Biomechanical analysis for the epidural needle insertion

In order to test the hypothesis about reduction in the deformation of the ligamentum flavum due to tension inside the ligamentum flavum, nonlinear finite element (FE) analysis was employed. As a preliminary analysis of natural tissue, nonlinear FE analysis was applied to a rubber plate. Assuming that the rubber is third-order Mooney-Rivlin model, the analysis and the experimental curves overlap with each other until pierced point. The maximum major strain calculated by FE analysis was feasible to predict pierced point. To apply nonlinear FE analysis for the porcine ligamentum flavum, the Mooney-Rivlin coefficient of the porcine ligamentum flavum was identified from the tensile test data. Assuming that the sharp bar pierced the ligamentum flavum when the maximum major strain reached a constant value, the required displacement became shorter by 1.0mm by applying the initial tension.

New automatic cell isolation system for flow cytometry: cell isolation unit and staining reagent kit

Flow cytometry is well-known cell analysis method and useful to gain quantitative information from cells in blood, however, it is not widely used for solid tissues in clinical settings. This is partly because it takes a long time to prepare samples and the operation can be complicated. To resolve these problems, we developed a new automatic cell isolation system which consists of cell isolation unit and staining reagent kit specialized for flow cytometry. With this new system, cell isolation can be done more rapidly and easily. By using this method, we could determine optimum condition to disintegrate porcine colon tissue and stain cells stably in 6 minutes. This result indicates that our method can provide analysis data within 10 minutes. We also evaluated our method in colorectal cancer patients, and the result was promising. All the data suggests that this method can support and facilitate rapid diagnosis.

Young's modulus measurement of the porcine ligamentum flavum for evaluating the deformation during epidural insertion

In order to check validity of the porcine ligamentum flavum as a substitute of human tissue for evaluating the epidural needles, the thickness and the Young's modulus were measured, and a finite element analysis was carried out. Twenty-four specimens were stained by the Elastica-van Gieson method. The average value of the thickness was 1.2 mm. The tensile tester was employed for measuring the Young's modulus. A cross sectional area was obtained by X-ray CT image. Young's modulus was 1.6 MPa. The measured properties of a porcine ligamentum flavum showed a reduced thickness and smaller Young's modulus than the human ligamentum flavum. On a finite element analysis, the shape of the ligamentum flavum was modeled as a square plate 5 mm in width and 5 mm in depth. The thickness and the Young's modulus were set at the measured value for a porcine model, and value from the literature for a human model. For simplicity, a constant load of 10 N was applied at the center of each model. The porcine model exhibited deformation 1.7 times that of the human model.

Epidural insertion simulator of higher insertion resistance & drop rate after puncture

Accidents such as dural puncture remain one of the problems of epidural anesthesia, and unskilled doctors can repeat such accidents. The purpose of the current research was to provide a new simulator for epidural insertion training. No reference data regarding the resistance force used when inserting a needle into patients have been reported. A comparative study was conducted to aid in the development of a new simulator. Pork loin (n=5) were employed as a substitute for patients. Thickness was set at 2 cm so as to improve the reproducibility. The authors took the conventional simulator apart, and picked a block as an analogue of muscle and ligamentum flavum. A new simulator was made of a melamine foam resin block and a latex rubber sheet. An epidural needle fixed on a motorized stage was inserted at the speed of 2 mm per second. The reaction force was measured while the needle was inserted into each specimen. Waveform of the pork loin exhibited two slopes of different inclines up to peaks and then falls after puncture. The conventional simulator showed a simple increase up to peak and a slow fall after puncture. In contrast, the new simulator showed two slopes up to peak and then a sudden fall after puncture. The insertion resistances were 2.5 N/s for the porcine, 0.8 N/s for the conventional and 2.1 N/s for the new simulator. The drop rates were 5 N/s for the porcine, 0.6 N/s for the conventional and 24 N/s for the new simulator. The higher insertion resistance and drop rate for the new simulator than the conventional simulator will be suitable for epidural insertion training.

Comparative phantom study on epidural anesthesia needle

The purpose of the current study was to evaluate the clinically used epidural anesthesia needles based on quantitative comparative data. Precise measurement of the tip shape and puncture force analysis were conducted on six different needles. Tip angle (alpha+beta) and tip length (L) were measured by X-ray computed tomography (CT). The one-axial puncture force through a silicone phantom (thickness of 3 mm) was obtained by a load cell. The speed was set at 4 mm/s, which equals the average of anesthesiologists' technique. The needle punctured twice at the same position to separate cutting and friction force. The X-ray CT revealed that 1) the alpha+beta ranged from 27.5 degrees to 38.8 degrees (average of 33.8 degrees), 2) the higher alpha+beta resulted in the lower L (ranges from 2.13 mm to 3.27 mm; average of 2.62 mm), and 3) the most popular needle was the one with average tip angle and length (the alpha+beta of 33.6 degrees, the L of 2.57 mm.). Puncture force analysis showed that 1) the peak value related the L (correlation coefficient of r2=0.65), and the most popular needle was the third-largest value, 2) the slope of increasing force related the alpha+beta (correlation coefficient of r2=0.79), and 3) the averaged force to cut of the most popular needle was the second-smallest value, which means less resistance for cutting.

