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Biomedical subjects

H Minamitani

Publications and source records attributed to H Minamitani.

At least 19 recordsLinked to original sources
PubMed2005

Human standing posture control system depending on adopted strategies.

Control of the standing posture of humans involves at least two distinct modes of operation to restore the body balance in the sagittal plane: the ankle strategy and the hip strategy. The objective of the study was to estimate the contribution of vestibular, visual and somatosensory feedbacks to these distinct strategies. The body dynamics was described as the motion of two linked rigid segments that represented the legs and the rest of the body. The posture controller received the inclination angles of the two body segments as inputs and regulated the moments around the ankle and hip joints. The controller had four feedback paths that were characterised by transfer functions connecting the two inputs and the two outputs. To evoke the distinct strategies, the floor conditions were varied by narrowing the support surface under the feet. A continuous pseudo-random external disturbing force was applied to the waist and the thigh independently. The inclination angles of the body segments and the ground reaction force were measured, and the transfer functions of the controller were estimated with the maximum-likelihood system identification procedure. Six healthy male adult subjects participated in the experiment. When the hip strategy became evident under the narrow support surface conditions, the transfer function relating the leg inclination angle and the ankle joint moment decreased its DC gain (16%), whereas the other three transfer functions increased the gains (20-140%) (ANOVA, p < 0.05). Based on a criterion for simplicity in the modification of the posture controller, these changes suggest a new hypothesis that, when posture control becomes difficult, the central nervous system selectively activates the somatosensory feedback paths from the hip joint angle to the moments around the ankle and hip joints.

Adult↗
PubMed2003

Determination of the position and orientation of artificial knee implants using markers embedded in a bone: preliminary in vitro experiments.

This study describes the method of determination of the position and orientation of artificial knee implants using a single-plane radiograph. To simplify the 3D/2D matching problem, we proposed to use small markers embedded in a bone. From the image coordinates of markers, it is possible to estimate the position and orientation of implants if the relationship between the markers and the implant is known. The results of the in vitro experiment showed that rms errors in in-plane/out-of-plane translations and rotations were 0.2/2.3 mm and 0.2/0.2 degrees, respectively.

Algorithms↗
PubMed2002

Kinematic analysis of mobile-bearing and fixed-bearing knee prostheses by simulation.

The object of the study was to model fixed-bearing knee prostheses (FBKs) and mobile-bearing knee prostheses (MBKs) during weight-bearing deep knee bends and to analyse and compare the kinematics of the two prosthesis types. To obtain quantitative data, an overall model of a leg was constructed, and this included a three-dimensional model of the tibiofemoral joint and simplified two-dimensional models of the ankle and patellofemoral joint. The simulated movement pattern of the tibiofemoral contact point in the FBK was analysed to show the posterior contact position on the tibia at full extension and anterior translation as the knee was flexed from 30 degrees to 90 degrees. The simulated maximum displacements of the medial and lateral contact positions of the FBK were 5.6 and 6.2 mm, respectively. These results were almost in agreement with experimental studies. Compared with the FBK, the movement pattern of the tibiofemoral contact point in the MBK for the anterior contact position on the tibia at full extension and posterior translation, with respect to the tibia as the knee was flexed, gave results closer to those of the normal knee. The simulated displacements of the medial and lateral contact positions of the MBK with respect to the tibia were 9.0 and 13.0 mm from full extension to 90 degrees flexion, respectively. The difference in the kinematic results between the FBK and the MBK could be accounted for by movement of the insert and the larger force of the posterior cruciate ligament on the MBK.

Biomechanical Phenomena↗
PubMed2001

Direct measurement of erythrocyte deformability in diabetes mellitus with a transparent microchannel capillary model and high-speed video camera system.

To measure erythrocyte deformability in vitro, we made transparent microchannels on a crystal substrate as a capillary model. We observed axisymmetrically deformed erythrocytes and defined a deformation index directly from individual flowing erythrocytes. By appropriate choice of channel width and erythrocyte velocity, we could observe erythrocytes deforming to a parachute-like shape similar to that occurring in capillaries. The flowing erythrocytes magnified 200-fold through microscopy were recorded with an image-intensified high-speed video camera system. The sensitivity of deformability measurement was confirmed by comparing the deformation index in healthy controls with erythrocytes whose membranes were hardened by glutaraldehyde. We confirmed that the crystal microchannel system is a valuable tool for erythrocyte deformability measurement. Microangiopathy is a characteristic complication of diabetes mellitus. A decrease in erythrocyte deformability may be part of the cause of this complication. In order to identify the difference in erythrocyte deformability between control and diabetic erythrocytes, we measured erythrocyte deformability using transparent crystal microchannels and a high-speed video camera system. The deformability of diabetic erythrocytes was indeed measurably lower than that of erythrocytes in healthy controls. This result suggests that impaired deformability in diabetic erythrocytes can cause altered viscosity and increase the shear stress on the microvessel wall.

