Parameter sensitivity analysis of a network model of systemic circulatory mechanics

A previous analytical model of the systemic circulatory system (Grodins,Quarterly Review of Biology, 1959,34, 93–116) was extended based on recent experimental studies. Major units considered are: large arteries, large veins, and the peripheral circulation. The latter is subdivided into three parallel functional units: (1) nutritional bed, (2) shunt pathway and (3) storage area. By addition of simplified linear descriptions for the heart and pulmonary circulation, the overall cardiovascular system was considered. Parameter values were mainly derived from right heart bypass (Grodins, Stuart, and Veenstra, American Journal of Physiology, 1960198, 552–560) and isolated hindlimb (Satoet al., 1971) experiments. An algebraic equation relating cardiac output to systemic circulatory parameters was derived which provided a convenient means of studying effects of parameter changes. This equation predicted that compliances and unstressed volumes have a unidirectional effect on cardiac output but arterial resistance has a variable effect which depends on the values of resistances and compliances of the parallel pathways. Circulatory responses to exercise were considered by changing compliance and resistance of the nutritional bed in accordance with experimental values obtained with a frequency response method (Vega, Ph.D. Thesis, University of Southern California, 1973). Possible mechanisms for blood flow restoration as required by the resistance change are discussed.In summary, systemic circulatory mechanics appear to influence cardiac output mainly by redistribution of blood volume between different segments rather than by redistribution of blood flow.