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At least 127 records · Page 7Linked to original sources

PubMed1977

Pulmonary mechanics in normal rats.

A versatile, whole-body pressure, or volume plethysmographic system for the study of pulmonary mechanics in anesthetized, tracheotomized rats has been described. Lung volumes and lung compliance values were in good agreement with those previously reported. Pulmonary resistance and chest wall compliance values were lower than those previously reported. Total dynamic compliance remained independent of respiratory frequency between 40 and 320 breaths/min. Flow-limiting behavior was demonstrated from a series of imposed forced expiratory maneuvers of graded effort. With a deflation pressure of 30 cmH2O, the effort-independent range of maximum flow extended to 40-50% of vital capacity. Maximal flow-static recoil pressure relationships were essentially linear over the effort independent portion of the flow-volume curve. Substitution of a low-density gas mixture (80% He-20% O2) for air resulted in increased forced expiratory flow rates but the magnitude of the response was considerably less than that which has been reported in man.

Airway Resistance↗

PubMed1995

The length dependence of work production in rat papillary muscles in vitro.

The influence of length on work production was investigated for rat papillary muscles using the work loop technique. Active and passive length-force relationships were first determined under isometric conditions and the length for maximum force production (Lmax) was derived. Starting from different lengths within the physiological range, a series of work loops was generated using the stimulation phase shift, strain amplitude and cycle frequency previously found to be optimal for power output at 37 degrees C. The relationship between muscle length and net work was used to determine the length at which work output was maximal (Lopt). In order to examine the dynamic passive properties of the muscles, unstimulated muscles were subjected to the same regime of sinusoidal oscillation as used for the active loops. From the hysteresis loops, lengthening work (work done to extend the passive muscle), passive shortening work (work returned during shortening) and net energy loss (hysteresis) could be measured. The decline in net work production at lengths greater than 95% Lmax could largely be attributed to the rapid and non-linear increase in muscle stiffness and the increase in net energy loss over this range of lengths. The physiological significance of the length-work relationship is considered and the mechanical properties of active and passive papillary muscles are discussed with reference to sarcomere length and cardiac muscle ultrastructure.

Animals↗

PubMed1992

Automatic focus correction for spot-scan imaging of tilted specimens.

The variation in defocus within an image of a highly tilted specimen can be a serious source of artifact. Spot-scan imaging can be combined with dynamic focusing to greatly reduce this range of defocus. A protocol is described for determining the parameters required for the automatic focus compensation during the recording of a spot-scan image. Images of a gold test specimen demonstrate the efficacy of this procedure in extending the area of the image that contains high-quality data. In case the tilt angle or resolution is high enough that the height difference of the specimen within each small illuminated area is larger than the depth of field, the image must be treated to compensate for the focus variation. The same principle is used as was developed for compensation of conventional images of tilted specimens.

Artifacts↗

PubMed1976

Force-velocity relations and fiber composition in human knee extensor muscles.

Standardized measurements of dynamic strength of the kneee extensor muscles were performed in 25 healthy male subjects (17-37 yr) by means of isokinetic contractions, i.e., knee extensions with constant angular velocities. Overall variation between double determinations of maximal torque throughout the 90 degrees arc of motion (0 degrees = fully extended leg) averaged 10% for the different constant velocities chosen. At any given angle of the knee the torque produced was higher for isometric than for dynamic contractions. Dynamic torque decreased gradually with increased speed of shortening. Peak dynamic torque was reached at knee angles in the range: 55-66 degrees, with a displacement toward smaller knee angles with higher angular velocities. Correlations were demonstrated between peak torque produced at the highest speed of muscle shortening and percent as well as relative area of fast twitch fibers in the contracting muscle. In addition muscles with a high percentage of fast twitch fibers had the highest maximal contraction speeds. These observations on intact human skeletal muscle are consistent with earlier findings in animal skeletal muscle preparations.

Adolescent↗

PubMed1992

Pantalar and tibiotalocalcaneal arthrodesis for post-traumatic osteoarthrosis of the ankle and hindfoot.