Adult↗
PubMed2001

Image analysis of quick phase eye movements in nystagmus with high-speed video system.

There are several methods of measuring horizontal, vertical and torsional nystagmus for the diagnosis of vertigo. Using Frentzel glasses, electronystagmography (ENG) and video-oculography (VOG) are common methods for observing nystagmus. In this study, a high-speed video camera is used to analyse high-speed eye movements, including three components of nystagmus, in order to monitor precisely the amplitude and velocity of the quick phase of nystagmus. To confirm the accuracy of the analysis, images of optokinetic nystagmus (OKN) evoked by a stimulating device were analysed. We obtained a high linearity with regard to the relation between the horizontal nystagmus amplitude detected with the high-speed video system and ENG (R2= 0.99). On comparison of the maximum velocities detected with 30Hz and with 250 Hz at each amplitude, the velocities calculated at 30Hz were smaller than those calculated at 250 Hz. At an amplitude of 5 degrees , the 30 Hz velocity decreased by 50%, while a decrease of 35% was observed at 15 degrees. The vertical nystagmus data obtained using high-speed VOG was different in appearance to that obtained using ENG. The torsional component of nystagmus was also measured, and was recorded in the form of a large number of sampling points.

Electronystagmography↗
PubMed2001

Circadian rhythm changes in heart rate variability during chronic sound stress.

To study the circadian rhythm changes of the heart rate variability (HRV) during chronic sound stress, Wistar rats were implanted with telemetry transmitters and exposed to chronic ultrasound stress for 14 days. The heart rate, mean R-R intervals (mean R-R) and body temperature were monitored hourly. The spectra of five-minute heart rate variability were plotted on a log-log scale of frequency versus power spectral density, and the spectral exponent beta of the regression line of this plot was calculated. The exponent beta, heart rate (HR) and body temperature recorded hourly were plotted and fitted to sine curves to observe the circadian rhythm of these parameters. The correlation coefficient of the fitted sine curves in beta decreased from 0.644 in the control period to 0.105 in the stress period, indicating that the rhythm of beta deceased during stress. This did not occur in the other two parameters, demonstrating that the HRV exponent can assess chronic stress.

Animals↗
PubMed2001

Facilitation of motor evoked potentials in the anterior tibial muscle by repetitive subthreshold electrical stimulation.

Subthreshold electrical stimulation with an intensity less than the threshold for evoking M-waves is applied repetitively to the common peroneal nerve via surface electrodes. The stimulation intensity is varied by adjusting the pulse width from 0 to 240 micros, while the pulse interval (40 ms) and current amplitude are kept constant. Single magnetic stimuli are applied to the motor cortex using a circular coil. Motor evoked potentials are recorded from the anterior tibial muscle in six normal subjects for various subthreshold stimulation intensities. Signal processing (filtering in the time and frequency domains) removes the artifact caused by the subthreshold electrical stimulation from the motor evoked potential. Statistically significant motor evoked potential facilitation (p < 0.05) is observed for pulse widths ranging from 72 to 240 micros in all the tested subjects. A pulse width corresponding to 90% of the electrical threshold facilitated the motor evoked potential in five of the six subjects.

Adult↗
PubMed2001

Characteristics of somatosensory feedback in postural control during standing.

In the present study, the function of the somatosensory feedback system in postural control was investigated. For the sake of simplicity, the present study considered only balancing in the anteroposterior direction using the ankle strategy, in which the ankle moment is mainly used to maintain balance. To suppress the vestibular and visual feedback paths, a subject stood on a force-measuring platform with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model that simulated the subject's load at the ankles. Information about the sway angle of the model was fed through the somatosensory feedback path. Frequency response functions of the ankle moment in response to the sway angle were calculated. The experimental results suggest that the human somatosensory feedback system has derivative characteristics and, consequently, can maintain an upright posture by itself. The results were compared with those of previous studies on vestibular and visual feedback systems. The comparison reveals that subject-to-subject variance in the somatosensory system is significantly smaller than that in the other systems. This may indicate that the somatosensory feedback is the most automatic of the systems and plays a dominant role when a subject maintains an upright posture using the ankle strategy.

