The effect of acute hypoxia on the viscoelastic properties of the myocardium.

The viscoelastic properties of the isolated rabbit papillary muscle were studied by constructing a semilogarithmic length-tension curve before and after it had undergone 5 minutes of stress relaxation before, during, and after exposure to a solution aerated with 95 per cent nitrogen and 5 per cent carbon dioxide. Stress relaxation was accomplished in each treatment group by a reduction in the tension intercept of the log length-tension curve without significant change in its slope. There was no significant change in either of these parameters between the control, hypoxia, and recovery groups. These findings lead to the conclusions that: (1) the loss of muscle tension during stress relaxation is not due to a change in the elastic properties of the myocardium and (2) hypoxia does not increase the fundamental stiffness characteristics of the cardiac muscle.