Download Physiology Objectives 35

Physiology Objectives 35
1.
Lung volume divisions:
a.
Residual volume: the amount of air left in the lungs after a complete
expiration
b.
Expiratory reserve volume: the amount of air exhaled forcibly from the
end of a tidal expiration to residual volume
c.
Tidal volume: the amount of air exchanged in a normal breath
d.
Inspiratory reserve volume: the amount of air inspired after tidal
inspiration to total lung capacity
Capacity divisions:
a.
Functional residual capacity: the sum of RV and ERV
b.
Vital capacity: the sum of ERV, TV, and IRV
c.
Inspiratory capacity: the sum of TV and IRV
d.
Total lung capacity: the sum of RV, ERV, TV, and IRV
2.
Elastic properties of the lung: the lung expands and contracts because of the
negative pleural pressure changes of inspiration and expiration. The negative
pleural pressure sucks the lung to the chest wall, and keeps the lung open for air
exchange.
Lung compliance changes with lung volume/growth: lung compliance is
greatest near FRC and is at its lowest near TLC. It also becomes greater with
larger lungs (larger volume for exchange with same pressures)
 Note: This makes sense because a patient needs air at FRC, and therefore,
wants to gain large volumes of air with little pressure exertion. At TLC, a
patient needs to get rid of air, and thus hinders any additional gain of air
by requiring enormous pressure.
3.
Elastic recoil: inspiratory recoil is caused by negative pleural pressure sucking
the lung to the chest wall. Expiratory recoil is caused by increased pressure in the
alveoli wanting to escape to the environment.
4.
Surfactant function: when lung is not inflated, surfactant remains in the water
layer and does not have much function; however, once lung is inflated, water
layer is spread more thinly, and surfactant can form a lattice network on the air
interface to decrease water surface tension. Thus, on expiration, there is greater
compliance per unit pressure than on inspiration (on inspiration, the lung has to
overcome surface tension).
Alveoli in absence of surfactant: diffuse alveolar collapse (IRDS in premature
infants – surfactant is produced in 8th month of gestation, and if infant is born
prematurely, there will be a critical lack of surfactant.
5.
Chest wall elastic properties and interaction with the lung: the chest wall is at
rest at around 70% of TLC. When the lung volume is less than 70% of TLC, the
chest wall wants to expand and cause inspiration; conversely, when lung volume
is greater than 70% of TLC, the chest wall wants to contract and cause expiration.
Creation of total respiratory volume-pressure relationship: summing the chest
wall and lung forces creates the respiratory pressure-volume diagram. Therefore,
after creation of both chest wall and lung pressure-volume curves, examining the
two forces working in concert may create the respiratory system curve.
6.
Role of gravity in regional ventilation differences: gravity adds pressure to the
base of the lung; therefore, the apex of the lung has a more negative pleural
pressure than the base and consequently has a lower volume. Since the base of
the lung needs more volume to reach TLC than the apex, they are more compliant.
 Note: this meets the demands of perfusion because gravity also pulls
additional blood flow to the base of the lung, and thus, the base needs
more gas exchange