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PubMed1997

Significance of slow upsloping ST-segment depression on exercise stress testing.

The supplementary value of varying degrees of upsloping ST-segment depression observed during treadmill exercise testing to the accuracy of the exercise ST-segment response for detection of ischemia was determined by employing a reversible thallium-201 (201Tl) defect as the criteria for ischemia. A group of 199 consecutive patients (168 men) with > or = 1 reversible 201Tl defects on quantitative planar perfusion imaging, and a normal group of 366 patients with normal 201Tl scans who achieved > or = 85% of age-predicted maximum heart rate were studied. Upsloping ST-segment depression was subcategorized for > or = 1.0, > or = 1.5, and > or = 2.0 mm of sustained ST-segment depression below baseline at 0.08 seconds after the J-point. If only > or = 1.0 mm of horizontal or downsloping ST-segment depression was designated as abnormal and all upsloping responses as normal, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the exercise electrocardiogram were 49% (98 of 199), 84% (281 of 336), 64% (98 of 153), 74% (281 of 382), and 71% (379 of 535), respectively. If in addition to > 1.0 mm of horizontal or downsloping ST-segment depression, > or = 2.0 mm of upsloping ST-segment depression is considered abnormal, these values were 52% (104 of 199), 81% (272 of 336), 62% (104 of 168), 74% (272 of 367), and 70% (376 of 535), respectively. If > or = 1.5 mm of upsloping ST-segment depression is considered an abnormal response, these values were 59% (117 of 199), 74% (248 of 336), 57% (117 of 205), 75% (248 of 330), and 68% (365 of 535), respectively. Finally, if > or = 1.0 mm of upsloping ST-segment depression is considered abnormal, these values were 71% (142 of 199), 56% (187 of 336), 49% (142 of 291), 77% (187 of 244), and 61% (329 of 535), respectively. Thus, if upsloping ST-segment depression is added to the criteria for a positive exercise test result, sensitivity for detection of ischemia is increased but at the expense of a fall in specificity and a significant decrease in the positive predictive value of the test.

Aged↗
PubMed1998

Relation between ST-segment changes and myocardial perfusion evaluated by myocardial contrast echocardiography in patients with acute myocardial infarction treated with direct angioplasty.

The aim of this study was to evaluate the relation between myocardial perfusion and ST-segment changes in patients with acute myocardial infarction treated with successful direct angioplasty. Thirty-seven patients, successfully treated with direct angioplasty, underwent myocardial contrast echocardiography before and after angioplasty. The sum of ST-segment elevation divided by the number of the leads involved (ST-segment elevation index) was calculated at 1, 5, 10, 20, and 30 minutes after restoration of a Thrombolysis In Myocardial Infarction trial grade 3 flow. After recanalization, myocardial reperfusion within the risk area was observed in 26 patients, whereas a no-reflow phenomenon occurred in 11. In patients with myocardial reperfusion, the ST-segment elevation index progressively declined, whereas in patients with no reflow, no significant change was observed. Reduction of > or = 50% in the ST-segment elevation index occurred in 20 of the 26 patients with reflow and in 1 of the 11 with no reflow (p = 0.0002). An additional increase of > or = 30% in the ST-segment elevation index occurred in 3 patients with reflow and in 7 with no reflow (p = 0.003). Sensitivity, specificity, positive and negative predictive values, and accuracy of the reduction in the ST-segment elevation index for predicting microvascular reflow were 77%, 91%, 95%, 62%, and 81%, respectively. The corresponding values of the increase in ST-segment elevation index for predicting no reflow were 64%, 88%, 70%, 85%, and 81%, respectively. In conclusion, after successful angioplasty, different patterns of myocardial perfusion are associated with different ST-segment changes. Analysis of ST-segment changes predicts the degree of myocardial reperfusion.

Aged↗
PubMed1995

Dobutamine-induced ST-segment elevation in patients with healed myocardial infarction. A marker of myocardial viability.

