Mechanics of Breathing, Pressures and Work

Question 1

What is ventilation?

Answer 1

Ventilation refers to the movement of air in and out of the lungs, which is also known as breathing.

Question 2

What is respiration?

Answer 2

Respiration refers to the process of gas exchange in the alveoli, involving the exchange of oxygen (O2) and carbon dioxide (CO2).

Question 3

What is cellular respiration?

Answer 3

Cellular respiration refers to the metabolic process that occurs in cells, specifically in the Krebs cycle, where nutrients are metabolized and energy is produced. It involves the consumption of oxygen (O2) and the release of carbon dioxide (CO2).

Question 4

What is the intrapleural space?

Answer 4

The intrapleural space is the space between the visceral and parietal pleura.

Question 5

What is tidal volume (VT)?

Answer 5

Tidal volume is the volume of air inhaled or exhaled during each breath. It is typically around 500 mL at rest.

Question 6

What is the normal respiratory rate (RR)?

Answer 6

The normal respiratory rate is approximately 15 breaths per minute, with a range of 12-18 breaths per minute.

Question 7

What is minute ventilation (V)?

Answer 7

Minute ventilation is the volume of air that enters the lungs per minute. It is calculated by multiplying tidal volume (VT) by the respiratory rate (RR). For example, if VT is 500 mL and RR is 15 breaths per minute, then the minute ventilation would be 7500 mL/minute.

Question 8

What is alveolar ventilation (VA)?

Answer 8

Alveolar ventilation refers to the volume of air that takes part in gas exchange per minute. It is slightly lower than minute ventilation due to the presence of dead space.

Question 9

What happens during inspiration?

Answer 9

Intercostal muscles elevate and evert the ribs.
The diaphragm moves downward.
Scalene muscles, inserted into the first two ribs, raise the upper ribs and push the sternum forward (pump action), increasing the anterior-posterior diameter of the thoracic cavity.
The sloping lower ribs rise and move out, creating the bucket handle action and increasing the transverse diameter of the chest wall.

Question 10

What happens when the diaphragm contracts during inspiration?

Answer 10

When the diaphragm contracts, there is a 75% increase in volume in the thoracic cavity.

Question 11

What happens during inspiration with the intercostal muscles?

Answer 11

The intercostal muscles contract, resulting in the bucket-handle movement of the ribs.

Question 12

What muscles are involved in the contraction during inspiration?

Answer 12

The scalene muscles contract, causing the sternum to rise.

Question 13

What effect does the contraction of the scalene muscles have?

Answer 13

The contraction of the scalene muscles leads to the expansion of the anterior-posterior diameter of the thoracic cavity.

Question 14

Which muscles are considered accessory muscles during forced inspiration?

Answer 14

The accessory muscles involved in forced inspiration are the sternomastoid (located in the upper neck), serratus anterior, and pectoralis major muscles.

Question 15

What type of ventilation is predominant in adults at rest?

Answer 15

In adults at rest, ventilation is largely diaphragmatic, meaning the diaphragm is primarily responsible for the movement of air during breathing.

Question 16

What happens when the inspiratory muscles (diaphragm and intercostals) contract during inspiration?

Answer 16

Contraction of the inspiratory muscles expands the thoracic cavity, resulting in an increase in thoracic volumes and a decrease in intrapleural and alveolar pressures (according to Boyle’s Law).

Question 17

What is the effect of the pressure gradient created during inspiration?

Answer 17

The pressure gradient between the alveoli and the mouth allows air to enter the lungs.

Question 18

When does the pressure in the alveoli equalize with the pressure in the mouth during inspiration?

Answer 18

At the end of inspiration, the pressures in the alveoli and the mouth are equal.

Question 19

What happens after inspiration?

Answer 19

Following inspiration, the lungs and chest wall undergo recoil, returning to their original positions.

Question 20

What type of process is expiration?

Answer 20

Expiration is a passive process.

