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Cardiovascular System

7 out of 7

A shift of posture from supine to upright posture is associated with cardiovascular adjustments. Which of the following is not true in this context:

A Rise in central venous pressure

B Rise in heart rate

C Decrease in cardiac output

D Decrease in stroke volume

Ans. A Rise in central venous pressure

I. In the standing position, as a result of the effect of gravity on the blood, the mean arterial blood pressure in the feet of a normal adult is 180— 200 mmHg and the venous pressure is 85—90 mmHg.

II. The arterial pressure at head level is 60—75 mmHg and the venous pressure is zero.

III. The major compensations on assuming the upright position are triggered by the drop in blood pressure in the carotid sinus and aortic arch.

IV. The heart rate increases, helping to maintain the cardiac output.

V. There is relatively little venoconstriction in the periphery, but there is a prompt increase in the circulating levels of renin and aldosterone.

VI. The arterioles constrict, helping to maintain blood pressure.

VII. We have got a figure from Ganong which will help you reach the answer.

Effect on the CVS of rising from supine to the upright: -

[Figures shown are average changes. Changes in abdominal and limb resistance and in blood pressure are variable from individual to individual]

  1. Arterial blood pressure decrease Q
  1. Central venous pressure decrease(3 mmHg) Q
  1. Heart rate increase (25) Q
  1. Abdominal and limb flow' decrease by 25% Q
  1. Cardiac output decrease by 25% Q
  1. Stroke volume decrease by 40% Q
  1. Abdominal and limb resistance increase Q
  1. Total peripheral resistance increase by 25% Q
  1. Small vein pressure increase 10 min Hg Q
  1. Cerebral blood pool decrease by 400 ml Q.