Filip Petersson

Particle separation using ultrasound can be used with human shed mediastinal blood

Background: Shed mediastinal blood collected by cardiotomy suction has been shown to be a large contributor to lipid microemboli ending up in different organs. The aim of this study was to test the separation efficiency on human shed blood of a new separation method developed to meet this demand. Methods: Shed mediastinal blood collected from the pericardial cavity of 13 patients undergoing cardiac surgery with cardiopulmonary bypass was collected. The blood was processed in an eight-channel parallel PARSUS separator, and separation efficiency was determined. Results: Erythrocyte recovery, in terms of a separation ratio, varied between 68% and 91%. Minor electrolyte changes took place, where levels of sodium increased and levels of potassium and calcium decreased. Conclusion: This study demonstrates that PARSUS technology can be used on human shed mediastinal blood with good separation efficiency. The technology is, thereby, suggested to have future clinical relevance.

Characterization of lipid particles in shed mediastinal blood.

BACKGROUND Shed mediastinal blood is known to be a source of microemboli in cardiac surgery. The aim of this study was to characterize in detail the lipid particles found in this blood. METHODS Blood samples were collected from 24 patients undergoing routine cardiac surgery with cardiopulmonary bypass. Arterial and shed blood was analyzed using the Coulter counter technique to establish the number and size of particles. The composition of these lipid particles was compared with that of adipose tissue from the mediastinum using gas chromatography. Scanning electron microscopy was used to visualize the lipid particles in samples of shed blood. RESULTS Lipid particles in the size range of 10 to 60 microm were characterized in shed mediastinal blood, and more than 300,000 particles per milliliter of blood were found. Triglyceride profiles in these lipid particles and in adipose tissue were similar, suggesting that their origin is the mediastinum. Scanning electron microscopy showed spherical formations corresponding in size to the particles counted using the Coulter counter. CONCLUSIONS During the past decade attention has focused on microembolism in cardiac surgery, and this study has helped define the problem. Different strategies, such as eliminating the use of shed mediastinal blood or purifying the blood by different techniques, may improve the results of cardiac surgery in the future.

Autologous blood recovery and wash in micro fluidic channels utilizing ultrasonic standing waves

It is known that suspended particles are affected by a radiation force when exposed to ultrasound. The particles in a fluidic microchannel of a rectangular crossection are gathered in the nodes when exposed to an ultrasonic standing wave. By introducing a flow splitter at the end of the microchannel, the particles can be separated from the rest of the fluid. If the fluid used in the separation is whole blood, it is possible to separate the erythrocytes from the plasma (Fig. 1). Another aspect of this separation is that fat embolies released and mixed with the blood, e.g. during cardiac surgery, also can be separated from the erythrocytes. Recovered contaminated blood is usually given back (autologous recovery) to the patient uncleaned which results in micro occlusions in the brain capillaries, e.g. fat embolies. The fat embolies are the cause of SCADS (Small Capillary Arteriolar Dilatations) in the brain, i.e. small brain damages which gives rise to a cognitive decay for the patient. The need to wash the blood clean from the fat embolies prior to reinfusion are therefore important. The difference in acoustic impedance between the red blood cells and the fat causes the red blood cells to gather in the nodes and the fat in the antinodes of the acoustic standing wave. It is therefore possible to separate the red blood cells from the fat (Fig.2). This paper describes the development of a microfabricated multichannel array for erythrocyte separation and fat emboli exclusion.

Manipulation os suspended particles in a laminar flow

For some time the art of separating suspended particles by applicating an ultrasonic standing wave field [1–3] has been investigated. The radiation force generated by the ultrasonic field causes the particles to move into the pressure nodal planes of the standing wave (Fig. 1). The radiation force Fr according to eqn.1 is proportional the acoustic pressure amplitude Po, and the particle volume VC and reciprocally proportional to the acoustic wavelenght in the fluid λ.