Question 21

What causes expiration?

Answer 21

Expiration occurs due to the elastic recoil of the lungs and the chest wall.

Question 22

What happens to the intrapleural and alveolar pressures during expiration?

Answer 22

During expiration, both intrapleural pressure and alveolar pressures rise.

Question 23

What is required for forced expiration, such as during coughing or sneezing?

Answer 23

Forced expiration requires the contraction of the abdominal walls, which push the diaphragm upward.

Question 24

How high can intrapleural pressures rise during forced expiration?

Answer 24

Intrapleural pressures may rise to +8 kPa (60 mmHg) during forced expiration.

Question 25

What is the atmospheric pressure at sea level?

Answer 25

The atmospheric pressure at sea level is 760 mmHg.

Question 26

How does intra-alveolar (intrapulmonary) pressure determine the movement of air in and out of the lungs?

Answer 26

Intra-alveolar (intrapulmonary) pressure determines whether air will enter or leave the lungs.
During inspiration, the intra-alveolar pressure is lower than atmospheric pressure (<760 mmHg), allowing air to enter the lungs.
During expiration, the intra-alveolar pressure is higher than atmospheric pressure (>760 mmHg), causing air to leave the lungs.

Question 27

What is the intrapleural pressure (Ppl) and its relationship with atmospheric pressure?

Answer 27

The intrapleural pressure (Ppl) does not equilibrate with the atmosphere because the pleural space is closed and fluid-filled. It is slightly sub-atmospheric, meaning it is lower than atmospheric pressure. This sub-atmospheric pressure is maintained due to the recoil of the chest and lungs away from each other. The negative intrapleural pressure helps prevent the lungs from collapsing.

Question 28

What is the role of the chest wall in generating airflow during breathing?

Answer 28

The chest wall exerts a distending pressure on the pleural space, which is transmitted to the alveoli, increasing their volume, lowering the pressure, and generating airflow inwards.

Question 29

What is the transmural pulmonary pressure (Ptp)?

Answer 29

The transmural pulmonary pressure (Ptp) is the distending pressure exerted on the alveoli by the chest wall. It is always positive under physiological conditions.

Question 30

What are the pressure conditions in the respiratory system during quiet breathing?

Answer 30

The transmural pulmonary pressure (Ptp) is always positive.
The intrapleural pressure (Ppl) is always negative.
The intra-pulmonary/alveolar pressure (Palv) moves from slightly negative to slightly positive as we breathe. It is always higher than the intrapleural pressure due to the recoil of the lungs. At the end of inspiration and expiration, it reaches 0, resulting in no air flow.

Question 31

How does the transmural pulmonary pressure (Ptp) prevent the collapse of the lungs?

Answer 31

For a given lung volume, the transmural pulmonary pressure is equal and opposite to the elastic recoil pressure of the lung. This pressure differential ensures that the lungs don’t collapse. It “sucks” the lungs out during inspiration and “sucks” them back in during expiration.

Question 32

What does FRC stand for and what does it represent?

Answer 32

FRC stands for Functional Residual Capacity, which is the volume of air left in the lungs at the end of a normal breath.

Question 33

What happens to the respiratory muscles, lungs, and chest wall at FRC?

Answer 33

At FRC, the respiratory muscles are relaxed, and the lungs and chest wall recoil in opposite directions.

Question 34

How is the balance between the outward recoil of the chest wall and the inward recoil of the lungs achieved at FRC?

Answer 34

At FRC, the outward recoil of the chest wall exactly balances the inward recoil of the lungs.

Question 35

What determines the volume of air at FRC?

Answer 35

The volume of air at FRC is determined by the elastic properties of the lungs and the chest wall.

Question 36

How does lung disease affect FRC?

Answer 36

FRC is decreased in pulmonary fibrosis, where the lungs are stiff and small with increased elastic recoil. FRC is increased in emphysema, which involves the loss of alveolar tissue and decreased elastic recoil.

