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PubMed2001

Conservation of microstructure between a sequenced region of the genome of rice and multiple segments of the genome of Arabidopsis thaliana.

The nucleotide sequence was determined for a 340-kb segment of rice chromosome 2, revealing 56 putative protein-coding genes. This represents a density of one gene per 6.1 kb, which is higher than was reported for a previously sequenced segment of the rice genome. Sixteen of the putative genes were supported by matches to ESTs. The predicted products of 29 of the putative genes showed similarity to known proteins, and a further 17 genes showed similarity only to predicted or hypothetical proteins identified in genome sequence data. The region contains a few transposable elements: one retrotransposon, and one transposon. The segment of the rice genome studied had previously been identified as representing a part of rice chromosome 2 that may be homologous to a segment of Arabidopsis chromosome 4. We confirmed the conservation of gene content and order between the two genome segments. In addition, we identified a further four segments of the Arabidopsis genome that contain conserved gene content and order. In total, 22 of the 56 genes identified in the rice genome segment were represented in this set of Arabidopsis genome segments, with at least five genes present, in conserved order, in each segment. These data are consistent with the hypothesis that the Arabidopsis genome has undergone multiple duplication events. Our results demonstrate that conservation of the genome microstructure can be identified even between monocot and dicot species. However, the frequent occurrence of duplication, and subsequent microstructure divergence, within plant genomes may necessitate the integration of subsets of genes present in multiple redundant segments to deduce evolutionary relationships and identify orthologous genes.

Arabidopsis↗
PubMed2000

An ultra-fast user-steered image segmentation paradigm: live wire on the fly.

We have been developing general user steered image segmentation strategies for routine use in applications involving a large number of data sets. In the past, we have presented three segmentation paradigms: live wire, live lane, and a three-dimensional (3-D) extension of the live-wire method. In this paper, we introduce an ultra-fast live-wire method, referred to as live wire on the fly, for further reducing user's time compared to the basic live-wire method. In live wire, 3-D/four-dimensional (4-D) object boundaries are segmented in a slice-by-slice fashion. To segment a two-dimensional (2-D) boundary, the user initially picks a point on the boundary and all possible minimum-cost paths from this point to all other points in the image are computed via Dijkstra's algorithm. Subsequently, a live wire is displayed in real time from the initial point to any subsequent position taken by the cursor. If the cursor is close to the desired boundary, the live wire snaps on to the boundary. The cursor is then deposited and a new live-wire segment is found next. The entire 2-D boundary is specified via a set of live-wire segments in this fashion. A drawback of this method is that the speed of optimal path computation depends on image size. On modestly powered computers, for images of even modest size, some sluggishness appears in user interaction, which reduces the overall segmentation efficiency. In this work, we solve this problem by exploiting some known properties of graphs to avoid unnecessary minimum-cost path computation during segmentation. In live wire on the fly, when the user selects a point on the boundary the live-wire segment is computed and displayed in real time from the selected point to any subsequent position of the cursor in the image, even for large images and even on low-powered computers. Based on 492 tracing experiments from an actual medical application, we demonstrate that live wire on the fly is 1.3-31 times faster than live wire for actual segmentation for varying image sizes, although the pure computational part alone is found to be about 120 times faster.

Algorithms↗
PubMed2001

Computer-aided characterization of mammographic masses: accuracy of mass segmentation and its effects on characterization.

Mass segmentation is used as the first step in many computer-aided diagnosis (CAD) systems for classification of breast masses as malignant or benign. The goal of this paper was to study the accuracy of an automated mass segmentation method developed in our laboratory, and to investigate the effect of the segmentation stage on the overall classification accuracy. The automated segmentation method was quantitatively compared with manual segmentation by two expert radiologists (R1 and R2) using three similarity or distance measures on a data set of 100 masses. The area overlap measures between R1 and R2, the computer and R1, and the computer and R2 were 0.76 +/- 0.13, 0.74 +/- 0.11, and 0.74 +/- 0.13, respectively. The interobserver difference in these measures between the two radiologists was compared with the corresponding differences between the computer and the radiologists. Using three similarity measures and data from two radiologists, a total of six statistical tests were performed. The difference between the computer and the radiologist segmentation was significantly larger than the interobserver variability in only one test. Two sets of texture, morphological, and spiculation features, one based on the computer segmentation, and the other based on radiologist segmentation, were extracted from a data set of 249 films from 102 patients. A classifier based on stepwise feature selection and linear discriminant analysis was trained and tested using the two feature sets. The leave-one-case-out method was used for data sampling. For case-based classification, the area Az under the receiver operating characteristic (ROC) curve was 0.89 and 0.88 for the feature sets based on the radiologist segmentation and computer segmentation, respectively. The difference between the two ROC curves was not statistically significant.

