Mechanics of breathing Flashcards
compliance
- how easy it is to inflate the lungs
- the slope of the pressure volume curve
- Volume change per unit of pressure change
- Change in V/Change in P
recoil
how well the lungs go back to original shape after inflating
Which law allows breathing to work?
Boyle’s Law
P1 x V1 = P2 x V2
what are the major muscles of inspiration?
diaphragm
external intercostals- raise the ribs up, increase thoracic cavity space
What are the accessory muscles of inspiration?
Sternocleidomastoid
scalenes- pull up first rib (all ribs follow)
What are the accessory muscles of expiration?
Abdominals- force internal muscles up, making thoracic cavity smaller
internal intercostal muscles
Explain intrapulmonary pressures that occur with normal breaths
- Inspiration- inspiratory muscles contract and chest expands.
- bigger volume = lower pressure; air flows into lungs until pressure equals atmospheric pressure
- Expiration- inspiratory muscles relax
- recoil of lung causes alveolar pressures to exceed atmospheric pressure, causing air to flow out of lungs

what causes the “suction” that keeps the lungs against the chest wall?
What forces work against that, trying to collapse the lung?
Intrapleural pressure space between the lung and thorax
4 mmHg lower than intrapulmonary pressure
alveolar surface tension and lung elasticity want to pull the lungs to collapse
At what point in the breathing cycle is the intrapulmonary pressure the lowest?
halfway into inspiration
*the inspiratory muscles have created more space, but air has not yet come in
At what point in the breathing cycle is the intrapulmonary pressure the highest?
halfway into exhalation
*the inspiratory muscles have relaxed, decreasing the space available and increasing the pressure, but the air has not yet escaped.
what happens when air enters the pleural cavity?
Negative pressure is lost, causing lung to collapse. Mediastinum shits toward other side because the negative pressure on that side is unopposed.

Regional differences in ventilation
- intrapleural pressure is less negative at the bottom of the lungs due to the weight of the lung
- lung is easier to ventilate at low volumes than at high volumes
- the apex has a big resting volume and smaller changes occur in inspiration
How is Laplace’s law applied to the lungs?
When the radius of the alveoli is smaller, more pressure is required to open it up.
P = 4T/r
T = surface tension
**If radius decreases by half, pressure increases x2
hysteresis
- when comparing the volume and pressure on inhalation to exhalation, the pressures will differ at the same volume
- pressures are higher during inhalation
- this is caused by the surface tension
- Lungs inflated with saline have greater compliance (the mouse video)

What happens in the absence of surfactant?
- reduction of lung compliance
- alveolar atelectasis
- pulmonary edema
How do you determin resistance and flow?
What is the greatest factor?
Pouseuille’s law
greatest factor is airway diameter
Q = (Change in pressure * πr4)/n*8*L
n=viscosity of air
what is the site of major airway resistance?
medium sized bronchi
*similary to capillaries, the resistance is high, but there are so many bronchi that the overall resistance is low
Where is the resistance low?
in the very small airways
Airway resistance _________ as lung volume ________ because airways are _________
Airway resistance decreases as lung volume increases because airways are pulled open
What controls the bronchial smooth muscle?
ANS
Breathing a dense gas _______ resistance as breathing a less dense gas ________ it. Example?
Breathing a dense gas increases resistance as breathing a less dense gas decreases it. Example: Helium
What characterizes restrictive lung disease?
reduced functional volume/compliance of the lungs; Difficult to get air into the lungs
Ex fibrosis and asbestosis

What characterizes obstructive lung disease?
reduced flow rate; eventualy causing increased compliance. Difficult to get air out of the lungs
Ex. COPD and asthma

FEV
What happens to the FEV in COPD?
Forced expiratory volume
FEV is reduced and the FEV/FVC ratio is less than the normal value of 75%
FVC = Forced vital capacity
What happens to the FEV/FVC ratio in in restrictive lung disease?
The FEV and FVC are both reduced so the ratio is the same
Total lung capacity and residual lung capacity is decreased. (residual the most)