chapter 7 Flashcards
Muscles of inspiration
Diaphragm
external intercostals (in pockets)
scalenes - top 2 ribs
sternomastoid - sternum
Muscles of expiration
Rectus abdominis Internal oblique muscles External oblique muscles Transversus abdominis Internal intercostal muscles
causes of increased compliance
normal aging lung
emphysema
causes of decreased compliance
pulmonary fibrosis
alveolar edema
collapse/atelectasis
what is normal compliance of human lung?
200 ml/cm water
what is specific compliance
compliance per unit volume of lung
What is Laplace’s law?
P = 4T/r
where P is pressure, T is surface tension, and r is radius.
When only one sur- face is involved in a liquid-lined spherical alveolus, the numerator is 2 rather than 4.
What is physiological advantage of surfactant?
- low surface tension on alveoli increases compliance of the lung and reduces the work of expanding it with each breath
- alveoli stability promoted (prevents small bubbles from collapsing while big bubbles keep getting bigger - Laplaces law)
- keeps alveoli dry
- reduced surface tension of alveoli reduces the hydrostatic pressure in the tissue outside the capillaries - prevents transudation of fluid
what is interdependence
support offered to lung units by those surrounding them
- same principle for blood vessels as the lung expands
regional difference in intrapleural pressure?
less negative at bottom psrt of lung
- harder to blow up from RV
- airway closure at base
What is the equation for the total compliance of the lung and chest wall?
1/CT = 1/CL + 1/CCW
At what TLC does the chest wall hit equilibrium?
75% VC
What is Reynolds number equation and what is the significance?
Re = 2rvd/n
r = radius, v = average velocity, d =density, n = viscosity
Measure of inertial forces to viscous forces
Re > 4000 = turbulent flow
Re > 2000 = transitional flow
Re < 2000 = laminar flow
Turbulent flow is more likely to occur when tube diameter high and velocity high
Fully laminar flow in small airways where Reynold number = 1
what is poiseuille law for laminar flow?
volume flow rate = P(pi)r^4/8nl
n = viscosity, l = length, pi= 3.`1415
P = K * volume flow rate
VISCOSITY OF GAS IS MORE IMPORTANT
What is pressure equation for turbulent flow?
P = K * (volume flow rate)^2
DENSITY OF GAS IS MORE IMPORTANT
What is airway resistance
Pressure difference between mouth and alveoli divided by a flow rate
Which part of airways are chief site of resistance?
intermediate sized bronchi
Why does intrapleural pressure fall during inspiration?
- Increased elastic recoil of lung
2. Reduction in alveolar pressure causes fall in intrapleural pressure
What are factors that affect airway resistance?
- lung volume - radial traction from surrounding lung tissue
- contraction of bronchial smooth muscle
- cigarette smoke
- parasympathetic activation
- CO2 - Density and viscosity of gas
- viscosity for laminar
- density for turbulent
Resistance = 8nl/(pi)r^4
What is the effective driving pressure in dynamic compression?
alveolar minus intrapleural
Dynamic compression of the airways during a forced expiration results in flow that is effort independent. The driving pressure is then alveolar minus intrapleural pressure. In patients with chronic obstructive lung disease, dynamic compression can occur during mild exercise, thus causing severe disability.
what are factors that worsen flow limitation?
airway resistance
low lung volume (reduced driving pressure)
reduced recoil pressure
What is transpulmonary pressure?
Pressure difference between inside and outside of lung
When alveolar pressure is atmospheric, it is numerically equal to the pressure around the lung
What happens to compliance during an asthma attack?
Increases (mechanism not known)
What is pulmonary resistance?
Airway and tissue resistance
20% of total resistance in normal subjects
What is work of breathing on inspiration made up of?
- Elastic forces
- Viscous forces (airway and tissues) resistance
- on expiration, the work is less because of the energy stored in the expanded elastic structures
What is the equation for efficiency of work of breathing? (O2 cost of breathing)
What is normal efficiency at rest?
efficiency % = useful work / total energy expended (or O2 cost) x 100
Efficiency at rest is 5-10%
