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PubMed1998

Segment-specific pattern of sympathetic preganglionic projections in the chicken embryo spinal cord is altered by retinoids.

Sympathetic preganglionic neurons exhibit segment-specific projections. Preganglionic neurons located in rostral spinal segments project rostrally within the sympathetic chain, those located in caudal spinal segments project caudally, and those in midthoracic segments project either rostrally or caudally in segmentally graded proportions. Moreover, rostrally and caudally projecting preganglionic neurons are skewed toward the rostral and caudal regions, respectively, of each midthoracic segment. The mechanisms that establish these segment-specific projections are unknown. Here we show that experimental manipulation of retinoid signaling in the chicken embryo alters the segment-specific pattern of sympathetic preganglionic projections and that this effect is mediated by the somitic mesoderm. Application of exogenous retinoic acid to a single rostral thoracic somite decreases the number of rostrally projecting preganglionic neurons at that level. Conversely, disrupting endogenous synthesis of retinoic acid in a single caudal thoracic somite increases the number of rostrally projecting preganglionic neurons at that level. The number of caudally projecting neurons does not change in either case, indicating that the effect is specific for rostrally projecting preganglionic neurons. These results indicate that the sizes of the rostrally and caudally projecting populations may be independently regulated by different factors. Opposing gradients of such factors along the longitudinal axis of the thoracic region of the embryo could be sufficient, in combination, to determine the segment-specific identity of preganglionic projections.

Animals↗
PubMed2006

Rapid assessment of left ventricular segmental wall motion, ejection fraction, and volumes with single breath-hold, multi-slice TrueFISP MR imaging.

BACKGROUND AND OBJECTIVE: To reduce imaging time and complexity, we sought to determine whether single breath-hold, multi-slice TrueFISP (SB-MST) magnetic resonance imaging (MRI) method is comparable to standard multi-breath-hold, multi-slice TrueFISP (MB-MST) for assessment of left ventricular (LV) wall motion abnormality (WMA), volumes, and ejection fraction (EF). METHODS AND RESULTS: We studied 62 patients having cardiac MRI at 1.5-Tesla. After acquiring standard MB-MST (one slice per breath-hold), SB-MST was performed, acquiring 3 short- and 2 long-axis views over only 20 heartbeats. Using both techniques, wall motion was scored using a 6-point, 17-segment LV model for all scans (62 patients x 2 techniques/patient = 124 scans) on two separate occasions. Separately, EF and ventricular volumes were evaluated using both MB-MST and SB-MST. For all analyses, MB-MST was considered the standard against which SB-MST was compared. Twenty-six of 62 patients exhibited at least one segmental WMA by MB-MST. Exact agreement for wall motion was found in 965/1054 segments (92%, kappa = 0.74, p < 0.001), and agreement was within 1 score point in 1010/1054 segments (96%). Considering a score >1 abnormal, exact agreement for presence of WMA was found in 131/193 segments (68%) abnormal by MB-MST and for absence of WMA in 838/861 segments (97%) normal by MB-MST. Agreement within 1 score point occurred in 167/193 abnormal (87%) and in 843/861 normal segments (98%). There were no significant differences in agreement between first and second read of the data. Variability of SB-MST on read one versus read two was small (5%, 996/1054 segments read identically, p = ns) and statistically identical to variability of MB-MST on read one versus read two (4%, 1007/1054 segments read identically, p = ns). For end-diastolic volumes, end-systolic volumes, and EF using SB-MST compared to MB-MST, mean differences were 9 +/- 15 ml, 6 +/- 12 ml, and 2 +/- 5%, and correlations were r = 0.97, 0.98 and 0.95, respectively. CONCLUSION: SB-MST accurately assesses wall motion, volumes and EF. This approach may serve as a screening exam for assessment of WMA and, under select circumstances, may substitute for standard multi-breath-hold method in situations requiring rapid accurate assessments of LV function.

Aged↗
PubMed2006

Primary spinal segment stability with a stand-alone cage: in vitro evaluation of a successful goat model.

