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Biomedical subjects

H Suga

Publications and source records attributed to H Suga.

At least 253 records · Page 14Linked to original sources
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↗
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

Length dependent potentiation and inhibition of post-rest twitch tension development in adult cat and kitten papillary muscles.

If a rest interval is applied to a regularly stimulated cardiac muscle, the first contraction after this interval (post-rest contraction) has either a greater (post-rest potentiation) or a smaller (post-rest inhibition) developed tension than the regular contraction. Positive inotropic interventions will augment the post-rest potentiation and reduce the post-rest inhibition. We examined the effects of muscle stretching on the post-rest contraction in papillary muscles isolated from adult cats and from kittens and compared the effects with those of two typical inotropic interventions: high frequency stimulation and high calcium concentration. We found that muscle stretching augmented the post-rest potentiation and reduced the post-rest inhibition in a manner similar to the two inotropic interventions in the adult cat papillary muscle, and that these effects were consistently reversed in the kitten papillary muscle. The similarity of the effect of muscle stretching to those of the two typical inotropic interventions in either adult cat or kitten papillary muscle suggests that the effect of muscle stretching is due to an inotropic effect of muscle length change.

Animals↗
PubMed1984

Oxygen consumption and pressure-volume area of abnormal contractions in canine heart.

Oxygen consumption rates (VO2) of isovolumic and normally ejecting contractions are closely correlated with their systolic pressure-volume areas (PVA) in a stable canine left ventricle. PVA is the area in the pressure-volume (PV) diagram that is circumscribed by the end-systolic and end-diastolic PV relation curves and the systolic segment of the PV loop trajectory. We studied whether VO2s of abnormally loaded ejecting contractions were similarly correlated with their PVAs. Various abnormally ejecting contractions were produced in the left ventricle of the cross-circulated canine heart. VO2 and PVA data of the various abnormal contractions and the isovolumic and normally ejecting contractions were pooled together, to which the correlation and regression analyses were applied. They could be fitted by a linear regression analyses were applied. They could be fitted by a linear regression line with a high correlation coefficient and a slight scatter in each heart. We therefore conclude that PVA is the primary correlate of VO2, not only in the isovolumic and normally ejecting contractions but also in various abnormally loaded contractions in a given canine left ventricle with a stable contractile state.

Animals↗
PubMed1984

Short-term memory in the in situ canine myocardium.

We studied the effect of intracycle (short-term) mechanical history on canine myocardial performance. Intracycle muscle force and/or length history was varied, and the resultant changes in end-systolic force-length relationship were analyzed. Antecedent isotonic shortening impaired, whereas isometric force development enhanced end-systolic myocardial performance. A history of shortening concurrent with force development produced an intermediate effect. We conclude that decreasing force or length impairs whereas increasing length or force enhances performance in the same cycle. Different combinations of antecedent force and length changes affect end-systolic performance by algebraic summation (superposition) of their disparate effects. Time measurements established that 1) total systolic time varied little with altered history, 2) isotonic shortening took longer than isometric contraction in reaching a point P in the force-length plane, and 3) less time was therefore available for contraction after P with antecedent isotonic shortening than with antecedent isometric force development. This history-dependent time differential accounts for the corresponding differential in performance.

Animals↗
PubMed1984

Independence of myocardial oxygen consumption from pressure-volume trajectory during diastole in canine left ventricle.

We have found that myocardial oxygen consumption is linearly correlated with the systolic pressure-volume area in the canine left ventricle. This pressure-volume area is a specific area in the pressure-volume diagram that is circumscribed by the end-systolic pressure-volume relation line, the end-diastolic pressure-volume relation curve, and the systolic segment of the pressure-volume trajectory. This area is equivalent to the total mechanical energy generated by ventricular contraction, consisting of the external mechanical work and the mechanical potential energy. In the present study, we specifically changed the course of the diastolic segment of the pressure-volume trajectory without changing the systolic segment of the pressure-volume trajectory and the systolic pressure-volume area. Although the fractions of external mechanical work and mechanical potential energy in the pressure-volume area were markedly changed, the simultaneously measured left ventricular oxygen consumption remained unchanged. This result indicates that the myocardial oxygen consumption is predominantly determined by the total mechanical energy generated during systole, or the systolic pressure-volume area, independent of how the total mechanical energy is converted effectively to external mechanical work during the cardiac cycle.

Animals↗
PubMed1984

Is regional ventricular wall work determined from regional force and shortening always consistent with the law of conservation of energy?

