SEARCH · Search PubMed

Results for “stepping”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources

PubMed2005

Hindlimb loading determines stepping quantity and quality following spinal cord transection.

We compared the bipedal hindlimb stepping ability of untrained and trained (step-trained 6 min/day) spinal rats (mid-thoracic spinal cord transection at post-natal day 5) at different levels of body weight support on a treadmill over a 40-day period, starting at 69 days of age. A robotic device provided precise levels of body weight support and recorded hindlimb movement. We assessed stepping ability using: (1) step quantity determined from the measured hindlimb movement, (2) ordinal scales of paw placement, weight-bearing, and limb flexion, and (3) the lowest level of body weight support at which stepping was maintained. Stepping quantity and quality depended strongly on the level of support provided. Stepping ability improved with time, but only at the higher levels of weight-bearing, and independently of training. Increasing limb loading by gradually decreasing body weight support altered the spatiotemporal properties of the steps, resulting in an increase in step length and stance duration and a decrease in swing and step cycle duration. The rats progressively improved their ability to support more load before collapsing from a maximum of about 42 g ( approximately 25% of body weight) at Day 1 to 73 g ( approximately 35% of body weight) at Day 40. We conclude that the level of hindlimb loading provided to a spinally transected rat strongly influences the quantity and quality of stepping. Furthermore, the relationship between stepping ability and loading conditions changes with time after spinal cord transection and is unaltered by small amounts of step training. Finally, load-bearing failure point can be a quantitative measure of locomotor recovery following spinal cord injury, especially for severely impaired animals that cannot step unassisted.

Animals↗

PubMedDate not supplied

Effect of washing on yield in one- and two-step steam pretreatment of softwood for production of ethanol.

Two-step steam pretreatment of softwood on laboratory scale has previously been shown to result in higher yields than one-step steam pretreatment. In this study, these results are verified on a larger scale. In an industrial process filtration and washing of the material between the two pretreatment steps are difficult without release of pressure. A worst case without filtration or washing was thus investigated to determine the influence of poor washing on the yield of sugars and the formation of byproducts. Steam pretreatment with SO(2) impregnation was investigated using three different procedures. One-step steam pretreatment was performed at 215 degrees C for 5 min. Two different kinds of two-step steam pretreatment were performed at 190 degrees C for 2 min in the first step and at 210 degrees C for 5 min in the second step. In one case the slurry obtained after the first pretreatment step was separated into a liquid and a solid phase, where the water-insoluble solid material was washed with water and then used for pretreatment in the second step. In the other case of two-step steam pretreatment, neither separation nor washing was performed. The pretreated material was evaluated using both enzymatic hydrolysis and fed-batch simultaneous saccharification and fermentation. Both two-step steam pretreatment process configurations investigated resulted in higher yields of ethanol (300 L/ton) than one-step steam pretreatment (227 L/ton). Separation and washing of the material between the pretreatment steps in the two-step steam pretreatment process did not improve the overall sugar yield, although the formation of sugar degradation products was reduced.

Cellulose↗

PubMed2005

The relationship between the National Board of Medical Examiners' prototype of the Step 2 clinical skills exam and interns' performance.

PURPOSE: To examine the relationship between graduates' performances on a prototype of the National Board of Medical Examiners' Step 2 CS and other undergraduate measures with their residency directors' ratings of their performances as interns. METHOD: Data were collected for the 2001 and 2002 graduates from the study institution. Checklist and interpersonal scores from the prototype Step 2 CS, along with United States Medical Licensing Examination (USMLE) Step 1 and 2 scores and undergraduate grade-point average (GPA), were correlated with residency directors' ratings (average score for six competencies, quartile ranking, and isolated interpersonal communication competency score). Stepwise linear regression was used to identify the best outcome predictors. RESULTS: Quartile ranking was more highly correlated with GPA than Step 2 CS prototype interpersonal score, USMLE Step 2 score, USMLE Step 1 score, and Step 2 CS prototype checklist score. The average score on the residency director's survey was more highly correlated with GPA than USMLE Step 2 score, USMLE Step 1 score, Step 2 CS prototype interpersonal score, and Step 2 CS prototype checklist score. The best predictors for both quartile ranking and average competency score were GPA and Step 2 CS prototype interpersonal score (R(2) = 0.26 and 0.28). CONCLUSION: Both scores from the Step 2 CS prototype significantly correlated with the interns' quartile ranking and average competency score. Only GPA and Step 2 CS prototype interpersonal score accounted for most of the variance of performance in the regression model.

