Distensibility

Distensibility refers to the ease of ventricular filling during diastole (ability to stretch).

Lusitropy refers to the ability of the ventricle to distend/relax and fill.

Factors affecting distensibility

Distensibility is reduced by:

• Reduced sympathetic tone
• Increased wall thickness
• Increased collagen, scarring, or cellular infiltration within the ventricular wall

Distensibility is increased by the opposite effects.

Measures of distensibility

Measurement of distensibility involves determining the instantaneous changes in pressure and volume within the chamber, which is invasive and difficult. Therefore, distensibility is not routinely measured clinically.

Indirect measures of the filling properties of the heart are obtained by echocardiography.

Effect of distensibility on myocardial performance

The effect of a reduction in distensibility is identical to the effect of an increase in preload. Thus, for the same volume of the heart at the end of diastole, there will be an increase in pressure in the ventricle.

Manifestations of abnormal distensibility

If distensibility is reduced:

• The clinical signs will be those of excessive preload with a reduction in stroke volume

If distensibility is increased:

• This is a situation not encountered in clinical practice.
• Disease typically results in reduced distensibility, not increased.

Effect of the autonomic nervous system on distensibility

Beta-adrenergic receptor activation increases the ability of the ventricle to relax.