Suppression of an amyloid beta peptide-mediated calcium channel response by a secreted beta-amyloid precursor protein

Secreted isoforms of the beta-amyloid precursor protein potently enhance neuronal survival in cell cultures exposed to toxic amyloid beta peptide. Lowering of intracellular calcium levels to offset the increases in intraneuronal calcium caused by amyloid beta peptide is thought to underly this neuroprotection. Because we have shown previously that an amyloid beta peptide-mediated potentiation of calcium channel currents may contribute to this cytosolic calcium overload, the present study examined the effects of a secreted beta-amyloid precursor protein on the calcium channel response to amyloid beta peptide. When compared with untreated cultured rat hippocampal neurons, cells that underwent a 24 h preincubation with beta-amyloid precursor protein 751 displayed decreases in the relative size of the calcium channel response to amyloid beta peptide. A membrane-permeable analog of cyclic GMP, a second messenger believed to be involved in the calcium regulation process mediated by beta-amyloid precursor proteins, also attenuated the modulatory calcium channel response. Co-application of beta-amyloid precursor protein 751 with amyloid beta peptide did not alter calcium channel response to amyloid beta peptide. Taken together, these findings suggest that secreted beta-amyloid precursor proteins can suppress a calcium channel response to amyloid beta peptide that is potentially injurious to the cell, and as such, may define a neuroprotective mechanism that is specific for amyloid beta toxicity.

Vehicle emission unit risk factors for transportation risk assessments

When the transportation risk posed by shipments of hazardous chemical and radioactive materials is being assessed, it is necessary to evaluate the risks associated with both vehicle emissions and cargo-related risks. Diesel exhaust and fugitive dust emissions from vehicles transporting hazardous shipments lead to increased air pollution, which increases the risk of latent fatalities in the affected population along the transport route. The estimated risk from these vehicle-related sources can often be as large or larger than the estimated risk associated with the material being transported. In this paper, data from the U.S. Environmental Protection Agency's Motor Vehicle-Related Air Toxics Study are first used to develop latent cancer fatality estimates per kilometer of travel in rural and urban areas for all diesel truck classes. These unit risk factors are based on studies investigating the carcinogenic nature of diesel exhaust. With the same methodology, the current per-kilometer latent fatality risk factor used in transportation risk assessments for heavy diesel trucks in urban areas is revised and the analysis expanded to provide risk factors for rural areas and all diesel truck classes. These latter fatality estimates may include, but are not limited to, cancer fatalities and are based primarily on the most recent epidemiological data available on mortality rates associated with ambient air PM-10 concentrations.

Intracellular elasticity and viscosity in the body, leading, and trailing regions of locomoting neutrophils

To investigate the mechanisms underlying pseudopod protrusion in locomoting neutrophils, we measured the intracellular stiffness and viscosity in the leading region, main body, and trailing region from displacements of oscillating intracellular granules driven with an optical trap. Experiments were done in control conditions and after treatment with cytochalasin D or nocodazole. We found 1) in the body and trailing region, the granules divided into a "fixed" population (too stiff to measure) and a "free" population (easily oscillated; fixed fraction 65%, free fraction 35%). By contrast, the fixed fraction in the leading region was <5%. 2) In the body and trailing region, there was no difference in stiffness or viscosity, but both were sharply lower in the leading region (respectively, 20-fold and 5-fold). 3) Neither cytochalasin D nor nocodazole caused a decrease in stiffness, but both treatments markedly reduced the fixed fraction in the body and trailing region to <20% and <40%, respectively. These observations suggest a discrete lattice structure in the body and trailing region and suggest that the developing pseudopod has a core that is more fluidlike, in the sense of a much lower viscosity and an almost total loss of stiffness. This is consistent with the contraction/solation hypothesis of pseudopodial formation.

