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At least 1,261 records · Page 70Linked to original sources
PubMed2001

Computer simulation of osteotomy correction.

This paper describes a novel approach to correct osteotomy deformities of long bones using virtual reality and image processing techniques on personal computers. The discussed method allows to simulate osteotomy corrections by implementing a single cut and a rearrangement of the dissected bone parts. It allows the surgeon to directly control the pre-operative situation and the post-operative result of the simulation by comparing bone-length, angles, and torsion of the bone. In addition, he or she obtains the coordinates and angles of the planned cut relative to anatomical landmarks.

Bone Malalignment↗
PubMed1989

Paraplegic standing controlled by functional neuromuscular stimulation: Part II--Computer simulation studies.

We simulated two types of body motion. First, the body position is assumed to be initially perturbed from the upright position, and all muscles are assumed inactive at the initial position. The control law developed in the preceding paper drives the body segments to the standing position. Arm movements are then applied to the body to investigate how performance is affected by an external disturbance. Simulated body motion indicated that the current output-feedback control law functions well. The body can recover upright posture from a highly flexed position, and the controller can then maintain the body near the vertical during arm movements. The simulation results showed three consistent activation patterns based on energy minimization: 1) no antagonistic muscle pairs are coactivated, 2) strong muscles are recruited before weak ones, and 3) fast muscles are recruited before slow ones. The reason for the second and third observations is that energy liberation rate depends heavily on the relative amount of muscle activation. Since the current control law requires muscles to generate specific joint torques at a prescribed time, strong muscles do not have to be activated as much as weak ones, and recruiting a fast muscle at low activation level consumes less energy than recruiting a slow one at high activation level. Although the output-feedback control law functions well according to our simulation results, the static optimization process would, in practice, take too much computational time to make it practical. Based on the consistent activation patterns found in our simulations, we therefore developed a simpler (suboptimal) activation-distribution scheme that takes much less time and still gives nearly identical performance.

Biomechanical Phenomena↗
PubMed2005

Clinical staging of prostate cancer: a computer-simulated study of transperineal prostate biopsy.

OBJECTIVE: To identify the precise location of prostate cancer within the gland and thus possibly permit more aggressive therapy of the lesion, while potentially sparing the noncancerous gland from ablative therapy. MATERIALS AND METHODS: Three-dimensional "solid" computer models were reconstructed for 86 autopsy specimens and 20 stage T1c radical prostatectomy specimens. Transperineal biopsies were simulated for grid sizes of 5-mm (method A) and 10-mm (method B) with an 18 G, 23-mm long biopsy needle. One or two biopsies per grid point were obtained for a total of 12-108 biopsies, depending on the size of the prostate. Clinically threatening cancers were defined as having volumes of > or = 0.5 mL or Gleason sum > or = 7. RESULTS: Method A detected significantly more carcinomas than method B in both the autopsy and prostatectomy specimens (autopsy, 72 vs 51; prostatectomy, 50 vs 32, both P < 0.001). Method A also detected more clinically threatening cancers found at autopsy (38/40 vs 31/40, P = 0.008). Among autopsy patients with negative sextant biopsies whose disease was localized to one side, method A detected 72% and method B detected 29-43% (P < 0.001). CONCLUSIONS: The results of this computer simulation show that 5- and 10-mm grid biopsies detect three-quarters and a third, respectively, at autopsy, of patients with the disease localized to one side of the prostate, which may be useful when planning highly selective ablative treatments in the future.

Adult↗
PubMed1992

Computer simulation of the initial proton transfer step in human carbonic anhydrase I.

The initial water proteolysis step in the proton transfer "half-reaction" of human carbonic anhydrase I is simulated using the empirical valence bond method in combination with free energy perturbation molecular dynamics calculations. A free energy profile for the enzyme catalysed reaction and the corresponding pKa associated with ionization of the zinc-bound water is calculated. The obtained pKa value of 7 to 8 appears to be in good agreement with experimental observations and the calculated rate constant for this step is also compatible with kinetic data. The simulations clearly emphasize the important electrostatic effect associated with the catalytic zinc ion.

Carbonic Anhydrases↗
PubMed2005

Computer simulations of the translocation and unfolding of a protein pulled mechanically through a pore.

Protein degradation by ATP-dependent proteases and protein import into the mitochondrial matrix involve the unfolding of proteins upon their passing through narrow constrictions. It has been hypothesized that the cellular machinery accomplishes protein unfolding by pulling mechanically at one end of the polypeptide chain. Here, we use Langevin dynamics simulations of a minimalist off-lattice model to examine this hypothesis and to study the unfolding of a protein domain pulled mechanically through a long narrow pore. We compute the potential of mean force (PMF) experienced by the domain as a function of its displacement along the pore and identify the unfolding intermediates corresponding to the local minima of the PMF. The observed unfolding mechanism is different from that found when the two termini are pulled apart, as in single-molecule mechanical unfolding experiments. It depends on the pore diameter, the magnitude of the pulling force, and on whether the force is applied at the N- or the C-terminus of the chain. Consequently, the translocation time exhibits a pulling force dependence that is more complex than a simple exponential function expected on the basis of simple phenomenological models of translocation.

Adenosine Triphosphate↗
PubMed1982

Relationship between EPSP shape and cross-correlation profile explored by computer simulation for studies on human motoneurons.

We used a computer model (making several simplifying assumptions) to explore the relationship between the characteristics of an excitatory postsynaptic potential (EPSP) and the profile of the change in firing probability that occurred when that EPSP was delivered to a rhythmically discharging neuron. In circumstances applicable to studies on human motoneurons we found that the magnitude of the period of increased firing probability in the cross-correlation (produced by the rising phase of the EPSP) was related to the number of stimuli and to the proportion of the interspike interval that the EPSP was within reach of threshold. The interstimulus interval and the statistical distribution of the motoneuron interspike intervals were of little consequence. For this model the subsequent period of reduced firing probability was proportional to the amplitude of the EPSP and not to the duration of its falling phase.

Afferent Pathways↗