Mechanics of the Respiratory System Flashcards
Describe negative-pressure breathing
Lowering alveolar pressure below atmospheric pressure
Atmospheric pressure is congenitally referred to as 0cm H2O
Describe positive-pressure breathing
Increasing the pressure at the nose or mouth above alveolar pressure.
Used on patients unable to generate a pressure gradient between the atmosphere and the alveoli by normal negative-pressure breathing
How does negative-pressure breathing work
A pressure gradient is developed where the pressure in the alveoli falls below atmospheric pressure and air flows in
What is Boyle’s law
at constant temperature the product of the pressure and the volume of a gas is constant
Describe the transmural pressure gradient
Generated by the muscles of inspiration, transmural pressure
Alveoli expand passively in response to an increased distending pressure across the alveolar wall
How is the transmural pressure gradient calculated
Subtracting the outside pressure (intrapleural pressure) from the inside pressure (alveolar pressure)
How do the lung and chest wall interact at the end of expiration
They attempt to move in opposite directions
The lung is tending to decrease its volume due to elastic recoil of the alveolar walls
The chest wall is tending to increase its volume because of its outward elastic recoil
The intrapleural pressure is normally (-5cm)
How is alveolar pressure calculated
Intrapleural pressure + Alveolar elastic recoil pressure = alveolar pressure
What are the 3 inspiratory muscles
- Diaphragm
- External Intercostal
- Accessory muscles of inspiration
Contraction of what 3 muscles raises and enlarges the ribcage
- External intercostal
- Parasternal intercostal
- Scalene muscles
These muscles increase the anteroposterior dimension of the chest by rotating the ribs upward.
Innervated by nerves leaving the spinal cord at the 1st to 11th thoracic segments
What is interdependence
Pressure at the pleural surface is transmitted through the alveolar walls to more centrally located alveoli and small airways, pulling them open
What are the main muscles of active expiration
muscles of the abdominal walls
inter intercostal muscles
List the branches of the airway from largest to smallest
Conducting Zones
- Trachea
- Bronchi
- Bronchioles
- Terminal bronchioles
Respiratory Zones
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
What are the conducting zone branches of the respiratory system
Conducting Zones
- Trachea
- Bronchi
- Bronchioles
- Terminal bronchioles
What are the respiratory zone branches of the respiratory system
Respiratory Zones
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
What is the anatomic dead space
Space in the conducting zone where air does not reach the alveoli
What are the events of normal inspiration
- Brain initiates inspiratory effort.
- Nerves carry the inspiratory command to the inspiratory muscles.
- Diaphragm ( and / or external intercostal muscles) contracts.
- Thoracic volume increases as the chest wall expands.*
- Intrapleural pressure becomes more negative. *
- Alveolar transmural pressure gradient increases. *
- Alveoli expand (according to their individual compliance curves) in response to the increased transmural pressure gradient. This increases alveolar elastic recoil. *
- Alveolar pressure falls below atmospheric pressure as the alveolar volume increases, thus establishing a pressure gradient for airflow. *
What are the events of normal expiration
- Brain ceases inspiratory command.
- Inspiratory muscles relax.
- Thoracic volume decreases, causing intrapleural pressure to become less negative and decreasing the alveolar transmural pressure gradient. †
- Decreased alveolar transmural pressure gradient allows the increased alveolar elastic recoil to return the alveoli to their preinspiratory volumes. †
- Decreased alveolar volume increases alveolar pressure above atmospheric pressure, thus establishing a pressure gradient for airflow. †
- Air flows out of the alveoli until alveolar pressure equilibrates with atmospheric pressure.
How is the pressure gradient calculated? AKA Transpulmonary pressure
transmural pressure = alveolar pressure - intrapleural pressure
in a resting lung:
Transmural pressure = 0 - (-5) = +5 mmH2O
Describe the pressure-volume curve
as the transpulmonary pressure increases (becomes more positive) the % of lung volume increases
What is Forced Vital Capacity (FVC)
Maximal expiratory effort made to force air from lungs
What are examples of Restrictive diseases?
Fibrosis
What are Obstructive diseases and what are some examples?
Problems with being unable to fully blow out a breath, usually a problem with increased alveolar compliance. Airway collapse and gas trapping occurs.
Asthma
Bronchitis
Emphysemia
What is Tidal Volume
The Volume of air entering or leaving the nose or mouth per breath
What is Residual Volume?
The amount of air left in the lungs after expelling a breath
What is the Forced Expiratory Volume in 1 second (FEV1)
The volume of air expired in the first second
What is the FEV1/FVC
In index of expiratory airway resistance
In normal subjects it is about .80; that is at least 80% of the FVC is expired in the first second
The person starts at TLC and expires all the air they can, in obstructive disease it is usually around .50, only about 50% is expired in the first second
It is normal or high in restrictive diseases
What is a flow-volume curve
Used to asses airway resistance and is obtained by having the subject make repeated expiratory maneuvers with different degrees of effort
What is effort-dependent and effort-independent curves of the flow-volume curve
Effort-dependent: As the subject exhales with heater effort, flow rates increase
Effort-independent: At low lung volumes, the expiratory efforts of different initial intensities all merge into the same curve
Why is the peak expiratory flow (PEF) decreased in restrictive diseases?
The TLC is decreased (and therefore the VC)
The effort-independent part is usually similar to normal lungs
FEV1/FVC may be normal or increased because the lung has low volume and because alveolar elastic recoil pressure may be increased
Why is the peak expiratory flow (PEF) and FEV1/FVC decreased in obstructive lung disease
The alveolar elastic recoil pressure is decreased
The effort-independent portion of the flow-volume curve is depressed inwards: flow rates are low for any relative volume
What is a fixed obstruction
Obstructions not affected by the inspiratory or expiratory effort
What is a variable obstruction
Changes in the transmural pressure gradient caused by the inspiratory or expiratory effort result in changes in the cross-sectional area of the obstruction
What is intrapleural pressure
AKA the intrathoracic pressure, the pressure in the pleural cavity
Normally around (-5)cmH2O on end expiration
If it is increased above normal due to air entering the pleural cavity the lung way collapse
It decreases during inspiration, pulling the alveolar open and increasing transpulmonary pressurek