Acinar flow irreversibility caused by perturbations in reversible alveolar wall motion

Mixing associated with "stretch-and-fold" convective flow patterns has recently been demonstrated to play a potentially important role in aerosol transport and deposition deep in the lung (J. P. Butler and A. Tsuda. J. Appl. Physiol. 83: 800-809, 1997), but the origin of this potent mechanism is not well characterized. In this study we hypothesized that even a small degree of asynchrony in otherwise reversible alveolar wall motion is sufficient to cause flow irreversibility and stretch-and-fold convective mixing. We tested this hypothesis using a large-scale acinar model consisting of a T-shaped junction of three short, straight, square ducts. The model was filled with silicone oil, and alveolar wall motion was simulated by pistons in two of the ducts. The pistons were driven to generate a low-Reynolds-number cyclic flow with a small amount of asynchrony in boundary motion adjusted to match the degree of geometric (as distinguished from pressure-volume) hysteresis found in rabbit lungs (H. Miki, J. P. Butler, R. A. Rogers, and J. Lehr. J. Appl. Physiol. 75: 1630-1636, 1993). Tracer dye was introduced into the system, and its motion was monitored. The results showed that even a slight asynchrony in boundary motion leads to flow irreversibility with complicated swirling tracer patterns. Importantly, the kinematic irreversibility resulted in stretching of the tracer with narrowing of the separation between adjacent tracer lines, and when the cycle-by-cycle narrowing of lateral distance reached the slowly growing diffusion distance of the tracer, mixing abruptly took place. This coupling of evolving convective flow patterns with diffusion is the essence of the stretch-and-fold mechanism. We conclude that even a small degree of boundary asynchrony can give rise to stretch-and-fold convective mixing, thereby leading to transport and deposition of fine and ultrafine aerosol particles deep in the lung.

Perturbed equilibrium of myosin binding in airway smooth muscle and its implications in bronchospasm

In asthma, the mechanisms relating airway obstruction, hyperresponsiveness, and inflammation remain rather mysterious. We show here that regulation of airway smooth muscle length corresponds to a dynamically equilibrated steady state, not the static mechanical equilibrium that had been previously assumed. This dynamic steady state requires as an essential feature a continuous supply of external mechanical energy (derived from tidal lung inflations) that acts to perturb the interactions of myosin with actin, drive the molecular state of the system far away from thermodynamic equilibrium, and bias the muscle toward lengthening. This mechanism leads naturally to the suggestion that excessive airway narrowing in asthma may be associated with the destabilization of that dynamic process and its resulting collapse back to static equilibrium. With this collapse the muscle undergoes a phase transition and virtually freezes at its static equilibrium length. This mechanism may help to elucidate several unexplained phenomena including the multifactorial origins of airway hyperresponsiveness, how allergen sensitization leads to airway hyperresponsiveness, how hyperresponsiveness can persist long after airway inflammation is resolved, and the inability in asthma of deep inspirations to relax airway smooth muscle.

Dynamically determined contractile states of airway smooth muscle

The contractile state of maximally activated bovine airway smooth muscle is altered during imposed tidal stretches that simulate the action of breathing. When the amplitude of imposed tidal stretch is very small (0.25% of muscle optimal length), the steady-state value of the muscle force, F, approximates the isometric force, the muscle stiffness, E, is large, and the muscle hysteresivity, eta, is small. When the amplitude is increased beyond 1%, however, F and E promptly decrease and eta promptly increases. The provocative stretch amplitude required to cause active force or muscle stiffness to fall by half, or hysteresivity to double, is slightly greater than 2%. By contrast, the stretch amplitude expected during quiet breathing at rest is 4%. Therefore, the isometric force generating capacity of airway smooth muscle may not be applicable to the force generated in normal physiologic circumstances, even during maximal bronchial provocation.

Is cytoskeletal tension a major determinant of cell deformability in adherent endothelial cells?

