bluuebunny/crossref_metadata_2025 huggingface dataset:
Smoking cessation increases gingival blood flow and gingival crevicular fluid
Authors: Morozumi Toshiya , Kubota Takehiko , Sato Tadashi , Okuda Kazuhiro , Yoshie Hiromasa
Published: March 2004

Objectives: The purpose of the present study was to determine the effect of smoking cessation on gingival blood flow (GBF) and gingival crevicular fluid (GCF).

Material and Methods: Sixteen male smokers (aged 22–39 (25.3±4.0) years), with no clinical signs of periodontal and systemic diseases, were recruited. The experiment was performed before (baseline) and at 1, 3 and 5 days, and at 1, 2, 4 and 8 weeks after smoking cessation. The status of smoking and smoking cessation was verified by exhaled carbon monoxide (CO) concentration, and by serum nicotine and cotinine concentrations. A laser Doppler flowmeter was used to record relative blood flow continuously, on three gingival sites of the left maxillary central incisor (mid‐labial aspect of the gingival margin and bilateral interdental papillae). The GCF was collected at the mesio‐ and disto‐labial aspects of the left maxillary central incisor and the volume was calculated by the Periotron 6000® system. The same measurements except for the GBF were performed on 11 non‐smoking controls (four females and seven males), aged 23–27 (24.4±1.2) years.

Results: Eleven of 16 smokers successfully completed smoking cessation for 8 weeks. At 1 day after smoking cessation, there was a significantly lower CO concentration than at baseline (p<0.01). Also, nicotine and cotinine concentrations markedly decreased at the second measurement. The GBF rate of smokers was significantly higher at 3 days after smoking cessation compared to the baseline (p<0.01). While the GCF volume was significantly increased at 5 days after smoking cessation compared to the baseline (p<0.01), it was significantly lower than that of non‐smokers until 2 weeks after smoking cessation (p<0.01).

Conclusion: The results show that the gingival microcirculation recovers to normal in the early stages of smoking cessation, which could activate the gingival tissues metabolism/remodeling, and contribute to periodontal health.
Modulation of clinical expression of plaque‐induced gingivitis
Authors: Tatakis Dimitris N. , Trombelli Leonardo
Published: March 2004

Objectives: The purpose of this article is to provide the necessary background and rationale for the accompanying studies, which are ultimately aimed at identifying genetic and environmental factors determining gingivitis susceptibility.

Materials and methods: The literature on factors reported to modify the clinical expression of gingivitis, i.e., factors that determine individual variability in gingival inflammatory response to plaque, is presented.

Results: Clinical evidence suggests that the gingival inflammatory response to plaque accumulation may differ substantially among individuals. However, most of the available studies are of small scale and not purposely designed to address the issue. Systemic factors implicated in modulation of the clinical expression of gingivitis include metabolic, genetic, environmental and other factors. The significance of such factors in designing and conducting a large‐scale experimental gingivitis trial and means to account for them are discussed.

Conclusion: Although several factors have been implicated, genetic or environmental factors underlying differences in gingivitis expression are not fully elucidated. The accompanying studies aim to identify and characterize, among participants in a specifically designed large‐scale experimental gingivitis trial, subjects that differ significantly in their gingival inflammatory response to plaque. This is the first step in an effort to determine genetic or environmental factors underlying such differences.
Modulation of clinical expression of plaque‐induced gingivitis
Authors: Trombelli Leonardo , Tatakis Dimitris N. , Scapoli Chiara , Bottega Sabrina , Orlandini Elisa , Tosi Marina
Published: March 2004

Aim: The aims of this study were to validate a randomized, split‐mouth, localized experimental gingivitis model and to identify subjects with different gingivitis susceptibility.

Material and Methods: In each of 96 healthy subjects, one maxillary quadrant was randomly assigned as “test” (experimental gingivitis) and the contralateral quadrant as “control”. Plaque index (PlI), gingival index (GI), gingival crevicular fluid volume (GCF), and angulated bleeding score (AngBS) were recorded in both quadrants at days 0, 7, 14, and 21. Cumulative plaque exposure (CPE), i.e. PlI over time, was calculated. Day‐21 GCF was standardized according to CPE, and residuals of GCF on CPE were calculated. Two subpopulations were then defined, based on upper and lower quartiles of GCF‐residual distribution and were, respectively, identified as “high‐responder” (HR; n=24) and “low‐responder” (LR; n=24).

Results: At test quadrants, all parameters significantly increased throughout the trial, while in control quadrants, PlI, GI, and AngBS remained low. Significant differences were noted between test and control quadrants on days 7, 14, and 21 for all parameters. Significant increases in GI, AngBS, and GCF were observed in test quadrants over the course of the study in both HR and LR groups. Significant differences were noted between HR and LR groups for all gingivitis parameters on day 21 in test quadrants, without any significant differences in PlI or CPE between the groups.

Conclusions: We identified two subpopulations characterized by significant differences in clinical parameters of plaque‐induced gingival inflammation, despite similar amounts of plaque deposits and plaque accumulation rates.
Modulation of clinical expression of plaque‐induced gingivitis
Authors: Trombelli Leonardo , Scapoli Chiara , Orlandini Elisa , Tosi Marina , Bottega Sabrina , Tatakis Dimitris N.
Published: March 2004

Aim: The aim of the present study was to characterize the subject‐based clinical behavior of the gingiva in response to a tooth‐cleaning regimen in two subpopulations, “high‐responder” (HR) and “low‐responder” (LR) groups, presenting a different inflammatory response to plaque accumulation.

