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PubMed2001

A comparison between dynamic pelvic magnetic resonance imaging and videoproctography in patients with constipation.

PURPOSE: This study attempts to compare the diagnostic efficacy of dynamic pelvic magnetic resonance imaging with that of videoproctography for the presence of rectocele, sigmoidocele, and intussusception as well as the measurement of anorectal angle and perineal descent in constipated patients. METHODS: Patients volunteering for the study and fulfilling the criteria for videoproctography to evaluate constipation were also scheduled for dynamic pelvic magnetic resonance imaging. Patients undergoing videoproctography were placed in the left lateral decubitus position, after which 50 ml of liquid barium paste was introduced into the rectum. After this, approximately 100 ml of thick barium paste similar to stool in consistency was injected into the rectum, and the patient was instructed to defecate while video images were taken. For dynamic pelvic magnetic resonance imaging, air, to be used as contrast, was allowed to accumulate in the rectum via examination with the patient in the prone position. A capsule was taped to the perineal skin immediately posterior to the anal orifice for marking. Sagittal and axial T1 images were obtained through the pelvis at 8-mm intervals with dynamic breathhold sagittal images of the anorectal region obtained at rest and during strain and squeeze maneuvers. Total acquisition time per maneuver was approximately 19 seconds. The tests were performed by different examiners blinded to the result of the other evaluation. The investigations were independently interpreted, findings compared, and patients questioned regarding their impression of dynamic pelvic magnetic resonance imaging and videoproctography. RESULTS: From June 1996 to April 1997, 22 patients (15 females) with a mean age of 68 (range, 21-85) years underwent both videoproctography and dynamic pelvic magnetic resonance imaging. Dynamic pelvic magnetic resonance imaging was only able to detect 1 of 12 (8.3 percent) anterior rectoceles and one of two (50 percent) posterior rectoceles identified by videoproctography. It failed to recognize any of the rectoanal intussusception (zero of four) but did show 9 of 12 (75 percent) sigmoidoceles. Significant discrepancy of measurement of the anorectal angle and perineal descent exists between the two studies, and dynamic pelvic magnetic resonance imaging was not able to detect any (0 of 11) of the patients with increased fixed perineal descent and only half (one of two) of the patients with increased dynamic perineal descent noted on videoproctography. All 22 patients preferred dynamic pelvic magnetic resonance imaging over videoproctography because of greater comfort. CONCLUSION: Occasionally, the increased cost of new technology can be justified by the enhanced diagnostic yield. The ability to avoid unnecessary surgery or, conversely, to continue to search for otherwise occult pathology that can be surgically corrected justifies routine application of these new tools. However, this study has shown that, despite a cost of approximately ten times more for dynamic pelvic magnetic resonance imaging than for videoproctography, no clinical changes were made. Thus, on the basis of this study, we cannot endorse the routine application of dynamic pelvic magnetic resonance imaging for the evaluation of constipated patients. In certain selected individuals, it may play a role, but further study is necessary to clarify its exact role.

Adult↗
PubMed2006

Effect of a posterior dynamic implant adjacent to a rigid spinal fixator.

BACKGROUND: A slightly degenerated disc adjacent to a segment that has to be fused is sometimes instrumented with a dynamic fixator. The dynamic implant is assumed to reduce disc loads at that level and to preserve disc function, thus inhibiting the progression of degeneration. METHODS: A three-dimensional finite element model of the lumbar spine was used to study the effect of a dynamic implant on the mechanical behavior at the corresponding level. After studying a healthy lumbar spine for comparison, a rigid fixator and a bone graft were inserted at L2/L3. Healthy and degenerated discs were assumed at the adjacent level, i.e. L3/L4. An additional paired dynamic posterior fixator was then implemented at level L3/L4. Finally, the segment with the dynamic fixator was distracted to the height of a healthy disc. The loading cases of walking, extension, flexion and axial rotation were simulated. FINDINGS: A dynamic implant reduces intersegmental rotation for walking, extension and flexion as well as facet joint forces for axial rotation at its insertion level. Intradiscal pressure is not markedly reduced by a dynamic implant. Moreover, there are no substantial differences between the mechanical behavior of rigid and dynamic fixators. INTERPRETATION: Our model does not predict major differences in the mechanical effects between rigid and dynamic fixators despite the extreme assumption that a dynamic implant does not transfer moments. The results do not support the assumption that disc loads are significantly reduced by a dynamic implant. For axial rotation, however, dynamic fixation devices do reduce the force in the facet joint.

