Forty patients aged > 65 years with severe chronic venous insufficiency ( CVI ; C4-C6 ) successively donned compression stockings in a randomized order : one 40mmHg ( CS40 ) or two superimposed 20mmHg ( CS20 +20 ) , each with open toe ( CS-o-t ) and closed toe ( CS-c-t ) , using donning devices ( three foot slips for CS-o-t ; two foot slips and three frames for CS-c-t ) .