THE EFFECTS OF TEMPERATURE ON TENSION, HYSTERESIS LOOP AND STRESS-RELAXATION OF THE BLOOD VESSELS

1. Mechanical characteristics of the toad blood vessels under different temperatures were investigated with the use of the universal tensile testing instrument. 2. The amplitude of tension generated by cyclic stretches of the aorta at 41% stretched state was constant throughout the temperatures between 3-40°C, while that induced at 100% stretched state increased with decrease of temperature. In both cases, however, the lower tension levels lowered as temperature fell. 3. Over 40-50°C, a marked increase of the tension amplitude was observed with distinct elevation of the upper tension level in both cases of 41% and 100% stretched states. 4. In the tempreature dependency of mechanical characteristics, the elastin dominant vessel treated with formic acid coincided well with the wall of vessel at 41% stretched state, while the tendon, aponeurosis plantalis, was in accord with the vessel at 100% stretched state. However, the marked increase of tension at temperatures over 50°C was never observed in the digested aorta, supporting a view that it depends on the thermal denature of collagen. 5. Hysteresis loops of the aorta and vena abdominalis became small at normal temperature and large at low (2-5°C) and high (40-42°C) temperatures. With the tendon and formic acid treated vessels, the hysteresis loops also tended to enlarge at low temperatures (2-5°C). However, over 50°C merely the tendon showed a great deal of increase in the loop. 6. Stress-relaxation curves of the aorta and vena abdominalis declined with a rise of temperature up to 40°C, but no detectable difference between their temperature dependencies of distribution function was observed. The relaxation modulus increased markedly at high temperatures over 50°C, showing distribution function of distinct box-shape.