Back↗
PubMed2001

Resistance to Taxol in lung cancer cells associated with increased microtubule dynamics.

Microtubule dynamics are crucial for mitotic spindle assembly and chromosome movement. Suppression of dynamics by Taxol appears responsible for the drug's potent ability to inhibit mitosis and cell proliferation. Although Taxol is an important chemotherapeutic agent, development of resistance limits its efficacy. To examine the role of microtubule dynamics in Taxol resistance, we measured the dynamic instability of individual rhodamine-labeled microtubules in Taxol-sensitive and -resistant living human cancer cells. Taxol-resistant A549-T12 and -T24 cell lines were selected from a human lung carcinoma cell line, A549. They are, respectively, 9- and 17-fold resistant to Taxol and require low concentrations of Taxol for proliferation. We found that microtubule dynamic instability was significantly increased in the Taxol-resistant cells. For example, with A549-T12 cells in the absence of added Taxol, microtubule dynamicity increased 57% as compared with A549 cells. The length and rate of shortening excursions increased 75 and 59%, respectively. These parameters were further increased in A549-T24 cells, with overall dynamicity increasing by 167% compared with parental cells. Thus, the decreased Taxol-sensitivity of these cells can be explained by their increased microtubule dynamics. When grown without Taxol, A549-T12 cells were blocked at the metaphase/anaphase transition and displayed abnormal mitotic spindles with uncongressed chromosomes. In the presence of 2-12 nM Taxol, the cells grew normally, suggesting that mitotic block resulted from excessive microtubule dynamics. These results indicate that microtubule dynamics play an important role in Taxol resistance, and that both excessively rapid dynamics and suppressed dynamics impair mitotic spindle function and inhibit proliferation.

Antineoplastic Agents, Phytogenic↗
PubMed2006

Stability of dynamic trunk movement.

STUDY DESIGN: Nonlinear systems analyses of trunk kinematics were performed to estimate control of dynamic stability during repetitive flexion and extension movements. OBJECTIVE: Determine whether movement pace and movement direction of dynamic trunk flexion and extension influence control of local dynamic stability. SUMMARY OF BACKGROUND DATA: Spinal stability has been previously characterized in static, but not in dynamic movements. Biomechanical models make inferences about static spinal stability, but existing analyses provide limited insight into stability of dynamic movement. Stability during dynamic movements can be estimated from Lyapunov analyses of empirical data. METHODS: There were 20 healthy subjects who performed repetitive trunk flexion and extension movements at 20 and 40 cycles per minute. Maximum Lyapunov exponents describing the expansion of the kinematic state-space were calculated from the measured trunk kinematics to estimate stability of the dynamic system. RESULTS: The complexity of torso movement dynamics required at least 5 embedded dimensions, which suggests that stability components of lumbar lordosis may be empirically measurable in addition to global stability of trunk dynamics. Repeated trajectories from fast paced movements diverged more quickly than slower movement, indicating that local dynamic stability is limited in fast movements. Movements in the midsagittal plane showed higher multidimensional kinematic divergence than asymmetric movements. CONCLUSION: Nonlinear dynamic systems analyses were successfully applied to empirically measured data, which were used to characterize the neuromuscular control of stability during repetitive dynamic trunk movements. Movement pace and movement direction influenced the control of spinal stability. These stability assessment techniques are recommended for improved workplace design and the clinical assessment of spinal stability in patients with low back pain.

Adult↗
PubMed2001

Theory of the generalized dynamic structure factor of polyatomic molecular fluids measured by inelastic x-ray scattering.

