4.4 Mechanisms of Ventilation Flashcards
Respiration involves which two processes?
- Ventilation (mechanical conduction of air; breathing)
- Gas exchange (diffusion)
Which muscles are used in respiration?
- Diaphragm
- Intercostal muscles
Which bones are involved in respiration?
- Ribs
- Sternum
- Vertebral column
What are the two layers of the pleura?
- Visceral (inside; think of Bloodborne)
- Parietal (outside)
Which extracellular structures are involved in respiration?
- Elastic fibres
Which afferent nerves are involved in respiration?
Sensors and processors in:
- Blood vessels
- Lungs
- Brainstem
Which efferent nerves are involved in respiration?
Phrenic (diaphragm) nerves and intercostal nerves
What is the border between the upper and lower airways?
The larynx (it talks, after all)
Why doesn’t gas exchange occur in our mouths?
Air must be modified before gas exchange
What modifications are made to air before gas exchange?
- Humidification
- Warming
- Cleaning
What is the anatomical dead space of the respiratory system?
Areas of no gas exchange
What is the volume of the respiratory dead space?
150mL
What is meant by alveolar dead space?
All alveoli that are not perfused with blood
What makes up the physiological dead space of the respiratory system?
Anatomical dead space + alveolar dead space
In which structures can gas exchange occur during respiration?
- Respiratory bronchioles
- Alveoli
What is meant by compliance?
Distensibility/resistance against stretching; how much volume of air can be added per pressure? (higher, more compliance)
What is meant by recoil?
The force that opposes stretching of the lungs
What is the relationship between recoil and compliance?
Inversely proportional; the more force acts against stretching, the lower the compliance of the lung.
What is the parietal pleura connected to?
The endothoracic fascia
What is the relationship between the visceral and parietal pleura?
They are connected: think: fist and balloon.
What is the purpose of the liquid between the visceral and parietal pleura?
Adhesion
Why is it important that the visceral and parietal pleura are connected?
The visceral pleura is connected to the parietal pluera, which is connected to the endothoracic cavity. Therefore, when the thoracic cavity increases in volume, so too do the lungs.
What structures must be able to move in order for the lungs to expand during ventilation? How do they do this?
- Diaphragm (contracts)
- Ribs (bucket handle and pump handle movement)
What is Boyle’s Law?
V1 x P1 = V2 x P2 (before and after inspiration)
What prevents alveoli from collapsing in on themselves, given that they want to?
Surfactant
How is work of breathing calculated?
Work = Pressure x Volume
What percentage of work is dedicated to quiet vs resistive work during quiet breathing?
- 65% elastic (expanding during inspiration)
- 35% resistive (overcome airway resistance etc.)
Why does airway resistance increase during intubation?
- Intubation increases the length of the airway
- When you increase the length, you also increase the resistance to flow (the same as blood vessels)
What two factors influence the simplified calculation of airway resistance?
- Pressure gradient
- Volumetric airflow
IT’S JUST OHM’S LAW (Poiseuille’s law also works)
Why does it make sense that people with asthma have increased resistance to breathing?
As airways become inflamed, they reduce in radius. Since resistance is proportional to the fourth power of the radius, this can result in a radical increase in airway resistance.
What are the four components of respiration?
- Ventilation
- Diffusion
- Gas Transport
- Gas Exchange
Summarise Boyle’s Law in words
Pressure of gas is inversely proportional to its volume
What mechanisms are involved in quiet inspiration and expiration?
INS: Diaphragm flattens, lungs lengthen
EXP: Diaphragm relaxes, elastic recoil of lungs and chest wall
What additional mechanisms are involved in forced/effortful breathing?
INS: Intercostal muscles (mostly external) act to to raise rib cage
EXP: Abdominal recti and (mostly) internal intercostals
What is transpulmonary pressure?
The gap between alveolar pressure and pleural pressure
Recall the equation for compliance
C = deltaV/deltaP
How does surface tension influence the collapse of alveoli?
The particles in the wall of the alveoli are attracted to one another, and so the lungs constantly want to collapse on themselves
Recall the law of LaPlace
Pressure = 2T/r
T: Surface tension
r: Radius
What air modification occurs during expiration?
- Air is cooled, returning some of the heat into the upper airways
- Some water is reclaimed through condensation
What is the opposite of turbulent?
Laminar
