Ch2 Part1 Flashcards
What is the main objective of understanding the mechanics of breathing?
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.
How is a pressure gradient established for airflow into the lungs?
By making alveolar pressure fall below atmospheric pressure, causing air to flow into the lungs.
This process is known as negative-pressure breathing.
What is negative-pressure breathing?
When alveolar pressure is lowered below atmospheric pressure to facilitate breathing.
This is achieved by contraction of inspiratory muscles.
What happens during positive-pressure ventilation?
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.
What is the role of the diaphragm during normal quiet breathing?
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.
What is the definition of functional residual capacity (FRC)?
The volume of air remaining in the lungs after a normal expiration.
Understanding FRC helps predict changes in lung function in various conditions.
What is the significance of negative intrapleural pressure?
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.
What muscles are primarily involved in inspiration?
Diaphragm, external intercostals, and accessory muscles such as the sternocleidomastoid and trapezius.
These muscles work together to increase thoracic volume.
Fill in the blank: The _______ pressure is calculated by subtracting the outside pressure from the inside pressure of the alveolus.
transmural
This pressure is critical for understanding lung expansion.
What is the function of pulmonary surfactant?
It reduces surface tension in the alveoli, aiding in lung expansion and recoil.
Pulmonary surfactant is crucial for maintaining proper lung function.
What factors contribute to airway resistance?
Airway diameter, lung volume, and the viscosity of air.
Changes in these factors can alter airflow and resistance.
True or False: Expiration is an active process during normal quiet breathing.
False.
Expiration is typically passive due to elastic recoil of the lungs.
What happens to intrapleural pressure during inspiration?
It becomes more negative.
This negative pressure increase helps to expand the alveoli.
What is the role of abdominal muscles during expiration?
They increase abdominal pressure and push the diaphragm upward into the thoracic cavity.
This aids in actively forcing air out of the lungs.
List the main muscles involved in active expiration.
- Rectus abdominis
- External oblique
- Internal oblique
- Transversus abdominis
- Internal intercostal muscles
These muscles contract during activities like exercise and coughing.
What is Boyle’s law in the context of breathing?
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.
What are the main muscles of expiration?
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.
How do abdominal muscles contribute to expiration?
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.
What is the function of the internal intercostal muscles during expiration?
Contraction of the internal intercostal muscles depresses the rib cage downward.
This action is opposite to the actions of the external intercostals.
What is the normal inspiratory to expiratory (I:E) ratio in eupneic breathing?
1:2 to 1:4
During normal quiet breathing, the expiratory phase is typically two to three times longer than the inspiratory phase.
What initiates the process of inspiration?
The brain initiates inspiratory effort.
This command is then transmitted to the inspiratory muscles via nerves.
What happens to thoracic volume during inspiration?
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.
What occurs to alveolar pressure during inspiration?
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.
What is the process of passive expiration?
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.
What is transpulmonary pressure?
The pressure difference across the whole lung, equal to the pressure in the trachea minus the intrapleural pressure.
It is crucial for understanding lung inflation.
Define lung compliance.
Compliance is defined as the change in volume divided by the change in pressure.
High compliance indicates that a small change in pressure results in a large change in volume.
What is hysteresis in the context of lung mechanics?
Hysteresis refers to the difference between the pressure-volume curve for inflation and deflation of the lung.
This can be attributed to the behavior of surfactant and recruitment of alveoli.
How does pulmonary fibrosis affect lung compliance?
It decreases lung compliance, making the lungs ‘stiffer’ and increasing alveolar elastic recoil.
Conditions leading to fibrosis include sarcoidosis and lung injuries.
What factors can decrease chest wall compliance?
Factors include:
* Obesity
* Musculoskeletal disorders (e.g., kyphoscoliosis)
* Ossification of costal cartilage
* Skin scars from burn injuries
* Abdominal distension
These conditions make it more difficult to move the diaphragm and rib cage.
What is the significance of measuring pulmonary compliance clinically?
It provides useful data for evaluating a patient’s respiratory system, as many diseases affect compliance.
Understanding compliance helps in diagnosing conditions that impact lung and chest wall mechanics.
What happens to chest wall compliance in obese individuals?
Decreased compliance
Moving the diaphragm downward and rib cage expansion is more difficult.
Which musculoskeletal disorder can lead to decreased chest wall compliance?
Kyphoscoliosis
It decreases mobility of the rib cage.
List conditions that can decrease chest wall compliance.