Twenty-one patients had a unilateral extended arthrodesis of the ankle and hindfoot (a tibiotalocalcaneal procedure in thirteen patients and a pantalar procedure in eight) for post-traumatic osteoarthrosis or deformity, or both. The operation was performed through a transfibular extended lateral approach, and autogenous bone graft and rigid internal fixation was used. A final alignment of 0 to 5 degrees of valgus, 0 to 5 degrees of calcaneus, and external rotation equal to that of the contralateral side was sought. Subjective and objective evaluation, including a personal interview, physical examination, and radiographic and dynamic pedobarographic analysis, was performed at a mean interval of thirty-two months (range, twenty-four to fifty-four months) after the operation. A solid fusion was achieved in eighteen (86 per cent) of the twenty-one patients. There were five malunions (24 per cent) and two superficial wound problems (10 per cent). Of the seventeen patients who were not retired from work, eleven returned to work: nine to an occupation that involved standing and two to a sedentary occupation. Although seventeen (81 per cent) of the twenty-one patients reported that they were much improved, twenty (95 per cent) had some pain, and most benefited from modifications in shoe-wear. Patients who had had a tibiotalocalcaneal arthrodesis were more mobile and functioned at a higher level than those who had had a pantalar arthrodesis. Extended arthrodesis of the ankle and hindfoot is a complex, technically demanding procedure, and should be regarded as a salvage operation capable of producing a satisfactory result and usually providing a reasonable alternative to amputation.

Adult↗

PubMed1991

Nuclear magnetic resonance investigations of calcium antagonist drugs. II: Conformational and dynamic features of verapamil in [2H6]DMSO.

Conformational features of verapamil in [2H6]DMSO have been delineated by measuring 13C and 1H NMR parameters. Spin-lattice relaxation rates were interpreted within the frame of an extended alkane chain with segmental motions hampered by the aromatic substituents at both ends. The effective correlation times were all evaluated in the range 0.16-0.22 ns at 293 K. The aromatic rings were found to lie somewhat out-of-plane with the alkane chain. The NMR data were used to construct a Dreiding model of the most probable spatial arrangement and a molecular modeling system was utilized to represent the "preferred" conformation of verapamil in solution.

Calcium Channel Blockers↗

PubMed1995

Search for nucleation sites in smaller fragments of chymotrypsin inhibitor 2.

There is a region of well-ordered structure in the transition state of folding of chymotrypsin inhibitor 2 (CI2) that consists of N-terminal residues in the unique alpha-helix (residues 12 to 24) plus some long range interactions, in particular those of Ala16 with Ile57 and Leu49 in the hydrophobic core. This is proposed to be a nucleation site. A crucial question for understanding the initiation of protein folding is: when is the nucleation site formed? Is the alpha-helix pre-formed in the nominally unfolded state, or does it require long-range interactions to be stabilized? To answer this question, we have characterized a series of N-terminal fragments of CI2, each containing an increasing number of subsets of the regular secondary structure. Four small fragments have been examined by circular dichroism and two-dimensional 1H and 15N NMR spectroscopy. The smallest, [1-5], comprises the sequence corresponding to the first beta-strand of the intact protein; the second, [1-13], contains also a type III reverse turn, the second beta-strand, and a type II reverse turn; the third [1-25], consists additionally of the sequence corresponding to the alpha-helix (residues 12 to 24); the fourth, [1-28], contains, in addition, the turn following the alpha-helix. All the fragments have disordered, non-compact structure in aqueous solution. In the structure-promoting co-solvent, trifluoroethanol, alpha-helical structure is stabilized in [1-25] and [1-28] in the region corresponding to the alpha-helix in the intact protein; however, the helix is frayed at both ends and is only fractionally populated, being in dynamic equilibrium with extended conformations. These observations indicate that there is little drive for independent formation of local secondary structure in CI2, and this is reflected in the highly concerted nature of the folding reaction of this protein. The nucleation site of folding of CI2 does not accumulate in the starting state for the folding reaction, but remains embryonic until there are sufficient long range interactions to stabilize it.

Amino Acid Sequence↗

PubMed1993

Social organization in a wild population of Callithrix jacchus. I. Group composition and dynamics.

Data are presented on group dynamics in a wild population of the common marmoset, Callithrix jacchus, in northeastern Brazil. Three marked and habituated groups were observed, and composition noted, for at least 5 days a month over 12-18 consecutive months. Group sizes ranged from 5 to 15 individuals, and changes in group composition were the result of births, immigrations, and disappearances. No immigrations into the main study groups were observed throughout the study period. None of the three known emigrants was known to join an established or incipient group for up to 10 weeks after their departure. One group contained only breeding individuals and their offspring. Observations of recruitment and loss in the other two groups suggest that they, too, were extended family groups. The group dynamics described in studies of other populations of Callithrix suggest that extended family groups, or at least groups consisting of breeding individuals and their close relatives, may be characteristic of those populations.

