Yasuhiro Fukui

Discrimination of walking patterns using wavelet-based fractal analysis

In this paper, we attempted to classify the acceleration signals for walking along a corridor and on stairs by using the wavelet-based fractal analysis method. In addition, the wavelet-based fractal analysis method was used to evaluate the gait of elderly subjects and patients with Parkinsons disease. The triaxial acceleration signals were measured close to the center of gravity of the body while the subject walked along a corridor and up and down stairs continuously. Signal measurements were recorded from 10 healthy young subjects and 11 elderly subjects. For comparison, two patients with Parkinsons disease participated in the level walking. The acceleration signal in each direction was decomposed to seven detailed signals at different wavelet scales by using the discrete wavelet transform. The variances of detailed signals at scales 7 to 1 were calculated. The fractal dimension of the acceleration signal was then estimated from the slope of the variance progression. The fractal dimensions were significantly different among the three types of walking for individual subjects (p < 0.01) and showed a high reproducibility. Our results suggest that the fractal dimensions are effective for classifying the walking types. Moreover, the fractal dimensions were significantly higher for the elderly subjects than for the young subjects (p < 0.01). For the patients with Parkinsons disease, the fractal dimensions tended to be higher than those of healthy subjects. These results suggest that the acceleration signals change into a more complex pattern with aging and with Parkinsons disease, and the fractal dimension can be used to evaluate the gait of elderly subjects and patients with Parkinsons disease.

Classification of waist-acceleration signals in a continuous walking record

We attempted to distinguish walking on level ground from walking on a stairway using waist acceleration signals. A triaxial accelerometer was fixed to the subjects waist and the three acceleration signals were recorded by a portable data logger at a sampling rate of 256 Hz. Twenty healthy male subjects were asked to walk through a corridor and up and down a stairway as a single sequence, without any instruction. The data were analyzed using discrete wavelet transform. Walking patterns were classified in two stages. In the first stage, the times when the walking pattern changed were detected using the low-frequency component of the anteroposterior acceleration (LF(A)) and of the vertical acceleration (LF(V)). In the second stage, the three types of walking patterns were classified by comparing powers of wavelet coefficients in the vertical direction (P(WCV)) and in the anteroposterior direction (RP(WCA)). Changes in walking patterns could be detected by using either LF(A) or LF(V). Walking down stairs could be distinguished from the other types of walking as it gave the largest value in P(WCV), and walking up stairs could be discriminated from level walking using RP(WCA). Level and stairway walking could be classified from continuous records of waist acceleration.

Phase composition of sputtered films from a hydroxyapatite target

Abstract Hydroxyapatite (HA) was coated onto a cellulose filter acting as a substrate from a crystalline HA powder target using radio-frequency magnetron sputtering at Ar pressure of 0.5–5.0 Pa and discharge power of 50–150 W. After coating, the films were heated to 700 °C to remove the substrate and the crystalline phases were identified using XRD. The Ca/P ratio of the films was analyzed using EDS. The films were composed of HA, β-tricalcium phosphate (TCP), β-calcium pyrophosphate (PYR) and CaO. The weight ratio of HA and the Ca/P ratio of the films decreased with increasing Ar pressure and were largest at 100 W of discharge power. After coating, the surface of the HA target was decomposed into α-TCP, β-TCP and CaO.

Classification of walking pattern using acceleration waveform in elderly people

We attempted to classify walking on level ground from walking on a stairway using a waist acceleration signal. A tri-axial accelerometer was fixed to the subjects waist and the three acceleration signals were recorded by a portable data logger at a sampling rate of 256 Hz. Eleven healthy, elderly subjects were asked to walk through a corridor and up and down a stairway as a single sequence, without any instruction. The data were analyzed using a discrete wavelet transform. Walking patterns were classified using two parameters; one was the ratio between the power of wavelet coefficients which were corresponded to locomotion and total power in the anteroposterior direction (RPA). The other was the ratio between root mean square of wavelet coefficients at the anteroposterior direction and that at the vertical direction (RAV). Walking up stairs could be distinguished by the smallest value in RPA from other walking patterns. Walking down stairs could be discriminated from level walking using RAV. It was possible to classify the walking pattern using acceleration signals in elderly people.

