Which of the following factors cause an increase in venous ...

[abarnes]

Which of the following factors cause an increase in venous return? I. increase in the lung compliance II. increase in mean systemic pressure III. increase in the right atrial pressure IV. decrease in right atrial pressure
 
  A. II, III only
  B. II, IV only
  C. I, III, IV only
  D. I, II, III only

Question 2

What is the functional upstream pressure for venous return, which is a primary determinant of cardiac output?
 
  A. pleural pressure
  B. right atrial pressure
  C. mean systemic pressure
  D. mean circulatory filling pressure

[EAN94]

Answer to Question 1

ANS: B
A. Incorrect response: See explanation B.
B. Correct response: An increased mean systemic pressure or a decrease in the right atrial pressure will increase venous return. Conversely, a reduction in the mean systemic pressure or an increase in the right atrial pressure decreases venous return.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.

Answer to Question 2

ANS: C
A. Incorrect response: Pleural pressure fluctuates throughout the ventilatory cycle regardless of whether the breathing is spontaneous breathing or positive-pressure breathing. During spontaneous ventilation (SV), pleural pressure remains subatmospheric. However, during positive-pressure ventilation (PPV), pleural pressure becomes supra-atmospheric.
B. Incorrect response: The right atrial pressure represents the end of the downstream end of the pressure gradient responsible for venous return.
C. Correct response: Mean systemic pressure is the weighted average of all pressure from all parts of the systemic circulation. The elastic properties of the blood vessels and the volume of blood they contain determine the magnitude of the mean systemic pressure.
D. Incorrect response: See explanation C.