We describe a theory for the calculation of the generalized dynamic structure factor S(k,omega) as measured by an inelastic x-ray scattering (IXS) experiment on single-component molecular or polyatomic molecular fluids. IXS spectrum of a simple fluid is proportional to the dynamic structure factor of a single species of atom. In the case of a molecular fluid, however, IXS spectrum is a weighted sum of partial dynamic structure factors of pairs of atomic species. The weighting factors are products of the atomic form factors of the pairs. We call this weighted average dynamic structure factor the generalized dynamic structure factor. We extend the formalism of a three effective eigenmode theory (TEE) developed previously for simple fluids to derive an approximate evolution equation for the generalized dynamic structure factor, which can be considered as a generalized hydrodynamic equation for molecular fluids. As examples, we first study the contributions of the partial dynamic structure factor to the generalized dynamic structure factor computed from molecular dynamics simulation of SPC/E model water. We found that the generalized dynamic structure factor of water measured by IXS can be well approximated by the center of mass or the oxygen atom dynamic structure factors. The generalized TEE model was then employed to analyze IXS spectra of nearly fully hydrated dilauroylphosphatidylcholine. The theory is able to fit all of the spectra in the k range from 5 to 32 nm(-1) quantitatively and gives their deconvoluted generalized dynamic structure factors.

Journal Article↗
PubMed2003

Evaluation of detector dynamic range in the x-ray exposure domain in mammography: a comparison between film-screen and flat panel detector systems.

Digital detectors in mammography have wide dynamic range in addition to the benefit of decoupled acquisition and display. How wide the dynamic range is and how it compares to film-screen systems in the clinical x-ray exposure domain are unclear. In this work, we compare the effective dynamic ranges of film-screen and flat panel mammography systems, along with the dynamic ranges of their component image receptors in the clinical x-ray exposure domain. An ACR mammography phantom was imaged using variable mAs (exposure) values for both systems. The dynamic range of the contrast-limited film-screen system was defined as that ratio of mAs (exposure) values for a 26 kVp Mo/Mo (HVL=0.34 mm Al) beam that yielded passing phantom scores. The same approach was done for the noise-limited digital system. Data from three independent observers delineated a useful phantom background optical density range of 1.27 to 2.63, which corresponded to a dynamic range of 2.3 +/- 0.53. The digital system had a dynamic range of 9.9 +/- 1.8, which was wider than the film-screen system (p<0.02). The dynamic range of the film-screen system was limited by the dynamic range of the film. The digital detector, on the other hand, had an estimated dynamic range of 42, which was wider than the dynamic range of the digital system in its entirety by a factor of 4. The generator/tube combination was the limiting factor in determining the digital system's dynamic range.

Breast Neoplasms↗
PubMed1999

Modulation of microtubule dynamics by drugs: a paradigm for the actions of cellular regulators.

Microtubules are intrinsically dynamic polymers. Two kinds of dynamic behaviors, dynamic instability and treadmilling, are important for microtubule function in cells. Both dynamic behaviors appear to be tightly regulated, but the cellular molecules and the mechanisms responsible for the regulation remain largely unexplored. While microtubule dynamics can be modulated transiently by the interaction of regulatory molecules with soluble tubulin, the microtubule itself is likely to be the primary target of cellular molecules that regulate microtubule dynamics. The antimitotic drugs that modulate microtubule dynamics serve as excellent models for such cellular molecules. Our laboratory has been investigating the interactions of small drug molecules and stabilizing microtubule-associated proteins (MAPs) with microtubule surfaces and ends. We find that drugs such as colchicine, vinblastine, and taxol, and stabilizing MAPs such as tau, strongly modulate microtubule dynamics at extremely low concentrations under conditions in which the microtubule polymer mass is minimally affected. The powerful modulation of the dynamics is brought about by the binding of only a few drug or MAP molecules to distinct binding sites at the microtubule surface or end. Based upon our understanding of the well-studied drugs and stabilizing MAPs, it is clear that molecules that regulate dynamics such as Kin 1 and stathmin could bind to a large number of distinct tubulin sites on microtubules and employ an array of mechanisms to selectively and powerfully regulate microtubule dynamics and dynamics-dependent cellular functions.

Animals↗
PubMed1995

MR diagnosis of hepatic metastases from neuroendocrine tumors versus hemangiomas: relative merits of dynamic gadolinium chelate-enhanced gradient-recalled echo and unenhanced spin-echo images.

