Lecture 1 (part 2): Static and Dynamic Mechanical Properties of Lungs, Diaphragm, and Chest Wall

Ribalet: slides 54-end

Exhale at rest is __.

passive

Inhalation creates __ pressure in pleural cavity, whereas exhalation creates __ pressure in pleural cavity.

negative; positive

Both lungs are invested by and enclosed in a serous pleural sac that consists of 2 continuous membrane known as __. What are the 2 parts of this membrane?

pleurae; visceral & parietal

The __ covers the lungs and adheres to all its surfaces including those of the horizontal and oblique fissures.

visceral pleura

The visceral pleura cannot be __ from the lungs and is innervated by __.

dissected; autonomics

The __ lines the pulmonary cavities, adhering to the thoracic wall, mediastinum, and diaphragm.

parietal pleura

What is the parietal pleura innervated by?

intercostal and phrenic nerves

The potential psace between the 2 pleura layers is the __.

pleural cavity

What fills the pleural cavity? Why?

serous fluid: lubricates the pleural surfaces which allows the pleura to slide smoothly during respiration

• gives frictionless surface so it can move

Visceral and parietal pleura reduce friction between the __ and __ with inhalation and exhalation.

chest wall; lungs

Visceral and parietal pleura creates __ to cause the lung to remain against the thoracic wall.

surface tension

Without the visceral and parietal pleural surfaces interacting, there will be a __.

pneumothorax

The tendency of the lung is to __.

recoil

In a normal lung at rest, the elastic recoil of the chest wall tries to pull the chest wall __, whereas the elastic recoil of the lung creates a __ pull.

outward; inward

In pneumothorax, the lung there is __ in the pleural cavity.

air (rather than fluid): sealed pleural cavity is opened to atmosphere (due to some trauma)

In a pneumothorax, how do the rib cage and lungs react?

• rib cage: expands slightly

• lung: collapses to unstretched size (lung recoils maximally)

What does pleural pressure affect? (4)

• cyclical variation with breathing

• equilibrium positions

• effect of change in recoil

• effect of gravity

At rest:

• respiratory muscles are __

• recoil of lung and chest wall are __ but __

• pressure along tracheobronchial tree is __

• there is no __

• respiratory muscles are at rest

• recoil of lung and chest wall are equal but opposite

• pressure along tracheobronchial tree is atmospheric

• there is no airflow

__ is the pleural pressure - pressure at surface of chest

elastic recoil of chest wall

__ is the alveolar pressure - pleural pressure

elastic recoil of lung

During inspiration, inspiratory muscles __ and chest __.

contract; expands

During inspiration, alveolar pressure becomes __ with respect to __ at the airway opening. Air then flows into __.

subatmospheric; pressure; lungs (bc air flows from high = airway to negative = alveoli)

During expiration, inspiratory muscles __. Recoil of lung causes alveolar pressure to __ pressure at airway opening. Air flows __ of lung.

relax; exceed; out

__ is the ratio of volume to pressure. It relates to the __ of the lung.

compliance; distensibility

• compliance = change in volume over change in pressure

If there is more compliance, then there is more __, which gives more __ for gas exchange.

If there is no compliance, there is no __, and more __ is required to obtain a given volume.

• lung expansion; volume

• expansion; pressure

__ in large airways but not alveolar ducts.

cartilage

In the alveolus, there is alveolar septal __ and __ within the alveolus.

interdependence; surface tension

How do airways in the gas exchange zone stay open without the support cartilage?

interdependence

A more extended alveoli is __ compliant, where as a less extended alveoli is __ compliant. Where are alveoli more extended vs less extended?

• less; more

• more extended near top of lung, less extended near bottom of lung (bc gravity)

more expanded alveoli are less compliant bc elastic fibers are already stretched, so additional expansion needs more pressure.

less expanded alveoli are more compliant bc tissue are more easily stretched with less pressure (inc lung expansion = more volume = more compliant)

What does it mean that alveoli are interdependent?

they are packed together and work as a unit

Alveoli have tendency to __, which gives the lung a tendency to__.

recoil; recoil

When alveoili recoil, they pull on the __

air duct

All alveoli have the same __ pressure and pull on the __ to keep it open.

recoil; air duct wall

If a membrane breaks, __ decreases, and this can cause __.

elastic recoil; emphysema

When dynamic compression occurs, __ helps to oppose it by traction on small airways.

alveolar elastic recoil

The __ becomes the effective driving pressure for airflow from the lung.

alveolar elastic recoil

Because bronchioles and alveolar ducts contain no cartilage support, they are subject to __ when compressed.

collapse

When collapse occurs, it is partially opposed by the attachment of the __, which contains __ on their walls. This is an example of interdependence.

alveolar septa; elastic tissue

The outer most layer of the bronchiolar wall is surrounded by __

dense connective tissue with many elastic fibers

Surfactant reduces __

surface tension

Which alveolar cell type secretes surfactant?

type II alveolar cells (septal cells)

Surfactant is __ and decreases __.

hydrophobic; recoil force/recoil pressure

Strong air/water interface has a strong tendency to __ alveoli, which initiates __.

collapse; elastic recoil

What is Laplace’s law for the respiratory system?

pressure in alveoli = directly proportional to surface tension and inversely proportional to radius of alveoli

• inc radius = dec pressure

• P = 2T/r (P= pressure, T = surface tension, r = radius)

Between these two bubbles, which has higher pressure if both have the same surface tension?

smaller bubble

Surfactant reduces __ and pressure is __ in the large and small bubbles.

surface tension; equalized

• bigger bubble has less surfactant

• smaller bubble has more surfactant and less tendency to collapse (more bc pressure in small bubbles = higher, so more surfactant to counter and prevent collapse)

If only pressure recoil is present, all __ will collapse. But if there is only surfactant, all __ will collapse.

small alveoli (bc they are more susceptible to pressure); big alveoli (bc they have less surfactant to prevent collapse)

How does gravity affect regional ventilation?

