Which of the following statements accurately describe pulmonary vascular capacitance? I. During lung ...

(Answer to Q. 1)  ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response: As the lungs inflate, alveolar vessels are compressed and they
experience a decrease vascular capacitance. At the same time, the extra-alveolar vessels experience an increased pulmonary capacitance. If alveolar capillaries are engorged with blood as during a hypervolemic state, inspiration causes a discharge of alveolar-capillary blood volume into the left atrium. However, if alveolar capillaries are less full, as in the case of hydration lung, inflation will result in a transient decrease in pulmonary vessel outflow as blood pools in the enlarged extra-alveolar vessels.

(Answer to Q. 2)  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 Q. 3)  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.

(Answer to Q. 4)  ANS: A
A. Correct response: Alveolar vessels are exposed primarily to alveolar pressure. Therefore, when the lungs inflate the alveolar vessels experience an increased pulmonary vascular resistance. In other words, as alveolar volume increases, alveolar vessels are compressed; therefore pulmonary vascular resistance increases through these vessels during inspiration. On the other hand, the extra-alveolar vessels are influenced essentially by pleural pressure. Consequently, when the lungs deflate, and pleural pressure increases, the extra-alveolar vessels experience an increased pulmonary vascular resistance.
B. Incorrect response: See explanation A.
C. Incorrect response: See explanation A.
D. Incorrect response: See explanation A.

(Answer to Q. 5)  ANS: A
A. Correct response: Because the right and left ventricles share the same space in the pericardium, and increase in the size, of one chamber requires a decrease in the size, shape and function of the other.
B. Incorrect response: See explanation A.
C. Incorrect response: See explanation A.
D. Incorrect response: See explanation A.

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