Photoplethysmography-based pulse wave analysis using a wearable device

#This disclosure provides devices and methods for estimating arterial stiffness using pulse wave analysis, particularly with photoplethysmograhy.

#Arteries harden as a result of vascular ageing and other physiological factors such as pathologies and diets. Arterial stiffness indicates cardiovascular dysfunction and is an established independent predictor of cardiovascular risk.

#The contraction of the left ventricle pumps blood into the aortic artery, causing blood volume and blood pressure to change in the arteries, forming an arterial pressure wave or pulse wave in the peripheral arteries. Arterial stiffness can be non-invasively estimated by pulse wave analysis (PWA) of blood pressure data obtained by a tonometer, or blood volume data of a photoplethysmogram (PPG) sensor. PWA involves obtaining pulse waveforms from pulse wave data, and extracting and analyzing morphological features of the pulse waveforms. Morphological features of the pulse waveforms, such as augmentation index, reflection index, pulse transit time, are shown to correlate with arterial stiffness.

#FIG. 1 shows a representation of a pulse waveform that can be obtained from PPG data and the first and second derivatives of the pulse waveform.

#FIG. 2 shows a flow chart illustrating a process 200 for determining arterial stiffness implemented by a wearable biometric monitoring device in some implementations.

#FIG. 3 shows a process flow chart for preprocessing pulse waveform data that can be performed by biometric monitoring device according to some implementations.

#Various morphological features of the pulse waveforms are correlated with arterial structures and functions including arterial stiffness. Morphological features of a pulse waveform as used herein include various aspects of the shape of the waveform and information derived therefrom including the slopes of various portions of the waveform, time separation between such portions, amplitudes of such portions, and the like. Morphological features of the pulse waveform also include various aspects of the shape of the derivatives of the waveform including a first derivative, a second derivative, and higher order derivatives. Unless otherwise qualified, any one or more of these features may be used in the analyses described herein.

#In some context not specific to the disclosure herein, the term pulse waveform can be interpreted as closely related to the shape of a PPG graph reflecting blood volume change caused by pulsed blood flow, while the term pulse wave may be interpreted as more closely related to the blood volume change caused by pulsed blood flow. However, the two terms are used interchangeably herein unless specified as different. For instance, pulse waveform analysis and pulse wave analysis are used interchangeably herein.

#Introduction