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Discussion Starter · #1 ·
A patient's airway pressure is being measured while he is breathing into a spirometer. Which of the following lung volumes would be associated with an airway pressure of +30 cm H2O?
A. Functional residual capacity
B. Minimal volume
C. Residual volume
D. Tidal volume
E. Total lung capacity
 

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E) Total lung capacity

My ans is E) Total lung capacity

AP +30 is a positive airway pressure, that mean its a Total lung capacity (TLC). Too much pressure that occupying in your lung so that you feel like you want to blow air out (exhale). This is b/c your TLC is increased and you've developed the maximum recoil force. Let me put it this way, any volume above functional residual capacity (FRC) will create a positive airway pressure, and any volume below FRC will create a negative airway pressure.

Hope this clear your doubt...lol
 

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Discussion Starter · #4 ·
There is a point i want to bring out in this q. Qs like these seem impossible at first, but when u look closely at choices, answer is smiling at ur face. u will get a few qs like this in usmle.

The correct answer is E. For this question, you need not worry about the actual value of the airway pressure. There is only one listed answer that would produce a positive airway pressure, and that is total lung capacity. To measure the airway pressure, a patient inspires or expires from a spirometer, and then relaxes while his airway pressure is measured. It is easy to determine whether the airway pressure would be negative or positive by practicing on yourself. Inhale to total lung capacity and relax. You will feel the sensation of wanting to blow air out--this creates a positive pressure in your airways. Any volume above functional residual capacity (FRC) will create a positive airway pressure, and any volume below FRC will create a negative airway pressure.

Finally u can practice a few more qs from the attached file.
 

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