Pneumothorax is characterized by lung collapse. Its effect on hemodynamics, especially on pulmonary arterial blood flow, remains unclear. This patient-specific study investigated the effects of lung deformation on pulmonary blood flow during acute phase and after recovery. Arterial geometry was extracted up to the fifth generation from computed tomography images in three patients and reconstructed. Different geometrical parameters (artery bores, area ratios, and between-branch angles) were computed. The shapes of the pulmonary trunk and its branches were affected strongly by pneumothorax. To clarify the effect of geometrical perturbations on blood flow, the Navier—Stokes equations for a steady laminar flow of Newtonian incompressible fluid were solved in a reconstructed domain. The change in flow structure between acute phase and recovery was associated with variations in flow rate ratio between the right and left lungs. This study shows, possibly for the first time, that from a patient-specific numerical test, pneumothorax has a considerable impact on pulmonary arterial morphology and hemodynamics.
Patient-specific nonlinear finite element analysis (FEA) is promising for evaluating the recovery of vertebral strength. Vertebral strength is closely related to inner vertebral stress distribution and is used to assess the fracture risk for individual osteoporotic patients during drug treatment. Moreover, stress distribution is affected by individual bone shape, bone density distribution and nonlinear behavior of the mechanical properties of bone. To investigate the effectiveness of FEA considering these factors for the evaluation of drug treatment effects, patient-specific nonlinear FEAs of the first lumbar vertebrae in patients undergoing a 3-year drug treatment were performed. Changes in fracture load and distribution of failure elements in the FE models at four time points (before therapy, and after 6 and 12 months and 3 years of therapy) were compared with those of average bone density. The FEAs demonstrated that failure elements decreased notably, and fracture load increased gradually by the 3-year time point, suggesting that the vertebrae were strengthened as a result of drug treatments. Furthermore, statistical tests indicated that mechanical evaluation using the nonlinear FEAs is more sensitive for evaluating drug effects on osteoporotic bone than assessments based on average bone density.
Tensile tests of a single cell were simulated in order to understand the effects of the initial orientation of actin fibers (AFs) on global tensile properties. The properties examined included cell deformation, stiffness, and AF behavior. In the model used, the mechanical properties of cellular components, including the cell membrane with an associated actin network, nuclear envelope, and AFs, are expressed as a result of springs that generate force as a function of their extension. Cell shape during the tensile test was determined by a quasi-static approach couched in the framework of the minimum energy concept. Cells with various initial AF orientations were prepared; in particular, AFs in four different initial orientations, namely random (mean ± SD of the initial orientation angle, 46.4 ± 26.9°), parallel to the stretched direction (3.8 ± 3.5°), perpendicular (85.9 ± 2.6°), and diagonally oriented (44.5 ± 3.6°) were examined. The results show a significant drop in initial stiffness with an increase in mean initial AF orientation angles of 0 to 45°. The initial stiffness of the cell with parallel-oriented AFs was much larger than that with perpendicularly oriented AFs. The results also demonstrate that cell elongation induces a passive reorientation of AFs in a stretched direction, thereby causing an increase in cell stiffness. When comparing the rate of change for cell stiffness of the diagonally oriented model with that of the randomly oriented model, our data reveal that the rate of change of cell stiffness is characterized not only by the mean of the initial AF orientation angle, but also by the variation of their distribution.
Three-dimensional maxillary bone models of a male and a female patient were constructed using their CT-images. The distributions of Young's modulus were estimated from their bone mineral density distributions. Total six implants were embedded into each of the maxillary models. Finite element analysis of the maxilla models was then performed in order to assess the concentrations of strain energy density especially in the vicinities of the embedded implants. It was found that in both models, strain energy density was concentrated especially around the right-molar implant, suggesting outbreak of damage and subsequent absorption of bone tissue in this region. The female model with smaller size and lower bone density exhibited much higher localized concentration of strain energy density than the male model. Therefore, a modified placement of the right-molar implant was then introduced into the female model and such high concentration was effectively reduced by using the inclined and longer implant. It is thus concluded that this kind of three-dimensional modeling can clinically be used to predict the optimal implant treatment for each of dental patients.