Clinical Competence↗

PubMed2002

Integra as a dermal replacement in a meshed composite skin graft in a rat model: a one-step operative procedure.

BACKGROUND: Current use of Integra, the collagen-based dermal analogue, requires a two-step grafting procedure to achieve wound closure with an "ultrathin" autograft. METHODS: A one-step operative procedure of meshed composite skin graft (MCSG) using Integra as a dermal template for a meshed split thickness autograft was developed in rats. The silicon layer of Integra was removed, the resulting dermal analogue was meshed (1:1.5), expanded, and placed on excised full thickness wound and covered with a meshed (1:1.5 or 1:6) split thickness autograft. Grafted wounds were dressed with BioBrane, Vaseline gauze, silver-impregnated nylon, or silver-nylon and direct current (SNDC). At scheduled intervals up to 3 months postgrafting, wounds were examined for epithelialization, collagen deposition and fibrosis, hair growth, and contraction. The results of wound closure and healing following the one-step procedure were compared with the outcome of the two-step grafting procedure where application of meshed Integra (step one) was followed in 14 days by removal of the silicon layer and application of the meshed autograft (step two). RESULTS: The one-step procedure applied to meshed autograft/Integra (1:1.5/1:1.5) composite graft accelerated wound closure by 6-19 days when compared with the two-step procedure. At 3 months postgrafting, the contraction of the healed wound dressed with SNDC, BioBrane, or Vaseline gauze was reduced by 13-16% following the one-step procedure compared with the two-step procedure (p < 0.05). The one-step procedure allowed the expansion of the autograft layer to 1:6 while achieving wound healing results similar to grafting with 1:1.5 meshed autograft layer using the two-step grafting procedure. CONCLUSION: Single-step application of meshed, thin, split thickness autograft over meshed Integra-derived dermal substitute allows more rapid wound closure with less contraction and more efficient use of graft donor skin than can be obtained with the commonly used two-step grafting procedure.

Analysis of Variance↗

PubMed2000

Roughening and preroughening transitions in crystal surfaces with double-height steps

We investigate phase transitions in a solid-on-solid model where double-height steps as well as single-height steps are allowed. Without the double-height steps, repulsive interactions between up-up or down-down step pairs give rise to a disordered flat phase. When the double-height steps are allowed, two single-height steps can merge into a double-height step (step doubling). We find that the step doubling reduces repulsive interaction strength between single-height steps and that the disordered flat phase is suppressed. As a control parameter a step doubling energy is introduced, which is assigned to each step doubling vertex. From transfer matrix type finite-size-scaling studies of interface free energies, we obtain the phase diagram in the parameter space of the step energy, the interaction energy, and the step doubling energy.

Journal Article↗

PubMed2003

Rotational stability of a modified step-cut for use in intercalary allografts.

