Abstract
Three types of microemboli filters were examined with the scanning electron microscope. The single layer 40 mu pore filter traps aggregates in the pores. The aggregates are extruded and pass on with the blood and can be demonstrated in a Dacron wool filter downstream. The polyurethane foam filter is an in depth multiple pore filter of variable pore size. This filter allows many aggregates to escape through the pores in the beginning of a transfusion and these aggregates were seen in a Dacron wool filter downstream. As aggregates become trapped, the pore sizes decrease, filtration improves, and flow through the filter becomes reduced. The Dacron wool filter absorbs the particulate material to the fibers of wool. This filter has a large capacity and was not observed to leak aggregates even when subjected to high filtration pressures.