BACKGROUND: Interbody cages have been developed to restore disk height and to increase stability of the spinal segment, and thereby enhance fusion. However, they often prove inadequate as a stand-alone device. It is unknown how much primary stability is required to facilitate fusion. In various goat studies, we have obtained spinal fusion routinely with a stand-alone cage device. However, data covering the mechanical conditions under which these fusions have been obtained are lacking. In this study, we addressed the issue of primary stability. METHODS: We used an established goat model for spinal fusion in vitro. 48 native lumbar spine segments were mechanically tested in flexion/extension, axial torsion (left/right), anterior/posterior shear, and left/right lateral bending. Then all segments were provided with a titanium cage using the exact surgical procedure of our earlier in vivo studies, and the mechanical tests were repeated. Under shear force and axial torsion, a significant loss of stiffness was seen in the operated segments as compared to nonoperated controls. No increase in stiffness was found in any of the loading directions. INTERPRETATION: Cage implantation in a lumbar spinal segment does not increase immediate postoperative stability as compared to the native segment in this goat model. This is attributable to both the annular damage during cage implantation and the subsequent loss of segment height. Yet previous in vivo studies using this goat model have generally shown fusion. This implies that high primary segment stability is not required for fusion or, alternatively, that the tested range of motion of the spinal segment in vitro does not occur at these magnitudes in vivo.

Animals↗
PubMed1998

Quality assurance of the dose delivered by small radiation segments.

The use of intensity modulation with multiple static fields has been suggested by many authors as a way to achieve highly conformal fields in radiotherapy. However, quality assurance of linear accelerators is generally done only for beam segments of 100 MU or higher, and by measuring beam profiles once the beam has stabilized. We propose a set of measurements to check the stability of dose delivery in small segments, and present measured data from three radiotherapy centres. The dose delivered per monitor unit, MU, was measured for various numbers of MU segments. The field flatness and symmetry were measured using either photographic films that are subsequently scanned by a densitometer, or by using a diode array. We performed the set of measurements at the three radiotherapy centres on a set of five different Philips SL accelerators with energies of 6 MV, 8 MV, 10 MV and 18 MV. The dose per monitor unit over the range of 1 to 100 MU was found to be accurate to within +/-5% of the nominal dose per monitor unit as defined for the delivery of 100 MU for all the energies. For four out of the five accelerators the dose per monitor unit over the same range was even found to be accurate to within +/-2%. The flatness and symmetry were in some cases found to be larger for small segments by a maximum of 9% of the flatness/symmetry for large segments. The result of this study provides the dosimetric evidence that the delivery of small segment doses as top-up fields for beam intensity modulation is feasible. However, it should be stressed that linear accelerators have different characteristics for the delivery of small segments, hence this type of measurement should be performed for each machine before the delivery of small dose segments is approved. In some cases it may be advisable to use a low pulse repetition frequency (PRF) to obtain more accurate dose delivery of small segments.

Biophysical Phenomena↗
PubMed1998

Molecular characterization of five neutralizing anti-HIV type 1 antibodies: identification of nonconventional D segments in the human monoclonal antibodies 2G12 and 2F5.

We have stabilized a panel of 33 hybridomas producing human monoclonal antibodies (MAbs) against HIV-1 gp160 and p24. Five of these antibodies were able to neutralize different HIV-1 isolates, and two of them (2F5 and 2G12) revealed remarkable potential to neutralize primary virus isolates of different clades in several in vitro tests. To determine whether a structural basis for neutralization could be identified, we analyzed the antibodies at the molecular level. This study reports the primary nucleotide and deduced amino acid sequences of the rearranged heavy and light chain V segments (VH, Vkappa) of the neutralizing MAbs (1B1, 1F7, 2F5, 2G12, and 3D5) and the nonneutralizing anti-gp41 MAb 3D6. Aligning the V segments with the nearest related germline genes illustrated the occurrence of somatic mutations. The neutralizing MAbs show mutational rates comparable to those of antibodies that appear in patients in whom the immune system is under constant antigenic pressure over a long period of time. In contrast, 3D6, which recognizes the immunodominant region on gp41, displays homologies as high as 97 and 98% compared with its VH and Vkappa germline genes. The diversity segments [D(H)] of 1B1, 1F7, 3D5, and 3D6 were assigned to single D(H) segments on the chromosomal D(H) locus. 2F5 presents a D(H) segment 52 nucleotides in length, which could be explained by fusion of two segments on the immunoglobulin heavy chain locus that have not yet been described as rearranged regions. 2G12 D(H) shows best homologies to a D(H) segment between D3-22 and D4-23. This D(H) segment could be the reason for the rare occurrence of antibodies competing with 2G12. Since this nearest related chromosomal region on the D(H) locus does not display recombination signals at the flanking regions, this segment is normally not taken into consideration as a site for immunoglobulin heavy chain rearrangement.