BACKGROUND: Intercalary allografts are used for the reconstruction of major skeletal defects. Step-cuts help to provide rotational stability when intramedullary fixation is used. A modified step-cut is proposed to reduce rotation at the interface. This study compares the rotational stability of conventional and modified step-cuts. METHODS: In Phase I, seven pairs of human cadaveric femora were divided into a conventional step-cut group (left femora) and a modified step-cut group (right femora). All femora were cut transversely at the mid-diaphysis. In the conventional group, a 1-cm step-cut was created in the exact midsagittal plane in both the proximal and distal segments. In the modified group, a 1-cm step-cut was created in the parasagittal plane, leaving 2 mm of additional bone on both the proximal and the distal fragment. Phase II was identical except that in the modified step-cut group only 1 mm of additional bone was left. Smooth femoral nails were then placed after standard reaming. Specimens were tested by fixing the proximal segment and applying +/-2 N-m (17.7 in-lb) of torque to the distal segments with ten oscillation cycles. Maximum rotation was measured. The data were analyzed with the paired Student t test. RESULTS: The average rotation in Phase I was 23.3 degrees for the conventional step-cut group and 3.0 degrees for the 2-mm modified step-cut group; the difference was significant (p < 0.001). Four femora sustained an incomplete fracture during nail insertion. The average rotation in Phase II was 20.6 degrees for the conventional step-cut group and 0.5 degrees for the 1-mm modified step-cut group without any fractures; the difference was significant (p < 0.001). CONCLUSIONS: Step-cut modification that leaves more bone in the sagittal plane provides rigid fixation and significantly more stability than the conventional step-cut technique.

Biomechanical Phenomena↗

PubMed1985

The influence of interstimulus interval on the development of vestibular habituation to repeated velocity steps.

In order to clarify the problem of which stimulus parameters affect vestibular habituation, a group of cats was submitted to repeated velocity steps involving changes in either the step amplitude or the interval between two consecutive steps. In the first two experiments, the protocol was the same as in a previous study which used steps of 160 degrees/s separated by 60 s, except that the steps were of 80 degrees/s and 16 degrees/s. In the remaining experiments the step amplitude was kept constant (160 degrees/s) and the interstimulus interval was changed: each step was delivered either immediately after the reversal of the nystagmus elicited by the preceding step (only a few beats in the reversed direction were allowed to occur) or immediately before (no beats in the reversed direction). Vestibular habituation was found to occur in both experiments of the first series. Nevertheless, the marked initial suppression of the response, that was reported as one aspect of vestibular habituation to steps of 160 degrees/s, was clearly present when steps of 80 degrees/s were used, but was not as clear when the step amplitude was reduced to 16 degrees/s. The experiments of the second series showed that a typical vestibular habituation still occurs when steps are delivered just after the reversal of nystagmus. On the contrary, no habituation was observed when steps preceded the reversal of nystagmus. It was concluded that the presence of an anticompensatory phase is interpreted by the central nervous system as a sign that the response evoked in a reflex way is functionally meaningless or even detrimental. An habituation process is then started to suppress the response.

Animals↗

PubMed1979

Influence of age and of desmotropic drugs on the step phenomenon observed in rat skin.

Comprehensive analysis of the mechanical properties of rat skin revealed the "step phenomenon". This particular observation was made after constant strain rate (analysis of stress strain curves) as well as after constant load (creep experiments). Relative low extensions or low loads were necessary to provoke the steps. In most cases two, sometimes three steps were observed. The step phenomenon was found mainly in skin strips punched out perpendicularly to the body axis. Probably some bonds in the fibrous network are broken giving way to additional elongation whereafter stronger links take over the stress. Since earlier studies demonstrated a pronounced influence of age and of desmotropic drugs on mechanical properties at ultimate load, e.g., tensile strength, ultimate modulus of elasticity, and ultimate strain, also the step phenomenon was studied under these conditions. In stress-strain experiments most of the steps were found at the ages of 2 and 4 months. Total stress loss and total work loss due to the steps were the highest at the age of 4 months. If, however, these values were calculated as percentage of ultimate values, the highest figures were found in young animals. Elongation gain due to the steps also showed a maximum at time of maturation, e.g., 4 months. Similar findings were achieved in creep experiments at medium load (200 g). After treatment with prednisolone acetate more steps and after treatment with D-penicillamine fewer steps were observed. In stress-strain experiments total stress loss and total work loss due to steps were more than twice as high than controls after prednisolone treatment and only one half after D-penicillamine. If calculated as percentage of ultimate stress or percentage of work input, these changes disappeared because of similar changes at ultimate load. However, elongation gain due to steps, which was not significantly influenced by prednisolone acetate but significantly decreased by D-penicillamine, showed the same changes when calculated as percentage of ultimate strain. Under all conditions the step phenomenon mainly influenced the extension parameters. The data presented here confirm earlier observations that mechanical properties at low loads or low and medium extensions show at least to some extent a different pattern under the influence of maturation and age and after treatment with desmotropic drugs compared to the mechanical parameters at ultimate load.

