Pulse Wave Velocity - What it is and why it matters
What is Pulse Wave Velocity?
Imagine a single health metric able to identify people in their 20’s at increased risk for development of Heart Disease, Stroke and Dementia. What if this health indicator could estimate how long you will live? Incredibly, for the last 20 years medical scientists have known that Aortic Pulse Wave Velocity, which is used to measure stiffness of the Aorta (shown below) is closely related to risk of death from all causes and able to define risk in young people for development of Heart Disease Stroke and Dementia.
Aortic Pulse Wave Velocity is closely related to and is a measure of stiffness along the spinal column. Increased stiffness of the spine results in decreased mobility of the body’s core regions affecting chest wall and diaphragmatic motion. When pulse wave velocity increases in speed, Core Mobility is reduced and the Internal Organs receive less of a massaging action with each breath. This decreases organ circulation, affecting organ function, overall health and longevity.
Aortic Pulse Wave Velocity not only assesses risk of illness but also shows improvement with attention to diet, exercise and stress management. Aortic Pulse Wave Velocity is a way to 'look inside' and can help people objectively appreciate the benefit of positive lifestyle choices. Read studies on AoPWV here.
How is Pulse Wave Velocity Measured?
You and your doctor probably haven’t heard of Aortic Pulse Wave Velocity because this measurement has required expensive and complicated equipment with a price tag of over $20,000 USD. Measurement in the past used pressure sensors placed precisely over the Carotid artery in the neck and the Femoral artery in the groin to measure speed with which pulse waves travel down the Aorta. Aortic Pulse Wave Velocity (AoPWV) is the common way scientists measure of Aortic Stiffness.
Recently it has become possible to measure AoPWV using a single fingertip pulse sensor called iHeart. iHeart uses a 30-second test to locate and characterize a wave in the fingertip pulse signal that travels down the Aorta, reflects back from the distal Aorta towards the heart and then travels on to the finger. The speed with which this Reflected Wave travels is closely related to Aortic Stiffness. iHeart Aortic Pulse Wave Velocity measurement has been tested against the ‘gold standard’ Carotid-Femoral AoPWV measurement system and found to correlate very well.
There are other ways to measure AoPWV. One alternative method uses a pulse sensor on a finger and a toe. The distance from the heart to a fingertip and the distance from the end of the Aorta and down a leg to a toe is about the same. The difference in arrival time of the finger and toe pulses is closely related to AoPWV but age creates errors when compared to Carotid-Femoral PWV.
Diagram copied from ‘A novel device for measuring arterial stiffness using finger-toe pulse wave velocity: Validation study of the pOpmètre’ Archives of Cardiovascular Disease (2015) 108, 227—234
Recently Withings has developed a weight scale sensitive enough to feel pressure changes associated with the beginning of each heart beat. This technique is called Ballistocardiography (BCG). The weight scale also includes optical sensors that detect arrival of the pulse wave in the feet. Time from the BCG signal to the optical pulse signal is used, with height, to compute Pulse Wave Velocity (PWV). The segment being measured consists of the aorta as well as the arteries of the entire thigh and leg and the PWV measured is not purely Aortic PWV. The Withings patent describing their technique is noted at http://www.google.com/patents/US20130310700
It is important to recognize that not all PWV measurements are good indicators of health and predictive for risk of illness. Aortic PWV is the only metric able to assess overall health and predict lifespan.