Biomedical subjects

H Akiho

Publications and source records attributed to H Akiho.

40 records · Page 3Linked to original sources

PubMed1991

Hydrodynamic endurance test of the prosthetic valve used in the various types of the ventricular assist device.

To evaluate the various basic designs of the pump chambers used in the ventricular assist devices (VADs), hydrodynamic endurance test was performed from the viewpoint of the durability of the prosthetic valves used in the VAD. For the hydrodynamic analysis, we designed three basic types of pump (sac type, diaphragm type, and pusher plate type) using the same material and having the same capacity and shape. Prosthetic valves in these VADs were tested from the standpoint of the water hammer effect, which affects the valve durability, to determine which pump design would be most durable as a prosthetic valve in the VAD. The water-hammer phenomenon was evaluated using the maximum pressure gradient (MPG) across the prosthetic valve in the moc circulatory loop. Maximum pump output was recorded when we used the diaphragm type model, and minimum MPG in the commonly used driving condition of the VAD were recorded when we used the sac type model. The results suggest that the sac type VAD model is the most durable design for the prosthetic value.

Adult↗

PubMed1991

Systemic circulation with high frequency blood flow--analysis from neurophysiological point of view.

The vibrating electromagnetically driven univalved artificial heart, which provided more than 10 1/min at 10 Hz/sec. vibration, was developed in our team. This vibrating electromagnetic pump (VEMP) produced the original flow pattern compared with the flow pattern of the natural heart, so that circulatory regulatory system during maintain the circulation with VEMP must be investigated before the clinical application. In order to assess the effect of high frequency blood flow produced by the VEMP from the neurophysiological point of view, power spectral analysis of the hemodynamics was performed. VEMP was implanted as the total left heart bypass in adult goats and right heart circulation was maintained by natural hearts. In arterial blood pressure during maintain circulation by the high frequency blood flow, Mayer waves (0.01-0.15 Hz) were significantly decreased, though respiratory waves (0.25-0.40 Hz) were not significantly changed. These results suggest that circulatory regulatory system was influenced by the high frequency blood flow produced by the VEMP.

Animals↗

PubMedDate not supplied

EUS-guided endoscopic resection using band ligation of oesophageal granular cell tumour: report of a case.

A 60-year-old Japanese man was referred for treatment of a polypoid oesophageal tumour. Radiographic examination of the upper gastrointestinal tract disclosed a nodule with central depression in the lower esophagus. By endoscopy the nodule was yellowish and appeared submucosal. Endoscopic ultrasonography demonstrated a hypoechoic solid tumour limited in submucosa without lymph node involvement. Endoscopic resection using band ligation was performed under guidance by endoscopic ultrasonography. By histologic examination the tumour consisted of large cells arranged in nests. These cells had abundant granular cytoplasm and small round nuclei. They expressed S-100 protein and were CD68, and periodic acid-Schiff positive. No expression of alpha-smooth muscle actin was noted. The tumour was limited in submucosa. Findings were consistent with complete endoscopic resection. This report may be the first concerning an oesophageal granular cell tumour successfully treated with EUS-guided endoscopic resection using band ligation.

Biopsy, Needle↗

PubMedDate not supplied

Deterministic chaos in the hemodynamics of an artificial heart.

To analyze the hemodynamic parameters during prosthetic circulation as an entity, non linear mathematical techniques were used. To compare natural and prosthetic circulation, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in chronic animal experiments using adult goats to consitute the biventricular bypass complete prosthetic circulation model with ventricular fibrillation. After implantation, these goats were placed in a cage and extubated after waking. All hemodynamic parameters with the natural circulation without biventricular bypass pumping, and the artificial circulation with biventricular bypass pumping under ventricular fibrillation were recorded under awake conditions. By the use of a non linear mathematical technique, the arterial blood pressure waveform was embedded into a four dimensional phase space and projected into three dimensional phase space. The Lyapunov numeric method is used as an adjunct to the graphic analysis of the state space. A phase portrait of the attractor showed a high dimension complex structure, with three dimensional solid torus suggesting deterministic chaos during natural circulation. However, a simple attractor, such as a limit cycle attractor, was observed during artificial circulation. Positive Lyapunov exponents during artificial circulation suggest the lower dimensional chaotic system. Thus, hemodynamic parameters during prosthetic circulation must be carefully controlled when unexpected stimuli are fed from outside.

Animals↗