We tested the hypothesis that mechanical tension in the cytoskeleton (CSK) is a major determinant of cell deformability. To confirm that tension was present in adherent endothelial cells, we either cut or detached them from their basal surface by a microneedle. After cutting or detachment, the cells rapidly retracted. This retraction was prevented, however, if the CSK actin lattice was disrupted by cytochalasin D (Cyto D). These results confirmed that there was preexisting CSK tension in these cells and that the actin lattice was a primary stress-bearing component of the CSK. Second, to determine the extent to which that preexisting CSK tension could alter cell deformability, we developed a stretchable cell culture membrane system to impose a rapid mechanical distension (and presumably a rapid increase in CSK tension) on adherent endothelial cells. Altered cell deformability was quantitated as the shear stiffness measured by magnetic twisting cytometry. When membrane strain increased 2.5 or 5%, the cell stiffness increased 15 and 30%, respectively. Disruption of actin lattice with Cyto D abolished this stretch-induced increase in stiffness, demonstrating that the increased stiffness depended on the integrity of the actin CSK. Permeabilizing the cells with saponin and washing away ATP and Ca2+ did not inhibit the stretch-induced stiffening of the cell. These results suggest that the stretch-induced stiffening was primarily due to the direct mechanical changes in the forces distending the CSK but not to ATP- or Ca(2+)-dependent processes. Taken together, these results suggest preexisting CSK tension is a major determinant of cell deformability in adherent endothelial cells.

A model for cytoplasmic rheology consistent with magnetic twisting cytometry

Magnetic twisting cytometry is gaining wide applicability as a tool for the investigation of the rheological properties of cells and the mechanical properties of receptor-cytoskeletal interactions. Current technology involves the application and release of magnetically induced torques on small magnetic particles bound to or inside cells, with measurements of the resulting angular rotation of the particles. The properties of purely elastic or purely viscous materials can be determined by the angular strain and strain rate, respectively. However, the cytoskeleton and its linkage to cell surface receptors display elastic, viscous, and even plastic deformation, and the simultaneous characterization of these properties using only elastic or viscous models is internally inconsistent. Data interpretation is complicated by the fact that in current technology, the applied torques are not constant in time, but decrease as the particles rotate. This paper describes an internally consistent model consisting of a parallel viscoelastic element in series with a parallel viscoelastic element, and one approach to quantitative parameter evaluation. The unified model reproduces all essential features seen in data obtained from a wide variety of cell populations, and contains the pure elastic, viscoelastic, and viscous cases as subsets.

Airway smooth muscle, tidal stretches, and dynamically determined contractile states

In the classic theory of airway lumen narrowing in asthma, active force in airway smooth muscle is presumed to be in static mechanical equilibrium with the external load against which the muscle has shortened. This theory is useful because it identifies the static equilibrium length toward which activated airway smooth muscle would tend if given enough time. The corresponding state toward which myosin-actin interactions would tend is called the latch state. But are the concepts of a static mechanical equilibrium and the latch state applicable in the setting of tidal loading, as occurs during breathing? To address this question, we have studied isolated, maximally contracted bovine tracheal smooth muscle subjected to tidal stretches imposed at 0.33 Hz. We measured the active force (F) and stiffness (E), which reflect numbers of actin-myosin interactions, and hysteresivity (eta) which reflects the rate of turnover of those interactions. When the amplitude of imposed tidal stretch (epsilon) was very small, 0.25% of muscle optimal length, the steady-state value of F approximated the isometric force, E was large, and eta was small. When epsilon was increased beyond 1%, however, F and E promptly decreased and eta promptly increased. The muscle could be maintained in these steady, dynamically determined contractile states for as long as the tidal stretches were sustained; when epsilon subsequently decreased back to 0.25%, F, E, and eta returned slowly toward their previous values. The provocative stretch amplitude required to cause active force or muscle stiffness to fall by half, or hysteresivity to double, was slightly greater than 2%. These observations are consistent with a direct effect of stretch upon bridge dynamics in which, with increasing tidal stretch amplitude, the number of actin-myosin interactions decreases and their rate of turnover increases. We conclude that the interactions of myosin with actin are at every instant tending toward those that would prevail in the isometric steady state, but tidal changes of muscle length cause an excess in the rate of detachment. These stretch-induced detachment events can come so fast compared with the rate of attachment that static equilibrium conditions are never attained. If so, then airway lumenal narrowing and the underlying contractile state would be governed by a dynamic mechanical process rather than by a mechanical equilibrium of static forces.