Material and Methods: The study population comprised of 96 systemically and periodontally healthy subjects, 46 males and 50 females, non‐smokers, enrolled in an experimental gingivitis trial. At completion of the experimental gingivitis period (day 21), all subjects were prescribed the same 21‐day treatment regimen of amine/stannous fluoride (AmF/SnF2)‐containing toothpaste and mouthrinse. Plaque index (PlI), gingival index (GI), gingival crevicular fluid volume (GCF), and angulated bleeding score (AngBS) were recorded on three selected teeth. Treatment efficacy was evaluated in the overall population as well as in HR and LR groups, separately.

Results: A statistically significant decrease of PlI was observed after treatment (p<0.001), with PlI reversing to baseline levels. Changes in PlI revealed the same trend in both HR and LR groups, without differences between groups. Treatment also resulted in a significant decrease of all gingivitis parameters (p<0.001 for all comparisons). After treatment, GI, AngBS, and GCF were comparable with baseline condition. However, when the two groups were compared, day 42‐GCF was significantly higher in the HR group than the LR group.

Conclusions: A treatment regimen based on mechanical plaque control supplemented with AmF/SnF2‐containing toothpaste and mouthrinse is effective in reducing plaque accumulation and re‐establishing healthy gingival conditions after experimentally induced gingivitis, even in subjects with different inflammatory response to plaque accumulation.
The effect of written information on pain experience during periodontal probing
Authors: Van Wijk Arjen J. , Duyx Michel P. M. A. , Hoogstraten Johan
Published: March 2004

Objectives: To study the effect of providing written information prior to periodontal treatment on the pain experience during periodontal probing.

Materials and Methods: Patients were randomly assigned to the experimental or control condition and had to read the accompanying information. Information was manipulated to enhance perceptions of control. Anticipated pain (Numerical Rating Scale, NRS), dental anxiety (short version of the Dental Anxiety Inventory, S‐DAI), and the Dental Control List were filled out before treatment; the McGill Pain Questionnaire (MPQ) and experienced pain (NRS) were filled out after treatment.

Results: No significant differences were found in anticipated or experienced pain. However, the experimental condition evaluated treatment as less negative (MPQ‐evaluative scale, F(1,55)=11.56, p<0.001), and scored lower on most measures. Subjects experiencing a discrepancy between desire for control and felt control showed the highest anticipatory distress (S‐DAI, F(3,53)=6.32, p<0.001; anticipated pain, F(3,53)=3.28, p<0.03).

Conclusion: Providing patients with written information prior to periodontal probing can alter the pain experience. Future research will be aimed at strengthening the impact of information.
Clinical and microbiological effects of subgingival administration of two active gels on persistent pockets of chronic periodontitis patients
Authors: Perinetti Giuseppe , Paolantonio Michele , Cordella Chiara , D'Ercole Simonetta , Serra Emanuela , Piccolomini Raffaele
Published: March 2004

Objectives:The present controlled, single‐blind study was performed to assess and compare the clinical healing and the microbiological findings following repeated intrasulcular applications of 1% metronidazole or 1% chlorhexidine gels in persistent periodontal pockets previously treated by scaling and root planing (SRP).

Material and Methods:Sixty‐three systemically healthy subjects, 25 males and 38 females (mean age 48.4±7.2 years), diagnosed for chronic periodontitis were enrolled in this study. They underwent SRP and received oral hygiene instructions (OHI). Three months later, at baseline, a single persistent pocket with a probing depth (PD) of 5–9 mm was chosen as the experimental site in each patient; the subjects were stratified into three matched experimental groups on the basis of the treatment to be performed, which consisted of the subgingival administration of 1% metronidazole gel (MG,n=19), 1% chlorhexidine gel (CG,n=20) or placebo gel (PG,n=24). The treatments consisted of four repeated administrations of subgingival gels, each separated by 7 days, starting at the baseline. Clinical assessment was performed at the baseline and at the 180‐day follow‐up, after the end of treatment. For microbiological evaluations, subgingival plaque was sampled from the experimental sites at baseline, prior to the first subgingival gel administration, and at 7, 15, 30 and 90 days after the end of the treatment (days 28, 36, 51 and 111 from baseline).

Results:Plaque accumulation did not change significantly in all three groups. Bleeding on probing and clinical attachment levels reduced in the MGs and CGs only. PD was significantly reduced by the same amount in all experimental groups. In the MGs and CGs a remarkable reduction in the frequencies of detection of several periodontopathic micoorganisms was recorded after the treatment. The same was not seen for the PGs.

Conclusions:Subgingival administration of MG or CG, both at 1%, may have a role in the management of persistent pockets during chronic periodontitis.
Resolution of bone defects of varying dimension and configuration in the marginal portion of the peri‐implant bone
Authors: Botticelli Daniele , Berglundh Tord , Lindhe Jan
Published: March 2004

Background: It was demonstrated that a marginal defect of about 1 mm between the bone wall and the metal surface after implant installation can heal with a high degree of bone fill and osseointegration.

Objective: The aim of the present animal experiment was to study bone healing at implant sites with hard tissue defects of varying dimensions and configuration.