Question 37

What is the impedance in lung mechanics?

Answer 37

Impedance in lung mechanics refers to the combined effect of frictional airway resistance and elastic resistance to stretching of the lungs and chest wall. It is the resistance encountered by the inspiratory muscles during breathing in.

Question 38

What is compliance in lung mechanics?

Answer 38

Compliance refers to the ability of the lungs to stretch and recoil, similar to a spring, during ventilation. Lung compliance (CL) is defined as the change in lung volume per unit change in distending pressure.

Question 39

How is the distending pressure (P) calculated in lung mechanics?

Answer 39

The distending pressure, P, is the pressure difference across the lung, which is the alveolar-intrapleural pressure.

Question 40

What happens during quiet expiration regarding elastic recoil?

Answer 40

During quiet expiration, there is elastic recoil of the lungs, which is balanced by the tendency of the chest wall to recoil in the opposite direction. At the end of quiet expiration, the pressures within the lungs and chest wall balance each other.

Question 41

What is observed in the static pressure-volume loop as lung volume approaches TLC (Total Lung Capacity)?

Answer 41

As lung volume approaches TLC, the curve on the static pressure-volume loop flattens.

Question 42

What is hysteresis in the context of the static pressure-volume loop?

Answer 42

Hysteresis refers to the slight difference between the inspiratory and expiratory curves on the static pressure-volume loop. It is a common property of elastic bodies.

Question 43

How is static lung compliance defined?

Answer 43

Static lung compliance is defined as the slope of the steepest part of the static pressure-volume loop, which is just above FRC (Functional Residual Capacity).

Question 44

How is a dynamic pressure-volume loop obtained?

Answer 44

A dynamic pressure-volume loop is obtained by continuously measuring intrapleural pressure and volume during a normal breathing cycle.

Question 45

What are the conditions at the end of inspiration and expiration in a dynamic pressure-volume loop?

Answer 45

At the end of inspiration and expiration, airflow and alveolar pressures are zero.

Question 46

What does the slope of the line joining the end points of inspiration and expiration represent in a dynamic pressure-volume loop?

Answer 46

The slope of the line joining the end points of inspiration and expiration represents dynamic compliance.

Question 47

What does the area of the dynamic pressure-volume loop indicate?

Answer 47

The area of the dynamic pressure-volume loop is a measure of the work done against airway resistance.

Question 48

How does dynamic compliance compare to static compliance in health?

Answer 48

In health, dynamic compliance is similar to static compliance.

Question 49

How does dynamic compliance differ in lung diseases characterized by stiff lungs?

Answer 49

In lung diseases characterized by stiff lungs, dynamic compliance will be different from static compliance.

Question 50

What does lung compliance depend on?

Answer 50

Lung compliance depends on how inflated or deflated the lungs are.

Question 51

What is hysteresis in the context of lung compliance?

Answer 51

Hysteresis differs between the compliance curves for inspiration and exhalation. It is caused by changes in frictional resistance.

Question 52

How does lung compliance change with lung volume?

Answer 52

The lung is less compliant at higher volumes, requiring more pressure to achieve the same volume change than at lower volumes.

Question 53

How does lung compliance change in interstitial fibrosis?

Answer 53

In interstitial fibrosis, lung compliance is decreased due to the stiffening of alveolar walls from scarring, resulting in reduced elasticity.

Question 54

How does lung compliance change in emphysema?

Answer 54

In emphysema, lung compliance is normal. The compliance is just right, allowing for low work of inhalation and effective exhalation while retaining the elasticity of alveolar units.

Question 55

How does lung compliance change in normal lung?

Answer 55

Compliance is typically within a normal range in a normal lung.

Question 56

What type of airflow occurs during quiet breathing?

Answer 56

During quiet breathing, there is laminar airflow in the airways, where gas particles move parallel to the walls of the bronchi.

