Biomedical subjects

Akimasa Ishida

Publications and source records attributed to Akimasa Ishida.

4 recordsLinked to original sources

PubMed2004

Time course analysis of angular control of the body and head while rising from a chair.

OBJECTIVE: To use time course information to improve understanding of the vestibular contribution to postural control as one rises from a chair. MATERIAL AND METHODS: A total of 24 healthy controls and 42 patients with varying degrees of vestibular dysfunction were studied. The time course of the angular motion of the body and head when rising from a chair with eyes open and closed was evaluated. The delay between the onset of the motions of the body and head was compared between subject groups. We also investigated transition points from forward lean of the body to backward reversion and from backward tilt of the head to forward reversion. RESULTS: With regard to the onset of chair rise, we found a significant difference in the delay between head and body motion between healthy controls and subjects with bilaterally impaired vestibular deficiency only when the eyes were closed. The time between the transition points of the head and body was stable between these groups. CONCLUSION: The mechanisms controlling the onset of head and body movements differ between normal subjects and those with bilateral vestibular deficits. In the latter, the loss of a reference of gravity causes a decrease in feed-forward postural control, which is compensated for by a somato-sensory feedback mechanism. Visual input seems to provide an alternative reference of gravity.

Caloric Tests↗

PubMed2003

Contribution of the vestibular apparatus to postural control when rising from a chair.

OBJECTIVE: The everyday act of rising from a chair is known to require the combined angular control of a number of the body's joints, especially those within the pitch plane. Precisely how this control is exerted, however, remains controversial. The aim of this study was to obtain a better understanding of the contribution made by the vestibular apparatus to postural control of the body and head when an individual rises from a chair. MATERIAL AND METHODS: A total of 24 healthy controls and 38 patients with varying degrees of vestibular dysfunction were examined. Electromagnetic motion sensors were used to analyze the angular control of the head and body as subjects rose from a chair with their eyes open or closed. RESULTS: We found that unilateral vestibular dysfunction caused fixation of the head with respect to the body, resulting in a loss of spatial stability of the head which was not compensated for by visual input. Visual input did appear to compensate for bilateral vestibular loss, enabling patients with bilateral vestibular apparatus impairment or central disorders to fix the position of their head in space. CONCLUSION: The act of rising from a chair is normally controlled by vestibular and proprioceptive input; the head is aligned according to the gravitational reference so as to obtain stable visual information. In patients with unilateral vestibular hypofunction, posture is still controlled by these two inputs, although the ability to align the head is diminished. In patients with bilateral vestibular hypofunction or a central disorder, head alignment is maintained using visual input, although it may not be the sole or predominant stabilizing force.

Adult↗

PubMed2002

Accurate in vivo measurement of polyethylene wear in total knee arthroplasty.

This study describes a new technique to evaluate accurate linear polyethylene wear and reports the in vivo annual linear wear rate in total knee arthroplasty. Patients (n = 69) were assessed using a single standing anteroposterior radiograph with 8 reference markers around the knee, where 3-dimensional (3D) locations of markers and 3D geometry of the implant were known. By matching the 3D locations of the markers and their projected points on the radiograph, 3D/2D transformation parameters were estimated. Using these parameters, the 3D coordinates of the implant were estimated from the projected x-ray silhouette. After calculating the femorotibial shortest distance, wear and creep deformity of the polyethylene was defined with an accuracy of 0.1 mm or better. Measured linear wear in the 69 knees varied from 0 mm (1 month postoperatively) to 2.71 mm (7 years postoperatively). The correlation of linear wear (Y) and year (X) was Y = 0.23 X -0.11 (P<.001). This study revealed that annual wear rate was 0.23 mm and 2 times greater than the average annual wear rate in total hip arthroplasties.

Aged↗

PubMed1998

A modified back-propagation method to avoid false local minima.

The back-propagation method encounters two problems in practice, i.e., slow learning progress and convergence to a false local minimum. The present study addresses the latter problem and proposes a modified back-propagation method. The basic idea of the method is to keep the sigmoid derivative relatively large while some of the error signals are large. For this purpose, each connecting weight in a network is multiplied by a factor in the range of (0,1], at a constant interval during a learning process. Results of numerical experiments substantiate the validity of the method.

Journal Article↗