Ch2 Part1

Question 1

What is the main objective of understanding the mechanics of breathing?

Answer 1

To understand the mechanical properties of the lung and the chest wall during breathing.

This includes concepts such as pressure gradients, lung expansion, and recoil.

Question 2

How is a pressure gradient established for airflow into the lungs?

Answer 2

By making alveolar pressure fall below atmospheric pressure, causing air to flow into the lungs.

This process is known as negative-pressure breathing.

Question 3

What is negative-pressure breathing?

Answer 3

When alveolar pressure is lowered below atmospheric pressure to facilitate breathing.

This is achieved by contraction of inspiratory muscles.

Question 4

What happens during positive-pressure ventilation?

Answer 4

Air flows into the lungs by raising the pressure at the nose and mouth above alveolar pressure.

This method is used for patients who cannot generate sufficient pressure differences.

Question 5

What is the role of the diaphragm during normal quiet breathing?

Answer 5

It is the primary muscle of inspiration, responsible for about two-thirds of the air entering the lungs in the supine position.

The diaphragm’s contraction increases the volume of the thoracic cavity.

Question 6

What is the definition of functional residual capacity (FRC)?

Answer 6

The volume of air remaining in the lungs after a normal expiration.

Understanding FRC helps predict changes in lung function in various conditions.

Question 7

What is the significance of negative intrapleural pressure?

Answer 7

It keeps the lungs inflated and is caused by the mechanical interaction between the lung and the chest wall.

Normal values range from -3 to -5 cm H2O.

Question 8

What muscles are primarily involved in inspiration?

Answer 8

Diaphragm, external intercostals, and accessory muscles such as the sternocleidomastoid and trapezius.

These muscles work together to increase thoracic volume.

Question 9

Fill in the blank: The _______ pressure is calculated by subtracting the outside pressure from the inside pressure of the alveolus.

Answer 9

transmural

This pressure is critical for understanding lung expansion.

Question 10

What is the function of pulmonary surfactant?

Answer 10

It reduces surface tension in the alveoli, aiding in lung expansion and recoil.

Pulmonary surfactant is crucial for maintaining proper lung function.

Question 11

What factors contribute to airway resistance?

Answer 11

Airway diameter, lung volume, and the viscosity of air.

Changes in these factors can alter airflow and resistance.

Question 12

True or False: Expiration is an active process during normal quiet breathing.

Answer 12

False.

Expiration is typically passive due to elastic recoil of the lungs.

Question 13

What happens to intrapleural pressure during inspiration?

Answer 13

It becomes more negative.

This negative pressure increase helps to expand the alveoli.

Question 14

What is the role of abdominal muscles during expiration?

Answer 14

They increase abdominal pressure and push the diaphragm upward into the thoracic cavity.

This aids in actively forcing air out of the lungs.

Question 15

List the main muscles involved in active expiration.

Answer 15

• Rectus abdominis
• External oblique
• Internal oblique
• Transversus abdominis
• Internal intercostal muscles

These muscles contract during activities like exercise and coughing.

Question 16

What is Boyle’s law in the context of breathing?

Answer 16

It states that pressure and volume are inversely related in a closed system, which explains how changes in thoracic volume affect alveolar pressure.

This principle underlies the mechanics of inhalation and exhalation.

Question 17

What are the main muscles of expiration?

Answer 17

Muscles of the abdominal wall, including:
* Rectus abdominis
* External oblique muscles
* Internal oblique muscles
* Transversus abdominis
* Internal intercostal muscles

These muscles work together to increase abdominal pressure and assist in expelling air from the lungs.

Question 18

How do abdominal muscles contribute to expiration?

Answer 18

They increase abdominal pressure and push the abdominal contents against the relaxed diaphragm, forcing it upward into the thoracic cavity.

This action also helps depress the lower ribs and pull down the anterior part of the lower chest.

Question 19

What is the function of the internal intercostal muscles during expiration?

Answer 19

Contraction of the internal intercostal muscles depresses the rib cage downward.

This action is opposite to the actions of the external intercostals.

Question 20

What is the normal inspiratory to expiratory (I:E) ratio in eupneic breathing?

Answer 20

1:2 to 1:4

During normal quiet breathing, the expiratory phase is typically two to three times longer than the inspiratory phase.