The purpose of this study was to determine the significance of transient ST-segment elevation during dobutamine infusions in patients with healed Q wave myocardial infarction. Twenty-seven patients with previous Q wave myocardial infarction were studied prospectively with dobutamine-thallium-201 single-photon emission computed tomography. The presence of ST-segment elevation in leads with Q waves was related to thallium reversibility at 4-hour redistribution imaging or after reinjection, to residual flow, as well as to wall motion abnormalities in the infarcted zone. ST-segment elevation in infarct-related leads was observed in 15 patients; 11 (73%) showed viability by thallium-201 in the infarcted zone. In patients without ST-segment elevation, viability was shown less frequently (33%, P < .05). Hypokinesis in infarcted segments was present in 60% of patients with ST-segment elevation and in 25% of patients without ST-segment elevation (.05 < P < .1). Finally, infarct-related artery was patent and/or collaterals were present in 10 patients with ST-segment elevation (67%) and in 4 patients without (33%, .05 < P < .1). In conclusion, ST-segment elevation during dobutamine infusion is a marker of residual viability in infarcted segments.

Adult↗
PubMed1975

Pathophysiology of aganglionic colon segment: an experimental study on aganglionosis produced by a new method in the rat.

Experimental aganglionosis was produced successfully in a colonic segment proximal to the peritoneal reflection by intraluminal filling under tension of the colorectum of rats with 0.01% corrosive sublimate in normal saline solution. Where the length of aganglionic segment was more than 3 cm, ileus appeared and megacolon proximal to a narrow segment was observed. Histologically and histochemically, a total denervation state was observed in the aganglionic segment, in contrast to findings in narrow segments of Hirschsprung's disease, in which intramural extraneous nerves are known to be increased. The fact that a definite narrow segment like that seen in Hirschsprung's disease appeared at the portion of the colon in which experimental aganglionosis was produced indicates that a narrow colonic segment certainly can be produced without presence of any intramural extraneous nerves, although the possibility that the presence of such nerves may exaggerate the narrowing cannot be denied. The fact that the cases in which length of aganglionosis was less than 2.5 cm did not have an ileus suggests that there may be some contributing factors other than aganglionosis in the etiology of Hirschsprung's disease of ultrashort segment, if this entity of the disease really exists. Aperistalsis observed in experimental aganglionic segments and that observed in aganglionotic segments of Hirschsprung's disease seem to be based on a common main factor, i.e., absence of the nonadrenergic, noncholinergic nerves.

Animals↗
PubMed1998

Segmental denervation and reinnervation of the iris sphincter as shown by infrared videographic transillumination.

OBJECTIVE: This study aimed to analyze the denervation and reinnervation history of individual segments of the iris sphincter in patients with Adie's syndrome. DESIGN: The irises of these patients were retroilluminated by shining an infrared-rich light through the lower eyelid and sclera and viewing the transilluminated iris from the front with an infrared-sensitive video camera. The irises of the same group of patients also were videotaped through a slit-lamp camera using routine frontal illumination. Both of these techniques also were used to examine a series of normal subjects. PARTICIPANTS: A total of 61 patients with Adie's syndrome or Adie's-like denervation of the iris sphincter (from surgery, trauma, or radiation) and 10 normal subjects were studied. MAIN OUTCOME MEASURES: Slit-lamp examination results of the segmental movement of the iris were compared to the infrared transillumination pattern of the iris sphincter before and during the light reflex, before and during the near-vision reaction, before and during eye movement, and before and after the application of dilute pilocarpine and 1% pilocarpine. RESULTS: Whenever an iris sphincter segment contracted, it also became denser by using these techniques. Reinnervated iris segments failed to contract to light but did contract and became denser with a near effort or with eye movement. Segments supersensitive to pilocarpine became denser than adjacent segments without supersensitivity, but atrophic-appearing segments looked translucent and thin, failing to become denser, even with 1% pilocarpine. CONCLUSIONS: The innervational history and current status of each clock-hour segment of the iris sphincter can be determined using this technique of videographic infrared transillumination, and the progression and pattern of iris denervation and reinnervation can be determined in patients with Adie's pupil. A miotic Adie's pupil that is "tonic," even in darkness, was found to be associated with a dense pattern of infrared transillumination in sphincter segments, which the authors interpret as being associated with a rich reinnervation from accommodative fibers. Segments that become densely reinnervated appear to lose their cholinergic supersensitivity.

