Ichiro Sakuma

A model analysis of aftereffects of high-intensity DC stimulation on action potential of ventricular muscle

The mechanism for aftereffects of high-intensity dc stimulation on ventricular muscle was studied by using Beeler-Reuters action potential model. A leak conductance (G/sub pore/ maximal value from 40 to 80 /spl mu/S for 1 cm/sup 2/ of membrane), which mimics reversible dielectric breakdown of the cell membrane by the shock, was incorporated into the model. To simulate resealing process, G/sub pore/ was assumed to decrease after the shock exponentially at a time constant (/spl tau//sub pore/) of 5-50 s. The simulation results are qualitatively consistent with the authors experimental observations in guinea pig papillary muscle (Amer. J. Physiol., vol. 267, p. H248-58, 1994); they include prolonged depolarization, diastolic depolarization or oscillation of membrane potential leading to a single or multiple spontaneous excitation. The phase-independence and shock intensity-dependence can also be reproduced. Analysis of current components has revealed that: (1) a large inward leak current (l/sub leak/) is responsible for the prolonged depolarization (2) time-dependent decay of outward current (I/sub X1/) in combination with I/sub leak/ and slow inward current (I/sub s/) results in diastolic depolarization or oscillation of membrane potential; (3) spontaneous excitation depends on an activation of I/sub s/. These findings support the authors hypothesis that strong shocks (>15 V/cm) will produce abnormal arrhythmogenic responses in ventricular muscle through a transient rupture of sarcolemmal membrane.

High-performance liquid chromatographic determination of catecholamine metabolites and 5-hydroxyindoleacetic acid in human urine using a mixed-mode column and an eight-channel electrode electrochemical detector

An HPLC system for the simultaneous determination of acidic catecholamine metabolites, related compounds and 5-hydroxyindoleacetic acid (5-HIAA) in human urine was developed. A mixed-mode (C18/anion-exchange) column with isocratic elution using citrate buffer and an eight-channel electrochemical detector were used. Vanilmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC), 4-hydroxy-3-methoxyphenyllactic acid (vanillactic acid, VLA), homovanillic acid (HVA), vanillic acid (VA) and 5-HIAA in urine were determined simultaneously. Detection limits and inter (n = 5) and intra-assay (n = 5) coefficients of variation were satisfactory. The mean of analytical recoveries (n = 3, +/- C.V. (%)) were between 97 +/- 3.2 (VMA) and 105 +/- 4.8 (VA). Correlations between the analytical results for VMA, HVA and 5-HIAA obtained by an established method and the present method were satisfactory. The mean +/- 2 S.D. of the excretion rates of VMA, DOPAC, VLA, HVA, 5-HIAA and VA in urine from healthy adult volunteers were 0.61-4.36, 0.13-1.02, 0-0.35, 0.67-6.55, 0.50-5.14 and 0-0.55 mg/g creatinine, respectively.

Acidic Catecholamine Metabolites and 5-Hydroxyindoleacetic Acid in Urine: The Influence of Diet

Concentrations of vanillylmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), vanillic acid (VA) and 5-hydroxyindoleacetic acid (5-HIAA) in urine from healthy subjects were determined by a high-performance liquid chromatography system with a mixed-mode (C18/ anion-exchange) column and an 8-channel electrochemical detector, in order to study the influence of diet, diurnal variation and age. The urinary excretion of 5-HIAA increased significantly after eating banana, pineapple, tomato, kiwi fruit and walnut. An increase in the urinary excretion of DOPAC and HVA after eating banana and that of VA after taking vanilla was also noted. The urinary excretion of VMA was not significantly influenced by any of the foods examined. The urinary excretion of 5-HIAA in the first-morning urine increased beyond the upper limit of the reference value when banana was taken at 2000 h the previous day. The excretion of all metabolites in the second-morning urine in the fasting state was within respective reference ranges. Diurnal variation of the excretion of VMA, DOPAC, HVA and 5-HIAA in urine was relatively small, but that of VA was large. The concentrations (mmol/mol creatinine) of VMA, DOPAC, HVA, 5-HIAA and VA in the first-morning urine from healthy subjects increased from 7 days after birth to 1 year and then decreased to adult levels at 13 years of age.

Regional Differences in Arrhythmogenic Aftereffects of High Intensity DC Stimulation in the Ventricles

Regional differences of the aftereffects of high intensity DC stimulation were investigated in isolated rabbit hearts stained with a voltage‐sensitive dye (di‐4‐ANEPPS). Optical action potential signals were recorded from the epicardial surface of the right and left ventricular free wall (RVep, LVep) and from the right endocardial surface of the interventricular septum (IVS). Ten‐millisecond monophasic DC stimulation (S2, 20–120 V) was applied to the signal recording spots during the early plateau phase of the action potential induced by basic stimuli (S1, 2.5 Hz). There was a linear relationship between S2 voltage and the S2 field intentisy (FI). S2 caused postshock additional depolarization. giving rise to a prolongation of the shocked action potential. With S2≥ 40 V (FI ≥≃20 V/cm), terminal repolarization of action potential was inhibited, and subsequent postshock S1 action potentials for 1–5 minutes were characterized by a decrease in the maximum diastolic potential and a decrease in the amplitude and a slowing of their upstroke phase. The higher the S2 voltage, the larger the aftereffects. The changes in postshock action potential configuration in RVep were significantly greater than those observed in LVep and IVS when compared at the same levels of S2 intensity. In RVep, 12 of 20 shocks of 120 V resulted in a prolonged refractoriness to S1 (> 1 s), and the arrest was often followed by oscillation of membrane potential. Ventricular tachycardia or fibrillation ensued from the oscillation in five cases. No such long arrest or serious arrhythmias were elicited in LVep and IVS. These results suggest that RVep is more susceptible than LVep and IVS for arrhythmogenic aftereffects of high intensity DC stimulation.