OBJECTIVE: Hepatic metastases from neuroendocrine tumors are often markedly hyperintense on unenhanced T2-weighted MR images, making their appearance similar to that of cavernous hemangiomas. In contrast, cavernous hemangiomas show characteristic enhancement on dynamic gadolinium chelate-enhanced gradient-recalled echo MR images. The purpose of this study was to determine the relative merits of dynamic gadolinium chelate-enhanced gradient-recalled echo MR imaging versus MR imaging with unenhanced spin-echo pulse sequences for distinguishing between hepatic metastases from neuroendocrine tumors and cavernous hemangiomas. MATERIALS AND METHODS: The unenhanced spin-echo and dynamic gradient-recalled echo MR images obtained after IV administration of a gadolinium chelate in 28 patients (14 patients with pathologically proven hepatic metastases from neuroendocrine tumors and 14 patients with hepatic cavernous hemangiomas) were reviewed blindly and independently by three interpreters. Unenhanced spin-echo and dynamic gadolinium chelate-enhanced gradient-recalled echo MR images were compared for accuracy in characterizing liver lesions. RESULTS: The most intense enhancement of hepatic metastases from neuroendocrine tumors was observed on early dynamic gadolinium chelate-enhanced gradient-recalled echo MR images; enhancement was peripheral in four patients, global and heterogeneous in seven patients, and global and homogeneous in three patients. On late dynamic gadolinium chelate-enhanced gradient-recalled echo MR images, enhancement of hepatic metastases from neuroendocrine tumors was predominantly peripheral in five patients, global and heterogeneous in five patients, and global and homogeneous in four patients. Differentiation between cavernous hemangiomas and hepatic metastases from neuroendocrine tumors was impossible in five cases with unenhanced spin-echo MR imaging alone, in five cases with dynamic gadolinium chelate-enhanced gradient-recalled echo MR imaging alone, and in no case with the combination of unenhanced spin-echo MR imaging and dynamic gadolinium chelate-enhanced gradient-recalled echo MR imaging. In comparison with unenhanced spin-echo MR imaging alone or dynamic gadolinium chelate-enhanced gradient-recalled echo MR imaging alone, the combination of unenhanced spin-echo MR imaging and dynamic gadolinium chelate-enhanced gradient-recalled echo MR imaging allowed significantly (p < .001) clearer differentiation between hepatic metastases from neuroendocrine tumors and cavernous hemangiomas. CONCLUSIONS: Early enhancement and heterogeneity on dynamic gadolinium chelate-enhanced gradient-recalled echo MR images are the most common features of hepatic metastases from neuroendocrine tumors. The combination of unenhanced spin-echo and dynamic gadolinium chelate-enhanced gradient-recalled echo MR images allows more accurate characterization of hepatic metastases from neuroendocrine tumors and clearer differentiation from cavernous hemangiomas.

Abdominal Neoplasms↗
PubMed1992

Mechanical enhancement and myocardial oxygen saving by synchronized dynamic left ventricular compression.

Dynamic cardiomyoplasty with synchronously paced skeletal muscle grafts has recently been developed to augment the performance of impaired myocardium. This method has been reported effective to improve patients' general status and some hemodynamic parameters. It is unknown, however, how a systolic dynamic cardiac compression, as in dynamic cardiomyoplasty, affects left ventricular energetics. The purpose of this study was to characterize the effects of dynamic cardiac compression on the ventricle in terms of the pressure-volume relationship and myocardial oxygen consumption. In an isolated cross-circulated dog heart model, a dynamic cardiac compression device was set to directly compress the ventricle during systole. End-systolic pressure, contractility index (Emax), pressure-volume area, external mechanical work, coronary blood flow, and myocardial oxygen consumption were determined before and during dynamic cardiac compression. Dynamic cardiac compression significantly increased Emax. When end-diastolic and stroke volumes were fixed, end-systolic pressure, pressure-volume area, and external mechanical work significantly increased during dynamic cardiac compression while coronary blood flow and myocardial oxygen consumption remained unchanged. When end-systolic pressure was matched with the pre-dynamic cardiac compression control level by decreasing end-diastolic volume at a constant stroke volume so that external mechanical work under dynamic cardiac compression returned to the control level, both pressure-volume area and myocardial oxygen consumption significantly decreased. In contrast to a marked increase in myocardial oxygen consumption for a given increase in external mechanical work by either volume loading or dobutamine, dynamic cardiac compression did not increase myocardial oxygen consumption for the same increase in external mechanical work. Thus dynamic cardiac compression augments left ventricular pump function without increasing myocardial oxygen demand or compromising coronary blood flow.

