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K Tamiya

Publications and source records attributed to K Tamiya.

At least 19 recordsLinked to original sources
PubMed1992

[Utility of intra-bladder pressure monitoring during closure of abdominal wall defects in newborn infants].

Recently, it was demonstrated that intra-bladder pressure (IBP) measured through a transurethral catheter accurately reflects intra-abdominal pressure (IAP). We monitored IBP during closure of abdominal wall defects in three newborn infants with gastroschisis. We were able to avoid complications due to increased IAP by keeping IBP below 20 mmHg. IBP correlated well with inferior vena cava pressure (r = 0.93) which reflects IAP. We advocate the use of IBP monitoring as a simple and reliable means of indirectly determining IAP during operations for closure of abdominal wall defects in newborn infants with omphalocele or gastroschisis.

Abdomen↗
PubMed1992

Role of the septal leaflet in tricuspid valve closure. Consideration for treatment of complete atrioventricular canal.

A septal leaflet of the tricuspid valve is thought to work differently from other anterior and posterior leaflets. We studied its role in valve closure in dogs by means of a dynamic area meter. During the control state, the tricuspid valve orifice area increased twice in diastole coincidentally with either atrial systole or rapid ventricular filling. We observed several findings after the septal leaflet resection: (1) two peak area patterns of the tricuspid valve orifice in diastole, (2) no elevation of right atrial pressure on ventricular systole (there was no V wave), (3) no tricuspid valve regurgitation on right ventriculography. These findings suggest that a complete valve closure occurred without the septal leaflet in regular sinus rhythm. An elevation of the right ventricular pressure produced by pulmonary artery stenosis without septal leaflet, however, easily caused tricuspid valve regurgitation in contrast to the same pressure of the right ventricle with the normal tricuspid valve. The right ventricular pacing caused severe valve regurgitation without the septal leaflet. Results indicate that in the repair of the complete atrioventricular canal defect and other tricuspid valve lesions, the septal leaflet of the tricuspid valve rarely requires attention. An atrioventricular block should be avoided, however, because electrical cardiac pacing on the right ventricle causes severe valve regurgitation without the septal leaflet.

Animals↗
PubMed1991

An in vivo area meter for real-time measurement of cross-sectional area in the cardiovascular system.

A direct real-time recording of the cross-sectional area of the heart valve is useful for the fluid dynamic study of the cardiovascular system. Electronic circuitry is described that is capable of driving the transmitter coil assembly placed outside the animal and detecting an area-related signal induced in the one-turn coil in vivo. When a piece of fine pliable metal thread encircles the area of interest (e.g. the mitral/aortic valve orifice) so as to form a single loop, the electrical potential between the ends of the loop is linearly related to the size of the area irrespective of its shape. The principle of measurement, construction of transmitter coil assembly, and simple but accurate direct calibration are also described.

Animals↗
PubMed1989

Real-time and simultaneous measurement of tricuspid orifice and tricuspid anulus areas in anesthetized dogs.

Tricuspid valve orifice and tricuspid valve anulus areas were measured simultaneously in the anesthetized dog with a newly developed area-measuring system based on electromagnetic induction. This system permitted real-time monitoring of the area enclosed by the edges of valve leaflets and by the juncture of the valve leaflet and the cardiac wall in situ, without artificial constraint to the valve motion. Right atrial and right ventricular pressures were measured with two catheter-tipped micromanometers. During control state, tricuspid valve orifice area (TOA) increased up to its peak [1.38 +/- 0.26 cm2 (mean +/- SD)] coincidently with either atrial systole or rapid ventricular filling. Atrial contraction evoked distinct presystolic tricuspid anulus narrowing with concomitant slow TOA reduction. This slow TOA reduction began 30.0 +/- 16.1 msec before systolic atrioventricular pressure crossover, and the following rapid TOA decrease was completed 38.7 +/- 12.2 msec after systolic atrioventricular pressure crossover. TOA began to increase 48.4 +/- 30.4 msec before diastolic atrioventricular pressure crossover at the end portion of the isovolumic relaxation phase, opposing residual transvalvular pressure gradient (3.33 +/- 1.79 mm Hg). The slow presystolic TOA decrease was considered to be a reflection of the presystolic anulus narrowing caused by atrial systole. An isolated atrial contraction induced by administering 1 mg acetylcholine chloride into the atrioventricular node artery or by vagus nerve stimulation could produce complete valve closure. Even in an isolated atrial contraction, the inflection point that marks the boundary between slow "atriogenic" closure presumably due to anulus narrowing and rapid closure presumably due to hemodynamic force was easily identified.

