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Physiology

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Cardiovascular System

Question
11 out of 12
 

Ejection fraction increases with



A End. Systolic volume

B End. Diastolic volume

C Peripheral vascular resistance

D Venodilation

Ans. B End. Diastolic volume

Ejection fraction: ­

  1. Definition the percentage of end diastolic ventricular volume that is ejected with each stroke and is about 65%
  2. End - diastolic ventricular volume = 130ml, stroke volume = 70-90ml, and End Systolic ventricular volume 50ml.

Ejection fraction = 70-90 x 100 65%

130

  1. The ejection fraction is a valuable index of the ventricular function Q
  2. If the stroke volume increases, definetinely ejection fraction also increases.
  3. According to frank-starling law of the heart "Energy of the contraction is proportional to the initial length of the cardiac muscle fibers". That is, the length of the muscle fibers (i.e. the extent of the pre-load) is proportionate to the end-diastolic volume. It means that if end diastolic volume increase increases the initial length of muscle fibers →↑es the force of contraction →↑es the stroke volume increases the ejection fraction.
  4. Factors that normally increase or decrease the length of ventricular cardiac muscle fibers: Q

A. Increase

a. Stronger atrial contractions

b. Increased total blood volume

c. Increased venous tone

d. Increased pumping action of skeletal muscle

e. Increased negative intrathoracic pressure

B. Decrease

a. Standing (Lying to standing in position)

b. Increased intrapericardiac pressure

c. Decreased ventricular compliance

Cardiovascular System Flashcard List

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