L27. Physiology - Mechanics of Breathing II

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Questions and Answers

What is the primary factor influencing dynamic compliance of the lungs during breathing?

Surface tension

Inertia

Airway resistance (correct)

Tissue resistance

According to Poiseuille's Law, which parameter has the greatest effect on airway resistance?

Fluid viscosity

Tube radius (correct)

Pressure difference

Tube length

What happens to airway resistance when the tube radius decreases?

It decreases sharply

It fluctuates unpredictably

It increases significantly (correct)

It remains constant

Which of the following factors predominantly affects the resistance of airflow in the lungs?

Viscosity of the fluid Signup and view all the answers

What characterizes dynamic lung compliance compared to static compliance?

It considers the effects of airway resistance. Signup and view all the answers

Which equation can be used to calculate airway resistance as described in the content?

R = 8ηl / πr^4 Signup and view all the answers

What does dynamic compliance measure specifically relate to during lung function?

Movement of air during respiration Signup and view all the answers

During normal breathing, what additional work is required to overcome in terms of respiratory mechanics?

Airway resistance Signup and view all the answers

What happens to thoracic wall compliance when the limits of wall collapse are reached?

It flattens. Signup and view all the answers

Which factor does NOT affect thoracic wall compliance?

Airway resistance Signup and view all the answers

What primarily determines airway resistance in the conducting zone?

The geometry of the airway branches Signup and view all the answers

How does an increase in lung volume affect airway resistance?

Airway resistance decreases with increased lung volume Signup and view all the answers

At what point does functional residual capacity (FRC) occur?

When the expansion force of the chest wall balances the lung recoil force. Signup and view all the answers

What is the resting position of the chest wall as a percentage of total lung capacity (TLC)?

80% Signup and view all the answers

Which part of the respiratory system contributes the most to airway resistance?

Intermediate-sized bronchi Signup and view all the answers

Which statement accurately describes the lung's role in compliance at high volumes?

The lung determines compliance at high volumes above resting position. Signup and view all the answers

What phenomenon occurs during expiration that affects airway diameter and resistance?

Dynamic compression of airways Signup and view all the answers

What happens to the supportive cartilage as the conducting airways become smaller?

It changes in character and diminishes Signup and view all the answers

What happens to airway pressure when lung volume is increased above the resting position of the chest wall?

Airway pressure increases. Signup and view all the answers

Which of the following best describes the relationship between airway resistance and gas exchange?

Lower airway resistance facilitates better gas exchange Signup and view all the answers

What limits compliance of the respiratory system when lung volumes are above the resting position?

The lung and chest wall combined. Signup and view all the answers

Which of the following statements about the chest wall's expansion force is true during inspiration?

It aids in inspiration under normal conditions. Signup and view all the answers

What does the term 'conductance' refer to in relation to airway resistance?

The ease of airflow through the airways Signup and view all the answers

During a forced vital capacity maneuver, which phase leads to significant changes in airway pressure?

Expiration from total lung capacity Signup and view all the answers

What is the pressure difference across the alveoli at functional residual capacity?

5 cmH2O Signup and view all the answers

What primarily contributes to the decrease in airway pressure as one moves from the alveoli to the upper regions of the tracheobronchial tree?

Increased resistance in the airways Signup and view all the answers

When does dynamic compression typically occur in healthy individuals?

At lower lung volumes Signup and view all the answers

How does the Bernoulli principle relate to airway pressure changes during forced expiration?

Pressure exerted by the fluid on vessel walls decreases with increased flow velocity Signup and view all the answers

What pressure signifies the occurrence of collapsing pressure in the airway in the given example?

8 cmH2O Signup and view all the answers

What phenomenon can lead to significantly elevated resistance in the small airways of individuals with chronic obstructive pulmonary disease (COPD)?

Hyperactive smooth muscle Signup and view all the answers

Why do individuals with COPD often breathe with pursed lips?

To increase the resistance point closer to small airways Signup and view all the answers

What happens to airway pressure during forced expiration in small compressible airways?

Pressure decreases due to increased resistance and airflow velocity Signup and view all the answers

What is the primary neurotransmitter responsible for bronchial smooth muscle constriction mediated by the parasympathetic nervous system?

Acetylcholine Signup and view all the answers

Which of the following plays a significant role in modulating airway resistance through the sympathetic nervous system?

Beta-2 agonists Signup and view all the answers

What type of flow is primarily observed in the small airways during normal tidal breathing?

Laminar flow Signup and view all the answers

Which endogenous mediator is known for its bronchodilator effects and originates from the nonadrenergic noncholinergic system?

