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
