Hypo/Hypercapnia

[stewiemd]

This is my first post, so please accept my apology if I post it in the wrong forum (I am an Aus medical student).

I have a problem understanding the following:
COPD --> Dyspnoea and tachypnoea. These patients may have hypercapnia (because increased ventilation cannot compensate (correct me if i am wrong))

However:
Pulmonary embolism --> Dyspnoea and tachypnoea. These patients have hypocapnia instead.

I don't understand why PE will lead to hypocapnia. Doesn't the clot causes inefficiency of gas exchange (which in some ways is similar to COPD)?

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[Jabbed]

Obstructive airway disease results in air trapping, causing late stage retention of CO2. The hypoxemia induced by V/Q mismatch of acute PE is partially compensated by tachypnea. Tachypnea increases CO2 ventilation and causes hypocapnia.