Clinical measures of balance and gait cannot differentiate somatosensory impairments in people with lower-limb amputation.

BACKGROUND: In addition to a range of functional impairments seen in individuals with a lower-limb amputation, this population is at a substantially elevated risk of falls. Studies postulate that the lack of sensory feedback from the prosthetic limb contributes heavily to these impairments, but the extent to which sensation affects functional measures remains unclear. RESEARCH QUESTION: The purpose of this study is to determine how sensory impairments in the lower extremities relate to performance with common clinical functional measures of balance and gait in individuals with a lower-limb amputation. Here we evaluate the effects of somatosensory integrity to clinical and lab measures of static, reactive and dynamic balance, and gait stability. METHODS: In 20 individuals with lower-limb amputation (AMP) and 20 age and gender-matched able-bodied controls (CON), we evaluated the effects of sensory integrity (pressure, proprioception, and vibration) on measures of balance and gait. Static, reactive, and dynamic balance were assessed using the Sensory Organization Test (SOT), Motor Control Test (MCT), and Functional Gait Assessment (FGA), respectively. Gait stability was assessed through measures of step length asymmetry and step width variability. Sensation was categorized into intact or impaired sensation by pressure thresholds and differences across groups were analyzed. RESULTS: There were significant differences between AMP and CON groups for reliance on vision for static balance in the SOT, MCT, and FGA (p < 0.01). Despite differences across groups, there were no significant differences within the AMP group based on intact or impaired sensation across all functional measures. SIGNIFICANCE: Despite being able to detect differences between able-bodied individuals and individuals with an amputation, these functional measures cannot distinguish between levels of impairment within participants with an amputation. These findings suggest that more challenging and robust metrics are needed to evaluate the effects of sensation and function in individuals with an amputation.

Including sheath effects in the interpretation of planar retarding potential analyzer's low-energy ion data.

The interpretation of planar retarding potential analyzers (RPA) during ionospheric sounding rocket missions requires modeling the thick 3D plasma sheath. This paper overviews the theory of RPAs with an emphasis placed on the impact of the sheath on current-voltage (I-V) curves. It then describes the Petite Ion Probe (PIP) which has been designed to function in this difficult regime. The data analysis procedure for this instrument is discussed in detail. Data analysis begins by modeling the sheath with the Spacecraft Plasma Interaction System (SPIS), a particle-in-cell code. Test particles are traced through the sheath and detector to determine the detector's response. A training set is constructed from these simulated curves for a support vector regression analysis which relates the properties of the I-V curve to the properties of the plasma. The first in situ use of the PIPs occurred during the MICA sounding rocket mission which launched from Poker Flat, Alaska in February of 2012. These data are presented as a case study, providing valuable cross-instrument comparisons. A heritage top-hat thermal ion electrostatic analyzer, called the HT, and a multi-needle Langmuir probe have been used to validate both the PIPs and the data analysis method. Compared to the HT, the PIP ion temperature measurements agree with a root-mean-square error of 0.023 eV. These two instruments agree on the parallel-to-B plasma flow velocity with a root-mean-square error of 130 m/s. The PIP with its field of view aligned perpendicular-to-B provided a density measurement with an 11% error compared to the multi-needle Langmuir Probe. Higher error in the other PIP's density measurement is likely due to simplifications in the SPIS model geometry.

Elevated sedimentation on coral reefs adjacent to a beach nourishment project.

An increasingly common method to restore eroding beaches is nourishment, a process by which lost sand is replaced with terrestrial or offshore sediments to widen beaches. The southeastern Florida coastline contains shore-parallel coral reef communities adjacent to eroding beaches. Scleractinian corals and other reef-associated organisms are known to demonstrate sensitivity to elevated sedimentation levels. Sediment traps were used to examine spatio-temporal sedimentation patterns and assess the effects of nourishment (dredge and fill) activities. Several environmental variables correlated with among-site spatial variability of sediment parameters. Intra-annual variability correlated with wind velocity and direction. Nourishment activities showed localized effects, with sites in close proximity to dredging areas exhibiting significantly higher collection rates and lower percent fines than control sites. A regional increase in sedimentation occurred while nourishment activities were ongoing. Due to concurrent impacts of hurricanes, only one during-construction sampling interval revealed substantially higher collection rates relative to corresponding pre-construction sampling intervals.

