11- Respiratory Structures and the mechanics of breathing

Question 1

what do the chest call and lungs both have in common

Answer 1

elastic structures

Question 2

Alveolar Pressure (P or PA )

Answer 2

Pressure within alveoli (equal to atmospheric when there is no airflow).

Question 3

Pleural Pressure (Ppl)

Answer 3

Pressure within pleural space(is sub- atmospheric when there is no airflow

Question 4

Transpulmonary or Recoil Pressure (PTP or PRe)

Answer 4

Difference between pleural and alveolar pressures (reflects elastic recoil pressure of the lung)

Question 5

values at end expiration

Answer 5

Ppl is -5, PRe is 5, PA is O cmH2O

Question 6

values during inspiration

Answer 6

Ppl is -8, PRe is 7, PA is -1 cm H2O

Question 7

what happens during inspiration

Answer 7

diaphragm contracts

pleural space is expanded which decreases pleural pressure

Question 8

Sequence of events during a normal breath

Answer 8

During Inspiration:
1. The brain initiates diaphragm and/or intercostal muscles contraction.

2. Pleural space increases as chest wall expands.
3. When the pleural space increases, the PPL becomes more negative countering recoil pressure thereby expanding alveoli.
4. Alveolar pressure falls below atmosphere pressure
5. Air flows into alveoli to equalize alveolar and atmospheric pressure.

Question 9

sequence of events during normal expiration

Answer 9

1. The brain ceases inspiratory command.
2. Inspiratory muscles relax.
3. Thoracic volume decreases causing PPL to become less negative and decreasing the alveolar pressure gradient.
4. Alveolar elastic recoil increases alveolar pressure above atmospheric
   providing airflow until alveolar and atmospheric pressure equalize.

Question 10

Changes in PA and PPL during a breath

Answer 10

PA changes less than PPL during a breath because a

portion of PPL is used to overcome lung recoil

Question 11

Reflects lung compliance

Answer 11

∆V/∆PTP

Question 12

Airway resistance

Answer 12

R=PA /airflow

Question 13

what happens to lung recoil pressure (PRe) as lung volume increases?

Answer 13

lung recoil pressure (PRe) increases

• lungs always want to be at a 0 pressure so the further away it is from 0 the more likely it is to collapse
• lung pressure and volume have a direct (non-linear) relationship

Question 14

lung recoil, tissue elasticity, and surface tension

Answer 14

• large pressure change required to initially inflate with air
• lung recoil due to elastic tissue and surface tension

Question 15

density of surfactant molecules determines surface tension

Answer 15

• higher density of surfactant in small alveoli prevent these alveoli from empting into large alveoli
• phospholipids in surfactant minimize surface tension in the lung

Question 16

Atelectasis

Answer 16

Collapse of Alveoli

• caused by obstruction of airway and subsequent absorption of gases
• absence of surfactant facilitates this b/c of high collapsing pressure (spend a lot of energy trying to reopen the lungs everytime)

Question 17

Sighs

Answer 17

large tidal volumes that alleviate atelectasis (large negative pleural pressure to pop open the alveoli that have collapsed)

Question 18

emphysema

Answer 18

destruction of lung elastic tissue (less surfactant)

Question 19

lung compliance and 2 diseases

Answer 19

Lung compliance is…

• increased in pts with emphysema
• decreased in pts with pulmonary fibrosis

Vital capacity vs pressure graphs

emphysema (closest to y-axis) -> normal -> fibrosis

Question 20

Elastic Characteristics of the Chest Wall

Answer 20

Equilibrium position 60% of vital capacity (VC)

Chest wall compressed to residual volume (RV)

• attempts to expand
• exerting a force of 40cm H20

Chest wall forced to total lung capacity (TLC)

• attempts to collapse
• exerting a force of about 15mmHg

Elastic Characteristics of the Chest Wall and lung
-the lung recoil pulls the chest in and the chest recoil pulls the lungs out

Question 21

abnormalities of chest wall (pretty low yield info here)

Answer 21

Most abnormalities decrease chest wall compliance to decrease TLC and capability for chest wall expansion.

1. Ankylosing spondylitis- stiff chest wall (inflammatory induced fibrosis) 2. Kyphosis (anteroposterior angulation)
2. Scoliosis (excessive lateral curvature)
3. Obesity (soft tissue restriction)
4. Aging (fibrosis)(Infants have a very compliant chest wall) Patients with an abnormal chest wall are dyspneic

Question 22

airway resistance

Answer 22

Determined primarily by diameter of airways.

The total area of multiple small airways is greater than that of the large airways.

Thus, resistance is greater in the trachea than in the combined terminal bronchi.

Question 23

airway resistance v. volume

Answer 23

airway resistance decreases as lung volume increases

Question 24

what acts like springs to expand the airways

Answer 24

elastic recoil of the alveolar septa attached to airways

Question 25

what happens to flow and lung volume during expiration

Answer 25

flow decreases as lung volume decreases

Question 26

what occurs at low lung volumes

Answer 26

flow is effort independent

increments in PA are offset by airway constriction

Question 27

emphysema and pulmonary fibrosis effect on expiratory flow

Answer 27

Emphysema and pulmonary fibrosis decrease maximal effort expiratory flow

Question 28

one reason breathing is regulated

Answer 28

to avoid high and low lung volumes

Question 29

four major diseases of increased airway resistance

Answer 29

1. Emphysema – due to decreased tethering of airways by lung elastic tissue, airway diameter is below normal.
2. Bronchitis – reduced airway diameter due to increased mucous and airway inflammation.
3. Asthma – hyperactive airway smooth muscle causes excessive muscle contraction that narrows airways.
4. Obstructive Sleep Apnea – Closure or compression of pharyngeal airway due to excessive adipose tissue and/or reduced airway dilator muscle activity.

Question 30

“time constant” of airway

Answer 30

reflects rate of alveolar filling when a pressure change is applied

Question 31

what happens if one lung is partially constricted?

Answer 31

one will start moving air into the constricted one so its not getting as much fresh air. also the not constricted one will move a lot faster at those conditions where you breath more

Question 32

correct sequence of changes during an inspiration

Answer 32

1. increased diaphragm activity
2. expansion of pleural space
3. decreased pleural pressure
4. decreased alveolar pressure
5. inspired flow

Question 33

correct sequence of changes during an expiration

Answer 33

1. increased diaphragm activity
2. decreased pleural pressure
3. decreased alveolar pressure
4. expiration