Damper design for improving S/N ratio of the seismocardiogram monitoring in the OpenMRI-guided operating theater

The final goal of this study is to establish a method of measuring precisely the seismocardiogram (SCG) of a patient who lying in an open magnetic resonance imaging (openMRI) machine for myocardial ischemia monitoring during surgery. Vibration isolation from the gantry vibration during MRI scan is essential for clinical use. Authors previously reported the comparison between the SCG and the gantry vibration. A damper to decrease vibration below 30 Hz should be designed. In this paper, authors fabricated a damper model to check the feasibility of the damping effect, and compared with the patient bed mat. Experiment using a vibrator showed 1) the viscosity damping coefficient of the current damper was 2 kN s/m, 2) owing to the damper, peak ratio between input and output amplitude decreased from 2.5 to 1.2, and 3) natural frequency decreased from 12 Hz to 5 Hz. Damping below 30 Hz was successfully achieved. The maximum S/N ratio was calculated 6, improving from 1.8. Simulation showed that the maximum S/N would be 75 under the viscosity damping coefficient of 1 N s/m.

New possibilities for stereotaxis. Information-guided stereotaxis

Information-guided stereotaxis, assisted by visualization of medical information, will become the next generation of neurosurgical systems. We performed 76 open MRI surgeries at Tokyo Women's Medical University between March 3, 2000 and April 12, 2001. Of them, comparisons of pre- and post-operative MR images for malignant gliomas in 21 cases revealed an average resection rate of 90.3% (the maximum 100%, the minimum 55%). In this article we describe real time updated navigation, augmented reality navigation, three-dimensional navigation, chemical navigation, information-guided navigation system (High definition visual Computer Aided Surgery System: HivisCAS), and open MRI-guided surgery that we are developing.

Preliminary study on the new self-closing mechanical mitral valve

Anatural mitral valve starts closing before systole. Conventional mechanical mitral valves start their closing motion after systole. In order to let the mechanical mitral valves start closing before systole, we propose a new self-closing valve by adjusting the center of gravity of the leaflet. As a first step, we adjusted the center of gravity by attaching a block of lead to the leaflet of a CarboMedics bileaflet valve and evaluated it using a pulse duplicator and an x-ray high-speed video camera. Comparative study was conducted under 60 bpm and 4 L/min as the mean flow rate. It was clarified that the self-closing valve started closing before systole, no influence on inflow volume was found, the final closing speed of the self-closing valve just before complete closure was slower than the conventional valve (1.9-0.34 m/s), a design strategy of a self-closing valve (sewing ring diameter 29 mm) was obtained from the experiment that momentum of inertia of the leaflet should be less than 14.9 x 10-9 kg.m2 and the torque caused by gravity should be more than 4.2 x 10-6 N. m, and only one leaflet should be designed as self-closing, and surgeons need to pay attention to the positioning of the two leaflets. In conclusion, the preliminary study showed the ability of starting to close before systole and the design strategy for future prototyping.

Comparison of the closing dynamics of mechanical prosthetic heart valves

To compare the closing dynamics of mechanical tilting disk prosthetic heart valves (OmniScience 25 [OS25], Medtronic-Hall 25 [MH25], Bjork-Shiley Monostrut 29 [BS29]) and bileaflet valves (CarboMedics 29 [CM29]) in the mitral position, an x-ray high speed video camera (XHVC) and a mechanical mock circulator were used. From the continuous images taken with the XHVC, the starting point of closing and the period during closing (PDC) were measured. Pressures and flow rate were recorded at 500 Hz synchronously with the XHVC. A pressure difference across the valves at the onset of closing (dpc) was newly introduced to compare the closing response. Using 60 and 100 bpm, the following results were obtained: 1) the CM29 had less PDC and maximum backflow rate than the BS29; 2) the dpc and the PDC at 100 bpm were larger than those at 60 bpm; 3) the dpc of the MH25 was the lowest; and 4) the PDC of the CM29 was the shortest. With regard to the effect of valve design on closing dynamics, it was shown that: 1) less momentum of inertia of the occluder and disk traveling angle resulted in lower dpc and shorter PDC, and 2) the higher the dpc and the PDC became, the larger the maximum backflow rate that was generated, and 3) low final closing speed will be achieved for small disk travelling angle.

Study of the effect of atrial contraction on mitral prosthetic valve by high speed video camera

To clarify the effect of atrial contraction on the dynamic behavior of mitral prosthetic valves, a mechanical mock circulatory system has been developed. It is able to simulate the inflow characteristics during diastole. The disc motions of Björk-Shiley Monostrut (BSM29) and CarboMedics (CM29) valves (both with an annulus diameter of 29 mm) were measured and compared with a high speed video camera. After contraction of the artificial atrium (100 ms), there was a delay of 75 ms before the onset of the ventricular contraction. Mitral flow similar to physiological conditions could be achieved. The BSM29 was tested in the anterior position (a) and the posterior position (p). Under the condition of active atrial contraction (AC), we confirmed that the closing motion was initiated and the period during closing motion (PDCM) was prolonged (BSM29[a]: 22.4 +/- 3.4-->63 +/- 3.2; BSM29[p]: 71.2 +/- 38-->94.2 +/- 11; and CM29: 14 +/- 0.0-->28.4 +/- 2.3 [unit: ms]), the prolongation of the PDCM of the CM29 due to the AC being smaller than that of the BSM29. We also confirmed that the closing volume (CV) increased slightly (BSM29 [a]: 7.8 +/- 0.4-->8.5 +/- 0.8; BSM29[p]: 6.9 +/- 0.6-->7.0 +/- 0.5; and CM29: 3.6 +/- 0.6-->4.1 +/- 0.6 [unit: ml]). The CM29 had a shorter PDCM, less prolongation of the PDCM due to the AC, and less CV than the BSM29. Thus, we confirmed that the CM29 produced better response at valve closure than the BSM29.