Biomedical subjects

K Naemura

Publications and source records attributed to K Naemura.

6 recordsLinked to original sources

PubMed2001

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.

Humans↗

PubMed2000

Synthesis and association behavior of butadiyne-bridged

Butadiyne-bridged [4(4)](2,6)pyridinophane and [4(6)](2, 6)pyridinophane derivatives were synthesized, and their heteroassociations with the corresponding metacyclophanes and complexations with organic cations were investigated.

Journal Article↗

PubMed2000

Synthesis and anion-selective complexation of cyclophane-based cyclic thioureas

Cyclic thiourea derivatives having three different types of cyclophane structure, ortho-meta, meta-meta, and meta-para, and a lariat-type thiourea, were synthesized, and their anion-binding ability was examined. The association constants for the complexation between the receptors and several anions in DMSO-d(6) were measured by the titration method using (1)H NMR spectroscopy. All receptors, except for the meta-para cyclophane, exhibit selective binding to the dihydrogenphosphate anion, which is stronger than that of the acyclic reference compound. The lariat-type receptor binds anions even more strongly than the cyclic receptors which do not possess the third binding site.

Journal Article↗

PubMed1999

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.

Biocompatible Materials↗

PubMed1997

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.

Atrial Function↗

PubMedDate not supplied

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.

Biomechanical Phenomena↗