Animals↗
PubMed2005

Cerebral palsy improvement achieved by coordination dynamics therapy.

Low-intensity coordination dynamics therapy, including crawling, treadmill walking, jumping on spring-board and exercising on a special coordination dynamics therapy device, was applied for 3 months (4 hours therapy per week) to 8 cerebral palsy patients (average age 15 years, range 7-27). All patients improved. The organization of the CNS, quantified by the low-load coordination dynamics between arm and leg turning movements, when exercising on the special coordination dynamics therapy device, improved by 46 +/- 17% (range 33-60%) for forward and by 48 +/- 15% (range 22-66%) for backward moving. Also improved the exercised crawling, jumping and walking, although not as much as the CNS organization quantified by coordination dynamics. The motor programs of the tibialis anterior, gastrocnemius, biceps brachii, and triceps brachii muscles, measured by surface electromyography (sEMG), improved only little. Evidence is provided for sEMG being a very suitable tool for optimizing the movement performance and the therapy since sEMG records show under what exercise conditions the recorded motor programs are best. However coordination dynamics, i.e. the integrative parameter for quantifying CNS organization, is better to show the progress in CNS functioning than movement and EMG improvements. When the patients stopped therapy, the value of their coordination dynamics, worsened 24% after 6 months. In one patient the coordination dynamics therapy was continued intensively for further 3 month, including 20 hours exercise per week. The value of the coordination dynamics even improved altogether by 85% and 82% for forward and backward turning movements respectively, and simultaneously movements, vegetative (sleep) and higher mental functions (aggressivity, learning capacity) showed strong improvements. The improvements of coordination dynamics for low-intensity therapy (46%, for forward movements) and additional high-intensity therapy (85%) lie within the recovery range for stroke (70%) and brain injury (69%) after 3 months of intensive coordination dynamics therapy. There is therefore indication that the CNS functioning in cerebral palsy patients can be improved by learning as much as the CNS functioning can be repaired by re-learning in stroke and brain injury. The improvement of the CNS functioning suggests that cerebral palsy can partly be cured if intensive coordination dynamics therapy is administered for 1 to 2 years. It is further suggested that inabilities, including mental inability, are diseases which can partly be cured rather than inabilities.

Adolescent↗
PubMed2006

Dynamic response of immature bovine articular cartilage in tension and compression, and nonlinear viscoelastic modeling of the tensile response.

Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2 = 0.970+/-0.019 at 1% strain and R2 = 0.992+/-0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10 Hz was approximately 2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was approximately 24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7+/-7.4 deg versus 53.5+/-12.8 deg at 10(-3) Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2 = 0.908+/-0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.

Animals↗
PubMed2001

Dynamic pelvic magnetic resonance imaging and cystocolpoproctography alter surgical management of pelvic floor disorders.

PURPOSE: Pelvic organ prolapse results in a spectrum of progressively disabling disorders. Despite attempts to standardize the clinical examination, a variety of imaging techniques are used. The purpose of this study was to evaluate dynamic pelvic magnetic resonance imaging and dynamic cystocolpoproctography in the surgical management of females with complex pelvic floor disorders. METHODS: Twenty-two patients were identified from The Johns Hopkins Pelvic Floor Disorders Center database who had symptoms of complex pelvic organ prolapse and underwent dynamic magnetic resonance, dynamic cystocolpoproctography, and subsequent multidisciplinary review and operative repair. RESULTS: The mean age of the study group was 58 +/- 13 years, and all patients were Caucasian. Constipation (95.5 percent), urinary incontinence (77.3 percent), complaints of incomplete fecal evacuation (59.1 percent), and bulging vaginal tissues (54.4 percent) were the most common complaints on presentation. All patients had multiple complaints with a median number of 4 symptoms (range, 2-8). Physical examination, dynamic magnetic resonance imaging, and dynamic cystocolpoproctography were concordant for rectocele, enterocele, cystocele, and perineal descent in only 41 percent of patients. Dynamic imaging lead to changes in the initial operative plan in 41 percent of patients. Dynamic magnetic resonance was the only modality that identified levator ani hernias. Dynamic cystocolpoproctography identified sigmoidoceles and internal rectal prolapse more often than physical examination or dynamic magnetic resonance. CONCLUSIONS: Levator ani hernias are often missed by physical examination and traditional fluoroscopic imaging. Dynamic magnetic resonance and cystocolpoproctography are complementary studies to the physical examination that may alter the surgical management of females with complex pelvic floor disorders.

