Inclusion Criteria- Acute ischemic stroke within 72 hours of symptom onset. In cases where onset time can not be established, it will be considered to be the time when the patient was last known to be well.
- 18 years or older.
- Patients with Partial Anterior Circulation Infarcts (PACI; Oxfordshire Stroke Classification Project; OSCP) will be included.
- Patients with Posterior Circulation Infarcts (POCI) will be included only if there is evidence of cortical infarction in the territory of the posterior cerebral artery or its branches, including the occipital and mesial temporal lobes.
Exclusion Criteria- Patients with a contraindication to the BP lowering protocol (i.e. known extracranial/intracranial arterial stenosis, high-grade stenotic valvular heart disease, or severe renal failure) will be ineligible, as will those with a definite indication for BP reduction (i.e. hypertensive encephalopathy, or aortic dissection).
- Patients with contraindications to MRI will be excluded, including metallic implants and any past sensitivity to gadolinium contrast media.
- Due to recent reports of nephrogenic systemic fibrosis associated with gadolinium exposure in individuals with pre-existing renal failure, patients with Creatinine > 160 μmol/l or Glomerular Filtration Rate (GFR) <60 ml/min will also be excluded.
- Patients with renal artery stenosis will be excluded from this study, irrespective of renal function.
- Due to the possibility that oxygen therapy may confound CBF measurements, patients requiring >4 lpm to keep Sp02 ≥92% by nasal cannulae will be excluded.
- Patients with a suspected hemodynamic stroke mechanism will be ineligible. This will include patients with known or suspected hypotensive periods and/or a watershed territory of cerebral infarction seen on CT or MRI.
- Due to the possibility of increased susceptibility to BP reduction in patients with raised intracerebral pressure (ICP), those with evidence of significant mass effect secondary to acute infarction, including any degree of midline shift and/or ventricular compression will be ineligible. For the same reason, patients with head and eye deviation or other clinical evidence of a Total Anterior Circulation Infarct (TACI; OSCP) will also be ineligible.
- Due to technical difficulties associated with PWI in the posterior fossa, patients with brainstem and cerebellar strokes will be excluded.
- Patients with known sensitivity to nitroglycerin/labetalol/adhesives in nitroglycerin patches/ACE inhibitors/Angiotensin Receptor Blockers will be excluded.
- Amplification of the vasodilatory effects of topical nitroglycerin by phosphodiesterase inhibitors such as sildenafil or tadalafil can result in severe hypotension. Patients who have used either of these drugs within 12 h of initial assessment will therefore be excluded.