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Biomedical subjects

S M Collins

Publications and source records attributed to S M Collins.

At least 163 records · Page 9Linked to original sources
PubMed1987

Measurement of right ventricular volume using cine computed tomography.

Volume measurements of the right ventricle are clinically important, particularly in the assessment of congenital heart disease. The complex configuration of the right ventricular cavity, however, makes assessment of its volume difficult. Cine computed tomography (CT) permits depiction of cardiac anatomy in parallel, sequential, high-resolution tomographic images. To test whether cine CT would allow accurate, reproducible determination of right ventricular volumes, 11 excised, fixed canine hearts were scanned ex vivo. The endocardial contours of the right ventricular cavity were traced by two independent observers. The right ventricular cavity areas were measured in each image and right ventricular volume calculated by a Simpson's rule approximation. Actual right ventricular volume (range 24-86.5 mL) was measured by cavity fluid capacity. Right ventricular volumes derived from cine CT data correlated closely with actual volumes (R = .96, cine CT volume = 0.99 X [actual volume] + 0.2 mL). Interobserver correlation was excellent (R = .99). It is concluded that cine CT scanning permits accurate, reproducible determination of right ventricular volume ex vivo. This technique should be immediately applicable to the noninvasive evaluation of right ventricular function in children and adults.

Animals↗
PubMed1987

Calcium and contractions of isolated smooth muscle cells from rat myometrium.

Smooth muscle cells were isolated from estrogenized rat myometrium by collagenase digestion. Electron microscopic examination and measurement of cell lengths by image-splitting micrometry were carried out after fixation with acrolein. Mean lengths of cells before and after isolation were 81.7 and 66.9 micron, respectively. Responses of cells were compared with contractions of isolated strips recorded isometrically. Effects of carbachol and KCl were examined in 2 mM Ca, 2 mM Ca + 4 mM EGTA, and 2 mM Ca + 10(-8) M nitrendipine solution. Carbachol and KCl produced concentration-dependent shortening of isolated cells maximal at 30 s after addition. The concentrations of carbachol required to produce shortenings were about 100-fold less than those required to produce isometric contractions; but no major difference was observed in the concentration dependence of cell shortening and isometric contraction produced by potassium-induced depolarization. In 2 mM Ca solution, there was a phasic response, followed by a tonic response such that more than 50% of maximum cell shortening was maintained for 10 min. However, in 2 mM Ca + 4 mM EGTA or 10(-8) M nitrendipine, the tonic contraction was abolished and cells rapidly relaxed after 30 s. If carbachol was added to cells after varying times in the EGTA-containing solution, the ability to initiate a contraction declined exponentially with a half-time of 160 s. Effects of depolarization by KCl were examined in 2 mM Ca plus nitrendipine and 2 mM Ca + 4 mM EGTA solution. Shortening occurred in 2 mM Ca solution by depolarization but not if nitrendipine was added. Though shortening was not observed in 2 mM Ca + 4 mM EGTA solution by KCl, subsequent addition of carbachol induced shortening. These results suggested that there was an intracellular Ca store site from which Ca was released by carbachol and which was not affected by depolarization in the absence of external Ca. No evidence was obtained that the contraction persists in Ca2+-free medium in isolated cells, which is in agreement with previous findings in small muscle strips in which only a similar transient response was obtained.

Animals↗
PubMed1987

Finite element analysis of myocardial diastolic function using three-dimensional echocardiographic reconstructions: application of a new method for study of acute ischemia in dogs.