Question 21

What initiates the process of inspiration?

Answer 21

The brain initiates inspiratory effort.

This command is then transmitted to the inspiratory muscles via nerves.

Question 22

What happens to thoracic volume during inspiration?

Answer 22

Thoracic volume increases as the chest wall expands.

This increase leads to a more negative intrapleural pressure and an increase in alveolar transmural pressure difference.

Question 23

What occurs to alveolar pressure during inspiration?

Answer 23

Alveolar pressure falls below atmospheric pressure, establishing a pressure difference for airflow.

Air flows into the alveoli until the alveolar pressure equilibrates with atmospheric pressure.

Question 24

What is the process of passive expiration?

Answer 24

Expiration occurs when the brain ceases the inspiratory command, causing:
* Inspiratory muscles to relax
* Thoracic volume to decrease
* Intrapleural pressure to become less negative
* Alveolar pressure to rise above atmospheric pressure

This results in airflow out of the alveoli until pressures equalize.

Question 25

What is transpulmonary pressure?

Answer 25

The pressure difference across the whole lung, equal to the pressure in the trachea minus the intrapleural pressure. ## Footnote It is crucial for understanding lung inflation.

Question 26

Define lung compliance.

Answer 26

Compliance is defined as the change in volume divided by the change in pressure. ## Footnote High compliance indicates that a small change in pressure results in a large change in volume.

Question 27

What is hysteresis in the context of lung mechanics?

Answer 27

Hysteresis refers to the difference between the pressure-volume curve for inflation and deflation of the lung. ## Footnote This can be attributed to the behavior of surfactant and recruitment of alveoli.

Question 28

How does pulmonary fibrosis affect lung compliance?

Answer 28

It decreases lung compliance, making the lungs 'stiffer' and increasing alveolar elastic recoil. ## Footnote Conditions leading to fibrosis include sarcoidosis and lung injuries.

Question 29

What factors can decrease chest wall compliance?

Answer 29

Factors include: * Obesity * Musculoskeletal disorders (e.g., kyphoscoliosis) * Ossification of costal cartilage * Skin scars from burn injuries * Abdominal distension ## Footnote These conditions make it more difficult to move the diaphragm and rib cage.

Question 30

What is the significance of measuring pulmonary compliance clinically?

Answer 30

It provides useful data for evaluating a patient’s respiratory system, as many diseases affect compliance. ## Footnote Understanding compliance helps in diagnosing conditions that impact lung and chest wall mechanics.

Question 31

What happens to chest wall compliance in obese individuals?

Answer 31

Decreased compliance ## Footnote Moving the diaphragm downward and rib cage expansion is more difficult.

Question 32

Which musculoskeletal disorder can lead to decreased chest wall compliance?

Answer 32

Kyphoscoliosis ## Footnote It decreases mobility of the rib cage.

Question 33

List conditions that can decrease chest wall compliance.

Answer 33

* Ossification of costal cartilage * Skin scars from burn injuries * Abdominal distension

Question 34

How do individuals with decreased lung compliance breathe compared to those with normal compliance?

Answer 34

They must generate greater transpulmonary pressures and do more work to inspire.

Question 35

At what lung volume is compliance greater?

Answer 35

Low lung volumes ## Footnote Compliance is lower at high lung volumes.

Question 36

What is the total compliance of a normal person near the functional residual capacity (FRC)?

Answer 36

About 0.1 L/cm H2O

Question 37

What is the compliance of the lungs and chest wall in a normal person?

Answer 37

Both are about 0.2 L/cm H2O

Question 38

What contributes to the elastic recoil of the lungs?

Answer 38

* Elastic properties of pulmonary parenchyma * Surface tension at the air-liquid interface

Question 39

What is surface tension?

Answer 39

A force at any gas-liquid interface generated by cohesive forces between liquid molecules.

Question 40

What is the unit of measurement for surface tension?

Answer 40

Dynes per centimeter (dyn/cm)

Question 41

What does Laplace’s law describe in relation to alveoli?

Answer 41

The relationship between pressure inside an alveolus and its wall tension.

Question 42

True or False: The surface tension of most liquids is dependent on the surface area of the air-liquid interface.

Answer 42

False ## Footnote Surface tension is constant and independent of surface area.