Adult↗
PubMed2000

Image correlation method for measuring blood flow velocity in microcirculation: correlation 'window' simulation and in vivo image analysis.

To elucidate the function of the microcirculation system, it is very important to know the blood flow velocity and its distribution in the microvessels. We have developed an automated system for measuring blood flow velocity in microcirculation by image correlation. The 'window' in the image correlation method is equivalent to the sensors in various other measurement methods. We performed simulations with virtual blood flow images consisting of random dots before measuring actual ones, and examined the optimum window shape and size. We found that by reducing the size of a circular window to the size of erythrocytes we could measure in vivo blood flow images with high accuracy. We recorded them with a high-speed video camera system at high temporal resolution, and measured the velocity in microvessels of normal Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). SHR had higher blood velocity than WKY even though the vessel diameters were the same. Using this method to measure the blood flow velocity profile at the bent corner of SHR's arteriole at the heart systole, we found that erythrocytes flow faster at the inner side of the bend, so the vessel wall was exposed locally to higher shear stress in the hypertensive condition.

Animals↗
PubMed1999

Characteristics of visual feedback in postural control during standing.

In the present study, the visual feedback system in postural control was investigated. To suppress the vestibular and proprioceptive feedback paths, a subject stood on a force-measuring plate with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model which simulated body dynamics. Information on the sway angle of the model was fed visually. Under this condition, frequency response functions for the ankle moment in response to the sway angle were calculated. The experimental results suggest that the visual feedback system contains a large time delay and, consequently, the visual system does not by itself allow a subject to maintain an upright posture. Index Terms- Feedback control, frequency characteristics, identification, posture, visual sensory feedback.

Adult↗
PubMed1997

Nonlinearity identified by neural network models in Pco2 control system in humans.

The nonlinearity included in the PCO2 control system in humans is evaluated using the degree of nonlinearity based on a difference of residuals. An autoregressive moving average (ARMA) model and neural networks (linear and nonlinear) are employed to model the system, and three types of network (Jordan, Elman and fully interconnected) are compared. As the Jordan-type linear network cannot approximate respiratory data accurately, the other two types and the ARMA model are used for the evaluation of the nonlinearity. The results of the evaluation indicate that the linear assumption for the PCO2 control system is invalid for three subjects out of seven. In particular, strong nonlinearity was observed for two subjects.

Adult↗
PubMed1997

Autonomic differences between athletes and nonathletes: spectral analysis approach.

The purpose of this study was to assess the adaptive effects of endurance training on autonomic function in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 mL.min-1.kg-1) and 15 nonathletes (VO2max < 45 mL.min-1.kg-1) during 10 min at sitting position. Autonomic function was assessed by low frequency power (LF power: 0.06-0.14 Hz) and high frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. The HF power, an index of parasympathetic activity, in RR interval spectra were significantly higher in athletes than in nonathletes. Meanwhile, the LF power (an indicator of sympathetic activities contributing to RR interval and of ABP variabilities) showed no significant difference between both groups, although that of athletes was slightly less than that of nonathletes. Also, BRSLF and BRSHF were not significantly different between athletes and nonathletes. These results indicate that endurance training results in the enhanced vagal activities in athletes, which may contribute in part to the resting bradycardia.

Adult↗
PubMed1996

Fatigue evaluation of lumbar muscles during repeated dynamic trunk exercise.

Muscle fatigue in the lumbar muscles for five normal subjects was investigated during repeated dynamic trunk exercise using a lumbar extension machine which is designed to isolated lumbar extension functions. The electromyogram (EMG) signal from erector spinae muscles at lumbar 1 (L1), lumbar 3 (L3) and lumbar 5 (L5) spinal level was detected by bipolar Ag-AgCl surface electrodes. Subjects were required to perform one set of variable resistance lumbar extensions through a 72 degrees range of motion (ROM) with a weight load (50% maximal voluntary contraction) that allowed 13 repetitions of fatigue contraction. Median frequency (MF) of EMG power spectrum was analyzed to compare the difference of fatigability between each lumbar muscle. The experimental results indicated: 1) each lumbar muscle has characteristic MF, especially at the beginning of the trunk exercise (i.e., L1 = 86 Hz, L3 = 96 Hz and L5 = 106 Hz); 2) Significant differences (P < 0.001) in MF between the beginning and the end of trunk exercise for all lumbar muscle sites; 3) Significant differences in the decreasing ratios of MF between L1, L3 and L5. Based on the theory that the decreasing ratio of MF is proportional to fatigability, L5 was more fatiguable than L1 and L3.