Amino Acid Sequence↗
PubMed2006

Initial changes of centres of rotation of the anterior segment in response to horizontal forces.

This study investigated the changes in the initial centres of rotation (Crot) of the upper six anterior teeth in response to a horizontal load. Six upper anterior teeth were extracted, splinted as a unit, and embedded in dental stone after the roots were uniformly coated with silicone. An aluminium fixture was bonded to the anterior segment and three linear variable differential transformers (LVDTs) were attached to measure the microdisplacement of the segment. A pulley and dead weight assembly were used to apply a 200 g occluso-gingivally varying horizontal force to the segment. The changes in the Crot for the anterior segment to the horizontal load were recorded. The results showed that the centre of resistance (Cres) of the upper anterior segment was located 14.5 mm apical and 9.5 mm distal from the incisal edge of the central incisors. A linear functional axis (a trace of the measured Crot) was recorded. The functional axis maintained an angle of 14.5 degrees to the vertical axis of the anterior segment passing through the Cres of the segment. The Crot constant, which determines the tipping sensitivity of the segment, was 23 mm(2). The results demonstrate that the upper anterior segment may be slightly intruded when a horizontal force is applied and is less prone to tipping than a single tooth.

Humans↗
PubMed1987

Prognostic importance of exercise-induced ST-segment depression in patients with documented coronary artery disease.

Exercise-induced ST-segment depression is a marker of impaired prognosis in patients with suspected or manifest CAD. Whether ST-segment depression remains of prognostic importance, after exercise tolerance and extent of CAD have been considered, is unknown. We analysed the prognostic importance of exercise-induced ST-segment depression (greater than 0.15 mV) in 1250 medically treated patients with angiographically determined CAD (mean follow-up after angiography 4.5 years). Based on exercise tolerance (supine bicycle ergometry) patients were divided into two groups: group A patients (n = 677) with lower exercise tolerance (less than or equal to 75 W) and group B patients (n = 573) with better exercise tolerance (greater than 75 W). Group A patients had a lower 5-year survival rate than group B patients (81.5% versus 94%, P less than 0.00001). In group A, patients with ST-segment depression had a lower 5-year survival rate than patients without ST-segment depression (76% versus 85%, P = 0.01). In group B, patients with and without ST-segment depression had similar 5-year survival rates (90% versus 96%, P = 0.11). Subgroup analysis of groups A and B according to number of diseased vessels and presence or absence of ST-segment depression revealed that exercise-induced ST-segment depression (greater than 0.15 mV) was of additional prognostic importance only in patients with triple vessel disease. 5-year survival rates in group A with triple vessel disease were 71% with and 80% (P = 0.057) without ST-segment depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Use of changes in ST segment elevation for prediction of infarct artery recanalization in acute myocardial infarction.

