The CardioCheck™ uses an infra-red beam to measure in a finger, the changes in blood volume caused by the pulse. It then compares features of the main pulse with the reflected pulse, which occurs as a result of narrowing of the arteries in the lower body. The measuring device is called a photoplethysmograph and attaches simply to any finger via a non-invasive clip-on finger cuff. Readings are taken over a short period, normally 10 or 15 seconds, and two statistics are calculated via algorithms within the hand-held recording device, which in turn can be linked to a computer for downloading data.
The two key statistics given by the device are the Stiffness Index (SI) and the Reflection Index (RI). In addition, the device gives an estimate of vascular age, measures heart rate and also allows blood pressure readings to be entered and stored. The Stiffness Index correlates with the 'gold standard' measurement for arterial stiffness. Pulse Wave Velocity (PWV) is a function of the time between the primary and reflected pulses, divided by the subject height. The Reflection Index is based on the proportional heights of the primary and reflected peaks.
In essence, a high SI means stiff arteries; stiff arteries develop with age and are a key determinant of cardiovascular disease risk. Basically, stiff arteries, akin to a copper tube, cause the reflected pulse to be returned very quickly, while more elastic arteries, as per a soft rubber hose, absorb more energy and cause a greater delay between the primary and reflected pulses. CardioCheck™ compares the SI with an existing database stored on the device to give an estimate of Vascular Age, i.e. the average age of a healthy population with the given SI (including 95% Confidence Limits).