Evaluation of hypertension using first derivative features of photoplethysmography

Abstract

The photoplethysmography (PPG) signal is the standard technique to measure blood oxygen saturation and cardiac output,
but the complete diagnostic value of PPG signals is not being used presently in clinical applications. Therefore, we are
proposing a simple algorithm to extract blood flow parameters from the PPG signals and prove that blood vessels are
altered, losing their elasticity in hypertensive people. Hypertension is a serious medical condition where the force of blood
pumping through the arteries is strong as compared to the normal force. Hypertension is defined as blood pressure above
140/90mmHg and is considered to be severe if it exceeds 180/120mmHg. Blood pressure can be measured using various
methods like auscultatory method and palpatory method. The manual method of blood pressure measurements based on a
calibrated sphygmomanometer will be accurate only if performed precisely. A PPG sensor shows us the vascular condition
of a person by allowing us to calculate blood flow parameters like systolic amplitude, pulse interval, augmentation index
and stiffness index. Our study population includes 25 normal and 25 known hypertensive subjects. Parameters from PPG
signal like systolic amplitude, pulse interval, and stiffness index was calculated directly. After taking first derivative of the
signal features like i). Crest Time (CT), ii). Peak to peak time (ΔT) and iii). Stiffness index was also calculated. The
parameters were statistically analyzed to prove that there is vascular wall health deterioration in prolonged hypertensive
subjects.