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Biomedical subjects

O Yamada

Publications and source records attributed to O Yamada.

At least 199 records · Page 11Linked to original sources
PubMed1986

Reconsideration of normalization of Emax for heart size.

We previously proposed Emax Vd as a normalized form of Emax for heart size relatively independent of wall volume Vm, where Emax is the slope of the end-systolic pressure-volume line and Vd is its volume axis intercept. When Emax Vd remains constant, average circumferential stress for a specified average circumferential strain in the ventricular wall also remains relatively constant, despite changes in Vd/Vm around its normal value. Because accurate determination of Vd is difficult and stress for a given Emax Vd changes slightly with Vd/Vm, we investigated whether Vd could be replaced with Vm in a normalized Emax in this analysis. As the result, we obtained a function of Vd/Vm as the coefficient by which to multiply Emax Vd or Emax Vm to yield stress for a specified strain. Using this coefficient, one can easily calculate stress for any strain from Emax, Vd, and Vm in order to compare myocardial contractility among left ventricles of different sizes. The present study confirms the importance of Vd as an indispensable reference volume for normalization of Emax, as well as the low sensitivity of Emax Vd as a normalized Emax to changes in Vd/Vm. Only when Vd/Vm remains constant is Emax Vm proportional to Emax Vd and can replace Emax Vd.

Blood Pressure↗
PubMed1986

Left ventricular regional work from wall tension-area loop in canine heart.

To quantitatively evaluate left ventricular (LV) regional work, LV pressure-volume relation and wall tension-regional area (TA) relation were analyzed in the excised cross-circulated left ventricle connected to a volume servo pump system. Wall tension was calculated using Laplace's law for a spherical model, and regional area was determined from orthogonal segment lengths measured with pairs of ultrasonic crystals. Data were obtained by changing LV end-diastolic volume or stroke volume before and after dobutamine infusion and before and after global ischemia. Regional work, assessed from the area within a TA loop during one cardiac cycle, correlated well with simultaneously obtained LV stroke work under all of the above experimental conditions (r = 0.90 +/- 0.09 to 0.97 +/- 0.02), and the linear regression line was not altered by changes in stroke volume, end-diastolic volume, or contractile state. Furthermore, measured regional work (RWm) proved to agree closely with the predicted value (RWp) calculated from LV stroke work and regional area [RWm = 0.91 RWp - 0.69 (mmHg . ml), r = 0.93]. Thus we conclude that TA relation may be useful for quantitative evaluation of regional work of the LV wall.

Animals↗
PubMed1986

Peak isovolumic pressure-volume relation of puppy left ventricle.

We studied peak isovolumic pressure-volume (PV) relation of the left ventricle in 3-mo-old mongrel puppies. A puppy heart was excised and cross circulated with an adult dog. Left ventricular pressure and volume were measured with a water-filled balloon. Peak isovolumic PV curve in control contractile state was convex upward, reaching a maximum pressure of 130 mmHg. Epinephrine (0.6 microgram/min intracoronary) shifted the curve leftward and up to a maximum pressure of 160 mmHg. Propranolol (0.8 mg intracoronary) shifted it rightward and down to a maximum pressure of 110 mmHg. These PV curves were reasonably fitted by an asymptotic equation: P = A (1 - exp[-B (V - Vd)]), where V was normalized volume for 100 g left ventricle and Vd (6 ml/100 g) was V at which peak pressure was zero. A and B are regression coefficients. A was 149, 169, and 120 mmHg, and B was 0.16, 0.19, and 0.06 ml, respectively, in control, enhanced, and depressed contractile states. These changes in A and B were statistically significant. We conclude that the puppy left ventricular peak isovolumic PV curve is convex upward and shifts sensitively with inotropic changes.

Animals↗
PubMed1986

Ventricular suction under zero source pressure for filling.

