitrogen pressure. Sheared chromatin is fractionated into two distinct heavy and light fractions by centrifugation on 5–20% linear sucrose gradient.     

Truncus arteriosus: A method for correcting right pulmonary artery stenosis created by pulmonary artery banding

Pulmonary artery banding can produce significant distortion of the branch pulmonary arteries including selective stenosis of one artery and only minor narrowing of the other. This may complicate total repair of the underlying anomaly. A successful technique is described for revising a severely stenotic orifice of the right pulmonary artery in truncus arteriosus.     

Preliminary studies on the effect of the Burkard alternate orifice on airborne fungal spore concentrations

The Burkard 7-day spore trap with standard orifice is commonly used by researchers in sampling outdoor air. The alternate orifice is reported to have higher efficiency in collecting small airborne fungal spores; however, no previous studies compared Burkard samplers with different orifices. This study was conducted to study the effect of the alternate orifice on the concentration of airborne fungal spores. Air samples were collected from July to October 2005 with two Burkard spore traps, one had the standard orifice and the second had the alternate orifice. The two spore traps were located on the roof of a building (12 m height) at the University of Tulsa, Oklahoma. Burkard daily slides were analyzed for airborne spores by light microscopy. The data from the two samplers were statistically analyzed using t-tests. The results indicated that the alternate orifice had significantly higher concentrations of Penicillium/Aspergillus-type spores and basidiospores than the standard orifice. By contrast, the standard orifice had significantly higher concentrations of Alternaria, ascospores, and other spores than the alternate orifice. The alternate orifice can be used to increase the efficiency of trapping small spores, which can be underestimated by using the standard orifice. However, additional comparison in other months of the year is recommended.     

A computational procedure for prediction of structural effects of edge-to-edge repair on mitral valve

Edge-to-edge technique is a surgical procedure for the correction of mitral valve leaflets prolapse by suturing the edge of the prolapsed leaflet to the free edge of the opposing one. Suture presence modifies valve mechanical behavior and orifice flow area in the diastolic phase, when the valve opens and blood flows into the ventricle. In the present work, in order to support identification of potentially critical conditions, a computational procedure is described to evaluate the effects of changing suture length and position in combination with valve size and shape. The procedure is based on finite element method analyses applied to a range of different mitral valves, investigating for each configuration the influence of repair on functional parameters, such as mitral valve orifice area and transvalvular pressure gradient, and on structural parameters, such as stress in the leaflets and stitch tension. This kind of prediction would ideally require a coupled fluid-structural analysis, where the interactions between blood flows and mitral apparatus deformation are simultaneously considered. In the present study, however, an alternative approach is proposed, in which results obtained by purely structural finite element analyses are elaborated and interpreted taking into account the Bernoulli type equations available in literature to describe blood flow through mitral orifice. In this way, the effects of each parameter in terms of orifice flow area, suture loads, and leaflets stresses can be expressed as functions of atrioventricular pressure gradient and then correlated to blood flow rate. Results obtained by using this procedure for different configurations are finally discussed.     

Deformability and other rheological interactions of red blood cells in electronic cell sizing

The red blood cell apparent-size spectrum, obtained using resistive pulse spectroscopy (RPS) with typical electrical response times, is characterized by a bimodality, which in turn is quantified by a bimodality index. The magnitude of the index reflects the nonuniformity in distribution of particle trajectories within the orifice, itself a function of cell deformability. In measurements of mixed populations of glutaraldehyde-fixed and native cells, the index is found to be linearly dependent on the fraction of deformable cells. The index, previously known to be a function of flow rate, is now found to be a function of the electric field strength within the orifice as well. Furthermore a previously reported time-dependent loss of bimodality, for the uncounted cells remaining in a counting-vial suspension, appears to be a function of the electric field strength far outside the orifice. The relationship between the pressure drop across the orifice and the average linear fluid velocity through the orifice has been measured, and it is concluded that the flow within the orifice is non-turbulent, at all but the highest flow rates. The non-turbulent flow condition, coupled with the short resident time within the orifice, implies that the observed selection of different trajectories (as a function of cell deformability) must take place well in front of the orifice.     

The automated multiparameter analyzer for cells (AMAC) IIA, a true bridge circuit Coulter-type electronic cell volume transducer.

