Compliance And Resistance

Question 1

Compliance

Answer 1

How “stretchy” the lungs are.
A measure of the elasticity, increasing the ease with which the lungs expand at any Ptp.
= ∆V/∆Ptp

Question 2

Resistance

Answer 2

How easy it is for air to move in or out.
The opposition to motion, governed by POISEUILLE’s LAW.

Question 3

Lung compliance measurements

Answer 3

∆V/∆Ptp, measured on the expiration limb as an average slope between two points of the volume-pressure graph.

Question 4

Lung compliance determinants

Answer 4

1. Stretchability of the lung tissues (innate elastic properties)
2. Surface tension at eh alveoli (decreased by surfactant, we want it LOW)

Question 5

Emphysema
“Floppy lungs”

Answer 5

Increased lung compliance; for every increase in pressure, the increase in volume is greater than in normal lung tissues causing destruction of tissues so that they may not bounce back after inspiration.
Expanded chest wall.

Question 6

Fibrosis
“stiff lungs”

Answer 6

Decreased lung compliance; for every increase in pressure, the increase in volume is less than normal, commonly caused by collagen fibre deposition.

Question 7

Compliance in liquid filled lungs

Answer 7

Lungs inflated with saline are much easier to distend (higher compliance).
This difference is caused by surface tension forces that become abolished.

Question 8

Surface tension of alveoli

Answer 8

Lined with a thin film of fluid = surface tension.
Governed by the law of LAPLACE.

Question 9

Law of laplace

Answer 9

P = 2T/r
P is the collapsing pressure on the alveolus (want to be low)
Small alveoli therefore have a high collapsing pressure and require more pressure to keep open, a problem which is solved by surfactant.

Question 10

Pulmonary surfactant characteristics

Answer 10

Mixture of proteins and phospholipids secreted by type II alveolar epithelial cells that acts to lower surface tension of the water layer. This increases COMPLIANCE making it easier for the lungs to expand.
Secretion is increased by taking a deep breath, which stimulates type II cells.

Question 11

Respiratory distress syndrome of the newborn

Answer 11

Normal develops within late gestation, but if not, the deficient production results in RDS within minutes of birth. High breathing rates thus require great effort.
Treated with corticosteroids and exogenous surfactants given after birth.

Question 12

Airway resistance determinants (4)

Answer 12

Lung volume - diameter is inversely proportional.
Viscosity - increased viscosity increases pressure, O2-He is (low viscosity) used to treat.
Autonomic nervous system - PS cholinergic fibres constriction, and SNS adrenergic fibres β2 relaxation.
Other agents - histamine, ACh, TxA2, leukotrines released in response to triggers, cause bronchoconstriction.

Question 13

Poiseulle’s law

Answer 13

R = 8ηL/(πr^4)

Question 14

Diseases associated with airway resistance

Answer 14

Asthma - airway smooth muscles constrict
increases resistance and thus the work of breathing increases.