Aging↗

PubMed2005

Step classification is useful for the determination of indications for systematized hepatectomy in hepatocellular carcinoma.

BACKGROUND/PURPOSE: The effectiveness of systematized hepatectomy with transection of Glisson's pedicle at the hepatic hilus has not been clarified in detail in relation to previous staging systems. Outcomes after systematized hepatectomy in patients with hepatocellular carcinoma (HCC) were examined in relation to our new staging system. METHODS: We retrospectively studied 955 patients with HCC who underwent hepatectomy from 1989 through 2002. We classified patients with HCC into four groups according to the pathological findings (pathological step [p-step]): p-step 1, HCC with absence of vascular invasion and absence of intrahepatic metastasis; p-step 2, HCC with vascular invasion and/or intrahepatic metastasis; p-step 3, HCC with major vascular invasion and/or intrahepatic metastasis to both lobes of the liver; and p-step 4, HCC with distant metastasis, including lymph node metastasis or ruptured HCC). We separated the liver into three segments (Takasaki's liver segments). Systematized hepatectomy was classified as systematized segmentectomy or larger resection, and partial segmentectomy. Segmentectomy refers to resection of one of Takasaki's segments. RESULTS: Systematized segmentectomy did not affect recurrence-free survival, by univariate analysis, in patients with p-step 1, p-step 3, or p-step 4. However, systematized segmentectomy or larger resection was significantly associated with patient recurrence-free survival, by univariate analysis, in patients with p-step 2. Multivariate analysis also showed systematized segmentectomy or larger resection as a significant independent prognostic factor in patients with p-step 2. CONCLUSIONS: Systematized segmentectomy is suitable for patients with p-step 2 HCC according to this step classification.

Aged↗

PubMed2005

Can initial and additional compensatory steps be predicted in young, older, and balance-impaired older females in response to anterior and posterior waist pulls while standing?

The initiation of a single compensatory step in response to balance perturbations has been predicted with accuracies of up to 71%. We sought to determine whether similar methods also could be used to predict the onset of additional compensatory steps in both healthy and balance-impaired older females. Anterior and posterior waist pulls of five different magnitudes were applied to 13 unimpaired young (mean age 23 years), 12 unimpaired older (mean age 71 years), and 15 balance-impaired older (mean age 76 years) women. Body segment kinematic data were recorded at 100 Hz. A step was predicted when the time for the center-of-mass to reach the vertical projection of the boundary of the base-of-support fell below a certain threshold. The results show that 83% of all steps and non-steps were correctly predicted at an optimal time-to-boundary threshold (tau(opt)) of 0.78 s. Step prediction accuracy did not differ significantly by group: 86% of steps and non-steps by young, 84% by unimpaired old, and 82% by balance-impaired old women were correctly predicted at tau(opt) of 0.58, 0.67, and 0.78 s, respectively. Anterior steps and non-steps were predicted more accurately than posterior ones (94% vs. 79% correct at tau(opt) of 0.52 and 0.84 s, respectively) and initial steps were better predicted than additional ones (87% vs. 81% correct at tau(opt) of 0.77 and 0.34 s, respectively). We conclude that this step prediction method reasonably predicts initial and additional steps in the anterior and posterior direction by all three subject cohorts.

