Lecture 2 Ventilation Continued

Question 1

Why do respiratory muscles generate work?

Answer 1

To overcome recoil tendency of lungs and frictional resistance to airflow by airways

Question 2

Elastance

Answer 2

A measure of the elastic recoil tendency of a balloon or lung

Question 3

Compliance (C)

Answer 3

1/ elastance
A measure of ease of stretch
C= delta vol / delta P

Question 4

How is the amount of change in PPL (transpulmonary P) determined?

Answer 4

By change in lung volume and lung compliance
Airflow rate (Vr)
Airway resistance (R)
Delta PPL = (delta V/C) + RVr

Question 5

What happens with a decrease in PPL?

Answer 5

Change in the volume of air is increased (more air sucked in)
Increased compliance

Question 6

Pneumothorax

Answer 6

At FRC, it’ll lead to collapse of lungs to their minimal volume due to elastic and collagen tissue and surface tension forces

Question 7

Surface tension

Answer 7

Measure of the force acting to pull a liquid’s surface molcules together at an air-liquid interface

Question 8

Pulmonary surfactant

Answer 8

A complex mix of lipids and proteins produced by Type 2 cells
Present at the alveolar air-water interface
Prevents an overstretch!!

Question 9

What are the 3 major effects of pulmonary surfactant?

Answer 9

Reduces surface tension and increase compliance
Reduce fluid accumulation in alveoli
Keeps alveolar size uniform during respiratory cycle

Question 10

What is the most abundant component of pulmonary surfactant?

Answer 10

DPPC and it’s hydrophilic and hydrophobic portions cause it to seek the surface of the alveolar lining

Question 11

What happens to the concentration of surfactant molecules at TLC?

Answer 11

It becomes sparse at the alveolar surface
Surface tension will increase helping deflation

Question 12

Hysteresis

Answer 12

Difference between inflation and deflation paths due to initial force need in surfactant’s role to stabilize the lungs

Question 13

Emphysema

Answer 13

Destroys lung tissue and makes lungs floppy (smoking)
Lungs have high compliance but tissue architecture is lost

Question 14

Fibrosis

Answer 14

Deposition of fibrous tissue
Restricts inflation
Lungs are poor in compliance

Question 15

________ in airways slows airflow

Answer 15

Frictional resistance
upper respiratory tract (60%)

Question 16

________ increases airflow during exercise

Answer 16

Mouth breathing

Question 17

Obligatory nasal breathers

Answer 17

Horses
Flare their nostrils and can constrict BVs to shrink mucosa

Question 18

Resistance

Answer 18

Inversely proportional to radius
Directly proportional to length (Poiseuille’s law)

Question 19

How is radius altered?

Answer 19

Inhalation dilates airways
Contraction of smooth muscle reduces airway diameter and increases resistance to airflow
Flaring of nares
Vasoconstriction
Bronchoconstrictors/ dilators

Question 20

Parasympathetic smooth muscle contractions

Answer 20

1. Vagus releases ACH and activate muscarinic receptors (induces bronchoconstriction)
2. Irritant subs induce reflex bronchoconstriction by activating PNS
3. Mediators of inflammation (histamine and leukotrines from mast cells) act on muscles directly or via PNS (heaves, asthma)

Question 21

Sympathetic smooth muscle contractions

Answer 21

Sympathetic NS inhibits airway smooth muscles (catecholamines, muscle realxation/ dilate airways)
NANC system (nitric oxide is the NT, inhibitory)

Question 22

Dynamic compression of airways

Answer 22

The negative transmural pressure that makes airways (nares, pharynx, larynx) collapse
Adductor muscles normally prevent

Question 23

When does dynamic compression occur?

Answer 23

During forced exhalation when PPL exceeds PA
ex: coughing air moves in high velocity in a dynamically collapsed airway facility removal of foreign material

Question 24

Laryngeal Hemipegia in horse

Answer 24

Loss of nerve supply
Abductor muscles atrophy then fail to contract during inhalation
Vocal fold sucked into lumen producing inspiratory roaring
Idopathic

Question 25

What does distribution of air depend on?

Answer 25

Local mechanical properties of the lung
Always uneven (esepcially in disease)

Question 26

Collateral Ventilation

Answer 26

Movement of air between adjacent lobules (septum)
Affected by type of CT between lung lobules
Better ventilation in species without separation

Question 27

Species variation of lung lobule separation

Answer 27

No separation (air moves between lobules): dogs and cats
Partial separation: horses and sheep
Complete separtion (obstruction dangerous): cattle and pigs