A true bridge Coulter effect (electronic cell volume) transducer has been developed. All resistances of this bridge are now the result of current flow through saline channels. Contamination by electrode products including gas bubbles has been completely eliminated since both power electrodes are now remote from the flow chamber. Since the orifice is in series with an approximately 10 K ohm resistance generated by a gel-filled capillary and a displacement rheostat, it floats electrically, at virtual ground. The other side of the bridge consists of a fluid side-wire. Removing the power electrode from the orifice outlet makes possible downward flow and the use of a single outer sheath, and eliminates noise generated by gas bubbles which could possibly be trapped. It should now be possible to combine this design with that of the AMAC III square orifice, to produce an electro-optical sorter where all parameters are measured simultaneously. This true bridge circuit possesses the further advantage that noise due both to the power supply and to overvoltage at the power electrodes is common-mode rejected, and any drift due to changes in electrode polarization is eliminated. Preliminary experiments confirm results with the AMAC II that hemoglobinopathies can be recognized by the increased coefficient of variation (CV) of the erythrocyte spectra.     

Roentgeno-functional studies in ectopia of the anal canal in children

Analysis of x-ray data on 70 pediatric patients aged one day-15 yrs, was performed. In 55 cases the investigation was conducted before the correction of ectopia of the anal canal, in 11 cases after the previously described operation for forming the anal orifice (FAO), in 4 cases there was stenosis of the anal orifice without ectopia. Radiograms performed during irrigoscopy and (or) with a Foley catheter were assessed. Weakening and then complete incompetence of the puborectal muscle, determining incontinence of feces, were shown to be proportional to age and a degree of stenosis of the colon orifice. A necessity of radical operation in the second half-year of the life or measures to ensure adequate bowel evacuation were shown.     

Flow-system measurement of cell impedance properties.

A flow-system technique has been developed that detects the high-frequency resistance and capacitance changes in a sensing orifice due to the passage of cells through the orifice. The resistance and capacitance changes are related to cell properties such as size, plasma membrane capacitance, and electrical resistivity of the cell interior. The relationship between measured impedances and cellular properties is discussed, and the prototype instrument for making such measurements is described. The instrument can simultaneously detect the dc Coulter volume and two ac parameters related to the complex ac impedance change. Some initial tests of the instrument using plastic microspheres and Chinese hamster ovary cells are described.     

A new automated method for the quantification of mitral regurgitant volume and dynamic regurgitant orifice area based on a normalized centerline velocity distribution using color M-mode and continuous wave Doppler imaging

Previous echocardiographic techniques for quantifying valvular regurgitation (PISA) are limited by factors including uncertainties in orifice location and hemispheric convergence assumption. Using computational fluid dynamics simulations, we developed a new model for the estimation of orifice diameter and regurgitant volume without the aforementioned assumptions of the PISA technique. Using experimental data obtained from the in vitro flow model we successfully validated our new model. The model output (y) and reference (x) values were in close agreement (y = 0.95x + 0.38, r = 0.96, error = 1.68 +/- 7.54% for the orifice diameter and y = 1.18x - 4.72, r = 0.93, error = 6.48 +/- 16.81% for the regurgitant volume).     

An arbitrary classification of the pore systems in avian eggshells

An arbitrary classification of the pore systems in shells has been based on the observations made during a survey with a scanning electron microscope of the eggs of c. 60 avian species. The classification is intended primarily to aid comparative studies of shell function and field studies of the overall contribution of the shell to the embryo's well-being. The location and form of the external orifice of the pore was used to define four major types of pore systems: (1) outer orifice open—the pore canal terminates at the surface of the shell; (2) outer orifice occluded—the pore canal terminates at the surface of the shell but the orifice is occluded by amorphous, waxy material; (3) outer orifice capped—the pore canal terminates at the outer edge of the true shell and its orifice is capped and, in many species, plugged by a stratum of vesicles, either organic or inorganic, which clothes the entire surface of the shell, and (4) outer orifice reticulate—the pore canal terminates at the edge of the column layer and its orifice is covered by a calcareous stratum containing a plexus of tubules. Each group was further divided on the form of the pore canals; shells having unbranched pore canals were put into one category and those in which some pores branched into another.     

Electrical Sizing of Particles in Suspensions: I. Theory

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.     

Formation and ultrastructure of the micropylar apparatus in Bombyx mori ovarian follicles

The formation of the micropylar apparatus during oogenesis in the silkworm, Bombyx mori, has been studied using light and transmission electron microscopy. The micropylar apparatus is formed by three types of cells: the micropylar channel-forming cells (MCFCs), the micropylar orifice-forming cells (MOFCs), and the micropylar rosette-forming cells (MRFCs). During the formation of the vitelline membrane and the chorion, each of the MCFCs extends a cytoplasmic projection serving as the mold of a micropylar-channel into the egg envelopes. The detachment and collapse of the projections takes place at the end of choriogenesis. The micropylar channels possess a common external orifice on the chorion and several internal orifices within the vitelline membrane. The MOFCs interact closely with the MCFCs and contribute to the formation of the external micropylar orifice. A petal-like rosette surrounding the orifice is imprinted on the outer chorionic surface by the MRFCs which enclose a group of the MCFCs and MOFCs.     

