A strain-gauge myograph for isometric measurements of tension in isolated small blood vessels and other muscle preparations.

Isometric tension measurements in vitro on small vessels are important in studies of pharmacodynamic vascular effects of drugs and autacoids. The present study describes a precision myograph equipped with a newly constructed highly isometric strain-gauge transducer used in conjunction with a very sensitive, low-noise and virtually drift-free dc-amplifier. The isometric quotient of the transducer, defined as deflection in micrometer per g of force, is about 5.2. The transducer resonance frequency is 341 c/sec with a damping constant of 1.05. The highest sensitivity of the transducer in connection with the matching dc-amplifier is about 170 mV/V/g force. The practical working range of the myograph is from 2 mg to about 10 g of applied tensile force. Tubular segments of vessels with internal diameters down to 150 micron can be mounted in the myograph on two stainless-steel pins submerged in a 5 ml preparation bath. Precise mounting and setting of passive (resting) tension is assured by the use of micrometer-equipped adjustable miniature mounting tables suspended by roller bearings. The myograph may be provided with electrodes for field-effect stimulation of the vessel preparations. Other muscle preparations may also be mounted in the myograph. Application of the myograph in studies on rabbit coronary arteries is demonstrated by a length-tension diagram obtained in experiments with tubular segments (inner diameter about 500 micron) of the circumflex branch on the left coronary artery, which shows a typical course in development of active and passive tension of the smooth musculature when exposed to alternating potassium depolarization and increasing mechanical stretching. The potassium contracture of the coronary vessels and the log-concentration/response relationship at accumulating potassium concentrations were also investigated.