Question 57

What happens during laminar airflow?

Answer 57

During laminar airflow, the center layers of gas particles move faster than the outer layers, creating a cone-shaped front.

Question 58

When does turbulent airflow occur?

Answer 58

Turbulent airflow occurs at higher linear velocities in wide airways and near branch points.

Question 59

When does turbulent airflow occur in the trachea?

Answer 59

Turbulent airflow occurs in the trachea during exercise, resulting in harsh breath sounds.

Question 60

What causes airway resistance (RAW)?

Answer 60

Airway resistance (RAW) originates from the friction between air and the mucosa lining the airways.

Question 61

How does airway resistance affect ventilation?

Answer 61

Airway resistance (RAW) needs to be overcome with elastic recoil to inflate the lungs and facilitate ventilation.

Question 62

How is airway resistance (RAW) calculated?

Answer 62

Airway resistance (RAW) is calculated as the pressure difference between the alveoli and the mouth divided by the flow rate.

Question 63

What is the relationship between airway resistance (RAW) and the radius of the airways?

Answer 63

Airway resistance (RAW) is inversely proportional to the 4th power of the radius of the airways.

Question 64

How is airflow related to the viscosity of the fluid?

Answer 64

Airflow is inversely proportional to the viscosity of the fluid.

Question 65

How can airway resistance (RAW) be assessed indirectly?

Answer 65

Forced expiratory measures such as FEV1 (forced expiratory volume in 1 second), FVC (forced vital capacity), and FEV1/FVC ratio can provide indirect information about airway resistance (RAW).

Question 66

What factors affect laminar flow and airway resistance?

Answer 66

Factors affecting laminar flow and airway resistance include the radius of the conducting airways, the presence of diseases in the peripheral airways, and the tone of bronchial smooth muscle and epithelium.

Question 67

How does the radius of the airways affect airway resistance?

Answer 67

According to Poiseuille’s equation, reducing the radius of an airway by half increases the airway resistance by 16 times.

Question 68

Which anatomical structures offer the most resistance in the airways?

Answer 68

The nose, pharynx, and trachea are the anatomical structures that offer the most resistance to airflow.

Question 69

How does mouth breathing affect airway resistance?

Answer 69

Breathing through the mouth, such as during exercise, decreases airway resistance compared to breathing through the nose.

Question 70

How does bronchial smooth muscle and epithelium tone affect airway resistance?

Answer 70

The tone of bronchial smooth muscle and epithelium can influence airway resistance. Parasympathetic nerve supply and acetylcholine acting on M3 receptors can increase bronchomotor tone and airway resistance, while β-adrenergic receptor activation by substances like adrenaline and salbutamol promotes relaxation and decreases airway resistance.

Question 71

What is the role of nitric oxide in airway resistance?

Answer 71

Nitric oxide causes bronchodilation, resulting in a decrease in airway resistance.

Question 72

What is the effect of resting bronchomotor tone on airway resistance?

Answer 72

Resting bronchomotor tone can influence airway resistance. Increased bronchomotor tone can cause bronchoconstriction, leading to a decrease in airway radius, increased resistance, and decreased airflow.

Question 73

How does bronchoconstriction affect airway resistance?

Answer 73

Bronchoconstriction, characterized by a decrease in airway radius, increases airway resistance and reduces airflow.

Question 74

What is the effect of bronchodilation on airway resistance?

Answer 74

Bronchodilation, which increases the radius of the airways, decreases airway resistance and promotes increased airflow.

Question 75

How does acute asthma affect airway resistance?

Answer 75

Acute asthma is associated with increased airway resistance. It is characterized by bronchoconstriction, mucosal edema (swelling of the airway lining), mucus hypersecretion, and mucus plugging, all of which contribute to increased airway resistance.

Question 76

How does chronic obstructive pulmonary disease (COPD) affect airway resistance?

