Conference Paper

An Unobtrusive Wearable Device for Ambulatory Monitoring of Pulse Transit Time to Estimate Central Blood Pressure

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... To our knowledge, IsenseU-BP+ is the first device aiming to measure BP changes with all components and processing integrated within a single, small unit strapped around the chest, thereby making it truly unobtrusive in daily life. In tests performed on healthy volunteers with normal range BMI using handgrip movement to change blood pressure, it has been verified that IsenseU-BP+ can be used to monitor blood pressure changes [17]. The hypothesis behind the present work was that IsenseU-BP+ can be used to measure PTT in a patient population with both genders and varying age, body shapes and body mass index (BMI). ...
... Fig. 2displays the raw signals during rest ( Fig. 2A) and during cycling (Fig. 2B) for test 8. The raw signals (ECG, PPG, ICG) from IsenseU-BP+ have previously been compared against validated reference sensor signals, see [17] for more information. In the current work the sampling time of the raw data (ECG, ICG, PPG) was 4 ms, data was collected and logged with Bluetooth disabled, and filter settings were held constant. ...
... Thus, the error caused by this method for ICG-B point detection will influence the possibility to detect small changes in blood pressure, and the beat-to-beat variation. For changes in the range evaluated during activity in this study (>20 mmHg and averaged over 10 heart cycles) the error of the ICG-B point detection were judged acceptable [17]. ...
Full-text available
Objective: One promising approach for a continuous, noninvasive, cuff-less ambulatory blood pressure (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 nonalcoholic 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 body mass index. 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 noninvasive continuous BP, although evaluation during exercise was limited due to inaccurate reference BP measurements. Significance: Continuous, noninvasive measurement of BP would be highly beneficial in a number of clinical settings. Systems currently considered as the gold standard for the investigation of hypertension carry considerable limitations, which could be overcome by the method proposed here.
... The test device is a fully wearable and easy-to-use chest belt with three standard electrodes for ECG and a PPG sensor with potential for seamless integration with clinical applications. Technical details on the device have been published previously [17,18], and an upgraded version (new casing, a higher sampling rate of 1 kHz, new PPG sensor) was used in the present study. PAT was calculated for each cardiac cycle from the R-peak in the ECG to the foot in the PPG waveform. ...
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Objective: Pulse arrival time (PAT) is a potential main feature in cuff-less blood pressure (BP) monitoring. However, the precise relationship between BP parameters and PAT under varying conditions lacks a complete understanding. We hypothesize that simple test protocols fail to demonstrate the complex relationship between PAT and both SBP and DBP. Therefore, this study aimed to investigate the correlation between PAT and BP during two exercise modalities with differing BP responses using an unobtrusive wearable device. Methods: Seventy-five subjects, of which 43.7% had a prior diagnosis of hypertension, participated in an isometric and dynamic exercise test also including seated periods of rest prior to, in between and after. PAT was measured using a prototype wearable chest belt with a one-channel electrocardiogram and a photo-plethysmography sensor. Reference BP was measured auscultatory. Results: Mean individual correlation between PAT and SBP was -0.82 ± 0.14 in the full protocol, -0.79 ± 0.27 during isometric exercise and -0.77 ± 0.19 during dynamic exercise. Corresponding correlation between PAT and DBP was 0.25 ± 0.35, -0.74 ± 0.23 and 0.39 ± 0.41. Conclusion: The results confirm PAT as a potential main feature to track changes in SBP. The relationship between DBP and PAT varied between exercise modalities, with the sign of the correlation changing from negative to positive between type of exercise modality. Thus, we hypothesize that simple test protocols fail to demonstrate the complex relationship between PAT and BP with emphasis on DBP.
... The developed device is about 4 cm long and 3.5 cm wide, which was smaller than a typical prototype (Austad et al., 2016;Kim et al., 2013). Figure 2 describes the block diagram of the signal detection system, which involves an ECG module (AD8232), a PPG module (MAX30102), a microcontroller with Bluetooth combined (NRF52832) and power management unit. ...
... The initial 17 enrolled patients were processed in order to assess whether Pulse Arrival Times (PAT) as estimated by 1) an ECG and a reflective PPG sensor at the chest correlated with PAT as measured by 2) an ECG and an arterial catheter inserted at the radial artery. Two reflective PPG sensors at the chest were tested: a single green channel PPG sensor (as claimed by [3] and [4]), and a multi-wavelength channel PPG sensor (as disclosed by [2]). For both sensors no pressure was applied onto the optical probe. ...
Conference Paper
Full-text available
Cuffless blood pressure monitoring at the chest requires accurate detection of the arrival time of arterial pressure pulses at chest skin. A clinical trial was designed (NCT02651558) in order to assess the performance of single-and multi-channel reflective PPG sensors when no pressure is applied onto optical probe. Experimental setup involved invasive monitoring of reference hemodynamic variables. Results suggest that multi-channel PPG sensors are required in order to obtain accurate hemodynamic measurements at the chest, questioning the reliability of single-channel PPG sensors.
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