Hydraulic study of aortic cannulation return nozzles



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This study is concerned with the hydraulic analysis of five different types of cannulae utilized during a cardiopulmonary bypass procedure. These cannulae are used for returning oxygenated blood from the heart-lung machine back to the arterial circulation of patients undergoing open heart surgery. The approach was experimental in nature. This procedure involved three transparent, plastic, hydraulic models of the aortic arch and its associated vessels under normal physiologic pressure. Measurements were made to determine the pressure drop across the cannulae, flow and pressure distributions in the aortic arch vessels, and flow patterns resulting from these cannulae at total perfusion rates ranging from 1800 to 4700 ml/min. Mean pressure gradients across the cannulae, when plotted against steady flow rate, increased in a non-linear, somewhat parabolic shape, with increasing flow. These gradients ranged from a minimum of 125 mm Hg to a maximum of 245 mm Hg at perfusion rate of 5 L/min. Dynamic pressure versus time recordings revealed instantaneous pressures outside the linear range of the transducers employed (over 500 mm Hg!). Depending on the jet flow direction resulting from some of the cannulae, an increase or decrease of pressure and flow in one or more of the aortic arch arteries were observed. Increases in left common carotid artery pressure of 24 mm Hg (24% deviation from control) and 60 ml/min (14% deviation from control) were found when the jet was oriented directly into this artery. A decrease of 11 mm Hg (11%) in pressure and 50 ml/min (8%) were recorded in the brachiocephalic artery when a negative hydrostatic pressure was generated at the emergence of the arterial cannula (Venturi effect). The high speed photography of the flow patterns resulting from the various cannulae under investigation provided a qualitative evidence of areas of turbulence and eddy formation as well as areas of stagnant flow. High intensity jets were observed along with areas of stasis at the site of cross-clamping of the aorta in all the cannulae tested. Static pressure gradients in the aortic arch region were measured using a bank manometer. The results were used to map equal pressure contours in the aorta. Out of the five different types of cannulae investigated, the. George Noon metal cannula demonstrated the best hydraulic characteristics in terms of pressure drop across it, mean pressure and flow distributions and/or favorable flow patterns.