dxtxpx
Forum Guru
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Decreasing an airway diameter by half would lead to which degree of change in airway resistance?
a) 50% decrease
b) 50% increase
c) 100% decrease
d) 100% increase
e) greater than 100% increase
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| dxtxpx
Forum Guru
Topics: 259
Posts: 1,233
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answer E
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| su
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How did you calculate that?
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| dxtxpx
Forum Guru
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No calculation required, just a fact:
Airway resistance is responsible for most of resistance during breathing. the airwya resistance changes dramatically with changes in airway diameter. A disease state that decreases airway diameter to half its healthy equivalent would result in a dramatic increase in airway resistance, perhaps 16-fold increase
Tone of smooth muscle that surrounds airways affects their diameter and therefore resistance. Smooth muscle reacts to both parasympathetic and sympathetic nervous activity. Stimulation of parasymp fibers releases Ach which causes smooth muscle contraction (thus constricting airways) while sympth activation releases NE which relaxes smooth muscle causing dilation of the airway. Epi and beta 2 agonists are powerful bronchodilators. In addition, there are large # of enteroendocrine cells in respiratory system whose secretions alter airway diameter. Substance P is potent bronchoconstrictor and stimulator of mucus secretion. VIP has the opp effect
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| IT153
Forum Newbie
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Posts: 29
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Rough math calculation:
Surface = 3.14 x R²
If diameter is decreased by a half (increase = ½), the surface will decrease by four times (increase = ¼) meaning 400% of increase in resistance.
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| dxtxpx
Forum Guru
Topics: 259
Posts: 1,233
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thanks IT153 
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| resp therapy gal
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delta p = (8 x viscosity x length of tube)/radius to the fourth power
airway resistance = delta P/flow
a decrease in diameter by half will create an increase in resistance by 16 times the original resistance.
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