Chronic stability and selectivity of four-contact spiral nerve-cuff electrodes in stimulating the human femoral nerve.

This study describes the stability and selectivity of four-contact spiral nerve-cuff electrodes implanted bilaterally on distal branches of the femoral nerves of a human volunteer with spinal cord injury as part of a neuroprosthesis for standing and transfers. Stimulation charge threshold, the minimum charge required to elicit a visible muscle contraction, was consistent and low (mean threshold charge at 63 weeks post-implantation: 23.3 +/- 8.5 nC) for all nerve-cuff electrode contacts over 63 weeks after implantation, indicating a stable interface with the peripheral nervous system. The ability of individual nerve-cuff electrode contacts to selectively stimulate separate components of the femoral nerve to activate individual heads of the quadriceps was assessed with fine-wire intramuscular electromyography while measuring isometric twitch knee extension moment. Six of eight electrode contacts could selectively activate one head of the quadriceps while selectively excluding others to produce maximum twitch responses of between 3.8 and 8.1 N m. The relationship between isometric twitch and tetanic knee extension moment was quantified, and selective twitch muscle responses scaled to between 15 and 35 N m in tetanic response to pulse trains with similar stimulation parameters. These results suggest that this nerve-cuff electrode can be an effective and chronically stable tool for selectively stimulating distal nerve branches in the lower extremities for neuroprosthetic applications.

Pentoxifylline rescue preserves lung function in isolated canine lungs injured with phorbol myristate acetate.

OBJECTIVE: We hypothesized that pentoxifylline, administered after phorbol myristate acetate (PMA), would diminish the severity of lung injury. SETTING: Animal research laboratory. DESIGN: Comparative study. SUBJECTS: Mongrel dogs (n = 33). INTERVENTIONS: Baseline measurements were obtained from the isolated blood-perfused dog lung lobes after 1 h of stable perfusion and ventilation. Four different measures of lung compliance were obtained along with WBC and neutrophil counts. Pulmonary vascular resistance (PVR) and capillary filtration coefficient (Kf) were calculated, and the ratio of a normalized maximal enzymatic conversion rate to the Michaelis-Menten constant (Amax/Km) was used to assess perfused capillary surface area. The control lobes (n = 8) were ventilated and perfused for an additional 40 min while the injured lobes (n = 17) received PMA (0.1 microg/mL of perfusate). The pentoxifylline-protected lobes (n = 8) were treated with pentoxifylline (1 mg/mL of perfusate) 10 min after injury with PMA. All measurements were then repeated. MEASUREMENT AND MAIN RESULTS: The three groups did not differ significantly at baseline. The control lobes remained relatively stable over time. The injured lobes demonstrated marked deterioration in compliance: 8.79 +/- 0.7 to 5.97 +/- 0.59 mL/cm H(2)O (p < 0.05) vs 10.1 +/- 1.0 to 8.07 +/- 0.72 mL/cm H(2)O and 9.6 +/- 1.1 to 9.9 +/- 0.85 mL/cm H(2)O in the control and protected lobes, respectively. Both groups receiving PMA had similar drops in WBC and neutrophil counts, but the pentoxifylline-protected lobes had preservation of all four compliance measures. PVR increased from 37.8 +/- 1.8 to 118.6 +/- 12.7 cm H(2)O/L/min (p < 0.05) in the injured lobes vs 35.4 +/- 0.5 to 36.3 +/- 2.8 cm H(2)O/L/min and 40.4 +/- 0.04 to 46.7 +/- 2.8 cm H(2)O/L/min (p < 0.05) in the control and protected lobes, respectively. Kf increased < 25% in the protected group but more than tripled in the injured group. Amax/Km dropped from 559 +/- 36 to 441 +/- 33 mL/min (p < 0.05) in the injured lobes vs 507 +/- 14 to 490 +/- 17 mL/min and 609 +/- 34 to 616 +/- 37 mL/min in the control and pentoxifylline-protected lobes, respectively. CONCLUSIONS: The use of pentoxifylline as a rescue agent prevented the PMA-induced deterioration of lung compliance, vascular integrity, and endothelial metabolic function in this acute lung injury model, despite significant pulmonary neutrophil sequestration.