The effect of acute myocardial ischemia on the myocardial elastic modulus has been a matter of controversy. To evaluate this question, diastolic elastic modulus was assessed by finite element analysis of left ventricular geometry using three-dimensional echocardiographic reconstructions and right and left ventricular pressure recordings. Elastic properties were estimated before and after coronary occlusion in 6 open-chest dogs. Elastic modulus values were derived by means of a computer program that determined the global elastic modulus that best predicted the diastolic changes in left ventricular geometry. In the finite element analysis after coronary occlusion, two analyses were performed: one utilizing the control elastic modulus for all segments of the left ventricle and one in which ischemic (dyskinetic) segments were assigned a higher elastic modulus. Results showed that the control elastic modulus was a poor predictor of diastolic left ventricular expansion after coronary occlusion. The finite element analysis in which the ischemic segments were assigned a higher elastic modulus better predicted ischemic diastolic wall motion patterns. Error values (difference between predicted and actual left ventricular segmental diastolic motion) were: control, 1.9 +/- 0.3 mm (mean +/- SD), ischemia, 2.9 +/- 0.5 mm, and 2.2 +/- 0.4 mm using the stiffer elastic modulus for ischemic segments. Error values were significantly higher (p less than 0.05) under ischemic conditions when the control elastic modulus was uniformly applied compared with control and ischemia with dyskinetic segments assigned a higher elastic modulus. From these data, it is concluded that the myocardial diastolic elastic modulus is increased by ischemia and that this approach may allow clinical assessment of intrinsic muscle stiffness.

Animals↗
PubMed1987

The action of trimebutine maleate on gastrointestinal motility is mediated by opiate receptors in human subjects.

The effects of trimebutine on interdigestive motor activity of the small intestine and the colon were studied in healthy volunteers. Trimebutine induced in all subjects phase III-like motor complexes, which were similar to spontaneously occurring phase III complexes of the interdigestive cycle in antrum and duodenum. Trimebutine-induced complexes were suppressed by naloxone. Trimebutine and/or naloxone had no consistent effect on interdigestive contractile activity in the colon.

Adult↗
PubMed1987

Reversibility of increased intestinal permeability to 51Cr-EDTA in patients with gastrointestinal inflammatory diseases.

Intestinal permeability in adults with inflammatory gastrointestinal diseases was investigated by measuring the 24-h urinary excretion of orally administered 51Cr-EDTA. Eighty controls along with 100 patients with Crohn's disease, 46 patients with ulcerative colitis, 20 patients with gluten-sensitive enteropathy, and 18 patients with other diseases were studied. In controls, the median 24-h excretion was 1.34%/24 h of the oral dose. Patients with Crohn's disease (median 2.96%/24 h), ulcerative colitis (median 2.12%/24 h), and untreated gluten-sensitive enteropathy (median 3.56%/24 h) had significantly elevated urinary excretion of the probe compared to controls (p less than 0.0001). Increased 24-h urinary excretion of 51Cr-EDTA had a high association with intestinal inflammation (p less than 0.0001). Test specificity and sensitivity were 96% and 57%, respectively. A positive test has a 96% probability of correctly diagnosing the presence of intestinal inflammation, whereas a negative test has a 50% probability of predicting the absence of disease.

Adult↗
PubMed1987

Frequency analysis of gut EMG.

The EMG of the gut smooth muscle plays an important role in the regulation of gastrointestinal motility in health and disease. The EMG in general consists of an omnipresent oscillatory electrical control activity (ECA) and spikes or other potentials that result in contractions of the smooth muscle. This paper addresses the question of how the ECA signals can best be processed and how inappropriate transformations of such signals may produce misleading results. The various factors affecting the composition of the gut EMG, in time and space along the gut, are discussed briefly. The need for the analysis of the ECA for its oscillatory nature is mentioned together with details regarding the widely used visual, period, and Fourier analysis techniques. Fourier analysis techniques have been applied with increasing frequency to gut EMG; the various features of Fourier analysis and considerations for their implementation on the computer are discussed. The visual, period, and Fourier analysis approaches as well as their uses and limitations in application to a variety of ECAs of the stomach and of the colon in dogs and humans are illustrated. This study indicates that period analysis techniques are well suited for the study of the visibly oscillatory upper gut EMG, while smoothed spectral analysis is more appropriate for the study of colonic EMG.