VIP (Vasoactive Intestinal Peptide) Signup and view all the answers

What type of airflow is most likely to be present at the points of bifurcation in the airways?

Transitional flow Signup and view all the answers

Which inflammatory mediator is released from mast cells and can alter airway tone, particularly during allergic reactions?

Leukotrienes Signup and view all the answers

Which statement best describes the effect of increased airflow velocity on airflow patterns in the respiratory system?

Airflow transitions from laminar to turbulent. Signup and view all the answers

Which of the following statements is true regarding the role of circulating catecholamines in airway resistance?

They play a more important role than direct sympathetic innervation. Signup and view all the answers

Study Notes

Chest Wall Compliance

Chest wall compliance describes the change in thoracic wall volume for changes in intrapleural pressure when lungs are absent.
Relaxed volume (V1) is observed when intrapleural pressure is zero.
Compliance curve flattens at low volumes due to the limitations of wall collapse.
Thoracic wall compliance is determined by the elasticity of chest wall tissue, respiratory muscle integrity, respiratory muscle innervation, and obesity.

Lung and Chest Wall Compliance

Chest wall determines the lung volume limits of the respiratory system at low volumes.
Functional residual capacity (FRC) is when the chest wall opposes the lung's recoil force.
Chest wall expands outward, aiding inspiration under normal conditions.
Lung determines the respiratory system compliance at high volumes below the resting position of the chest wall.
Lung and chest wall limit the system's compliance when volumes exceed the chest wall's resting position.
Airway pressure increases as lung volume increases above this point, due to the lung's greater inward recoil force.

Dynamic Lung Compliance and Airway Resistance

Static compliance describes the compliance of the lung and chest wall when air is not moving, determined by the elasticity of lung and chest wall and surface tension.
Dynamic compliance considers the compliance when air is moving, along with airway resistance, tissue resistance, and inertia.
Airway resistance is significant in dynamic compliance.
Airway resistance can be calculated with Poiseuille's Law, which predicts resistance to laminar flow is directly proportional to viscosity and tube length, and inversely proportional to tube radius.

Factors that determine Airway Resistance – Airway Geometry

The airway resistance is greatest in the intermediate-sized bronchi.
Small airways contribute less to airway resistance because of the increase in cross-sectional area.

Factors that determine Airway Resistance – Lung Volume

Airway resistance decreases, and conductance increases as lung volume increases.
This effect is due to expanding lung volume exerting radial traction on surrounding lung tissue, reducing airway collapse and resulting in increased airway resistance.

Factors that determine Airway Resistance – Dynamic compression of the airway

Dynamic compression is a significant modifier of airway diameter and resistance.
This occurs during expiration, leading to flow limitation.
During a forced vital capacity maneuver, a collapsing pressure may occur when airway pressure decreases to a point where it is less than the intrapleural pressure.
This dynamic compression increases airway resistance, typically occurring at lower lung volumes in healthy individuals.
In individuals with chronic obstructive pulmonary disease, dynamic compression can occur at higher lung volumes due to compromised lung elasticity, resulting in mitigated radial traction and hyperactive smooth muscle.
To compensate, these individuals breathe with pursed lips, bringing the point of greatest resistance closer to the top of the tracheobronchial tree.

Factors that determine Airway Resistance – Airway Smooth Muscle Tone

Airway resistance is influenced by endogenous mediators affecting airway smooth muscle tone.
Noxious stimuli activate receptors beneath the epithelium of smooth muscle, triggering a reflex response through the vagus nerve, leading to bronchial smooth muscle constriction.
Parasympatholytic drugs can block this efferent response.
Sympathetic system plays a role in modulating bronchial smooth muscle tone, but circulating catecholamines are more dominant than direct innervation.
Nonadrenergic noncholinergic system may also contribute, with vasoactive intestinal peptide (VIP) and nitric oxide acting as potential bronchodilators.
Inflammatory mediators can alter airway tone, with histamine and serotonin being key examples released from mast cells.

Factors that determine Airway Resistance – Airflow Patterns

Airflow changes from laminar to turbulent as airflow velocity increases.
During normal tidal breathing, airflow is turbulent in the upper airways and usually laminar in smaller airways.
Transitional flow may occur at airway bifurcations.

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Description

This quiz explores the concept of chest wall compliance, examining its role in thoracic wall volume changes in response to intrapleural pressure. It covers how chest wall elasticity, muscle integrity, and obesity influence compliance, as well as the interplay between lung and chest wall during inspiration and expiration. Test your knowledge of these critical respiratory mechanics.