Effect of convective stretching and folding on aerosol mixing deep in the lung, assessed by approximate entropy

There is a surprisingly substantial amount of aerosol mixing and deposition deep in the lung, which cannot be explained by classic transport mechanisms such as streamline crossing, inertial impaction, or gravitational sedimentation with reversible acinar flow. Mixing associated with "stretch and fold" convective flow patterns can, however, be a potent source of transport. We show such patterns in experimental preparations using rat lungs and in the theoretical Baker Transform. In both cases, mixing is associated with the temporal evolution of two length scales. The first is the slowly increasing diffusive length scale. The second is the rapidly decreasing lateral length scale, due to "stretching and folding," over which diffusion must take place. This interaction leads to aerosol mixing in much shorter times than previously appreciated. Finally, we propose a new method by which to quantify the state of mixing, using an approximation to the entropy of the aerosol concentration distribution. The results of the analysis suggest that stretching and folding may be a key feature underlying peripheral aerosol transport.

The elephant's respiratory system: adaptations to gravitational stress

Elephants have had to adapt to gravitational stresses imposed on their very large respiratory structures. We describe some unusual features of the elephant's respiratory system and speculate on their functional significance. A distensible network of collagen fibers fills the pleural space, loosely connects lung to chest wall but appears not to constrain lung-chest wall movements. Myriad spaces within the network and its rich supply of capillaries suggest effective local sources and sinks for pleural fluid that may replace the gravity-dependent flows of smaller mammals. The lung is partitioned into approximately equal to 1 cm3 parenchymal units by a system of thick, elastic septa that ramify throughout the lung from origins on the lung's elastic external capsule. Parenchymal units suspended upon the elastic septal system protect dependent alveoli from compression, thereby reducing the usual gravitational gradient of lung expansion. Intra-pulmonary airways are devoid of cartilage, instead they appear to derive resistance to collapse from tethering forces of the attached septa.

Fractional changes in lung capillary blood volume and oxygen saturation during the cardiac cycle in rabbits

Changes in local pulmonary capillary blood volume (Vc) and oxygen saturation (S) have been difficult to measure in live animals. By utilizing the differences in absorption of light at two wavelengths (650 and 800 nm), we estimated the fractional change in Vc and S during the course of the cardiac cycle in eight anesthetized, ventilated rabbits at low and high lung volumes. Observations were made of the pattern of diffusely backscattered light, from an approximately 1-cm3 volume of lung illuminated with a point source placed on the pleural surface through a thoracotomy. At low lung volume, the fractional change in Vc was approximately 13%, the change in S was approximately 4.6%, and the mean S was close to 77%. The fluctuations in Vc and S lagged behind peak systemic blood pressure by about one-fifth and three-fifths of a cycle, respectively. At high lung volume, there were no important fluctuations in Vc or S, and the mean S was approximately 82%. These results are consistent with fluctuations in pulmonary capillary pressure and gas exchange over the cardiac cycle, and with decreasing capillary compliance with increasing lung volume.