Adult↗
PubMed2004

The effect of anterior cruciate ligament reconstruction on lower extremity relative phase dynamics during walking and running.

The purpose of this investigation was to use relative phase dynamics to evaluate gait in individuals with a reconstructed anterior cruciate ligament (ACL) during walking and running. Relative phase dynamics can describe the coordination strategies between the interacting segments at the lower extremity. Ten subjects who had undergone ACL reconstruction using the central third of their patellar tendon and ten healthy controls walked and ran on a treadmill at a self-selected pace. Relative phase dynamics were calculated for the foot-shank and shank-thigh coordinative relationships. Statistical differences between the groups were noted for the foot-shank relationship (p < 0.05) during both walking and running and for the shank-thigh relationship (p < 0.05) during walking. Our results indicate that current ACL reconstructive techniques may result in altered relative phase dynamics. These changes in relative phase dynamics could be related to a loss of sensory information about joint position and velocity that is typically provided by the intact ACL. Additionally, relative phase adaptations could be a learned response from the early stages of postsurgical rehabilitation. Relative phase dynamics provide quantitative information about the dynamic status of the ACL-reconstructed knee that cannot be gained from the conventional time-series evaluation of gait analysis data. Relative phase dynamics measures should supplement the conventional gait analysis measures that are used today for the clinical evaluation of the functional dynamic stability of the reconstructed knee. The examination of relative phase dynamics could be clinically important for the quantification of new ACL surgical interventions and of patient performance at various stages of rehabilitation. Further research should incorporate relative phase dynamics to understand the influence of ACL reconstruction on coordination and functional patient outcomes.

Adult↗
PubMedDate not supplied

Advanced dynamic flow imaging with contrast-enhanced ultrasonography for the evaluation of tumor vascularity in liver tumors.

To examine the usefulness of advanced dynamic flow imaging in diagnosing hepatic tumor and in assessing therapeutic effects in patients with hepatocellular carcinoma (HCC) and metastatic hepatic tumor, we performed contrast-enhanced ultrasonography (US) with Levovist, a microbubble contrast agent. Twenty-two patients of 35 HCC nodules infected with hepatitis C virus (HCV) and six patients with metastatic liver nodules were studied. They were diagnosed as having HCC or metastasis with helical dynamic computed tomography (CT) and/or celiac angiography. Tumor vascularities in the early arterial and postvascular phases were assessed by real-time scanning of advanced dynamic flow imaging and intermittent interval-delay scanning of contrast pulse subtraction imaging with a wide-band power Doppler technology. All patients showed hypervascular enhancement of HCC on contrast-enhanced US and/or dynamic CT. The advanced dynamic flow could be obtained as vascular and perfusion images of hepatic tumors. Tumor vascularities, including tumor vessels and parenchymal flow, were able to demonstrate in 27 of 29 nodules including 17 patients with 27 HCC nodules and 2 patients with 2 metastatic nodules before radiofrequency ablation (RFA) treatment by the advanced dynamic flow on contrast-enhanced harmonic US. Two nodules gave insufficient dynamic flow which were located approximately 12 cm in depth from the body surface. The advanced dynamic flow, which was done 7-10 days after RFA, indicated disappearance of the tumor vessels in 27 of visible 27 nodules. The study on early phase of helical dynamic CT revealed the same results as noted in early vascular phase of dynamic flow US. No major complication of RFA procedure was noted. The results indicated that contrast-enhanced advanced dynamic flow imaging on US clearly depicted intratumoral vascularity in real time and thus it is useful to diagnose and assess therapeutic efficacy in patients with HCC and metastatic liver tumor.

