Noninvasive photoplethysmographic monitoring of pulse wave velocity and vascular stiffness for hypertension applications

Cardiovascular diseases are the leading cause of death globally. These usually have two main types of risk factors namely modifiable risk factors and non-modifiable risk factors. Among these, hypertension is the primary risk factor. Accurate noninvasive monitoring of hypertension in high risk patients is therefore essential in order to tackle or prevent their cardiovascular diseases. In terms of hemodynamics, increased vascular stiffness has been recognized as the main contributing factor to hypertension. This leads to the observed increase in pressure pulse propagation velocity, or pulse wave velocity, in conduit arteries. Thus, a method that can afford continuous noninvasive monitoring of vascular stiffness will be clinically desirable. To achieve this, the current investigation provides a new method of application of a photoplethysmograph (PPG) that employs light emitting diodes of visible wavelengths coupled with new ambient light detectors for optimal recording of propagating pulses. PPG sensors are placed at two different superficial arterial sites (Dual PPG) for monitoring pulse transit time (PTT) and hence pulse wave velocity (PWV) in patients. Data were simultaneously recorded in a human model, sampled by means of a Biopac System and selective filtering was applied to enhance the signal-to-noise ratio. Vascular stiffness is obtained as elastic modulus through the Moens-Korteweg formula. Interventions were imposed to observe induced changes in vascular stiffness. Results show that our current design is accurate for continuous monitoring of vascular stiffness changes. Measured pulse wave velocities agree well with clinically reported values for different arterial sites, such as ear lobe artery to radial artery and brachial artery to index finger artery. The light-weight, low cost, continuous and noninvasive PPG design can be used for future routine screening of vascular stiffness. This can be used to predict hypertension, its severity in terms of structural changes, and potential evaluation of therapeutic efficacy of anti-hypertensive drugs in hypertensives.M.S.Includes bibliographical referencesby Taaha Jamkhanawal