Answer 76

COPD is associated with increased airway resistance. It involves both bronchoconstriction and chronic mucosal hypertrophy (thickening of the airway lining), leading to increased airway resistance and reduced airflow.

Question 77

What causes surface tension forces in the alveoli?

Answer 77

Surface tension forces in the alveoli are caused by the air-fluid interface. Cohesive forces between molecules at the surface of the alveolar bubble create tension, which tends to shrink the bubble.

Question 78

Why are alveoli and small airways inherently unstable?

Answer 78

Alveoli and small airways are inherently unstable because they tend to collapse during expiration, leading to a condition called atelectasis.

Question 79

How do surface tension forces affect inspiration?

Answer 79

During inspiration, the surface tension forces in the alveoli must be overcome to expand the alveolar bubbles and allow for air entry into the lungs.

Question 80

How does surface tension change with age and lung disease?

Answer 80

Surface tension can be affected by age and lung disease. Changes in surfactant production or composition can alter surface tension, leading to increased lung stiffness and decreased compliance. These changes contribute to respiratory difficulties seen in certain lung diseases.

Question 81

What is pulmonary surfactant?

Answer 81

Pulmonary surfactant is a mixture of phospholipids, primarily phosphatidylcholine, and proteins. It is produced by Type II pneumocytes and floats on the surface of the alveolar fluid.

Question 82

How does pulmonary surfactant reduce surface tension?

Answer 82

Pulmonary surfactant reduces surface tension by interfering with the attractive forces between liquid molecules at the air-fluid interface. The hydrophilic and hydrophobic ends of the surfactant molecules repel each other, creating a film that lowers the surface tension in the alveoli.

Question 83

What is the role of surfactant in the lungs?

Answer 83

Surfactant plays a crucial role in the lungs by reducing surface tension. This prevents the collapse of alveoli during expiration, promotes lung compliance, and facilitates the expansion of the alveoli during inspiration.

Question 84

What happens when there is a deficiency or dysfunction of pulmonary surfactant?

Answer 84

Deficiency or dysfunction of pulmonary surfactant can lead to increased surface tension, resulting in decreased lung compliance and the development of respiratory distress syndrome, particularly in premature infants.

Question 85

How does surfactant production change with fetal lung development?

Answer 85

Surfactant production increases as the fetal lungs develop, particularly in the third trimester. This is essential for lung function after birth and the prevention of respiratory complications.

Question 86

How does pulmonary surfactant affect lung compliance?

Answer 86

Pulmonary surfactant reduces surface tension, which increases lung compliance by reducing the forces that tend to shrink the alveoli. This allows for easier expansion of the lungs during inspiration.

Question 87

What is the role of pulmonary surfactant in maintaining alveolar stability?

Answer 87

Pulmonary surfactant prevents alveolar collapse by reducing surface tension. It keeps small alveoli from collapsing completely during expiration and prevents large alveoli from becoming overly distended during inspiration.

Question 88

How does pulmonary surfactant prevent fluid accumulation in the lungs?

Answer 88

Pulmonary surfactant reduces surface tension, which helps prevent the accumulation of fluid in the lungs. By reducing the hydrostatic pressure in the tissue outside the capillaries, it helps to keep the lungs dry and prevents fluid from being drawn from the capillaries into the alveoli.

Question 89

What is the role of pulmonary surfactant in defense against infection?

Answer 89

Pulmonary surfactant plays a role in the defense against infection by enhancing the clearance of pathogens from the lungs. It contains antimicrobial proteins that help to neutralize and eliminate microorganisms, contributing to lung health.

Question 90

What is Neonatal Respiratory Distress Syndrome (NRDS)?

Answer 90

Neonatal Respiratory Distress Syndrome is a condition that occurs in premature babies who have a lack of surfactant. Without sufficient surfactant, the alveoli cannot remain open, leading to difficulty in breathing and inadequate oxygenation. NRDS is a significant cause of morbidity and mortality in premature infants.