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Outline elastic recoil properties of the two compartments of respiratory system and specify relationship between elastic recoil pressure and transmural pressure? What's FRC

Lungs recoil inwards
Chest recoils outwards, equal and opposite directoins.

Functional residual capacity is air in lungs at the end of a normal breath.

Transpulmonary pressure keeps lungs open against their inward elastic recoil
transmural pressure keeps chest wall from going out.
Whole system at rest.


Describe changes in alveolar, intrapleural and transmural pressures, airflow, lung volume during quiet breath. identify units to do this.

Measured in cm/h20 to see small changes
Atmospheric pressures are called zero (relatively)
Intrapleural space is -5cm than that when airways are open at FRC.


Describe the sequential order of changes (muscle contraction, thoracic lung volume, intrathoracic pressures and airflow) during inspiration and expiration.
Draw the different curves.

1. Inspiratory muscles contract (diaphragm)
- Neural input has to provide that info to the inspiratory muscles to contract.
2. Chest wall gets bigger (changed volume)
- Thoracic volume is larger
- Two pressures will decrease
§ Pleural pressure (by 3cmh20) Ppl
§ Alveolar pressure (by1cmh20) PA
When this pressure drops, you have a difference in pressure between atmosphere
and alveoli and air flows in
Transpulmonary distending pressure is increasing (pa-ppl)
3. Air flows into the lungs (negative pressure) drop in alveolar pressure relative to atmosphere)

We need negative pressure to inspire.

Inspiration is active, requires brain to generate contraction to inspiratory muscles, leads to expansion.

Expiration is not active. Inspiratory drive must stop.
1. Inspiratory muscles stop contracting. Are they contracting during inspiration the whole time?
2. Lungs recoil inwards, their transmural pressure has been increased, they will recoil
- Reduce thoracicl volume
- Two pressures increase Alveolar must increase relative to atmosphere. Until airway becomes the same as atmospheric
3. Air flows out until pA = Pb (atmospheric)
Now youre at functional residual capacity

Quiet expiration is passive. Lung recoil increases alveolar pressure ABOVE atmospheric pressure which drives air out of the lungs


Describe the role of respiratory muscles in changing the thoracic dimensions during quiet and forceful breathing

Inspiration: active muscles of the sternocleoidomastoid process for forceful breath but mostly the diaphragm and external intercostal muscles.
- dome shaped diaphragm flattens and moves down
- external intercostals shorten moving ribs up and out
- overall lifting of the chest
- external intercostal muscles move like bucket handle
- accessory muscles lift like a water pump

Expiration: internal intercostal muscles between ribs and abdominal muscles.
- bring ribs down and inwards
- abdominal pushes diaphragm up to reduce volume inside chest (forceful)


Descrie motor innervation of respiratory muscles and predict impact of complete spinal cord injury on breathing with high low cervical, thoracic and lumbar/sacral regions.

Phrenic nerve provides input to diaphragm: roots c3,4,5 cervical spine
Sternomastoid c2-3
Internal intercostals t1-11 thoracic spine
abdominal also t7-l1


Describe the fluid filled pleural cavity

Each lung is a lolipop: surrounded by a fluid filled sac
- Push it into.
- Each lung has its own pleural sac (with fluid in it)
○ Like the pericardial sac around the heart.
- The fluid acts as a glue which attaches chest wall and lung together. Lungs and chest wall will move together. The chest wall is what really moves.
- Fluid allows for reduced friction as the wall and lung glide past each other during breathing.
○ Putting some water between two plates of glass.
○ The fluid is not that big its tiny.


What is transmural pressure?

- Pressure across a given compartment or container.
○ Defined as the pressure across a wall (inside - outside)
○ Across the lungs, 5cm/water, because alveolar - plural pressure is 5cm/water.
○ Across the chest wall, plural pressure - atmospheric pressure. -5cm/water.
○ Magnitude is the same, but negative value = zero.
Whole system is 0 - 0 = 0 is at rest. But individual components are either recoiling in or out.

The 5cm water pressure keeps the lungs open.


What is a pneumothorax?

Air in the plural sapce ( a hole in chest wall or lung wall.
Spontaneous pneumothorax can happen to anyone and be deadly (air rushes in until all pressures are equal)
(traumatic is hole in chest wall, spontaneous is hole in lung)

Can be small/partial/large/complete collapse.
Can result in hemothorax (blood in the pleural cavity)


What is boyle's law?

Pressure is force per unit area. As volume increases pressure decreases by that amount (fraction form)