Accidental Falls↗

PubMed2026

Long-term outcomes of top-down therapy versus a conventional step-up strategy in adults newly diagnosed with Crohn's disease: 5-year follow-up of the PROFILE trial.

BACKGROUND: The PROFILE trial previously reported better 48-week outcomes for patients with Crohn's disease who received top-down anti-TNF treatment from diagnosis, compared with a conventional step-up strategy. Through subsequent follow-up of PROFILE participants, we aimed to assess whether the benefit of top-down treatment from diagnosis results in modification of the long-term disease course. METHODS: PROFILE was a multicentre, open-label, randomised controlled trial completed in 40 hospitals in the UK, which included patients aged 16-80 years with newly diagnosed Crohn's disease. Eligible patients were randomly assigned via a secure online platform to a top-down (infliximab plus immunomodulator) or a step-up protocolised treatment strategy for 48 weeks, after which participants reverted to local standards of care. Objective outcome data were extracted for up to 5 years after the week 48 visit, including need for Crohn's-related abdominal surgery as the primary outcome. Data were analysed based on the original PROFILE randomisation and intention-to-treat population. Participants without long-term follow-up data were censored at the week 48 visit. Time-to-event analyses were performed using the Kaplan-Meier method and Cox proportional hazards model. The trial was registered with the ISRCTN registry, number 11808228 and is complete. FINDINGS: Between Dec 29, 2017, and Jan 5, 2022, 483 patients were assessed for inclusion. 389 patients were enrolled and randomly assigned (three patients were excluded due to ineligibility), 193 to top-down treatment and 193 to step-up treatment. Of the 386 participants in the PROFILE primary trial, 358 (93%) had post-week 48 records available for review (182 [51%] top-down and 176 [49%] step-up). Median follow-up was approximately 5 years from randomisation (1809 days [IQR 1300-2101]), by which point 172 (89%) of 193 patients in the step-up group and 191 (99%) of 193 patients in the top-down group had received biological or immunomodulator therapy. Relating to the primary outcome, during follow-up there were 28 Crohn's disease-related abdominal surgeries in 26 patients treated with a step-up approach versus six surgeries in six patients treated with a top-down approach. Time to surgery was shorter in the step-up group than the top-down group (adjusted hazard ratio [aHR] 5·23 [95% CI 1·99-13·76]; p=0·0008). For the secondary outcomes, incidence of Crohn's disease-related hospital admissions was higher in patients originally managed with step-up treatment versus top-down treatment (41 [21%] of 193 patients vs 22 [11%] of 193 patients); and time to first hospital admission was shorter with step-up treatment than with top-down treatment (aHR 2·01 [95% CI 1·18-3·41], p=0·017). Progression to B2 or B3 complications was also more frequent in those originally managed with step-up treatment compared with top-down treatment (32 [17%] of 192 patients vs 13 [7%] of 193 patients); with time to disease progression being shorter in the step-up group than in the top-down group (aHR 2·46 [95% CI 1·25-4·86]; p=0·010). There was no difference in safety outcomes between groups for either serious infections (12 [6%] of 193 step-up patients and 14 [7%] of 193 top-down patients) or malignancies (five patients [3%] and three patients [2%] respectively). INTERPRETATION: Early top-down anti-TNF treatment from diagnosis was associated with improved long-term outcomes at 5 years compared with step-up treatment and is suggestive of a disease-modifying effect in Crohn's disease. FUNDING: Wellcome and Celltrion.

Journal Article↗

PubMed1995

A mammalian activity required for the second step of pre-messenger RNA splicing.