Material and Methods: Four Labrador dogs were used. All mandibular premolars and first molars were extracted. After 3 months of healing, five experimental sites, two control (C1, C2) and three test (T1, T2, T3) sites, were identified. In all five sites, custom‐made implants with a sand‐blasted, large‐grit, acid‐etched (SLA) surface and with an outer dimension of 3.3×10 mm, were used. In site C1, traditional implant installation was performed. In site C2, the marginal 5 mm of the canal, prepared for the implant, was widened to 5.3 mm using a step‐drill. Thus, following the installation of the implant, a circumferential gap occurred between the bone tissue and the metal rod that was 5 mm deep and between 1 and 1.25 mm wide. In test site T1, the canal was widened to establish a marginal gap of 2–2.25 mm. In test sites T2 and T3, the marginal 5 mm of the canal was first widened to 5.3 mm (T2) or 7.3 mm (T3). The buccal bone wall opposite the defect was subsequently removed. Following the placement of a cover screw in sites C2, T1, T2, and T3, a resorbable membrane was placed over the defect. All implants were submerged. After 4 months of healing, block biopsies of each implant site were dissected and processed for ground sectioning.

Results: The observations disclosed that four‐wall defects of different dimensions (1–2.25 mm wide) that occurred in the marginal portion of the recipient sites following implant installation were resolved during healing. Further, at sites where the buccal bone wall during defect preparation was intentionally removed, healing resulted in defect resolution at the mesial, distal, and lingual aspects. At the buccal aspects, healing was incomplete but the dimension of the defect was reduced by the limited amounts of new bone formation extending from the lateral and apical borders of the defect.

Conclusion: Wide marginal defects may during healing be filled with bone. In such defects a high degree of osseointegration may occur to implants designed with an SLA surface.
Modulation of arterial baroreflex dynamic response during mild orthostatic stress in humans
Authors: Ichinose Masashi , Saito Mitsuru , Kitano Asami , Hayashi Keiji , Kondo Narihiko , Nishiyasu Takeshi
Published: March 2004

We tested the hypothesis that in humans, carotid‐baroreflex dynamic responses (evaluated by examining the time course of the carotid‐baroreflex‐induced alterations in muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP) and heart rate (HR)) would be altered during mild orthostatic stress in ways that serve to limit orthostatic hypotension. In 12 healthy subjects (10 male, 2 female), 5‐s periods of neck pressure (NP) (50 mmHg) and neck suction (NS) (− 60 mmHg) were used to evaluate carotid baroreflex function at rest (CON) and during lower body negative pressure (LBNP) (−15 mmHg). During LBNP (as compared with CON) (a) the augmentations in MSNA and MAP elicited by NP were greater, (b) the NS‐induced period of MSNA suppression was, if anything, shorter, (c) the peak decrement in MAP elicited by NS, although not different in amplitude, occurred earlier and recovered to its initial level more quickly after NS, and (d) the HR responses to NP and NS were greater. These results suggest that during mild orthostatic stress, carotid‐baroreflex dynamic responses are modulated in ways that should help maintain blood pressure and limit orthostatic hypotension.
Identification of the tracheal and laryngeal afferent neurones mediating cough in anaesthetized guinea‐pigs
Authors: Canning Brendan J. , Mazzone Stuart B. , Meeker Sonya N. , Mori Nanako , Reynolds Sandra M. , Undem Bradley J.
Published: March 2004

We have identified the tracheal and laryngeal afferent nerves regulating cough in anaesthetized guinea‐pigs. Cough was evoked by electrical or mechanical stimulation of the tracheal or laryngeal mucosa, or by citric acid applied topically to the trachea or larynx. By contrast, neither capsaicin nor bradykinin challenges to the trachea or larynx evoked cough. Bradykinin and histamine administered intravenously also failed to evoke cough. Electrophysiological studies revealed that the majority of capsaicin‐sensitive afferent neurones (both Aδ‐ and C‐fibres) innervating the rostral trachea and larynx have their cell bodies in the jugular ganglia and project to the airways via the superior laryngeal nerves. Capsaicin‐insensitive afferent neurones with cell bodies in the nodose ganglia projected to the rostral trachea and larynx via the recurrent laryngeal nerves. Severing the recurrent nerves abolished coughing evoked from the trachea and larynx whereas severing the superior laryngeal nerves was without effect on coughing. The data indicate that the tracheal and laryngeal afferent neurones regulating cough are polymodal Aδ‐fibres that arise from the nodose ganglia. These afferent neurones are activated by punctate mechanical stimulation and acid but are unresponsive to capsaicin, bradykinin, smooth muscle contraction, longitudinal or transverse stretching of the airways, or distension. Comparing these physiological properties with those of intrapulmonary mechanoreceptors indicates that the afferent neurones mediating cough are quite distinct from the well‐defined rapidly and slowly adapting stretch receptors innervating the airways and lungs. We propose that these airway afferent neurones represent a distinct subtype and that their primary function is regulation of the cough reflex.
Activation properties of Kv4.3 channels: time, voltage and [K+]o dependence
Authors: Wang Shimin , Bondarenko Vladimir E. , Qu Yujie , Morales Michael J. , Rasmusson Randall L. , Strauss Harold C.
Published: March 2004