Adie Syndrome↗
PubMed1996

Evidence that intersegmental competition influences the segmental distribution of the central terminals of muscle sensory afferents in the chicken embryo.

The possibility that muscle sensory afferents that enter the spinal cord at different segmental levels compete for terminal space in the lateral motor column was tested by unilaterally ablating neural crest cells destined to generate dorsal root ganglia (DRGs). Newly migrating neural crest was surgically removed from several lumbosacral segments on one side of the spinal cord on day 3 of embryogenesis (d3). The resultant experimental preparations developed without DRGs on the operated side at the segmental levels where the ablation was performed. At d18 the central projection from the intact DRG immediately caudal to the operated segments was anatomically mapped with a lipophilic axonal tracer. The central projection from the same DRG on the opposite, unoperated side was mapped as a control. The density of terminals along the longitudinal axis of the lateral motor column was quantified in serial sections with an image analysis program. On both the operated and control sides, the majority of terminals were found within the segment of entry and the rostral and caudal neighboring spinal segments. However, the rostral neighboring segment received a larger proportion of terminals on the operated side compared to the control side. Thus, the absence of primary afferents entering the spinal cord at specific segments leads to a shift of the afferent projection to the lateral motor column from the neighboring segments towards the deafferented segments.

Animals↗
PubMed1998

Segmental distribution of the motoneurons innervating trunk muscles in the spinal cord of the cat and rat.

The current progress in developmental biology suggests a genetically stable peripheral pathway formation. However, this may be incompatible with the variations or anomalies observed in the segmental origins of motor nerves in the mammals including the human. For the consideration of the causes raising this inconsistency, we examined the distribution of motoneurons for the serratus dorsalis cranialis muscle of the cat using a retrograde labeling method because this muscle consists of segmentally-arranged parts which receive segmental dual innervation. Consequently, the distribution of the labeled motoneurons for one part spread throughout the full extent of two spinal cord segments, while the distributions for the intercostal muscles in the cat and rat were segmental and in accordance with each spinal cord segment. This may indicate the more precise correspondence between the spinal nerve segments and the distribution of motoneurons projecting axons through them. We think, therefore, that segments of the spinal nerves supplying a given target exactly indicate the segmental levels of supplying motoneurons and suggest the segments of somites from which primordial cells of the target migrate.

Animals↗
PubMed2003

Segmental mobility of the lumbar spine during a posterior to anterior mobilization: assessment using dynamic MRI.

OBJECTIVES: To quantify segmental mobility of the lumbar spine during a posterior to anterior spinal mobilization procedure. DESIGN: Descriptive study using dynamic magnetic resonance imaging. BACKGROUND: The posterior to anterior spinal mobilization procedure is frequently used in the assessment and management of spinal dysfunction. How this procedure influences segmental spinal motion however, is not known. METHODS: Eleven asymptomatic subjects were positioned prone within a vertically open double donut design magnetic resonance imaging system. An anteriorly directed force was applied manually at each lumbar spinous process while magnetic resonance images were obtained continuously in the sagittal plane. The intervertebral angle was used to quantify segmental motion. RESULTS: The direction of motion at the tested segment was always extension, with values ranging from 1.2 (SD 2.2) at L2 to 3.0 (SD 2.3) degrees at L5. When the force was applied at L3, L4 and L5, the non-tested (adjacent) segments also were observed to move into extension. However, when the posterior to anterior force was applied at L1 and L2 the three caudal segments moved into flexion. CONCLUSIONS: Posterior to anterior spinal mobilization consistently caused extension at the tested segment, while the motion of the collective lumbar spine was either an increase or decrease in lordosis depending on the segment at which the force was applied. RELEVANCE: Passive movement techniques are commonly used to identify the symptomatic lumbar segment(s) and can be used as a treatment aimed at increasing mobility and/or decreasing pain. Knowledge of how this procedure influences segmental motion of healthy spines is important in understanding how altered mobility is related to symptoms.

