Effects of Blood Flow Pulse Frequency on Mass Transfer Efficiency of a Commercial Hollow Fibre Oxygenator

The clinical advantages achievable through pulsatile blood perfusion during cardio-pulmonary bypass have recently suggested the design of new pulsatile systems for extracorporeal circulation. Still it is not clear whether current commercial membrane oxygenators could be adopted with such systems, since their behaviour with pulsatile perfusion has not been satisfactorily documented yet. In a previous paper, we assessed that pulsatile perfusion of a widely used hollow fibre oxygenator (Sorin® Monolyth) at 60 bpm provides more time-consistent oxygen transfer than steady perfusion. The present work is aimed to evaluate how the pulse frequency influences the gas transfer performance of the same device. The oxygenator was subjected to in vitro trials using a roller pump with pulsatile module (Stöckert Instrumente®) to generate pulsed flow. Four different pulse frequencies (45, 60, 75 and 90 bpm) were investigated at a fixed blood flow rate (4.0 l/min). The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standards requirements. Blood samples were withdrawn every hour and O2 and CO2 transfer rates were evaluated. The experimental findings confirm that with pulsatile blood flow no time decay take place during prolonged perfusion. Moreover, when pulse frequency increases, transition levels occur for both O2 and CO2. Over these thresholds gas transfer rates display significant increases (p < 0.05), though of little magnitude (up to 2.5% for oxygen over 60 bpm; up to 3.7% for carbon dioxide over 75 bpm).

Left ventricular heart failure model for testing cardiac assist devices

During the development of a new circulatory support system, we have used different animal models with and without heart failure for hemodynamic testing. As the normally functioning heart does not always allow for proper evaluation of a circulatory support system, a good and adjustable animal heart failure model is needed. The aim of the study was to develop a left ventricular failure model in calves for acute hemodynamic studies. The principle is based on the negative inotropic effect of drugs with bypass of the right ventricle. Seven calves were used in the study. Metoprolol and verapamil were both given intravenously as a bolus, and verapamil was continued as an infusion. The animals were equipped with a VVI pacemaker to treat the expected arteriovenous blockade. A centrifugal pump provided an adjustable flow with a two-stage inflow cannula draining both the upper and lower caval veins and with the outflow cannula in the pulmonary artery. The pump counteracted the effects of right ventricular failure and enabled us to increase the left atrial pressure to more than 20 mm Hg. Pressure in the left atrium rose from 5+/-3 to 25+/-4 mm Hg (p < 0.001), the left ventricular diastolic pressure increased from 2+/-3 to 17+/-7 mm Hg (p = 0.003), and the mean pulmonary pressure increased from 17+/-5 to 33+/-5 mm Hg (p < 0.001). Cardiac output was not significantly changed from 4.0+/-0.8 L/min in the healthy animals to 3.5+/-0.5 L/min (p = 0.25) in failure. The model allowed us to create an adjustable and isolated left ventricular failure well suited for short-term hemodynamic testing of a left ventricular support device.