Animals↗
PubMed1989

[Experimental study on the optimal size of the tricuspid valve annular area on annuloplasty].

The optimal size of tricuspid valve annular area (TVAA) by annuloplasty for tricuspid regurgitation remains controversial. Recently, we developed a new measuring system which permits to do real-time measurement of tricuspid valve annular area in anesthetized dogs. Using this system, we studied the optimal size of TVAA by annuloplasty. After the right atrial incision, a metal thread which functions as a sense loop of the electromagnetic fields was stitched along the tricuspid valve annulus (visible juncture of the valve leaflets and the cardiac wall). The drive coil assembly was placed perpendicular to the extension of the long axis of the heart and was directed toward the tricuspid valve region. During control conditions, the maximum TVAA appeared at the onset of ventricular systole. The minimum TVAA appeared during the early ventricular diastolic phase which included the ventricular isovolumic relaxation phase. The maximum TVAA varied in five dogs between 2.2 cm2 and 3.1 cm2, the minimum TVAA also varied between 1.8 cm2 and 2.5 cm2: During regular sinus rhythm, a decrease of TVAA during one cardiac cycle ranged between 11.9% and 22.4% of the maximum size. When TVAA was not decreased by annuloplasty to the minimum area which was observed during cardiac cycle in the control state, the cardiac output and the right atrial pressure remained unchanged, because the ventricular filling was not obstructed. On the other hand, when TVAA was decreased smaller than this minimum area, the cardiac output decreased and the right atrial pressure rose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

In vitro analysis of performance of porcine xenografts with inward bending of stent posts: real-time measurement of valve orifice area using an area meter.

The influence of inward bending of the stent posts on bioprosthetic valve function was assessed in a hydromechanical simulation of the left heart. A Carpentier-Edwards mitral xenograft (31 mm) and an aortic xenograft (27 mm) were used. Valve function was evaluated before and after the stent posts were bent inward 15 degrees by suture constriction of the tops of the three posts. To evaluate the effects of the stent-post deformity on valve performance, the mean transvalvular pressure drop during steady flow, the bioprosthetic valve orifice area, and the maximum valve opening and closing speeds during pulsatile flow were measured using an area meter. Steady-flow data showed identical transvalvular pressure drops, and no significant difference in valve performance was detected in the pulsatile-flow study under the two experimental conditions (i.e., normal valve and deformed valve). We conclude that a 15-degree inward bending of the stent posts does not appreciably affect valve function in vitro.

Aortic Valve↗
PubMed1988

Real-time measurement of tricuspid valve annular area for annuloplasty. Experimental study.

We used real-time measurement of the tricuspid valve annular area in anesthetized dogs to study the optimal size of the annular area for annuloplasty. During control conditions, the maximum tricuspid annular area appeared at the onset of ventricular systole. The minimum tricuspid annular area appeared between the ventricular isovolumic relaxation phase and the early ventricular filling phase. The maximum annular area varied in seven dogs between 2.18 and 3.10 cm2, and the minimum annular area ranged between 1.68 and 2.45 cm2. In regular sinus rhythm (heart rates 97 to 120 beats/min), the maximal decreases in tricuspid annular area during one cardiac cycle ranged from 14.3% to 23.6% of the maximum size. When the tricuspid annular area after the annuloplasty was kept larger than the minimum area that was observed during the cardiac cycle in the control study, cardiac output and right atrial pressure remained unchanged, as a result of unobstructed ventricular filling. On the other hand, when the annular area was reduced to smaller than the minimum area seen in the control study, a decrease in cardiac output and an elevation of right atrial pressure ensued. These findings suggest that the tricuspid annular area can be safely decreased by annuloplasty to the minimum area seen in the control study without causing a reduction of cardiac output or an elevation of right atrial pressure.

Animals↗
PubMed1986

A new approach to defining regional work of the ventricle and evaluating regional cardiac function: mean wall stress-natural logarithm of reciprocal of wall thickness relationship.