Cytoskeletal mechanics in confluent epithelial cells probed through integrins and E-cadherins

Mechanical forces associated with the cytoskeleton (CSK) and transmitted to adjacent cells or to the extracellular matrix (ECM) influence cellular functions. We investigated the force transfer across cell-to-ECM and cell-to-cell connections using magnetic twisting cytometry. We probed the CSK through integrins and E-cadherins in confluent epithelial cell lines (MCF7). At high applied stress (> 10 dyn/cm2), stiffness (stress/strain) of the CSK coupled through integrins was greater than stiffness coupled through E-cadherins. The stiffness reduction after microfilament or microtubule disruption with cytochalasin D or colchicine was greater for integrins. At low applied stress, disruption of microfilaments had very little effect on stiffness probed through either receptor type, indicating a correspondingly small contribution of microfilaments to the CSK mechanics in these confluent cells. This differs from results in nonconfluent MCF7 cells and from predictions that are based on prestressed models in which tensile stresses presumably associated with the microfilaments are the origin of prestress and, in consequence, cell stiffness. In addition, there was substantial cell spreading on collagen I-coated dishes, in contrast to little spreading on dishes coated with E-cadherin antibody. This result, together with observations of a relatively high cell stiffness probed through integrins compared with the small stiffness probed through E-cadherins, suggests that mechanical force transmission might also be important in regulating cell spreading. We conclude that the degree of confluency may be associated with different mechanics and functions of the CSK network.

Friction in airway smooth muscle: mechanism, latch, and implications in asthma

In muscle, active force and stiffness reflect numbers of actin-myosin interactions and shortening velocity reflects their turnover rates, but the molecular basis of mechanical friction is somewhat less clear. To better characterize molecular mechanisms that govern mechanical friction, we measured the rate of mechanical energy dissipation and the rate of actomyosin ATP utilization simultaneously in activated canine airway smooth muscle subjected to small periodic stretches as occur in breathing. The amplitude of the frictional stress is proportional to eta E, where E is the tissue stiffness defined by the slope of the resulting force vs. displacement loop and eta is the hysteresivity defined by the fatness of that loop. From contractile stimulus onset, the time course of frictional stress amplitude followed a biphasic pattern that tracked that of the rate of actomyosin ATP consumption. The time course of hysteresivity, however, followed a different biphasic pattern that tracked that of shortening velocity. Taken together with an analysis of mechanical energy storage and dissipation in the cross-bridge cycle, these results indicate, first, that like shortening velocity and the rate of actomyosin ATP utilization, mechanical friction in airway smooth muscle is also governed by the rate of cross-bridge cycling; second, that changes in cycling rate associated with conversion of rapidly cycling cross bridges to slowly cycling latch bridges can be assessed from changes of hysteresivity of the force vs. displacement loop; and third, that steady-state force maintenance (latch) is a low-friction contractile state. This last finding may account for the unique inability of asthmatic patients to reverse spontaneous airways obstruction with a deep inspiration.

Effect of macroscopic deformation on lung microstructure

Using an anisotropic theory of diffuse light scattering in lungs, we measured the fractional changes in geometric mean linear intercepts in orthogonal directions when freshly excised rabbit lungs were subjected to isovolume uniaxial strains. Results from the optical technique were compared with morphometric estimates of fractional changes in mean linear intercepts from the same strained and unstrained (control) lobes, with the conclusion that diffuse light scattering is adequate to estimate changes in mean free paths in different directions. We compared optical estimates of fractional changes in mean linear intercepts with the macroscopic strain field measured by displacements of pleural markers; this relationship did not significantly differ from the line of identity. We conclude that the microscopic strain field is closely matched to the macroscopic strain field during uniaxial distortion. This suggests that surface reorientation may not play a large role in the origin of the low shear modulus of the lung, but this cannot be definitively stated without comparison of these experimental results to specific model predictions of the changes in mean linear intercepts in shear deformation.

Dihedral angles of septal "bend" structures in lung parenchyma

Alveolar parenchyma comprises two interacting tensile systems: the cable system (a network of linear condensations of connective tissue) and the membrane system (a network of quasiplanar alveolar septa). Inferences can be drawn about the mechanics of this structure from it configuration. We reported earlier (E.H. Oldmixon, J.P. Butler, and F.G. Hoppin, Jr. J. Appl. Physiol. 64: 299-307, 1988) that the angles between alveolar septa at the common three-way junctions (J) are nearly uniform, indicating that septal tensions are also nearly uniform. We now report on the interseptal angles at the next most common class of septal junction (B), a structure where two septa meet along a segment of the cable system. We find, first, that the distributions of interseptal angles at B junctions have means > 120 degrees, are narrow, and have few, if any, angles < 120 degrees. The findings of uniform 120 degrees angles at J junctions and a cutoff below 120 degrees at B junctions are also characteristic of soap films supported on a frame, which follows the physical principle of surface area minimization. We suggest that this principle may be operative in parenchymal development and remodeling.

