A Comparison of Wearable Tonometry, Photoplethysmography, and Electrocardiography for Cuffless Measurement of Blood Pressure in an Ambulatory Setting

OBJECTIVE

While non-invasive, cuffless blood pressure (BP) measurement has demonstrated relevancy in controlled environments, ambulatory measurement is important for hypertension diagnosis and control. We present both in-lab and ambulatory BP estimation results from a diverse cohort of participants.

METHODS

Participants (N=1125, aged 21-85, 49.2% female, multiple hypertensive categories) had BP measured in-lab over a 24-hour period with a subset also receiving ambulatory measurements. Radial tonometry, photoplethysmography (PPG), electrocardiography (ECG), and accelerometry signals were collected simultaneously with auscultatory or oscillometric references for systolic (SBP) and diastolic blood pressure (DBP). Predictive models to estimate BP using a variety of sensor-based feature groups were evaluated against challenging baselines.

RESULTS

Despite limited availability, tonometry-derived features showed superior performance compared to other feature groups and baselines, yielding prediction errors of 0.329.8 mmHg SBP and 0.547.7 mmHg DBP in-lab, and 0.868.7 mmHg SBP and 0.755.9 mmHg DBP for 24-hour averages. SBP error standard deviation (SD) was reduced in normotensive (in-lab: 8.1 mmHg, 24-hr: 7.2 mmHg) and younger (in-lab: 7.8 mmHg, 24-hr: 6.7 mmHg) subpopulations. SBP SD was further reduced 1520% when constrained to the calibration posture alone.

CONCLUSION

Performance for normotensive and younger participants was superior to the general population across all feature groups. Reference type, posture relative to calibration, and controlled vs. ambulatory setting all impacted BP errors.

SIGNIFICANCE

Results highlight the need for demographically diverse populations and challenging evaluation settings for BP estimation studies. We present the first public dataset of ambulatory tonometry and cuffless BP over a 24-hour period to aid in future cardiovascular research.

Soil nitrogen dynamics during an oilseed rape (Brassica napus L.) growing cycle in a humid Mediterranean climate

Nitrogen budgets help explain the supply pattern of N from the soil to the crop. Through budgeting, an improvement of the N fertilization strategy can be achieved. The objective of the present study, which was carried out under humid Mediterranean climate conditions, was to assess the influence of N fertilization, temperature and soil humidity on soil N dynamics during a whole oilseed rape growing cycle. A field experiment was conducted with two treatments: without N (0 N) and with application of 180 kg N ha⁻¹(180 N). Mineralization was calculated from N balances made throughout the growing cycle, all while taking into account measured N uptake by oilseed rape and N losses by leaching and N₂O emissions. Nitrogen net mineralization was negative after fertilization, reaching –6.73 kg N ha^−1, day⁻¹_, but total net mineralization over the year was similar for the 0 N and 180 N treatments (21 and 8 kg N ha⁻¹, respectively). Temperatures over 5 °C were sufficient for initiating the mineralization processes. In the summer, when the soil water content was below the wilting point, immobilization took place; however, there is a risk of N leaching if rainfall occurs thereafter, mainly in the 180 N treatment.