Biomedical subjects

Tsuyoshi Koga

Publications and source records attributed to Tsuyoshi Koga.

7 recordsLinked to original sources

PubMed2006

Fetal aortic distension waveforms for evaluating cardiac function and changes in blood pressure: fetal lamb validation.

AIM: To investigate which part of the fetal aortic distension waveform is mainly influenced by changes in fetal cardiac contractility and aortic blood pressure. METHODS: In acute preparation, aortic distension waveforms were recorded using an echo-tracking system, and aortic and left ventricular pressure waveforms were obtained from six late-gestation catheterized fetal lambs. Dobutamine and angiotensin II were separately infused and the correlations between the maximum value in the first derivative of left ventricle pressure waveforms (Max dP/dt) and fetal blood pressure, and the parameters obtained from aortic distension waveforms were analyzed using linear regression analysis. RESULTS: With a change in cardiac contractility, the maximum value of first derivative of the systolic rising slope in the aortic distension waveform had a positive correlation with Max dP/dt (r = 0.93, P < 0.0001). With changes in fetal blood pressure, both the amplitude and the ratio of increase from the end diastolic diameter obtained from the aortic distension waveform had a significant positive correlation with aortic blood pressure amplitude (r = 0.60, P < 0.01; r = 0.61, P < 0.01, respectively). CONCLUSION: The maximum first derivative of the systolic rising slope in the aortic distension waveform and the amplitude in the aortic distension waveform enable us to non-invasively substitute for fetal cardiac contractility and aortic blood pressure amplitude, respectively.

Animals↗

PubMed2005

Multicanonical Monte Carlo simulations on intramolecular micelle formation in copolymers.

The formation of intramolecular micelles in copolymers with periodic sequence, where hydrophobic units (stickers) are periodically placed along the chain, is studied by using multicanonical Monte Carlo computer simulations for an off-lattice bead-rod model in three dimensions. With decreasing the temperature, a transition from random-coil conformations to micelles occurs and flower-type micelles are formed via the transition. The number of stickers forming a micelle core is limited by the excluded-volume effect of loop chains around micelle cores. By this effect, two intramolecular micelles are formed for long polymer chains with 60 bonds via the coil-to-micelle transition. By further decreasing the temperature, we find that another transition, i.e., a micelle-to-micelle transition, takes place. At this transition point, the two intramolecular micelles merge into one micelle. Furthermore, we extend the multicanonical MC method to study elastic properties of single polymer chains with strong attractive interactions under external force fields, and study how the intramolecular micellization affects the elastic property of single polymer chains.

Binding Sites↗

PubMed2005

Noninvasive measurement of isovolumetric contraction time during hypoxemia and acidemia: Fetal lamb validation as an index of cardiac contractility.

OBJECTIVES: The objectives of this study are firstly to clarify how the Doppler isovolumetric contraction time (ICT) is influenced by arterial oxygen pressure (PaO2) or pH, and secondly to confirm the relationship between the Doppler ICT and myocardial contractility during hypoxemia and/or acidemia in the fetal lamb. MATERIAL AND METHODS: In 12 pregnant ewes, fetal hypoxemia and acidemia were induced by giving ewes a variable mixture of gases for 120 min. The chronological change of fetal PaO2, pH, Doppler ICT and maximum first derivative of the left ventricular pressure waveform (Max dp/dt) was recorded every 30 min. RESULTS: Doppler ICT and PaO2 had no significant regression. On the other hand, Doppler ICT and pH demonstrated a significant negative regression. Moreover, one critical given pH point was indicated with statistical significance at 7.20 and the prolongation of the Doppler ICT was found more markedly in the range below the pH of 7.20 compared with the range above 7.20. A significant negative linear regression was found between the Doppler ICT and the Max dp/dt. CONCLUSION: The measurement of Doppler ICT enables us to predict severe acidosis and a decrease of myocardial contractility in the fetus.

Acidosis↗

PubMed2004

Jamming concepts in cold polymeric glasses.

The purpose of the present paper is to propose an idea to construct the volume function W for polymer glasses and calculate the volume of polymer glasses as a function of the compactivity X utilizing a statistical-mechanical method developed for semiflexible polymers. We also discuss the analogue for glasses of "tapping" experiments which show the validity of statistical mechanics and the entropy concept in powders.

Journal Article↗

PubMed2004

Prenatal diagnosis of slow-rate ventricular tachycardia using fetal electrocardiography.

OBJECTIVES: We report a case in which fetal ventricular tachycardia (VT) could be diagnosed, in utero, using a transabdominal fetal electrocardiogram (fECG) with motion-mode (M-mode) echocardiography. METHODS: The fetus was referred at 32 weeks' gestation due to tricuspid atresia. The fetal cardiotocogram demonstrated paroxysmal tachycardia with a ventricular rate of 155 to 160 bpm within the confines of normal sinus rhythm. RESULTS: M-mode echocardiography showed atrioventricular dissociation with a rather slow ventricular rate. To identify the level of the ectopic focus for tachyarrhythmias, we attempted to detect the electrical signals of the fetal heart and succeeded in recording the fECG. Morphological assessment of the fECG allowed for the extraction of both the normal QRS complex and apparently dissimilar ectopic QRS beat, which has a different polarity despite a relatively similar width. CONCLUSION: Consequently, the case proved to have VT at a slow rate, probably originating from the focus near the atrioventricular junction inside the ventricle.

Adult↗

PubMed2003

A new ultrasound technique to measure the isovolumetric contraction time as an index of cardiac contractility: fetal lamb validation.

OBJECTIVE: We developed a noninvasive Doppler technique for measuring fetal cardiac isovolumetric contraction time (ICT). The purpose of this study was to determine how well our method reflects real cardiac performance using fetal lamb as an instrumented model. METHODS: The true ICT was measured by simultaneous recording of the pressure waves of the left ventricle and ascending aorta. The maximum first derivative of the left ventricular pressure wave (Max dp/dt) was calculated. The Doppler ICT was measured in the appropriately filtered Doppler cardiac signals. Positive and negative inotropic agents were administered to change the cardiac contractility. RESULTS: There was an inverse relationship between the Doppler ICT and the Max dp/dt. Excellent linear correlation was found an absolute value and changes from control value between the true ICT and the Doppler ICT (r = 0.959, r = 0.962). CONCLUSIONS: The Doppler ICT measurement provides useful information about changes in ventricular performance.

Adrenergic beta-Antagonists↗

PubMed2002

Aortic pulse waveforms for evaluating cardiac performance in the human fetus.

Pulse waveforms of the fetal descending aorta were obtained using an echo-tracking system to clarify the gestational age-related changes and the usefulness for detecting cardiac dysfunction. Peak systolic (PSD) and end diastolic diameter (EDD), pulse amplitude (Amp) and Amp:EDD ratio, calculated from the pulse waveforms, were adopted for analysis. In 196 normal fetuses after 20 weeks, the PSD, EDD and Amp increased, and Amp:EDD ratio decreased linearly with advancing gestation. The 19 fetuses with suspected cardiac dysfunction were divided into healthy and altered cardiac function subgroups, according to the values of fractional shortening and preload index. Of these, 7 fetuses with cardiac dysfunction had significantly higher incidence of low Amp (p < 0.01) and Amp:EDD ratio (p < 0.001) than remaining 12 fetuses with normal cardiac function. The pulse waveform analysis in the fetal descending aorta proved useful for detecting fetal cardiac dysfunction in utero.

Aorta, Thoracic↗