Controlled pulsatile architecture in cardiopulmonary bypass : in-vitro and clinical studies
The clinical effects of pulsatile cardiopulmonary bypass (CPB) has been the focus of study for some time. In an effort to establish which aspects of pulse architecture are responsible for these clinical benefits, it is necessary to describe, in hydrodynamic terms, the pulse flow and pressure patterns, or architecture. A model of the human systemic circulation was designed and constructed for this purpose and two pulsatile perfusion pumps were studied, one was a roller pump, the other a new ventricular pump. It was anticipated that the ventricular mechanism would offer a higher degree of control of pulse architecture. Both systems were found to offer a high degree of output control and as anticipated the ventricular system offered better control of output architecture than the roller pump. In all aspects of the study of output architecture the ventricular pump was more powerful than the roller pump. However it was found that the ventricular pump was associated with the gen eration of significantly more microbubbles and this precluded its use in the clinical study. Having established four different architectures with the roller mechanism, one of which was non-pulsatile, the clinical study proceeded with this pump alone. The pulsatile groups as a whole, were found to offer metabolic and haemodynamic advantages over the non-pulsatile group. There were no differences between the various groups in terms of measures of organ damage during CPB. The non-pulsatile flow group had the highest level of nitric oxide activity, which appeared not to be related to any haemodynamic effect, but to a reperfusion or hypo-perfusion phenomenon. The differences between the pulsatile flow groups were in general not significant. The difficulty in achieving statistical significance between the pulsatile flow groups was thought to be related to the very small differences between the groups in terms of the magnitude of the parameters which contribute to the architecture . The methodology developed in this study can help to establish which aspects of pulse architecture are of importance during clinical CPB. This may not be possible however until the microbubble generation problems associated with the use of the ventricular mechanism has been solved.