Adult↗
PubMed2002

Clinical correlates of PR-segment depression in asymptomatic patients with pericardial effusion.

OBJECTIVES: The purpose of this study was to determine the clinical correlates of PR-segment depression among consecutive asymptomatic patients with pericardial effusion (PE) detected by routine echocardiography. BACKGROUND: Pericardial effusion is a relatively common finding in clinical practice, but not many studies have evaluated electrocardiographic (ECG) changes associated with the occurrence of PE. METHODS: Among 4,061 consecutive patients referred to our echocardiography laboratory, 176 asymptomatic patients had PE correlated with their clinical history and ECG findings. RESULTS: PR-segment depression was detected in 40 patients (23%). There were no significant differences in age, gender distribution or heart rate between patients with and without PR-segment depression. Fifteen post-pericardiotomy patients (33%), 19 patients (40%) with malignant disease and 6 patients (46%) with connective tissue disease had PR-segment depression, whereas no patient with heart disease (dilated cardiomyopathy, hypertensive heart disease, old myocardial infarction, valvular heart disease), renal disease or hypothyroidism had PR-segment depression, nor widespread ST-segment elevation. Among 40 patients with PR-segment depression, 8 had ST-segment elevation in the leads of epicardial derivation, 8 had upright T waves, 20 had low to inverted T waves with an isoelectric ST-segment and 4 had ST-T-wave changes due to bundle branch block. CONCLUSIONS: PR-segment depression was a relatively common ECG sign associated with clinically silent PE, and it was an ECG indicator of inflammatory pericardial involvement.

Adolescent↗
PubMed1984

Early dilation of the infarcted segment in acute transmural myocardial infarction: role of infarct expansion in acute left ventricular enlargement.

Left ventricular enlargement after myocardial infarction is a poor prognostic sign, the mechanism of which has not been well defined. Early left ventricular dilation may be due to the Frank-Starling effect, which results in an increase in the length of uninfarcted segments in response to a reduction in contractile muscle mass. In contrast to this adaptive physiologic mechanism, left ventricular dilation may alternatively be caused by a pathologic process that stretches and thins the infarcted myocardial segment (that is, infarct expansion). To determine the relative contributions of these two mechanisms to left ventricular dilation after an initial transmural anterior myocardial infarction, two-dimensional echocardiograms were obtained from 27 patients within 72 hours of the onset of symptoms of myocardial infarction and from 13 healthy control subjects. In the minor-axis echocardiographic view at the level of the papillary muscles, anterior and posterior endocardial segment lengths at end-diastole were measured with a microprocessor-based graphic system. The papillary muscles were used as internal landmarks to demarcate the anterior and posterior segments. Anterior (infarcted) segment length in patients with myocardial infarction was 11.6 +/- 2.2 cm (mean +/- SD), whereas in control subjects, anterior segment length was 8.6 +/- 1.2 cm (p less than 0.001). Posterior (uninfarcted) segment length in the patients was not significantly different from posterior segment length in the control subjects (5.4 +/- 1.2 versus 5.3 +/- 1.0 cm, respectively). Measurable left ventricular dilation during the first 3 days after transmural anterior myocardial infarction is due to dilation of the infarcted segment and not of the normal uninfarcted segment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1999

Use of segmental tissue Doppler velocity to quantitate exercise echocardiography.

