Lecture 4: Respiratory Cycle Flashcards
Is inspiration passive or voluntary?
Voluntary
Is expiration passive or voluntary?
Passive
What are the muscles of inspiration?
- Diaphragm
- External intercostal muscles
Diaphragm and inspiration
The diaphragm is innervated by the phrenic nerve and moves moves down to increase the volume of the thorax
External intercostal muscles and inspiration
The external intercostal muscles are located in between the ribs. When contracting, the raise the ribs by increasing the anteriorposterior diameter of the thorax (bucket handle motion). This increases the area, allowing us to breathe in.
What are the other muscles for inspiration?
- Scalene muscle- raises the 1st and 2nd rib
- Sternomastoid muscle- raises the sternum
- Muscles in the head and neck
What kind of muscle are the respiratory muscles?
Skeletal muscle
What are the 2 pros of respiratory muscles being skeletal muscle?
- Activation is uniform and rapid.
- Can respond rapidly to changes in conditions
What are the 2 cons of respiratory muscles being skeletal muscle?
- Damage to the brain and spinal cord can stop breathing.
- If the lungs get too big, it can stretch the muscle (length-tension curve)
What are the events during inspiration?
- Inspiratory muscles contract, increasing the thoracic volume.
- Intrapleural pressure decreases from -5cm H20 –> -8cm H20. Pressure stays -8cm until the end of inspiration.
- As the lungs increase, the alveolar pressure decreases from [0cm H20 –> -1cm H20] due to an increase in alveolar size. At the end of inspiration, alveolar pressure will go back to [0cm H20].
Pressure changes during 1 inspiration
Intrapleural pressure: -5cm H20 –> -8cm H20
Alveolar pressure: 0 –> -1 (at mid breath) –> 0
Are the lungs and mucles/ribs physically connected to one another?
No. The viseral pleura and parietal pleura, plus the fluid in between, adhered the lungs with the ribs and muscles.
Intrapleural pressure at rest
-5cm H20
This means that the pressure is 5cm lof H20 less than the outside.
Alveolar pressure at rest
Same as atmospheric because there is no air movement: 0cm H20
Air flows into the lungs when alveolar pressure _____ atmospheric pressure
**Palv
atm**
When alveolar pressure drops below atmospheric pressure.
Intrapleural pressure reaches its lowest point when?
At the end of inspiration (-8cm H20)
Airflow into the lungs will decrease as …
alveolar pressure returns back to 0cm H20
What is tidal volume (VT)?
Tidal volume (VT)
The amount of air inhaled in a given breath.
Typically, it is about 500 mL.
Expiratory Muscles
- Abdominal muscles- push into the abdomen to move the diaphragm up
- Internal intercostal muscles- decrease the AP diameter of the thorax
- Accessory muscles
Expiration is passive because the lungs WANT to be smaller.. Thus, in a normal breath we do not use these muscles.
What are the events during expiration?
- Inspiratory muscles relax, allowing the volume of the thorax decreases and the diaphragm and rib cage go back starting position.
- Decrease in volume causes the intrapleural pressure to go back to normal (-5cm H20).
- Alveolar pressure will increase to -1cm H20 at midbreath due to the action of the rib cage.
- A pressure gradient is created that produces airflow OUT of the lungs—
- As expiration proceeds and the volume of air in the lungs decrease, the alveolar pressure will go back to 0.
- Eventually, all of the air that entered during inspiration is exhaled.
What is the intrapleural pressure and alveolar pressue at rest?
Intrapleural pressure: -5cm H20
Alveolar pressure: 0cm H20
Intrapleural pressure becomes more ____ with inspiration
Negative
When does the peak negative value of the intrapleural pressure occur?
At the end of inspiration
In normal expiration, the intrapleural pressure remains _____
Negative
Alveolar pressure becomes ______ with inspiration
negative
Peak negative alveolar pressure occurs when?
Mid-inspiration
In any expiration, the alveolar pressure becomes ______
Postive.
Peak positive value of alveolar pressure occurs when?
Mid-expiration
Why does the intrapleural pressure not return to resting value until the end of the respiratory cycle?
Why did the alveolar pressure return to 0 at the end of each phase?
Because air enters the alveoli (more molecules takes up the added space), but nothing should enter the intrapleural space.
Thus, the intrapleural space has the same number of molecules spread out over a bigger volume.
What is minute ventilation?
Minute ventilation–> how much air is inhaled every minute
V(dot)= Vt (tidal volume) * frequency
What are anatomic deadspaces?
The first 16 generations of the airway do not have alveoli, thus, they are called anatomic dead spaces because they do not particpate in gas exhange.
To figure out ones anatomic deadspace, take their weight in lbs and change it to mL.
150 lbs–> 150 mL of dead space
What is alveolar ventilation?
How much of every breath gets into the alveoli
VT-VDS
Tidal volume minus the volume of the anatomic dead space
Alveolar ventilation.
150lb person who breathes 500 Lm with each breath
500- 150= 350 mL of every breath gets into the alveoli
Minute alveolar ventiliation
How much of every breath gets into the alveoli/minute
Valv*frequency
What is the minute alveolar ventilation?
Same 150lb patient is breathing 12 breaths/minute.
350 * 12= 4,200 mL/minute
Transpulmonary pressure
Palv-PIP
