Surface Tension/Airway Resistance Flashcards
Why does surface tension arise?
Because water molecules attract other water molecules at their poles, whereas air is nonpolar
What is respiratory distress syndrome?
A disorder in which neonates don’t produce surfactant, leading to the following: collapse of small alveoli, decreased compliance, and fluid entry into the alveoli
The majority of airway resistance occurs in the ____________.
bronchioles and medium-sized bronchi
How is resistance related to radius?
R is proportional to 1/(r^4)
Flow is equal to ________.
∆P/R
What are bronchoconstricting chemicals?
Parasympathetic acetylcholine input, arachidonic acid metabolites, and histamine
What are three categories of bronchodilating chemicals?
Sympathetic input (epinephrine and norepinephrine), other ß2 adrenergic ligands (isoproteronol and albuterol), and CO2 in bronchioles
What are three mechanical factors that influence lung resistance?
Mucus, dynamic airway collapse, and lung volume
What is dynamic airway collapse?
Airways close when P(IP) > P(AW) and open when P(IP)
Surface tension decreases lung _________.
compliance
By LaPlace’s formula, we know that surface tension causes small alveolae to ________.
collapse (pressure = 2 x T/r)
Surfactant reduces ___________.
surface tension forces
Most air flow is ____________.
“transitional” (i.e., not purely laminar or turbulent)
Normally IP is negative, which helps keep the airway open, but during forced expiration __________.
IP can become positive and temporarily close the airway
Why do emphysema patients have more of a tendency to engage in dynamic collapse?
They don’t have the normal elastic recoil that a healthy person has, so they have to put more exertional pressure on expiration, increasing the P(IP)
