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H Suga

Publications and source records attributed to H Suga.

At least 307 records · Page 17Linked to original sources
PubMed1979

Total internal mechanical work of ventricle assessed from quick release pressure-volume curve.

A method is proposed for direct assessment of the total internal mechanical work of the cardiac ventricle from a pressure-volume diagram. First, a quick release pressure-volume curve of the lumped series elasticity of the ventricle is recorded. Next, this curve is transcribed on a pressure-volume loop diagram of a contraction of interest in such a way that the quick release curve passes through the end-systolic pressure-volume data point of the loop. Finally, planimetry of the triangular area bounded by the quick release curve, the isovolumic relaxation segment of the loop and the diastolic pressure-volume curve gives total ventricular mechanical internal work performed on the lumped series elasticity of the ventricle during systole. This method is much simpler and more direct than the conventional analytical method which requires a relatively simple geometric model of the ventricle, a formula for series elasticity with appropriate stiffness constants and a series of mathematical calculations based on many unverified assumptions on the shape, structure and mechanical properties of the ventricle.

Animals↗
PubMed1978

Diastolic stress-strain relation of nonexcised blood-perfused canine papillary muscle.

We studied diastolic stiffness of 10 coronary-perfused twitching papillary muscles of the canine right ventricle. The muscle beat at a regular sinus rhythm of 122 +/- 20 (SD) beats/min at 37 degrees C. They were stretched slowly at a constant rate. Diastolic force increased exponentially with the stretch. Calculating Lagrangian stress (sigma) and strain (epsilon) from diastolic force and length, we found a linear relationship between ln sigma and epsilon within the physiological range of strain (0.025 less than epsilon less than 0.4). This indicates that the diastolic stress-strain relationship of the canine papillary muscle can be approximated by a single exponential curve: sigma = a.exp(b.epsilon). The mean +/- SD of the stiffness constant b was 18.0 +/- 3.2 (dimensionless). Our b values are comparable to those of dogs and human subjects, either indirectly assessed from the ventricular pressure-volume relationship or directly obtained in excised quiescent muscle specimens. Different coronary perfusion pressures (75-125 mmHg) in 10 muscles showed a statistically significant positive correlation to b values.

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PubMed1978

Transient force responses in blood-perfused papillary muscle after step changes in load.

In in situ canine papillary muscles, we studied transient responses in peak isometric force at control length, after contraction was suddenly switched from isotonic contractions at various forces and isometric contractions at different lengths. Peak isometric force rapidly decreased after isotonic contractions at relatively low forces and isometric contractions at shorter lengths. In contrast, peak isometric force rapidly increased after isotonic contractions at relatively high forces and isometric contractions at longer lengths. There was no transient response when the preceding isotonic force was about half of the present peak isometric force. Magnitude and direction of the transient force response depended on magnitude and direction of the change in the mean muscle force level produced by the sudden switch of loading conditions. Transient force responses were accompanied by simultaneous changes in time to peak isometric force in the same direction. We proposed that, in the blood-perfused papillary muscle, a sudden change in the mean muscle force causes an abrupt change in coronary flow supply-demand relation which in turn causes a transient change in contractile force.

Animals↗
PubMed1978

Dynamic stiffness of cat heart muscle in Ba2+-induced contracture.

We analyzed mechanical properties of kitten papillary muscles both at rest and in Ba2+ contracture by the frequency response method. The muscle length was perturbed sinusoidally, with an amplitude less than 0.3% of Lmax over a frequency range from 0.1 to 60 Hz to determine the dynamic stiffness, F(omega)/L(omega), in which F(omega) = amplitude of the force response wave, L(omega) = amplitude of sinusoidal length wave, and omega = frequency, and the phase shift of F(omega) relative to L(omega). In resting muscles, the dynamic stiffness increased minutely with increasing frequency and the phase relation showed a small lead over the entire frequency range. In muscles in contracture at low temperature (22-24 degrees C), the stiffness first decreased with increasing frequency from about 0.2 to 1 Hz, then increased with a slope of 10-fold/decade, and finally plateaued over the range above 8 Hz. The phase relation showed a small lag between 0.3 and 0.5 Hz, but a clear lead of up to 60 degrees between 0.8 and 16 Hz. With an increase in temperature to 36 degrees C, the peculiar decrease in stiffness and the phase lag in the low frequency region decreased in size and shifted to a higher frequency region (about 4 Hz). These findings led us to two alternative, approximate analogues, which are similar to but simpler than that previously proposed for a twitching papillary muscle.

Animals↗
PubMed1977

End-systolic pressure/volume ratio: a new index of ventricular contractility.

A thesis recently developed from a series of experiments on the isolated canine left ventricle is described. It is claimed that the ventricular presure/volume ratio at end-systole is relatively insensitive to cardiac loading and varies greatly in response to changes in ventricular contractility. The clinical viability of this basic finding rests on the substitution of diameter for volume in this formulation. Diameter can be measured using a noninvasive ultrasonic technique in the clinic. Accordingly, end-systolic pressure/diameter ratio was studied in the isolated preparation and found to be similarly insensitive to loading conditions and sensitive to inotropic interventions. A further analysis of the pressure/diameter ratio in the ventricle of the conscious dog is in progress. In parallel with these studies, use of the pressure/diameter ratio to evaluate contractility in cardiac patients is being tested. The preliminary findings from conscious dogs and clinic patients are briefly discussed.