BACKGROUND: The role of the ECG in evaluating reperfusion status after thrombolytic treatment in acute myocardial infarction is not clear. Dramatic ST segment changes have been observed during recanalization of an infarct-related artery, but ST criteria have not been definitively established for prediction of coronary artery patency. Differences in ST segment changes in relation to infarct localization have not been evaluated, and further investigation is required into reciprocal ST depression, which provides information independent from ST elevation. Therefore, the aim of this study was to evaluate how early changes in ST segment elevations and depressions predict vessel patency after fibrinolysis for patients with anterior and inferior/lateral infarcts. METHODS AND RESULTS: Two hundred patients with a Pardee wave in the ECG and chest pain of less than 6 h duration were given thrombolytic treatment. The result of the therapy was assessed simultaneously with coronary angiography. Patients were divided into two groups: I (50 patients) without recanalization (TIMI grade 0, 1 or 2), and II (150 patients) with successful recanalization (TIMI grade 3). Before and after therapy, analysis of the 12 lead ECG included maximum ST elevation measurement (H1, H2 respectively), the sum of ST elevations (sigma H1, sigma H2), the sum of ST segment depressions (sigma h1, sigma h2), and the ratios of ST segment changes (R1 = H2:H1, R2 = sigma H2:sigma H1, R3 = sigma h2:sigma h1). The mean interval from the first to the second ECG was 3.5 +/- 1 h. Successive values of R1 and R2 were examined to find that which best distinguished between the two groups. The best values for prediction of reperfusion were: (1) For anterior wall infarct [table: see text] (2) For inferior and lateral infarct [table: see text] In 13 patients with a complete right or left bundle branch block in the first or second ECG, the result of treatment was predicted in 11 patients using criteria for factor R1 and in 12 patients using criteria for R2. Analysis of ST segment depressions revealed a significant correlation between normalization of ST segment depressions and elevations (R3 vs R1: r = 0.60, P < 0.05; R3 vs R2 r = 0.59, P < 0.05). Multivariate discriminant analysis showed an independent value of R3 for discrimination between the two groups, but only in patients with inferior/lateral infarcts. The overall accuracy of the common algorithm in predicting reperfusion was significantly better in patients with inferior/lateral infarcts (Chi2 test, P = 0.0078). When separate algorithms were used, there was no significant difference between patients with anterior or inferior/lateral infarcts because of the significant improvement in prediction of reperfusion in patients with anterior infarcts (McNemar's test: P = 0.041). CONCLUSIONS: We conclude that analysis of ST segments on the standard 12-lead ECG offers valuable help in the early identification of successful recanalization of infarct-related arteries after thrombolytic therapy in patients with acute myocardial infarction. Use of the ratio of ST segment normalization according to the separate criteria for anterior and inferior/lateral infarcts gives the test a high sensitivity and specificity, even in the presence of interventricular conduction disturbances.

Adult↗
PubMed1995

An analysis of structural instances of low complexity sequence segments.

Amino acid sequence databases contain many low complexity, compositionally biased sequence segments. However, only a limited number of relatively short instances of these segments occur in proteins of known structure. An analysis is presented of structural instances of these low complexity sequence segments in the Brookhaven Protein Data Bank with regard to preferences for sequence composition, secondary structural conformation and the local atomic environment. The complexity varies almost linearly with segment length, reflecting the absence of very long, low complexity segments in the structural database. The low complexity segments identified are not disordered and have temperature factors which are generally the same as the rest of the protein. It is observed that these segments are predominantly exposed and either helical or coiled, in excess of what would be expected by chance. Secondary structure prediction methods perform well in correctly predicting those low complexity segments which are helical but poorly in correctly predicting segments that are strands.

Amino Acid Sequence↗
PubMed1998

Regulation of gamma-glutamyl transpeptidase catalytic activity and protein level in the initial segment of the rat epididymis by testicular factors: role of basic fibroblast growth factor.