BACKGROUND: A quantitative technique is required to reduce the subjectivity and improve the reproducibility of stress echocardiography. Tissue Doppler imaging may offer these benefits, but its feasibility with exercise echocardiography (ExE) is undefined. This study sought the determinants of the exercise tissue Doppler velocity (TDV) response and the feasibility and accuracy of color TDV during ExE. METHODS AND RESULTS: Fifteen volunteers and 85 patients (age 60 +/- 10 years, 19 women) with known or suspected coronary artery disease were studied with standard 2-dimensional (2D) echocardiography and pulsed wave (PW) and color TDV before and after they underwent exercise treadmill testing. After the study PW TDV was measured in 6 basal segments, and off-line software was used to display color TDV data from all myocardial segments. Color TDV was compared with PW TDV in the basal segments at rest and stress with the use of linear regression. Color TDV in mid and basal segments was compared with wall motion on 2D echocardiography. The predictors of the TDV response to exercise were defined in a multiple linear regression. A logistic regression model was used to integrate clinical, exercise, and TDV variables for prediction of abnormal regional left ventricular function. Color and PW correlated well at rest (r = 0.81) and stress (r = 0.84), but PW was greater than color velocities at rest and stress. On the basis of 2D echocardiography, 752 myocardial segments were classified as normal in patients without evidence of coronary disease, 309 were normal in patients with abnormal wall motion in another territory, and 128 showed ischemia or scar. Segmental comparison of velocities assessed by color TDV showed that scar segments had a lower velocity than normal segments at rest and stress (P <.001). Ischemic segments had a lower peak TDV and less increment in velocity than normal segments. Heart rate, functional capacity, and regional dysfunction (scar or ischemia) were independent predictors of TDV at peak exercise. With the use of receiver operating characteristic analysis, the "correction" of TDV by these other variables increased the accuracy of the technique for the detection of regional left ventricular dysfunction. CONCLUSION: Color TDV is feasible during ExE. The correlation found between TDV and wall motion analysis of experienced observers indicates that TDV may be useful as a quantitative tool for interpretation of ExE.

Blood Flow Velocity↗
PubMed2000

Quantitation of T2 lesion load in patients with multiple sclerosis: a novel semiautomated segmentation technique.

RATIONALE AND OBJECTIVES: The authors designed a segmentation technique that requires only minimal operator input at the initial and final supervision stages of segmentation and has computer-driven segmentation as the primary determinant of lesion boundaries. The technique was applied to compute total T2-hyperintense lesion volumes in patients with multiple sclerosis (MS). A semi-automated segmentation technique is presented and shown to have a test-retest reliability of <5%. MATERIALS AND METHODS: The method used a single segmented section with MS lesions. A probabilistic neural net performed segmentation into four tissue classes after supervised training. This reference section was deconstructed into the entire set of possible 4 x 4-pixel subregions, which was used to segment all-brain sections in steps of 4 x 4-pixel, adjacent image blocks. Intra- and interimage variabilities were tested by using 3-mm-thick, T2-weighted, dual-echo, spin-echo MR images from five patients, each of whom was imaged twice on the same day. Five different reference sections and three temporally separated. training sessions involving the same reference section were used to test the segmentation technique. RESULTS: The coefficient of variation ranged from 0.013 to 0.068 (mean +/- standard deviation, 0.037 +/- 0.039) for results from five different reference sections for each brain and from 0.007 to 0.037 (mean, 0.027 +/- 0.021) for brains segmented with the same reference section on three temporally separated occasions. Test-retest (intra-imaging) reliability did not exceed 5% (except for a small lesion load of 1 cm3 in one patient). Interimaging differences were approximately 10%. CONCLUSION: The segmentation technique yielded intra-imaging variabilities (2%-3%, except for very small MS lesion loads) that compare favorably with previously published results. New repositioning techniques that minimize imaging-repeat imaging variability could make this approach attractive for resolving MS lesion detection problems.