Influence of structural geometry on the severity of bicuspid aortic stenosis

Doppler-derived gradients may overestimate total pressure loss in degenerative and prosthetic aortic valve stenosis (AS) due to unaccounted pressure recovery distal to the orifice. However, in congenitally bicuspid valves, jet eccentricity may result in a higher anatomic-to-effective orifice contraction ratio, resulting in an increased pressure loss at the valve and a reduced pressure recovery distal to the orifice leading to greater functional severity. The objective of our study was to determine the impact of local geometry on the total versus Doppler-derived pressure loss and therefore the assessed severity of the stenosis in bicuspid valves. On the basis of clinically obtained measurements, two- and three-dimensional computer simulations were created with various local geometries by altering the diameters of the left ventricular outflow tract (LVOT; 1.8-3.0 cm), orifice diameter (OD; 0.8-1.6 cm), and aortic root diameter (AR; 3.0-5.4 cm). Jet eccentricity was altered in the models from 0 to 25 degrees. Simulations were performed under steady-flow conditions. Axisymmetric simulations indicate that the overall differences in pressure recovery were minor for variations in LVOT diameter (<3%). However, both OD and AR had a significant impact on pressure recovery (6-20%), with greatest recovery being the larger OD and the smaller recovery being the AR. In addition, three-dimensional data illustrate a greater pressure loss for eccentric jets with the same orifice area, thus increasing functional severity. In conclusion, jet eccentricity results in greater pressure loss in bicuspid valve AS due to reduced effective orifice area. Functional severity may also be enhanced by larger aortic roots, commonly occurring in these patients, leading to reduced pressure recovery. Thus, for the same anatomic orifice area, functional severity is greater in bicuspid than in degenerative tricuspid AS.     

A formulation for calculating the translational velocity of a vortex ring or pair

Cephalopods, among other marine animals, use jet propulsion for swimming. A simple actuator is designed to loosely mimic pulsatile jet formation in squid and jellyfish. The actuator is comprised of a cavity with an oscillating diaphragm and an exit orifice. Periodic oscillation of the diaphragm results in the formation of an array of vortex rings and eventually could generate a periodic pulsatile jet. A general formulation for calculating the velocity of a steadily translating vortical structure in two-dimensional and axi-symmetric shear flows is presented. This technique is based on taking the variational derivative of an energetic function at its critical point. This technique is general, applicable to vortices in liquid and gas media, with no limitation on the relative size of the vortex core. The technique is then implemented to estimate the translational velocity of a vortex ring in a Helmholtz vortex ring generator.     

A three-dimensional insight into the complexity of flow convergence in mitral regurgitation: adjunctive benefit of anatomic regurgitant orifice area

Mitral effective regurgitant orifice area (EROA) using the flow convergence (FC) method is used to quantify the severity of mitral regurgitation (MR). However, it is challenging and prone to interobserver variability in complex valvular pathology. We hypothesized that real-time three-dimensional (3D) transesophageal echocardiography (RT3D TEE) derived anatomic regurgitant orifice area (AROA) can be a reasonable adjunct, irrespective of valvular geometry. Our goals were to 1) to determine the regurgitant orifice morphology and distance suitable for FC measurement using 3D computational flow dynamics and finite element analysis (FEA), and (2) to measure AROA from RT3D TEE and compare it with 2D FC derived EROA measurements. We studied 61 patients. EROA was calculated from 2D TEE images using the 2D-FC technique, and AROA was obtained from zoomed RT3DE TEE acquisitions using prototype software. 3D computational fluid dynamics by FEA were applied to 3D TEE images to determine the effects of mitral valve (MV) orifice geometry on FC pattern. 3D FEA analysis revealed that a central regurgitant orifice is suitable for FC measurements at an optimal distance from the orifice but complex MV orifice resulting in eccentric jets yielded nonaxisymmetric isovelocity contours close to the orifice where the assumptions underlying FC are problematic. EROA and AROA measurements correlated well (r = 0.81) with a nonsignificant bias. However, in patients with eccentric MR, the bias was larger than in central MR. Intermeasurement variability was higher for the 2D FC technique than for RT3DE-based measurements. With its superior reproducibility, 3D analysis of the AROA is a useful alternative to quantify MR when 2D FC measurements are challenging.     