The objective of this study was to test the hypothesis that gamma-glutamyl transpeptidase (GGT) catalytic activity and protein level in the initial segment are regulated by testicular factors. In the rat epididymis, levels of GGT catalytic activity were initial segment > caput > corpus = cauda. GGT catalytic activity and protein level in the initial segment decreased after efferent duct ligation (EDL) for 3 days, but were recovered when initial segment pieces were incubated with ovine or rat rete testis fluid (oRTF or rRTF, respectively). Factors responsible for the recovery were shown to be greater than 10 kDa and protein-like, but these factors were not androgen-binding protein or testosterone in oRTF. Further experiments were designed to test the hypothesis that growth factors within oRTF and rRTF regulate GGT catalytic activity and GGT protein level. Basic fibroblast growth factor (bFGF) but not epidermal growth factor recovered GGT catalytic activity and protein level in the initial segment following 3-day EDL. Western blot analyses also revealed that bFGF-like proteins were present in rRTF, epididymal luminal fluid, and rat initial segment homogenate, and that the level of bFGF-like proteins declined in the initial segment following 3-day EDL. Using a bFGF monoclonal antibody, a small amount of bFGF-like proteins was found to be also present in oRTF. Our studies suggest that bFGF is one of the testicular factors involved in the regulation of epididymal GGT catalytic activity and protein level. Since decreased GGT catalytic activity caused by 3-day EDL in the rat initial segment was also recovered by a tumor promoter, phorbol 12-O-tetradecanoylphorbol 13-acetate, it is possible that a signal transduction pathway is involved in the regulation of GGT catalytic activity and GGT protein level by testicular factors. Western blot analyses also indicated that the 43-kDa bFGF-like protein in the lumen of the rat epididymis originates from the testis, is concentrated in the initial segment, and is reabsorbed by the epididymal epithelia from proximal to distal epididymal regions.

Animals↗
PubMed2001

Mechanical testing of a single rod versus a double rod in a long-segment animal model.

This study involved the mechanical testing of single-rod segmental hook fixation and double-rod segmental hook fixation in a long-segment animal model. The goals were first to compare the flexibility of a single-rod scoliosis construct with that of a double-rod construct when tested in torsion, and second, to determine the effect of not using instrumentation with every vertebral segment for the single rod. Another study found that the single-rod construct was as stiff in torsion as the standard double-rod construct in a model of 10 vertebral segments. The amount of neutral zone (NZ) rotation was tested in five calf spines using an MTS (Material Testing System) machine. Five constructs were tested and included 1) a single rod with hooks at every level except the apex; 2) a single rod with two fewer hooks; 3) a single rod with four fewer hooks; 4) a double-rod construct; and 5) no instrumentation. The amount of NZ rotation between vertebral segments was measured over 12, 10, 8, 6, 4, and 2 vertebral segments. An analysis of variance with all constructs showed that the instrumented spines had significantly less movement than did the uninstrumented spine. Statistical comparison using analysis of variance of constructs (constructs 1 to 4) showed that over 12 vertebral segments (T4-L3), all single-rod constructs (constructs 1 to 3) allowed more NZ rotation than did the standard double-rod construct. This testing indicated that over 12 vertebral segments the single rod allowed more NZ rotation than a double-rod construct.

Animals↗
PubMed1998

Prevalence of episodes of ST-segment depression among mild-to-moderate hypertensive patients in northern Italy: the Cardioscreening Study.

