A standing person lies down. Which of the following physiological change occurs immediately? (D. REPEAT Feb 2014)

Ans: C (Immediate increase in venous return) Ref: Guyton 12th edition and A Textbook of Practical Physiology By C. L. Ghai, pg 243ExplanationStanding to Lying PositionDecreased peripheral vascular resistance.Increased venous return to heart.Rise in HR followed by slowing of heart.The rise and fall in HR is due to changes in vagal tone.Sudden Standing from Supine PositionSudden standing - Pooling of blood in lower parts of body - Fall in venous return - Decrease in Cardiac output and Blood pressure - Decreased baroreceptor activity - Increase in sympathetic tone and decrease in parasympathetic activity - Reflex increase in heart rate and peripheral vasoconstriction - Heart rate falls.Heart rate rises immediately on standing and continues to rise for next 15-20 seconds, after which it slows down to a maximum degree as a result of variations in vagal tone.