Needle assemblies with anti-backflow features

A needle assembly for use in resisting backflow of blood being collected from a patient comprising:

• a housing having a forward end, a rearward end and a chamber therein;
• a first access opening through the forward end of said housing in fluid communication with said chamber;
• a cannula extending outwardly from said first access opening in fluid communication with said chamber and being adapted for insertion in a patient;
• a second access opening through the rearward end of said housing in fluid communication with said chamber adapted for communication with collection means for receiving said blood;
• and
• means positioned in said chamber to provide flow resistance to the flow of blood from said chamber toward said first access opening, said flow resistance means including a plurality of substantially rigid, non-operative objects within said chamber to limit the flow area of blood within said chamber, said objects including tapered cones being substantially centrally mounted within said chamber while leaving annular clearance for blood to flow therearound, said cones positioned so that their narrow, tapered portions face toward said first access opening whereby flow of blood is favored in the direction from said first access opening into said chamber and is resisted in the opposite direction.