They will undergo a thorough history taking focussed primarily on past medical history and drug history and a brief physical examination. The hemodynamic parameters such as heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressure will be checked and recorded. If any positive findings are detected during clinical examination such as anaemia, pedal oedema, dehydration or raised blood pressure, the volunteers will be excluded from the study.

All ultrasound measurements will be performed with the volunteers in a supine position with their head turned approximately 30° to the left side (without using a head pillow) and the ipsilateral arm adducted. All ultrasound scans will be conducted from the head end using the 35 mm high‐frequency broadband linear array transducer (HFL 13–6 MHz) of the portable Edge II (FUJIFILM Sonosite, Inc, Bothel, USA) ultrasound system. The “artery preset” will be selected and depth adjusted to get the artery at the centre of the screen. A scout scan of the right carotid artery from the upper neck to the clavicle will be done to ensure that the carotid artery does not have any obvious anatomical variations or abnormalities such as irregularities of the intima. The volunteers will be excluded if there are any anatomical variations or abnormalities.

A short axis view of the carotid artery at the level of the lower border of thyroid cartilage will be obtained and frozen. The maximum diameter of the carotid artery at this point will be recorded. All the other measurements will be taken using a longitudinal scan of the right carotid artery, with the transducer marker oriented cephalic and the mid-point of the transducer at the level of the lower border of the thyroid cartilage. Minor adjustments to the transducer will be made to obtain the same diameter of the carotid artery as was previously recorded. This will ensure that the ultrasound beam passes across the midline of the carotid artery. The anterior and posterior walls of the carotid artery on the image should be parallel and the intima visualized crisp and clear. The power doppler key will then be activated and the angle of insonation set at 60°. Once a good quality Doppler spectral trace is obtained, the image will be frozen and measurements obtained.

The maximum peak systolic velocity, the minimum peak systolic velocity and the end-diastolic velocity on the frozen waveform will be measured. The δPV will be calculated. The volume flow and time average peak (TAP) velocity will be determined using the automatic trace option after providing input for the diameter . The cFT will be determined by measuring the cycle time and systole time on the frozen image as previously described by Blehar et al. cFT will be determined using the formula systole time/√systole time.

All parameters will be measured by three observers (the PG student who will be the principal investigator, the guide and co-guide) who will be trained in carotid artery anatomy, the use of power spectral Doppler imaging and the scanning protocol. A minimum of 10 carotid scans and measurements will be done by each observer to become proficient in doing the scan and taking measurements.

Each observer will take three measurements on each subject included in the study.