Experimental studies on myocardial contractility: direct measurements of the contractility of left ventricular myocardium with the strain gauge arch

Abstract

The application of the resistance-wire strain gauge arch by BONIFACE et al. to the beating heart in situ has recently conducted to allow the direct measurements of the mechanical function of the heart, and several models of apparatus for this purpose have been devised. The use of a semiconductor as the transducing element makes the strain gauge arch smaller and more efficient in transduce than the use of the wire strain gauge. The present report describes the structures and the performances of some models of the new instruments which have been designed using semiconductor strain gauge elements. This report also provides the discussion on the propriety of this method manifesting the accurate myocardial contractility of the left ventricle through the detailed analysis of myocardial tension curves recorded with the new strain gauge arch. Methods 1) Mechanical properties of the strain gauge arch. The strain gauge arches, which were used in this investigation, were transducers capable of translating the forces acting on their attachments into proportional changes in the bridge output voltage. The body of the transducer was made of a kind of spring-steel in the form like an arch as a whole, consisting of a beem between two legs with two attachments. The distance between two legs was 15 mm (in Model L-3) or 10mm (in Model L-6), and the whole weight was less than 1g. The modified arch (Model VL-5), which could be adjusted the distance between two legs by means of a micro-screw, was also developed. As strain gauge elements, four pieces of n type Ge [111] were cemented on both sides of the upper parts of the legs. A "four active full-bridged circuit" which was constituted by the semiconductor elements was supplied with 3V in DC. There was a linear relation between the force necessary to displace the attachments and the increase of the distance between the attachments, and even a force of 250g wt. could move the attachments less than 5 per cent of length of the beem. There was also linear relation between the force acting attachments and the bridge output voltage and 210mV of output voltage was obtained by 250g wt of force in Model L-3. The frequency response of the strain gauge arch was found to be uniform through 350cps.