Abstract Body: Introduction: We present the design and initial testing results for a small, convenient, and accurate blood pressure monitoring device. The user holds the device in the non-dominant hand and presses the index finger from the dominant hand down on the device while a smartphone app guides the user to gradually increase the pressure such that the arteries in the finger are occluded. The device includes a high resolution, miniature pressure sensor and a set of light emitting diode and photodiode pairs to acquire photoplethysmogram (PPG) signals. From this pressure sensor and PPG array, an oscillometric curve is derived, allowing for the precise determination of blood pressure without the need for any calibration or demographic information.

Methods: We enrolled 251 participants, with ages 41.1±10.3, body mass index (BMI) 30.6±7.4, 53.4% with Fitzpatrick skin tone 5 or 6, 22.7% with Stage I hypertension (systolic blood pressure [SBP] of 140-160 mmHg or diastolic blood pressure [DBP] of 90-100 mmHg), and 7.2% with Stage II hypertension (SBP ≥ 160 mmHg or DBP ≥ 100 mmHg), to participate in this study aimed at training, tuning, and evaluation of the algorithms on board the device. The study included a dual-observer auscultation design as per the ISO81060-2:2018 standard. All procedures outlined in that standard regarding blood pressure drift, observer discrepancy, etc. were followed directly. We evaluated the device accuracy based on Bland Altman methods of assessing agreement, and specifically the mean error and standard deviation (SD) of errors between the device and the reference blood pressure values.

Results: The device had a leave-one-subject-out error of -0.29±6.78 (mean±SD) for DBP, and -0.21±7.17 for SBP. The corresponding error for Fitzpatrick skin tone 5 or 6 (n=134) was 0.46±6.46 for DBP and -0.72±7.04 for SBP, as compared to -1.01±7.00 for DBP and 0.27±7.26 for SBP for Fitzpatrick skin tone 1-4 (n=117). The error for BMI ≥ 30 (n=123) was -0.65±6.75 for DBP and -1.39±6.87 for SBP, as compared to 0.02±6.81 for DBP and 0.85±7.27 for SBP for BMI < 30 (n=128). There were thus no appreciable differences found with respect to device performance across skin tone or BMI.

Conclusion: The device holds promise as a calibration-free, cuffless blood pressure monitoring technology that can be used conveniently in everyday settings, allowing for ubiquitous screening, monitoring, and management of hypertension.