Rapidly inactivating, voltage‐dependent K+ currents play important roles in both neurones and cardiac myocytes. Kv4 channels form the basis of these currents in many neurones and cardiac myocytes and their mechanism of inactivation appears to differ significantly from that reported for Shaker and Kv1.4 channels. In most channel gating models, inactivation is coupled to the kinetics of activation. Hence, there is a need for a rigorous model based on comprehensive experimental data on Kv4.3 channel activation. To develop a gating model of Kv4.3 channel activation, we studied the properties of Kv4.3 channels in Xenopus oocytes, without endogenous KChIP2 ancillary subunits, using the perforated cut‐open oocyte voltage clamp and two‐electrode voltage clamp techniques. We obtained high‐frequency resolution measurements of the activation and deactivation properties of Kv4.3 channels. Activation was sigmoid and well described by a fourth power exponential function. The voltage dependence of the activation time constants was best described by a biexponential function corresponding to at least two different equivalent charges for activation. Deactivation kinetics are voltage dependent and monoexponential. In contrast to other voltage‐sensitive K+ channels such as HERG and Shaker, we found that elevated extracellular [K+] modulated the activation process by slowing deactivation and stabilizing the open state. Using these data we developed a model with five closed states and voltage‐dependent transitions between the first four closed states coupled to a voltage‐insensitive transition between the final closed (partially activated) state and the open state. Our model closely simulates steady‐state and kinetic activation and deactivation data.
Mapping the architecture of the ATP‐binding site of the KATP channel subunit Kir6.2
Authors: Dabrowski Michael , Tarasov Andrei , Ashcroft Frances M.
Published: March 2004

ATP‐sensitive potassium (KATP) channels comprise Kir6.2 and SUR subunits. The site at which ATP binds to mediate KATP channel inhibition lies on Kir6.2, but the potency of block is enhanced by coexpression with SUR1. To assess the structure of the ATP‐binding site on Kir6.2, we used a range of adenine nucleotides as molecular measuring sticks to map the internal dimensions of the binding site. We compared their efficacy on Kir6.2–SUR1, and on a truncated Kir6.2 (Kir6.2ΔC) that expresses in the absence of SUR. We show here that SUR1 modifies the ATP‐binding pocket of Kir6.2, by increasing the width of the groove that binds the phosphate tail of ATP, without changing the length of the groove, and by enhancing interaction with the adenine ring.
Brain and central haemodynamics and oxygenation during maximal exercise in humans
Authors: González‐Alonso José , Dalsgaard Mads K. , Osada Takuya , Volianitis Stefanos , Dawson Ellen A. , Yoshiga Chie C. , Secher Niels H.
Published: March 2004

During maximal exercise in humans, fatigue is preceded by reductions in systemic and skeletal muscle blood flow, O2 delivery and uptake. Here, we examined whether the uptake of O2 and substrates by the human brain is compromised and whether the fall in stroke volume of the heart underlying the decline in systemic O2 delivery is related to declining venous return. We measured brain and central haemodynamics and oxygenation in healthy males (n= 13 in 2 studies) performing intense cycling exercise (360 ± 10 W; mean ±s.e.m.) to exhaustion starting with either high (H) or normal (control, C) body temperature. Time to exhaustion was shorter in H than in C (5.8 ± 0.2 versus 7.5 ± 0.4 min, P < 0.05), despite heart rate reaching similar maximal values. During the first 90 s of both trials, frontal cortex tissue oxygenation and the arterial–internal jugular venous differences (a‐v diff) for O2 and glucose did not change, whereas middle cerebral artery mean flow velocity (MCA Vmean) and cardiac output increased by ∼22 and ∼115%, respectively. Thereafter, brain extraction of O2, glucose and lactate increased by ∼45, ∼55 and ∼95%, respectively, while frontal cortex tissue oxygenation, MCA Vmean and cardiac output declined ∼40, ∼15 and ∼10%, respectively. At exhaustion in both trials, systemic declined in parallel with a similar fall in stroke volume and central venous pressure; yet the brain uptake of O2, glucose and lactate increased. In conclusion, the reduction in stroke volume, which underlies the fall in systemic O2 delivery and uptake before exhaustion, is partly related to reductions in venous return to the heart. Furthermore, fatigue during maximal exercise, with or without heat stress, in healthy humans is associated with an enhanced rather than impaired brain uptake of O2 and substrates.
The action potential‐evoked sarcoplasmic reticulum calcium release is impaired in mdx mouse muscle fibres
Authors: Woods Christopher E. , Novo David , DiFranco Marino , Vergara Julio L.
Published: March 2004

