Computer simulation of the propagation of contrast medium in a coronary artery during one cardiac cycle.

In some angiographic methods for measurement of mean coronary flow in ml/min, a threshold is applied to 'concentration-distance' curves obtained from a constant rate injection by computing the intravascular contrast medium concentration along the main coronary branches. If the shape of the velocity profile would remain parabolic throughout the cardiac cycle, the correct threshold value would be '50% of the concentration at the injection site'. But, coronary flow being strongly pulsatile, the shape of the velocity profile must be expected to vary appreciably within the cardiac phase. In order to investigate if a single, appropriate threshold value nevertheless exists for a great variety of coronary flow pulses and velocity profiles, the spreading of contrast medium injected continuously in a tube perfused by a time varying flow Q(t) was studied by computer simulation. While the particular time courses of flow and velocity profile appear to be of secondary importance, the ratio 'injection rate to peak coronary flow' has a major impact. If it is equal to or greater than 1, a threshold value of 47% is the best choice. If the ratio is markedly less than 1, no appropriate threshold exists and use of the 47% threshold will result in considerable flow underestimations. This was fully confirmed by measurements of absolute coronary flow performed in patients.

Preliminary analysis of the effects of blood vessel movement on blood flow patterns in the coronary arteries.

Blood flow patterns are believed to be involved in the formation and progression of arterial diseases. It is possible that the normal physiologic movement of blood vessels during the cardiac cycle affects blood flow patterns significantly. For example, the contraction of the heart in systole and subsequent relaxation in diastole create movements of the coronary arteries, as evidenced in real-time angiography. The effects of this movement on coronary artery flow patterns have never been previously analyzed. This work was undertaken to provide a preliminary estimate of the importance of the effects of such physiologic movements on blood flow patterns in the coronary arteries. A Womersley-type solution was used to determine the effect of axial movement on the wall shear rate in a simplified model of the coronary arteries. The pulsatile pressure gradient was derived from previously published coronary artery flow waveforms. The axial movement function was obtained from a three-dimensional reconstruction of a biplanar coronary angiogram. Significant changes in wall shear rate were noted when the movement was taken into account. The maximum and minimum wall shear rates were 10 percent smaller and 107 percent larger in magnitude respectively, and the Oscillatory Shear Index (OSI) was doubled. Most of the changes in wall shear rate were observed in systole, when the pressure gradient is minimal and the movement is strongest. The results indicate that blood vessel movement during the cardiac cycle has a significant effect on hemodynamic phenomena which have been associated with the development of atherosclerosis.

3D determination of the intravascular volume and flow of coronary arteries.

An angiographic method for measurement of absolute coronary blood flow in patients was developed. It is based on 3D-reconstruction of the left or right coronary tree from digitized biplane coronary cineangiograms. The apparatus is presently composed of a 35-mm cinefilm projector with video camera and a 512 x 512 x 8-bits image array processor controlled by a VAX-11/750 computer. First, the parameters of the two projections are determined in the form of two 4 x 3 matrices from a pair of cineframes showing a 4-cm cube bearing markers. The cube is filmed after the coronary injection, with unchanged geometric configuration. The coronary arteries of interest are then 3D-reconstructed from a pair of cineframes showing them fully opacified. This allows the intravascular volumes needed for flow determination to be computed. Preliminary measurements in 12 patients showed that flow values obtained angiographically in the left descending coronary artery correlate well with the values measured simultaneously by thermodilution in the great cardiac vein (Qangio = 0.83 x Qthermo + 16.1 ml, r = 0.87, n = 29).

[Regional coronary flow in ml/min measured with conventional coronarography]. / Débit coronaire régional en ml/min mesuré à partir de coronarographies conventionnelles.

We have developed a new method of measuring absolute coronary blood flow (CBF) in all major branches of the coronary circulation using computer analysis of conventional cineangiograms. A coronary cineangiogram is obtained in any biplane projections at 50 fps and digitized into a 512 x 512 x 8 matrix. The artery is reconstructed in 3D using the x-ray projection matrices calculated from a cube filmed in the same projections. All diameters along the artery are automatically determined. The arterial volume is calculated from the 3D reconstructed true arterial length and diameters. The absolute flow is obtained by dividing the arterial volume filled by contrast medium during the first cardiac cycle following the injection by the duration of that cycle. The method was validated in vivo by comparing LAD flow measured by angiography with great cardiac vein flow simultaneously measured by thermodilution. Ten patients were studied at baseline and during pacing-induced hyperemia at 100 and 120/min. Mean flow was 52.1 ml/min (range 28-93) by angiography and 51.5 ml/min (range 11-115; NS) by thermodilution. The two methods correlated well: r = 0.82, SE = 9.8 ml/min, n = 27, p less than 0.0001. Thus, absolute CBF can be measured by computer analysis of conventional biplane coronary cineangiograms.