Basic principles of electrical sizing of cells and particles and their realization in the new instrument "Metricell".

To understand the basic events during the passage of particles through the Coulter orifice, three experiments were performed. (1) The denpendence of the volume results on the particle path has been shown by ink-colored particle beams. (2) The deformation and alignment of cells during their passage through the orifice have been photographed by a nano-second photographing technique. (3) The absolute volume evaluation of particles has been studied with model particles in enlarged model orifices of different lengths. A new compact sizing instrument, "Metricell," equipped with a particle-independent electrical calibrating system, is described.     

Analysis of pharyngeal resistance and genioglossal EMG activity using a model of orifice flow.

A model of orifice flow has been used to analyze the relationships among pressure, flow, and genioglossal electromyographic activity in the human pharynx during inspiration. The orifice flow model permits one to assess the character of airflow (laminar or turbulent) and to estimate the cross-sectional area of the orifice from pressure and flow measurements. On the basis of other data (J. Appl. Physiol. 73: 584-590, 1992), this analysis suggests that pharyngeal airflow is turbulent. Furthermore the area of the pharynx appears to increase as flow increases, but the actual change in pharyngeal diameter necessary to fit the pressure-flow data is quite small (0.11-0.87 cm, depending on the assumptions in the model). The flow-related increase in orifice area can be attributed, in part, to the activation of the genioglossus muscle. However, other flow-related factors may also contribute to pharyngeal dilation as airflow increases. Different airway shapes (circular and elliptical) and orientations (major axis anteroposterior and lateral) were incorporated into the model calculations; these factors modify considerably the apparent efficiency of genioglossal electromyographic activity. Genioglossal muscle shortening increases pharyngeal area and reduces pharyngeal resistance more effectively when the pharynx is elliptical, with the long axis of the ellipse oriented laterally. Hence the genioglossus may operate at a significant mechanical disadvantage in those patients with obstructive sleep apnea with a small sagittally oriented pharyngeal lumen.     

Design of static mixers for inclined tubular photobioreactors

Static mixers, which improve gas-liquid mass transfer inside tubular photobioreactors and move the cells between the upper and lower parts of the tubes were designed. Each static mixer was equipped with an opening (v-cut slit) at the top (for gas dispersion) and an orifice at the lower part (for liquid circulation). When the static mixers were installed in the riser tube of an inclined tubular photobioreactor, vertical movement of the liquid was induced so that cells were moved between the surface and bottom part of the photobioreactor. The mass transfer rates in the tubular photobioreactor without static mixers decreased sharply when they were scaled up by increasing the tube diameters. However, by installation of static mixers, the mass transfer rates in 12.5-cm diameter tubes were almost as high as those of 3.8-cm tubes without static mixers. The effectiveness of the static mixers in improving the mass transfer characteristics of the tubular photobioreactors was higher in large than small diameter tubes. The ratio of the diameters of the static mixers to the diameter of the tube, the areas of the v-cut slits and the orifice were the important design parameters that affected the mass transfer characteristics. The gas hold up and and k_La were higher when the areas of the slits (v-cut) and the orifice were reduced.     

A new approach for the evaluation of the severity of coarctation of the aorta using Doppler velocity index and effective orifice area: in vitro validation and clinical implications

Early detection and accurate estimation of COA severity are the most important predictors of successful long-term outcome. However, current clinical parameters used for the evaluation of the severity of COA have several limitations and are flow dependent. The objectives of this study are to evaluate the limitations of current existing parameters for the evaluation of the severity of coarctation of the aorta (COA) and suggest two new parameters: COA Doppler velocity index and COA effective orifice area. Three different severities of COAs were tested in a mock flow circulation model under various flow conditions and in the presence of normal and stenotic aortic valves. Catheter trans-COA pressure gradients and Doppler echocardiographic trans-COA pressure gradients were evaluated. COA Doppler velocity index was defined as the ratio of pre-COA to post-COA peak velocities measured by Doppler echocardiography. COA Doppler effective orifice area was determined using continuity equation. The results show that peak-to-peak trans-COA pressure gradient significantly increased with flow rate (from 83% to 85%). Peak Doppler pressure gradient also significantly increased with flow rate (80-85%). A stenotic or bicuspid aortic valve increased peak Doppler pressure gradient by 20-50% for a COA severity of 75%. Both COA Doppler velocity index and COA effective orifice area did not demonstrate significant flow dependence or dependence upon aortic valve condition. As a conclusion, COA Doppler velocity index and COA effective orifice area are flow independent and do not depend on aortic valve conditions. They can, then, more accurately predict the severity of COA.