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Biomedical subjects

J F Lehmann

Publications and source records attributed to J F Lehmann.

At least 19 recordsLinked to original sources
PubMed2001

X-ray crystal structures of alpha-KrF(2),[KrF][MF(6)](M=As,Sb,Bi),[Kr(2)F(3)][SbF(6).KrF(2), [Ke(2)F(3)2[SbF(6)]2.KrF(2), and [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)]; synthesis and characterization of [Kr(2)F(3)][PF(6).nKrF(2); and theoretical studies of KrF(2), KrF+, Kr(2)F(3)+, and the [KrF][MF(6)](M=P,As,Sb,Bi) ion pairs.

The crystal structures of alpha-KrF(2) and salts containing the KrF(+) and Kr(2)F(3)(+) cations have been investigated for the first time using low-temperature single-crystal X-ray diffraction. The low-temperature alpha-phase of KrF(2) crystallizes in the tetragonal space group I4/mmm with a = 4.1790(6) A, c = 6.489(1) A, Z = 2, V = 113.32(3) A(3), R(1) = 0.0231, and wR(2) = 0.0534 at -125 degrees C. The [KrF][MF(6)] (M = As, Sb, Bi) salts are isomorphous and isostructural and crystallize in the monoclinic space group P2(1)/c with Z = 4. The unit cell parameters are as follows: beta-[KrF][AsF(6)], a = 5.1753(2) A, b = 10.2019(7) A, c = 10.5763(8) A, beta = 95.298(2) degrees, V = 556.02(6) A(3), R(1) = 0.0265, and wR(2) = 0.0652 at -120 degrees C; [KrF][SbF(6)], a = 5.2922(6) A, b = 10.444(1) A, c = 10.796(1) A, beta = 94.693(4) degrees, V = 594.73(1) A(3), R(1) = 0.0266, wR(2) = 0.0526 at -113 degrees C; [KrF][BiF(6)], a = 5.336(1) A, b = 10.513(2) A, c = 11.046(2) A, beta = 94.79(3) degrees, V = 617.6(2) A(3), R(1) = 0.0344, and wR(2) = 0.0912 at -130 degrees C. The Kr(2)F(3)(+) cation was investigated in [Kr(2)F(3)][SbF(6)].KrF(2), [Kr(2)F(3)](2)[SbF(6)](2).KrF(2), and [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)]. [Kr(2)F(3)](2)[SbF(6)](2).KrF(2) crystallizes in the monoclinic P2(1)/c space group with Z = 4 and a = 8.042(2) A, b = 30.815(6) A, c = 8.137(2) A, beta = 111.945(2) degrees, V = 1870.1(7) A(3), R(1) = 0.0376, and wR(2) = 0.0742 at -125 degrees C. [Kr(2)F(3)][SbF(6)].KrF(2) crystallizes in the triclinic P1 space group with Z = 2 and a = 8.032(3) A, b = 8.559(4) A, c = 8.948(4) A, alpha = 69.659(9) degrees, beta = 63.75(1) degrees, gamma = 82.60(1) degrees, V = 517.1(4) A(3), R(1) = 0.0402, and wR(2) = 0.1039 at -113 degrees C. [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)] crystallizes in the monoclinic space group P2(1)/c with Z = 4 and a = 6.247(1) A, b = 24.705(4) A, c = 8.8616(6) A, beta = 90.304(6) degrees, V = 1367.6(3) A(3), R(1) = 0.0471 and wR(2) = 0.0958 at -120 degrees C. The terminal Kr-F bond lengths of KrF(+) and Kr(2)F(3)(+) are very similar, exhibiting no crystallographically significant variation in the structures investigated (range, 1.765(3)-1.774(6) A and 1.780(7)-1.805(5) A, respectively). The Kr-F bridge bond lengths are significantly longer, with values ranging from 2.089(6) to 2.140(3) A in the KrF(+) salts and from 2.027(5) to 2.065(4) A in the Kr(2)F(3)(+) salts. The Kr-F bond lengths of KrF(2) in [Kr(2)F(3)][SbF(6)].KrF(2) and [Kr(2)F(3)](2)[SbF(6)](2).KrF(2) range from 1.868(4) to 1.888(4) A and are similar to those observed in alpha-KrF(2) (1.894(5) A). The synthesis and Raman spectrum of the new salt, [Kr(2)F(3)][PF(6)].nKrF(2), are also reported. Electron structure calculations at the Hartree-Fock and local density-functional theory levels were used to calculate the gas-phase geometries, charges, Mayer bond orders, and Mayer valencies of KrF(+), KrF(2), Kr(2)F(3)(+), and the ion pairs, [KrF][MF(6)] (M = P, As, Sb, Bi), and to assign their experimental vibrational frequencies.

