Two-dimensional echocardiography and magnetic resonance imaging in diagnosis of idiopathic dilation of the right atrium.
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Adult↗
Biomedical subjects
K Miyaguchi
Publications and source records attributed to K Miyaguchi.
[Determinants of left ventricular inflow: the relation of the transmitral velocity profile to loading conditions].
To clarify the factors controlling left ventricular inflow, hemodynamics and Doppler-derived indices were analyzed in six anesthetized open-chest dogs with intact pericardia. Low molecular dextran was intravenously infused at 1 L/hr. During rapid infusion, an electrocardiographic lead, left ventricular pressure curve, and a transmitral Doppler signal were recorded at various heart rates produced by right atrial pacing. In five of the six dogs, the relationship of the ratio of peak velocity during atrial contraction to that during rapid filling (A/R) and left ventricular end-diastolic pressure (LVEDP) showed a non-linear quadratic curve concave to the LVEDP axis. Data from the ascending and descending limbs of the A/R-LVEDP relationship were subjected to stepwise multiple linear regression analysis (criterion variables: A/R; explanatory variables: peak dP/dt, maximum left ventricular pressure, time constant T, minimum left ventricular pressure, LVEDP, and heart rate). In both limbs, the A/R correlated positively with maximum left ventricular pressure (left ventricular afterload) and negatively with LVEDP (left ventricular preload). The time constant T was selected as a positive correlate only in the ascending limb. The transmitral flow velocity profile is determined in a complex manner by multiple factors, including left ventricular loading conditions and heart rate, as well as the left ventricular diastolic property. It was suggested that the A/R is not altered unidirectionally by the changes in cardiac function and loading conditions, but that it returns to the initial value accompanied by systolic and diastolic cardiac dysfunction.
Animals↗
Evaluation by exercise Doppler echocardiography of maintenance of cardiac output during ventricular pacing with or without chronotropic response.
To examine the effectiveness of activity-initiated rate-responsive pacing, this study assessed the increases in stroke volume and cardiac output during randomized treadmill exercise in rate-responsive and fixed-rate ventricular (VVI) pacing in 10 patients. Stroke volume index and cardiac index were determined by suprasternal Doppler measurements. Compared with the findings during VVI pacing, the rate-responsive pacing was associated with (1) prolongation of exercise duration (8.0 +/- 4.0 vs 7.3 +/- 3.6 minutes, p less than 0.05); (2) greater exercise-induced positive chronotropic response (mean maximal heart rate 127 +/- 12 vs 78 +/- 15 beats/min, p less than 0.001); (3) smaller increase in stroke volume index (38 +/- 10 vs 50 +/- 11 ml/m2, p less than 0.001), and (4) greater increase in cardiac index (4.7 +/- 1.1 vs 3.9 +/- 1.0 liters/min/m2, p less than 0.001). A significant correlation was observed between age and percent increase in stroke volume index during VVI pacing (p less than 0.05). These findings indicate that VVI pacing increased stroke volume more than did rate-responsive pacing, especially in younger patients, but the increase in cardiac output was less than that seen with rate-responsive pacing due to the absence of chronotropic response. Accordingly, an activity-sensing, rate-responsive pacemaker can effectively increase the heart rate, significantly augment cardiac output and extend the duration of exercise.
Adult↗
[Hemodynamic study of negative pressure ventilation using diaphragm pacing].
A negative pressure ventilation (NPV) by unilateral or bilateral diaphragm pacing (DP) was prepared for canine experiments. A shift from positive pressure ventilation (PPV) to NPV resulted in elevation of mean aortic pressure, increase in stroke volume and depression of mean pulmonary arterial pressure. Examination of the interaction between respiratory cycle and cardiac function during PPV, disclosed a reduction of right ventricular stroke volume and elevation of mean aortic and right ventricular end-diastolic pressure at end inspiration, compared to those at end expiration. During NPV with DP, left ventricular stroke volume, heart rate and mean aortic pressure were increased immediately after DP (immediately after inspiration) compared to those at end expiration. The experimental model of DP, in which respiratory condition could be easily altered, was considered to be useful to evaluate the effect of NPV on cardiac function.
