Cuff-less and noninvasive measurements of arterial blood pressure by pulse transit time.

The current blood pressure (BP) measurement devices are mostly built on the principle of auscultation, oscillometry or tonometry, all of which use an inflatable cuff to occlude or unload the artery. The need of a cuff in these devices limits the further reduction in size and power consumption, and restricts the frequency and ease of their usage. Therefore, this study aims to develop a cuff-less and noninvasive technique for measuring BP by pulse transit time. The technique was evaluated on 85 subjects, aged 57+/-29 yrs., including 36 males and 39 hypertensives, over an average period of 6.4 wks. A total of 999 pairs of systolic BP (SBP) and diastolic BP (DBP) estimations were made. The average of BP readings reported by an experienced registered nurse and those obtained from a clinically approved automatic BP meter was used as reference. It is found that the estimated SBP and DBP differed from the reference BP by 0.6+/-9.8mmHg and 0.9+/-5.6mmHg respectively. When compared to the AAMI requirement (5+/-8mmHg for both SBP and DBP estimation), the results suggest that the cuff-less technology has great potential to be developed into wearable devices that are useful in self BP monitoring for home healthcare and eventually in clinical diagnosis.