Animals↗

PubMed2026

Engineering the Vero Cell Lineage: Toward a Programmable Vaccine Manufacturing Platform.

Vero cells remain an indispensable continuous substrate for human viral vaccine manufacturing. Despite decades of empirical process optimization, intrinsic genomic instability, including segmental aneuploidy and dynamic chromatin rearrangements, continues to limit the durability of engineered phenotypes under sustained viral burden and bioreactor stress. Here, we review the expanding engineering toolkit for the Vero lineage across a three-layered functional framework: the membrane interface, cytoplasmic foundry, and nuclear blueprint, evaluating translational prospects at each level. Receptor transplantation and morphological reprogramming have broadened viral entry range and enabled suspension-adapted culture formats, while metabolic flux management and temporally controlled apoptosis modulation have addressed intracellular production bottlenecks, albeit often with trade-offs between productivity, biosafety, and long-term population stability. At the genomic level, targeted perturbations of transcriptional regulators and emerging epigenetic interventions offer more durable gains, yet expression drift, clonal heterogeneity, and karyotypic instability during extended passaging highlight the need for locus-level precision rather than constitutive trait installation. Looking forward, infection-responsive dynamic logic circuits and the systematic identification of Vero-specific genomic safe harbors could shift the paradigm toward a conditionally responsive manufacturing architecture. Collectively, these advances suggest a pathway for transitioning the Vero lineage from a passive, empirically optimized biological substrate into a conditionally responsive, genomically stable, and programmable platform for modern vaccine preparedness.

Vero cells↗

PubMed1993

13C-NMR determination of the molecular dynamics of cholesterol in dimyristoylphosphatidylcholine vesicles.

Using 13C-NMR measurements of T1, T2 and the nuclear Overhauser enhancement factor at 50.32, 90.56 and 150.87 MHz, we have measured the dynamics of cholesterol in dimyristoylphosphatidylcholine (DMPC) vesicles from 28 to 50 degrees C. Using the model-free approach of Lipari and Szabo, we have found that at 37 degrees C the motion of the rigid steroid ring can be described by an equal contribution from two effective motions with correlation times of 63 and 0.85 ns. The C26 and C27 carbon atoms of cholesterol were found to have an effective correlation time of 8 +/- 2 ps and a value for the square of the generalised order parameter of 0.03 +/- 0.01. The corresponding values for the C25 carbon atom were 17 +/- 4 ps and 0.09 +/- 0.02, showing slower motion and greater order for this carbon atom, which is nearer to the rigid steroid ring. Apart from the effect of vesicle size on T2, no concentration dependence of the dynamics of cholesterol was detected over the cholesterol concentration range 2-30 mol%. The order parameters and correlation times from the present 13C-NMR experiments are shown to be compatible with those from 2H-NMR experiments. This establishes the validity of the present approach, which we are currently extending to low concentrations of cholesteryl oleate in DMPC vesicles.

Carbon Isotopes↗

PubMed1991

A 1H NMR study of human calcitonin in solution.

Human calcitonin (hCT) has been investigated by NMR at 400 MHz in DMSOd6 and in an 85% DMSOd6-15% 1H2O (v/v) cryoprotective mixture. All backbone and side-chain resonances have been assigned, and the secondary structure has been determined in both solvents. In DMSOd6, the simultaneous presence of d alpha N, dNN, and some specific weak medium-range nuclear Overhauser effects, together with the amide temperature coefficients and the analysis of the NH-alpha CH spin-spin coupling constants, indicates that hCT is highly flexible but with three domains (comprising segments Asn3-Gly10, Gln14-Thr21, and Thr25-Ala31) in extended conformations which dynamically transform into isolated beta turns in the N- and C-terminal regions and into adjacent tight turns, resembling a 3(10) helix structure, in the central part. The DMSO-water mixture rigidifies the polypeptide chain, favoring an ordered, extended conformation. NOESY data indicate the presence of a short double-stranded antiparallel beta sheet in the central region made by residues 16-21 and connected by a two-residue hairpin loop formed by residues 18 and 19. Two tight turns, formed by residues 3-6 and 28-31, were also identified. The central beta sheet does not favor an amphipathic distribution of the residues as found for salmon calcitonin [Motta, A., Castiglione Morelli, M. A., Goud, N., & Temussi, P. A. (1989) Biochemistry 28, 7998-8002]. This is in agreement with the smaller tendency of hCT to form the amphipathic alpha helix, postulated to be responsible for the interaction of hCT with lipids. The possible role of the cis-trans isomerism of Pro is discussed.