Algorithms↗
PubMed2000

Phantom-based performance evaluation: application to brain segmentation from magnetic resonance images.

This paper presents a new technique for assessing the accuracy of segmentation algorithms, applied to the performance evaluation of brain editing and brain tissue segmentation algorithms for magnetic resonance images. We propose performance evaluation criteria derived from the use of the realistic digital brain phantom Brainweb. This 'ground truth' allows us to build distance-based discrepancy features between the edited brain or the segmented brain tissues (such as cerebro-spinal fluid, grey matter and white matter) and the phantom model, taken as a reference. Furthermore, segmentation errors can be spatially determined, and ranged in terms of their distance to the reference. The brain editing method used is the combination of two segmentation techniques. The first is based on binary mathematical morphology and a region growing approach. It represents the initialization step, the results of which are then refined with the second method, using an active contour model. The brain tissue segmentation used is based on a Markov random field model. Segmentation results are shown on the phantom for each method, and on real magnetic resonance images for the editing step; performance is evaluated by the new distance-based technique and corroborates the effective refinement of the segmentation using active contours. The criteria described here can supersede biased visual inspection in order to compare, evaluate and validate any segmentation algorithm. Moreover, provided a 'ground truth' is given, we are able to determine quantitatively to what extent a segmentation algorithm is sensitive to internal parameters, noise, artefacts or distortions.

Algorithms↗
PubMed2000

A 3D generalization of user-steered live-wire segmentation.

We have been developing user-steered image segmentation methods for situations which require considerable human assistance in object definition. In the past, we have presented two paradigms, referred to as live-wire and live-lane, for segmenting 2D/3D/4D object boundaries in a slice-by-slice fashion, and demonstrated that live-wire and live-lane are more repeatable, with a statistical significance level of P < 0.03, and are 1.5-2.5 times faster, with a statistical significance level of P < 0.02, than manual tracing. In this paper, we introduce a 3D generalization of the live-wire approach for segmenting 3D/4D object boundaries which further reduces the time spent by the user in segmentation. In a 2D live-wire, given a slice, for two specified points (pixel vertices) on the boundary of the object, the best boundary segment is the minimum-cost path between the two points, described as a set of oriented pixel edges. This segment is found via Dijkstra's algorithm as the user anchors the first point and moves the cursor to indicate the second point. A complete 2D boundary is identified as a set of consecutive boundary segments forming a "closed", "connected", "oriented" contour. The strategy of the 3D extension is that, first, users specify contours via live-wiring on a few slices that are orthogonal to the natural slices of the original scene. If these slices are selected strategically, then we have a sufficient number of points on the 3D boundary of the object to subsequently trace optimum boundary segments automatically in all natural slices of the 3D scene. A 3D object boundary may define multiple 2D boundaries per slice. The points on each 2D boundary form an ordered set such that when the best boundary segment is computed between each pair of consecutive points, a closed, connected, oriented boundary results. The ordered set of points on each 2D boundary is found from the way the users select the orthogonal slices. Based on several validation studies involving segmentation of the bones of the foot in MR images, we found that the 3D extension of live-wire is more repeatable, with a statistical significance level of P < 0.0001, and 2-6 times faster, with a statistical significance level of P < 0.01, than the 2D live-wire method, and 3-15 times faster than manual tracing.

Algorithms↗
PubMedDate not supplied

Segmental pedicle screw fixation or cross-links in multilevel lumbar constructs. a biomechanical analysis.

