Chapter 7 Flashcards
Is inspiration passive or active?
- Active always
Is Expiration Passive or Active?
- Passive during rest
- Active during exercise
What is the most important muscle for inspiration? What is it innervated by?
Muscle
- Diaphragm
Innervation
- Phrenic Nerves that originate from cervical segments 3,4,5
What plays a key role in active expiration?
- contraction of the abdominal muscles
What are the Primary Muscles of Inspiration? What are they innervated by?
- Diaphragm: Phrenic, C3-C5
- Scalenes: C2-C7
What are the Accessory Muscles of Inspiration and Muscles of Expiration? What are they innervated by?
- Sternomastoid: Accessory Nerve & C2-C3
- Intercostal: T1-T11
- Abdominal Muscles (especially Transversus Abdominus): T7-L1
What is the shape of the Pressure-Volume curve of the lung? why is it that shape?
- Linear: because the lung gets stiffer at higher volumes
What is Hysteresis?
the amount of energy/work needed to surpass the airways resistance during inspiration, and expiration.
What is Compliance of the lung?
The slope of Change in Volume/ Change in Pressure
What is responsible for the compliance behaviour of the lung?
- Structural proteins: Collagen and Elastin
- Surface Tension
What can cause a reduction in compliance?
- Pulmonary Fibrosis
- Alveolar Edema
- Increased Venous Pressure
What causes an increase in Compliance?
- Emphysema
- Normal Aging
What balances the tendency of the lung to recoil to its deflated volume?
- The tendency of the chest cage to bow out
What is a similarity about the lungs and the thoracic cage?
- they are both elastic
What is the intra-pleural pressure compared to atomospheric pressure? Why?
Sub-atmoshperic: Because the tendency of the lung to recoil to its deflated volume is balanced by the tendency of the chest cage to bow out
What determines the Pressure-Volume Curve?
- Elastic properties of both the lung and chest wall determine the combined volume
What happens at FRC? (functional reserve capacity)
- The inward pull of the lung is balanced by the outward spring of the chest wall
At what volumes does the Lung retract?
- All volumes above minimal volume
At what volumes does the chest wall expand?
- Volumes up to 75% of vital capacity
What does Pulmonary Surfactant do?
- Reduces the surface tension of the alveolar lining layer
What is Pulmonary Surfactant Produced by?
- Type II alveolar Epithelial cells
What does Pulmonary Surfactant Contain?
- DPPC
What results from the absence of Pulmonary Surfactant?
- Reduced Lung compliance
- Alveolar Atelectasis (complete or partial collapse)
- Pulmonary Edema
What are some regional differences in lung Ventilation?
- Weight of the upright lung causes a higher (less negative) intrapleural pressure around the base compared with apex
- Because pressure-volume curve is non-linear, alveoli at the base expand more than do those at the apex
- If a small inspiration is made from residual volume (RV), the extreme base of the lung is unventilated
What is Laminar Flow Governed by?
Poiseuille’s Law: V. = P(pi)r^4 / (8nl)
or
R = 8nl / (pi)r^4
R (resistance)
n (viscosity)
l (length)
r (radius)
P (driving pressure)
What happens if the radius is halved for laminar flow?
Resistance is Increase 16-fold. r^4.
What is Reynolds Number?
Re = 2rvd/n
d (density)
v (average velocity)
r (radius)
n (viscosity)
What is resistance inversely proportional to in Laminar Flow?
- the fourth power of the radius
What does the velocity profile show for laminar flow?
A central spike of fast gas
When is turbulent flow most likely to occur?
- At a high Reynolds number: when inertial forces dominate over viscous forces
Where is airway resistance the highest?
- Medium-sized Bronchi
Where is Airway Resistance Low?
- Very small airways
What happens to airway resistance when lung volume increases?
It decrease: because airways are pulled open
What is the Bronchial smooth muscle controlled by?
- Autonomic Nervous system
What causes Bronchodilation?
- Stimulation of the B2-Adrenergic Receptors
What happens when you breath in a dense gas?
- Increase in airway resistance
When is flow effort independent? Why?
- Low to Mid Volumes: Because the flow rate reaches a plateau and cannot be increased with further increase in intra-pleural pressure
When is flow effort dependent? Why?
- High Volumes: Because the expiratory flow rate continues to increase with effort (passive at low-mid volume)
What does Dynamic Compression of the airways do in normal subjects during a forced expiration?
- Limits air flow
When might dynamic compression occur during low expiratory flow rates? what might be the consequence?
- In a diseased lung: Reduces exercise ability
What is flow determined by during Dynamic Compression?
- Alveolar pressure minus pleural pressure (not mouth pressure)
When might Dynamic Compression be exaggerated?
- In some lung diseases, due to reduced lung elastic recoil and a loss of radial traction on airways
What does an increase in resistance of peripheral airways do? Why?
Exaggerates flow-limiting mechanisms:
- magnifies the pressure drop
- decreases the intrabronchial pressure during expiration
What does low lung volumes do?
Exaggerates flow-limiting mechanisms: because it reduces the driving pressure (alveolar-intrapleural)
What can emphysema do to flow?
Reduces Flow by:
- Reduces Recoil Pressure: reduces driving pressure
- Reduces Radial Traction on Airways: they compress more readily
What is the difference between flow limitation in healthy subjects vs subjects with severe obstructive lung disease?
Healthy subject: only seen during forced expiration
Lung Disease: seen during normal breathing
How does a forced expiration test help diagnosis?
- used to evaluate patients with chronic dyspnea
- Distinguishes between obstructive and restrictive disease
Where might you see a lack of surfactant? what can it lead to?
- in premature infants: leads to low compliance and respiratory failure