The mdx mouse, a model of the human disease Duchenne muscular dystrophy, has skeletal muscle fibres which display incompletely understood impaired contractile function. We explored the possibility that action potential‐evoked Ca2+ release is altered in mdx fibres. Action potential‐evoked Ca2+‐dependent fluorescence transients were recorded, using both low and high affinity Ca2+ indicators, from enzymatically isolated fibres obtained from extensor digitorum longus (EDL) and flexor digitorum brevis (FDB) muscles of normal and mdx mice. Fibres were immobilized using either intracellular EGTA or N‐benzyl‐p‐toluene sulphonamide, an inhibitor of the myosin II ATPase. We found that the amplitude of the action potential‐evoked Ca2+ transients was significantly decreased in mdx mice with no measured difference in that of the surface action potential. In addition, Ca2+ transients recorded from mdx fibres in the absence of EGTA also displayed a marked prolongation of the slow decay phase. Model simulations of the action potential‐evoked transients in the presence of high EGTA concentrations suggest that the reduction in the evoked sarcoplasmic reticulum Ca2+ release flux is responsible for the decrease in the peak of the Ca2+ transient in mdx fibres. Since the myoplasmic Ca2+ concentration is a critical regulator of muscle contraction, these results may help to explain the weakness observed in skeletal muscle fibres from mdx mice and, possibly, Duchenne muscular dystrophy patients.
Effects of wortmannin and latrunculin A on slow endocytosis at the frog neuromuscular junction
Authors: Richards D. A. , Rizzoli S. O. , Betz W. J.
Published: March 2004

Phosphoinositides are key regulators of synaptic vesicle cycling and endocytic traffic; the actin cytoskeleton also seems to be involved in modulating these processes. We investigated the effects of perturbing phosphoinositide signalling and actin dynamics on vesicle cycling in frog motor nerve terminals, using fluorescence and electron microscopy, and electrophysiology. Antibody staining for β‐actin revealed that actin surrounds but does not overlap with synaptic vesicle clusters. Latrunculin A, which disrupts actin filaments by binding actin monomers, and wortmannin, an inhibitor of phosphatidyl inositol‐3‐kinase (PI3‐kinase), each disrupted the pattern of presynaptic actin staining, but not vesicle clusters in resting terminals. Latrunculin A, but not wortmannin, also reduced vesicle mobilization and exocytosis. Both drugs inhibited the stimulation‐induced uptake of the styryl dye FM1‐43 and blocked vesicle reformation from internalized membrane objects after tetanic stimulation. These results are consistent with a role of PI3‐kinase and the actin cytoskeleton in the slow pathway of vesicle endocytosis, used primarily by reserve pool vesicles.
Modal Damping for Monitoring Bone Integrity and Osteoporosis
Authors: Panteliou Sofia D. , Xirafaki Agathi L. , Panagiotopoulos Elias , Varakis John N. , Vagenas Nikos V. , Kontoyannis Christos G.
Published: March 2004

We applied a noninvasive method to assess bone structural integrity. The method is based on the measurement of the dynamic characteristics of the bone (quality factor and modal damping factor) by applying vibration excitation in the range of acoustic frequencies, in the form of an acoustic sweep signal. Excised sheep femora were tested to detect changes in modal damping, density (kg/m3), bone mineral density (kg/m2) and bone mineral (hydroxyapatite) percentage. The changes were recorded after each time of chemical treatment of the bones performed to gradually cause mineral removal, thus simulating osteoporosis. It was shown that the change in quality factor and damping was in all cases on average equal or greater to the change in all other measured characteristics, thus strengthening the potential of the proposed method to become a valuable assessment tool for monitoring bone integrity and osteoporosis.
An In Vivo Method for Measuring Turbulence in Mechanical Prosthesis Leakage Jets
Authors: Travis Brandon R. , Christensen Thomas D. , Smerup Morten , Olsen Morten S. , Hasenkam J. Michael , Nygaard Hans
Published: March 2004

This work introduces a method for the in vivo measurement and analysis of turbulence within the leakage of a mechanical heart valve. Several analysis techniques were applied to ultrasound measurements acquired within the atrium of a pig, and error associated with these techniques was analyzed. The technique chosen applies cyclic averaging to mean and maximum velocity measurements within small, normalized phase windows to calculate Reynolds normal stresses in the direction of the ultrasound beam. Maximum shear stresses are estimated from these normal stresses using an analytical technique. The stresses observed were smaller than those reported from previous in vitro simulations.
Modes and Balance of Energy in the Piezoelectric Cochlear Outer Hair Cell Wall
Authors: Spector Alexander A. , Jean Ronald P.
Published: March 2004

Here, we analyze energy transformations in the outer hair cell and its effectiveness as a piezoelectric-type actuator in the cochlea. The major modes of energy are introduced, and a method to estimate the coefficients of their tension-dependence is proposed. Next, we derive balance of the mechanical and electrical parts of energy, and show two forms of the active energy associated with the motors driving electromotility. The two forms of the active energy, stored mechanical energy, and external electrical work are then introduced as functions of voltage and applied force. We use the energy balance to introduce and estimate the effectiveness of the cell’s electromotile response.
Intra-Aneurysmal Flow With Helix and Mesh Stent Placement Across Side-Wall Aneurysm Pore of a Straight Parent Vessel
Authors: Liou Tong-Miin , Liou Shun-Nan , Chu Kai-Lung
Published: March 2004

Pulsatile flow fields in a cerebrovascular side-wall aneurysm model with a wide ostium after stenting are presented in terms of particle tracking velocimetry measurements and flow visualization. Among the stent parameters the shape, helix versus mesh, was selected to study its effect on the changes of intraaneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The blocking ratio of the stents was fixed at 30%. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. Four consecutive flow-rate phases were selected to characterize the intra-aneurysmal flow. The results are characterized in terms of velocity vector field, regional average velocity, and intra-aneurysmal vorticity/circulation/wall shear stress. It is found that the hemodynamic features inside the aneurysm alter markedly with the shape of the stent and the size of the orifice. Both stents investigated induce favorable changes in the intra-aneurysmal flow stasis as well as direction and undulation of wall shear stresses. A comparison of the results of the helix to mesh stent shows that the former is more favorable for endovascular treatment.
A Novel Robotic System for Joint Biomechanical Tests: Application to the Human Knee Joint
Authors: Fujie Hiromichi , Sekito Takeshi , Orita Akiyuki
Published: March 2004