BACKGROUND CONTEXT: The placement of segmental pedicle screws and cross-links in short segment posterior pedicle screw constructs has been shown to increase the construct stiffness in some planes. To date, no studies have looked at the contributions of segmental pedicle screw and cross-link placement in longer constructs. PURPOSE: To evaluate the influence of segmental pedicle screw and/or cross-link placement on flexion/extension, lateral bending and axial torsion stiffness in two- and three-level posterior pedicle screw fixation constructs. STUDY DESIGN/SETTING: An in vitro biomechanical analysis of two- and three-level posterior pedicle screw constructs with and without segmental fixation and/or cross-links was performed using calf lumbar spines. Stiffness of the constructs was compared. METHODS: Six calf lumbar specimens were used to test stiffness in one-, two- and three-level posterior pedicle screw fixation constructs in 12 configurations. A custom-made, four-axis spine simulator applied pure cyclical (+/-5 Nm) flexion/extension, lateral bending and axial torsion moments at 0.1 Hz under a constant 50-N axial compressive load. The stiffness of each construct was calculated about each axis of rotation. Data were analyzed using nonparametric techniques with statistical significance determined at alpha less than .05. RESULTS: The stiffness of the instrumented spines were significantly greater than the noninstrumented intact spines in all loading conditions for one-, two- and three-level constructs. There were no significant changes in flexion/extension stiffness with the addition of either the cross-links or the segmental pedicle screws. In lateral bending, the addition of segmental pedicle screws significantly increased the stiffness in the two- and three-level constructs. The addition of two cross-links increased lateral bending stiffness in the longer three-level constructs, with little change in the two-level constructs. In axial torsion, the progressive addition of cross-links showed a tendency toward increased stiffness in both the two- and three-level constructs. Segmental pedicle screws further increased torsional stiffness of the longer, three-level constructs. CONCLUSIONS: As the use of segmental spinal instrumentation progresses from one to two and three levels, the contribution of cross-links and segmental pedicle screws to the overall construct stiffness increases.

Animals↗
PubMed2000

The segment polarity network is a robust developmental module.

All insects possess homologous segments, but segment specification differs radically among insect orders. In Drosophila, maternal morphogens control the patterned activation of gap genes, which encode transcriptional regulators that shape the patterned expression of pair-rule genes. This patterning cascade takes place before cellularization. Pair-rule gene products subsequently 'imprint' segment polarity genes with reiterated patterns, thus defining the primordial segments. This mechanism must be greatly modified in insect groups in which many segments emerge only after cellularization. In beetles and parasitic wasps, for instance, pair-rule homologues are expressed in patterns consistent with roles during segmentation, but these patterns emerge within cellular fields. In contrast, although in locusts pair-rule homologues may not control segmentation, some segment polarity genes and their interactions are conserved. Perhaps segmentation is modular, with each module autonomously expressing a characteristic intrinsic behaviour in response to transient stimuli. If so, evolution could rearrange inputs to modules without changing their intrinsic behaviours. Here we suggest, using computer simulations, that the Drosophila segment polarity genes constitute such a module, and that this module is resistant to variations in the kinetic constants that govern its behaviour.

Animals↗
PubMed2006

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode.

Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the approximately 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of approximately 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975-84) Krafla events in Iceland, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia-Arabia plate boundary.

Journal Article↗
PubMed2003

Extrinsic cardiac nerve segments in the domestic dog (Canis familiaris- Linnaeus, 1758). Comparative study in young and adult dogs.

In this paper, important connections between the two main contingents of the autonomic nervous system, intrinsic and extrinsic visceral plexus were analysed. Concerning heart innervation, the territories of extrinsic innervation are very important in the treatment of congenital or acquired cardiopathy, thoracic neoplasia and aortic arch persistence, among others. This research compared young and adult extrinsic cardiac innervation and described the surgical anatomic nerve segments. Animals were perfused with a 10% formaldehyde solution in PBS (0.1 m) (pH 7.4) and submitted to macro- and meso-scopic dissection immersed in 60% acetic acid alcoholic solution and 20% hydrogen peroxide aqueous solution. The nerve segments were assigned as: right vagus nerve segment, left vagus nerve segment, right middle cervical ganglion segment, left middle cervical ganglion segment, right caudal laryngeal nerve segment, left caudal laryngeal nerve segment, right phrenic nerve segment and left phrenic nerve segment.

Aging↗