Title: Hemodynamic analysis could resolve the pulsatile blood flow controversy
Abstract: Reasons for fluctuations in the popularity of pulsatile cardiopulmonary bypass are discussed.The advantages of pulsatile flow have previously been stated in terms of physiologic parameters.This has produced a weak theoretic framework that has led to serious misunderstandings of the fundamental mechanical properties of pulsatile flow.Failure to consider these properties in the past L ong before the birth of open heart surgery, mechanical pumps had been designed, manufactured, and used to establish circulatory support in isolated organs and whole animals [1,2].By the time technologic developments had proceeded sufficiently to permit the first open heart operation with cardiopulmonary bypass [3], it was widely believed that pulsatile flow was better than nonpulsatile flow because the body was adapted to it.However, the practice of open heart surgery was commenced and continued for many years with the aid of ripple (nonpulsatile) flow, extracorporeal circulation.There were probably three main reasons for this.First, the case for pulsatile flow rested on classic physiologic theory [1,[4][5][6], and evidence from studies of kidney, limb, and total body perfusion suggested that there were no changes in reactivity, function, or survival time associated with nonpulsatile flow, so long as blood flow rates and mean arterial pressures were maintained within the normal range [7-9].Wesolowski's publications during the early 1950s were an influential barrier to the adoption of pulsatile flows for extracorporeal circulation.He and his colleagues showed that nonpulsatile right heart bypass in dogs was compatible with normal respiratory functions and associated with no permanent alterations in circulatory dynamics [10].This was later confirmed by Clarke [11] and Wemple [12] and their colleagues.In the same series of experiments, Wesolowski's group produced preliminary evidence that pulsatile perfusion caused less systemic hypotension than did nonpulsatile perfusion, but this point was subsequently negated by their finding no significant differences in the hemodynamics, kidney function, vascular tone, recovery rate, blood indices, and organ histologic characteristics [13].The criticism later made of these results was that Wesolowski's use of high-flow rates probably eliminated the differences [14].However, by this time, operative mortality