The effect of tranexamic acid on cochlear blood flow in guinea pigs measured by laser Doppler flowmetry.

OBJECTIVE: This study investigated the vasoactive effect of tranexamic acid on the cochlear blood flow in guinea pigs. METHOD: 3 ml solution (infusion speed, 0.5 ml/min) containing different concentrations of tranexamic acid was intravenously infused into 15 guinea pigs under general anesthesia. The guinea pigs were grouped according to four levels of dosage of the medicine (470 mg/kg, n=6; 220 mg/kg, n=3; 4 mg/kg, n=3; 1 mg/kg, n=3). Before administering medicine, saline solution was administered in similar volume and speed as a control. The cochleas were surgically exposed and laser Doppler flowmetry monitored cochlear blood flow volume (CBF). The left femoral artery was cannulated to permit a transducer to monitor systemic blood pressure (BP). RESULTS: (1) Stimulatory effect of tranexamic acid on CBF was dose-dependent at concentrations of 1-470 mg/kg and, (2) the time course of changes in CBF was almost identical to that in BP following tranexamic acid administration. CONCLUSION: Preliminary findings suggest that intravenous administration of tranexamic acid increases CBF due to vasomotorial mechanism effect on BP.

Histological reaction of auditory bulla bone to synthetic auditory ossicle (Apaceram) in rats.

To investigate the biocompatibility of a synthetic auditory ossicle to host bone, small thin Apaceram disks composed of dense hydroxyapatite were implanted under the periosteum of the left auditory bulla in 32 rats for periods ranging from 1 day to 270 days. A sham operation performed on 10 rats served as a control. Decalcified histological sections stained with hematoxylin and eosin were observed using light microscopy. The experiment showed: 1) a time-dependent mature fibrous connective tissue surrounding the Apaceram disk, 2) no evidence of inflammatory reaction caused by the implant from 90 days after implantation until the end of the experiment, 3) no evidence of osteolysis by osteoclasts caused by the implant, and 4) direct contact of bone to the implant on the bone-disk interface at 180 and 270 days after implantation. The findings suggest that Apaceram has a high degree of implant biocompatibility, making it a satisfactory substitute biomaterial for otological reconstructive surgeries.

Long-term microstructural analyses of hydroxyapatite implanted in rats using laser-Raman spectrometry and scanning electron microscopy.

To investigate the long-term surface microstructure of a synthetic auditory ossicle (Apaceram) composed of dense hydroxyapatite (HA), thin HA disks were implanted subcutaneously into the interscapular regions of 12 rats. After 6, 14 and 20 months, implanted HA surfaces were observed using stereoscopic microscopy, scanning electron microscopy (SEM) and laser-Raman spectrometry. Visual observation by SEM at 6 months and by stereoscopic microscopy at 14 months indicated a progressive degradation of the HA disk surfaces implanted in the subcutaneous tissue. Visual observation by SEM at 14 and 20 months and by stereoscopic microscopy at 20 months indicated a progressive redeposition on the surfaces of the implants. Raman spectra compared half-peak breadths of v1 signal (PO4(3-), 960 cm(-1)) on the gray and white surface areas of implanted HA disks observed by stereoscopic microscopy. Analysis demonstrates that demineralization at 14 months and remineralization at 20 months occur on the gray areas; demineralization at 6 months and remineralization at 14 months occur on the white areas.

Long-term observation of subcutaneous tissue reaction to synthetic auditory ossicle (Bioceram) in rats.

To evaluate biocompatibility to tissue in long-term implantation, Bioceram discs made of aluminum oxide (Al2O3) were implanted subcutaneously within the interscapular region of 64 rats for six to 20 months. Histological sections stained with haematoxylin and eosin (H&E) and the surface of the implant material were observed using light microscopy. Different cell types and the thickness of fibrous capsules surrounding the implants were examined quantitatively by light microscopy. Small numbers of macrophages (2.8 +/- 0.7%) and lymphocytes (2.7 +/- 0.9%) were observed at six months after implantation, gradually decreasing to zero at 16, 18 and 20 months. Neither neutrophils nor foreign body giant cells were seen in any specimens. The thickness of fibrous capsules surrounding the implants was closely related to the shape of the implant, but there was no significant change between six and 20 months after implantation. No change in Bioceram surfaces were observed under stereoscopic microscopy from six to 20 months after implantation. The study results indicate that Bioceram is a satisfactory biocompatible material for reconstructive surgery from the viewpoint of long-term tissue response. Present results of experiments with Bioceram are also compared to previous results with Apaceram and different tissue responses of the two materials are discussed.