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California Institute of Technology

Virgil H Culler

Cyril Feldstein

Gilbert W Lewis

James C Fletcher

Robert H Silver

Alan M Lovelace

Samuel Merrbaum

A transducer is described for simultaneously measuring several parameters of a small region of a muscle tissue or other object, with minimal traumatizing or damage of the object. A trifunctional transducer which can measure the force applied by a muscle fiber, the displacement of the fiber, and the change in thickness of the fiber, includes a device having three legs with inner ends joined together and outer ends formed to pierce the tissue and lie therein. Two of the legs are relatively stiff, to measure force applied by the tissue, and a third leg is relatively flexible to measure displacement of the tissue relative to one or both stiff legs, and with the three legs lying in a common plane so that the force and displacement measurements all relate to the same direction of muscle movement. A flexible loop is attached to one of the stiff legs to measure changes in muscle thickness, with the upper end of the loop fixed to the leg and the lower end of the loop bearing against the surface of the tissue and being free to slide on the leg.

Multifunctional transducer

A myocardial transducer for simultaneously measuring force and displacement within a very small area of myocardium comprising an elongated body forked at one end to form an inverted Y-shaped beam, each branch of the beam constituting a low-compliant tine for penetrating the myocardium to a predetermined depth. Each tine has a transverse indentation formed around at least a part of it. When the tines are inserted into a heart, the surface membrane of the myocardium closes around the indentations to hold the tines in place. Bonded to one of the low-compliance tines is a small piezoresistive element for converting a force acting on the beam into an electrical signal. A third high-compliant tine of the transducer, which measures displacement of the myocardium in a direction in line with the two low-compliant tines, is of a length that just pierces the surface membrane. A small piezoresistive element is bonded to the third tine at its upper end where its bending is greatest. Displacement of the myocardium causes a deformation in curvature of the third tine, and the second small piezoresistive element bonded to the surface of its curved end converts its deformation into an electrical signal. A separate electrode placed on the epicardium and referenced to the transducer body provides an ECG signal simultaneously with force and displacement signals.

Simultaneous muscle force and displacement transducer

A force transducer for measuring dynamic force activity within the heart of a subject essentially consists of a U-shaped beam of low elastic compliance material. Two tines extend from the beam's legs and a long coil spring is attached to the beam. A strain gauge is coupled to one of the beam's legs to sense deflections thereof. The beam with the tines and most of the spring are surrounded by a flexible tube, defining a catheter, which is insertable into a subject's heart through an appropriate artery. The tines are extractable from the catheter for implantation into the myocardium by pushing on the end of the spring which extends beyond the external end of the catheter. The tines are retractable back into the catheter, prior to catheter removal from the subject, by pulling on the externally exposed spring end.

Catheter tip force transducer for cardiovascular research

A myocardium wall thickness measuring transducer comprises a circular beam of high compliance and an elongated spike which extends in the plane in which the beam is disposed. The spike is connected at one point to the beam while a working end of the spike to which a barb is attached, extends through an opening in the beam at a substantially diametrically opposite point. The beam portion, surrounding the opening, is free to move or be displaced relative to the spike. A sensitive strain gauge is bonded to the beam to sense changes in the tension thereof. The working end of the spike is inserted through the epicardium into the myocardium so that the spike and the beam are in a plane substantially perpendicular to the epicardium at the point of insertion. The spike is inserted, to a depth at which a minimal beam deforming force is applied by the myocardium to the beam portion surrounding the opening. As the heart contracts and myocardium thickness increases larger beam-deforming forces are applied to the beam which increase the beam tension, which is sensed by the strain gauge whose changing output is supplied to an appropriate recorder.

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Virgil H Culler