Guanghong Ding

Non-Newtonian Computational Hemodynamics in Two Patient-Specific Cerebral Aneurysms with Daughter Saccules

Hemodynamic factors play important roles in the formation, progression and rupture of cerebral aneurysms, and the Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) on the aneurysms are considered to be correlated with their growth and rupture. In this article, two computational models based on patient-specific cerebral aneurysms with daughter saccule are constructed from 3D-RA image data, one is lateral aneurysm located in middle cerebral artery (CA1) and the other is terminal aneurysm located in anterior communicating artery (CA2), The corresponding models of the two aneurysms by removing daughter saccule are established in order to investigate the initiation and growth of the daughter saccule. The flow patterns and the distributions of hemodynamic factors in the two aneurysms before and after daughter saccule is removed are obtained by solving the governing equations with the commercial CFD software Ansys CFX11.0 under the non-Newtonian fluid assumption. By analyzing the flow patterns, it is concluded that the aneurysms with daughter saccules have more complex and unstable flow patterns and hence are prone to rupture. By comparing the distribution of OSI, a hypothesis that a high OSI causes the growth of the daughter saccule is presented.

Effect of different LLLT on pituitrin-induced bradycardia in the rabbit

The objective of this paper was to observe the effect of low-level combined- or single-laser irradiation on bradycardia produced by pituitrin in rabbits. A combined-laser apparatus was made. A 10.6-μm CO2 laser and a 650-nm semiconductor laser, transmitted by different optical fibers, converged to output and irradiate on the Neiguan (PC6) acupuncture point in rabbits with bradycardia produced by pituitrin. Thirty minutes after the model was set, the heart rates of the combined-laser Neiguan group made quicker recoveries than those of the model control group, the laser-control group, or the single-laser Neiguan group (P<0.05), and the heart rates of the single-CO2-laser Neiguan group were similar to those of the normal group (P>0.05). However, there were significant differences between the 650-nm-laser Neiguan group and the normal control group (P<0.05). The combined-laser irradiation certainly has a curative effect on bradycardia produced by pituitrin. A single CO2 laser could accelerate the recovery from bradycardia, while single 650-nm-laser irradiation on the Neiguan acupoint does not produce such an effect.

A Fluid Mechanics Model of Tissue Fluid Flow in Limb Connective Tissue-A Mechanism of Acupuncture Signal Transmission

This article explores the mechanisms of acupuncture meridians by determining characteristics of the tissue fluid flow in the connective tissue along meridians. Based on deep dissection of acupoints on the upper and lower limbs of the human body and micro and macro observation and measurement, a mathematical model of the flow of tissue fluid in interosseous membranes is constructed. It is shown that the signal transmission along acupuncture meridians may be determined by unique anatomical and physiological factors that govern the flow of tissue fluid in the connective tissue and involve mast cell degranulation. Our results provide a preliminary explanation of the phenomenon of the “de qi” sensation and the mechanism of acupuncture signal transmission along acupuncture meridians.

Hydrodynamic modeling of cochlea and numerical simulation for cochlear traveling wave with consideration of fluid-structure interaction

The cochlea is an important structure in the hearing system of humanity. Its unique structure enables the sensibility to the sound waves of varied frequencies. The widely accepted model of the cochlea is expressed as a long tube longitudinally divided by a membrane named the Basilar Membrane (BM), into two fluid-filled channels. Based on various assumptions for the cochlear fluid and structure, simplified mathematical and mechanical cochlear models were developed to help to understand the mechanism of the complex coupled system in the past decades. This paper proposes a hydrodynamic numerical cochlear model with consideration of the Fluid-Structure Interaction (FSI). In this model, the cochlear lymph is considered as in a Newtonian viscous fluid, and the basilar membrane is modeled as a composite structure. The traveling wave is simulated. Also focusing on the pressure in the fluid field, the results are compared with studies of Peterson and Bogert, where it was assumed that the slow compressive waves are traveling along the BM. Furthermore, the transmitting time of the cochlear traveling wave is also discussed.

Function of Collagen and Mast Cells in Acupuncture Points

The acupoint is the responsive point that is stimulated during acupuncture treatment, and its structural basis and action mechanism have been largely elucidated by researchers. Clinical medical imaging and extensive studies on anatomy have indicated that the structural and functional basis for the human body’s meridians and acupoints is a complex system that primarily comprises connective tissues with numerous intertwining blood vessels, nerves, collagen fibers, and mast cells. Nevertheless, how the effective acupunctural signals transmit through acupoints to induce analgesia through a series of biochemical reactions along the meridians is a mystery. We have applied different acupuncture methods combined with morphology observations, mechanical signal detection, and animal pain threshold measurements to analyze the correlation between acupuncture analgesia and collagen fiber mechanical deformation as well as mast cell degranulation at acupoints. Furthermore, to explore the structural and functional basis of acupoints and the initiation of acupunctural signals, the patch clamp technique was used to investigate the dynamic characteristics of mechanosensitive proteins in relation to acupuncture at the cellular level. The results indicated that acupuncture analgesia was induced by physical stimulation at acupoints, where collagen fibers were deformed by stress and the surrounding mast cells were activated. The acupoint response is based on the spatial conformations of the blood vessels–mast cells–nerves. Once activated, mast cells are degranulated and release several types of bioactive substances, which increase blood vessel permeability. In addition, they act on the surrounding peripheral nerve endings, which induce a local peripheral nerve impulse and then transfer the acupunctural signal to the central nervous system. During this process, a positive feedback signal is generated by neurotransmitters acting on the mast cells and distributed along the meridians. An analgesic effect is produced and transmitted through an indirect effect on the organs and tissues along the meridians.