Bone structure is renewed or restructured in part by a load-dependent remodeling. In this study, a mathematical model of bone surface remodeling over a wide range of strain was established. We assumed that in a low strain range, bone resorption occurs at an accelerated rate with strain decrease owing to low strain-induced osteocyte apoptosis, and that in a high strain range, bone formation occurs at an accelerated rate with strain increase (targeted remodeling). In a physiological strain range, bone formation or resorption was assumed to occur stochastically according to the degree of local stress non-uniformity. The utility of the present model was examined through three-dimensional numerical simulation of femoral trabecular architecture.
Trabecular bone structure is determined by a balance between osteoblastic bone formation and osteoclastic bone resorption, which is regulated partly by osteocytes according to their mechanical environments. There have been a number of studies on bone remodeling in response to mechanical stimuli, mainly in the physiological range. This study uses a mathematical model previously formulated for surface remodeling available even for disuse and overuse ranges considering osteocyte apoptosis and targeted remodeling. Thus, the present model allows exhibiting the changes of trabecular bone structure under, below, and beyond the daily loading condition. In this study, we carried out computer simulation of bone remodeling in human femur under normal daily loading condition and reduced weight-bearing conditions (infrequent and cane-assisted walking conditions). Decreased trabecular bone with reducing loading condition was shown, and the trabecular bone structure at various degrees of disuse was consistent to Singh Index for osteoporosis diagnosis.
The nasal cavity performs several important functions for the inhaled air, such as temperature and humidity adjustments. Although it is necessary to obtain velocity, temperature, and humidity distributions during inhalation in order to understand the nasal cavity's functions, it is difficult to measure them noninvasively in the nasal cavity. Therefore, we have continued to study nasal flow simulation with heat and humidity transport. In such a simulation, the governing equations include a continuum equation and the equations describing momentum, energy, and water transport. The temperature and humidity of the inhaled air are adjusted by heat and water exchange on the nasal cavity wall's surface. Therefore, in the simulation, these roles of the wall in the energy and water transport equations were included as the boundary conditions. Although in related studies of nasal flow simulation with heat and humidity transport, the nasal cavity wall's surface temperature and humidity were constant, here they were treated as degrees of using Newton's cooling law. A flow including temperature and humidity in a realistic human nasal cavity shape was simulated. The simulation results agreed well with the measurements reported by Keck at al. Therefore, this study concludes that our model can simulate the heat and humidity exchange occurring in the nasal cavity. In addition, it was found that the temperature and humidity adjustment functions worked effectively in the front and narrow regions of the nasal cavity.
Blood is a concentrated suspension of blood cells in plasma. Motion and deformation of red blood cells (RBCs) and their mechanical interaction play important roles in determining blood rheology. Here, we propose a computational model of mesoscopic blood flow where the particulate and continuum natures of blood coexist. We modeled blood flow at two different scales, RBC flow at the microscopic level and continuum at the macroscopic level. A hematocrit-dependent viscosity was considered to take account of the effects of the spatial variation of RBC concentrations on the macroscopic flow. Starting with a Poiseuille flow, the blood flow in a cylindrical channel was simulated. Due to fluid shears, RBCs migrated radially toward the center of flow channel, causing a higher fluid viscosity around the central axis than that near the wall of the channel. Such a spatial variation in viscosity altered the velocity profile of macroscopic blood flow and further changed the RBC distribution within the channel. An iterative calculation resulted in a decrease in flow velocity at the center of the flow channel, as observed in vivo and in vitro. These results address the potential of the present computational approach in the analysis of mesoscopic blood flow.
Insects exhibit exquisite control of their flapping flight, capable of performing precise stability and steering maneuverability. To tackle this highly nonlinear problem we have developed two simulation-based methods to investigate the dynamic passive stability of insect flight: linear and nonlinear methods. In the linear theory, the equations of body motion are linearized and the techniques of eigenvalue and eigenvector analysis are employed to obtain the natural modes. Three natural modes are identified including an unstable oscillatory mode, a stable fast subsidence mode and a stable slow subsidence mode, which indicate that the fruit fly hovering flight is dynamic unstable. While in the nonlinear theory, the equations of 6 DoF motion are solved directly by coupling with the N-S equations. The time-varying time histories of the state variables are calculated, indicating that the state of fruit fly under disturbance conditions shows a very nonlinear transient interval initially but turns to unstable eventually. However, our results also illustrate that a fruit fly does have sufficient time to apply some active mediation to sustain a steady hovering before losing body attitudes.