Splicing of precursors to messenger RNAs occurs via a two-step mechanism. In the first step, the 5'-exon is released concomitant with the production of a lariat intermediate, and in the second step, the exons are joined, releasing the intron in the form of a lariat product. Several gene products of the yeast Saccharomyces cerevisiae have been shown to be required exclusively for the second step. Although mammalian proteins have been implicated in the second step of splicing, none have been shown to act only at this step. We identify here the first mammalian activity shown to be exclusively required for the second step. The activity was shown to increase by 5-fold the rate for this splicing step, whereas it had no effect on the rate of the first step. The activity was not affected by treatment with micrococcal nuclease, whereas it is sensitive to heating to 55 degrees C, suggesting that it is not dependent on an RNA, but more likely is a protein. The second step activity was separated from other factors required for the first step and from PSF, a splicing factor thought to have a second step activity. The activity does not require ATP hydrolysis, suggesting that it acts at a late stage of the second step of splicing.

Adenosine Triphosphate↗

PubMed2001

Lateral stability during forward-induced stepping for dynamic balance recovery in young and older adults.

BACKGROUND: Balance dysfunction related to lateral instability has been associated with falls and fall-related injuries among older individuals. Protective stepping for dynamic balance recovery requires the effective control of lateral body motion. This study investigated the relationship between aging, falls, and lateral stability during forward-induced stepping for dynamic balance recovery. METHODS: Forward steps were induced by a motor-driven waist-pull system in 12 younger adults, 20 healthy community-dwelling older adult nonfallers, and 18 older adults who had reported falls. Group differences in kinetic and kinematic stepping characteristics for a range of postural disturbance magnitudes were evaluated. RESULTS: Despite group similarities in anticipatory postural adjustments for minimizing lateral instability, the older fallers demonstrated significantly greater sideways body motion toward the stepping side at first-step foot contact and a more laterally directed foot placement. During the first step, forward-stepping characteristics were generally comparable between the groups, but the older fallers had an earlier liftoff time and longer step duration. CONCLUSIONS: During forward-induced protective stepping, otherwise healthy older adults who had experienced falls showed particular differences in their control of lateral body motion that were not attributable to changes in anticipatory postural mechanisms. Aging changes in controlling lateral body motion during protective stepping appear to involve factors that intervene between the first-step liftoff and foot contact and/or adaptations in stepping patterns related to prior planning.

Accidental Falls↗

PubMed1994

Stepping responses of young and old adults to postural disturbances: kinematics.

OBJECTIVES: When large disturbances of upright stance occur, balance must usually be restored by taking a step. We undertook this study to examine the biomechanics of stepping responses to sudden backward pulls at the waist. Primarily, response differences between young and old healthy adults were sought. DESIGN: A controlled laboratory study. SUBJECTS: Two groups of healthy and physically-fit adult females, 12 of mean age 22 (Young) and 12 of mean age 73 years (Old). MEASUREMENTS: Response kinematics were measured. From them, the stepping strategies of the subjects were derived, including the timing, length, and height of the first step taken and the rotations of major body segments and at major body joints that occurred. RESULTS: In response to sufficiently large backward pull forces, all subjects responded by taking one or more steps backwards. No significant age group difference appeared in the smallest disturbance for which subjects sometimes used a step response. A significant age group difference appeared in the smallest disturbance at which subjects began consistently to use step responses, and that disturbance was larger for the Old than for the Young. Distinct age group differences were found in stepping strategy. At large disturbance levels, the Young mostly responded by taking a single step, whereas the Old mostly responded by taking multiple steps. The steps taken by the Old, compared with those of the Young, were significantly shorter, had significantly smaller heights, and were taken significantly earlier in the responses. Body segment and joint rotations were generally modest, and few significant age group differences were found in these kinematics. CONCLUSIONS: In restoration of perturbed balance by step-taking, the responses of the healthy, physically-fit young and old adults studied here were similar in many respects, but they differed in some important features. Joint range of motion (ROM) limitations are unlikely to explain age group differences in stepping responses to postural disturbances among healthy subjects because the ROM actually used in any of the responses observed were substantially smaller than the ROM available.

Adult↗

PubMed2005

Split-belt treadmill stepping in infants suggests autonomous pattern generators for the left and right leg in humans.