- Ossification of costal cartilage
- Skin scars from burn injuries
- Abdominal distension
How do individuals with decreased lung compliance breathe compared to those with normal compliance?
They must generate greater transpulmonary pressures and do more work to inspire.
At what lung volume is compliance greater?
Low lung volumes
Compliance is lower at high lung volumes.
What is the total compliance of a normal person near the functional residual capacity (FRC)?
About 0.1 L/cm H2O
What is the compliance of the lungs and chest wall in a normal person?
Both are about 0.2 L/cm H2O
What contributes to the elastic recoil of the lungs?
- Elastic properties of pulmonary parenchyma
- Surface tension at the air-liquid interface
What is surface tension?
A force at any gas-liquid interface generated by cohesive forces between liquid molecules.
What is the unit of measurement for surface tension?
Dynes per centimeter (dyn/cm)
What does Laplace’s law describe in relation to alveoli?
The relationship between pressure inside an alveolus and its wall tension.
True or False: The surface tension of most liquids is dependent on the surface area of the air-liquid interface.
False
Surface tension is constant and independent of surface area.
What stabilizes alveoli against collapse despite pressure differences?
- Pulmonary surfactant
- Mechanical interdependence of alveoli
What is pulmonary surfactant primarily composed of?
- 85% to 90% lipids
- 10% to 15% proteins
Which surfactant protein is necessary for surfactant function?
Surfactant B
What happens to infants born prematurely regarding pulmonary surfactant?
They may lack functional pulmonary surfactant, leading to difficulty inflating lungs.
What is the role of pulmonary surfactant in the lungs?
Decreases work of inspiration by lowering surface tension and elastic recoil.
What is alveolar interdependence?
The mechanical relationship where adjacent alveoli share walls and support each other.
How does positive end-expiratory pressure help patients with respiratory distress?
Opposes increased elastic recoil and tendency for atelectasis.
What is the significance of hysteresis in lung pressure-volume curves?
It appears to be a property of the fluid lining the alveoli.
What happens to surface tension at low relative areas in lung extract?
It decreases dramatically, indicating variable surface tension in different-sized alveoli.
What two factors help stabilize the alveoli and oppose alveolar collapse?
Pulmonary surfactant and mechanical interdependence of alveoli
Pulmonary surfactant reduces surface tension in alveoli, while mechanical interdependence refers to the structural support alveoli provide to each other.
What happens to the alveoli when a subdivision of the lung collapses?
The first reinflated alveolus helps pull other alveoli open due to mechanical interdependence.
What is the functional residual capacity (FRC)?
The volume of gas left in the lungs at the end of a normal tidal expiration when no respiratory muscles are actively contracting.
What defines the lung volume at the FRC?
The outward recoil of the chest wall is equal to the inward recoil of the lungs.
What is the effect of a penetrating chest injury on lung function?
It disrupts the lung-chest wall interdependence, causing lung volume to decrease and alveoli to collapse.
True or False: The chest wall tends to expand when the lung-chest wall system is intact.
False
The chest wall expands due to its outward recoil being opposed by the inward recoil of the lung.
What happens to intrapleural pressure when air enters the pleural space due to a wound?
Intrapleural pressure equalizes with atmospheric pressure, abolishing the transpulmonary pressure gradient.
What happens to lung volume and alveolar collapse tendency when the lung-chest wall system is not intact?
Lung volume decreases, and the tendency for alveoli to collapse increases.
What does the static pressure-volume curve represent?
The relationship between lung elastic recoil and chest wall elastic recoil.
What occurs to the chest wall recoil at high lung volumes?
The chest wall recoil becomes inward due to stretching.
Fill in the blank: The volume of the thorax when lungs are maximally expanded is approximately ______ of the relaxed volume of the thorax.
70%
What is the relationship between lung volume and mouth pressure below the FRC?
The relaxation pressure measured at the mouth is negative.
How does body position (sitting vs. supine) affect functional residual capacity (FRC)?
FRC decreases by about one-third when changing from standing to supine.
What factor contributes to the decreased outward recoil of the chest wall when lying down?
Gravity causes abdominal contents to push inward against the diaphragm.
What is the significance of the dashed line labeled ‘system’ in the pressure-volume curves?
It represents the total recoil pressure of both lungs and the chest wall.
What happens to the recoil pressure of the chest wall at thoracic volumes above 70% of total lung capacity?
The recoil pressure of the chest wall becomes inward.
True or False: The lung elastic recoil curve is significantly altered by body position.
False
The lung elastic recoil curve remains relatively unchanged regardless of body position.