OBJECTIVES: To assess the prevalence of episodes of ST-segment depression in a population of consecutive patients with mild-to-moderate essential hypertension who are free of clinical signs of coronary artery disease. METHODS: The study involved 28 Italian centers that enrolled 414 hypertensive patients (aged 50-70 years; diastolic blood pressure > or = 95-115 mmHg or systolic blood pressure > or = 150-220 mmHg, or both, 10 days after withdrawal of medications). Silent myocardial ischemia was assessed by means of exercise stress testing and 48 h Holter monitoring. An ischemic episode was defined as a horizontal or downward sloping ST-segment depression > or = 100 microV, occurring 80 ms after the J point, and lasting for at least 1 min. RESULTS: Of the 414 patients enrolled, 411 completed the exercise stress test. During the test significant ST-segment depression occurred for 25 patients (6.1%) and all episodes but one were asymptomatic and not associated with arrhythmias. Of the 396 patients for whom we analyzed a 48 h Holter recording, 43 (10.9%) had at least one episode of ST-segment depression and seven of these had also had one during the exercise stress test The median number of episodes per patient was five (range 1-19), median duration was 9 min (range 1-20 min), and the mean amplitude of the ST-segment depression was 190 +/- 180 microV. None of these episodes was associated with symptoms and all of them occurred under resting condition. Patients with (n = 61) and without (n = 335) ST-segment depression during Holter monitoring or exercise stress testing had similar ages (59 +/- 6 versus 58 +/- 6 years) and did not differ for tobacco smoking, plasma lipid levels, blood pressure values and prevalence of echocardiographic left ventricular hypertrophy (57% of patients had left ventricular mass indexes > or = 134 g/m2 for men and > or = 110 g/m2 for women in both groups). Women had a higher prevalence of ST-segment depression than did men during Holter monitoring [32 of 183 (17.5%) versus 11 of 213 (5.2%)], whereas the prevalences of ischemia during the exercise stress test were similar. Female sex was the only significant factor associated with the occurrence of silent myocardial ischemia [odds ratio 2.56 (95% confidence interval 1.40-4.71)]. CONCLUSIONS: Our results show that 15% of patients with mild-to-moderate hypertension, who are free of clinical signs of coronary artery disease, experience episodes of ST-segment depression during Holter monitoring or exercise stress testing. Most of these episodes are asymptomatic and are not associated with the severity of hypertension, the presence of left ventricular hypertrophy, and other risk factors for coronary artery disease. Episodes of ST-segment depression are more common for women than they are for men, particularly during Holter monitoring. The early detection of silent myocardial ischemia by Holter monitoring or by the exercise stress test might be useful for the identification of hypertensive patients who should be investigated further and administered a more specific treatment.

Age Factors↗
PubMed2000

Surgical approaches for the treatment of aneurysms on the P2 segment of the posterior cerebral artery.

OBJECTIVE: The P2 segment of the posterior cerebral artery has remained a challenging region to expose surgically. We establish a surgical strategy for P2-segment aneurysms. METHODS: Each segment of the posterior cerebral artery was classified according to Zeal and Rhoton's classification. Fourteen of 18 P2-segment aneurysms were surgically treated. The patient's outcome, the aneurysm location, and the surgical procedures were evaluated. A cadaveric study was performed to clarify the surgical view obtained via three different surgical approaches. RESULTS: Nine aneurysms were clipped, two were trapped, one was coated, and one was excised with parent artery reconstruction. Cerebral revascularization techniques were used for three patients. The pterional approach exposed the anterior half of the P2a segment. The subtemporal approach revealed the P2a segment, but its exposure was restricted by its localization in the ambient cistern. Via the occipital interhemispheric transtentorial approach, the P2p segment was visible and could be manipulated. When the posterior half of P2a segment was high on a coronal view of magnetic resonance imaging, it was extremely hard to access via any approach. CONCLUSION: A surgical strategy for the P2 aneurysm can be planned with accurate prediction of the aneurysm location. When the localization of an aneurysm on the posterior half of P2a segment is high, a resection of brain tissue may be required.

Adolescent↗
PubMed1996

Segmental variations of bone mineral density in the cervical spine.

STUDY DESIGN: This study assessed the variability of segmental bone mineral density in the lower cervical spine (C4 through C7). A mean segmental bone mineral density value at each level was determined for all specimens, and a mean coefficient of variation among the 17 specimens was calculated. OBJECTIVES: To quantify the degree of intersegmental bone mineral density variations within cadaveric lower cervical spine segments. SUMMARY OF BACKGROUND DATA: Bone mineral density studies in the thoracic and lumbar spine have shown a high degree of variability between spinal segments; however, the extent of segmental bone mineral density variability in the cervical spine is unknown. METHODS: Seventeen human cadaveric cervical spine specimens (C4 through C7) were scanned in a water bath using dual energy x-ray absorptiometry in a lateral direction. Segmental bone mineral density of the vertebral bodies of all specimens were analyzed with respect to differences between segments within each specimen. RESULTS: The mean coefficient of segmental bone mineral density variations within each specimen for all spines was 14.8% (range, 5.8%-22.9%). Bone mineral density mean values and ranges at each level were as follows: C4, 0.720 g/cm2 (range, 0.367-1.161 g/cm2); C5, 0.784 g/cm2 (range, 0.348-1.268 g/cm2); C6, 0.735 g/cm2 (range 0.367-1.450 g/cm2); C7, 0.590 g/cm2 (range, 0.340-1.040 g/cm2). Paired analysis of difference between all levels for 16 specimens demonstrated the bone mineral density at the C7 level to be significantly lower than at all other levels (P < 0.05). CONCLUSION: Our data show that significant interlevel bone mineral density variability exists in the lower cervical spine, and suggests that random single segment bone mineral density sampling or mean specimen bone mineral density values may not be relevant.

