You are working in a rehabilitation setting performing exercise testing and pres

Question

You are working in a rehabilitation setting performing exercise testing and prescription. You have a subject who has a measured airway resistance of 25 cm H2O/L/sec and a measured static compliance of 110 ml/cm H2O. Select correct or incorrect for each of the following statements.  

This subject's elastance is higher than normal.

This subject's time constant is greater than 2500 seconds

This subject most likely has emphysema.

This subject likely has a very small FRC.

This subject's elastance is higher than normal.

This subject's time constant is greater than 2500 seconds

This subject most likely has emphysema.

This subject likely has a very small FRC.

Explanation / Answer

1) the subject's elastance is higher than normal is incorrect as we know that elastance is inversely proportional to compliance,as the subjects compliance is increased,elastance will decrease.

Normal compliance is 30 - 40ml/ cm H2O.

2) the subjects time constant is greater than 2500 seconds is incorrect as time constant = compliance × airway resistance

K= 25 cm H20/L/sec × 110 mL = 2750/1000 seconds = 2.750 seconds

3)this subject most likely has emphysema is correct,as increased compliance,increased airway resistance and decreased elastance is present in cases of COPD as emphysema.

4) this subject likely has very small FRC is incorrecf as compliance is increased,now if the lungs are more compliant,there is disturbance in inward recoiling of lungs and outward recoil of chest wall,so FRC in this case should increase.

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