Dead Space Ventilation

During general anesthesia with spontaneous ventilation, a patient has a Vd/Vt of 0.5. Which is most likely to decrease this ratio?

a. acute bronchospasm
b. continuous positive airway pressure
c. decreased tidal volume
d. increased cardiac output
e. pulmonary embolism

Please discuss.

Source: ITE 1996 Book A Q 46

Sh!t...I meant to put this in the keyword forum...