On the theory of muscle contraction: filament extensibility and the development of isometric force and stiffness

The newly discovered extensibility of actin and myosin filaments challenges the foundation of the theory of muscle mechanics. We have reformulated A. F. Huxley's sliding filament theory to explicitly take into account filament extensibility. During isometric force development, growing cross-bridge tractions transfer loads locally between filaments, causing them to extend and, therefore, to slide locally relative to one another. Even slight filament extensibility implies that 1) relative displacement between the two must be nonuniform along the region of filament overlap, 2) cross-bridge strain must vary systematically along the overlap region, and importantly, 3) the local shortening velocities, even at constant overall sarcomere length, reduce force below the level that would have developed if the filaments had been inextensible. The analysis shows that an extensible filament system with only two states (attached and detached) displays three important characteristics: 1) muscle stiffness leads force during force development; 2) cross-bridge stiffness is significantly higher than previously assessed by inextensible filament models; and 3) stiffness is prominently dissociated from the number of attached cross-bridges during force development. The analysis also implies that the local behavior of one myosin head must depend on the state of neighboring attachment sites. This coupling occurs exclusively through local sliding velocities, which can be significant, even during isometric force development. The resulting mechanical cooperativity is grounded in fiber mechanics and follows inevitably from filament extensibility.

Contour of the GnRH pulse independently modulates gonadotropin secretion in the human male

GnRH pulse frequency, amplitude, and interpulse interval have all been demonstrated to regulate gonadotropin secretion individually. We tested the hypothesis that the contour of the GnRH pulse also modulates gonadotropin output in 10 men with isolated GnRH deficiency in whom a fixed GnRH dose was administered at a constant physiologic frequency by either instantaneous bolus or by 1-, 5-, or 30-min infusions. LH, FSH and free alpha subunit (FAS) responses were also compared to spontaneous gonadotropin secretion in normal adult men. While the LH and FAS pulses following the instantaneous bolus and 1-min infusion of GnRH were indistinguishable, further increases in the duration of gonadotrope stimulation by GnRH were associated with progressive decreases in all parameters of gonadotropin secretion (mean levels, amplitude, peak levels, AUC). FSH secretion was also decreased following variations in the contour of the GnRH pulse, although overall changes were less dramatic than for LH and FAS. The LH pulses following the bolus GnRH stimulation were indistinguishable from spontaneous LH pulses occurring in normal men whereas those stimulated by the 1-, 5-, and 30-min infusions of GnRH became progressively blunted with the lowest levels of secretion occurring after the longest infusion. In sharp contrast, FAS pulse parameters in the GnRH-deficient subjects greatly exceeded those of normal men regardless of the contour of the GnRH stimulus, whereas mean FSH levels were all modestly (although significantly) higher than those of normal adult men. These results demonstrate that the pituitary is sensitive to subtle changes in the contour of the GnRH stimulus, with a more prolonged duration of GnRH stimulation resulting in a diminished pituitary response. Alterations of the contour of endogenous GnRH secretion may represent an additional mechanism for altering gonadotrope function and provide additional evidence for the differential regulation of LH, FAS, and FSH by GnRH. However, the previously reported elevated levels of FAS secretion in GnRH-deficient men undergoing long-term GnRH replacement are not explained by abnormalities of GnRH contour.