Arrhythmogenic changes in action potential configuration in the ventricle induced by DC shocks

Failure of defibrillation by direct current (DC) shocks is the result in part of new ventricular tachyarrhythmias induced by the shocks. We investigated the arrhythmogenic substrate produced by the shocks. Fluorescent action potential (AP) signals were recorded from rabbit hearts perfused in vitro with the use of our original optical recording system. Localized application of 10-ms shocks (S2) during the plateau phase of APs by basic stimuli (S1) caused field intensity (FI)-dependent changes in APs: (a) S2 > 7 V/cm caused additional depolarization, giving rise to a prolongation of AP duration (APD); (b) With S2 > 20 V/cm, terminal repolarization was inhibited, and subsequent postshock S1 APs for 1 to 5 min were characterized by decreases in the maximum diastolic potential and amplitude of APs; and (c) S2 > 30 V/cm often resulted in a prolonged refractoriness, oscillation of membrane potential leading to ventricular tachycardia or fibrillation (VT/VF). The right ventricle was more susceptible than other regions for the aftereffects of high-intensity shocks. Using an 8-channel recording system, we compared the effect of 10-ms monophasic (M) and 5/5-ms biphasic (B) shocks applied to the whole ventricles with FI of 1 to 20 V/cm at the signal recording sites. B shocks were less potent than M shocks in the FI-dependent action potential duration (APD) prolongation, and in the shock-induced enhancement of APD dispersion. Incidence and duration of VT/VF induced by M shocks were significantly greater than those by B shocks. These findings suggest that DC shocks will cause two types of arrhythmogenic substrate: one induced at sites of high FI, and the other at sites with moderate FI. The former would produce local block or focal repetitive excitation due to prolonged depolarization and oscillation of membrane potential, and the latter circuitous movement of wavefronts through an enhancement of spatial inhomogeneity of repolarization.

Resolution of unresolved peaks containing unknown components by high-performance liquid chromatography with multi-wavelength detection

Abstract A method for the resolution of unresolved peaks obtained by high-performance liquid chromatography with multi-wavelength detection was developed. The method estimates the elution profiles and absorption spectrum of a component eluting at the rising edge or trailing edge of the unresolved peak and estimates the relative intensity of the derived three-dimensional chromatogram of one component by rank annihilation. Artificial unresolved peaks and actual unresolved three-component peaks were resolved by the developed method. The results showed that the method can estimate peak area with errors of less than about 10% when the resolution R s of the components is greater than about 0.4. The accuracy of estimation is considered to be superior to that of the method based on principal component analysis followed by multiple regression analysis, especially if the elution profiles of components are distorted from a Gaussian shape such as with tailing, where the estimation of elution profiles by principal components analysis seems erroneous.

Study of Secondary Flow in Centrifugal Blood Pumps Using a Flow Visualization Method with a High‐Speed Video Camera

Four pump models with different vane configurations were evaluated with flow visualization techniques using a high-speed video camera. These models also were evaluated through in vivo hemolysis tests using bovine blood. The impeller having the greatest fluid velocity relative to the impeller, the largest velocity variance, and the most irregular local flow patterns in the flow passage caused the most hemolysis. Even if the pumps were operated at almost the same speed (rpm) at the same output, the impeller showing more irregular flow patterns had a statistically greater rate of hemolysis. This fact confirms that the existence of local irregular flow patterns in a centrifugal blood pump deteriorates its hemolytic performance. Thus, to optimize the design of the pump, it is very important to examine the secondary flow patterns in the centrifugal blood pump in detail using flow visualization with a high-speed video camera.

Development of an optical-fibre sensor using a functional membrane

Abstract A new functional membrane which changes its reflectance spectra according to the pH of the test solution is described. A chloromethylstyrene (CMS)/methylmethacrylate (MMA) copolymer was chosen as the base for the immobilized reagent. A basic ion-exchanger was then added to the CMS/MMA copolymer. Bromothymol Blue (BTB) was then immobilized on the copolymer. A functional membrane could then be fabricated in various shapes since chemical modification of CMS/MMA copolymer could be performed before casting. The fabricated pH sensitive functional membrane showed a maximum reflectance change at a wavelength of 540 nm for pH changes from 4.0 to 9.0. Dissolution of BTB from the CMS/MMA copolymer was minimal so that good reproducibility of the reflectance change was obtained.