Algorithms↗
PubMed2006

Supervised learning-based cell image segmentation for p53 immunohistochemistry.

In this paper, we present two new algorithms for cell image segmentation. First, we demonstrate that pixel classification-based color image segmentation in color space is equivalent to performing segmentation on grayscale image through thresholding. Based on this result, we develop a supervised learning-based two-step procedure for color cell image segmentation, where color image is first mapped to grayscale via a transform learned through supervised learning, thresholding is then performed on the grayscale image to segment objects out of background. Experimental results show that the supervised learning-based two-step procedure achieved a boundary disagreement (mean absolute distance) of 0.85 while the disagreement produced by the pixel classification-based color image segmentation method is 3.59. Second, we develop a new marker detection algorithm for watershed-based separation of overlapping or touching cells. The merit of the new algorithm is that it employs both photometric and shape information and combines the two naturally in the framework of pattern classification to provide more reliable markers. Extensive experiments show that the new marker detection algorithm achieved 0.4% and 0.2% over-segmentation and under-segmentation, respectively, while reconstruction-based method produced 4.4% and 1.1% over-segmentation and under-segmentation, respectively.

Algorithms↗
PubMed2006

Segmentation of VOI from multidimensional dynamic PET images by integrating spatial and temporal features.

Segmentation of multidimensional dynamic positron emission tomography (PET) images into volumes of interest (VOIs) exhibiting similar temporal behavior and spatial features is a challenging task due to inherently poor signal-to-noise ratio and spatial resolution. In this study, we propose VOI segmentation of dynamic PET images by utilizing both the three-dimensional (3-D) spatial and temporal domain information in a hybrid technique that integrates two independent segmentation techniques of cluster analysis and region growing. The proposed technique starts with a cluster analysis that partitions the image based on temporal similarities. The resulting temporal partitions, together with the 3-D spatial information are utilized in the region growing segmentation. The technique was evaluated with dynamic 2-[18F] fluoro-2-deoxy-D-glucose PET simulations and clinical studies of the human brain and compared with the k-means and fuzzy c-means cluster analysis segmentation methods. The quantitative evaluation with simulated images demonstrated that the proposed technique can segment the dynamic PET images into VOIs of different kinetic structures and outperforms the cluster analysis approaches with notable improvements in the smoothness of the segmented VOIs with fewer disconnected or spurious segmentation clusters. In clinical studies, the hybrid technique was only superior to the other techniques in segmenting the white matter. In the gray matter segmentation, the other technique tended to perform slightly better than the hybrid technique, but the differences did not reach significance. The hybrid technique generally formed smoother VOIs with better separation of the background. Overall, the proposed technique demonstrated potential usefulness in the diagnosis and evaluation of dynamic PET neurological imaging studies.

Algorithms↗
PubMed1993

Responsiveness of human isolated bronchial segments and its relationship to epithelial loss.

1. The responsiveness of human and bovine bronchi was examined by comparing the magnitude of responses to agonists applied to the adventitial (outside) and to the luminal (inside) surfaces. The development of smooth muscle tone was measured as both an increase in pressure in isovolumic bronchial segments and narrowing in perfused segments. 2. In both closed and perfused human segments, ACh added to the adventitial surface produced highly homogeneous responses while responses to ACh added to the luminal side were extremely variable. 3. Histological examination of the human segments showed that they possessed variable degrees of pre-existing epithelial loss from the mucosal circumference, ranging from 0 to 82%. 4. Denuded human isovolumic segments (exhibiting > 30% epithelial loss) were 40 fold more sensitive to ACh inside than intact segments (< 30%). Denuded segments were also equally responsive to KCl inside or outside while KCl inside produced a contraction that was 50% of that to KCl outside in intact segments. 5. A strong and highly significant relationship was determined between the proportion of epithelial loss and both the responsiveness and rate of contraction of human segments to ACh and KCl introduced onto the lumen. No relationship was observed between epithelial denudation and responsiveness or contractility to agonists added to the adventitial surface. 6. Mechanical denudation of the epithelium from bovine segments had no effect on responsiveness to ACh or KCl added to the outside while significantly augmenting the sensitivity to ACh (9 fold) and reactivity to KCl introduced into the lumen to the extent that it became the same as outside.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1992

[The segmental organization and horny structure of the claw of the dog].