Journal Article↗
PubMed1998

Mass and mass distribution of below-knee prostheses: effect on gait efficacy and self-selected walking speed.

OBJECTIVE: To study mass and mass distribution effect on function of below-knee prostheses. DESIGN: Design modifications were done to produce proximal center of mass location versus distal center of mass location variations, and prosthesis weight was modified from 42% to 70% of normal limb weight. Work across joints of affected and unaffected extremities was compared to assess the ability of the prosthesis to substitute for function loss. SETTING: University biomechanics laboratory. PARTICIPANTS: Fifteen volunteers with below-knee amputations, residual limb length greater than 8.3 cm, but excluding Syme amputations. INTERVENTIONS: Patients walked with all configurations at self-selected walking speeds and 120 m/min. MAIN OUTCOME MEASURES: Self-selected walking speed and metabolic efficiency. Work across the joints of affected and unaffected sides was compared. RESULTS: Proximal center of mass location produced a more efficient gait. Weight change from 42% to 70% of normal had no significant effect. Mechanical studies show that the prosthesis is a relatively poor substitute for the normal limb; most work is done by the nonamputated side. Particularly, the prosthesis failed to produce effective forward impulses on the body, resulting from push-off and deceleration of the swing leg. CONCLUSIONS: For a proximal center of mass, lightweight distal components (e.g., feet) should be used; it is questionable whether further expenditure to develop ultralightweight prostheses would be cost effective for level walking.

Adolescent↗
PubMed1996

The stretch reflex response in the normal and spastic ankle: effect of ankle position.

OBJECTIVE: The influence of stretch of the gastrocnemiussoleus muscle on the stretch reflex activity was studied, by varying the ankle angle in steps from 10 degrees of plantarflexion (PF) to 5 degrees of dorsiflexion (DF). DESIGN: Nonrandomized control trial. SETTING: Department of Rehabilitation Medicine of a university medical center. PATIENTS: Sixteen subjects with and 16 subjects without spasticity. MAIN OUTCOME MEASURES: The passive elastic stiffness and active reflex response, expressed by the total and elastic path lengths, were determined at each ankle angle as a sinusoidal displacement of 5 degrees was applied to the joint at frequencies from 3 to 12 Hz. RESULTS: The elastic stiffness showed no difference between the spastic and normal subjects for all ankle angles (p > .05). The elastic stiffness increased linearly similarly in both groups when the ankle was dorsiflexed. The reflex response was significantly greater in the spastic group for all positions (p < or = .01). The total and elastic path lengths showed a linear increase in both groups when the ankle angle was varied from PF to DF. The spastic group, however, had a significantly faster increase (p < or = .005). Between-group comparison showed a significant quadratic trend in the elastic path length for the spastic group (p < or = .05), with a maximum at 2.5 degrees of DF. CONCLUSIONS: This study showed that the stretch reflex activity varies with the ankle position. This must be considered when performing spasticity tests subsequent to an intervention that has changed the available range of motion and when comparing subjects measured at different ankle positions.

Adult↗
PubMed1994

The quantitative measurement of spasticity: effect of cutaneous electrical stimulation.

The goal of this research was to determine if cutaneous electrotherapy would temporarily reduce muscle spasticity. Five traumatically brain injured (TBI) and five spinal cord injured (SCI) subjects, all with clinically evident spasticity, received surface electrical stimulation over the tibialis anterior muscle. Using the Spasticity Measurement System, stiffness around the ankle was measured before, immediately after, and 24 hours after treatment. With stimulation, ipsilateral ankle viscoelastic stiffness immediately decreased in 9 of 10 subjects and remained significantly depressed for up to 24 hours. Contralateral ankle spasticity did not significantly change. Using the same subjects under sham conditions, no significant decrements in spasticity occurred. In a subjective survey, only SCI participants reported functionally evident spasticity reductions. Also within this subgroup, efficacy of treatment was directly proportional to the severity of pre-stimulation clonus. We conclude that (1) cutaneous electrotherapy transiently decreases both TBI and SCI related spasticity and (2) pre-stimulation clonus may function as a clinical indicator of SCI patients most likely to benefit from this process.

