Since 1966, we have been measuring the local tension of the outer surface of the myocardium by using an arched semiconductor straingauge.
When it comes to discuss contractility of the myocardium, the attention should be concentrated on the myocardial architecture which is consisted of three layers, the outer oblique, mid circular and inner oblique layer with spiral arrangement.
Okada and Nishijo in our institute have studied the morphological changes in the mid circular muscle of hypertrophied heart. The mid circular muscle plays the most vital role to squeeze out blood as a pump and dysfunction of it is considered to cause cardiac failure.
In order to study the cardiodynamics, it is desirable that the tension curve should be obtained directly from each myocardial layer and fibre. For the purpose of this, a newly divised transducer is introduced to elicit the tension curve selectively from mid circular musle.
It is made of four hard needles of sewing machines fixed to both edges of the previous small and light straingauge arch. The tension curve is recorded applying the legs of needle iust to the direction and depth of middle layer of left ventricular free wall.
Another needle typed transducer is also manifactured to measure the intramyocardial pressure at the given site. The rotating and vibrating needles are given the changes in damping by myocadial contraction, and to perceive the changes in voltage of secondary coil. The constant was determined by silicon oil with known visicosity coefficient, the quantitative Measurement of intramyocardial pressure was obtained. The intramyocardial pressure obtained was 100mm Hg/max, not exceeding the intraventricular pressure.
The author measured the changes in tension of mid-curcular muscle of canine heart with pressure and volume loaded in a short period using an arched transducer.
In a control group of canine heart, the legs of needle were inserted to the depth of certain myocardial fibre along its running direction. With increase in depth, the magnitude of the tension curve and the maximum velocity of dT/dt were increased.
Greater magnitude of tension curve was attained when the arch was especially fixed along the mid-circular muscle. Analysing these (tension) curves, it is possible that the tension from each layer could be detected.
In acute pressure load, the magnitude of tension is unchanged or slightly diminished and Max. dT/dt is increased. In volume load, however, both decreased. These results as certained the morphological changes in the autopsied heart.
The Experimentally produced cardiogenic shock by ligation of coronary arteries demonstrates the changes in diastolic phase, namely delay in tension curve at diastole. In other words, that decrease in compliance of the myocardium is (reasonably) estimated to induced acute power failure of the heart.
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