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Biomedical subjects

Y Koiwa

Publications and source records attributed to Y Koiwa.

46 records · Page 3Linked to original sources
PubMed1983

Assessment of the magnitude of aortic regurgitation by dye injection into the descending aorta.

A technique simpler than the angiographic method for estimating aortic regurgitant volume was tried with 31 patients with aortic insufficiency. During cardiac catheterization, we injected dye into the descending aorta while recording the dye dilution curve in the left ear. The distance between the aortic arch and the tip of the catheter at the lowest point from which the injected dye could be detected in the left ear was rated in terms of the number of corresponding vertebral bodies. This "distance score" closely correlated with the regurgitant stroke volume and with the fraction to total stroke volume, which were measured by angiocardiography (r = 0.927, p less than 0.001; and r = 0.900, p less than 0.001, respectively). The correlation coefficients of the aortographic grade to those parameters were not as high as they were in the relationship of the score to the same parameters. Therefore, these results indicate that the "distance score" is a practical method for assessing the magnitude of aortic regurgitant volume.

Adolescent↗
PubMed1982

A comparison of left ventricular volume-pressure relations of excised perfused canine hearts in isovolumic contraction, arrest and fibrillation.

The purpose of the present investigation was to study the effects of various conditions such as beating, arrest and fibrillation on left ventricular (LV) diastolic compliance. In coronary-arterially perfused canine isolated hearts, LV volume-pressure (v-p) relations for both inflation and deflation were obtained by infusing and withdrawing a saline. The v-p curves of inflation and deflation were both sigmoidal, but the resultant v-p relations for deflation produced a shift to the left inflation curves, showing hysteresis between inflation and deflation in three ventricular states. The effect of arrest or fibrillation, especially of fibrillation, on LV distensibility was discernible, and the resultant v-p relations produced a marked shift to the right, showing an apparent decrease in LV volume (LVv) at a given filling pressure. It was concluded that it is very questionable to identify the stiffness of the beating heart with the non-beating heart.

Animals↗
PubMed1982

The acoustic characteristics of the left ventricle.

A new method was developed to describe the instantaneous resonance curve (IRC) of the left ventricle (LV), which represents the acoustic characteristics and instantaneous viscoelastic properties of LV. This method was evaluated using coronary-perfused isolated canine LV preparations.

Animals↗
PubMed1981

Experimental study of afterload-reducing therapy: the effects of the reduction of systemic vascular resistance on cardiac output, aortic pressure and coronary circulation in isolated, ejecting canine hearts.

The relationship between cardiac output (CO) and peripheral resistance (Rp) was examined under the following conditions for coronary perfusion: constant coronary flow perfusion; perfusion with a pressure equal to mean aortic pressure (AoP perfusion); and perfusion with a pressure equal to the mean AoP - 30 mm Hg (AoP - 30 mm Hg perfusion). We also examined the coronary pressure-flow relationship. For these studies, we used paced, isolated, ejecting canine hearts, which were loaded by a hydraulic system that simulated the input impedance of a dog's systemic arterial tree. The CO in the constant coronary flow perfusion continued to increase with the reduction of Rp. The CO in the AoP perfusion became maximal at a slightly subphysiologic Rp, or at an average mean AoP of 65 mm Hg. This mean AoP was closely associated with the lower limit of the autoregulation of coronary blood flow. In the AoP - 30 mm Hg perfusion, the mean AoP at which CO became maximal was 72 mm Hg and the corresponding coronary perfusion pressure appeared to be lower than the lower limit of the perfusion pressure range for coronary flow autoregulation. The Rp value at that point was slightly higher than the physiologic range. We conclude that when coronary perfusion pressure changes with mean AoP, and when left ventricular end-diastolic pressure is fixed, there is a clear optimal Rp at which CO becomes maximal, and this optimal Rp is higher if coronary perfusion pressure is biased from mean AoP to a significant degree.

Animals↗
PubMed1980

Effects of changes in the aortic input impedance on systolic pressure-ejected volume relationships in the isolated supported canine left ventricle.

We examined the effects of aortic input impedance alteration on left ventricular pressure, aortic flow and ejected volume (integral value of aortic flow), in an isolated blood perfused ejecting canine heart, with special reference to end-systolic values. A hydraulic model which stimulates an aortic input impedance was attached to the aortic root of an excised heart. Left ventricular end-diastolic pressure was kept constant by electrical pacing. Three coronary arteries were perfused with arterial blood from support dogs. When the peripheral resistance in the hydraulic model was changed, there were inverse linear relationships between stroke volume and mean left ventricular systolic pressure and between ejected volume and pressure at end-systole. Time interval from the onset of contraction to end-systole did not change. Thus the relation between stroke volume and mean left ventricular pressure obtained by changes in peripheral resistance is governed by a source resistance, which can be considered as the contractile state of the ventricle. When the capacitance (arterial compliance) was changed, there was no inverse linear relation between stroke volume and mean systolic pressure. In many cases, there was an inverse linear relationship between ejected volume and pressure at end-systole. However, an increase in capacitance prolonged the time interval from the onset of contraction to end-systole. We conclude that the end-systolic pressure-ejected volume relationship in the ejecting heart is governed not only by contractility but also by arterial capacitance.

Animals↗
PubMed1980

The effect of graded coronary flow reduction in the left anterior descending and septal arteries on left ventricular function in the canine heart.

WE quantitatively analyzed the effect of graded left anterior descending and septal coronary flow (LAD + septal flow) reduction on left ventricular function with a left ventricular end-diastolic pressure (LVEDP) of 6 mm Hg and 12 mm Hg. We used an isolated, ejecting, canine heart preparation ( n = 8), the coronary flow of which could be controlled independently of the aortic pressure. We kept the other hemodynamic variables - heart rate, left circumflex coronary flow, right coronary flow and aortic input impendance - constant within their normal physiologic range. We considered this reduction in LAD + septal flow to be analogous to that of the most frequent lesion in ischemic heart disease. There was no plateau in the left ventricular work caused by this reduction of the regional coronary flow. Therefore, the plateau commonly reported in previous studies may be partially a result of the compensatory elevation of LVEDP, which is necessary to maintain the left ventricular work.

Animals↗
PubMedDate not supplied

Mechanical interaction between the ventricles.

We investigated ventricular interaction by the use of six excised, perfused, canine hearts. In this preparation, we could change the filling pressure of the right and left ventricles independently, thereby breaking the normal series-pump arrangement. We found that mechanical ventricular interaction exists in diastole and in systole. Namely, not only decreased diastolic ventricular compliance, but also the reduced performance in either ventricle was found, when the opposite ventricular pressure was increased. Thus, when the opposite ventricular filling pressure increases, we suspect that systolic ventricular function of either ventricle will be depressed significantly by these two factors; i.e., the Frank-Starling effect due to decreased ventricular diastolic volume following decreased diastolic ventricular compliance, and the depressed systolic ventricular function. Clinically, these findings may be important in considering the mechanism of the occurrence of simultaneous reduced performance of both ventricles in cases when only one side of the ventricle is affected hemodynamically and its filling pressure is greatly increased in various pathological states such as heart failure.

Animals↗