Cerebral autoregulation can be assessed non-invasively by the use of Trans Cranial Doppler (TCD). This means using ultrasound probes over both sides of the head to measure changes in blood flow in one of the main brain arteries (the middle cerebral artery) in response to beat to beat changes in blood pressure dynamic cerebral autoregulation. This research will use the noninvasive technique of Trans Cranial Doppler to see how blood flow changes during different head position between acute ischaemic stroke patients and healthy controls, as well as over time during recovery after a stroke. This knowledge will help us to understand the changes in brain blood flow control and blood pressure in stroke patients, with implications of diagnosis, prognosis, and treatment of the disease.