Animals↗
Effects of diltiazem on left ventricular diastolic behavior in patients with hypertrophic cardiomyopathy: evaluation with exercise pulsed Doppler echocardiography.
To estimate the effects of diltiazem on the left ventricular diastolic abnormalities in patients with hypertrophic cardiomyopathy, transmitral flow velocity during diastole was studied before and immediately after dynamic leg exercise with the pulsed Doppler technique combined with two-dimensional echocardiography. Seventeen patients with hypertrophic cardiomyopathy and 24 apparently healthy men performed bicycle ergometer exercise in the supine position with the target heart rate set at 120 beats/min. The patients with cardiomyopathy were directed to perform the exercise at the same intensity after receiving 30 to 60 mg of diltiazem, three times daily, for 1 or 2 weeks. The pattern of transmitral flow velocity in diastole had two components, one corresponding to the rapid filling phase in early diastole and the other to the atrial contraction phase in late diastole. To assess left ventricular diastolic behavior, the following variables were analyzed: peak velocity in the rapid filling and atrial contraction phases, the ratio of peak velocity in the atrial contraction phase to that in the rapid filling phase, and pressure half-time. The changes in peak velocity in the atrial contraction phase, pressure half-time and the ratio of peak velocity in the atrial contraction phase to that in the rapid filling phase with exercise differed significantly between patients with hypertrophic cardiomyopathy with no medication and control subjects. After diltiazem, the response of these variables to exercise was almost identical in the two groups. These results suggest that diltiazem can lessen the left ventricular diastolic abnormality in patients with hypertrophic cardiomyopathy on dynamic exercise of mild intensity.
Adult↗
[The effects of nicardipine on hemodynamics, regional myocardial function and myocardial metabolism in the dog with coronary artery occlusion].
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Animals↗
High-performance liquid chromatography followed by peroxyoxalate chemiluminescence detection of acetylcholine and choline utilizing immobilized enzymes.
A sensitive and selective method for the simultaneous determination of acetylcholine (ACh) and choline (Ch) is reported. ACh and Ch were separated on a reversed-phase column, passed through an immobilized enzymes (acetylcholine esterase and choline oxidase) column, and converted to hydrogen peroxide. The generated hydrogen peroxide was detected by the peroxyoxalate chemiluminescence reaction. The linear determination ranges were from 10 pmol to 10 nmol. The detection limit for both cholines was 1 pmol.
Acetylcholine↗
Evaluation of left atrial rhythm with pulsed Doppler echocardiography.
To evaluate the origin of ectopic atrial rhythms, the beginning of atrioventricular inflow due to left and right atrial ejection was estimated using the pulsed Doppler combined with two-dimensional echocardiography. In ten normal controls, the beginning of transtricuspid flow due to atrial ejection preceded that of transmitral by 0 to 40 msec with an average of 22 msec. In contrast, the beginning of right atrial ejection flow lagged behind that of left atrial by 40 to 80 msec in case 1 and by 20 to 50 msec in case 2 of ectopic atrial rhythm. The significant delay of atrioventricular inflow due to right atrial ejection in these two patients strongly suggests that the ectopic atrial rhythm is of left atrial origin. The pulsed Doppler echocardiography is considered to be a useful clinical tool for noninvasive evaluation of the left atrial rhythm.
Adult↗
Direct visualization of a transmembrane channel associated with ribosomes.
Examination of directly frozen rough endoplasmic reticulum (ER) of retinal pigment epithelial cells by freeze-fracture and freeze-substitution revealed distinct paired transmembrane proteins associated with membrane ribosomes. Ribosomal subunits on intact ER membrane are directly visualized for the first time, providing a global view of the structure of the ribosome and the corresponding structures on the ER membrane. The ribosomal intersubunit cleft appears to be continuous with a cleft between paired transmembrane proteins that extends into the lumen of the ER. This continuous cleft may be the path taken by nascent polypeptides.
Animals↗