• apex of lung: larger alveoli, expands less

• base of lung: smaller alveoli, expands more

Describe ventilation and perfusion at the apex of the lung.

ventilation:

• intrapleural pressure = more negative

• greater transmural pressure gradient

• alveoli larger, less compliant

• less ventilation/gas exchange

perfusion:

• lower intravascular pressures

• less recruitment & distention

• higher resistance

• less blood flow (less capillaries)

Describe ventilation and perfusion for the base of the lung.

ventilation:

• intrapleural pressure = less negative

• smaller transmural pressure gradient

• alveoli smaller, more compliant

• more ventilation (more gas exchange)

perfusion:

• greater vascular pressures

• more recruitment, distention

• lower resistance

• greater blood flow (more capillaries)

If a patient has trouble breathing, what position can you put them in?

supine/prone position (to inc ventilatin/perfusion in upper half of lung)

There are various lung zones that have higher local __ and __, and these can be changed based upon __ of patient, as well as their __.

ventilation; perfusion; positioning; activity state

__ = collapse of airways

atelectasis

In an injured alveolus during acute phase, __ is inactivated.

surfactant

• injured alveolus during acute phase = acute respiratory distress syndrome

What is prone position?

laying on stomach

Surfactant plays a role in __ seen on the volume pressure curve.

hysteresis (diff bw P-V curve during inhalation vs exhalation)

Surfactant plays a significant role in pathophysiology of the __.

acute respiratory distress syndrome (ARDS)

Pleural fluid between visceral and parietal pleura acts to reduce __ between the chest wall and the lungs.

friction

Pleurae create __ to cause the lung to remain against the thoracic wall. Without this, the lungs have a tendency to __.

surface tension; collapse

Air flows along a negative pressure gradient during __.

inhalation

Due to the __ of the chest wall, we can never fully exhale all the air from our lungs. This is considered __.

elastic recoil; residual volume

As the lungs expand more, they reach a point in which compliance goes __ as increases in __ make __ changes in volume.

down; pressure; small

Compliance is a function of the difference in __ over the difference in __, and reflects how __ the lung is.

volume; pressure; distensible

__ helps prevent an alveolus from collapsing spontaneously.

alveolar interdependence

__ reduces surface tension.

surfactant

In the Acute respiratory distress syndrome, there is lack of __.

surfactant

__ positioning redistributes blood and air flow more evenly, reducing imbalance and improving gas exchange in acute respiratory distress syndrome.

prone

The pressure in the __ is the sum of total elastic recoil pressure (Pst) and pleural pressure (Ppl).

alveoli (Palv)

If equal pressure point is at a point where cartilage is, there will be no __. But if it is in a place where cartilage isn’t there will be __, causing __.

collapse; collapse; emphysema

What is the equal pressure point?

point where intrapleural pressure and alveolar pressure are equal

In forced exhalation, both intrapleural pressure and alveolar pressure will __. However, alveolar pressure will __ along the length of the airway until a pressure of __ at the mouth, whereas intrapleural pressure will remain the __.

increase; decrease; 0; same

There will be a point where intrapleural pressure will be __ and subsequently __ than alveolar pressure. However, this is generally reached at the __. Therefore, they do not __.

equal; greater; cartilaginous airways; collapse

Bronchioles and alveolar ducts contain no __, so they are subject to __ when compressed.

cartilage; collapse

Collapse in bronchioles and alveolar ducts is partially opposed by the attachment of the __, which contains __.

alveolar septa; elastic tissue to walls

• interdependence

The outer most layer of the bronchiolar wall is surrounded by:

dense connective tissue with many elastic fibers

When EPP occurs at the cartilaginous airway, the airway does not __.

collapse

When EPP occurs at non-cartilaginous airways, there is __.

air trapping

• can breathe in but breathing out increases pressure ion airway where there is no cartilage since EPP is lowered to a more distal point

Increasing the force of expiration does not __, since it will increase both: (2)

overcome EPP; alveolar and intrapleural pressure

EPP moves distally as expiration progresses bc:

as air leaves alveolar unit, the pressure in the alveolar decreases hence pressure in airway decreases as well

In healthy individuals, EPP occurs at the __ airways. In patients with high compliance (emphysematous) or high resistance (bronchitis w mucus) in airways, the EPP occurs more __.

cartilaginous; distally (in non-cartilaginous airways → air trapping)

Why does emphysema predominant occur?

• loss of elastic recoil of lungs on expiration

• loss of tethering or support of the most distal portions of airway leading to collapse on expiration (air trapping)

Air trapping occurs with high __ and high __.

resistance; compliance

__ flow occurs in smaller airways and therefore a relatively small __ is needed to produce a certain flow rate.

laminar; driving pressure

Equal pressure points can occur at __ along the airway. In normal individuals, this is reached at the point of the __.

various points; cartilaginous airways

Dynamic air trapping occurs in:

highly compliant lung tissue (emphysema) and highly resistant airways (chronic bronchitis)