Mechanics of breathing

Question 1

Air flow direction

Answer 1

Air flows IN as long as Palv is < Patm
Air flows OUT as long as Palv is > Patm
Airflow will stop when Palv = Patm

Question 2

Palv is inversely proportional to

Answer 2

Alveolar volume

Question 3

Distending pressure and elastic recoil effects

Answer 3

Application of a distending pressure increases alv volume lowers Palv
This causes inward airflow

Elastic recoil decreases alv volume increases Palv
This causes outward airflow

Question 4

Distending pressure

Answer 4

= transpulmonary pressure (Ptp)

Like a transmural pressure, it is the different between the inside and outside pressure

Ptp is generated by inspiratory muscles (which act on the chest wall to alter Ppl)

Ptp = Palv – Ppl

Question 5

Lungs want to be smaller

Answer 5

Lung tissue is elastic. Higher elastic recoil = more difficult
to inflate the lungs. Elastic recoil is a measure of how
stretchy or stiff the alveoli and connective tissue are.

Question 6

Chest wants to be bigger

Answer 6

Chest wall has elastic properties too, but also acts as a spring.
At nearly all lung volumes the chest wall wants to expand
outwards.

Question 7

Intrapleural pressure

Answer 7

The inward force of the lungs + the outward force of the chest

Question 8

Longer radius

Answer 8

flatter diaphragm = less pressure force generated for a breath

Question 9

Ppl

Answer 9

Average of pleural pressures throughout the lung. Reminder that pleural pressure varies by lung height (highest in the apex).

Question 10

Compliance

Answer 10

Distensibility of a chamber/hollow organ/inflatable object due to changes in transmural pressure. Slope of

Compliance of the lung (Ccw): relationship between changes in lung volumes and Ptp ( = Palv – Ppl)

Compliance of the chest wall (Cl): relationship between changes in lung volumes and transmural pressure. transmural pressure = inside – outside pressure = Ppl - Patm

Question 11

Hysteresis

Answer 11

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Question 12

Pulmonary surfactant

Answer 12

Phospholipoproteins made by type II alveolar cells:
Reduce surface tension -> increase lung compliance

Premature babies (< 30 weeks) have not made enough surfactant and are at risk for infant respiratory distress syndrome

Question 13

Preventing alveoli collapse

Answer 13

Alveolar interdependence

Pulmonary surfactant

Question 14

Breathing

Answer 14

Overcoming recoil pressures (elastic and surface tension), to change the lung volume, and
airway resistance during airflow

Question 15

Types of flow

Answer 15

Laminar
Turbulent
Transitional

Question 16

Reynold’s number

Answer 16

predicts conversion to turbulent flow

Question 17

Airway radius and airflow (Reynold’s number)

Answer 17

In a laminar flow system (Ohmic), resistance is described by the law equating resistance and radius (Poiseuille’s law): ∆P/Q = R = (8 n l) / ( r4)

Resistance varies directly with the fourth power of the airway radius

When the airways narrow (ie asthma) resistance increases, and flow decreases dramatically