The role of multiple noncritical arterial stenoses in the pathogenesis of ischemia.

The hemodynamic effects of multiple noncritical lesions in series were studied in in vitro experiments and in 15 animals. Flow visualization studies were also carried out to obtain insight into the flow pattern in the region of stenosis. Symmetrical stenosis pieces with a 50 per cent reduction in area were placed inside a plexiglass tube and used for both in vitro and in vivo experiments. Varying the number of stenoses and the spacing between them enabled us to study twelve different stenosis configurations during both pulsatile and steady flow. Flow conditions encountered clinically were simulated by varying the average Reynolds number between 30 and 380. Pressure drops across the stenosis test section were measured with a differential pressure transducer and used to calculate critical values for multiple, uniform, noncritical stenoses and for combinations of stenoses of different degrees. Results from steady and pulsatile flow in vitro were comparable, as were those results from the in vivo experiments. The pressure drop across a series of noncritical stenoses was nearly the sum of the individual pressure drops, with only slight dependence upon the spacing between stenoses, Thus it is concluded, from both experimental results and from the theoretical calculations, that the total effect of a series of noncritical stenoses may become critical and produce symptoms of arterial insufficiency.