Adult↗
PubMed1995

The power spectral analysis of heart rate variability in athletes during dynamic exercise--Part I.

In this study, the effects of long-term physical training on autonomic function in athletes and the response of the autonomic nervous system to dynamic exercise were investigated in nonathletes and athletes with power spectral analysis of heart rate variability (HRV). This study was performed on 13 healthy subjects (5 athletes and 8 non athletes). Electrocardiographic (ECG) signals were continuously recorded during (1) 15 min of rest in a sitting position on a bicycle ergometer, (2) the dynamic exercise test to the point of exhaustion, and (3) a 15 min postexercise period. After the recorded ECG signals were sampled at 500 samples/s, the instantaneous HRV signal was constructed from the detected R peaks and then resampled at 4 Hz in order to obtain an evenly spaced time series applicable to power spectral analysis. After linear trends were removed by the robust locally weighted regression algorithm, the power spectrum of HRV was estimated for contiguous records of 512 samples by Burg's maximum entrophy method. HRV was quantified by determining the spectral area (power) in two frequency bands, low-frequency power (LF power: 0.05-0.15 Hz) and high-frequency power (HF power: 0.15-0.8 Hz), and their ratio. The comparison between athletes and nonathlete was performed in terms of the above-mentioned parameters. Although both groups showed similar trends in heart rate (HR) at all stages of protocols, HR in athletes was significantly lower than that in nonathletes during rest and postexercise. In athletes and nonathletes, LF and HF powers gradually decreased with exercise. As recovery progressed, they continued to increase gradually, but remained below resting level. During rest and postexercise, HF power in athletes was significantly (p < 0.05) higher than than in nonathletes. Also, the recovery of HR and HF powers during early recovery (PO1) was more rapid in athletes than in nonathletes. Both groups showed an attenuation of LF and HF powers during dynamic exercise. It is likely that, in athletes, the lower HR during rest and the more rapid recovery of HR postexercise was due to a high level of HF power, indicating that vagal activity was enhanced by the adaptive changes in neural regulation produced by long-term physical training.

Adolescent↗
PubMed1995

Conversion of the rabbit gracilis muscle for transposition as a neoanal sphincter by electrical stimulation.

To re-establish anal function in fecally incontinent patients it may be feasible to transpose the gracilis muscle around the anal canal, using electrical stimulation to trigger contraction. However, because the fast-twitching gracilis muscle is incapable of prolonged contraction without fatigue, it is necessary to convert it to a slow-twitching, fatigue-resistant muscle. We demonstrated this conversion by longterm electrical stimulation at low frequencies using a rabbit model. The nerve to the gracilis muscle was continuously stimulated at 2 Hz, 5 Hz, and 10 Hz for 2, 4, or 6 weeks. In the 6-week conditioning group, the percentage of type I fibers, identified by ATPase staining, increased as the conditioning frequency became higher, but the twitch contraction speed reduced with conditioning at a frequency of more than 5 Hz. The fatigue resistance improved by conditioning at 10 Hz, and conversion occurred in 6 weeks. Thus, we concluded that conditioning at 10 Hz for 6 weeks can convert rabbit gracilis muscle to a slow-twitching, fatigue-resistant muscle suitable for use as a neoanal sphincter.

Anal Canal↗
PubMed1995

Assessment of training-induced autonomic adaptations in athletes with spectral analysis of cardiovascular variability signals.

The purpose of this study was to assess the adaptive effects of endurance training on autonomic functions in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 ml/(kg.min)) and 15 nonathletes (VO2max < 45 ml/(kg.min)) in the sitting position during controlled respiration (tidal volume 700 ml and 15 cycles/min). The autonomic functions were assessed by the normalized low-frequency power (LF power: 0.06-0.14 Hz) and high-frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of the RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity (BRS) was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between the RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. In the case of RR interval spectra, the HF power was significantly higher in athletes than in nonathletes, whereas the LF power was significantly lower in athletes than in nonahtletes. These differences might reflect an alteration of sympathovagal interaction with a predominance of parasympathetic activity. However, there was no significant difference in the LF power of SAP and DAP autospectra, reflecting the sympathetic vascular control. The BRSLF and BRSHF were significantly higher in athletes as compared with nonathletes. These results indicate that endurance training induces autonomic imbalance (i.e., the enhanced vagal activities/the attenuated sympathetic tone), which may in part contribute to the resting bradycardia and an increase in the spontaneous BRS in athletes.

Adaptation, Physiological↗