Journal of Mechanics in Medicine and Biology

Assessment of intermediate coronary lesions with diameter stenosis of 40% to 70% severity is being a challenge for cardiologist to identify potentially ischemic stenosis for revascularization and nonculprit stenosis which can be deferred from stenting. An invasive coronary angiography and intravascular ultrasound provide anatomic information of stenosis severity whereas an invasive fractional flow reserve index (FFR) provides the functional significance of the stenosis severity. The measurement of functional significance of stenosis severity minimizes the procedural complications such as coronary dissection, in stent restenosis etc. rather than anatomical significance measure. The FFR cutoff value of $\le$0.8 is used to distinguish ischemic and nonischemic stenosis. The FFR is clinically well validated even though it is influenced by the mechanical factors such as hyperemic flow and guide wire insertion. In recent times, noninvasive coronary computed tomography (CCTA) modality has become popular in the diagnosis of coronary artery disease. The CCTA permits the assessment of cross-sectional parameters such as minimum lumen area and lumen diameter, lesion length and plaque morphology. However, the CCTA provides limited information on the functional significance of stenotic lesions as compared to FFR. The purpose of this review is to discuss the mechanical factors influencing the invasive FFR while assessing the functional significance of intermediate stenosis severity. In addition, the hidden mechanical factors influencing the noninvasive CCTA assessment of stenosis severity will be discussed from the critical information obtained from FFR which could be beneficial for the clinician particularly in the assessment of intermediate stenosis severity.

This research was carried out to establish the relationship between human anthropometric data and corresponding gait variables. A group comprising 35 participants (18 male and 17 female) was selected for the current study. The study consisted of trials in which each participant was asked to walk the length of the instrumented walkway (Kistler’s force platform inset) at a self-selected speed. Using a four-camera motion analysis system, the kinematic and kinetic parameters of each trial were calculated. The peak values obtained from the data curves were used to generate the necessary regression fits. In order to establish the correlation between the anthropometric data of human and the gait parameters, the univariate, multivariate and stepwise fits were generated. Further, the statistical methods were employed to evaluate the $R^2$, $p$ and $F$-values for each fit. The current multivariate study indicates an increasing trend in $R^2$ values and decreasing trend for $p$-values when compared with the univariate fits and the results follow the expected line.

A new approach of human activity monitoring with a single Inertial Measurement Unit (IMU) capable of gait recognition and assessment is proposed for home-based applications. The method estimates the foot motion using a single IMU, then automatically segments the motion into steps, and extracts multiple kinematics templates. It classifies each segment by extracting Mahalanobis distance-based features from multiple sections of the motion templates and then training a Support Vector Machine. The proposed wearable system can distinguish between nine classes of activities with a classification accuracy of 99.6%. It can also discriminate between normal and abnormal gait patterns with an accuracy of 98.7%. In addition to a high recognition rate, the proposed approach provides a Gait Similarity Score (GSS) of the performed gait to its desired/normal pattern. The experimental results indicate the capability of GSS measure for assessing the quality of motion in “pre-”, “initial”, “mid” and “terminal” stages of swing phase.

Recent years have seen a renewed interest in the theories of extended continuum mechanics. These allow for a finer and relatively simple modeling of physical phenomena occurring on the microscopic level. The Eringen’s micromorphic medium belongs to this class and allows accounting for the material microstructure. A subclass of this model was applied to model the mechanical behavior of cardiac tissue. With the aid of a specifically developed numerical tool, the validity of the approach is demonstrated using different myocardial infarct scenario.

Myringoplasty is one of the routine surgeries in the treatment of tympanic membrane (TM) perforation. Since the anatomic structure of the middle ear cannot be simulated in clinical treatment, the surgery is mainly directed by experiences. Based on the mechanical properties of TM in the anatomy, four hypotheses are presented and TM is simplified as a sectorial annulus plate with fixed boundary condition. This paper proposes a free vibration model of TM. Its natural frequencies of free vibration are obtained by variables separation method and Bessel function. The system of fundamental solutions of fourth-order homogeneous equations can be solved for the analytical expressions of corresponding natural vibration mode. The theoretical model is proved to be valid since the natural frequency of the model is consistent with the experimental data. The effect of geometric parameters and material parameters on TM natural frequency is subsequently discussed in the numerical examples. Especially, the diameter and thickness of TM will cause different natural frequency errors above 40%, while the Young’s modulus and density of TM cause errors below 15% as well.

This study focuses on the functional assessment of the upper extremity of stroke patients via analysis of angular kinematics features. Amplitudes and angular velocities of multi-joint movements more precisely describe functional state at different impairment levels. However, the arm movement as a whole could be analyzed by means of joint angle–angle diagrams, which illustrate the 2D trajectory of upper extremity during movement and show the visual ranges of upper extremity in different cycles of motion. The functional range of motion of each upper extremity segment in all patient groups for more accurate assessment of capability was calculated. Moreover, we calculated the area (S) between two curves in joint angle–angle diagrams as a novel index of the complete upper extremity movement range evaluation. Our findings correspond to clinical rates and upper extremity assessment based on joint angle–angle diagrams seems to be a promising method for accurate assessment and/or predicting the outcomes of rehabilitation programs.