This study classifies the segments of the dog claw and presents a new conception to define crown and wall segments that deviates from the common statements in literature. The perioplic segment extends along the internal surface of the claw fold (vallum). The crown segment lies in the unguicular groove, and there in a semicircular zone. In the crown segment there is development of horn tubuli, but these lose their tubular structure before they have reached the top of the claw. The wall segment, adjacent distally, comprises a dorsal ridge, and lateral surfaces proximally and distally which are all marked by superficial lamellar-shaped surface configurations. The sole segment shows desquamative soft horn and is situated between the free margin of the wall segment palmar/plantar to the unguicular process. The new conception of homology of dog claw distinguishes between main and secondary criteria. The main criterion is the epidermal and dermal configuration. Secondary criteria are the typical horn products (for example perioplic horn) and dimension, shape and topography of segments. The sterile/fertile-bed theory, which was believed to be the determining factor for the classification of the dog claw, is neither the proper method to define the individual segments nor to judge the rate of cornification.

Animals↗
PubMedDate not supplied

Growth patterns during segmentation in the two polychaete annelids, Capitella sp. I and Hydroides elegans: comparisons at distinct life history stages.

Many animals generate new body segments sequentially from a posterior growth zone, and this is generally thought to be the case for the annelids. Most annelids, including polychaetes, have an indirect life cycle and generate their earliest segments during larval life. We have characterized the nature of the growth zone in two polychaetes, Hydroides elegans and Capitella sp. I, during both larval and juvenile stages of segment formation by examining cell division patterns with 5-bromo-2'-deoxyuridine incorporation. Cell division patterns show commonalities between the two species, even though they have distinct body plans and life history characteristics. In both polychaetes, larval segments arise from a field of dividing cells located in lateral regions of the body, rather than from a localized posterior growth zone. Circumferential expansion of the forming segmental tissue is particularly pronounced in Capitella sp. I. Post-metamorphic segments, in contrast, originate from a classical posterior growth zone, with the exception of four posterior thoracic segments of H. elegans, which appear to arise from an area in the middle of the body, indicating plasticity of segment-generating mechanisms present in different annelid life histories. The distinct nature of larval versus juvenile growth zones in H. elegans and Capitella sp. I raises the question of the mechanistic relationship between these two growth zones. The results of this study increase our understanding of the cellular origins of segments in annelids, and serve as a basis for interpretation of molecular expression patterns associated with segment formation in polychaetes.

Animals↗
PubMed1983

Variations in kallikrein-like esterase activity in different segments of the rat nephron during salt-load and salt-depletion.

Histochemical changes in kallikrein-like activity in the rat nephron induced by chronic salt-load or salt-depletion were investigated semiquantitatively, using a synthetic substrate for kallikrein, pro-phe-arg-naphthylester. The location of the changes in the different segments of the nephron was established by comparison with neighbouring freeze-dried sections, where the various structures of the tubular segments were identified. The enzyme activity was graded semiquantitatively and the percentage of tubular segments possessing enzyme activity was recorded. In salt-loaded rats, the enzyme activity in the deep half of the renal cortex was decreased in the first and second segments of the proximal tubule as well as in the third segment in the cortex. In salt-depleted rats, the enzyme activity in the deep half of the renal cortex was also decreased in the first segment of the proximal tubule as well as in the third segment in the cortex. In contrast, the enzyme activity in the second segment of the proximal tubule was increased in the superficial cortex as well as in the deep cortex. Furthermore, in the salt-depleted rats the enzyme activity was decreased in the cortical part of the ascending thick limb of Henle, but increased in the medullary part. In the superficial part of the cortex, the enzyme activity was decreased in the distal convoluted tubule. In the kidneys from both salt-loaded and salt-depleted rats, the differences in enzyme activity between zones--such as found in the normal kidney--disappeared in the case of the first and second segments of the proximal tubule. However, in the other segments of the nephron, the zonal differences were preserved in both experimental conditions.

Animals↗
PubMed1987

The sarcomere length-tension relation determined in short segments of intact muscle fibres of the frog.

