Assessment of vascular smooth-muscle mechanisms using isolated segments of the vessel wall.

Isolated segments of the blood vessel wall in the form of strips or rings offer advantages for the assessment of vascular smooth-muscle contractile function and its contribution to the properties of blood vessels. Several criteria must be met to obtain these advantages. These requirements are outlined in the context of an analytical framework based on the sliding filament/crossbridge model. The applicability of this model to smooth muscle is discussed, and the concept of a "functional unit" in the vascular wall is introduced. A functional unit is defined as all the smooth-muscle cells that are mechanically linked in series and bear equal stress. Several factors contribute to heterogeneity among functional units. The constraints imposed on the estimation of the static and dynamic mechanical properties of the smooth muscle are discussed. Various experimental strategies to minimize the effects of inhomogeneities in functional units can enhance the value of mechanical measurements.