We quantified ventricular suction flow, volume, and pressure under hydrostatically zero source pressure for filling. A large-bore electromagnetic flow probe was placed in the valve-free mitral annulus of the dog heart that had been excised and was cross circulated with the left atrium widely opened. With the heart immersed in a blood pool, ventricular suction flow and transmural pressure were measured. After a rapid ejection flow [peak: 110 +/- 47 (SD) ml . s-1 . 100 g left ventricle-1] during systole, a slow suction flow (peak: 26 +/- 20 ml . s-1 . 100 g-1) occurred during diastole despite the zero source pressure for filling. Peak transmural pressure during ejection was 6 +/- 3 mmHg, and peak negative transmural pressure during suction was 2 +/- 1 mmHg. Suction volume, which was equal to ejection volume in steady state, was 8 +/- 3 ml/100 g left ventricle. Increases in paced heart rate markedly decreased suction volume by curtailing diastolic filling time. Epinephrine, propranolol, calcium, and verapamil variably changed suction volume, and these effects were primarily accounted for by the accompanied heart rate changes.

Analysis of Variance↗
PubMed1986

Long-term management of patients with cardiac valve prostheses.

Marked improvements have been achieved in the results of valve replacement due to recent developments in cardiac valve prostheses, surgical procedures, myocardial protection methods, and supportive techniques. Since 1974, the aortic valve has been replaced with mechanical valves and the mitral valve with biological valves at our institution. During a cumulative follow-up of 1024 patient-years after 306 valve replacements (126 AVR, 148 MVR and 32 AVR + MVR), the 10-year survival rates were 88% for AVR, 72.6% for MVR and 77.5% for AVR + MVR. The cardiac function of 90% of the survivors was evaluated as Class I or II according to NYHA Functional Classification. As for valve-related postoperative complications, thromboembolism was observed in 2.3%/pt-yr, hemorrhage in 0.5%/pt-yr, prosthetic valve endocarditis in 1.3%/pt-yr, perivalvular regurgitation in 1.3%/pt-yr and valve malfunction in 1.1%/pt-yr. Of the causes of late deaths, 62.5% were related to valve complications. Re-replacement of the prosthesis was necessary in 17 patients due to valve-related complications, and early death occurred in 1 (5.9%) of these 17. While cardiac valve replacement contributes to improvements in the quality of the patients' long-term postoperative life, currently employed artificial valves are still not ideal with regard to their materials and design, and re-replacement may become necessary in the late postoperative period. Therefore, in addition to selection of the appropriate valve prosthesis for different disorders and optimal prevention of valve-related complications, early diagnosis by non-invasive techniques and early treatment of these complications if they have occurred are of particular importance for the long-term management of patients following cardiac valve replacement.

Activities of Daily Living↗
PubMed1985

Mechanical efficiency of the left ventricle as a function of preload, afterload, and contractility.

We have recently shown that the mechanical efficiency of the contractile machinery of the canine left ventricle is constant at 30%-50%, independent of its loading, heart rate, and inotropic conditions. In contrast, the conventional mechanical efficiency of the ventricle is known to vary between 0 and 30%, depending on these conditions. In this study, we derived an equation for the conventional mechanical efficiency as a function of ventricular preload, afterload, and contractility, based on the constant mechanical efficiency of the contractile machinery. In deriving this equation, we fully utilized our new concept of the total mechanical energy of the left ventricle, i.e., systolic pressure-volume area, and our recent findings of the linear relationship between left ventricular oxygen consumption and the systolic pressure-volume area as well as the dependence of this relation on the ventricular inotropic state. As a result, the conventional mechanical efficiency of the left ventricle was found to change between 0 and 25% as an explicit function of these cardiodynamic and inotropic conditions. Using this function, we obtained combinations of loading and inotropic conditions to maximize the conventional mechanical efficiency of the left ventricle.

Animals↗
PubMed1985

Lysis of lymphoma cells by autologous and allogeneic natural killer cells.

Studies were undertaken to determine whether natural killer (NK) cells would lyse autologous and allogeneic lymphoma cells. When large granular lymphocytes, which are known to mediate NK activity, were enriched from peripheral blood and used as effector cells, they lysed autologous lymphoma cells of all of eight patients tested, and those of healthy donors lysed lymphoma cells of all of ten patients tested. The addition of interferon to the culture medium enhanced their cytotoxicity in three of the eight patients in the autologous effector-tumor system and in four of the ten patients in the above allogeneic system. On the basis of the unlabeled target competition test and the decrease in cytotoxicity with anti-NK antibody treatment, NK cells appeared to be the main cytotoxic effector cells for autologous and allogeneic lymphoma cells.

Adolescent↗