The objectives of the work reported in this article were to develop a novel 6-degree-of-freedom (DOF) robotic system for knee joint biomechanics, to complete a hybrid force-position control scheme, to evaluate the system performance, and to demonstrate a combined loading test. The manipulator of the system utilizes two mechanisms; the upper mechanism has two translational axes and three rotational axes while the lower mechanism has only a single translational axis. All axes were driven with AC servo-motors. This unique configuration results in a simple kinematic description of manipulator motion. Jacobian transformation was used to calculate both the displacement and force/moment, which allowed for a hybrid control of the displacement of, and force/moment applied to, the human knee joint. The control and data acquisition were performed on a personal computer in the C-language programming environment with a multi-tasking operating system. Preliminary tests revealed that the clamp-to-clamp compliance of the system was smaller in the vertical (Z) and longitudinal (Y) directions (0.001 mm/N) than in lateral (X) direction (0.003 mm/N). The displacement error under the application of 500 N of load was smallest in the vertical direction (0.001±0.003 mm (mean±SD), and largest in the lateral direction (0.084±0.027 mm). Using this test system, it was possible to simulate multiple loading conditions in a human knee joint in which a cyclic anterior force was applied together with a coupled, joint compressive force, while allowing natural knee motion. The developed system seems to be a useful tool for studies of knee joint biomechanics.
How Cyclic Loading Affects the Migration of Radio-Opaque Markers Attached to Tendon Grafts Using a New Method: A Study Using Roentgen Stereophotogrammetric Analysis (RSA)
Authors: Roos P. J. , Hull M. L. , Howell S. M.
Published: March 2004

An increase in anterior laxity following reconstruction of the anterior cruciate ligament (ACL) can result from lengthening of the graft construct in either the regions of fixation and/or the region of the graft substance between the fixations. RSA could be a useful technique to determine lengthening in these regions if a method can be devised for attaching radio-opaque markers to soft tissue grafts so that marker migration from repeated loading of the graft is limited. Therefore, the objectives of this study were 1) to develop a method for attaching radio-opaque markers to an ACL graft that limits marker migration within the graft, 2) to characterize the error of an RSA system used to study migration, and 3) to determine the maximum amount of migration and the time when it occurs during cyclic loading of ACL grafts. Tendon markers were constructed from a 0.8-mm tantalum ball and a stainless steel suture. Ten double-looped tendon grafts were passed through tibial tunnels drilled in bovine tibias and fixed with a tibial fixation device. Two tendon markers were sewn to one tendon bundle of each graft and the grafts were cyclically loaded for 225,000 cycles from 20 N to 170 N. At specified intervals, simultaneous radiographs were obtained of the tendon markers and a radiographic standard of known length. The bias and imprecision in measuring the length of the radiographic standard were 0.0 and 0.046 mm respectively. Marker migration was computed as the change in distance between the two tendon markers along the axis of the tibial tunnel. Marker migration was greatest after 225,000 cycles with a root mean square (RMS) value of less than 0.2 mm. Because the RMS value indicates the error introduced into measurements of lengthening and because this error is small, the method described for attaching markers to an ACL graft has the potential to be useful for determining lengthening of ACL graft constructs in in vivo studies in humans.
Effects of Ischemia on Epicardial Deformation in the Passive Rabbit Heart
Authors: Gaudette Glenn R. , Krukenkamp Irvin B. , Azeloglu Evren U. , Saltman Adam E. , Lense Miriam , Todaro Joseph , Chiang Fu-Pen
Published: March 2004

Background Surgically induced ischemia in the arrested heart can result in changes in the mechanical properties of the myocardium. Regions of ischemia may be characterized based on the amount of epicardial deformation for a given load. Computer aided speckle interferometry (CASI), which tracks the movement of clusters of particles, is developed as a technique for measuring epicardial deformation, thereby determining the perfusion status of the passive heart. Materials and Methods Silicone carbide particles and retroreflective beads were dispersed randomly onto the epicardial surface of 11 isolated rabbit hearts to form speckle images. The hearts were arrested with hyperkalemic Krebs-Henseleit buffered solution. Each heart was then exposed to a series of intracavitary pressures, and at each pressure speckle images were acquired with a charge-coupled device (CCD) camera. Nine hearts were exposed to global ischemia, and two hearts were exposed to regional ischemia by occluding the second diagonal branch of the left anterior descending artery (LAD). The hearts were again loaded and the speckle images were acquired. CASI was used to determine the distribution of deformation field. Results CASI was able to determine displacements with a spatial resolution of about 50 microns. Global ischemia resulted in a significant increase in the maximum principle strain and the first invariant of the 2-D strain tensor. In the regionally ischemic heart, a large difference in deformation between the ischemic and perfused regions was clearly observed. Conclusion Based on epicardial deformation, CASI is able to distinguish between perfused and ischemic myocardium, with a spatial resolution of 50 μm.
Mechanical Properties of Rat Middle Cerebral Arteries With and Without Myogenic Tone
Authors: Coulson Rebecca J. , Cipolla Marilyn J. , Vitullo Lisa , Chesler Naomi C.
Published: March 2004

