Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909



Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909
Textbook Problem

Which of the following cause(s) passive

changes in the pulmonary vascular resistance?

1. pH changes

2. Transpulmonary pressure changes

3. Pco 2 changes

4. Blood viscosity changes

A. 2 only

B. 3 only

C. 1 and 3 only

D. 2 and 4 only

Summary Introduction


The vascular resistance is usually calculated by dividing mean arterial pressure with cardiac output. It is directly proportional to blood pressure, that is, when vascular resistance increases, blood pressure increases. There are two mechanisms through which vascular resistance is affected, active and passive. The passive mechanism refers to a secondary change of vascular resistance in response to some mechanical change.


Justification/explanation for the correct answer:

Option (d) states that changes in the transpulmonary pressure and blood viscosity lead to passive changes in pulmonary vascular resistance. Transpulmonary pressure is defined as the pressure difference between the alveolar and intrapleural pressure. It is correct because the thickness of blood (blood viscosity) is the direct ability of the blood to move through the vessels. When blood viscosity increases, vascular resistance increases. Also, as transpulmonary pressure increases, vascular resistance decreases. Vascular resistance decreases because when the intraluminal distending pressure increases, the cross-sectional area of the vessel increases, thereby decreasing the pulmonary vascular resistance. Hence, option (d) is correct.

Explanation for the incorrect answers:

Option (a) states that transpulmonary change causes passive changes in pulmonary vascular resistance. It is incorrect because not only transpulmonary pressure changes but also changes in blood viscosity cause a change in vascular resistance...

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