CPR 46-47 - Respiratory Muscles and Breathing Cycle; Mechanics of Lung and Chest Flashcards
What are the accessory muscles of inspiration? What do they do upon contraction?
External intercostals - pull ribs up and out
Scalene - helps stabilize first rib
Sternomastoid - helps stabilize first rib
What are the accessory muscles of expiration? What do they do upon contraction?
Internal intercostals
Rectus abdominis
Obliques
Transversus abdominus
All serve to pull ribcage downwards and inwards
What creates the pressure required for tidal expiration?
Elastic recoil of lung and chest wall. Mostly lung though
Describe the positioning of the internal and external intercostal muscles.
How is chest wall recoil pressure calculated?
Pcwr = Pip - Patm
What is Pip normally and what does it fall to during normal tidal inspiration?
Normally -5 atm
Falls to -8 atm during tidal inspiration
Does tidal inspiration or expiration take longer? Why?
Expiration
During inspiration, radial traction from alveolar expansion pulls the airways open wider. This does not occur during expiration which means there is more airway resistance during expiration.
Draw these four graphs for one tidal inspiration and expiration:
Lung Volume vs Time
Pip vs Time
Flow vs Time
PA vs Time
Explain the concept of hysteresis and how it applies to the lungs.
Hysteresis refers to the dependance of the state of a system on that system’s past. This applies to lung compliance because the lungs are more compliant upon deflation (expiration) then they are on inflation (inspiration). This occurs because to inflate the lungs have to pull apart the alveoli (fighting surface tension).
Why does the surface of a liquid act as an elastic sheet?
Surface Tension
Molecules below the surface are attracted to each other from all angles. Molecules at the surface are only attracted to molecules below the surface or also at the surface. As a result, the forces holding surface molecules together is unbalanced and this creates the elastic tension.
How is the force of surface tension measured?
Force per unit length or energy per unit area
What is LaPlace’s Law and why is this important to respiratory physiology?
Surface tension tends to form a sphere with a pressure inside. LaPlace’s Law is an equation for calculating that pressure - P = 4T/r (for a bubble) or P = 2T/r (for alveoli). This concept is important because without surfactant small alveoli would collapase to inflate large alveoli.
T/F - Lung surfactant has hydrophobic and hydrophilic components.
True
Describe the composition of lung surfactant. Mention what percentage each component makes up and the purpose of each component.
- 90% Phospholipids to interrupt surface tension
- 60% phosphatidylcholine (DPPC)
- 7-15% phosphatidylglycerol
- 25-33% other phospholipids
- 10% Protein
- SP-A & SP-D for lung defense
- SP-B & SP-C to facilitate surfactant monolayer formation
Describe how the surface tension across the alveoli changes throughout inspiration and expiration. Explain why these changes occur.
Overall surface tension is higher during expiration than inspiration. This is because at the beginning of inspiration the surfactant molecules are much more concentrated. The opposite is true at the beginning of expiration. Refer to image.
What common lung diseases increase/decrease lung compliance?
Emphysema/COPD increase lung compliance
Pulmonary fibrosis and respiratory distress syndrome decrease lung compliance
Draw the chest wall and lung recoil graphs. Mark where each force is at residual volume, FRC, and TLC.
What sets the FRC?
FRC is the lung volume at which the lung elastic recoil is equal to the chest wall elastic recoil (no muscular input)
Describe how and why lung dynamic compliance changes throughout the breathing cycle. Why is this an important concept?
Airway resistance decreases the flow rate of air into or out of the lung. Because of this, when breathing frequency increases the expiratory muscles begin contracting before the lungs have filled with air. This causes a decrease in dynamic compliance and a reduction in tidal volume. This effect is negligible in a healthy person but significant in patients with increased airway resistance (ie-asthma).