The inner diameter and wall thickness of rat middle cerebral arteries (MCAs) were measured in vitro in both a pressure-induced, myogenically-active state and a drug-induced, passive state to quantify active and passive mechanical behavior. Elasticity parameters from the literature (stiffness derived from an exponential pressure-diameter relationship, β, and elasticity in response to an increment in pressure, Einc-p) and a novel elasticity parameter in response to smooth muscle cell (SMC) activation, Einc-a, were calculated. β for all passive MCAs was 9.11±1.07 but could not be calculated for active vessels. The incremental stiffness increased significantly with pressure in passive vessels; Einc-p 106 dynes/cm2 increased from 5.6±0.5 at 75 mmHg to 14.7±2.4 at 125 mmHg, (p<0.05). In active vessels, Einc-p 106 dynes/cm2 remained relatively constant (5.5±2.4 at 75 mmHg and 6.2±1.0 at 125 mmHg). Einc-a 106 dynes/cm2 increased significantly with pressure (from 15.1±2.3 at 75 mmHg to 49.4±12.6 at 125 mmHg, p<0.001), indicating a greater contribution of SMC activity to vessel wall stiffness at higher pressures.
Determinants of Left Ventricular Shape Change During Filling
Authors: Holmes Jeffrey W.
Published: March 2004

Left ventricular shape and shape change are easy to measure and their analysis has been proposed as a noninvasive method to determine myocardial anisotropy. In preparation for applying this approach to studies of rats with experimentally induced cardiac hypertrophy, the goals of this study were to describe normal shape changes during diastolic filling in the rat and to utilize a finite-element model to estimate the relative importance of three factors that determine left ventricular shape change during filling: global chamber compliance, fiber to crossfiber stiffness ratio, and fiber architecture. The results suggest that left ventricular shape change is least sensitive to fiber to cross fiber stiffness ratio, and that this will likely limit the practical utility of using shape changes to diagnose changes in myocardial anisotropy.
An Improved Method to Analyze the Stress Relaxation of Ligaments Following a Finite Ramp Time Based on the Quasi-Linear Viscoelastic Theory
Authors: Abramowitch Steven D. , Woo Savio L.-Y.
Published: March 2004

The quasi-linear viscoelastic (QLV) theory proposed by Fung (1972) has been frequently used to model the nonlinear time- and history-dependent viscoelastic behavior of many soft tissues. It is common to use five constants to describe the instantaneous elastic response (constants A and B) and reduced relaxation function (constants C, τ1, and τ2) on experiments with finite ramp times followed by stress relaxation to equilibrium. However, a limitation is that the theory is based on a step change in strain which is not possible to perform experimentally. Accounting for this limitation may result in regression algorithms that converge poorly and yield nonunique solutions with highly variable constants, especially for long ramp times (Kwan et al. 1993). The goal of the present study was to introduce an improved approach to obtain the constants for QLV theory that converges to a unique solution with minimal variability. Six goat femur-medial collateral ligament-tibia complexes were subjected to a uniaxial tension test (ramp time of 18.4 s) followed by one hour of stress relaxation. The convoluted QLV constitutive equation was simultaneously curve-fit to the ramping and relaxation portions of the data r2>0.99. Confidence intervals of the constants were generated from a bootstrapping analysis and revealed that constants were distributed within 1% of their median values. For validation, the determined constants were used to predict peak stresses from a separate cyclic stress relaxation test with averaged errors across all specimens measuring less than 6.3±6.0% of the experimental values. For comparison, an analysis that assumed an instantaneous ramp time was also performed and the constants obtained for the two approaches were compared. Significant differences were observed for constants B, C, τ1, and τ2, with τ1 differing by an order of magnitude. By taking into account the ramping phase of the experiment, the approach allows for viscoelastic properties to be determined independent of the strain rate applied. Thus, the results obtained from different laboratories and from different tissues may be compared.
Mechanical Properties of a Reversible, DNA-Crosslinked Polyacrylamide Hydrogel
Authors: Lin David C. , Yurke Bernard , Langrana Noshir A.
Published: March 2004

Mechanical properties of a polyacrylamide gel with reversible DNA crosslinks are presented. In this system, three DNA strands replace traditional chemical crosslinkers. In contrast to thermoset chemically crosslinked polyacrylamide, the new hydrogel is thermoreversible; crosslink dissociation without the addition of heat is also feasible by introducing a specific removal DNA strand. This hydrogel is characterized by a critical crosslink concentration at which gelation occurs. Below the critical point, a characteristic temperature exists at which a transition in viscosity is observed. Both temperature-dependent viscosity and elastic modulus of the material are functions of crosslink density.
Mechanical Properties of Shock-Absorbing Pylons Used in Transtibial Prostheses
Authors: Berge, Jocelyn S. , Klute, Glenn K. , Czerniecki, Joseph M.
Published: March 2004