The behavior of the pattern generator for walking in human infants (7-12 months of age) was studied by supporting the infants to step on a split-belt treadmill. The treadmill belts could be run at the same speed (tied-belt), different speeds, or in different directions (split-belt). We determined whether the legs could operate independently under these conditions, as demonstrated by taking different numbers of steps or by stepping in different directions. Video, surface electromyography, electrogoniometry, and force platform data were recorded. The majority of infants who could step under tied-belt conditions also stepped under split-belt conditions. During forward stepping at low speed differentials between the two belts (ratio, <4), infants adopted a step cycle duration that was intermediate between that expected from tied-belt stepping at each of the speeds. At large speed differentials between the two belts (ratio, 7-22), the infants took extra steps on the fast leg during the stance phase on the slow leg. When the two belts ran in opposite directions, one leg stepped forward, and the other stepped backward. During all forms of stepping, the legs maintained a reciprocal relationship, so that swing phase occurred in one leg at a time. Timing of muscle activity suggests a strong inhibition between the flexor-generating centers on each side and a weaker inhibition between the extensor-generating centers. The stepping behavior resembled that reported for other animals under similar conditions, suggesting that the pattern generator for each limb is autonomous but interacts with its counterpart for the contralateral limb.

Electromyography↗

PubMed2003

Microtensile bond strengths of one- and two-step self-etch adhesives to bur-cut enamel and dentin.

PURPOSE: To evaluate the bonding effectiveness of one- and two-step self-etch adhesives in comparison with a total-etch approach. METHODS: From 55 non-carious human third molars, mid-coronal dentin and enamel bur-cut surfaces were prepared. The bonding surfaces were treated strictly following the manufacturers' instructions with three one-step self-etch (all-in-one) adhesives, AQ bond, Reactmer and Xeno CF Bond; two two-step self-etch adhesives, experimental ABF and Clearfil SE Bond, one two-step total-etch adhesive, Prime & Bond NT, and one three-step total-etch adhesive, OptiBond FL. Composite built-ups were made using Z100. After storage overnight in 37 degrees C water, the bonded specimens were sectioned into rectangular slabs of approximately 2x2 mm width and 9 mm length. They were then trimmed into a round cross-sectional shape resulting in an interface area of approximately 1 mm2, and subsequently subjected to microtensile bond strength (microTBS) testing with a cross-head speed of 1 mm/minute. Differences in microTBS were determined for enamel and dentin using the Kruskal-Wallis test at P < 0.05. RESULTS: The microTBS to enamel varied from 10.3 MPa for the one-step self-etch adhesive AQ bond to 49.5 MPa for the total-etch adhesive Prime & Bond NT. The microTBS to dentin varied from 15.5 MPa for the one-step self-etch adhesive Reactmer to 59.6 for the three-step total-etch adhesive OptiBond FL. The microTBS of the total-etch adhesives to enamel was significantly higher than that of the one-step self-etch adhesives. Comparing the dentin microTBS, only OptiBond FL performed significantly better than the one-step self-etch adhesives. Specimen failure during preparation occurred with each one-step adhesive, but more frequently when bonding to enamel than to dentin. Most one-step self-etch adhesives failed predominantly adhesively between the tooth substrate and the bonding layer in contrast to the two- and three-step adhesives that revealed generally more mixed adhesive-cohesive failures.

Acid Etching, Dental↗

PubMed1987

Tactile discrimination of shape: responses of slowly and rapidly adapting mechanoreceptive afferents to a step indented into the monkey fingerpad.