Amino Acid Sequence↗

PubMed1994

Evaluation of patellar tracking in patients with suspected patellar malalignment: cine MR imaging vs arthroscopy.

OBJECTIVE: The purpose of this study was to compare results of motion-triggered cine MR imaging of active extension of the knee with arthroscopic findings in cases of suspected femoropatellar malalignment. SUBJECTS AND METHODS: Twenty patients with clinically proved or suspected patellar subluxation or dislocation were examined prospectively with motion-triggered cine MR imaging to analyze patellar tracking from 30 degrees of flexion to full extension during active extension of the knee. The patellar tracking pattern was evaluated by measuring the following: bisect offset and lateral patellar displacement to assess lateralization of the patella and the patellar tilt angle to assess tilting of patella. The slopes of the linear regression lines of the MR findings vs the knee angle position, representing the patellar tracking, and the position of the patella at 30 degrees and 0 degrees of flexion were correlated with a semiquantitative arthroscopic classification of patellar tracking that had four categories ranging from normal to highly abnormal. RESULTS: The results showed a significant correlation between the semiquantitative arthroscopic findings of patellar tracking and the slopes of the linear regression lines of the bisect offset, lateral patellar displacement, and patellar tilt angle, as measured with cine MR imaging (p < .01). The arthroscopic findings also correlated significantly with the position of the patella when the knee was extended (p < .01), but not with the knee flexed 30 degrees. CONCLUSION: We conclude that motion-triggered cine MR imaging of active extension of the knee enables the dynamic evaluation of patellar bracing and is therefore suitable for noninvasive analysis of patellar tracking.

Adult↗

PubMed1992

Intracellular HRP study of nociceptive neurons within the ventrobasal complex of the cat thalamus.

Locations and morphological characteristics of nociceptive specific (NS) and wide dynamic range (WDR) neurons of the ventrobasal (VB) thalamic complex were studied using an intracellular HRP injection technique in cats anesthetized with urethane and chloralose. Both NS and WDR neurons were found within the marginal zone of the VB complex. Their somata were confined to the VB complex, but dendrites were extended into the structures of the thalamus surrounding the VB complex. NS neurons were found in the caudal part of the VB complex, whereas WDR neurons were found more rostrally. Examinations of their locations within the marginal zone of the VB complex confirmed the somatotopic organization, as found previously. We also confirmed the previous reports that there are 3 different types of low-threshold mechanoreceptive (LTM) neurons within the VB complex. They are type I, type II and type III neurons. Both NS and WDR neurons were either type I or type II neurons. Obvious morphological differences were not found between LTM neurons and two classes of nociceptive VB neurons investigated.

Animals↗

PubMedDate not supplied

Controlled deposition of tantalum powder in a cast of the human airways: applications for aerosol bronchography.

A hollow latex cast of the human larynx and tracheobronchial tree extending to 2 mm diameter airways "inhaled" tantalum powder (mass median aero-dynamic diameter equals 9.2 mum, omicron-g equals 1.41) at 8 liters/min. Tantalum deposited within the cast as predicted by preliminary deposition calculations. These calculations predicted deposition surface densities among greater than 2 mm diam. airways to have a range of similar to 2:1, and also predicted less than 5% alveolar deposition. A deposition surface density of 8 mg/cm-2 provided good bronchographic visualization. Single rice grains located within some airways were distinctly outlined. The small amount of tantalum needed to outline the airways be a simulated voluntary inhalation indicates that tantalum may be suitable for use as a bronchographic contrast medium when administered under strictly controlled exposure conditions.

Aerosols↗

PubMed1991

Mean field stochastic boundary molecular dynamics simulation of a phospholipid in a membrane.

