Abstract
Isometrical contraction tension was studied under varied rates of stimulation in the canine right ventricle, which was perfused with blood from a donor dog. In such preparations, a spontaneous rhythm of about 20 beats/ min was usually observed. Stimulus threshold and tension developed by stimulation with a voltage approximately twice threshold did not change significantly for 10 to 20 hours of continuous driving at constant rate (120/min). Contractile force was increased by raising the frequency of stimulation and a definite and reproducible frequency-force relationship was observed in the range of stimulation rate from 30 up to 200 per minute at a constant temperature of 38-39°C. Atropine, β-adrenergic blocking agent or tetrodotoxin did not modify the frequency-force relationship. It was concluded that such frequency-force relationship as observed in the papillary muscle preparation having sufficient blood supply is the inherent characteristic property of the ventricular muscle. Alternation in contractile tension was observed at rates of stimulation above 200 per minute. The degree of alternans became reduced by catecholamines.