Interactions among ventilation, the circulation, and the uptake and distribution of halothane--use of a hybrid computer multiple model: I. The basic model.

The authors describe an 18-compartment hybrid computer multiple model of the uptake and distribution of halothane. This model uses 88 equations and 124 parameter settings. Three submodels are incorporated into the basic model: 1) The mass transport of halothane is simulated on the digital portion of the hybrid computer. 2) A breath-by-breath pulmonary model with two compartments describes air pressure-flow relations in the airway system. 3) A beat-to-beat cardiovascular model with 15 compartments describes in detail blood pressure-flow relations. In addition, a baroreceptor-heart rate loop is included: an increase in arterial pressure causes a decrease in heart rate. The slope of the baroreceptor response is progressively decreased by halothane until at 2 per cent there is no response.The model of halothane uptake and distribution is separate from the blood and air pressure-flow models, but is, in effect, driven by them. Myocardial “contractility” (stroke volume) and certain regional vascular resistances can be affected by the concentration of halothane in one or any proportion of any combination of three compartments: arterial blood (arteriolar concentration), cerebral gray matter, or myocardial. In turn, these factors significantly affect the uptake and distribution of halothane.The responses to three steady-state concentrations, as well as to a step change in concentration from 0 to 2 per cent, were examined. Twenty-four outputs were recorded, including halothane concentrations in ten compartments; myocardial “contractility”; left and right ventricular and right atrial pressures; cardiac output; stroke volume, R–R interval; and blood flows in six regions. Two variables—alveolar concentration of halothane and arterial blood pressure—were recorded during a step change of 0 to 5 per cent.The model describes the appropriate steady-state and dynamic cardiovascular responses to halothane. It also demonstrates the complex interrelationships among cardiac output, regional blood flow distribution, and the uptake and distribution of halothane. During step changes in halothane concentration, most of the responses occur early, a phenomenon also seen in man and goats.Thus, the model is useful not only for representing organ and tissue halothane concentrations, but also for gaining new insights into cardiovascular alterations produced by rapidly changing concentrations of halothane and into the complex interactions between the circulation and the uptake and distribution of halothane.

A functionally graded titanium/hydroxyapatite film obtained by sputtering.

A functionally graded film of titanium/hydroxyapatite (HA) was prepared on a titanium substrate using a radio frequency magnetron sputtering. The ratio of titanium to HA was controlled by moving the target shutter. The film was composed of five layers, with overall film thickness of 1 μm. The HA was concentrated close to the surface, while the titanium concentration increased with proximity to the substrate. The bonding strength between the film and the substrate was 15.2 MPa in a pull-out test and the critical load from a scratch test was 58.85 mN. The corresponding values of a pure HA sputtered film were 8.0 MPa and 38.47 mN, respectively. The bonding strength of a pure HA plasma spray coating was 10.4 MPa in the pull-out test. The graded film and the pure HA film were sputter-coated to a thickness of 1 μm on titanium columns (10 mm in length and 4 mm in diameter). These columns were implanted in diaphyses of the femora of six adult dogs and a push-out test was carried out after 2, 4, and 12 weeks. After 12 weeks, the push-out strengths of the graded film, the pure HA film and the non-coated columns were 3.7, 3.5, and 1.0 MPa.

Automatic control in anesthesia: a comparison in performance between the anesthetist and the machine.

This report is divided into two parts. First, we developed two new servo control systems by modifying an existing one. The original system was designed to control inspired halothane concentration using mean arterial pressure; the two new systems were designed to control inspired halothane concentration using end-tidal concentration or to control mean arterial pressure using the automated infusion of nitroprusside. Second, we compared the performance of each of the three systems against the performance of experienced physician and nurse anesthetists (nine, six, and six experiments, respectively). The experiments incorporated a standardized testing sequence of two changes in desired blood pressure (set point) and two pharmacologically induced disturbances in blood pressure (perturbations). The scoring was designed to examine how fast blood pressure changed (90% response time), how far past the set point it went (overshoot), how long it took to eliminate most of the fluctuations in blood pressure (settling time), and the degree of fluctuation of blood pressure after settling (stability). Given three systems to be tested, there were (3 × 14) 42 possible mean scores for the machine and 42 for the anesthetists. The machine scored better than the anesthetists in 38 out of 42 of the mean scores; the differences were statistically significant in 19 out of 42 scores. The wide scatter in performances of the anesthetists prevented the achievement of significance in nine cases with large differences between means. Thus when the scores from the three systems were combined to achieve a larger n value, the machine outperformed the anesthetist in 12 out of 14 scores. We concluded that systems such as these could assume certain discrete tasks of the anesthetist, much as the mechanical ventilator has, and possibly perform better than anesthetists in these tasks.

