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Biomedical subjects

W Matsuura

Publications and source records attributed to W Matsuura.

8 recordsLinked to original sources
PubMed2004

Mechanical behavior of bioactive composite cements consisting of resin and glass-ceramic powder in a simulated body fluid: effect of silane coupling agent.

Time-dependent strength behavior was investigated for bisphenol-a-glycidyl methacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) resin cements combined with glass-ceramic A-W filler treated with various kinds of silane coupling agents. The fracture strength of the composite resin cements was measured by three-point bending as a function of stressing rate in a simulated body fluid (SBF), and thereby the stress-corrosion susceptibility constant was evaluated. The fracture strength was found to depend on the kind of coupling agent used. For the present Bis-GMA/TEGDMA resin, the silane coupling agents without hydrophilic amine groups can be used to obtain good adhesion between resin and A-W filler owing to their nature of co-polymerizing with the resin. On the other hand, all the composite resin cements showed nearly the same degree of stress-corrosion susceptibility whether the A-W fillers were treated or untreated with silane coupling agents. This means that the stress-corrosion susceptibility of the present composite cements is predominantly affected by that of the matrix resin. Thus, the microcrack formation and growth at the resin matrix near particle - resin interface were thought to determine overall time-dependent strength behavior of the composite cements.

Biocompatible Materials↗
PubMed1999

Development of a servo-controller of heart rate using a cycle ergometer.

In exercise training, precise control of exercise intensity would maximize the training efficacy while minimizing risks. To adjust work rate, heart rate (HR) has been used as a measure of exercise intensity. Thus, we developed a servo-controller of HR using a cycle ergometer. After estimating the transfer function from work rate to HR, we optimized feedback parameters for achieving a quick and stable HR response by means of a computer simulation. We then examined the performance of the servo-controller of HR in 55 healthy volunteers. We set the target HR at 60% and 75% of the age-predicted maximum HR. Times required for HR to reach 90% of the target HR were 136 +/- 33 and 137 +/-22s in the respective protocols. Standard deviations of the steady-state difference between the target and measured HRs were 2.5 +/- 0.6 and 3.8 +/- 1.1 beats/min. We conclude that the developed servo-controller makes it possible to precisely regulate HR and, thereby, exercise intensity.

Adult↗
PubMed1999

Novel method to estimate ventricular contractility using intraventricular pulse wave velocity.

We developed a novel technique for estimating ventricular contractility using intraventricular pulse wave velocity (PWV). In eight isolated, cross-circulated canine hearts, we used a fast servo pump to inject a volume pulse into the base of the left ventricular chamber at late diastole and at late systole. We measured the transit time of the volume pulse wave as it traversed the distance from base to apex and calculated the intraventricular PWV. The intraventricular PWV increased from diastole (2.3 +/- 0.4 m/s) to systole (11.7 +/- 2.4 m/s, P < 0.0001 vs. diastole). The square of the intraventricular PWV at late systole correlated linearly with the left ventricular end-systolic elastance (r = 0.939, P < 0.0001) and with the end-systolic Young's modulus (r = 0.901, P < 0.0001). Moreover, the intraventricular PWV was insensitive to preload. We conclude that the intraventricular PWV at late systole reflects left ventricular end-systolic elastance reasonably well. The fact that estimation of PWV does not require volume measurement or load manipulation makes this technique an attractive means of assessing ventricular contractility.

Animals↗
PubMed1998

A new method to measure regional myocardial time-varying elastance using minute vibration.

We developed a new technique to evaluate regional myocardial elastance using minute vibration. In 13 isolated cross-circulated canine hearts, we applied small sinusoidal vibrations of displacement to the left ventricular surface at various frequencies (50-100 Hz). Using the measured displacement and force between the vibrator head and myocardium, we derived myocardial elastance on the basis of the equation of motion for a given moment of the cardiac cycle. Simultaneous solution of the equations of motion at different frequencies yielded a unique value of elastance. Time-varying myocardial elastance increased from diastole (0.028 +/- 0.211 x 10(6) dyn/cm) to systole (0.833 +/- 0.391 x 10(6) dyn/cm). The end-systolic elastance (ees) linearly correlated with end-systolic left ventricular elastance (r = 0.717, P < 0.001) and also with the end-systolic Young's modulus (r = 0.874, P < 0.0001). We also measured ees at both ischemic and nonischemic regions during coronary occlusion. Young's modulus, estimated by normalizing ees by the wall thickness and by the estimated mass, did not change significantly at the nonischemic regions, whereas it decreased significantly from 2.303 +/- 0.556 to 1.173 +/- 0.370 x 10(6) dyn/cm2 at the ischemic region after coronary occlusion (P < 0.005). We conclude that this technique is useful for the quantitative assessment of regional myocardial elastance.

Animals↗
PubMed1997

Vagal stimulation decreases left ventricular contractility mainly through negative chronotropic effect.

Although an increase in vagal tone is known to slow heart rate (HR), whether it also depresses left ventricular contractility through mechanisms independent of the bradycardic effect remains unknown. The chief aim of this investigation, therefore, was the separation of the observed vagally mediated depression of ventricular contractility into direct and indirect vagal effects, the latter resulting via negative chronotropism. In 12 anesthetized, sympathectomized open-chest rabbits, we measured left ventricular contractility through determination of the end-systolic elastance (Ees). We found that tonic vagal stimulation administered at 0, 5, and 10 Hz decreased both HR (226.9 +/- 39.7, 201.9 +/- 25.7, and 171.3 +/- 18.5 beats/min, respectively; P = 0.0003) and Ees (109.5 +/- 25.7, 85.1 +/- 34.1, and 71.9 +/- 33.1 mmHg/ml, respectively; P = 5 x 10(-6)) in a frequency-dependent fashion. However, we observed that as long as HR was kept constant through fixed-rate atrial pacing, vagal stimulation resulted in little or no change in Ees. Thus we conclude that the negative inotropic effect of vagal stimulation is attributable primarily to its negative chronotropic effect when sympathetic tone is minimal.

Animals↗
PubMed1996

Neural arc of baroreflex optimizes dynamic pressure regulation in achieving both stability and quickness.

The baroreflex loop consists of a fast neural arc and a slow mechanical arc. We hypothesized that the neural baroreflex arc compensates the slow mechanical response and thus improves the quality of blood pressure regulation. We estimated the open-loop transfer characteristics of the neural baroreflex arc (HP), i.e., from carotid sinus pressure to sympathetic nerve activity (SNA), and that of the effective peripheral baroreflex arc (Hp), i.e., from SNA to arterial pressure, in anesthetized rabbits. The gain of Hn was constant below 0.12 +/- 0.057 Hz and increased with a slope of 6.1 +/- 0.06 dB/octave above its frequency up to 1 Hz. In contrast, the gain of Hp was constant below 0.071 +/- 0.03 Hz and decreased with a slope of -11.0 +/- 1.48 dB/octave above the frequency. These data indicate that Hn accelerates slow peripheral responses in the frequency range of 0.1-1 Hz. Although too much acceleration in the high-frequency range could result in instability of the system, numerical analysis of the closed-loop baroreflex response indicated that the neural arc optimized arterial pressure regulation in achieving both stability and quickness.

Animals↗