High-yield synthesis and purification of an alpha-helical transmembrane domain.

Polypeptides corresponding to hydrophobic transmembrane alpha-helices, such as residues 69-101 of glycophorin A, are notoriously difficult to prepare in quantities sufficient for biophysical experiments. Simple synthetic and purification approaches reported here have been developed by combining a few modifications to standard procedures, without resorting to elevated temperatures, expensive activation strategies, or complex hydrophobic solvent mixtures. The cost of screening projects, preparing labeled peptides, and examining sequence variations is thereby significantly reduced. The quality of the peptide synthesized by this small-scale 9-fluorenylmethoxycarbonyl (Fmoc) strategy is comparable to that of the peptide synthesized by an experienced resource facility using a large-scale tert-butyloxycarbonyl strategy. Using reverse-phase HPLC, the desired peptide was separated from the primary side product (a Leu or Ile deletion) and quantitatively recovered at greater than 98% purity. Baseline resolution was achieved using a water:acetonitrile gradient to elute the peptides from a cyanopropyl column at ambient temperature. Combining these approaches readily yields 10 to 20 mg of pure transmembrane peptide from a small-scale Fmoc synthesis. The approaches are readily transferable to transmembrane sequences not previously synthesized and do not require setting up a specialized facility. The time and start-up expense required to launch new studies are thereby reduced expanding the range and detail with which questions in membrane protein biophysics can be explored.

Day persons, night persons, and time of birth: preliminary findings.

The authors conducted 2 surveys to determine the relationship between time of birth and being a day person or a night person. Day persons are most alert during daylight hours; night persons are most alert during hours of darkness. In Survey 1, the authors asked U.S. high school students to complete the Alertness Questionnaire (B. Wallace, 1993) and to respond to other items related to daytime or nighttime activity. In Survey 2, the authors administered the same items to a U.S. college population. In both surveys, time of birth was significantly related to being a day person or a night person. The results suggest that a critical period for setting the biological clock for alertness may be the moment of birth.

Detergents modulate dimerization, but not helicity, of the glycophorin A transmembrane domain.

Understanding how the lipid environment influences transmembrane helix association requires thermodynamic measurements that can be interpreted in terms of specific chemical interactions. We have used Förster resonance energy transfer to measure dimerization of the glycophorin A transmembrane helix in detergent micelles. The observed Kd is at least two orders of magnitude weaker in sodium dodecyl sulfate than it is in zwitterionic detergents. In contrast, neither dimerization nor the detergent affects the secondary structure of the glycophorin A helix as measured by far-UV circular dichroism. These measurements support a long standing assumption about the glycophorin A transmembrane domain, that detergents uncouple helix formation from helix dimerization. The approach is applicable to a variety of systems in diverse environments, extending our ability to measure how interactions with complex solvents affect the thermodynamics of oligomerization.

Ventilation above closing volume reduces pulmonary vascular resistance hysteresis.