Animals↗
PubMed1986

Altered calcium-handling properties of jejunal smooth muscle from the nematode-infected rat.

We examined changes in contractility of jejunal longitudinal muscle from rats infected 8 days previously with the enteric parasite Nippostrongylus brasiliensis. In uninfected control rats, carbachol-induced contraction was maximal at 1 microM carbachol. In muscle from infected rats, there was no change in ED50 for carbachol, but contraction induced by 1 microM carbachol was increased greater than 75% over that in control rats. No significant differences were observed in muscarinic receptor binding characteristics in smooth muscle cells from control and infected rats when [3H]QNB was used as radioligand. Contraction induced by 5-hydroxytryptamine was also substantially greater in muscle from infected rats. In control rats, carbachol-induced contraction was largely independent of extracellular Ca2+, whereas in muscle from infected rats, withdrawing extracellular Ca2+ reduced contraction to below control levels. Furthermore, whereas adding nitrendipine in the presence of extracellular Ca2+ had no effect on carbachol-induced contraction in control rats, it significantly inhibited contraction in muscle from infected rats.

Animals↗
PubMed1986

Comparison of methodologies for the measurement of antroduodenal motor activity in the dog.

We have compared the abilities of intraluminal strain gauges and manometry to record motor activity from the antrum and duodenum of the anesthetized dog. Responses to intraarterial carbachol, vagal stimulation, and field stimulation recorded by these devices were compared to those registered by strain gauges sewn onto the overlying serosa. In the antrum, the perfused tube (PT) recorded 98% and 97% of field- and vagal-stimulated phasic contractions, respectively, compared with 83% and 90% (p less than 0.005) registered by the intraluminal tube-mounted strain gauges (TSGs). In contrast, in the duodenum there was no difference between the accuracy of these devices in recording phasic activity induced by field stimulation (PT 90% and TSG 87%). Similarly, there was no difference between the abilities of these devices to record tonic contraction induced by carbachol in the antrum (PT 87% and TSG 90%) or duodenum (PT 82% and TSG 87%). However, TSGs misrepresented the configuration of phasic or tonic contractions, producing bifid, negative, or biphasic contractions substantially more frequently than did PT (p less than 0.005). These results illustrate that the accuracy of these two commonly used techniques may be influenced by anatomic factors as well as by the type of contraction recorded.

Animals↗
PubMed1986

Measurement of left ventricular mass in vivo using gated nuclear magnetic resonance imaging.

Alterations of left ventricular mass occur in a variety of congenital and acquired heart diseases. In vivo determination of left ventricular mass, using several different techniques, has been previously reported. Problems inherent in some previous methods include the use of ionizing radiation, complicated geometric assumptions and invasive techniques. We tested the ability of gated nuclear magnetic resonance imaging to determine in vivo left ventricular mass in animals. By studying both dogs (n = 9) and cats (n = 2) of various sizes, a broad range of left ventricular mass (7 to 133 g) was examined. With a 0.5 tesla superconducting nuclear magnetic resonance imaging system the left ventricle was imaged in the transaxial plane and multiple adjacent 10 mm thick slices were obtained. Endocardial and epicardial edges were manually traced in each computer-displayed image. The wall area of each image was determined by computer and the areas were summed and multiplied by the slice thickness and the specific gravity of muscle, providing calculated left ventricular mass. Calculated left ventricular mass was compared with actual postmortem left ventricular mass using linear regression analysis. An excellent relation between calculated and actual mass was found (r = 0.95; SEE = 13.1 g; regression equation: magnetic resonance mass = 0.95 X actual mass + 14.8 g). Intraobserver and interobserver reproducibility were also excellent (r = 0.99). Thus, gated nuclear magnetic resonance imaging can accurately determine in vivo left ventricular mass in anesthetized animals.

Animals↗
PubMed1986

Ultrasound study of acoustic properties of the normal canine heart: comparison of backscatter from all chambers.