A new method of defining regional mechanical work done by a unit volume of myocardium of the ventricular wall and evaluating regional cardiac function is proposed. This method uses the relationship between mean wall stress (sigma) and the natural logarithm of the reciprocal of wall thickness (ln(1/H)). 1/H at a point on the epicardial surface is proportional to the regional area (A) of the ventricular wall containing that point. The value for regional work obtained from the relationship between the sigma and ln A or sigma and ln(1/H) has a true dimension of work, i.e., [J/m3]. The sigma-ln(1/H) relationship was studied in ten anesthetized dogs. Wall thickness and internal diameter of the left ventricle were measured with ultrasonic dimension gauges. Regional work per unit volume of myocardium multiplied by the total myocardial volume of the left ventricle correlated well with the total mechanical work of the entire left ventricle calculated from the pressure-volume relationship during pressure loading, contractility change, and volume loading. During pressure loading, the end-systolic sigma-ln(1/H) relationship showed linearity. After bolus injection of isoproterenol the sigma-ln(1/H) loop shifted to the left. We concluded that the sigma-ln(1/H) relationship provides a method of characterizing regional function normalized to the unit volume of myocardium. In addition, our methods have a potential for echocardiographic application.

Animals↗
PubMed1986

Technique with lock-in amplifier for real-time measurement of tricuspid valve annulus area.

A new measuring system that permits real-time registration of the tricuspid valve annular area (TVA) using lock-in amplifier is devised and applied in open-chest anesthetized dogs. The tricuspid valve annulus was stitched with a fine, pliable, metal thread made of 10 30-micron urethane resin-coated copper wires during inflow occlusion. Both ends of the thread were guided out from the right atrium through a single pinhole in the right atrial wall. The signal intensity induced in the sense loop is linearly related to the area encircled by the thread, i.e., the area of the tricuspid annulus. During control state, TVA varied by an average of 24.5% (3.8-46.5%) of its maximum. Presystolic peak and valley of TVA due to atrial contraction and a decrease in TVA during ventricular ejection were generally observed. An increase in TVA during the initial portion of isovolumic contraction phase was prominent in dogs with filariasis, whereas in the other dogs it was not.

Acetylcholine↗
PubMed1985

Regional work of the ventricle: wall tension--area relation.

We clarified that the set of the isotropic component (T) of wall tension and the area (A) of a selected region of the left ventricular wall expresses the regional work with sufficient accuracy. The area surrounded by the locus of the T-A relation in the T-A plane is approximately equal to the real work done by that region. The behavior of the T-A loop was studied in nine anesthetized dogs under various conditions. The regional area and diameter of the left ventricle were measured with ultrasonic crystal pairs. The wall tension was calculated from measured left ventricular pressure and diameter by a generalized Laplace's equation for a thick-walled model. During volume loading, administration of methoxamine, and aortic constriction, the regional work per stroke increased with the increase in end-diastolic regional area, which is considered to be the regional Frank-Starling mechanism. With the development of ischemia, the T-A loop for the ischemic region shifted to the right and the work done by that region decreased. After a certain stage in the development of ischemia, the work done by the ischemic region became negative. When only one of the segmental lengths, rather than the area, is measured, difficulty arises in the physical interpretation of pressure-length or tension-length data in some cases. The T-A loop diagram resolves such difficulty by defining the regional work correctly. We conclude that the T-A loop diagram is a useful tool for analyzing the regional ventricular function.

Animals↗
PubMed1984

A mechanical model of mitral insufficiency using canine papillary muscle preparation.

A canine papillary muscle is loaded to mimic the load of the myocardium in the wall of the left ventricle with atrio-ventricular valvular insufficiency. This mechanical model which simulates the atrio-ventricular valvular regurgitation is based on two simple assumptions. The assumptions arranged for the papillary muscle experiment are as follows: 1) the force that the myocardium encounters during muscle shortening is proportional to the muscle shortening velocity due to regurgitation through a narrow regurgitant orifice; and 2) the myocardium exerts a constant force while the aortic valve is open. The muscle shortening except the isotonic phase is ascribed solely to regurgitation since the aortic valve is closed during these phases. In the combined antegrade/retrograde ejection phase, which is characterized by a constant muscle force, the shortening velocity due to regurgitation is constant because of the assumed functional relation between the muscle force and shortening velocity. The amount of shortening assigned to regurgitation in this phase is given by the product of the velocity at the beginning point of the isotonic phase and the duration of this phase. The present in-vitro studies offer an alternative explanation for decrease in the regurgitant fraction as total load was reduced at a constant preload. The regurgitant fraction decreased as preload was increased at a constant total load in the present study. The regurgitant fraction also decreased by either isoproterenol or CaCl2 administration via the coronary artery.

Animals↗
PubMed1984

[Contractility].

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Animals↗