3D-reconstruction of coronary arteries in view of flow measurement.

An angiographic method for measurement of absolute coronary blood flow in patients was developed. It is based on 3D-reconstruction of the left or right coronary tree from digitized biplane coronary cineangiograms. The apparatus is presently composed of a 35 mm cinefilm projector with a video camera and a 512 x 512 x 8 bits image array processor controlled by a VAX-11/750 computer. First, the parameters of the two angiographic projections are determined in form of two 4 x 3 matrices from a pair of cineframes showing a 4 cm cube bearing markers. The cube is filmed after the coronary injection, with unchanged geometric configuration. The coronary arteries of interest are then 3D-reconstructed from a pair of cineframes showing them fully opacified. This allows to compute the intravascular volumes needed for flow determination. In vitro experiments showed that the obtained volume are reasonably accurate. For the measurement of coronary flow, the concentration of contrast medium along the involved arteries is computed (in arbitrary units) from two cineframes taken one (or two) cardiac cycle after onset of the injection. This yields a 'concentration-distance' curve per artery. The volume of fluid (contrast medium mixed with blood) which flows into the arteries during this (or these two) cardiac cycle is determined by applying a concentration threshold to the obtained concentration-distance curves. Measurements performed on a constant flow model were satisfying. Preliminary measurements in 12 patients showed that flow values obtained angiographically into the left anterior descending coronary artery correlate well with the values measured simultaneously by thermodilution in the great cardiac vein (Qangio = 0.83 x Qthermo + 16.1 ml, r = 0.87, n = 29).

Morphometry versus densitometry--a comparison by use of casts of human coronary arteries.

Geometric and densitometric methods for quantitative coronary arteriography have generally been compared by use of phantoms simulating arteries with circular lumina ('Hole phantoms'). We have used more adequate phantoms obtained by casting disease-free and atheromatous human coronary arteries. The phantoms, filled with contrast medium, were imaged digitally (1024 x 1024 x 10 matrix) under experimental conditions simulating routine coronary angiography. The angiographic 'diameters' and the densitometric cross-sectional areas of 59 marked lumina were determined in single plane and orthogonal biplane raw images. Geometric calibration was performed by help of a 7F coronary catheter. For the densitometric calibration, we used a 'hole phantom' attached to the image intensifier. The obtained luminal areas were compared to their true values determined previously by planimetry. The mean absolute error of single plane cross-sections obtained geometrically was 1.53 mm2. Biplane imaging reduced it by a factor 2.4 to 0.64 mm2. The corresponding mean absolute errors for densitometry were 0.56 mm2 and 0.51 mm2. Single plane 'diameter' measurements appear thus of very limited value for hemodynamic conclusions. In contrast, biplane geometric quantification was not markedly inferior to single plane and biplane densitometry.

Spatial reconstruction of coronary arteries from angiographic images.

A method for 3D reconstruction of coronary arteries from two angiographic projection views is presented (cinefilm 35 mm, 50 images/s). The geometric information defining the two projections is secured by filming a cube bearing 15 steel markers in the approximate location of the heart. For 3D reconstruction, a pair of images of the cube and two simultaneous images of the coronary tree are digitized on a computer assisted system. Two matrices describing the two projections are obtained from the 15 x 2 x 2 image coordinates of the cube markers. Next, the operator draws with a mouse the approximate centre lines of the coronary arteries to be 3D reconstructed. The program then determines the centre lines and the edges of the vessels in the two images accurately. The 3D centre lines are reconstructed and the true local vessel diameters determined. Intravascular volumes are obtained by summation of elementary volumes. The reconstructed arteries are visualized on a colour TV monitor. Measurements on various phantoms have shown that lengths of a few centimetres can be measured with typically 2% error. The accuracy of volume determination was somewhat less due to the inaccuracy of lumen determination. For real coronary arteries the volume error is estimated to be about 15% because of the poorer image quality.