Much effort has recently been directed toward ultrasound characterization of normal and abnormal left ventricular myocardium. The purpose of this study was to evaluate the normal acoustic properties of all four cardiac chambers as a first step toward tissue characterization of the atria and ventricles. The hypothesis was that integrated ultrasound backscatter would follow the pattern of collagen concentration in the cardiac chambers, being higher in the right side of the heart than in the left and in the atria compared with the ventricles. Seven normal canine hearts, perfusion-fixed in 10% formalin, were examined. Sections of the free walls of right and left ventricles and atria were studied in vitro with a 5 MHz transducer positioned at the focal distance from the epicardium. The radio frequency ultrasound signal energy from each specimen was derived, corrected for sample thickness and expressed as integrated backscatter, in decibel units less than the reflected energy from a stainless steel block. The backscatter was higher from the right ventricle than from the left ventricle (-64.5 +/- 1.25 [mean +/- SEM] [n = 7] versus -73.6 +/- 1.32; p less than 0.05), higher from the right atrium than from the right ventricle (-58.5 +/- 0.83 versus -64.5 +/- 1.25; p less than 0.05) and higher from the left atrium than from the left ventricle (-62.8 +/- 1.14 versus -73.6 +/- 1.32; p less than 0.05). These data show that backscatter is higher in the right ventricle than in the left ventricle and in the atria compared with the ventricles.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustics↗
PubMed1986

Calcium utilization by dispersed canine gastric smooth muscle cells.

Smooth muscle cells were isolated by collagenase digestion from the circular layer of the canine gastric corpus, and cell length was measured by image-splitting micrometry. Cells contracted following incubation with KCl, carbachol, and pentagastrin. While contraction induced by 40 mM KCl was inhibited by adding nitrendipine (10 nM) or by removing extracellular calcium and adding EGTA (2 mM), the contraction induced by carbachol (10 pM) was not affected by these measures. Nitrendipine partially inhibited contraction induced by pentagastrin, and pentagastrin also contracted cells that had been depolarized by prior exposure to KCl and nitrendipine. Removing extracellular calcium and adding EGTA partially inhibited contraction induced by maximally (10 pM) or submaximally effective (0.3 pM) concentrations of pentagastrin but did not affect that induced by 300 pM pentagastrin. These results indicate that isolated smooth muscle cells utilize calcium for contraction by three distinct mechanisms. The extent to which each mechanism contributes to contraction depends on the nature of the stimulus and, in the case of pentagastrin, the concentration of the stimulating ligand.

Animals↗
PubMed1986

Muscarinic receptor size on smooth muscle cells and membranes.

The loss of [3H]quinuclidinyl benzilate ([3H]QNB) binding following high-energy radiation was used to compare the muscarinic receptor size on single smooth muscle cells isolated by collagenase digestion from the canine stomach and on plasma membranes derived from intact gastric smooth muscle without exposure to exogenous proteolysis. Radiation inactivation of galactose oxidase (68 kdaltons), yeast alcohol dehydrogenase (160 kdaltons), and pyruvate kinase (224 kdaltons) activities were used as molecular-weight standards. Radiation inactivation of [3H]QNB binding to rat brain membranes, which gave a target size of 86 kdaltons, served as an additional control. In isolated smooth muscle cells, the calculated size of the muscarinic receptor was 80 +/- 8 kdaltons. In contrast, in a smooth muscle enriched plasma membrane preparation, muscarinic receptor size was significantly smaller at 45 +/- 3 kdaltons. Larger molecular sizes were obtained either in the presence of protease inhibitors (62 +/- 4 kdaltons) or by using a crude membrane preparation of gastric smooth muscle 86 +/- 7 kdaltons).

Animals↗
PubMed1986

Dissociation of contraction and muscarinic receptor binding to isolated smooth muscle cells.