1. Single fibres isolated from the tibialis anterior muscle of Rana temporaria were stimulated to produce a 1 s fused tetanus, while a short (ca. 0.5 mm) segment of the fibre was held at constant length. The segments were defined by opaque markers of hair that were placed on the fibre surface. The distance between two adjacent markers (one segment) was monitored by means of a photo-electric recording system. The length of a given segment could be controlled to within 0.2% of the segment's length by adjusting the over-all length of the fibre by means of an electromagnetic puller and servo system. 2. Segments producing constant force (no 'tension creep') during length-clamp recording were studied at different striation spacings within the following ranges of sarcomere length: 2.20-3.70, 1.90-2.45 and 1.50-2.20 microns. The absence of tension creep suggested (Edman & Reggiani, 1984 a) that the sarcomere pattern remained stable within the length-clamped segment during contraction at different lengths. 3. The tetanic force of a given length-clamped segment was consistently found to increase, as the sarcomere length was reduced from 2.20 to 1.98-2.02 microns, the mean increase in force being 6.9 +/- 0.4% (S.E. of mean, thirty-two segments). By further decreasing the sarcomere length active force was reduced. 4. The increase in force-producing capability between 2.20 and 2.00 microns sarcomere length was further explored by recording the maximum rate of force redevelopment, dF/dtmax, after a quick release during the plateau of a fixed-end tetanus. dF/dtmax varied with sarcomere length between 2.20 and 2.00 microns in the same way as the isometric force of a short, length-clamped segment, increasing by ca. 10% over this range. This finding provides further support for the view that the fibre's capacity to produce force is not constant between 2.20 and 2.00 microns sarcomere length. 5. The descending limb of the length-tension relation extended between 2.00 and approximately 3.65 microns sarcomere length. Its middle, straight portion (between 2.30 and 3.30 microns sarcomere spacings) extrapolated to zero tension at 3.49 microns sarcomere length. The upper and lower portions of the descending limb were slightly curved (at sarcomere lengths less than 2.30 and greater than 3.30 microns, respectively) giving the descending limb a symmetrical sigmoid appearance.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2004

An extensive log-file analysis of step-and-shoot intensity modulated radiation therapy segment delivery errors.

We present a study to evaluate the monitor unit (MU), dosimetric, and leaf-motion errors found in the delivery of 91 step-and-shoot IMRT treatment plans performed at three nominal dose rates using a dual modality high energy Linac (Varian 2100 C/D, Varian Medical Systems Inc., Palo Alto, CA) equipped with a 120-leaf multileaf collimator (MLC). The analysis was performed by studying log files generated by the MLC controller system. Recent studies by our group have validated that the automatically generated MLC log files accurately record the actual system delivery. A total of 635 beams were delivered at three nominal dose rates: 100, 300, and 600 MU/min. The log files were manually retrieved and analysis software was developed to extract the recorded MU delivery and leaf positions for each segment. Our analysis revealed that the magnitude of segment MU errors were independent of the planned segment MUs. Segment MU errors were found to increase with dose rate having maximum errors per segment of +/-1.8 MU at 600 MU/min, +/-0.8 MU at 300 MU/min, and +/-0.5 MU at 100 MU/min. The total absolute MU error in each plan was observed to increase with the number of plan segments, with the trend increasing more rapidly for higher dose rates. Three dimensional dose distributions were recomputed based on the observed segment MU errors for three plans with large cumulative absolute MU errors. Comparison with the original treatment plans indicated no clinically significant consequences due to these errors. In addition, approximately 80% of the total segment deliveries reported at least one collimator leaf moving at least 1 mm (projected at isocenter) during segment delivery. Such errors occur near the end of segment delivery and have been previously observed by our group using a fast video-based electronic portal imaging device. At 600 MU/min, between 5% and 23% of the plan MUs were delivered during leaf motion that had exceeded a 1 mm position tolerance. These leaf motion errors were not included in the treatment plan recalculations performed in this study.

Biophysical Phenomena↗
PubMed2005

Centerline-based colon segmentation for CT colonography.

We have developed a fully automated algorithm for colon segmentation, centerline-based segmentation (CBS), which is faster than any of the previously presented segmentation algorithms, but also has high sensitivity as well as high specificity. The algorithm first thresholds a set of unprocessed CT slices. Outer air is removed, after which a bounding box is computed. A centerline is computed for all remaining regions in the thresholded volume, disregarding segments related to extracolonic structures. Centerline segments are connected, after which the anatomy-based removal of segments representing extracolonic structures occurs. Segments related to the remaining centerline are locally region grown, and the colonic wall is found by dilation. Shape-based interpolation provides an isotropic mask. For 38 CT datasets, CBS was compared with the knowledge-guided segmentation (KGS) algorithm for sensitivity and specificity. With use of a 1.5 GHz AMD Athlon-based PC, the average computation time for the segmentation was 14.8 s. The sensitivity was, on average, 96%, and the specificity was 99%. A total of 21% of the voxels segmented by KGS, of which 96% represented extracolonic structures and 4% represented the colon, were removed.