The representation of shape in the responses of monkey cutaneous mechanoreceptive afferents to steps of varying shape vertically indented into the fingerpad was studied. A series of flat plates was used, each with a step change in thickness in the middle so that one-half of the plate was thicker than the other. The cross-sectional shape of the step approximated that of a half-cycle sinusoid, 0.5 mm high, that was varied in half-cycle wavelength (step width) and hence in steepness and curvature. The steps fell into 2 categories, characterized as "steep" and "'gradual." Evoked action potentials were recorded from single, slowly adapting and from rapidly adapting Meissner corpuscle mechanoreceptive afferent fibers (SA and RA, respectively) innervating the fingerpad of the anesthetized monkey while each step was indented at a succession of lateral positions across the fiber's receptive field. The responses of each SA provided a spatial response profile (number of evoked impulses as a function of step position) that was directly related to the variation in curvature across the step. The rate of discharge was greatest under the sharpest (convex) portion of the step, least under the adjacent concave portion, and intermediate under the flat portions of the steps. The results indicated an exquisite sensitivity of the SA, even during the ramp phase of vertical indentation, to the changes in skin curvature. The spatial response profile remained relatively undistorted over time during the ensuing steady phase, while the contrast between the peak and the minimum response improved. RAs responded only during the ramp phase and with fewer responses, and gave rise to a poorly modulated spatial response profile, even though half of the RAs tested showed limited sensitivity to the amount or rate of change of skin curvature. It was hypothesized that RA responses are predominantly influenced by the vertical velocity of the most sensitive spot in the receptive field. When the same step stimuli were applied to the human fingerpad, the capacities of humans to discriminate differences in step shape were found to correlate with the discriminability of SAs, as opposed to the considerably poorer discriminability of RAs. It is concluded that information concerning the local curvature and hence the shape of objects indenting the skin is primarily coded by the SAs. In the 2 preceding papers (LaMotte and Srinivasan, 1987a, b), we investigated the responses of SAs and RAs to the same sinusoidal steps stroked back and forth across the fingerpad under constant compressional force.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed2004

Step characteristics during obstacle avoidance in hemiplegic stroke.

Whereas several animal studies have indicated the important role of the motor cortex in the control of voluntary gait modifications, little is known about the effects of cortical lesions on gait adaptability in humans. Obstacle avoidance tasks provide an adequate paradigm to study the adaptability of the stepping pattern under controlled, experimental conditions. In the present study, an exploratory assessment was made of the failure rate, the preferred stepping strategies (step lengthening vs step shortening), and the spatiotemporal stride characteristics (percentage increases in stride length, duration, and velocity of the crossing and postcrossing strides) during obstacle avoidance in 11 hemiplegic stroke patients and seven healthy controls. Patients were less successful in avoiding obstacles than controls (14% failure rate vs 0.5% in controls), independent of whether the affected or the unaffected leg led the obstacle avoidance. The number of failed trials increased systematically when the available response time became shorter. During successful trials, lengthening of the step was generally preferred over shortening. This bias towards step lengthening was more pronounced in stroke patients (step lengthening in 91% of the trials vs 75% in controls), irrespective of the side of obstacle presentation. For both groups, overall strategy preference did not adhere to a principle of minimal foot displacement, since step lengthening was used even if it would be more spatially efficient to shorten the step. No statistically significant group differences were found for the increases in length, duration, and velocity of the crossing and postcrossing strides. However, for a subgroup of more slowly walking patients, large percentage increases were found in crossing stride length, duration, and velocity. Similar results were obtained for the postcrossing stride, indicating that, for this subgroup of patients, restoration of the normal walking cadence was more difficult. Overall, no systematic differences were found between the affected and the unaffected leg in stroke patients with respect to failure rates, stepping strategies, or spatiotemporal measures of obstacle avoidance. The present findings suggest that the ability to adequately modify the stepping pattern in response to imposed spatiotemporal constraints is impaired in persons with stroke, especially when modifications have to be performed under time pressure. In addition, the stepping strategies employed by subjects with stroke are different from those found in controls, possibly to reduce the complexity of the avoidance maneuver and to enhance safety. Finally, unilateral cortical damage results in an impaired ability to avoid obstacles on both sides of the body, suggesting that the reduced ability of stroke patients to negotiate obstacles may be related to problems of a more general coordinative nature.

Adult↗