Contractile properties of a ventricular wall region have often been analyzed by regional force, shortening, and work. Regional force cannot be measured directly and is often indirectly determined from ventricular pressure and geometry, although regional shortening can be measured directly. Regional work can be calculated from these force and shortening values. We examined whether the calculated regional work, which may be mechanically reasonable, is also reasonable from an energetics viewpoint. We calculated regional contractile power (time rate of work) from the regional force and shortening velocity and integrated it globally over the entire ventricular wall, using some conventional geometric models of the ventricle and assumptions of ventricular wall mechanics. We then compared this globally integrated power with the stroke power of the entire ventricle determined directly from ventricular pressure and volume. Results show that the globally integrated regional power is not always identical with stroke power, depending on the model and assumptions used. Therefore, the regional ventricular wall work determined from the regional force and shortening is not always consistent with the law of conservation of energy.

Humans↗
PubMed1984

Normalization of end-systolic pressure-volume relation and Emax of different sized hearts.

A shift of the ventricular end-systolic pressure-volume (P-V) relation and a change in its slope Emax reasonably reflect a change in contractility in a given ventricle. However, comparison of Emax's of different sized hearts may be difficult without an appropriate normalization. We attempted to normalize Emax of different sized hearts to the force-length (F-L) relation of unit mass of myocardium in the ventricular wall. We formulated the end-systolic P-V relation as (end-systolic pressure) = Emax (end-systolic volume Vi - Vd), where Vd = volume axis intercept of the end-systolic P-V relation line. As a first step, both thick wall sphere and cylinder models of the ventricle with a wall volume of Vm were used. Circumferential F-L relation of unit myocardium in different ventricular wall layers were formulated as functions of Emax, Vd, and Vm. We found that as long as the product of Emax and Vd remains constant, the F-L relation in the midwall layer and the average F-L relation in the wall remain relatively unchanged regardless of wide changes in Vm and Vi. The elevation of the F-L relation curve, which represents myocardial contractility, was found to change in proportion to Emax Vd, largely independent of Vm and Vi, or the size of the ventricle.

Cardiac Volume↗
PubMed1984

Constant mechanical efficiency of contractile machinery of canine left ventricle under different loading and inotropic conditions.

We have recently proposed that the total mechanical energy generated in each cardiac contraction can be quantified by the systolic pressure-volume area (PVA). PVA is the area in the pressure-volume (P-V) diagram that is circumscribed by the end-systolic and end-diastolic P-V relation curves and the systolic segment of the P-V trajectory. This area has dimensions of energy and comprises the external mechanical work and the elastic potential energy. In the left ventricle of cross-circulated canine hearts, we studied the relation between PVA and oxygen consumption per beat (VO2) above VO2 for mechanically unloaded contraction. We assumed that this excess VO2 is utilized for mechanical contraction by the contractile machinery. The percentage of PVA in the excess VO2, both in the same unit of energy, J, would then represent the efficiency of energy conversion from the excess VO2 to the total mechanical energy in the contractile machinery. We obtained this efficiency in variously loaded contractions in both control and enhanced contractile states with epinephrine and calcium. We found that the efficiency was constant at 30-50 (mean 40) % regardless of the changes in both loading conditions and contractile states. By this constant efficiency and a variable fraction of external work in PVA, we accounted for the load- and contractility-dependent variability of the conventional mechanical efficiency (0-30%) of the heart.

Animals↗
PubMed1984

Neurotransmitters in dementia.

Changes in the activity of neurotransmitters in dementia were studied by measuring the activities of each of choline acetyltransferase (CAT), dopamine-beta-hydroxylase (DBH) and hydroxylase cofactor (tetrahydrobiopterine; BPH4), and the concentrations of homovanillic acid (HVA) and vasopressin. CAT activity was low in the cerebral cortex of patients with senile dementia of Alzheimer's type (SDAT). The CAT activity was high in the nucleus basalis, which correlated well with the CAT activity in the cerebral cortex, Brodmann areas 22 and 17. DBH activity was lower in the cerebrospinal fluid (CSF) of SDAT and multi-infarct dementia (MID) patients than in that of control subjects. No age-related change was observed in control subjects. Serum DBH activity was decreased in patients with SDAT but not in patients with MID. DBH activity was especially low in the serum of SDAT patients with a low dementia rating score and/or severe brain atrophy shown on computed tomography (CT) scan. Serum DBH activity was also decreased in older normal subjects (greater than or equal to 80 years). The concentration of HVA in the CSF of control subjects decreased with the advance of age, but the decrease in HVA concentration was more pronounced in the CSF of SDAT patients, which would reflect the lowered dopaminergic activity in SDAT. BPH4 activity was also decreased in the CSF of SDAT patients. Arginine-vasopressin was widely demonstrated in the cerebral cortex of control subjects but could not be detected in many areas of the cerebral cortices of demented patients. These results suggest that a deficit of dopamine, noradrenaline or vasopressin as well as acetylcholine may occur in the brain of SDAT patients. The evidence presented points toward areas for consideration in the search for methods of therapy or prevention of SDAT.

Adult↗