The diastolic viscous properties of cat papillary muscle.

The measurement of ventricular diastolic compliance is complicated by the presence of viscous properties. To approach this problem, cat papillary muscles contracting isometrically at 15/min at 26 degrees C were stretched at different velocities during diastole. At a given length there was no excess of force above that defined by the static force-length curve until velocity of stretch exceeded 1 muscle length/sec. At greater velocities of stretch there was an increase of force with increasing velocity of stretch denoting viscous resistance to stretch. The viscous characteristic was alinear and increased with muscle length. At a given muscle length potentiation of contractile state by paired pulse stimulation caused a change in the diastolic force-length curve but there was no apparent relationship between viscous resistance to stretch and contractile state or the length of the "series viscous element." These results lead one to expect viscous resistance to stretch during rapid filling of the intact left ventricle.