A microstructural approach to cytoskeletal mechanics based on tensegrity

Mechanical properties of living cells are commonly described in terms of the laws of continuum mechanics. The purpose of this report is to consider the implications of an alternative approach that emphasizes the discrete nature of stress bearing elements in the cell and is based on the known structural properties of the cytoskeleton. We have noted previously that tensegrity architecture seems to capture essential qualitative features of cytoskeletal shape distortion in adherent cells (Ingber, 1993a; Wang et al., 1993). Here we extend those qualitative notions into a formal microstructural analysis. On the basis of that analysis we attempt to identify unifying principles that might underlie the shape stability of the cytoskeleton. For simplicity, we focus on a tensegrity structure containing six rigid struts interconnected by 24 linearly elastic cables. Cables carry initial tension ("prestress") counterbalanced by compression of struts. Two cases of interconnectedness between cables and struts are considered: one where they are connected by pin-joints, and the other where the cables run through frictionless loops at the junctions. At the molecular level, the pinned structure may represent the case in which different cytoskeletal filaments are cross-linked whereas the looped structure represents the case where they are free to slip past one another. The system is then subjected to uniaxial stretching. Using the principal of virtual work, stretching force vs. extension and structural stiffness vs. stretching force relationships are calculated for different prestresses. The stiffness is found to increase with increasing prestress and, at a given prestress, to increase approximately linearly with increasing stretching force. This behavior is consistent with observations in living endothelial cells exposed to shear stresses (Wang & Ingber, 1994). At a given prestress, the pinned structure is found to be stiffer than the looped one, a result consistent with data on mechanical behavior of isolated, cross-linked and uncross-linked actin networks (Wachsstock et al., 1993). On the basis of our analysis we concluded that architecture and the prestress of the cytoskeleton might be key features that underlie a cell's ability to regulate its shape.

Alveolar surface area-to-lung volume ratio in oleic acid-induced pulmonary edema

It is unknown how the in vivo alveolar surface area-to-volume ratio (S/V) changes in low-pressure pulmonary edema. Here, the S/V is the area of the air-tissue interface per unit total volume (air plus tissue). We hypothesized that in oleic acid (OA)-induced edema inactivation of the pulmonary surfactant may increase surface tension and decrease the S/V at any given lung volume. OA (0.04 mg/kg) was intravenously injected into dogs. We measured the in vivo S/V (equivalent to the inverse of optical mean free path by light-scattering stereology and the pressure-volume (PV) curve 60-90 min after OA administration. OA administration decreased the lung volume at each transpulmonary pressure and increased the wet-to-dry weight ratio. The S/V decreased after OA administration (optical mean free path increased). The air-filled PV curves shifted downward after OA, but the saline-filled PV curves after OA administration did not differ significantly from control saline-filled curves. The difference in transpulmonary pressure between air- and saline-filled PV curves (an index of the magnitude of surface tension) was increased in OA-induced pulmonary edema. This study suggests that in OA-induced pulmonary edema the alveolar surface tension increases and the S/V decreases, presumably due to inactivation of surfactant by serum leakage to alveoli.

Intracellular pressure is a motive force for cell motion in Amoeba proteus

The cortical filament layer of free-living amoebae contains concentrated actomyosin, suggesting that it can contract and produce an internal hydrostatic pressure. We report here on direct and dynamic intracellular pressure (P(ic)) measurements in Amoeba proteus made using the servo-null technique. In resting apolar A. proteus, P(ic) increased while the cells remained immobile and at apparently constant volume. P(ic) then decreased approximately coincident with pseudopod formation. There was a positive correlation between P(ic) at the onset of movement and the rate of pseudopod formation. These results are the first direct evidence that hydrostatic pressure may be a motive force for cell motion. We postulate that contractile elements in the amoeba's cortical layer contract and increase P(ic) and that this P(ic) is utilized to overcome the viscous flow resistance of the intracellular contents during pseudopod formation.