Adult↗
PubMed1993

Comprehensive analysis of dynamic elastic response feet: Seattle Ankle/Lite Foot versus SACH foot.

This study evaluated biomechanical and metabolic performance differences between two prosthetic foot designs in light of their mechanical properties. Ten unilateral below-knee amputee subjects, at least 1 year after amputation, capable of walking and running, were studied. Differences in heel and forefoot compliance explained differences in gait events and alignment. Increased efficiency of pushoff in the Seattle Ankle/Lite Foot exists as evidenced by the decrease loading on the opposite limb during double support and a less shortened step length on the sound side compared to the SACH foot. The natural frequency of oscillation for the prosthetic feet was determined to be too high to provide energy storage and release synchronized with kinematic requirements because neither metabolic cost savings nor differences in metabolic efficiency were found. Comfortable walking speed and the nadir of metabolic rate and efficiency are not different. Via accelerometer measurement, it was found that the more compliant and lossy SACH foot heel was less likely to transmit high frequency vibration.

Adult↗
PubMed1993

Comprehensive analysis of energy storing prosthetic feet: Flex Foot and Seattle Foot Versus Standard SACH foot.

This study compared the mechanical and biomechanical functions, metabolic demand, and shock absorption of two dynamic elastic response (DER) prosthetic foot designs with the SACH foot. Nine individuals who had undergone unilateral below knee amputation were studied. Mechanical properties of the feet were related to gait biomechanics. Forefoot compliance is greatest for the Flex Foot and least for the SACH foot, hence, Flex Foot demonstrates (1) the longest midstance phase, (2) the greatest ankle angle range, and (3) greater forward movement of the center of pressure. There was some evidence that the DER feet produced a better push-off. However, neither the self-selected walking speed nor the metabolic rate or efficiency over a spectrum of walking speeds (73 to 120m/min) and running speeds (140 to 200m/min) was significantly different. Because no energy savings resulted for the DER feet, the release of stored energy in the flexible feet may not occur at the proper time to assist in ambulation as a result of the natural frequency of oscillation.

Adult↗
PubMed1993

Push-off and propulsion of the body in normal and abnormal gait. Correction by ankle-foot orthoses.

The biomechanics of push-off and propulsion are described as part of normal gait. Deviations from a normal gait pattern, as well as secondary complications, are discussed in reference to common limps, such as gastrocnemius and soleus weakness and the hemiparetic stroke gait. In addition to the lack of propulsion, major abnormalities include the instability of the knee and the lack of motion at the ankle, associated with muscle imbalance and spasticity. The correction of the abnormalities by ankle-foot orthoses is described in quantitative terms. Proper adjustment of the orthosis is essential for optimal guided correction.

Ankle↗
PubMed1993

Influence of cryotherapy on spasticity at the human ankle.

The application of cryotherapy to temporarily reduce spasticity is a widespread clinical practice. A method of quantifying spasticity, based on viscoelastic stiffness measurements at the ankle, was applied to objectively determine the efficacy of cryotherapy in reducing spasticity of the calf. Baseline, cryotherapy and one-hour postcryotherapy measurements of spasticity were performed in 25 subjects with clinical signs of spasticity secondary to traumatic brain injury, spinal cord injury, and stroke. A statistically significant reduction in spasticity occurred during cryotherapy. Postcryotherapy results were equivocal, although there was a tendency for diminished spasticity relative to the baseline measurement. Two subjects showed a clear aggravation of spasticity following cryotherapy, thus leading to the conclusion that dichotomous results are possible.

Adolescent↗
PubMed1992

Effect of lower limb on body propulsion.

The purpose of this study was to analyze and compare the effects of the leg during swing and stance phases of forward propulsion of the body for both men and women. Twelve able-bodied subjects, six men and six women, were studied with a Vicon(a) gait-analysis system. A two-dimensional, sagittal-plane biomechanical analysis featuring a link-segment model was used to determine the force at the hip in the horizontal direction. Integrating this force curve over time during the swing and stance gait phases produced linear impulses, representing swing and stance contributions to the propulsion of the body, and it allowed quantitative comparisons using student t and Fisher tests. The deceleration of the swing leg was found to be the major contributor to the forward propulsion of the body. The stance leg initially exerted the major restraining or negative impulse during early stance; then it generated a positive impulse during push-off in late stance. A typical pattern of gait impulses was defined for normal gait. Male and female gait impulses were not significantly different for all gait phases.

Adult↗
PubMed1991

Quantitative measurement of spasticity in children with cerebral palsy.