Aged↗
PubMed2004

Spatial models of virus-immune dynamics.

To date, the majority of theoretical models describing the dynamics of infectious diseases in vivo are based on the assumption of well-mixed virus and cell populations. Because many infections take place in solid tissues, spatially structured models represent an important step forward in understanding what happens when the assumption of well-mixed populations is relaxed. Here, we explore models of virus and virus-immune dynamics where dispersal of virus and immune effector cells was constrained to occur locally. The stability properties of our spatial virus-immune dynamics models remained robust under almost all biologically plausible dispersal schemes, regardless of their complexity. The various spatial dynamics were compared to the basic non-spatial dynamics and important differences were identified: When space was assumed to be homogeneous, the dynamics generated by non-spatial and spatially structured models differed substantially at the peak of the infection. Thus, non-spatial models may lead to systematic errors in the estimates of parameters underlying acute infection dynamics. When space was assumed to be heterogeneous, spatial coupling not only changed the equilibrium properties of the uncoupled populations but also equalized the dynamics and thereby reduced the likelihood of dynamic elimination of the infection. In line with experimental and clinical observations, long-lasting oscillation periods were virtually absent. When source-sink dynamics were considered, the long-term outcome of the infection depended critically on the degree of spatial coupling. The infection collapsed when emigration from source sites became too large. Finally, we discuss the implications of spatially structured models on medical treatment of infectious diseases, and note that a huge gap exists in data accurately describing infection dynamics in solid tissues.

Chronic Disease↗
PubMed2006

Study on the usefulness of precise and simple dynamic balance tests for the evaluation of recovery from intravenous sedation with midazolam and propofol.

BACKGROUND AND OBJECTIVE: Dynamic balance involving movement of the centre of gravity is important for the evaluation of street fitness after sedation. The purpose of this study was to compare the recovery of dynamic balance after intravenous sedation with propofol or midazolam, and to investigate the usefulness of simple dynamic balance tests in evaluating the recovery. METHODS: Fourteen young male volunteers underwent intravenous sedation with propofol and midazolam for 1 h each at an interval of more than 1 week. Computerized dynamic posturography using a multi-axial tilting platform, the 10-m maximum-speed walking test and the timed 'up & go' test (subjects stand up from a chair, walk 5 m and back with maximum speed and sit down again) were performed before and after sedation. The increase in each variable of the tests described above represents a reduction of function. RESULTS: The score of the computerized dynamic posturography was significantly lower in propofol sedation than that in midazolam sedation until 40 min after the end of sedation (P = 0.006). The scores of maximum-speed walking test and timed 'up & go' test were significantly lower in propofol sedation than those in midazolam sedation till 60 min after the end of sedation, respectively (P = 0.035 and 0.042). The timed 'up & go' and maximum-speed walking tests were well and significantly correlated with computerized dynamic posturography in midazolam sedation (timed 'up & go' test vs. computerized dynamic posturography: r = 0.66, P < 0.01; and maximum-speed walking test vs. computerized dynamic posturography: r = 0.53, P < 0.01). CONCLUSION: The timed 'up & go' and maximum-speed walking tests are useful simple dynamic balance tests well correlated with precise computerized dynamic posturography for the evaluation of the recovery of dynamic balance from midazolam sedation in younger adults.

Adult↗
PubMed2004

Contact pair dynamics during folding of two small proteins: chicken villin head piece and the Alzheimer protein beta-amyloid.

