2013-08-19 Physiology Review

Question 1

What factors influence compliance of lung?

Answer 1

A. The fibrous networks of the lung: 1. axial (connects tissue supporting large aa., brochi and veins at the lung hilum and their proximal ramifications.); 2. visceral pleura; 3. insterstitium (alveolar septal walls) [IMAGE FROM SLIDE 4]

B. Surface-acting forces: decr = saline-filled, incr = surfactant deficiency

Question 2

What factors influence compliance of chest wall?

Answer 2

.

Question 3

What factors influence compliance of respiratory system?

Answer 3

presence of cartilage:
Large - cartilaginous; diameter and patency are independent of parenchyma
Small - non-cartilaginous; patency depends on “traction” from surrounding parenchyma

Question 4

What factors determine the resistance to airflow?

Answer 4

R = (P1-P2)/V

• -nose, pharynx and tracheobronchial tree all contribute
• -most resistance is from MEDIUM and LARGE airways (total cross-sectional area)
• -decreases as you inhale, increases as you exhale (varies with lung volume)

Question 5

Describe the structural characteristics of the lung that play an important role in determining its mechanical properties.

Answer 5

.

Question 6

What’s the difference between passive and forced expiration?

Answer 6

Passive: lung elastic recoil drives’t
Forced: added muscle force to empty ERV

Obvious but key pt is that “Beyond a certain point, increases in expir. effort don’t result in increases in expir. flow.”

Question 7

What factors determine maximal expiratory flow?

Answer 7

P_alv, P_collapse, and the R_upstream

Question 8

Explain the concept of flow limitation.

Answer 8

occurs because the airways are collapsible and narrow as P outside the airway builds

Question 9

Explain P_crit and how it relates to expiratory flow limitation.

Answer 9

The transmural pressure at which the airway collapses. (If airway collapses you really get expiratory flow limitation!) Not sure about sign convention. See page 5 of notes

Question 10

Describe mechanisms that can lead to airflow obstruction.

Answer 10

1. decreased lung elastic recoil
2. increased P_crit (increased tendency of airways to collapse)
3. increased R_upstream 2° to swelling/mucus

Question 11

Why is RV often increased in disorders like asthma and emphysema?

Answer 11

RV is reached when you stop breathing out.

• -you stop breathing out when there is no pressure gradient to drive expiratory flow
• -this occurs when P_elastic = P_crit
• -in emphysema, P_elastic is decreased
• -in asthma, P_crit is increased