Prosthetic manufacturers have developed shock-absorbing pylons to attenuate the transient forces of foot-ground contact in order to supplement the residual capacity of lower limb amputees. The purpose of this study was to measure the elastic and damping properties of two frequently prescribed pylons (the ICON™ Shock Pylon and the Mercury TT Pyramid Pylon) at frequencies enveloping those observed during gait using pseudo-static compressive and dynamic cyclic testing methods. Results showed that the spring constants were linear functions of deformation (ranging from 74 to 110 N/mm and 91 to 157 N/mm for the ICON and the TT Pylons, respectively) while the damping force was a function of the square root of velocity combined with a coulomb element (1.6x˙0.5+21 and 7.4x˙0.5+102 N for the ICON and the TT Pylon, respectively).
Preparation of On-Axis Cylindrical Trabecular Bone Specimens Using Micro-CT Imaging
Authors: Wang, Xiang , Liu, and Xiangyi , Niebur Glen L.
Published: March 2004

The Orientation of trabecular bone specimens for mechanical testing must be carefully controlled. A method for accurately preparing on-axis cylindrical specimens using high-resolution micro-CT imaging was developed. Sixteen cylindrical specimens were prepared from eight bovine tibiae. High-resolution finite element models were generated from micro-CT images of parallelepipeds and used to determine the principal material coordinate system of each parallelepiped. A cylindrical specimen was then machined with a diamond coring bit. The resulting specimens were scanned again to evaluate the orientation. The average deviation between the principal fabric orientation and the longitudinal axis of the cylindrical specimen was only 4.70±3.11°.
Molybdenum Isotope Evidence for Widespread Anoxia in Mid-Proterozoic Oceans
Authors: Arnold G. L. , Anbar A. D. , Barling J. , Lyons T. W.
Published: March 2004

How much dissolved oxygen was present in the mid-Proterozoic oceans between 1.8 and 1.0 billion years ago is debated vigorously. One model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen ∼2.3 billion years ago. Recent evidence for H
2
S in some mid-Proterozoic marine basins suggests, however, that the deep ocean remained anoxic until much later. New molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid-Proterozoic compared to the present-day ocean. Consequently, oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years.
Environmental Genome Shotgun Sequencing of the Sargasso Sea
Authors: Venter J. Craig , Remington Karin , Heidelberg John F. , Halpern Aaron L. , Rusch Doug , Eisen Jonathan A. , Wu Dongying , Paulsen Ian , Nelson Karen E. , Nelson William , Fouts Derrick E. , Levy Samuel , Knap Anthony H. , Lomas Michael W. , Nealson Ken , White Owen , Peterson Jeremy , Hoffman Jeff , Parsons Rachel , Baden-Tillson Holly , Pfannkoch Cynthia , Rogers Yu-Hui , Smith Hamilton O.
Published: March 2004

We have applied âwhole-genome shotgun sequencingâ to microbial populations collected en masse on tangential flow and impact filters from seawater samples collected from the Sargasso Sea near Bermuda. A total of 1.045 billion base pairs of nonredundant sequence was generated, annotated, and analyzed to elucidate the gene content, diversity, and relative abundance of the organisms within these environmental samples. These data are estimated to derive from at least 1800 genomic species based on sequence relatedness, including 148 previously unknown bacterial phylotypes. We have identified over 1.2 million previously unknown genes represented in these samples, including more than 782 new rhodopsin-like photoreceptors. Variation in species present and stoichiometry suggests substantial oceanic microbial diversity.
An Antigenic Peptide Produced by Peptide Splicing in the Proteasome
Authors: Vigneron Nathalie , Stroobant Vincent , Chapiro Jacques , Ooms Annie , Degiovanni Gérard , Morel Sandra , van der Bruggen Pierre , Boon Thierry , Van den Eynde Benoît J.
Published: March 2004

CD8 T lymphocytes recognize peptides of 8 to 10 amino acids presented by class I molecules of the major histocompatibility complex. Here, CD8 T lymphocytes were found to recognize a nonameric peptide on melanoma cells that comprises two noncontiguous segments of melanocytic glycoprotein gp100
PMEL17
. The production of this peptide involves the excision of four amino acids and splicing of the fragments. This process was reproduced in vitro by incubating a precursor peptide of 13 amino acids with highly purified proteasomes. Splicing appears to occur by transpeptidation involving an acyl-enzyme intermediate. Our results reveal an unanticipated aspect of the proteasome function of producing antigenic peptides.
The
Ashbya gossypii
Genome as a Tool for Mapping the Ancient
Saccharomyces cerevisiae
Genome
Authors: Dietrich Fred S. , Voegeli Sylvia , Brachat Sophie , Lerch Anita , Gates Krista , Steiner Sabine , Mohr Christine , Pöhlmann Rainer , Luedi Philippe , Choi Sangdun , Wing Rod A. , Flavier Albert , Gaffney Thomas D. , Philippsen Peter
Published: March 2004

We have sequenced and annotated the genome of the filamentous ascomycete
Ashbya gossypii
. With a size of only 9.2 megabases, encoding 4718 protein-coding genes, it is the smallest genome of a free-living eukaryote yet characterized. More than 90% of
A. gossypii
genes show both homology and a particular pattern of synteny with
Saccharomyces cerevisiae
. Analysis of this pattern revealed 300 inversions and translocations that have occurred since divergence of these two species. It also provided compelling evidence that the evolution of
S. cerevisiae
included a whole genome duplication orfusion of two related species and showed, through inferred ancient gene orders, which of the duplicated genes lost one copy and which retained both copies.