Algorithms↗
PubMed1995

In vitro packaging of individual genomic segments of bacteriophage phi 6 RNA: serial dependence relationships.

Bacteriophage phi 6 has a genome of three segments of double-stranded RNA enclosed in a procapsid composed of four different proteins. The preformed procapsid is capable of packaging plus-strand transcripts of the genomic segments in an in vitro reaction. The packaging of the three segments shows a strong order of dependence in that segment S packages alone, but segment M requires S and and segment L requires S and M for efficient packaging. Packaging of individual segments is dependent on unique packaging sequences of about 200 nucleotides near the 5' ends of the segments. Deletions that invade these regions destroy packaging competence for the particular segment and for the dependent segments as well. In the presence of 2 mM phosphate and at magnesium ion concentrations above 4 mM, packaging becomes progressively more independent and ultimately nonspecific with respect to phi 6 sequences.

Bacteriophage phi 6↗
PubMed1983

Significance of exercise induced ST segment elevation in patients with previous myocardial infarction.

In order to determine the significance of exercise induced ST segment elevation in patients with previous myocardial infarction, we have studied 156 patients, 26 months (mean) after myocardial infarction. Each patient underwent 16 lead precordial electrocardiographic mapping before, during, and after exercise and in addition coronary arteriography was performed. There was no significant difference in the extent of coronary disease or abnormalities of left ventricular function between patients with exercise induced ST segment elevation that was noted to occur in leads with Q waves and those with ST segment elevation plus depression or those with ST segment depression alone. Patients without exercise induced ST segment changes had fewer coronary arteries involved than those who developed ST segment changes. Nineteen patients with exercise induced ST segment elevation alone underwent coronary artery bypass surgery; in 11 this resulted in complete abolition of the exercise induced ST segment elevation and was associated with symptomatic relief and patent grafts without alteration of left ventricular function. Thus, exercise induced ST segment elevation in patients with previous myocardial infarction should be considered as important as ST segment depression in terms of underlying myocardial ischaemia, coronary anatomy, and left ventricular function.

Adult↗
PubMed1985

Morphology of ambulatory ST segment changes in patients with varying severity of coronary artery disease. Investigation of the frequency of nocturnal ischaemia and coronary spasm.

The frequency and magnitude of objectively determined myocardial ischaemia during normal daily activities of patients with varying severity of coronary artery disease are unknown. Furthermore, the incidence of nocturnal resting myocardial ischaemia and frequency of coronary spasm in patients with normal coronary arteries and chest pain are also not known. One hundred consecutive patients with chest pain referred for coronary angiography were therefore investigated with exercise testing and ambulatory ST segment monitoring. Fifty two of 74 patients with significant coronary artery disease and six of 26 with no significant coronary narrowing had episodes of ST segment change during 48 hours of ambulatory monitoring. Two patients, one with normal coronary arteries and localised spasm and one with three vessel disease, had episodes of ST segment elevation, whereas all other patients had episodes of ST segment depression. The frequency, duration, and magnitude of ST segment changes were greater in patients with more severe types of coronary artery disease. Thus more than six episodes of ST segment change per day occurred in patients with two or three vessel disease or left main stem stenosis and in the only patient with coronary spasm and normal coronary arteries. Nocturnal ischaemia occurred in 15% of patients with coronary artery disease and was almost an invariable indicator of two or three vessel coronary artery disease or left main stem stenosis. Episodes of ST segment change occurred most commonly during the morning hours and least commonly during the night, in parallel with changes in basal hourly heart rates. The heart rate at the onset of ST segment change tended to be lower in patients with coronary artery disease than in those with normal coronary arteries. The duration of exercise to ST segment depression tended to be shorter in patients with more severe disease, but it could not predict patients with nocturnal myocardial ischaemia, left main stem stenosis, or coronary spasm, whereas ambulatory ST segment monitoring was able to identify most of these patients.

Activities of Daily Living↗
PubMed1988

The ST segment of the ambulatory electrocardiogram in a normal population.