Improved blood compatibility of DLC coated polymeric material.

There is currently an increasing interest in the use of DLC (diamond like carbon) films in biomedical applications. These investigations making use of DLC in the biomedical area indicate its attractive properties. In this study, we succeeded in depositing DLC on polymer substrates and found the best conditions and method for this application. We evaluated the blood compatibility of polycarbonate substrates coated by DLC (PC-DLC) under different conditions by using epifluorescent video microscopy (EVM) combined with a parallel plate flow chamber. Segmented polyurethane (SPU), which has been used to fabricate medical devices including an artificial heart, and proven to have acceptable blood compatibility, was compared with polycarbonate substrates coated with DLC film. The EVM system measured platelet adhesion on the surface of the DLC, by using whole human blood containing Mepacrine labeled platelets perfuse at a wall shear rate of 100 s-1 at 1 min intervals for a period of 20 min. PC-DLC demonstrated that Tecoflex showed higher complement activation than PC-DLC. There were significant differences between the PC-DLC substrates. On the basis of these results, it is recommended for use as a coating material in implantable blood contacting devices such as artificial hearts, pacemakers, and other devices. This DLC seems to be a promising candidate for biomaterials applications and merits further investigation.

An investigation of blood flow behavior and hemolysis in artificial organs

In our previous study, in vitro hemolysis tests showed that collision flow against wall roughness had an effect on hemolysis when the flow velocity was more than 3 m/s and surface roughness was more than Ra = 1.54 &mgr;m. However, the specific portion of the flow on the wall that induced hemolysis was not clarified.Therefore, the purpose of this study was to present the relationship between flow behavior and hemolysis by means of in vitro tests and computational fluid dynamics (CFD) analysis. We investigated the relationship between the location of surface roughness and hemolysis. In CFD, we investigated the flow behavior on the wall. The highest rate of hemolysis was observed in a region around the center of the surface roughness on the bottom plate. On CFD analyses, the flow behavior included the highest wall shear stress (304 Pa) and the highest flow acceleration (2.8 m/s2) around the center of the bottom plate. Therefore, it is concluded that the causes of hemolysis during collision flow depend upon wall shear stress and flow acceleration.

A dynamic action potential model analysis of shock-induced aftereffects in ventricular muscle by reversible breakdown of cell membrane

To elucidate the subcellular mechanism underlying the aftereffects of high-intensity dc shocks, a small pore, which mimics reversible breakdown of the cell membrane (electroporation), was incorporated into the phase-2 Luo-Rudy (L-R) model of ventricular action potentials. The pore size was set to occupy 0.15%-0.25% of the total cell membrane during the 10-ms shock. The pore was assumed to decrease after the shock exponentially with a time constant of 100-1400 ms to simulate resealing process. In normal myocytes, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by prolonged depolarization and oscillation of membrane potential like early afterdepolarization (EAD). Time- and voltage-dependent changes in the delayed rectifier K/sup +/ currents (I/sub Kr/, I/sub Ks/) in combination with those of L-type Ca/sup 2+/ current (I/sub Ca/, /sub (L)/) and ion flux through the pore (I/sub pore/) are responsible for the potential changes. Spontaneous excitation from the oscillation depends on activation of I/sub Ca, (L)/. In myocytes overloaded with Na/sup +/ and Ca/sup 2+/ secondary to 90% inhibition of Na/sup +/-K/sup +/ pump, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by slower cyclic depolarization in response to spontaneous release of Ca/sup 2+/ from the sarcoplasmic reticulum (SR). This delayed after depolarization-type oscillation is abolished by complete block of Ca/sup 2+/ release from the SR. These findings suggest that high-intensity electric field application will cause arrhythmogenic responses through a transient rupture of sarcolemma. with different subcellular events in ventricular cells under normal and pathological conditions.