The aim of this study was to determine the relationship of pulmonary vascular resistance (PVR) hysteresis and lung volume, with special attention to the effects of ventilation around closing volume (CV). Isolated, blood-perfused canine left lower lung lobes (LLL) were incrementally inflated and deflated. Airway and pulmonary artery pressures (PAP) were recorded after each stepwise volume change. Constant blood flow was provided (600 ml/min) and the pulmonary vein pressure (PVP) was held constant at 5 cm H2O. PAP changes, therefore, were a direct index of PVR changes. Group 1 lobes underwent a full inflation from complete collapse to total lobe capacity (TLC) followed by a full deflation. Group 2 lobes underwent two deflation/inflation cycles, after an initial full inflation. These cycles, both beginning at TLC, had deflation end above and below CV, respectively. Significant PVR hysteresis was noted when the first inflation and deflation were compared. The maximum difference in PAP on deflation was 3.3 cm H2O or 11%. The mean decrease was 2.7 cm H2O for 18 lobes (p < 0.0001). The PAPs on all subsequent inflations or deflations that began above CV remained 9% lower than the initial inflation (n = 9, p < 0.0001), but were not different from each other. However, the final inflation which began from below CV resulted in a 30% return of PVR hysteresis (mean increase in PAP of 0.8 cm H2O, n = 7, p < 0.004). We conclude that there is hysteresis in the PVR response during ventilation, with decreased PVR during deflation relative to the initial inflation, that this hysteresis is absent when lung volume is maintained greater than CV, and that hysteresis returns when inflation occurs after deflation below CV.

Unaltered pulmonary capillary surface area in the presence of changing arterial resistance.

We hypothesized that capillary recruitment may not be solely dependent on extracapillary factors. To test this hypothesis, rabbits were anesthetized and placed on total cardiac bypass at a constant, physiological pulmonary blood flow. Vascular occlusion techniques were combined with measurement of the transpulmonary metabolism of an angiotensin-converting enzyme substrate, allowing the concomitant assessment of changes in segmental resistances and dynamically perfused capillary surface area. Intra-arterial serotonin infusion increased upstream pulmonary vascular resistances without affecting dynamically perfused capillary surface area. Intra-arterial isoproterenol infusion diminished serotonin-induced increased upstream resistances, also without affecting capillary surface area. These findings support the hypothesis that pulmonary capillary recruitment may not be solely dependent on extracapillary factors.

Simultaneous determination of midazolam and flumazenil concentrations in human plasma by gas chromatography.

A gas chromatographic method for the simultaneous determination of midazolam and flumazenil concentrations in human plasma has been developed, using clinazolam as the internal standard. A mixture of chloroform and ethyl acetate (80:20) was used to extract the two compounds. A 2-microliters volume of the reconstituted sample was injected using a 1:20 split injection mode. Intra-day coefficients of variation ranged from 2 to 6.9%. The assay was linear over the range 3-1000 ng/ml. This assay was subsequently used to analyze samples from a human pharmacokinetic study.

Effects of hyperthermia on the auditory-evoked brainstem responses in mice.

This study investigated the effects of increased body temperature on the latencies and amplitudes of the auditory-evoked brainstem response (ABR) in mice. Six eleven-week-old male CBA/CaJ mice were anesthetized with pentobarbital and screened for normal hearing. Hyperthermia was induced by placing the animal in a thermostatically controlled chamber; a thermistor connected to a digital thermometer measured the rectal temperature. ABRs were evoked with broad-band clicks presented at repetition rates of 21.1/s and 61.1/s. The latencies and amplitudes of waves I-V were measured at 1-degree and/or 0.5-degree intervals between 37 and 42 degrees C. Temperature elevation between 37 and 41 degrees C shortened the latencies of all the ABR waves, the effect being linear and cumulative across the time window. Change in this trend occurred between 41 and 42 degrees C, whereby the latencies of all the waves stabilized or showed minimal prolongation. Amplitudes of the most robust waves I and II showed a trend similar to the latencies, whereas the later waves showed erratic and uninterpretable changes. These findings in the mouse may be indicative of the physiological limit of thermal tolerance and as such may be regarded as a premonitory signal of permanent damage.

The isolation and characterization of milleri group streptococci from dental periapical abscesses.

Reports of the isolation of streptococci from dental abscesses have shown an association of the "S. milleri" group with such lesions. There has been considerable confusion regarding the taxonomy of these organisms, but the milleri group has recently been reclassified into three distinct species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. In this study, 45 samples from dental periapical abscesses were examined. Milleri group streptococci were isolated from 16 patients (37%), 15 being identified as S. anginosus and one as S. intermedius. In one patient, S. anginosus was isolated in pure culture, and it would appear that this is the predominant species of milleri group streptococci associated with periapical abscesses.