Aerosol transport and deposition in the rhythmically expanding pulmonary acinus

Little is known about factors controlling the dynamics of aerosol dispersion and deposition in the lung periphery, though this knowledge becomes increasingly important in many fields such as environmental and occupational exposure, diagnostic applications, and therapeutic deliver of drugs via aerosols. For the last several years, we have been studying aerosol behavior in the pulmonary acinus, where the airway structure and the associated fluid mechanics are distinctly different from those in the conducting airways. Our major research efforts have been focused on the basic physics underlying acinar fluid mechanics and particle dynamics, which are likely to be conditioned by the two key geometric factors of acinar airways: structural alveolation and rhythmic expansion and contraction of the alveolar walls. A combination of computational and experimental analyses revealed that due to these unique geometric features acinar flow can be extremely complex despite the low Reynolds number, and can have substantial effects on particle dynamics. In particular, chaotic mixing can occur in the lung periphery. In the course of such a mixing process, the inhaled aerosol particles quickly mix with the residual alveolar gas in a manner that is radically different from the previously considered classical diffusion process. The objective of this paper is to briefly review our current understanding of these processes, to discuss existing deposition models, and to describe our ongoing research efforts toward a basic understanding of aerosol behavior in the pulmonary acinus.

An intermeniscal fibrous band in a recreational runner

An intermeniscal fibrous band was found to produce anterior knee pain in a recreational runner. Arthroscopic resection of the band eliminated the symptoms of pain with running. A literature review found no prior reports of this entity. The differential of plica syndrome and Hoffa's disease was reviewed.

Assessment of patellar height after autogenous patellar tendon anterior cruciate ligament reconstruction

In this study, we sought to determine if a significant change in patellar height occurs after autogenous patellar tendon anterior cruciate ligament (ACL) reconstruction at our clinic. In a series of 71 patients (52 males and 18 females; average age: 22 years; range: 12 to 41) randomly selected, all had undergone an identical autogenous patellar tendon ACL reconstruction, by the same surgeon, and followed the same postoperative accelerated rehabilitation program. All patients had standardized preoperative and postoperative lateral knee radiographs. The patellar tendon length as well as the patellar height and ratio of Blackburne and Peel were measured by the same person for all subjects. The length of the patellar tendon shortened by an average of 0.4 mm (range: 6% lengthening to 12% shortening) which is less than 1% and not statistically significant (P = .068). The Blackburne and Peel ratio for patellar height decreased by 1%, which was also not statistically significant (P = .060). The evidence obtained from this study indicated no significant change in patellar height after autogenous patellar tendon ACL reconstruction combined with postoperative accelerated rehabilitation and no correlations with postoperative complications, secondary surgeries, timing of surgery, age, or anterior knee symptoms.

Chaotic mixing of alveolated duct flow in rhythmically expanding pulmonary acinus

We examined the effects of rhythmic expansion of alveolar walls on fluid mechanics in the pulmonary acinus. We generated a realistic geometric model of an alveolated duct that expanded and contracted in a geometrically similar fashion to simulate tidal breathing. Time-dependent volumetric flow was generated by adjusting the proximal and distal boundary conditions. The low Reynolds number velocity field was solved numerically over the physiological range. We found that for a given geometry, the ratio of the alveolar flow (QA) to the ductal flow (QD) played a major role in determining the flow pattern. For larger QA/QD (as in the distal region in the acinus), the flow in the alveolus was largely radial. For small QA/QD (as in the proximal region in the acinus), the flow in the alveolus was slowly rotating and the velocity field near the alveolar opening was complex with a stagnation saddle point typical of chaotic flow structures. Performing Lagrangian fluid particle tracking, we demonstrated that in such a flow structure the motion of fluid could be highly complex, irreversible, and unpredictable even though it was governed by simple deterministic equations. These are the characteristics of chaotic flow behavior. We conclude that because of the unique geometry of alveolated duct and its time-dependent motion associated with tidal breathing, chaotic flow and chaotic mixing can occur in the lung periphery. Based on these novel observations, we suggest a new approach for studying acinar fluid mechanics and aerosol kinetics.