Effects of parent artery segmentation and aneurismal-wall elasticity on patient-specific hemodynamic simulations

It is well known that hemodynamics and wall tension play an important role in the formation, growth and rupture of aneurysms. In the present study, the authors investigated the influence of parent artery segmentation and aneurismal-wall elasticity on patient-specific hemodynamic simulations with two patient-specific cases of cerebral aneurysms. Realistic models of the aneurysms were constructed from 3-D angiography images and blood flow dynamics was studied under physiologically representative waveform of inflow. For each aneurysm three computational models were constructed: Model 1 with more extensive upstream parent artery with the rigid arterial and aneurismal wall, Model 2 with the partial upstream parent artery with the elastic arterial and aneurismal wall, Model 3 with more extensive upstream parent artery with the rigid wall for arterial wall far from the aneurysm and the elastic wall for arterial wall near the aneurysm. The results show that Model 1 could predict complex intra-aneurismal flow patterns and wall shear stress distribution in the aneurysm, but is unable to give aneurismal wall deformation and tension, Model 2 demonstrates aneurismal wall deformation and tension, but fails to properly model inflow pattern contributed by the upstream parent artery, resulting in local misunderstanding Wall Shear Stress (WSS) distribution, Model 3 can overcome limitations of the former two models, and give an overall and accurate analysis on intra-aneurismal flow patterns, wall shear stress distribution, aneurismal-wall deformation and tension. Therefore we suggest that the proper length of extensive upstream parent artery and aneuri-smal-wall elasticity should be considered carefully in establishing computational model to predict the intra-aneurismal hemodynamic and wall tension.

Can a carbon dioxide laser substitute for moxibustion

Dear Sirs, Thank you for the opportunity to respond to the letter to the editor from Drs. Jang and Park. We welcome and appreciate comments from readers of the journal and believe that discussion helps to improve clinical research in the field. We are pleased that our article [1] has generated a discussion and raised an important question: “Can a carbon dioxide laser substitute for moxibustion?” This was one of the questions that we attempted to answer in our pilot study. We concluded that the carbon dioxide (CO2) laser mimics and simulates moxibustion based on two facts: (1) the CO2 laser has a thermal effect similar to that of moxibustion. We previously reported that, after 3 min, a CO2 laser applied to an acupuncture point on a healthy volunteer raised the skin temperature by 1.22±0.37°C, indicating that the CO2 laser has a fairly persistent thermal effect [2, 3]. (2) The wavelength of the CO2 laser is very close to that of traditional moxibustion. The CO2 laser wavelength is reported to be 10.6 μm [4], which can be absorbed by the epidermis to a depth of 0.2 mm, while the wavelength of the infrared radiation peak of traditional indirect moxibustion is approximately 10 μm [5]. Dr. Jang and Dr. Park suggest in their letter that moxibustion heat reaches a different depth from that of the CO2 laser. To support this notion, one must know the thermal radiation depth reached by both laser and moxibustion. But, although there are reports that the thermal energy of the CO2 laser penetrates the epidermis to a depth of 0.2 mm [4, 6], there are no reports on the depth of penetration by moxibustion thermal radiation. We agree with the correspondents that a high drop-out rate in the control group at the 4-week time point is problematic. However, we only analyzed and reported the data from the 2-week time point, which had a relatively lower drop-out rate (4/20 of the control group and 1/20 of the treatment group) [1]. This should not cause the blinding issue that concerns the correspondents. Furthermore, as reported in our results, we asked patients to give their reasons for dropping out of the study. Of the total of 11 drop-outs in the placebo control group, four felt the treatment was “ineffective,” four were “too busy” to continue treatment, and three were lost to follow-up. None of these patients indicated that they were dropping out because they believed that they were assigned to the placebo control group. As most laser devices do not produce a thermal effect, patients were not aware that they were supposed to feel heat during the treatment. This method for validating blinding has been widely used and reported by others in the acupuncture literature [7], and, according to the data from our study, there is no evidence to show that the blinding in our study was unsuccessful, as assumed by the correspondents. Thus, we are confident with our conclusion that patient blinding was successful. However, as we indicated in the title of the article, this was a ‘pilot study’ to explore the feasibility of a clinical trial. Lasers Med Sci (2009) 24:291–292 DOI 10.1007/s10103-008-0587-6

Three-dimensional finite element hydrodynamical modeling of straight and spiral cochlea

A stabilized finite element scheme for the 3D cochlear fluid-structure interaction (FSI) problem is proposed. The FSI involves the interaction between the cochlear basilar membrane (BM) and its sur...

PARAMETER ANALYSIS OF 2D COCHLEAR MODEL AND QUANTITATIVE RESEARCH ON THE TRAVELING WAVE PROPAGATION

The traveling wave is the most important phenomenon in cochlear macromechanics. The behaviors of the traveling wave that greatly alter the auditory discrimination, are tightly related with the mechanical properties of the basilar membrane (BM) and its surrounding lymph. As an addition to the blanks of related researches, this paper focuses on some of the key parameters that affect the cochlear response most: the BM stiffness, damping parameters and the fluid viscosity. The influence of these parameters on the traveling wave is discussed, based on our former developed 2D finite element hydrodynamic cochlear model. Moreover, the traveling wave velocity and its transmitting time are calculated based on the simulating results. Although generally a rapid fall of the velocity from the cochlear base to the characteristic frequency (CF) location is confirmed, our quantitative analysis also indicates the traveling wave velocity may be both location and frequency dependent.