Computer simulations of phospholipid membranes have been carried out by using a combined approach of molecular and stochastic dynamics and a mean field based on the Marcelja model. First, the single-chain mean field simulations of Pastor et al. [(1988) J. Chem. Phys. 89, 1112-1127] were extended to a complete dipalmitoylphosphatidylcholine molecule; a 102-ns Langevin dynamics simulation is presented and compared with experiment. Subsequently, a hexagonally packed seven-lipid array was simulated with Langevin dynamics and a mean field at the boundary and with molecular dynamics (and no mean field) in the center. This hybrid method, mean field stochastic boundary molecular dynamics, reduces bias introduced by the mean field and eliminates the need for periodic boundary conditions. As a result, simulations extending to tens of nanoseconds may be carried out by using a relatively small number of molecules to model the membrane environment. Preliminary results of a 20-ns simulation are reported here. A wide range of motions, including overall reorientation with a nanosecond decay time, is observed in both simulations, and good agreement with NMR, IR, and neutron diffraction data is found.

Computer Simulation↗

PubMed1982

Higher order folding of two different classes of chromatin isolated from chicken erythrocyte nuclei. A light scattering study.

Bulk chromatin fragments were excised from chicken erythrocyte nuclei by digestion with micrococcal nuclease. Fractionation into S chromatin (soluble at physiological ionic strengths) and I chromatin (insoluble at physiological ionic strengths) was achieved by dialysis against buffers containing 0.15 M NaCl. The effects of NaCl concentration on the molecular dimensions of S and I chromatins were determined by dynamic and static light scattering. Series of fragment lengths were obtained by gel filtration of S and I chromatins under ionic conditions which lead to maximal intramolecular compaction. Hydrodynamic radii and radii of gyration were determined for fragment lengths ranging from 8 to 53 nucleosomes. These data are in excellent agreement with calculations for extended helical structures. Close-packed solenoidal or superbead structures are not compatible with these data. Comparisons of molecular dimensions derived from light scattering and electron microscopy indicate that considerable shrinkage of chromatin fragments can occur when common methods of sample preparation are used for microscopy.

Animals↗

PubMed1994

Bionomics of adult Anopheles pseudopunctipennis (Diptera: Culicidae) in the Tapachula foothills area of southern Mexico.

Field studies on the bionomics of adult Anopheles pseudopunctipennis Theobald were conducted to assess its relative importance as a primary vector of vivax malaria in southern Mexico. In four malaria endemic villages in a foothill region near Tapachula, Mexico, population densities of A. pseudopunctipennis increased during the dry seasons of 1990 and 1991. The pattern of nocturnal host-seeking activity indoors was unimodal with a late night peak at 0100 hours enhancing its vectorial significance, because it occurred when most residents were asleep and fully exposed to the anophelines. Comparisons of trapping methods showed that a horse-baited trap was more effective than human landing catches or UV light traps. Pit shelters, on the other hand, were more effective than indoor and natural shelter resting collections. Results of enzyme-linked immunosorbent assays performed on wild-caught A. pseudopunctipennis specimens documented the presence of natural infections with the VK210 and new VK247 circumsporozoite polymorphs of P. vivax. These findings verify the importance of A. pseudopunctipennis as a major vector of vivax malaria at higher elevations and extend the geographical range of the VK247 P. vivax polymorph in Mexico.

Animals↗

PubMed1986

Extension of a binaural cross-correlation model by contralateral inhibition. I. Simulation of lateralization for stationary signals.

Running interaural cross correlation is a basic assumption to model the performance of the binaural auditory system. Although this concept is particularly suited to simulate psychoacoustic localization phenomena, there exist some localization effects which cannot be explained by pure cross correlation. In this paper a model of interaural cross correlation is extended by a "contralateral-inhibition mechanism" and by "monaural detectors" in order to simulate a wide range of psychoacoustic lateralization data. The extended model explains lateralization of pure tones with interaural time differences as well as with interaural level differences. Multiple images are predicted for tones with characteristic combinations of interaural signal parameters and for noise signals with different degrees of interaural cross correlation. The model is also capable of simulating dynamic lateralization phenomena, such as the "law of the first wave front" which is dealt with in a companion paper [Lindemann, J. Acoust. Soc. Am. 80, 1623-1630 (1986)]. The present paper is restricted to a comparison of the model predictions for stationary signals with the results of dichotic listening experiments.

Auditory Perception↗