Spasticity was quantified in nine children with spastic diplegia, using a sinusoidal displacement of the foot at frequencies from 3 to 12Hz. Ankle-joint stiffness was separated into elastic (energy-storing) and viscous (energy-dissipating) components. 'Path length' was used to represent the variation in stiffness over this frequency range. Compared with 11 unaffected children, a significant difference in path lengths was demonstrated for the children with spasticity. An age-dependent effect was demonstrated when path lengths of unaffected children were compared with those of 10 unaffected adults. A modified path-length measure is proposed which minimizes age dependency, yet enables detection of spasticity. Passive stiffness properties of unaffected adults showed higher elastic stiffness, viscosity and friction than unaffected children. A method was developed to evade the need for temporary nerve blocks to calculate inerital properties of the foot in persons with spasticity.

Biomechanical Phenomena↗
PubMed1991

Footwear and posture. Compensatory strategies for heel height.

The belief that wearing high-heeled shoes increases lumbar lordosis is firmly ingrained in clinical folklore. Proponents of negative heel footwear argue that because high positive heels increase the lumbar lordosis, negative heels will decrease the lumbar lordosis. Quantitative documentation of the assumption regarding high heels is not to be found in the literature, although sporadic attempts to prove this assumption have been made throughout the 20th Century. Although other effects, such as decreased gait speed and step length, and increased knee flexion at heel strike have been found in more than one study, no increase in lumbar lordosis has been found. Where an actual decrease in lordosis has been found, authors tend to explain it away as inconsistent with what every clinician feels that he or she has observed. We felt it appropriate, then, to conduct both a static and a dynamic study to assess the effects of heel height on lumbar spine and lower limb joint kinematics in the sagittal plane, as well as other strategies to compensate for heel height. The results indicate that the greatest compensation is at the ankle and knee. Where a significant effect occurred in the lumbar spine (males, dynamic study), high heels decreased the lumbar lordosis, i.e., resulted in less swayback rather than more.

Adolescent↗
PubMed1990

Spasticity in spinal cord injured persons: quantitative effects of baclofen and placebo treatments.

Spasticity commonly occurs after a spinal cord injury and is characterized by increased resistance to passive movement of peripheral joints. This study examined the effect of an antispasticity medication on stiffness from the myotatic reflex response generated by passive sinusoidal ankle motion. A repeated measures, multiple base-line, single-subject, double-blind design was employed. The independent variable was spasticity medication treatment, where the levels were 40 mg/day and 80 mg/day of baclofen v placebo treatment. Viscous and elastic stiffness measurements were taken at the ankle joint during a placebo base-line phase and during treatment with baclofen for five adult males with traumatic spinal cord injuries. Ankle sinusoidal oscillation frequencies were from 3 to 12 Hz during test sessions. Mean viscous and elastic stiffness scores for all frequencies were calculated for each phase of the study. Randomization tests of mean changes in stiffness measurements between each treatment phase of the study failed to provide any convincing evidence of a significant treatment effect for reduction of spasticity in the traumatic spinal cord injured subjects studied. Further testing is needed to exclude potential confounding factors before this conclusion can be confirmed. The results suggest that baclofen is not a universal treatment of choice for all individuals with spasticity resulting from traumatic spinal cord injury.

Adult↗
PubMed1990

Quantitative evaluation of sway as an indicator of functional balance in post-traumatic brain injury.

The test of sway, using different conditions of stance with measurements of the average radial deviation of the center of pressure and its path length of sway per unit of time, has been shown to be a useful clinical tool in determining balance problems in traumatic brain injury (TBI) patients. Normative values were established to determine if an individual patient's sway values fell within the normal range (mean +/- 2SD). The tests have shown good test-retest reliability for TBI patients. In addition, it has been shown that the sensitivity of the test is sufficient to identify changes in patients' performances as their clinical conditions change. It has been demonstrated that the different stance conditions of the battery of tests become progressively more difficult to perform (from comfortable stance, eyes open and eyes closed, through narrow stance, eyes open and eyes closed, to tandem stance with right or left foot forward, eyes open and eyes closed). By using these subtests, it is easy to distinguish between the performances of able-bodied patients and TBI patients with very mild balance problems. The validity of the measure has been documented by correlating the sway performance with clinical functional performance tests. The test performance also correlates with the patient's own assessment of his or her gait difficulties. The limited data available suggest that the test of sway relates difficulties in static balance to the frequency of falls. Finally, subtests permit identification of specific problems in maintaining balance as a basis for therapeutic intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Influence of muscle cooling on the viscoelastic response of the human ankle to sinusoidal displacements.