Pharmacoimmunodynamics of methylprednisolone: trafficking of helper T lymphocytes.

A two-compartment closed model was used to characterize the cell trafficking behavior of helper T cells in response to various single doses of methylprednisolone. Steroids are assumed to inhibit the circadian-determined cell return from extravascular sites to blood in a classic inhibitory pattern reflected by an IC50. The rate of cell efflux from tissues is modeled with a cosine function having a period of 24 hr and a maximum at about 1 AM. Nonlinear least-squares regression employing differential equations was used to analyze helper T-cell data from three human studies from our laboratory. The IC50 value of methylprednisolone of 12-19 ng/ml approximates receptor KD values. Simulations were performed to demonstrate the log-linear role of steroid dose or AUC on the integral of effect of helper T cells over a wide range of methylprednisolone doses. This pharmacodynamic model allows flexibility for characterizing any type of steroid dosing regimen and is relevant in describing complex response data for corticosteroid immunosuppressive effects in man.

Pharmacokinetics and pharmacodynamics of methylprednisolone when administered at 8 am versus 4 pm.

The temporal variations in the pharmacokinetics and pharmacodynamics of methylprednisolone at 8 AM versus 4 PM were investigated in six healthy male volunteers. Subjects completed three phases: no drug administration, 20 mg intravenous methylprednisolone at 8 AM, and the same dose at 4 PM. Methylprednisolone clearance was 28% greater in the afternoon. The suppressive effects of methylprednisolone on basophils (measured as whole blood histamine), helper T lymphocytes, and cortisol concentrations, assessed by the ratio of the area under the curve (AUC) after methylprednisolone to the baseline AUC, were not different between the phases. The 50% inhibitory concentration values for methylprednisolone derived from pharmacodynamic models were also similar, indicating no difference in intrinsic responsiveness. However, cortisol concentrations returned to baseline about 4 hours earlier after the 4 PM compared with the 8 AM dose because of the enhanced afternoon methylprednisolone clearance. These findings are in agreement with other studies that suggest adequate clinical effects and less disturbance of cortisol circadian behavior when methylprednisolone is administered as a single dose in the morning.

1,9-Alkano-bridged 2,3,4,5-tetrahydro-1H-3-benzazepines with affinity for the alpha 2-adrenoceptor and the 5-HT1A receptor.

A number of 1,9-alkano-bridged 2,3,4,5-tetrahydro-1H-3-benzazepines were prepared and evaluated for 5-HT1A receptor and alpha 2-adrenoceptor affinity by using radioligand receptor binding techniques. Several compounds displayed 5-HT1A receptor affinity comparable to, or greater than, the known 5-HT1A ligand buspirone. The highest affinity 5-HT1A receptor ligands were N-alkyl-, N-allyl-5-chloro-, and 5-methoxy-1,2,3,4,8,9,10,10a-octahydronaphth[1,8-cd]azapines (4c, 4m, 4n), which had pKi values of 7.9-8.1. The S enantiomer of 4c had a higher affinity for the 5-HT1A receptor than the corresponding R isomer (pKi of 8.2 for (S)-4c vs 7.7 for (R)-4c). These compounds had a relatively low affinity for the alpha 2-adrenoceptor (pKi of 7 or less). On the other hand, the closely related 5-chloro-2-methyl-2,3,4,8,9,9a-hexahydro-1H-indeno[1,7-cd]azepine (3b) had high affinity for both the alpha 2-adrenoceptor (pKi = 8.1) and 5-HT1A receptor (pKi = 7.6). These results indicate that the two receptors may share common recognition sites.

Localization of antigenic sites in the primary sequence of the Sendai virus NP protein.

Monoclonal antibodies were used to localize five antigenic sites in the sequence of the Sendai virus NP gene. NP-specific peptides, expressed in Escherichia coli from the cloned gene served as antigens for blot analyses to determine the specificity of antibody binding. The antigenic sites were associated primarily with the C-terminal half of the protein.