Mechanics of Breathing Flashcards
What are the two compartments of the mechanical respiratory system? What is a common property that they share?
- lungs
- chest wall – pump that moves lung
both have elastic properties
Describe the state of the respiratory system, chest wall, and lungs at functional residual capacity (FRC).
- respiratory system is at rest
- outward recoil of chest wall
- inward recoil of lungs
these two opposing elastic properties are equal in magnitude, but opposite in direction
What is a pleural sac?
sac filled with ~!0 mL of fluid that lies between lungs and chest wall, one surrounding each lung
What do the cohesive forces of pleural fluid do? (2)
attach chest wall and lungs together
- allows lungs to inflate and deflate with chest wall movement
- movement of chest wall is followed by movement of lungs
reduce friction as lung tissue glides past chest wall during breathing
What are the units for pressure in respiratory mechanics? Why?
centimetres of water (cm H2O)
- mmHg is much larger relative to cm H2O
- cm H2O allows easier visual detection of pressure change
Where is atmospheric/barometric pressure?
surrounds chest wall and opening of airways
Why do we set PB = 0?
atmospheric pressure can change
when observing pressures, we observe them relative to atmosphere
What are the pressures (PA and Ppl) at FRC if the glottis is open (open airway to alveoli)?
PA = PB = 0, as long as you are at the end of a normal breath
Ppl = -5
What is transmural pressure?
pressure across wall (inside - outside)
What are the two types of transmural pressures?
- transpulmonary pressure (Ptp)
- chest wall transmural pressure (Ptw)
What is transpulmonary pressure (Ptp)?
pressure gradient across lung
Ptp = PA - Ppl = 0 - (-5) = 5 cm H2O
keeps lungs open at FRC, against their inward elastic recoil tendency
What is chest wall transmural pressure (Ptw)?
pressure gradient across chest wall
Ptw = Ppl - PB = -5 - 0 = -5 cm H2O
keeps chest wall from recoiling outward
(same as Ptp in magnitude, but opposite in direction)
Describe the state of chest wall and lung at FRC.
chest wall is squishing lung
What is the pressure of the respiratory system with 0 transmural pressure?
respiratory system is at rest with 0 transmural pressure
Prs = PA – PB = 0 - 0 = 0
What is a pneumothorax?
air entering pleural cavity, causing collapsed lung
- can be large/small which results in complete/partial collapse of lungs
- can be life threatening/fatal (ie. tension pneumothorax
Pneumothorax
What pressure has consequences?
-5 average Ppl
What is a traumatic pneumothorax?
puncture wound in chest wall that results in opening to pleural space
- opens chest wall
- allows air to enter (from higher to lower pressure)
- can also result in hemothorax (blood entering pleural cavity)
What is a spontaneous pneumothorax?
spontaneous rupture/hole in lung that results in opening to pleura from inside of airway
- allow air from lung to enter pleura
- air enters until the two pressures in pleura, and outside become the same
- results in air-filled pleura and collapsed lung
What is Boyle’s law?
relationship between pressure and volume
- pressure is related inversely to volume at constant temperature
- closed system
What is pressure?
force per unit area caused by gas molecules striking walls of container
Respiratory Pressures During Quiet Breath – Inspiration
see notes
Respiratory Pressures During Quiet Breath – Expiration
see notes
What are the muscles of active expiration? (2)
internal intercostal muscles
abdominal muscles
recall: normal quiet breathing is passive – these muscles have to do with active breathing, such as taking deeper breaths, or forcing breath out (blowing)
What are the accessory muscles of inspiration? (2)
muscles in neck used for very large/deep breaths, in patients who have problems breathing
- sternocleidomastoid
- scalenus
What are the major muscles of inspiration? (2)
diaphragm
external intercostal muscles – between ribs, closest to skin
Muscles of Inspiration
What does the diaphragm do? Describe the movement.
- 75% of air that moves into lung is due to diaphragm
- moves downward, increases vertical dimension of chest wall
Muscles of Inspiration
What do external intercostal muscles do? Describe the movement.
brings lower rib up to rib above it
up-down bucket handle motion
- elevates rib upward and outward
- increases horizontal dimension of chest wall
Muscles of Inspiration
What do accessory muscles do? Describe the movement.
attached to sternum and upper ribs – lifts them upward and outward
- sternocleidomastoid: lift sternum
- scalene muscle: lift first 2 ribs
up-down pump handle motion
- sternum moves upward and outward
- increases front-back dimension of chest wall for air to move into lungs
Muscles of Expiration
What are internal intercostal muscles? What do they do? Describe the movement.
layer below external intercostals, run 90º to them
contraction bring ribs down
- further reduces horizontal and front-back dimensions of chest wall
Muscles of Expiration
What are abdominal muscles? What do they do? Describe the movement.
3 layers
contraction pushes abdominal cavity towards diaphragm
- further reduces vertical dimension of chest wall
What happens when inspiratory muscles relax?
diaphragm, ribs, and sternum return to resting position, which restores thoracic cavity to pre-inspiratory size
What innervates muscles of quiet inspiration?
C3-C5 (cervical spinal roots), which give rise to phrenic nerves that supply hemi diaphragms
- two phrenic nerves – one left, one right
- if one gets hurt, the other is still functional on their side of the diaphragm
What innervates muscles of quiet expiration?
passive expiration: none – due to inward recoil of lung
active expiration: T7-L1 – abdominal muscles active, especially transversus abdominus
What innervates external or internal intercostal muscles?
T1 - T11
What innervates sternomastoid muscle?
- accessory nerve
- C2-C3