The changes in passive mechanical muscle properties due to cooling of the calf in healthy human volunteers were investigated. The technique, using sinusoidal driving of the foot, permitted the separation of muscle stiffness response into its elastic and viscous components. Cooling the calf with ice for 30 minutes increases the rate of change of elastic stiffness with frequency, and it increases the frictional stiffness over a frequency range of 3 to 12Hz. Such cooling would produce an estimated 3% to 10% increase in total stiffness, on average, in a spastic person. This increase in stiffness would counteract reductions in total stiffness achieved during the application of cryotherapy to relieve spasticity. However, one could expect that for a clinically significant reduction of spasticity, the increase in passive stiffness of the muscle generated by cooling would be largely overshadowed by the decrease in reflex reactivity.

Adult↗
PubMed1989

Spasticity: quantitative measurements as a basis for assessing effectiveness of therapeutic intervention.

Spasticity, a common problem in upper motor neuron lesions, frequently results in uncontrolled involuntary motion that interferes with function. A quantifiable method related to the mechanical output of the muscle is needed to test and improve therapeutic intervention. A sinusoidal displacement of 5 degrees was used to measure elastic and viscous stiffness around the ankle at frequencies from 3 to 12Hz. To isolate viscoelastic response, the influences of inertia and equipment drag were eliminated. Test-retest correlation values were 0.953 for elastic and 0.992 for viscous stiffness. The elastic stiffness in 13 spastic subjects under nerve block was significantly higher than that of 13 healthy subjects (p less than or equal to 0.05), indicating early changes associated with contracture. Elastic and viscous response is expressed by the total stiffness vector containing both components, the Nyquist diagram. This diagram's pathlength from 3 to 12Hz was calculated and showed high test-retest reliability in healthy subjects. The median pathlength value for the spastic group was 98 Newton-meters/radian (N-m/rad) and, for the normal group, 24N-m/rad, a statistically significant difference (p less than or equal to 0.0001). A mathematical model of the spastic response shows that the Nyquist diagram's pathlength relates to reflex loop gain and is independent of the shift in passive properties. The model predicts a shift in passive properties during spastic responses relative to responses measured during nerve block. Thus, subtraction of passive responses measured during nerve block may not isolate the remaining reflex response, but the pathlength measure relating to the reflex response gain was unaffected, allowing evaluation of therapeutic intervention effectiveness.

Adult↗
PubMed1987

Effect of cooling on H- and T-reflexes in normal subjects.

The local application of cold has been used to decrease spasticity and facilitate neuromuscular function, but previous attempts to identify its effect on the stretch reflex have not been entirely successful. We examined the effects of cold on the Hoffmann (H) reflex and on the tendon tap (T) reflex in 16 subjects. A series of H/M recruitment curves and T-reflexes were recorded via surface EMG electrodes before and during cooling of the triceps surae. Skin and intramuscular temperatures were recorded with average decreases of 18.4C and 12.1C, respectively. Peak-to-peak amplitude of the M, H, and T compound action potentials (CAPs) was measured. In all cases, the amplitude of the maximal M-wave decreased (p less than 0.001) in response to cooling. These changes in the recording of CAPs should be considered when cooling experiments result in alterations in H or T waveforms. When using the M-wave as a covariant in our analysis, there were no significant changes in the H-reflex amplitude; the height of CAPs elicited by T decreased (p = 0.025). Our findings do not support earlier claims that simple cooling facilitates the excitatory alpha motoneuron pool as measured by the H-reflex; we do confirm that muscle spindle activity, as measured by the T-reflex, is decreased by muscle cooling.

Adult↗
PubMed1987

The role of the biomechanics laboratory in the analysis of the gait of individuals with arthritis.

The function of a biomechanics laboratory is to measure those aspects of an individual patient's performance that cannot be quantitatively assessed in the clinical setting. Essential equipment provides the ability to measure gait events, ground reactive forces, kinematics (movement of the body and its segments in 3 dimensions), electromyographic activity, and oxygen consumption. A minicomputer with video screen is required to process the data and allow visual checks of the functioning of the system. Such things as moments around joints and deforming forces may be calculated from the measured variables. Illustrations are given of a schematic laboratory system, computer generated stick diagrams, real-time changes in forces, moment-arms, moments, and excursions, in addition to the alteration of these variables in tibial nerve paralysis and degenerative arthritis of the knee.

Arthritis↗