Question 43

What stabilizes alveoli against collapse despite pressure differences?

Answer 43

* Pulmonary surfactant * Mechanical interdependence of alveoli

Question 44

What is pulmonary surfactant primarily composed of?

Answer 44

* 85% to 90% lipids * 10% to 15% proteins

Question 45

Which surfactant protein is necessary for surfactant function?

Answer 45

Surfactant B

Question 46

What happens to infants born prematurely regarding pulmonary surfactant?

Answer 46

They may lack functional pulmonary surfactant, leading to difficulty inflating lungs.

Question 47

What is the role of pulmonary surfactant in the lungs?

Answer 47

Decreases work of inspiration by lowering surface tension and elastic recoil.

Question 48

What is alveolar interdependence?

Answer 48

The mechanical relationship where adjacent alveoli share walls and support each other.

Question 49

How does positive end-expiratory pressure help patients with respiratory distress?

Answer 49

Opposes increased elastic recoil and tendency for atelectasis.

Question 50

What is the significance of hysteresis in lung pressure-volume curves?

Answer 50

It appears to be a property of the fluid lining the alveoli.

Question 51

What happens to surface tension at low relative areas in lung extract?

Answer 51

It decreases dramatically, indicating variable surface tension in different-sized alveoli.

Question 52

What two factors help stabilize the alveoli and oppose alveolar collapse?

Answer 52

Pulmonary surfactant and mechanical interdependence of alveoli ## Footnote Pulmonary surfactant reduces surface tension in alveoli, while mechanical interdependence refers to the structural support alveoli provide to each other.

Question 53

What happens to the alveoli when a subdivision of the lung collapses?

Answer 53

The first reinflated alveolus helps pull other alveoli open due to mechanical interdependence.

Question 54

What is the functional residual capacity (FRC)?

Answer 54

The volume of gas left in the lungs at the end of a normal tidal expiration when no respiratory muscles are actively contracting.

Question 55

What defines the lung volume at the FRC?

Answer 55

The outward recoil of the chest wall is equal to the inward recoil of the lungs.

Question 56

What is the effect of a penetrating chest injury on lung function?

Answer 56

It disrupts the lung-chest wall interdependence, causing lung volume to decrease and alveoli to collapse.

Question 57

True or False: The chest wall tends to expand when the lung-chest wall system is intact.

Answer 57

False ## Footnote The chest wall expands due to its outward recoil being opposed by the inward recoil of the lung.

Question 58

What happens to intrapleural pressure when air enters the pleural space due to a wound?

Answer 58

Intrapleural pressure equalizes with atmospheric pressure, abolishing the transpulmonary pressure gradient.

Question 59

What happens to lung volume and alveolar collapse tendency when the lung-chest wall system is not intact?

Answer 59

Lung volume decreases, and the tendency for alveoli to collapse increases.

Question 60

What does the static pressure-volume curve represent?

Answer 60

The relationship between lung elastic recoil and chest wall elastic recoil.

Question 61

What occurs to the chest wall recoil at high lung volumes?

Answer 61

The chest wall recoil becomes inward due to stretching.

Question 62

Fill in the blank: The volume of the thorax when lungs are maximally expanded is approximately ______ of the relaxed volume of the thorax.

Answer 62

70%

Question 63

What is the relationship between lung volume and mouth pressure below the FRC?

Answer 63

The relaxation pressure measured at the mouth is negative.

Question 64

How does body position (sitting vs. supine) affect functional residual capacity (FRC)?

Answer 64

FRC decreases by about one-third when changing from standing to supine.

Question 65

What factor contributes to the decreased outward recoil of the chest wall when lying down?

Answer 65

Gravity causes abdominal contents to push inward against the diaphragm.

Question 66

What is the significance of the dashed line labeled 'system' in the pressure-volume curves?

Answer 66

It represents the total recoil pressure of both lungs and the chest wall.

Question 67

What happens to the recoil pressure of the chest wall at thoracic volumes above 70% of total lung capacity?

Answer 67

The recoil pressure of the chest wall becomes inward.

Question 68

True or False: The lung elastic recoil curve is significantly altered by body position.

Answer 68

False ## Footnote The lung elastic recoil curve remains relatively unchanged regardless of body position.