In @ % of these patients ( n = @ ) , COx became highly negative after vasoactive drug administration ( from -@ -LSB- -@ to @ -RSB- to -@ -LSB- -@ to -@ -RSB- after administration of phenylephrine , and from -@ -LSB- -@ to @ -RSB- to -@ -LSB- -@ to -@ -RSB- after administration of nitroprusside ) .