Morphometric versus densitometric assessment of coronary vasomotor tone--an overview.

The main advantage of the morphometric approach is that the spatial orientation of the vessel with respect to the image intensifier is not very important. Its most severe limitations are that reasonable accuracy can only be obtained with circular lumina, and that accuracy decreases rapidly with the vessel diameter. The densitometric approach is much less dependent on the shape of the lumen and on the correct identification of the vessel wall in the image. A further essential advantage is that one measures directly the cross-sectional area of the vessel instead of a 'diameter' of low haemodynamic relevance. Severe requirements must however be met if the potential accuracy of densitometry is to be fully exploited. The morphometric approach seems thus preferable for absolute or relative diameter measurements on intact vessels, while densitometry is superior in case of irregular or small lumina. Morphometric calibration using the injection catheter can induce non-negligible errors in both approaches. Grid calibration is probably more accurate, but also more tedious. In the densitometric approach, '3D-calibration' by help of a cube of known size allows also determination of the spatial orientation of the vessel in space. This solution requires however biplane imaging.

Identical transcription initiation sites for proinsulin messenger ribonucleic acid in three insulin-expressing tissues.

Proinsulin mRNA was analyzed by RNA blot hybridization from four insulin-expressing tissues of the rat, including adult and fetal pancreas, yolk sac, and an insulinoma cell line (RIN 5F). The proinsulin mRNA transcripts from the insulinoma cell line and fetal pancreatic tissue were estimated to be, respectively, 100 and 50 bases larger than the transcript from adult pancreas. Yolk sac proinsulin mRNA comigrated with the fetal transcript. While glucose is an important regulator of proinsulin mRNA in the adult, there is a marked increase in the concentrations of proinsulin mRNA and insulin in the developing rat, although plasma glucose levels are quite low. Expression of proinsulin mRNA independent of glucose levels is also found in insulinoma tissue. In addition, there is a second TATA sequence upstream of the putative start site in rat insulin II gene, and the transcription initiation site(s) has not been mapped in all of these tissues. These observations suggested that alternative transcription initiation sites may place the genes under different promoter control during development. To map the 5' end of the gene, primer extension was performed using a synthetic oligonucleotide primer complementary to the first 20 bases of the coding portion of the rat insulin I gene. The extended products of the proinsulin mRNAs from adult insulinoma cell line and fetal pancreas were identical and consistent in size with those predicted if transcription occurs at the putative start site. The 3' ends of the proinsulin mRNA transcripts were evaluated by ribonuclease H digestion, and it was shown that the noted size differences could be accounted for by different lengths of 3'-polyadenylation. Northern blot analysis of proinsulin mRNA from animals treated under conditions where mRNA varied from low to high levels failed to show any modulation of polyadenylation. The role of polyadenylation of proinsulin mRNA in the physiological regulation of insulin biosynthesis, if any, is currently unknown.

Thiol-dependent subunit interactions of a major fat cell plasma membrane glycoprotein.

A major glycoprotein fraction of the isolated adipocyte plasma membrane migrated in the 200,000-dalton region of dodecyl sulfate polyacrylamide gels following solubilization in 2% dodecyl sulfate/4M urea at room temperature in the absence of reductant. Limited heat treatment allowed resolution of the glycoprotein into two distinct bands in the same high-molecular-weight region plus a new 94,000-dalton glycoprotein band. Prolonged incubation of solubilized plasma membranes at 100 degrees C for 15-30 min or incubation with reductant resulted in complete conversion of the high-molecular-weight bands to the 94,000-dalton region, indicating dissociation of dimers to the monomeric form. When the dimer bands on column gels were electrophoresed in the second dimension on slab gels in the presence of reductant, no low-molecular-weight bands were observed other than that in the 94,000-dalton region. The effects of limited heat treatment to permit resolution of the two dimers and the extended treatment to convert the dimers to the monomeric form were markedly inhibited by alkylation of the solubilized membrane protein with N-ethylmaleimide or oxidation with H2O2 or diamide. However, these latter treatments did not prevent complete dissociation of dimers due to addition of reductants. These results suggest that two glycoprotein fractions may exist as dimers in the native fat cell plasma membrane. The data are consistent with a model in which the glycoprotein subunits are linked by hydrophobic bonds that are sensitive to reduction of intramolecular disulfides but are stabilized by alkylation or oxidation of the glycoprotein sulfhydryls.