Absorptiometry, Photon↗
PubMed1997

The spondylolytic vertebra and its adjacent segment. Mobility measured before and after posterolateral fusion.

STUDY DESIGN: By using roentgen stereophotogrammetric analysis in six patients having tantalum indicators implanted at a preoperative external fixation test, the mobility in the spondylolytic lumbosacral level and its adjacent segment could be studied before fusion and during the course of postoperative fusion consolidation. OBJECTIVE: To study the mobility effects on the segment adjacent to a lumbar fusion over time from the preoperative situation until fusion healing as defined by roentgen stereophotogrammetric analysis. SUMMARY OF BACKGROUND DATA: In vitro studies indicate that the altered biomechanical situation after lumbar fusion increases the intradiscal pressure and changes the kinematics in the juxtafused segment. METHODS: Six patients with low grade spondylolysisolisthesis were scheduled for fusion of the spondylolytic lumbosacral segment after a preoperative external fixation test. The latter procedure also included implantation of tantalum markers for spinal roentgen stereophotogrammetric analysis. Each patient was examined by roentgen stereophotogrammetric analysis at four separate occasions: before fusion (2 months after removal of the external frame) and 3, 6, and 12 months after surgery. The translatory movements of the L5 vertebra in relation to sacrum and of the L4 vertebra in relation to the L5 vertebra were calculated at each examination. RESULTS: For the juxtafused L4-L5 level, increased and decreased mobility patterns could be identified. Transformation of the preoperative mobility in the lumbosacral segment to the adjacent segment during fusion consolidation was verified in two patients but was not a general phenomenon. CONCLUSION: Fusion of the lumbosacral segment can alter the kinematics of the adjacent segment, redistributing the mobility toward relative hypermobility in the juxtafused segment.

Adult↗
PubMed1998

A kinematic study of the cervical spine before and after segmental arthrodesis.

STUDY DESIGN: The acute kinematic consequence of segmental arthrodesis in the cervical spine on the remaining open motion segments was studied in a cadaveric model. OBJECTIVES: To evaluate the distribution of motion across unfused cervical motion segments after a segmental arthrodesis. The applied load was determined as a function of arthrodesis length and level by using a fixed range of motion for the cervical spine (C2-T1). SUMMARY OF BACKGROUND DATA: An increased incidence of degenerative disease may exist at the levels immediately adjacent to a cervical arthrodesis as a result of alteration in biomechanical behavior at these levels. METHODS: One-, two-, and three-level fusions were simulated in multilevel ligamentous human cervical spines. Specimens were tested nondestructively through a 30 degrees range of sagittal plane rotation. Motion was recorded using three-dimensional stereophotogrammetry. Sagittal plane rotation of each motion segment in the fusion models was compared with the corresponding rotation in the unfused specimen. RESULTS: In the C2-C4 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increase at C7-T1. In the C2-C5 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increases at C6-C7 and C7-T1. For each of the five other fusion types tested, no statistical differences existed between the increases in sagittal rotation at any of the open motion segments. The bending moment necessary to produce 30 degrees of sagittal rotation increased nonlinearly as the number of motion segments fused increased. CONCLUSIONS: Under what was considered a realistic loading paradigm, sagittal plane rotation was not increased disproportionately at the motion segments immediately adjacent to a segmental arthrodesis in the cervical spine. The nonlinear rise in applied bending moment to achieve constant displacement was characteristic of the behavior of the ligaments and intervertebral discs throughout the spine as they underwent increasing deformation.

