Abstract
Cardiopulmonary bypass procedures are one of the most common operations and blood oxygenators are the centre piece for the heart-lung machines. Blood oxygenators have been tested as entire devices but intricate details on the flow field inside the oxygenators remain unknown. In this study, a novel method is presented to analyse the flow field inside oxygenators based on micro Computed Tomography (μCT) scans. Two Hollow Fibre Membrane (HFM) oxygenator prototypes were scanned and three-dimensional full scale models that capture the device-specific fibre distributions are set up for computational fluid dynamics analysis. The blood flow through the oxygenator is modelled as a non-Newtonian fluid. The results were compared against the flow solution through an ideal fibre distribution and show the importance of a uniform distribution of fibres and that the oxygenators analysed are not susceptible to flow directionality as mass flow versus area remain the same. However the pressure drop across the oxygenator is dependent on flow rate and direction. By comparing residence time of blood against the time frame to fully saturate blood with oxygen we highlight the potential of this method as design optimisation tool.In conclusion, image-based reconstruction is found to be a feasible route to assess oxygenator performance through flow modelling. It offers the possibility to review a product as manufactured rather than as designed, which is a valuable insight as a precursor to the approval processes. Finally, the flow analysis presented may be extended, at computational cost, to include species transport in further studies.
Highlights
According to the National Health Service (NHS [19]) and Health and Safety Executive (HSE [10]), up to 25,000 people die of Chronic Obstructive Pulmonary Disease (COPD) every year and the disorder affects over a million individuals in Great Britain
If Qbc is the prescribed mass flow rate through the device and ACS is the cross-sectional area of the oxygenator an area A can be defined for every value of the flow fraction Q, where the flow fraction is defined as 0 ≤ Q ≤ 1
The presented μCT scans provide a feasible way to reconstruct an Hollow Fibres Membranes (HFM)-oxygenator with computer-aided design software (CAD) based on individual hollow fibres
Summary
According to the National Health Service (NHS [19]) and Health and Safety Executive (HSE [10]), up to 25,000 people die of Chronic Obstructive Pulmonary Disease (COPD) every year and the disorder affects over a million individuals in Great Britain. In addition up to 400 people develop Acute Respiratory Distress Syndrome (ARDS) with a mortality rate of over 50%. Mechanical ventilation, mainly controlled by pressure and/or volume (Chatburn et al [4]), transfers oxygen into the lungs of the patient for the gas exchange. Often the ventilation pressure and oxygen concentration are set very high to overcome the impaired lung function. For details on the development of ECMO, the reader is referred to Haworth [8]
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