Presented is the analytical solution of Pennes bio-heat equation, under localized moving heat source. The thermal behavior of one-dimensional (1D) nonhomogeneous layer of biological tissue is considered with blood perfusion term and modeled under the effect of concentric moving line heat source. The procedure of the solution is Eigen function expansion. The temperature profiles are calculated for three tissues of liver, kidney, and skin. Behavior of temperature profiles are studied parametrically due to the different moving speeds. The analytical solution can be used as a verification branch for studying the practical operations such as scanning laser treatment and other numerical solutions.

Bone drilling is a common procedure in Medicine, mainly in traumatology and orthopedic procedure for fractures fixation and in reconstructive surgery. The success of this surgical procedure is dependent on many factors, namely, on heat generation control during the bone drilling. The main concern in bone drilling is the mechanical and thermal damage of the bone induced by inappropriate parameters such as drill speed and feed-rate during the drilling. This study focuses on the temperature generated during drilling of cortical bone tissue (bovine origin) and solid rigid polyurethane foams with similar mechanical properties to the human bone tissue. Different parameters such as drill speed, feed-rate and hole depth were tested. All results showed that improvement of the drilling parameters and the drill temperatures can be estimated. It was concluded that when the drill speed and feed-rate were higher, the bone temperature increase was lower. The obtained results of temperature in the drilling process of polyurethane foam blocks or bovine bone were compared with a good agreement in between both.

This study aimed to determine the effect of muscle co-contraction on balance recovery by using a simulation model. The muscle-driven forward simulation model included an inverted pendulum with two ankle muscles, a plantar flexor muscle (PF), and a dorsal flexor muscle (DF). The model was created based on experimental data obtained from balance recovery after applying backward platform translation to a standing elderly woman. Baseline simulation was performed using this model. Additionally, we performed two simulations with increased DF excitation at the same level of simulation and at the same pattern of simulation. The same level of simulation had the same PF excitation level as the baseline simulation with increased DF excitation. The same pattern simulation had the same increased or decreased PF excitation pattern but with a constant increase in PF excitation level to offset the increased DF excitation. Our results revealed that the same pattern simulation decreased the maximum dorsal flexion angle after platform translation. During the same level of simulation, the insufficient PF force used to recover balance resulted in a forward fall. These results imply that co-contraction is an effective strategy for recovering balance at the expense of additional muscle excitation in the elderly.

The asymmetrical loading applied to legs was proposed as a risk factor for low back pain development. However, this proposed mechanical risk factor was not investigated in the athletes with LBP engaged in rotational demand activities. The aim of the present study was to examine symmetry of weight-bearing in patients with rotational demand activities compared to that in healthy people during gait. In total, 35 subjects, 15 males with LBP and 20 males without LBP, participated in the study. The participants were asked to walk 12 trials in gait lab. Forces applied to legs were recorded by a force plate. Then, the peaks of anteroposterior, mediolateral, and vertical forces were measured. Next, the asymmetrical loads applied to the legs were calculated. The results of our study demonstrated that people with LBP exhibit more asymmetry of vertical peak forces in heel strike and mid-stance. They also exhibited more asymmetry of loading in the anterior direction. But the mean values of ASI of mediolateral and posterior forces in these participants were not significantly different compared to those in the control group. It can be concluded that, in comparison to the healthy subjects, patients with LBP walk with a greater magnitude of asymmetrical weight-bearing at a comfortable speed.

In this paper, the validity of local thermal equilibrium assumption in a tissue-like porous medium is investigated numerically, with an interstitial heat source. The study is based on comparison between two three-equation local thermal nonequilibrium (LTNE) model and one-equation local thermal equilibrium (LTE) model. The LTNE model is validated by an steady-state 1D analytical solution which is presented for first time. The presented results indicate the small temperature difference between fluid and solid phases in heat-affected region, which leads to considerable errors in prediction of tissue thermal behavior. According to records, increasing perfusion rate or intensity of heat source increases the differences between LTE and LTNE models. It is found that in a counter-current vascular tissue if the perfusion rate of blood into tissue becomes higher, the prediction error of LTE model will be more considerable. Moreover, the higher the intensity of heat source is, the greater the difference between LTE and LTNE models is. These findings could be extended to heat transfer modeling of actual tissue during various interstitial hyperthermia treatments.

The deformability of the substrate stimulating cell mechanotransduction depends not only on elastic modulus but also on the thickness. Polydimethylsiloxane (PDMS) which is widely used in microfluidic chips and platforms can be fabricated in a wide range of elastic modulus and thickness. In this study, we cultured human umbilical vein endothelial cells (HUVECs) on four groups of PDMS substrates of varying thickness and elastic modulus to examine effects of these parameters on morphology, viability and proliferation of cells. Both elastic modulus and thickness affected cell behavior. In general, the thickness of substrates had relatively higher impact on endothelial morphology than elastic modulus. Elongation of HUVECs on thick substrates was more intense compared to those on thin substrates. Both lowering thickness and reducing elastic modulus of PDMS decreased the viability of HUVECs, although thickness was more influential. Decrease in substrate thickness reduced cell proliferation regardless of substrate elastic modulus. In conclusion, our results suggest that endothelial behavior depends on substrate deformability, but cells react differently to the elastic modulus and thickness of PDMS by morphology, viability and growth. Results can improve the comprehension of cell mechanotransduction.