We examined changes in [3H]QNB binding and cell length induced by muscarinic ligands in a suspension of single smooth muscle cells isolated from the canine stomach. Cells contracted following a brief (30 s) exposure to picomolar concentrations of muscarinic agonists and yielded ED50 values of 1.0 +/- 0.7 pM for oxotremorine, 12.5 +/- 1.8 pM for carbachol, and 16.0 +/- 2.9 pM for metacholine. Contraction was inhibited by atropine with a pA2 value of 10.2 +/- 1.1. The binding of [3H]QNB was rapid and reversible and was stereospecific and pharmacologically appropriate. Specific binding of [3H]QNB was saturable and bound with high affinity (KD 1.04 +/- 0.23 nM) to a single class of sites, of which there were approximately 200,000/cell. In competition experiments antagonist binding was generally homogeneous, whereas that of agonists was heterogeneous and subpopulations of binding sites with different affinities for agonists were identified. The Ki value of 8.1 +/- 1.1 nM for inhibition of QNB binding by atropine was greater than the pA2 of 10.2 +/- 1.1 derived from contraction studies. Furthermore, whereas picomolar concentrations of agonists induced cell contraction, substantially higher concentrations (10 nM to 10 mM) were required to inhibit [3H]QNB binding to the isolated cells.

Animals↗
PubMed1986

Changes in cross-sectional area of the coronary lumen in the six months after angioplasty: a quantitative analysis of the variable response to percutaneous transluminal angioplasty.

Although immediate and late changes in coronary stenoses after percutaneous transluminal coronary angioplasty (PTCA) have been reported, most investigators have employed qualitative or semiquantitative techniques to analyze the angiograms. Such data is not optimal because of considerable interobserver variability and the use of relative instead of absolute changes in lesion geometry. Analysis is further compounded by the indistinct edges that characterize coronary lesions immediately after angioplasty. To quantify the changes in minimal cross-sectional area (MCSA) of the coronary lumen that occur during and after PTCA, we analyzed the angiograms of 23 patients before PTCA, immediately after PTCA, and at 7.2 +/- 3.0 (mean +/- SD) months follow-up using two computer-assisted methods of angiographic analysis--quantitative coronary angiography (QCA) and videodensitometry (VID). QCA provides an absolute measure of the area of the lumen; VID is a nongeometric method that is not dependent on exact border recognition. Based on these quantitative methods, we found that successful angioplasty is associated with about a three-fold increase in the MCSA of the lesion (from 1.0 to 3.2 mm2). This area is, however, well below normal and is less than half of the average MCSA of the inflated dilating balloon. Analysis of follow-up angiograms demonstrated that eight of 23 patients had a substantial late increase in the MCSA of the lesion (from 2.7 to 4.1 mm2) after the angioplasty procedure. Clinical, hemodynamic, and angiographic characteristics immediately after PTCA were not predictive of MCSA of the lumen at follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1986

Ultrasound characterization of acute myocardial ischemia by quantitative texture analysis.

In this study we tested the efficacy of quantitative texture analysis in the identification of acute myocardial ischemia using an ultrasound data acquisition system that digitizes and stores echocardiographic data in polar format. In nine closed-chest dogs, data were acquired before and after coronary occlusion using a 2.4 MHz echocardiographic system. Regions of interest were analyzed at end-diastole and end-systole from the ischemic area and normal area at the same depth of field. Ultrasound data were evaluated using previously reported quantitative gray level texture measures. After occlusion, texture changes indicative of ischemia were found in systolic images. The directional component of the data analysis was important; analysis in the azimuthal direction was more accurate than in the axial direction. Six texture measures exhibited significant changes in the ischemic region from control to occlusion when analyzing data in the azimuthal direction. One false positive result occurred (significant texture change in the normal region from control to occlusion) in the azimuthal direction. Several false positive alterations in the normal regions from control to occlusion were found when the texture was evaluated in the axial direction. For accurate assessment of ischemic changes, preocclusion image data were required. We conclude that quantitative echocardiographic texture analysis using polar format data can identify subtle changes in myocardial texture such as that due to acute ischemia, using data acquired through the chest wall.

Acute Disease↗