pulmonary Flashcards
air-blood barrier
alveolar epithelium
capillary epithelium
basement membrane
very thin for easy diffusion
ventilation definition/equation
Transport of gas from the atmosphere to the alveolar surface
minute ventilation (ml/min) = respiratory rate (breaths/min) x tidal volume (ml/breath)
anatomic dead space
volume of conducting airways
~30% of tidal volume
physiologic dead space
volume of alveoli that are ventilated but are not perfused with blood
low in healthy lungs. May be high in lung diseases
collapsing tendency of lungs comes from
1/3 from elastic fibers in lung CT
2/3 from alveolar surface tension
pressure is function of:
1) surface tension of the fluid
2) radius of the sphere
Small alveoli need more pressure to keep it open
surfactant
Lowers surface tension by disrupting water-water interactions.
Secreted by type II alveolar cells
Detergent: dipalmitoyl phosphatidylcholine
common problem with premature infant lungs
Lack surfactant –> cyanotic
Tx: inhaler with surfactant
compliance of lung
Refers to change in volume as transmural pressure is changed
[high or low] compliance at low lung volumes?
Low compliance at low lung volumes bc of high alveolar surface tension
lung compliance in inflation vs deflation
Different slopes.
A greater pressure is needed to open a previously closed airway than to keep an open airway from closing.
2 mechanisms to inflate the lungs
1) positive pressure: blowing up from pressure applied to trachea
2) applying negative pressure to the outside surface to suck it against the inner chest wall [* normal mechanism*]
transpulmonary pressure
P(tp) = P(alv) - P(ip)
Keeps the lungs expanded in thoracic cavity.
accessory muscles of inspiration
sternocleidomastoid
scalenes
pectoralis minor
serratus anterior
accessory muscles of exhalation
internal intercostals transversus thoracis external oblique rectus abdominus internal oblique
How does the thoracic cage change during inhalation?
Ribcage moves up/out (increases diameter of thoracic cage). Diaphragm moves down (increases height of thoracic cage). Lung expands (due to the expansion of the thoracic cage) --> decreased pressure in lungs --> air flows in
How does the thoracic cage change during exhalation?
Ribcage moves down/in (decreases diameter of thoracic cage). Diaphragm moves up (decreases height of thoracic cage). Lung shrinks (due to the decreased volume of thoracic cage) --> increased pressure in lungs --> air flows out
effect of airway resistance on ventilation
Smaller radius = larger resistance = decreased ventilation
A change in radius changes the resistance by a factor of 4
Functional Residual Capacity (FRC)
amount of air left in lungs after normal expiration
how to determine FRC
Helium dilution method
residual volume (RV)
amount of air left in lungs after maximum expiration
total lung capacity (TLC)
Total air possible in lung.
Max inspired, including residual volume.
vital capacity (VC)
maximum inspired + expired
tidal volume (VT)
normal, resting breath
