Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909



Cardiopulmonary Anatomy & Physiolo...

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

When arranged for flow Poiseuille’s law states that flow is

1. inversely proportional to r4.

2. directly proportional to P.

3. inversely proportional to η .

4. directly proportional to l.

A. 1 only

B. 2 only

C. 2 and 3 only

D. 3 and 4 only

Summary Introduction


The normal inspiration occurs when the intrapleural pressure decreases from its normal negative value to a more negative value, which causes the bronchial airways to dilate, lengthen and increase in the diameter. The expiration process also decreases the diameter of the airways. These anatomical changes depend on a number of factors which are decided by Poiseuille’s law. The law is as follows:

V = ΔPr4π8lη

where V is the volume of gas or fluid flowing through the tube,

Ƞ is the viscosity of gas or fluid,

∆P is the change in pressure from one end of the tube to the other,

Π and 8 are the constants, and r is the radius of the tube and l is the length of the tube.


Justification/ Explanation for the correct answer:

Option (c) states that the flow is directly proportional to pressure and inversely to viscosity. The above equation shows that the pressure changes from one end of the tube to another directly influences the volume flow. The flow always occurs on the basis of pressure gradient. A gas or fluid flows from a higher pressure to a lower pressure. Viscosity is the resistance due to friction between the layers of the gas or fluid, so, if it increases, the flow volume decreases. Hence, option (c) is the correct answer.

The explanation for the incorrect answers:

Option (a) states that the flow is only inversely proportional to the radius (r4). If the radius of tube increases, then there will be more space for the fluid or gas to flow, and thus the flow should increase so this factor is directly proportional to the flow...

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