Each year, approximately 30,000 people in the United States suffer an intra-cranial
hemorrhage due to aneurysmal rupture. Of those surviving the initial event, up to 40% will go
on to have further neurological injury secondary to stroke (delayed cerebral ischemia) caused
by constriction of blood vessels (i.e. vasospasm). Previous studies have shown that the
medication sildenafil, given intravenously, improves vasospasm, but has an associated degree
of hypotension. The degree of hypotension was well within safety thresholds for these
Sildenafil is a medication that strongly inhibits the protein phosphodiesterase-V (PDE-V).
The hypothesis for this study is that oral sildenafil will also improve vasospasm, but does
not result in as much hypotension. Specifically, the investigators look to show that
comparable doses of oral sildenafil produces the same degree of PDE-V inhibition as an
intravenous dose while the degree of hypotension is reduced. Additionally, using measurements
of cerebral blood flow regulation acquired using transcranial Doppler ultrasound, the
investigators look to show that oral sildenafil produces the same degree of improvement in
vasospasm and blood flow regulation.