The preparation of an implant site using a surgical drill is a common procedure in orthopedic surgery, such as for the internal fixation of fractures. An increase in temperature during such a procedure results in the potential for thermal invasion of the bone, which may delay healing or reduce the stability of the fixation. Therefore, minimizing invasion during bone drilling is important to ensure the stability of the implant, and this requires surgical drills with an optimal design. This study investigated the optimal design of surgical drills by comparing the drilling characteristics (i.e., the cutting force and temperature increase) using the Taguchi fractional factorial method. The control factors (helix angle, web thickness, point angle, and the levels of these three parameters) were placed in an L9 orthogonal array and drilling tests were conducted with nine experimental drills based on the array. The results show that the optimal levels of the three design factors of the surgical drill and their percentage contribution depend on the drilling characteristics. However, confirmation tests indicated that the design optimization did not greatly affect the performance improvement and its results showed poor reproducibility. This is possibly because the various cutting conditions encountered in actual clinical situations were not adequately considered.
Background. Ultrasound evaluation of articular cartilage is not accurate if the ultrasound probe is not perpendicular to the cartilage surface. However a probe angle adjustment is difficult because of the manual procedure and the lack of angle index for the measurer. The aim of this study is to propose “Rise-to-Peak time” as an index of probe angle and to evaluate its effectiveness in evaluating articular cartilage surfaces. Methods. The “Rise-to-Peak time” is defined as the time interval between the rise of the first peak (50% amplitude of the first peak) and the first positive peak following the minimum peak of the echo. The relationship between the Rise-to-Peak time and probe angle was evaluated using several reflection surfaces including that of articular cartilage. Findings. The “Rise-to-Peak time” increased monotonically with increases in the angle between the probe and the reflection surface, and showed good agreement with calculated values for small angle changes (<3 degrees). Interpretation. The “Rise-to-Peak time” provides an index of probe angle in the ultrasound measurement of articular cartilage. Availability of echo-amplitude correction using the “Rise-to-Peak time” is evaluated.
In order to investigate vascular diseases such as cause of atherosclerosis and myocardial infarction, relationships of endothelial cells (ECs) covered with surface blood vessels and blood flow stimulation have been experimentally studied. In the study, in order to investigate the relationship between response of ECs and shear stress caused by blood flow, a non-intrusive measurement method for shear stress distribution and topography of living ECs with subcellular resolution was developed based on velocity distributions measured by micro PIV (Particle Image Velocimetry) technique. ECs were cultured with higher shear stress stimulation in a straight microchannel with width of 400 µm and depth of 100 µm made from polydimethylsiloxane (PDMS) microchip. By optimizing cells cultured condition such as the liquid introduction method and the surface coating for enhancement of cell attachment on the microchannel wall, a cell culture method in the microchip with continuous shear stress stimulation was developed. Height and wall shear stress distributions of ECs cultured with shear stresses of 0.1 and 1.0 Pa were measured. The developed technique is useful to study relationships between wall shear stress distribution and transient morphological response in the living cells.
Cyclic mechanical loading can stimulate bone cells in vivo, resulting in the mechano-adaptive osteogenic response of bone. The objective of this study was to investigate the capability of mechanical loading to promote three-dimensional osteoblastic calcification in vitro. A bone-like construct was made by seeding osteoblasts that were obtained from mesenchymal stem cells of rat bone marrow into a type I collagen sponge scaffold. A sinusoidal compressive mechanical load with a peak of 0.2% deformation was applied to the construct at 0.8 Hz for 3 min per day for 35 consecutive days using a piezoelectric mechanical stimulator. This mechanical loading applies not only substrate strain, but also oscillatory fluid flow strain to the cells in the sponge. The degree of osteoblastic calcification was monitored non-destructively once a day utilizing a near-infrared light. The degree of calcification was evaluated as bulk density or calcium content (mg/cm3) based on the optical data. In constructs stimulated by mechanical loading, the degree of calcification started to increase after day 10 and ultimately reached a bulk density of about 44 mg/cm3 and a calcium content of about 4 mg/cm3. In contrast, controls without stimulation did not display a noticeable increase in calcification. Microscopic observation of cross-sectioned samples revealed a heterogeneous distribution of calcification, where a rich calcified matrix was observed in the upper region of the construct, which also had a higher cell density. In conclusion, mechanical loading could enhance osteogenesis in vitro, suggesting its applicability to bone tissue engineering.