Positive G effect ?
Ans. is 'b' i.e., Black outEffects of positive G:Venous return decreases --> hence, cardiac output decreases.Blood rushes towards lower limbs --> hence increased pressure in lower limb vessels.Blood is drawn away from upper body --> hence decreased cerebral aerial pressure.At very high positive G:Difficulty in blood flow to brain --> results in cerebral ischemia & unconsciousness.Moments before unconsciousness, there is gray-out.Everything appears gray - Due to ischemia of cone & loss of color vision.Eg: Gray-out serves as warning sign for pilots - Indicates need for slowing down aircraft & reduce positive'G'.Gray-out followed by black-outBlack-out means total loss of vision.
Red out
Black out
Increased cerebral aerial pressure
Increased cardiac output