The behaviour of the ST segment in everyday life was studied by ambulatory electrocardiography in 111 normal volunteers. Fifteen were excluded because of abnormal exercise responses (10 subjects) and significant postural ST segment shifts (five subjects). This left 62 men and 34 women, mean (SD) age 40.5 (12.6) years (range 20-67 years). Ambulatory monitoring of leads CM5 and CC5 for 24 hours was followed by a maximal treadmill exercise test. The tapes of the ambulatory monitoring were analysed by a computer aided system. The computer printed trend plots of the ST segment (measured both at the J point and at J + 60 ms) to detect episodes of ST segment elevation and depression, which were confirmed by visual analysis of real time printouts. Twelve subjects showed "ischaemic" ST segment depression and nine subjects showed ST segment elevation. Eight people with ambulatory ST segment changes were studied during exercise by radionuclide ventriculography and thallium-201 imaging scans. Although seven of the eight thallium studies were normal, radionuclide ventriculography showed functional impairment in five cases. Seven of the 10 subjects with abnormal exercise tests were similarly investigated and their results followed the same pattern, with normal thallium images in six and functional impairment in four. Ambulatory electrocardiography was repeated in 20 people after a median of 20 days. The ST segment changes were reproducible. ST segment changes of an apparently ischaemic nature occur even in a carefully defined normal population but they do not necessarily represent latent clinically significant coronary artery disease. This indicates that ST segment changes seen in patients with known obstructive coronary artery disease should be interpreted with caution.

Adult↗
PubMed1997

Relation between ST segment elevation during dobutamine stress test and myocardial viability after a recent myocardial infarction.

OBJECTIVE: To assess the relation between ST segment elevation during the dobutamine stress test and late improvement of function after acute Q wave myocardial infarction. PATIENTS AND DESIGN: 70 patients were studied a mean (SD) 8 (3) days after acute myocardial infarction with high dose dobutamine-atropine stress echocardiography and a follow up echocardiogram at 85 (10) days. A score model based on 16 segments and four grades was used to assess left ventricular function. Functional improvement was defined as a reduction of wall motion score > or = 1 in > or = 1 segments at follow up. INTERVENTION: Myocardial revascularisation was performed in 23 patients (33%) before follow up studies. RESULTS: ST segment elevation occurred in 40 patients (57%). Late functional improvement occurred in 35 patients (50%). Functional improvement was more common in patients with ST segment elevation (68% v 30%, P < 0.005) and they had a higher mean (SD) number of improved segments at follow up (1.9 (2.2) v 0.5 (1.1), P < 0.005). The wall motion score index decreased between baseline and follow up in patients with ST segment elevation (1.54 (0.50) v 1.48 (0.43), P < 0.05) but not in patients without ST segment elevation (1.39 (0.60) v 1.45 (0.47)). The accuracy of ST segment elevation for the prediction of functional improvement was similar to that of low dose dobutamine echocardiography in patients with anterior infarction (80% v 83%) and in patients who underwent revascularisation (78% v 83% respectively). CONCLUSION: In patients with a recent Q wave myocardial infarction, dobutamine-induced ST segment elevation is a valuable marker of myocardial viability particularly when the test is performed without or with suboptimal echocardiographic imaging.

Cardiotonic Agents↗
PubMed1989

Oxygen requirements of the dyskinetic myocardial segment.

Oxygen requirements of a noncontracting myocardial segment subjected to passive systolic stretch (dyskinesis) have not been well described. The purpose of this study was to measure oxygen consumption (MVO2) of a myocardial segment made dyskinetic by intracoronary infusion of lidocaine. In 12 anesthetized open-chest dogs, segmental shortening was measured sonomicrometrically in regions perfused by the left anterior descending (LAD) and circumflex (Cfx) coronary arteries. MVO2 was measured by arterial-venous oxygen content differences and transmural blood flow. Dose-response curves to intracoronary lidocaine showed that complete dyskinesis was achieved by a 0.25-mg/ml dose of lidocaine, whereas the Cfx region maintained a constant level of segmental shortening. MVO2 of the LAD segment was similar to that of the Cfx segment under control conditions. With lidocaine-induced dyskinesis, MVO2 in the arrested segment was reduced by 33% (P less than 0.05), despite the loss of contractile function. When bulging was prevented by ventricular unloading, MVO2 in the arrested segment decreased to 2.65 ml O2.min-1.100 g-1 (i.e., basal oxygen requirements). In conclusion, MVO2 in a pharmacologically arrested myocardial segment undergoing systolic bulging is paradoxically high relative to both basal requirements and MVO2 in the normally contracting segment.

Animals↗