Aged↗
PubMedDate not supplied

Resolution of ST-segment elevation after thrombolytic therapy in elderly patients with acute myocardial infarction.

We examined the resolution of ST-segment elevation after thrombolytic therapy in elderly versus younger patients with acute myocardial infarction. Electrocardiograms were recorded before, on completion of, and on day 1 and day 2 post-thrombolytic therapy (streptokinase or tissue thromboplastin activator) in 36 patients older than 65 years and 36 patients younger than 65 years. There was no significant different in the pre-thrombolytic ST-segment elevation per lead in both elderly and younger patients (3.7 +/- 0.7 versus 3.5 +/- 0.8 mm; P = NS). On completion of thrombolytic therapy, both groups demonstrated resolution of ST-segment elevation and, although the ST-segment elevation per lead was higher in elderly patients (3.0 +/- 0.9 versus 2.5 +/- 0.9 mm; P = 0.008), the percentage resolution per lead was not significantly different (19% versus 29%; P = NS). On day 1 post-thrombolytic therapy, there was further resolution of ST-segment elevation in both groups, but at this point, the percentage resolution per lead was significantly less in the elderly than in the younger patients (51% versus 66%; P = 0.03), and the ST-segment elevation per lead remained higher in elderly patients (1.8 +/- 1.0 versus 1.2 +/- 0.6 mm; P = 0.0009). On day 2 post-thrombolytic therapy, although there was further resolution of ST-segment elevation in both groups, the percentage resolution per lead remained significantly less (68% versus 80%; P = 0.05) and ST-segment elevation per lead remained significantly higher in elderly patients (1.2 +/- 0.7 versus 0.7 +/- 0.4 mm; P = 0.0002). Resolution of ST-segment elevation after thrombolytic therapy was less marked in elderly patients, indicating a reduced response to thrombolytic therapy in this patient population.

Age Factors↗
PubMed2005

Reduction of vertebral blood flow by segmental vessel occlusion: an intraoperative study using laser Doppler flowmetry.

STUDY DESIGN: During anterior spinal surgery, vertebral perfusion was assessed by laser Doppler flowmetry. Blood flow changes were assessed after unilateral ligation and contralateral compression of the segmental vessels. OBJECTIVE: To assess the influence of unilateral and bilateral segmental vessel occlusion on vertebral blood flow. SUMMARY OF BACKGROUND DATA: During anterior spinal surgery, segmental vessels are frequently being ligated. The reduced blood supply to the vertebrae may impair intervertebral fusion, and the decreased spinal cord perfusion may lead to ischemic myelopathy. To our knowledge, this is the first in vivo study to investigate vertebral blood flow. METHODS.: There were 10 patients who underwent anterior release for adult idiopathic scoliosis (n = 6), Scheuermann disease (n = 3), and posttraumatic kyphosis (n = 1). A high-power laser Doppler flowmeter was used to assess vertebral blood flow. Measurements were performed in 19 thoracic and 4 lumbar vertebrae (n = 23) after unilateral segmental vessel ligation and additional temporary digital compression of the contralateral vessels. RESULTS: Initial mean blood flow was 49.1 +/- 27.6 arbitrary units, and all signals were pulsatile. The blood flow decreased by a mean of 8% after unilateral ligation of the segmental vessels. With additional compression of the contralateral vessels, the signal heights decreased significantly by 54% (mean 18.3 +/- 7.8 arbitrary units, P = 0.00003), and a loss of the pulsatile pattern was observed in 75% of the vertebrae. On release of digital compression, the signal height as well as the pulsatility promptly returned. CONCLUSIONS: Unilateral ligation of segmental vessels led only to a slight decrease of the vertebral blood flow. Future studies may show whether sparing the segmental vessels during anterior fusion enhances bone graft incorporation, thus decreasing the rate of pseudarthrosis. According to clinical data, the risk of neurologic injury through unilateral ligation is negligible. Bilateral segmental vessel occlusion markedly reduced vertebral bloodflow. Therefore, when treating patients with a higher neurologic risk or in revision cases, the surgeon should always consider sparing the segmental vessels.

Adolescent↗