Animals↗
PubMed1977

Reduction of the duration of isovolumic relaxation in the ejecting left ventricle of the dog: residual volume clamping.

1. The individual effects of stroke volume and speed of ejection on the duration of the isovolumic relaxation phase were analysed in the canine left ventricle with a constant end-systolic residual volume.2. A new technique was employed to maintain the ventricular end-systolic residual volume at a desired constant value regardless of wide changes in stroke volume and speed of ejection in a given inotropic background.3. The duration of isovolumic relaxation, which was defined to be the time taken for ventricular pressure to fall from its end-systolic level to its 75, 50 and 25% levels, markedly decreased with increases in stroke volume. The reduction amounted to as much as 30-50% when stroke volume was increased from zero (isovolumic) to 20-25 ml.4. The degree of shortening of the duration of isovolumic relaxation was largely independent of changes in speed of ejection which ranged from about 100-800 ml./sec at a constant stroke volume of 15 ml.5. It was therefore concluded that stroke volume itself could be a major determinant of the duration of isovolumic relaxation.6. It was speculated that the mechanism of the observed phenomenon might be a manifestation of the uncoupling effect of muscle shortening on contractile state.

Animals↗
PubMed1977

An X-ray diffraction study of the cross-circulated canine heart.

1. The equatorial X-ray diffraction pattern was recorded from a papillary muscle of a cross-circulated canine heart at different phases of the cardiac cycle. The intensity ratio of the 1, 0 and the 1, 1 reflexions (I1, o/I1,1) was 0-79 in the systolic phase and 1-19 in the diastolic phase. 2. Using the intensity ratio obtained, the approximate proportion of the myosin projections present in the vicinity of the thin filaments was calculated. This was 70-71% in the systolic phase and 51-52% in the diastolic phase of the total myosin projections. 3. The peak systolic tension was roughly proportional to the proportion of the projections present in the vicinity of the thin filaments during systole. 4. The projections which stayed in the vicinity of the thin filaments during diastole did not produce significant contractile force.

Animals↗
PubMed1977

Nonexcised papillary muscle preparation: force and length measurement and control.

An electromechanical servocontrol system was developed to analyze mechanical properties of a nonexcised, blood-perfused papillary muscle. A miniature load cell mounted on the moving arm of a pen motor measured muscle force, and a shaft angle sensor built in the motor measured the length. The pen motor was actuated by a servocontrol command signal. A papillary muscle was exposed in the right ventricle of an excised, cross-circulated canine heart. The tendinous end of the papillary muscle was connected to the load cell. The intact root of the muscle was fixed by a metal ring. The preparation was stable over 5 h heating at a regular spontaneous heart rate (95-150/min) at 37 degrees C. The system allowed the muscle to contract in various modes such as isometric, isotonic, auxotonic, afterloaded isotonic, quick released, lengthening, etc. Changes in the contraction mode, preload, and afterload could be achieved at the investigator's disposal simply by turning switches and potentiometers, or by feeding external command signals of desired wave forms.

Animals↗
PubMed1977

End-systolic force-length relationship of nonexcised canine papillary muscle.

End-systolic force-length (F-L) relationships were studied in blood-perfused papillary muscles remining in the canine right ventricle. The muscles contracted spontaneously at a regular rate of 114 +/- 4 (SE, N = 31) beats/min at 37 degrees C. In each muscle, end-systolic F-L curves were obtained in different modes of contraction at different diastolic lengths between the unstressed length (9.4 +/- 0.7 mm) and 143 +/- 4% of it. At the latter length, muscles developed a peak isometric force of 46 +/- 4 g (5.1 +/- 0.5 g/mm2). The isotonic F-L curve was lower than the isometric F-L curves to various extents. An auxotonic F-L curve fell between the two curves. At identical end-systolic lengths peak isometric forces were greater than isotonic forces by 14.4 +/- 1.4% in the first transient beats after switching the contraction mode from isometric to isotonic. The difference increased to 28.5 +/- 3.5% in the steady-state beats. The reduced force in the first isotonic beat was suspected to be due to the uncoupling effect of shortening. The further reduction of isotonic force in the steady-state beats was caused by viscous properties (creep and stress relaxation) and by a gradual decrease in contractility.

Animals↗
PubMed1977

End-diastolic and end-systolic ventricular volume clamper for isolated canine heart.

We devised a servo-controlled pump system which can clamp both end-diastolic and end-systolic volumes of the left ventricle of an excised, supported canine heart at desirable values in the face of changing patterns of ejection and filling. The system consists of a Bellofram cylinder and a powerful electromagnetic shaker which is driven by a position servo circuit. A water-filled balloon placed in the ventricle was connected to the water housing of the cylinder. As the ECG triggered the system, a fixed amount of water reciprocated between the heart and the cylinder in a programmed manner. The onset, duration, and speed of ejection and those of filling can be programmed separately. The performance of this pump system was tested in experiments on 15 cross-circulated hearts and proved satisfactory for precise analysis of the instantaneous pressure-volume relation in the ventricle.

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