TBME-00879-2016.R1 Copyright (c) 2016 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending an email to pubs-permissions@ieee.org. Abstract—Objective: One promising approach for a continuous, non-invasive, cuff-less ambulatory BP monitor is to measure the pulse wave velocity or the inversely proportional pulse transit time (PTT), based on electrical and optical physiological measurements in the chest area. A device termed IsenseU-BP+ has been developed for measuring continuous BP, as well as other physiological data. The objective of this paper is to present results from the first clinical evaluation with a wide range of patients. The study was set up to verify whether IsenseU-BP+ can be used to measure raw signals with sufficient quality to derive PTT. Methods: The test protocol, run 23 times on 18 different patients with non-alcoholic fatty liver disease, includes both supine measurement at rest as well as measurements during indoor cycling. Changes in PTT were compared with the BP changes measured using validated reference sensors. Results: IsenseU-BP+ measured signals with good quality during rest on 17 of 18 patients despite the high diversity in age, body shape and BMI. Evaluation during cycling was difficult due to a lack of good reference measurements. Conclusion: IsenseU-BP+ measures PTT with high quality during supine rest and exercise and could therefore be suitable for deriving non-invasive continuous BP, although evaluation during exercise was limited due to inaccurate reference BP measurements. Significance: Continuous, non-invasive measurement of BP would be highly beneficial in a number of clinical settings. Systems currently considered gold-standard for the investigation of hypertension carry considerable limitations which could be overcome by the method proposed here. Index Terms—cuff-less blood pressure, pulse transit time, pulse wave velocity, unobtrusive sensing, hypertension I. INTRODUCTION Hypertension (elevated blood pressure (BP)) is the major risk factor for early mortality in Western society. It is The work has been carried out within the d-LIVER project, which is supported by the 7th Framework Program of the European Union under grant agreement no. 287596. T. M. Seeberg (Trine.Seeberg@sintef.no), H. O. Austad (Hanne.Opsahl.Austad@sintef.no), M. H. Røed (Morten.Roed@sintef.no), S. Dalgard, (steffen.dalgard@sintef.no, F. Strisland (frode.strisland@sintef.no), and are all with SINTEF Informatics and Communication Technology, NO- 0314 Oslo, Norway. J.G. Orr (James.Orr@newcastle.ac.uk), D. Houghton (David.Houghton@newcastle.ac.uk) and D.E.J. Jones (David.Jones@newcastle.ac.uk) are with Institute of Cellular Medicine, Newcastle University, UK. estimated to contribute to around 12.8% of all deaths, and globally affects 40% of adults aged 25 and over, according to the World Health Organization [1]. Treating systolic BP (SBP) and diastolic BP (DBP) to below 140/90mmHg is associated with a reduction in cardiovascular complications [2]. Increasingly, the medical community is also focusing on blood pressure variability [3] and nocturnal BP in the assessment and treatment of hypertension. Point BP measurements taken in the clinic tend to be inadequate or misleading due to diurnal variation and the so-called “white-coat hypertension”. The clinical practice for 24-hour ambulatory monitoring is to use cuff-based equipment with a unit for control and data storage usually worn on a lanyard around the neck. Typically, point measurements are restricted to three times an hour during daytime and once an hour overnight. There are considerable limitations to this method: the equipment is usually only validated at rest [4] and patients are instructed to sit down when the measurements are taken. This means that measurements are not representative of the full range in BP over the 24-hour period. The monitoring interferes with patients’ activities of daily living, and a large group of patients finds the cuff inflation uncomfortable and disruptive. This is problematic overnight, in particular, when the cuff inflation can disturb the patient’s sleep and can, itself, impact the BP. One approach for a continuous, non-invasive, cuff-less ambulatory BP monitor is to measure the pulse wave velocity or the inversely proportional pulse transit time (PTT). Several studies based on different technical solutions shows correlation between PTT and BP [5]-[11], but improvements are necessary. Most of the studies measured the time from ECG R-peak to the pulse wave reached a peripheral artery. This time measurement includes both PTT and part of the pre- ejection period, which is the period from start of the depolarization of the heart, represented with the ECG-Q wave, to the aortic valve opening. Both the pre-ejection period and the PTT vary with blood pressure, and combining the two makes extraction of blood pressure values difficult [12]. Including the pre-ejection period also makes the measurements dependent on posture [13]. Also, in most studies, as well as in commercially available devices [14], a peripheral point such as the finger or earlobe is used. Measuring PTT peripherally means that vasoconstriction A novel method for continuous, non-invasive, cuff-less measurement of blood pressure: evaluation in patients with non-alcoholic fatty liver disease Trine M. Seeberg - Member IEEE , James G. Orr, Hanne O. Austad, Morten H. Røed, Steffen Dalgard, David Houghton, David E J Jones and Frode Strisland