The folding of an extended protein to its unique native state requires establishment of specific, predetermined, often distant, contacts between amino acid residue pairs. The dynamics of contact pair formation between various hydrophobic residues during folding of two different small proteins, the chicken villin head piece (HP-36) and the Alzheimer protein beta-amyloid (betaA-40), are investigated by Brownian dynamics (BD) simulations. These two proteins represent two very different classes-HP-36 being globular while betaA-40 is nonglobular, stringlike. Hydropathy scale and nonlocal helix propensity of amino acids are used to model the complex interaction potential among the various amino acid residues. The minimalistic model we use here employs a connected backbone chain of atoms of equal size while an amino acid is attached to each backbone atom as an additional atom of differing sizes and interaction parameters, determined by the characteristics of each amino acid. Even for such simple models, we find that the low-energy structures obtained by BD simulations of both the model proteins mimic the native state of the real protein rather well, with a best root-mean-square deviation of 4.5 A for HP-36. For betaA-40 (where a single well-defined structure is not available), the simulated structures resemble the reported ensemble rather well, with the well-known beta-bend correctly reproduced. We introduce and calculate a contact pair distance time correlation function, C(P) (ij)(t), to quantify the dynamical evolution of the pair contact formation between the amino acid residue pairs i and j. The contact pair time correlation function exhibits multistage dynamics, including a two stage fast collapse, followed by a slow (microsecond long) late stage dynamics for several specific pairs. The slow late stage dynamics is in accordance with the findings of Sali et al. Analysis of the individual trajectories shows that the slow decay is due to the attempt of the protein to form energetically more favorable pair contacts to replace the less favorable ones. This late stage contact formation is a highly cooperative process, involving participation of several pairs and thus entropically unfavorable and expected to face a large free energy barrier. This is because any new pair contact formation among hydrophobic pairs will require breaking of several contacts, before the favorable ones can be formed. This aspect of protein folding dynamics is similar to relaxation in glassy liquids, where also alpha relaxation requires highly cooperative process of hopping. The present analysis suggests that waiting time for the necessary pair contact formation may obey the Poissonian distribution. We also study the dynamics of Forster energy transfer during folding between two tagged amino acid pairs. This dynamics can be studied by fluorescence resonance energy transfer (FRET). It is found that suitably placed donor-acceptor pairs can capture the slow dynamics during folding. The dynamics probed by FRET is predicted to be nonexponential.

Alzheimer Disease↗
PubMed1977

Control of dynamic and static nuclear bag fibres and nuclear chain fibres by gamma and beta axons in isolated cat muscle spindels.

1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles with a blood supply, during stimulation of dynamic gamma axons, dynamic beta axons, or static gamma axons in ventral root filaments was observed and recorded on still and moving film. 2. Most spindles were controlled by one dynamic gamma axon (sometimes a beta axon) and three static gamma axons, one of which was often non-selective in distribution. A large majority of fusimotor axons controlled one pole of the spindle only. 3. Dynamic gamma and beta axons produced focal contraction in only one of the two nuclear bag fibres in any spindle and this fibre was never activated by static gamma axons. Maximal tetanic contraction was attained slowly and the primary sensory spiral on this fibre was stretched by a small amount only. This fibre has been named the 'dynamic nuclear bag fibre'. 4. Static gamma axons produced either: (a) focal contraction in the second of the two nuclear bag fibres only; (b) local contraction in the bundle of nuclear chain fibres only; or (c) contraction in one nuclear bag fibre and the nuclear chain fibres together. Maximum tetanic contraction of this nuclear bag fibre stretched its primary sensory spiral considerably and the time to plateau was relatively short. This fibre has been named the 'static nuclear bag fibre'. 5. 'Driving' of the Ia afferent discharge could always be produced by non-selective static gamma axons, frequently by static gamma axons controlling nuclear chain fibres alone, and was probably due to mechanical oscillation in nuclear chain fibres. It was never produced by dynamic gamma axons and on one occasion only by a static gamma axon controlling a nuclear bag fibre alone. 6. The conduction velocities of dynamic gamma and static gamma axons overlapped extensively, though dynamic gamma axons were absent from the lower end, and static gamma axons innervating nuclear chain fibres only were absent from the upper end, of the range of velocities. 7. The observations are correlated with spindle structure and histochemistry. Dynamic and static nuclear bag fibres are shown to correspond with 'bag1 fibres' and 'bag2 fibres', respectively (Ovalle & Smith, 1972). 8. The possible origin of the dynamic and static actions of fusimotor axons and the role of the dynamic and static intrafusal systems in motor control are discussed.

Action Potentials↗