An asthmatic is having an acute asthma attack, and the airway radius has gone fr
ID: 3472920 • Letter: A
Question
An asthmatic is having an acute asthma attack, and the airway radius has gone from 10 mm to 5 mm. What has happened to the pressure needed to maintain the same flow through the airway as was attained prior to the narrowing? Assume laminar flow.
An asthmatic is having an acute asthma attack, and the airway radius has gone from 10 mm to 5 mm. What has happened to the pressure needed to maintain the same flow through the airway as was attained prior to the narrowing? Assume laminar flow. O The pressure needs to be 16 times previous. O The pressure can be 16 times less than previous. The pressure needs to be 2 times previous O The pressure can be 2 times less than previous.Explanation / Answer
Asthma causes constriction of airway, resulting into increase in airway resistance. Increased resistance makes passage of air difficult and requires increased air pressure in order to ensure proper breathing. The radius of airway is inversely proportional to airway resistance. The relationship is denoted by the formula, R= 8(Length X gas viscosity)/ r4 (where R is the airway resistance and r is the radius of airway). So, assuming other factors to be constant if r is halved, the airway resistance becomes 16 times. [R=8(Length X gas viscosity)/ 1/2r4 = 16(8(Length X gas viscosity)/ r4) i.e. resistance increases 16 times). So, in order to provide same air flow, the air pressure needs to be increased 16 times when the radius decreases from 10 mm to 5 mm (i.e. halved). So, the correct option is A (pressure needs to be 16 times previous).
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